2228 - national fire protection association · 2228_ report of committee on ovens and furnaces...

2228_

Report of Committee on

Ovens and Furnaces

J a m e s T. B l a c k m o n , J r . , Chairman, Union Carbide Corp., Nuclear Div., Bldg. 9733-2, Oak Ridge, T N 37830

A. Baese t t , Lindberg Hevi-Duty Canada, Limited

E. C. Bayer , Holcroft & Co. L. M. Bolz, Improved Risk Mutuals D. P. C o n g d o n , Factory Insurance Assn. Lowel l F. Crouse , Gas Appliance Manu-

facturers Assn. R. C. Davis , Chevrolet Motor Div., GMC S. B. G a m b l e , Flian and Dreffein Engineer-

ing Co. P a u l H. Goodel l , The Institute of Electrical

& Electronics Engineers E. W. Grobe l , Lindberg Hevi-Duty R. F. G u n o w , Metal Treating Institute F. K. J e n s e n , Jensen, Inc. Mer le J o h n s o n , Johnson Manufacturing Co. K. N. L a w r e n c e , National Electrical Manu-

factursrs Assn. J o h n P. M a l o n e y , Forging Industry Assn. Flo~d .B. McCoy , Mgr., Instrument En-

gmeermg W. J . M c E l h a n e y , Leetromelt Corp. R a y Os t rowsk i , Protection Controls Inc.

. J a m e s H. Panas lewicz , Motor Vehicle Manufacturers Assn.

H. E. P a r k e r , The Electric Furnace Co. W. F. P a r k e r , Midla~d-Rcss Corp. H . R. R l c h a r d s , Industrial Ovens, Inc. L. D. Slbley, EBV Systen~, Inc.

J . M. S i m m o n s , Factory Mutual Corp.

A r t h u r S p i e g e l m a n , American Insurea~ Assn.

George S t u m p f , Industrial Heat ing Equip. Assn.

G. E. Wai te r s , Caterpillar TractOr Co. A b r a h a m Wll lan , Aerospace Industries

Assn. Geo rge M. Woods, J r . , Kemper Insuranee

Company

Alternates.

J o h n P. Benedic t , Metal Treating Institute. (Alternate to R. F. Gunow)

L. H . F l ande r s , Factory Mutual Research Corp. (Alternate to J. M. Simmons)

J o h n R. Hixson, Ga~ Appliance Manufae. turers Assn. (Alternate to Lowell F. Crouss)

R a y m o n d A. Kolakowsk i , Motor Vehicle Manufacturers Assn. (Alternate to J. H. Panasiewics)

F r a n k E. R a d e m a c h e r , Factory Insuranee Assn. (Alternate to D. P. Congdon)

N. L. T a l b o t , Improved Risk Mutuals (Alternate to L. M. Bolz)

G. I. Ta t e , National Electrical Manufae- turel's Assn. (Alternate to K. N. Lawrence)

G. W. W e i n f u r t n e r , Forging Industry Assn. (Alternate to John P. Maloney)

S e c t i o n a l C o m m i t t e e o n C l a s s A O v e n s a n d F u r n a c e s

A r t h u r S p l e g e l m a n , Chairman,

P. H. Goode l l George S t u m p f W m . C. W h i t i n g

S e c t i o n a l C o m m i t t e e o n C l a s s B E l e c t r i c a n d F u e l - F i r e d F u r n a c e s

D. P. C o n g d o n , Chairman,

A. Baese t t J o h n P. M a l o n e y G . W . W e i n f u r t n e r (Alternate to John P.

L. M. Bolz L . D . Sibley Maloney) Lowell F. C r o u s e N . L . T a l b o t

(Alternate to L. M. Boiz)

REVISIONS TO NFPA NO. 8 6 A 2 2 2 9

Sectional C o m m i t t e e o n Clas s C a n d V a c u u m F u r n a c e s

G. M. Woods, Chairman,

g. (I, Bayer E.W. Grobel Ray Ostrowek/ John P. Benedict • R .F . Gunow H.E. Parker ~R~F. ~un~o K.N. Lawrence W.F . Parker ( w) W.J . McElhaney Frank E. Rademacher I~C. Davis

J. M. Simmons

The report of the Committee on Ovens and Furnaces is in three parts.

par t I of the report, prepared by the Sectional Gommittee on Class A Ovens and Furnaces, proposes amendments and new material for NFPA No. 86A-1973. Amendments are primarily directed toward obtaining more consistency between this Standard and Nos. 86B and 86G. The major new material concerns requirements for powder coating.

Part I has been submitted to letter ballot of the Committee, but results were not available at the time of printing oaf the Technical Committee Reports. Results of balloting will be announced at the Annual Meeting.

Part I

Proposed Revisions to Standard for

Ovens and Furnaces

NFPA No. 8 6 A - - 1971

I. Delae lO0--l(e).

2. Add a new 100--2(c) asJollows:

(c) "Authori ty Having Jurisdiction." The authority having jurisdiction is the organization, office, or individual responsible for approving equipment, an installation, or a procedure.

NOTE: The phrase "authority having jurisdiction" is used in NFPA standards in a broad manner since jurisdictions and approval agencies vary as do their responsibilities. Where public safety is primary, the authority having jurisdiction may be a federal, state, local, or other regional depart-

2230 ment or individual such as a fire chief, fire marshal, chief of a fire prevention bureau, labor department, health department, building official, electrical inspector, or others having statutory authority. For insurance PnUrposes, an insurance inspection department, rating bureau, or other

surance company representative may be the authority having jurisdiction. In many circumstances, the property o.wn..er or his delegated ag.ent .~.

sumes the role of the authority having junsdictmn, at government mstadla. tions, the commanding officer, or a departmental official may be the authority having jurisdiction.

3. Add a new 100-2(d) as follows:

(d) "Operators" are the individuals responsible for file light-up, operation, shutdown, and emergency handling of the specific installation, consisting of the atmosphere gas generator and/or furnace and the associated equipment through or into which the atmosphere gas flows.

4. In 100-3(c) substitute the words "be provided" for "conform to Joint Industrial Conference Standards (J.I .C.)."

5. Add a new 100-5 as follows:

100-5. Opera tor Tra in ing (a) I t is fully recognized that the most essential safety considera-

tion is the selection of alert and competent operators. Their knowl- edge and training are vital to continued safe operation.

(b) New operators shall be thoroughly instructed and shall dem- onstrate an adequate understanding of the equipment and its operations.

(c) Regular operators shall receive scheduled retraining to maintain a high level of proficiency and effectiveness.

(d) Operators shall have access to operating instructions at all times. An outline of these instructions shall be posted in a suitable location.

(e) Operating instructions shall be provided by the equipment manufacturer. These instructions shall include schematic piping and wiring diagrams. All instructions shall also include:

1. Light-up procedures. 2. Shutdown procedures. 3. Emergency procedures. 4. Maintenance procedures.

(f) Operator training shall include: 1. Combustion of air-gas mixtures.

o v a R vxsio,s To , ,PA ,o . 86A 2 2 3 1

2. Explosion hazards. 3. Sources of ignition and ignition temperature. 4. Atmosphere gas analysis. 5. Handling Of flammable atmosphere gases. 6. Handling of toxic atmosphere gases. 7. Functions of control and safety devices. 8. Purpose and basic principles of the gas atmosphere generators.

6. Replace 200-2(a) and (b) with the following:

200-2 (a) Class A ovens and furnaces should be located at or above grade to make maximum use of natural ventilation and to minimize restrictions to adequate explosion relief.

(b) Special consideration shall be given to Class A Equipment processing flammable materials or when using fuels with a specific graviW greater than air. Class A Equipment may be located in basements where additional consideration has been given to ventilation and the abili W to safely provide the required explosion relief. (See NFPA Explosion Venting Guide, No. 68.)

Z Replace 200-3(a) and (b) with thefoUowing:

200-3. Ovens and furnaces shall be located and erected so that building structural members will not be adversely affected by the maximum anticipated temperatures. (See Article 200, Section E.)

8. In 200-5, first line, replace, "Ovens shall" with "Ovens and furnaces should", and in the fourth line change "ovens" to "oven", and add "or furnaces".

9. Replace 200-6(a) and (b) with the following:

200-6. Personnel. Furnaces and ovens shall be located to minimize exposure to people from the possibility of injury from fire, explosion, asphyxiation, and toxic materials, and shall not obstruct personnel travel to exitways.

10. In 200--7(a), fifth line, after "exposure" add "from or", and in the eighth line add "(See NFPA Nos. 30, 33, and 34)."

H. In 200-7(b), add at the end of the first paragraph "(See NFPA Nos. 30, 33, and 34)", and delete the second paragraph starting "Suitable, well- designed units . . . . "

12. In 200-9(b), first line, change "should" to "shall".

2232

13. In 200-9(b) 2, seventh line, change "should" to "shall".

" " I - " 14. In 200-9(b) 3, make the second paragraph starting ,. nsulataa~ c e m e n t . . . " a "Note :", add "for 700°F. oven heat" after "cemen~ in the first line of the Note, and in the second line replace "50 :riO by weight with Portland" with "with."

i ,

15. Delete 200-9(b) 4, and replace with the Joliowing" "-

4. Where electrical wiring will be present in the channels of certain types of floors, the wiring shall'be i/astalled in accordance with Article 356 of the National Ele'ctrical Code (NFPA No. 70).

16. Delete 210-2, and replace with the Jollowing:' "

210--2 (a) Ovens and furnaces shall be consixueied of noncombustible materials. •

(b) Furnace structural supports and conveyorsshall,be.designed w i ~ adequate factors of safety at themaximum operating tempera. tures, consideration being give.n tO the straifis imposed by expansion

(c) Adequate facilities for access shall be provided to permit proper inspection and maintenance. ~

(d) Burners and heating elements of all types'shall be substantially • constructed or guarded to resist mechanical da.mage.i . ' (e) Where'refractory materials are used, they sfiall be supported so that they will not fall out of place.

(f) Corrosion resistance. Wher e iubject to corrosion, metal, parts shall be protected. " " ~

(g) Accessibility and mounting of controls. Pro+i§ion s/aall be made for the rigid attachment of .control devices. Combustion safeguard mounts shall be arfange~" so that the electrode'br other flame,detecting element is correctly, positioned.. Valves, and control panel shall be so Iota_ted that alL necessary-obse~ation andadjust- ment m a y b e readily m a d e . . . . . . • , :. ..,

(h) Exterior of furnaces in excess of 160 ° F (71 ° C) should be guarded by location, guard rails, shields or insulation to prevent accidental contact with .personnel. All parts o f equipinent operating at elevated temperatures shall" be installed in ace6r, dance with Article 200, Section E, Floors and Clearances. Where ira- .practical to guard, warning signs, or permanent floor markings shall • b~.provided or mounted to be visible to,personnel entering the area.

(i) Bursting discs or panels, mixer openings, or other parts of the furnace from which flame or hot gases may be discharged should be located or guarded to prevent injury to personnel.

REVISIONS TO NFPA NO. 8 6 A 2233

j) Properly located observation ports shall be rovided to - . , . P

pernut the operator to observe-the hghtmg of individual burners. (k) Devices such as relief valves, open Sight drains, and water

flow switches from water cooling systems shall be designed and installed for ready observation by operator.

(1) Gas-fired heaters shall not be located direcdy under the product being heated where combustible materials may drop and accumulate. Neither shall they be located direcdy over readily ignited materials such as~cotton unless for. controlled exposure time, as in continuous processes where further automatic provisions and/or arrangement of guard baffles preclude the possibility of ignition.

(in) The metal frames of ovens shall ina l l casesbe electrically

~ ounded throughout for the safe removal of static electric .charges. ee Recommended Practice on Static Electricity, NFPA No. 77).

17. In 210~-3, third line, change "shall" to "should", and in the eleventh line after "those" add "fuel-fired."-

18. In 210--4, first line of the second paragraph , change "should" to "shall".

19. In 210-:.4(c), first line, change "should" to "shall", and in the third line of the second paragraph change "should" to "shall."

20. Add new 220-1(p) as follows:

(p) All duet work shall conform to NFPA No. 91.

21. Delete 230-1 and 230-2 and replace with the following:

230-1. Adequate facilities for access shall be provided to permit proper inspection .and maintenance.

230-2. When such openings are intended to permit persons to climb inside for inspection and cleaning, there should be provided such additiorial equipment as ladders, steps, and grab-rails to permit safe and easy access and egress.

22. Replace 240-7. and 240-2 with the following:

240-1. Hydraulic systems for furnace door operation, lifts for work loads, and conveyor systems should not use petroleum or other combustible hydraulic fluids. The use of fire resistant fluids is recommended.

2 2 3 4 coM x E oN ovE ,s A,,D F R AC S

240-2. When petroleum oils or other combustible fluids must be used, the system shall be designed to minimize the ~possibility of fluid release which may result in a fire or explosion.

23. Revise Article 300 to read as follows:

AR TI C LE 300. GENERAL REQUIRF_,MENT~3

300-1. Scope. (a) For the purpose of this s tandard-the term "furnace heating system" shall include the heating source and associated ductwork and circulating fans used to convey heat to the furnace or work therein.

(b) Other heating systems such as coal or other solid fuel fire. box and firing equipment, and hot oil or other liquid circulating systems are not included in this section.

(c) The source of heat may be internal, i.e., within the furnace, external, i.e., outside the furnace, and the means of transfer of heat may be direct, i.e., the products of combustion enter the furnace and contact the work in process, or indirect if the p r o d u c e o f combustion do not contact the materials in process.

(d) The transfer of heat into and throughout the furnace may be by convection, radiation, or conduction; also combinations .of these means.

300-2. Control Equipment . For control equipment requirements, including combustion safeguards, air flow switches, time relays and temperature controls, see Chapter 5.

300-3. Fuel Supplies. For the handling of fuel supplies up to the point of connection with the furnace, see Section C, Articles 310 and 320, of this standard and the following NFPA standards: Oil Burning Equipment (No. 31), Liquefied Petroleum Gases (No. 58) and Gas Piping and Gas Equipment on Industrial Premises (No. 54A).

300-4. Electrical Equipment . Electrical installation shall be in accordance with the National Electrical Code (NFPA No. 70) and as described hereafter.

24. Delete 310-1 and 310-2 and replace with the following:

310-1. Scope. This section includes heating systems fired with natural gas, commercial manufactured gas, mixed gases, and liquefied petroleum gases.

310-2. Gas burners and associated mixing and control equipment shall be of a construction and proper type for safe operation and suitable for:

REVISIONS TO NFPA NO. 86A 2 2 3 5 OF-8

(a) The Btu content and specific gravity of the gas used.

(b) The operating pressures available.

(c) The maintenance of an adequate air supply to fuel-air mixers for reliable combustion throughout the burner operating range.

(d) In the case of excess air burners, an air-gas ratio for the particular burner shall be maintained throughout the turn-down range. Sufficient air and gas pressures or mixture pressures depending on the type of burner shall be maintained throughout the turndown range so that safe conditions of pressure and secondary air will prevail in the combustion space.

(e) The use of safety interlocks. See Chapter 5, Safety Control Equipment.

(f) A stable pilot flame, either manually or spark ignited, if required. (See 520-8.)

(g) Temperature exposure, air movement and flame propagation as may prevail.

25. Delete 310-4, 310-5, 310-6, 310-7, and 310-8, and replace with the foUowing :

310-4. Other Standards Applicable. (a) Gas piping and valves for natural and manufactured gases shall be installed in accordance with the following paragraphs. Where high pressure services (above 0.5 psig) are utilized, the installation requirements shall comply specifically to the following paragraphs and to the applicable provisions of the Standard for Installation of Gas Piping and Gas Equipment on Industrial Premises and Certain Other Premises (NFPA No. 54A).

(b) Installation of liquefied petroleum gas storage and handling systems used to supply furnace heating systems shall be made in accordance with the Standard for Liquefied Petroleum Gases (NFPA No. 58).

310-5. Pipe Material. Gas piping shall be so constructed and installed in accordance with the Standard for Installation of Gas Piping and Gas Equipment on Industrial Premises and Certain Other Premises (NFPA No. 54A).

310-6. Size of Piping. Piping shall be of a size and so installed

2236 C O M M I T T E E O N O V E N S A N D F U R N A C E S

as to provide a supply of gas sufficient to meet the maximum de. mand at the point of use.

3 1 0 7 . Emergency Manual Shutoff Valves. Manually o p e r a t ~ shutoff.valves, operated separately from a n y automatic valve, shall be provided to permit turning off the fuel in emergency and shall be located so that fires, explosions, etc., at furnaces will not prevent access to these valves.

310-8. Pressure Regulator. Where a pressure regulator or governor is used as part Of a furnace heating system, including gas mixing blowers and gas mixing machines, the a i r space of the diaphragm or bellows housing shall be vented outdoors, or to a safe location unless construction does not require a vent. The vent is not required when the diaphragm discharges through a restricted, orifice into spac e large enough so that escaping gas would not present a hazard (not to be used on 'high pressure gas lines or an LP-Gas System). Also, the vent: is not required for regulators having, t h e diaphragm space connected tod i scha rge piping from mixers through a restricted orifice. T h e foregoing does not apply to zero governors or loaded ratio regulators.

26. Delete 310--1i, 310-12, 310-13, and 310-14, and replace with the following:

3i0-9. G e n e r a l . There are .numerous variations, combinations, and trade names for mixers and burners. A description and definition of the various types of burners and mixers may be found in Appendix D.

310-10. Bu rne r Air Adjus tment shall be fixed or provided with a locking device which will prevent accidental change of setting and shall be so located that adjustments may be readily made.

310-11. Mult ip le Port Burners . (a) Burners having many individual ports shall maintain a stable •flame over the entire length (or surface) of the burner under all draft conditions which may arise in the operation of the furnace. They shall light easily, flash across the entire burner surface and n o t blow off or flash back when the burner is at operating temperatures.

Such burners shalI be careful ly maintained and should be so located that foreign material cannot enter ports.

(b) Multiple port burners shall be.so designed tha t ignition of

OF-10 REVISIONS TO NPPA NO. 8 6 A 2237

gas from e v e r y port shall result rapidly from the ignition of gas at any single port when gas is supplied to the burner at the highest and lowest rates of the control device.

(c) When "modulating" Or "proportional" control is used, the low rate must be set so that burners will light dependably over their entire length or area from the ignition source provided.

$10-12. Tunne l , Nozzle Mix or Torch Burners shall be so con- strncted that a stable flame condition without tendency to flash back or blow off will be maintained over the entire range of turndown and under all operating conditions which may be encountered in furnace operations.

Where a number of nozzle burners are supplied from a single inspirator, the provisions of 310-14, Grouped Burners, shall apply.

27. Renumber 310-15, as 310-13, 310-16 as 310-14, 310-17 as 310-15, 310-18 as 310-16, 310-19 as 310-17, and 310-20 as 310-18.

28. Delete 310-21 and replace with the following:

310-19. B u r ne r Limitations. (a) In any single gas mixing burner assembly when only one burner is used, no valve or control device except a fixed orifice for balancing purposes shall be inserted in piping between the proportioning device and any firing point.

(b) The burner head, tip or line burner shall maintain a stable flame when supplied with correctgas-air mixture over the full range of turn-down.

(e) Line burners (including blast tip burners, radiant types, "infrared burners," and other grouped burners) Shall light over their entire l~ngth when an ignition source is applied to any point on the burner over the entire operating range of the burner. Line burners shall not be used where ports may be subject to obstruction without adequate protection to eliminate the possibility of such obstruction.

(d) All burners shall be regulated to light reliably.

29. Renumber 310-22 as 310-20, and delete (el).

30. Renumber 310-23 as 310-21, and add after "burners" in the third line ojf (a), "except a fixed orifice for purposes of balancing."

2235 COMMITTEE ON OVENS AND FURNACES '"

31. Renumber 310-24 as 310-22, find in the eighth line after "siva~] • taneously," delete the remainder of the sentence and replace with thefollotoin." "and no valves, control devices, or obstructions which will cha~: overall manifold pressure during operation shall, be" pe rmi i~ between the blower discharge and the burner or. burners." -'~

j

32. In 310-22 (former 310-24) (at), third line, change "should', to "shall."

33. In 310-22 (former 310-24) (e), in the second and fourth lines chaagt "should"-to "shall." : , . ,

34. In 310-22 (former 310-24) (h), in the first .line change "should', to "shall", and in the second line after "hydrogen" add "(H~)."

35. Add new 310-23 and 310-24 as follows:

310-23. Pressure-Loaded Regulator Systems usually involve a "Zero Governor" which is cross-connected by means of an Impulse Line to a source of varying pressure for which compensation is desired. Examples include (1) Proportioning Mixers with sealed. in nozzles, with varying furnace pressure, and (2) Nozzle Mixing Burners with single (air) valve control. "

(a) I f a shutoff valve or an adjustment device isin~talled in the impulse line, it shall be done only at the direction of the equipment manufacturer.

310-24. Mechanical Air-Gas Propor t ioning Valves consist of (1) an air valve and (2) an adjustable gas valve and are essentially an interlocked Two Valve Syste m with one valve in the air line and the other in the gas line. - ,

The two valves may depend upon approximately equivalent inlet pressures and flow characteristics for maintaining proPer gas-air ratios throughout the range, or their movement may be synchr0. nized by adjustment of a flexible cam to give desired :gas-air rati~ at multiple positions in the range. ' ' "

(a) If any adjustment device is located downstream from the air-gas valve it shall be done only at the 'direction of the mixer manufacturer and should be protected against tampering.

36. Delete 310-25, 310-261 310-27 and 310-28, a'nd replace with tl~ following: '

$10-25. General. ,Any combination of proportioning control

• R E V I S I O N S T O N F P A N O . 86A 2239 d : C o. blowers or compressors : w h i c h ' s u p p l y mixtures of ~as e v l ~ .

and air to burners • where control devices o r other obstructions a r e installed between, the mixing device a n d , b u r n e r is defined,as~ a ,,gas mixing machine" a n d the provisions of 310-26, 310-27 and 310--28 shall a p p l y .

Nccm: The essential difference between the mixing devices used with automatic p.roportioning b .m-ne.rs, Section E: and the gas mixing machines, is me p.ro .vmlon os a proporuonmg vmve which responds to changes in rate of gas oenvery controlled,atany point between the machine and burner. There are ~e~eral d~. tinct types of g~ mixing " d.evi.'c~ which come within the scope o.i tins secUon axed. ma.y suppl.y premmed gas within the explosive range or wtm only part ot the mr reqmred for complete combustion.

A g~_,, .mi~..~.. g machine . .usually :comprises a pressure regulator or "zero gov .emor wmcn reo.uces megas supply p.ressure to atmospheric and a pro- porUonmg valve ana compressor.

Gas mixing machines may deliver gas-air mixtures which are not within the explosive range, additional combustion air being secured at the burner, either from a burner mixer or directly from the combustion space. They also may, supply mixtures, within the explosive range and, when so installed,..mearm, to prevent flash backs, occurring :in piping containing the flammable rmxture or to prevent damage if flash back should occur should also be provided. , :~ -, ~ ' .:~ :~ . . . . . •

$10-26. Nonexplos ive Mix tu re s (outside flammabili ty limits). Gas mixing machines supplying gas-air mixtures which are above the upper explosK, e ' l imi t shall be :instzilltd ~ follows: . . . .

- 3 .

(a) A stop or other means shall be provided which will prevent effectively adjustment of the machine within or approaching the explosive range.

(b) The machine should be located in a large well-ventilated. area. I f the machine is in a small, detached building or cut-off room, explosion vents shall-be provided in .the ratio of 1 square foot of vent area to each 20 cubic feet of room volume (see N F P A No. 68, Guide for Explosion. Venting).

The choice of location varies considerably in individual installations. I n large, well-ventilated manufactur ing areas there is relatively little chance of leakage accumulat ing in dangerous proportions and, under such conditions, the machine m a y well form an integral par t of a l~urnace heating system.

In considering small rooms where dangerous gas-air mixtures could be formed, the machine is better located in a detached building or i n a small room cut off by concrete walls bonded into the floor and ceiling and provided with explosion relief vents to outdoors. Ent rance t o this room should be directly from outdoors.

(e) W h e n gas mixing machines are installed in well-ventilated areas, the type of electrical equipment shall be governed by the

2 , 2 4 0 on F R .,C S

National Electrical Code requirements for general service con. ditions Unless other hazards in the area prevail.

When gas mixing machines arc installed in small detached lduildings or cut-off rooms, the electrical equipment and'wiring shall be installed in accordance with the National Electrical Code requirements for hazardous locations (Article 500, Class I, Division 2). , .

(d) Machines should, if practical, be constructed so that, in the event of an explosive mixture forming, and flash back resulting, the machine •casing wilinot be ruptured.

(e) Air intakes for gas mixing machines and' combustion blowera using compressors or blowers should be taken from outdoors where. ever practical.

310-27. Explosive Mixtures (Within flammability limits) ~ Ga8 mixing machines supplying gas-air mixtures within the explosive range shall lad installed in accordance With paragraphs 310-26 (b), (c) and (e), and the following paragraphs shall also apply.

(a) Automatic fire checks and safety blowouts shall be provided as called for in 520-7. "

(b) Burners used with explosive mixtures shall be designed with port areas and length of gas passage through each port such that the possibility of backfire is largely' eliminated. When necessary to secure stability of operation, water-cooled burners may be used.

310--28. Controls for gas mixing machines shall include interlocks and safety shutoff valve of ,the manually-opening, automatic- closing type in the gas supply connection to each machine arranged to ,automatically shut off the gas supply in the event of air and/or gas supply failures. (See Article 520.)

37. In 310o29, delete the third paragraph.

38. In 310-34(b), first line, change "should" to "shall."

39. In 310-3d(c), second line, change "should" to "sha l l . " , ¢

dO. In 37003d(d), first line, change "should" to "shall."

4L In 3tO-34(e),first line, change "should" to "shall." '

42. In 31003d (D, second line, change "should" to "shall."

REVISIONS TO NFPA NO. 86A • 2 2 4 1

43. In 310-34(g), replace "prescribe the" with "suggest suitable" in the second line, and in the third line change "should" to "shall."

d4. In 310--35(b); fifth line, change "should" to "shall."

45. In 310--35 (at), sixth line, change "should" to "shall."

46. In 310-35(e), third line, change "should" to "shall".

4Z Delete all of "L Oven H e a t e r Const ruct ion" and replace with the foUowing : •

I. Furnace Heating Systems ' ~

310-$6 General . Furnace heating systems are of two general types, direct-fired and indirect-fired.

310-37. Direct-fired shall mean any heating system 'in which the burners fire within the work chamber. S u c h a system may have multiple burners (see'Fig. 14).

510-38. Indirect-fired heating systems are so arranged that the products O f combustion do not e n t e r the work chamber, heating being accomplished by radiation or convection from iubes or muffles.

(a) Radiant tubes are defined as tubular elements open at one or both ends, constructed gas-tight' Of suitable heat-resistant material, and capable of withstanding explosion pressure from ignition of fuel- air mixtures<,,The tube- has an inlet and/or burner arrangement where combustion is initiated, a suitable length where combustion occurs, and an outlet for the.combustionprodu.cts formed. The fuel- air mixture izan be mixed before, duririg o r after introduction into the tube. The introduction can be accomplished under high pressure, under• slight'pressure, or .unddr suction. Ignition can be accomplished at either the inlet or the outlet of the tube.

Radiant tubes can be located in the actual heating chamber of the furnace or remotely in another chamber. In the latter instance, heat transfer is accomplished by recirculation of heated gases (see Fig. 15).

(b) Muffles are enclosures within a furnace which soparate the products of combustion from the work and from any special atmosphere which may be required for .the process. Burners may be used for direct-firing of the space within the furnace but outside the muffle, or heating of the muffle may be by indirect means using radiant tubes or external furnace heaters (see Fig. 16).

48. Add new Figures ld, 15, and 16.

2242 C O M M I T T E E O N O V E N S A N D F U R N A C E S 0 _ _ ~

L cv°"~ i ~ ~ ~ ~ . ~ . ~ ~.M~ ~

,A-A l O O 0 0 0 0 0 0 0 0 0 ~

• ~ . . . . _ . _ . ~ ' I I ~ f ~ r ~ ' ~ ' ~ ' ~ > > > > ' ~ ' ~ " ' ~ - . - . . . . . . , - . . : . . , - - . . . . . . " - ' , i ' , ' . ' . - ' . ' . - . ' ~ , . ~ ~-.-.... ~. ' . : -.. -#-. v • -. "-'~ :: :--'-"e, '. ," '.~,

CROSS SECTION HORIZONTAL. SECTION

Pi.lo| . NO~e: ~overnor SupFl~es TunnGl Several nurners

TYPICAL PIPING~ DIRECT INTERNAL-FIRED MULTIBURNER FURNACE

F i g . 14. T y p i c a l p i p i n g , d i r e c t f i r e d m u l t i b u r n e r f u r n a c e .

REVISIONS TO NFPA NO. 86A 2243

f To P rod .O f Comb. E x h a u s t SysFem

,,°<,o~11 Y ~ ! I

CROSS SECTION HORIZONTAL SECTION

E. • • ,,Lll .Raw6asisFromOlafra~.mCo.trolValveWh;chlsLoaded oucxo -.,~l~l I /" ~ From'~irSuoolyLineTo Eductor.

))lJ~ ( .... t~ , / / / , , /J TemperatureC~f~oller Regulates Educf0r W'* .u.uq ( ( ( ( I u r // L'-IF'..-.=:_" _, . . . . . . . . . . ~ A i " r P r e s s e

-ressedAirSu-p y) / ~ ~ F < ! ~ / ) ) / Cc~ r~w ~ , ~- ~'~".'~;~;.. ~, ........ ~ = ~

"I"YPIC,~L RADIANT-TUBE BURNER TYpiCAL INDIRECT INTERNAL-FIRED RADIANT-TUE~E FURNACE(CAR-BOTTOM TYPE)

Fig. 15. Typical indirect fired radiant-tube furnace (car-bottom type).

I I I I CROSS SECTION - - HORIZONTAL S E C T I O N - -

Muffli 'typ¢ int=rnel f ir=l muHtb.rn~r furnac=.

Fig. 16. Muffle-type internal-fired multiburner furnace.

2244 COMMITTEE ON OVENS AND FURNACES OF-17

49. In 320-1, third line, change "convertible" to "dual-fuel."

50.(a). In 320-5(c), first line, delete "Oil burners should include:.,, (b). In 320-5(d), second line, change "should" to "shall."

51. Following "E. O v e n a n d Fur na c e Heaters - - O i l Fired" add "(See 310-29, 30, 31, 32, 33, and 38).", and delete 320-8, 320-9, and 320-10.

52. Revise 330-2(c) to read as foUows:

(c) INDUC~ON H~Aaa~R- a heating system by means of which a current-carrying conductor induces the transfer of electrical energy to the work by eddy currents. (See Article 665 of NFPA No. 70-1971.)

53. Replace 330-3 and 330-4, including the Note, with the following:

330-3. Control Equipment. For control equipment requirements, including air flow interlocks, time relays and temperature switches, see Chapter 5.

330-4. Electrical Installation. All parts of the electrical installation shall b.e in accordance with the National Electrical Code, NFPA No. 70.

54. In 330-7(a), delete the last sentence starting "Heaters s h a l l . . . "

55. In 330--8(0, second line, delete "adequately."

56. In 330-10, last line, change "10Kc" to "10KHz."

57. Revise 330-11 to read as foUows:

330--11. Installation. High frequency induction equipment and dielectric heating systems shall not be installed in hazardous locations. (See Article 665 of NFPA No. 70-1971.)

58. Revise 330-12(b), (c), and (d) to read as follows:

(b) Combustible electrical insulation shall be reduced to a minimum. Transformers should be of the dry or nonflammable liquid type. Dry transformers should be in compliance with NEMA TR27-4.03, 150 ° C rise insulation.


(c) Protection shall be installed to prevent overheating of any part of the equipment, in accordance with the National Electrical Code.

(d) When water cooling is used for ti'ansformers, capacitors, electronic tubes, spark gaps, o r high-frequency conductors, cooling coils and connections shall be arranged so that leakage or condensation will not damage the electrical equipment. Thecooling-water supply shall be interlocked with the power supply so that loss of water will cut off the power supply. Parallel water paths should have their own pressure or flow interlock.

59. In 330-13, revise the second line to read: "as required in Article 665 of NFPA No. 70-1971 when applicable."

60.(a). In 340-2(a), fourth line, change "should" to "shall."

b. In 340-4(a), second.line, change, "should" to "shall."

61. In 350-3, second line, change "should" to "shall."

62. In 400-1, delete the last sentence starting "This chapter . . . . "

63. Delete 400-2 and replace with the foUowing:

400-2. The determination of safe oven ventilation shall be based on:

1. The volume of combustion products (if any) entering the oven heating chamber.

2. The weight of flammable constituents, from organic powder or solvents, released during the heating process.

3. Design of the oven heating and ventilation system as to:

a. Materials to be processed.

b. Temperature to which these materials will be raised.

c. Method of heating as to direct or indirect venting of combustion products vs. alternate use of steam or electrical energy.

d. General design of oven as to continuous or batch-type operation.

e. Type of fuel and chemicals to be used and consequent by- products that may be generated in the heating chamber during normal or excessive temperature cycles.

Ovens used to fuse organic powders will require safety ventilation on the same basis as ovens used to evaporate flammable solvents,

2 2 4 6 coM x -- on ov .s Fu.. c s

when expressed in terms of cubic feet of standard 70 ° F air required per pound of the various organic materials being released.

64. In 400-3(b),fourth line, change "should" to "shall."

. . . . . xtLx -~n~e "should" to "shall", in thefirst line, and in the , 9 . I n / 4 U O ~ - J k u ) ~ t . lu.~ ~ , , • , , • .

thffd line add after the word "practtcal the followzng: m accordance with applicable environmental (EPA) regulations."

66. Revise 400-5(d) to read as follows:

(d) Each oven should be equipped with an individual exhaust system not connected to an exhaust system serving other equipment.

Groups of ovens or ovens divided into several compartments may be exhausted by a common exhaust fan or individual oven exhaust fans connected to a common exhaust system• These manifold exhaust systems shall be designed so that the failure or non-operation of one or more exhausts shall not adversely affect the remaining exhausts. Conversely, the operating units will not create a hazard in the failed or non-operating unit(s).

67. Delete 400-5 (0.

68. In 400--12, change "should" to "shall", in the third line, and add ca the end of the sentence "in accordance with applicable environmental

• " n s s ' (EPA) regutatto .

69. Add new 410-3 and d lO-4 as follows:

410-3. Calculated Rate of Ventilation for Powder Fusing or Curing Ovens.

Dilution of the powder constituents released at theoretical minimum explosive condition will require ventilation of:

1. W x R x 360 = cubic feet per hour referred to 70 ° F (Stan-

dard density). 2. To provide a factor of safety of 4 and convert to cubic feet per

minute, the equation above becomes:

W x R x 360 x 4 = SCFM (Standard density) 60

3. To determine the weight of powder for use in the above calculation, the following equation may be used:

W S x T Weight of powder in pounds entering oven per hour C

OF-20 • R E V I S I O N S T O N F P A N O . 86A 2247

The following description is to 'identify the letter symbols above:

W = Maximum intended hourly rate of powder delivery into the o v e n .

R ~ Percent of powder constituents released during oven cure cycle. (Approved value for characteristic powders and operating conditions is 9.0% based on experimental determination.)

360 = Cubic feet of air rendered barely explosive per pound of powder constituent released (based on x y l o l - reference Appendix B).

S = Surface area of parts to be coated in square feet per hour.

T = Maximum powder coating thickness in mils.

C = Manufacturers' recommended coverage in square feet per pound for one mil thickness (135 typical).

410-4. When a direct-fired combustion system (within the oven chamber" or remote) is used to heat a paint or powder curing oven, the volume of combustion products from burners shall be determined for stoichiometric operation by the formula:

BTU (Total Burner Rating) Cubic feet of air per minute - - = (SCFM) referred to 70 ° F

95 x 60 (Standard density)

When this calculation for 70 ° F equivalent volume is greater than one third ( ~ ) of the volume determined for removal of chemical by-products (from 410--1-2 or -3) , the minimum exhaust volume for the oven will be the sum of the two computations, adjusted for thermal expansion as per 400-10. When the combustion products are less than one third of the volume determined for removal of chemical by-products, the minimum exhaust volume for the oven shall be based on the volume for removal of chemical by-products only, with adjustment for thermal expansion as per 400-10.

70. In 420-1(b), second line, change "should" to "shall."


7Z In 430--4, first line, change "handholes" to "access" and delete the second sentence.

73. Delete all o f Article 440.

74. Delete the last two sentences in 500-1(c) and all oaf (d), and in 500-1(c) after "a t all." in the fifth line add the following:

2248 C O M M I T T E E O N O V E N S A N D F U R N A C E S ' OF-21

"Safety devices shall be properly designed and installed Where prescribed in this standard. Safety devices shall not be shorted out or by-passed in the systems. All safely devices, including the oven or furnace, shall be inspected and maintained in accordance wifh the typical maintenance check list in Appendix I. Where 'special main. tenance and inspection procedures are required due to' the" nature • of the equipment, plant management and the authority having "urisdiction shall rescribe the time interval at which the equil~ JmUent ~and controlP: shall be tested for service, reliability based on reco.mmendations of the equipment manufacturer."

75. In 510-1, in the second line after "dampers," add "position limit switches."

76. In 520-1, in the second line after "switches" add "(high and low)."

77. In 520-2, replace "can usually be considered as" in the fourth and fifth lines with "is"; change "should" to "shall" in the elebenth, fourteenth, and sixteenth lines;" and delete "I n general," in the sixteenth line.

78. In 520-3, delete "periodic" in the second line, after "provided." in the third line add "(See Appendix I)." Delete tl~. last sentence starting "Two procedures . . . " , and delete the "Note." .

79. Transfer Fig. 15 to Appendix I and renumber as Fig. 27.

80. In 520-,t, renumber "2" as "3", and "3" as "2. '~ ,?.

81. ~Ddete 520-5 and replace with the foUowing: :

520--5." Pressure Limit or Supervisory Switches. Pressure Limit or Supervisory Switches shall be provided to prove

fuel, atomizing medium and combustion air pressures are Within design limits for the burner or furnace. These pressure limits or supervisory switches are, but not necessarily limited to:

(a) HIOH GAS PRESSURE SWITCH. A pressure activated device arranged to effect a safety shutdown of the burner or burners or prevent the burner or burners from starting in the event of abnormally high gas pressures. The attention of qualified personnel shall be required before restart.

(b) L o w GAS PRESSURE SWITCH. A pressure activated device arranged to effect a safety shutdown of the burner, or burners or prevent the burner or burners from starting in the event of abnormally low gas pressure. The attention of qualified personnel shall be required before restart.

0~--2~ RETISION8 TO NFI'A NO. 8 6 A 2 2 4 9 t

(c) L o w OIL PRESSURE SWITCH; A pressure activated device ar, ranged to effect a safety shutdown of the oil burner or burners or to prevent ~t or them' from starting when the oil pressure falls below that recommended by the burner manufacturer. The attention o f qualified personnel should be required before restart.

(d) ATOMIZING MEDIUM PRESSURE SWITCH. A pressure activated device arranged to effect a. safety shutdown or to prevent the oil burner or burners from starting in the event of inadequate atomizing medium and oil is the preferred supervisory method when system" design permits.

(e) COMBUSTION AIR PRESSURe. SWITCH. A pressure activated device arranged to effect a safety shutdown or to prevent the burner or burners from starting in .the event-the combustion air supplied to the burner or burners falls below that recommended by the burner manufacturer.

82. In 520-8, revise I and 2 to read as.follows:

1. FIXED PREMIXED PILOTS FOR MANUAL-LIGHTED FURNACES. The main burners of gas- and oil-fired manual-lighted furnaces should have fixed premixed pilots. These pilots shall have sufficiently large capacities to insure ignition of the main burners, and their flames shall b e stable even during substantial fluctuations in draft or back pressure. Each pilot-mounting assembly shall be ~ designed and installed so tha't the pilot cannot be moved out of the position and will furnish reliable ignition for the burner.

Exception (a): The main. burners ~ gas- and oil-lired manual-lighted furnaces do not require premixed pilots but may be ignited by gas- or oil-fired portable burner pilots or by oil-soaked swabs placed in proximity to the burner nozzles by the burner man, provided approved combustion safeguards are wired into the safety-control circuit as described under Com- bustion Safeguards, 560-14, or they are indirect-fired with radiant tubes.

Exception (b): The main burners of gas- and light (Nos. 1, 2, and 4) oil-fired manual-lighted /urnaces do not require premixed pilots but may have direct electric ignition, if the burner design makes, premixed pilots impractical.

Exception (c): Self-piloted burner. A burner having no pilot burner as such; but one where the main flame's fuel and combustion air are, after being issued from the nozzle arrangement, immediately merged with the piloting flame for continuance as a single flame that has a single flame envelope.

When a burner is self-piloted, there is absolutely no safety advantage to ~ interruption of the pilot flame.

2250 COMMITTEE ON OVENS AND FURNACES ' OF--~

• 2. FIXED PREMIXED PILOTS FOR SEMIAUTOMATIC-LIGHTED" FUR. NACES. The main burners of gas- and oil-fired semiautomatic. lighted furnaces should have fixed premixed pilots. These pilots shall have sufficiently large capacities to insure .ignition of the' rnaha burners, and their flames shall be stable even during substantial fluctuations in draft or back pressure. Each pilot-mounting assembly shall be designed and installed so that:the pilot cannot.be movec [ out of the positio nand it will furnish reliable ignition lor tlae ~urner.

Exception (a): The main burners of light (No. 4 or lig.~.er)~oil-fired semiautomatic-lighted furnaces do not require premixed pilots bu~ may have direct electric ignition if the design of the burners makes gas pilots impractical. , ; .... - Exception (b): The main burners of.gas-fired semiautomatic-lighted

furnaces do not require premixed pilots but may have direct electric ignition if the number of burners or their design makes ~emixed pilots impractical.

Exception (c): The main burners of oil-fired automatic-and, semiauto. matic-lighted furnaces do not require 'premixed pilots but may have oil.

,fired portable burner pilots. . Such pilots shOuldhave suffcien¢ly large capacities to insure provision of reliable ignition for the main burners, and their flames should be stable even under conditions of substantial fluctuations in draft or.back pressure. , , " ,

Exception (~ : ~Self-pilqted "buiner: A "burrie~' having no pilot burner as such; but one where the main flame's fuel and combustion air are, after being issued:f thin'the nozzle arrangement, immediately merged with the piloting flame for continuance as a single flame that 'has a single flame envelope. When a burner is Self-piloted, there is absolutely no safety advantage to

.interruption of the pilot flame. . , "

83.:. In 520 °0 lO(a) i in the fifth line,'change "60 seconds" to "15 seconds."

hnechange 6 seconds" to seconds 84. In 520--10(0), in the fourth " " 0 "30 when using heavy 0il and '15 seconds when using light oil," and in the sixth and seventh ,lines." change "60 seconds in all events" tO "30 seconds when using heavy oil and 15 seconds when using light oil."

85. In 540--l(b),fourth line, change "should',,t0 "shall", and delete the • . . ' , , .

last sentence starting "Higher settings . . . , : ' 7 . . . . ,

86. In 540002, sixth line, delete "(Class D).'" "

87. In 540004, first line, change "should" to "shall," and delete "only" in the second line.

• R E V I S I O N S T O N F P A NO. 8 6 A 2251

88. In 5J0--5, Change "should" to "shall" in the second and sixth lines.

89. Revise 560--5 to read as foUows:

560-5. Pilots (does not apply to radiant tubes - - see 560-24). (a) Gas pilots should be provided for ignition of main gas and

oil burners. These pilots shall be: 1. Stable under a l l operating conditions of the equipment. 2. Properly sized to give a reliable ignition of the main burner. 3. Properly posit!~ned to give a smooth ldghtoff of the main

burner. 4. Fixed in position in relation to the main burner.

(b) Ignition . . . . . of pilot burners may be either manual or electrical. If manual lgnmon is employed, either a supervising cock system or a flame detecticin system Shall be provided to insure that the fuel to the main-and pilot bu÷ners is shut off before ignition can be attempted. '

(c) Ignition "of pilot burners shall not be attempted unless the furnace is in the preventilated condition relating to fan operations, open doors, and full open dampers.

(d) Where 'main burners operate continuously, and)or flame supervisory equipment is provided, interrupted pilots may be employed. Continuous burning pilots may be used where main burner operations so dictate.

(e) Spark'ignition of main gas and oil burners is permitted provided that the burner is provided with proper combustion safeguard equipment (see 560-14).

90. In 560--7, revise (b) to read as foUows:

(b) Pressure or air flow switches installed at proper locations may be required to prove the required air supply. (See 510-1 and Ap- pendix D.)

91. In 560-8, in the first line, delete "Direct."

9Z In 560-9(d),.delete the last sentence starting "Where cond i t ions . . . "

93. In 560-10(b)i in the sixth line, change "should" t0 "shall."

94. Revise 566-14 to read as follows: ' ~

560-14. Combustion Safeguards. In general, i~ach, burner should be equipped with an approved instantaneous (flame sensing).corn-

2252 0F-25

bustion safeguard (see 520-4), arranged through suitable approved safety shutoff valves to shut off fuel to the burner and its pilot in the event of flame failure.

" cn r o ~ (~L l | l g l ~.JLJ T~ ~ . b u r n e r f u r n a c e s w.m p _ - ' ~ ' " a l so a hes t o t hose temperatures both above and below 1400 F. This pp zones of a multizone furnace where zone operating temperatures are under 1400 ° F.

ized that properly applied and applicable combustion, safe- It is recog~. . . . . . . . . tection on higher temperatmre fumacea

• ,dugOng c a n a t s o g zve v~uau~ l~"~ . . . _ _ _ u ~ ~er iocls w h e r e t e m p e r a t u r e s t h e i n i t i a l lighting-oil a n Q .w~,u,,- ly. v _ ~ . _

c a n b e u n d e r 1 4 0 0 ° F . f o r c o n s i d e r a b l e t e n g t h S oa u m g .

The flame-sensing element of the combustion safeguard should be located so as to prove the pilot flame and monitor at the inter. section of the main and pilot burner flame paths, so that prompt reliable ignition by the pilot is assured before the main fuel valves can be opened. In addition, these approved combustion safeguards shall be wired into the safety control circuits to provide a n ac. ceptable sequence of operation during lighting off, firing, and relighting as follows:

(a) Gas-fired semiautomatic lighted furnaceswi th fixed gas

pilots. 1. Before permit t ingthe m a i n gas safety shutoff valves to be

energized and opened, the existence of a gas pilot flame should be proven at locations where flaey will reliably ignite the main burners.

2. The main I~urners shall be immediately ignited by the pilots even when they are reduced to a minimum flame that will barely h d d the flame-sensing relay of the combustion safeguard in the energized (flame) position.

3. There shall be no automatic recycling after accidental flame failure; all fuel shall be shut off (safety'shutoff valves tripped closed) and electric ignition deactivated.

4. The pilot flame establishing perio d and/or the mare burner trial for ignition period shall be automatically limited to notmore than 15 seconds unless the authority having jurisdiction grants an extension. If the authority having jurisdiction considers such an extension, the following conditions must be met:

(4a) A written justification must be submitted for the extension. (4b) "The time period shall not exceed 60 seconds. (4c) An extension for the timing will be granted 0nly after it

has been determined that no more than 25 per cent • of L . E . L . is the maximum permitted under the most• extreme o~ra t ing con-

ditions. At continuous-line burners, including~ "those composed of a

limited number of individual radiant burners o r line-burner

0F-26 REVISIONS TO NFPA NO. 86A 2253

sections located directly adjacent to one another, supplied from a common burner manifold and having reliable flame propagation between the consecutive individual burners without special external flame-propagation devices, the length of burner supervised by a single approved combustion safeguard shall not be more than 50 ft: At burners where the total length exceeds 20 ft., the trial-for-ignition periods should be automatically limited to not more than 15 seconds after fuel is available at the burner head. (See Figure 17.)

At continuous-line burners composed of a number of individual radiant-cup burners that are not located directly adjacent to one another but a~:e supplied from a common burner manifold and have reliable flame-propagation devices, the maximum number of individual burners in a group supervised by a single approved combustion safeguard shall be 50. The total distance of the single-flame path from the first burner ignited to the last in the group, where the flame-sensing element should be located, shall not exceed 50 ft., the individual burners should not be spaced more than 30 in., the trial-for-ignition periods should be auto- raatically limited to not more than 15 seconds, and it is not necessary during lighting-off to prove the pilots before permitting the main safety shutoff valves to be energized and opened. (See Figure 18.)

(b) Gas-Fired Manual Lighted Furnaces. 1. At main gas burner s ignited by pilots or portable torches, the

existence of the pilot or torch flames should be proven at locations where they will reliably ignite the main burners before permitting the main gas safety shutoff valves to be energized and opened.

2. There should be no automatic recycling after accidental flame failure.

3. T h e pilot flame establishing or main burner trial-for-ignition periods shall be automatically limited to not more than 15 seconds.

4. When using, fixed pilots, the 15 second flame establishing period shall apply to pilot ignition only. When using portable otorches, the 15 second trial-for-ignition period shall apply to main

• burner ignition only.

The following are exceptions to 560-14:

Exception (a): Multiple burners where combustion safeguards for each burner are too numerous to be practical, but continuous line-burner type pilots Jor groups of burners (see Section 310-11) can be used: An approved practically instantaneous combustion safeguard shall be provided at the far end of each line-burner type pilot, awayJrom the pilotJuel source, with sensing element located at the junction oJ the flame paths of both pilot and last main burner. The pilot safety shutoff valve must be initially opened by a manual momentary push button.

2254 C O M M I T T E E O N O V E N S A N D F U R N A C E S

.

Exception (b): Where two burners, which will reliably ignite o~ from the.other, are used, it shall be permissible to use a single .approved in. stantaneous combustion safeguard supervising one oJ the burners; the supervised burner shall burn continuously at a firing"rateat alg times suffdent tO reliably ignite the unsupervised burner.

Ex pce tzon "( ).c Burner for direct fired, gas heating systems which sub,t,.., r - . ,

a Jurnace at a fuel rate not. exceed, ng 150,000 Btu/.h.r may be equq~ed with heat actuated combustion saJeguards or sajety puo~s, t~ee Article 520.). For small equipment under constant attendance, ap.pro~hing in size the household gas range or very small laboratory test .[ur.nace, corn.

' bustion safeguards may be omitted, subject to approval oJ the authority having jurisdiction.

Exception (d): In general,/or greatest security, all burners should be protected with combustion sa.[eguards as outlined in the .[oregoing sections. When this is impractical the maximum practical protection should be

.furnished by providing a reliable continuous pilot at each burner, and[o~ operating burners on high-low flame, and by installing devices (press~e switches and sa.[ety shutoff valves) (See Article 520) to assure, where practical, closure "of all individual burner cocks beJote the main burner safety shutoff valve can be opened, and to shut off all gas in case q I~'gh and low ~gas pressure and low air pressure, where air pressure is necessary

.[or operation of burners and controls, subject to the ap~oval of the au. thority, having jurisdiction.

A method o.[ assuring closure o[ all individual gas burner cocks be[ore the main burner gas safety shutoff valve can be opened is the supervising cock and gas safety control system. A typical piping and w#ing arrange. ment using the pneumatic type supervising cock is iUustrat'ed in Fig. 20. (See 520-9.[or details o.[ Supervising Cock.) The number and location

L . / / / / / / A . 1 ~ / / / / / / 1

• - ~ ~ U ~ - L = / ( F v 4 c ° c t

. . . . ,,,,or . ~ , " ~ ~ J - ' l T , . 4 ¢ : m ) . ' l ' f - - d : ~ i ~ - t ~

P,*ot r - ~ ~ ~ z ~ o , , . I

, ~ 1 ~ , . ~ - - - = 1,0~ I ' ~ ' l ~ . . k ~ll us- ~ r~ . . ' , , - ,~ , , ,o , , i " ~ Line - l¢ ~1 . Checkinq Pressure F i l t I r

Cow.A;, ' - [ k ' ~ - ' / - " " - " '

V81vcI,Moe, u~ll~A~$ek 'foe" I ¢ l k , l q l l t e l t O f ~l~ll~hOm~zilro~jovsfl~...u~F.~n " l r ~ - i [ i / l l . ) • .. . Safetg, Shul:.owV~lv e irn~ir~a~r au'ld~Supcrws*n9~...s

• ' Cock I t e ~ h burner . to pe r~ ~C indiv idu~t t igh~in 9.

¥ig. 20. Supervi~ng Cock an(I Gas Safety ~ontrol System


of pressure switches, arrangement of tubing and Other details will vary ~vith the individual installation. In the illustration, the main burner safety shutoff valve cannot be opened until all supervising cocks are closed, combustion air pressure is normal,: and normal gas pressure present in the pilot burner manifold. Power failure, loss of combustion a#, and/or oWmpa s pressure failure during normal firing will shut and lock out the main

net and pilot safety shutoff valves. Once the initial check has been' leted and the main burner safety shu'toff valve is opened, the low gas

pressure switch dow'nstream jriom thi safety' shutoff valve shunts the checking pressure swztch so that, after lighting the' pilots~ the supervising cocks can be opened to light off. " ~; : ~ '

A typical piping and wiring arrangement for the elec'tric interlocking type supervising cock is"also illustrated in 'trigs: 26. T h e main burner safety shutoff, valve cannot be opened until all supervising cocks are closed (cock switck contacts in series are al l closed), ventilation )Cans operating, preventilation purge completed and other interlocks satisfied." "

• . ' . j - . ) , . - ]

95. Renumber Figures ~ 16, 17, and 18 as Figures 17, 18, .and 19, re- speaively. ~l . . . .

96. Revise 560-15 to read.as..foUows:

560-15. Safety Shutoff ,Valves (See 520--2.) : : .. ,,

(a) When the main heating system input of the furnace is greater than 400,000 Btu's per hour, an approved safety shutoff valve shall be provided i n the main gas line to the burner.• A second approved safety shutoff valve shall be pro;tided 'downstream from the first safety shutoff valve. An appropriately sized normally open dectrically operated valve shall be provided i n a vent line between the two safety shutoff valves. •The vent line pipe shall be run to a safe location, .preferably outdoors, and shall be accessible for inspection.

The safety shutoff valves" shall be arranged to dose and the vent valve shall b e arranged to open in the event of failure of combustion air, excessive combustion a i r pressure, flame failure, excessive temperature, excessive gas pressure, too low a gas pressure and failure of electric current.

When recirculating and/or exhaust fans are used and are essential to the proper operation and safety of the furnace, the failure of the recirculating fan and/or exhaust fan shall also close the safety shutoff valves and open the vent valves.

(b) When gas pilot systems are piped up stream from the main line gas burner Safety shutoff valves and the pilot system capacity is greater than 400,000 Btu's per hour, this same double safety shotoff valve system with a vent valve shall be used.

2256,. ( c ) When the main heating system input of the furnace is 400,000

Btu's per hour or less, a Single approved safety shutoff valve with. out a vent line may be used in place of the double safety shutoff valve and vent valve system described in 560-15(a) and 560-15(b). , : • noid valves may b e used as the prirna~

1 . S p r m g l o a d ` sol~L, c--~i flow uo 'to 400 000 Btu's per hour, dr safet shuton valve wm~ ~u~- _--- . _ . . _, . . , _ . - .Y . _t . . . . . ~-.,toil valve w~th the aoume smety shutoff ag tlae seconaary sax~ty ~i~, valve and vent system described in 560-15(a) provided:

a. The seating force of the spring is a minimum of five pounds, exclusi've o f"dead weight" of the assembly and fuel pressure

exerted. • ° .' b. Their use does not necessitate any 'abnorrrial settings of

' eithei" the high or low gas pressure switches to counter any • transient' pressure fluctuations created by sudden operations

of the valve. 2. Other solenoid valves, not meeting the above specifications

may be used when all three of the following conditions prevail:

a. The flow is less than 150,000 Btu's per hour. b. The valve size and pipe size is a/~ in. or less. c. The gas pressure is five (5) Psig, orless'.

(d) The attention of the operator shall always be required before

restart. (e) A leak test facility shaR be provided downstream of each

safety shutoff valve. See Fig. 27 in Appendix I for proper location

and procedure. (f) Vent lines, where specified above, shall be as follows:

1. For fuel line diameters larger'than 8 in., the Ventpipe shall be at least 15 percent of the cross sectional area of the' main gas pipe. If the main line is less than 3/~ in., then the vent line shall be equal to the cross sectional area of the main line. .,

2. Vent valve ports shall have a cross aectional area equal to the

specified vent line. 3. Vent lines should have a maximum length of 40 feet and

discharge to outside atmosphere. If longer runs are unavoidable, or an unusual number of fittings are necessary, a n increase in vent

size may be necessary. 4. Manifolding of vent lines should be avoided. If manifolding

is absolutely necessary, then the cross sectional area of the manifold pipe must be equal or greater t han t he sum of the cross sectional areas of all individual vents involved.

5. See Figure 28 in Appendix I.

R E V I S I O N S T O N F P A N O . 8 ( ~ A 2257

VENT 'PIPE SIZE TABLE

• F U E L L I N E • • V E N T L I N E

• ~ D I A M E T E R " D I A M E T E R

up to 1½"

• 2 ½ " 3" 3 ½ " 4 "

-4½" 5"

• 5 ½ " 6 " ' " -" - ' "

6.1/2', 7 " "

7 ½ "

8"

1"

11/~" 1½" 2" 2" 2"

. 2 ½ " ...... 2 ½ "

"" 3 " ,

3 " ' 3" 3 ½ "

97. Relocate Fig. 19a.to Appendix I and renumber as Fig. 25.•

98. Relocate Fig. 20 to'Appendix D and renwaber as Fig. 26.

99. In Article 560, delete "E" , and replace with the following:

E. Safety Control Application - - Indirect Fired Gas Heat ing Systems

Using Radiant T u b e s - - • Explosion Resistant

560-24. These systems are defined in 310-38(a). Each radiant tube heating system or combination of systems (when two or more are combined into a single processing line with a common combustion system) shall have the.following, sa_feguards, as covered in 560-25 through 560-31.

560-25. The main fuel supply shall be supervised by means of suitable pressure switches. Both: automatic and manual reset • types are acceptable. Switches shall be arranged to detect abnormally high or low fuel pressure. They shall be interlocked With a safety shutoff valve to stop the flow of fuel when abnormal pressure occurs. The low pressure switch shall be set below, but still within, the operable

2,258 COMMITTEE ON OVENS AND FURNACES

range of the combustion system. The high pressure switch shall 1~ set above, but still within, the operable range of the combusti~ system.

The safety shutoff valve used in the main fuel supply line shall be manually-opened, automatically-closed type. This valve shall h~ properly interlocked to shut down upon any abnormal operating condition or failure of the safety control circuit.

A leak test facility shall be provided downstream of the fuel supply safety shutoff valve.

Pilots should be piped upstream of the main gas safety shutoff valve with a separate safety shutoff valve and low gas pressure switch. If the manufacturer decides to locate pilot supply line downstream of the main gas safety shutoff valve, means shall he pr.ovided to prevent the introduction of gas to the main burners prior to energizing pilot valve.

560-26. On units utilizing a pressurized combustion air supnlv a suitable pressure switch shall be provided to supervise this suppl~'. Both automatic and manual reset types are acceptable. The low pressure setting shall be within the operable range of the combustion system. This switch shall be satisfied before the safety shutoff valve can be opened.

On combustion systems requiring pressure reduction, a high pressure combustion air switch shall also be provided. It shall be interlocked to shut off main flow of fuel when excessive air pressure is detected. This setting shall be above but still within operable range of the combustion system, Radiant tube installation employing pull-through or induced draft for induction of combustion air shall provide suitable interlocks to close fuel valve upon loss of adequate combustion air.

560-27. Purging of Radiant Tube-Type Heating Systems. Pre- ignition purging of radiant tube-type heating systems is not required, however, special conditions may require purging of furnace work chamber.

560-28. Flame Supervision and Burner Ignition. Flame supervision of the radiant tube burners is not required; however, a suitable means of ignition shall be provided. Initial ignition can, be manual or automatic. Subsequent ignition can be by auxiliary pilot, by continuous self-piloted burner, or by direct spark ignition.

560-29. Flue Product Venting. A suitable collecting and venting system for the radiant tube-type heating systems shall be provided by the user. The system shall be of sulticient capacity to render the total unburiaed input capacity of the radiant tubes noncombustible.

The flue venting products system is to be considered as part of the plant exhaust system.

R E V I S I O N S T O N F P A NO. 86A 2 2 5 9

9~0.~0 . An Excess Temperature Limit Switch or Switches should be provided as outlined in 560-16.

5(~..31. Auxiliary Interlocks shall be provided as outlined in

560-17-

i^,, Renumber "560-30" through "560-50" as "560-32" through 0 ~]" , ,

,,560-52, respectively.

101. In 560-38 (former 560-36),first line, change "310-39" to "310-31 and 310--38."

102. In 560-45 (former 560-43), Exception (b), fifth line, change ,,should" to "shall".

103. In 560-47 (former 560-45),fourth line, change "should" to "shall", and delete the "Exception."

104. In 560-50 (former 560-48), first line, change "Program Relays" to ,,Combustion Safeguards".

105. Rtoise 570-1 to read as follows:

570-1. Safety control application for furnaces lacking fuel hazards shall provide protection from excess temperatures, loss of secondary systems (cooling, material handling, etc.) essential to normal operation of the furnace. Controls and arrangement shall be as outlined in the safety control application for electric furnaces. Instru- ments shall be of the fail-safe type (see Appendix A).

tO6. Replace 570-2, 3, 4, 5, 6, and 7 with the/oUowing:

570-2. For a description of these systems, refer to Article 330. Each furnace, or heat processing system (including resistance, induction, electric arc or plasma device) shall be provided with the following control devices and safety control circuits for proper operation.

570-3. Heating Equipment Controls. (a) Electric heating equipment of other than the portable type shall be equipped with a main disconnect device, capable of de-energizing the entire heating system under load to provide safety for secondary measures necessi- tated by one or more of the following conditions:

1. A system short circuit not cleared by supplemental branch circuit protection.

2 2 6 0 COMMITTEE ON OVENS AND FURNACES O F - ~

2: Excess furnace temperatui'e. " 3. Failure of normal operating controls. 4. C~mplete or partial loss 6f poweri'such as single phasing of a

multiple phase power system. The interrupting capacity of the main disconnect device (see

AppefldixF) shall be adequate to clear the maximum 'fault'current capability of the immediate power supply system (fault ~ current shall be determined from the voltage and impedance of the furnace power supply circuit, not from. the summation of We operating load currents). Other disconnect means in this power supply circuit may be used as the heating equipment main disconnect" provided furnace operation can be terminated without affecting operation of o ther essential equipment. Automat ic versus supervised operation of the "main heating system disconnect" shall be governed by the furnace size, design characteristics and the potential hazards involved. • ' . . . . ~ :"

• , " , .

NoTs: Whcn operation of a multiple phase "main" disconnect'" ts to be manually supervised, each phase of the 'power supply circuit should be equipped to show electrical potential on. the protected or load side,, as an indication of intended operation, partial or Complete lpss of power.

Portable furnaces may be equipped with main disconnect devices • e above re uirements, b u t if not, the power supply circuit tt° ~heeeftr~ace shall ~q so equipped: Supplemental el~cmcal controls (contact0rs, circuit: breakers, relays~ signaling devices, etc.)' shall be provided in accord-with.~safety, temperature control, branch circuit and auxiliary system requirements. ' , !:._;

(b) The capacity of all electr.ical dev{ces iased t 0 control energy for the heating load shall b6 s'elected off the basis Of continuous duty load ratings when fully equipped f0r: the.location and type of service proposed. This may require de-rating some components as listed by manufacturers for other types o f indus'trial service, motor control, etc., and shown in Table I I .

(c) All controls, ,using thermal protection o r 'trip mechanisms, shall be so located or protected as to preclude ffiult~; ope r~tioff due to abnormal temperatures;or other furnace hazards . . . . .

570-4. Ventilation Controls. When removal Of by-product vapors is essential to the safe operation of the furnace, controls and interlocks shall be provided as outl!ne'd in Article 560, Section B.,

570-5. Material handliiig or positioning ~oritrols shall b@ arranged for proper sequence of operation with other furnace (sp&ial atmosphere and safety contrOls), and also to assure'emergency action as may be needed in the event of. malfunction of the material handling system. - •

017-"34 RE¥ISIONS TO NVPA NO. 86A "~ 2 6 1

TABLE II

ReSistance Type Heating Devices

Control Device Rating in % Permissible

of Actual" Current in % Load of Rating

Fusible Safety Switch p%rating of Fuse em- loyed) : '~,

Individu/Llly Enclosed Gircuit Breaker

Circuit Breakers in En- closed Pandboards

M a g ~ Con tactors .Amperes

30-100 Amperes " 150-600 Amperes

125 80

125 80

133. 75

111 90 111 90 111 90

Rating in % p ~ of Actual Current in %

Load of Ratin~"

133 75

125 80

133 75

200 50 167 60 125 80

NoTs: The above applies to "maximum load" or open ratings for safety switches,~circuit breakers, and industrial controls approved under current NEMA standards.

Exceptioh" I t is permissible to install provision for operating conveyors manually or by means of a constant pressure pushbutton for the purpose of removing material from the furnace in event of malfunction in the automatic system.

570-6. Where a furnace is subject, to damage, a n excess furnace temperature limit control shall be provided for annunciat ion and interruption of power supply to the furnace heating system.

Manual reset shall be provided to prevent automatic restoration of power.

These controls shall be in addition to any normal operating temperature control devices.

570-7. Branch circuits and branch circuit protection for all electrical circuits in the furnace heating system shall be provided in accordance with the National Electrical Code (NFPA No. 70).

570-8. Main Disconnect to Power. See Appendix F.

107. In 640-2,first line, change "should" to "shall."

108. In 640-3, first line, change "should" to "shall."


A P P E N D I X B. T A B L E O F P R O P E R T I E S O F C O M M O N L Y U S E D F L A M M A B L E L I O U I D S

• I N M E T R I C U N I T S . . . . . . . . The d a t a in this table have been obtained, with f . . . . . pt ions ~ noted, from N F P A Pamp ld, et No. 3.25 (1960iEdit ion). de~ theProPue~ t t iyeSoo~da~o~a~e~ l lqUa l~Sc i

Gases, an d Volatfl.' .e Solids. A v a ~ b l e .~llrc~ from numerous so ur.c.es wili be found . to ~orar~mfOVre~a~naea~r~n~en~r~a~ida~V~no~ aPd a~U~not to b ~ r e ~ r d e d as official s t aada .r.~... on the tss t .conmtions preach, v:c~. n y mneren~onser~'em. ~ a e n g u v ~ v~L~_ ~ a c ~ u a ~ t ~ t e on p a ~ i ' c o ~ r l~aint formulation in~nse needs to be em.ph,,osized.. Some of these multz- componThn~ pmePprr~ta~cL°f°b~psr~c~a~v°nt~nei~tewi°~e~aaPiffrareU°~valuce of "Io ..... plos ive l~mzt~ -~s~e~ cxfic grawty , and.~a,por den~i'ty~.. Unut~uchdel~r~Zunat~o ~

-o~1~ * ~ ~ t ~ n n ~hnnld be on the side of safety Therefore the individual solvent wnoce oa ta re~ulz in m e [arges~ r e q u t ~ . ~ u , . ~ ~* ~.- ~,~ . . . . . . ~ t~e ~ a ~ for safe venti lat ion. C u r e ' o n e and factors o~cefety for final vent i la tmn values are to he applied as indicated xn the footnotes j

Approx., Cu. A B C D E F G H I Meters of Air

Molecular Flash Ign. Explo. Limits Specif. Vapor Boil ing Kg. Cu. l~,leters of Vapor rendered barely Weight (a) Point Temp. % by Volume Grav i ty Density Point Per Per Liter Per Kg. explosive per

Deg. C. Deg. C. Lower Upper (Water ~ 1) (Air ~ 1) I)eg. C. Li ter Liquid Liqmd Liter of Solvent Acetone 58 --18 538 2.6 12.8 0.8 2.00 56 0.797 0,332 0.416 12.44 Amyl Acetate n 130 25 378 1.1 7.8 0.9 4.5 159 0.899 0.166 0.185 14.78 Amyl Accetate iso 88 25 379 1.0 7.5 0.9 4.6 144 0.899 0.166 0.185 10.44

@ 100°C. Amy | Alcohol n 88 33 300 1.2 10.0 0.8 3.0 138 0.797 0.221 0.277 18.23

@ 100°C. Benzine (Petroleum Ether) < - 1 8 288 1.1 5.9 0.6 2.5 35 - 6 0 0 .598 0.199 0.332 17.89 Benzol (Benzene) ' '7"8 --11 562 1.4 7.1 0.9 2.8 80 0.899 0.267 0.297 18.72

100°C. Bu ty l Aceta te n l lO 22 421 1.7 7.0 0.9 4.00 126 0.899 0,186 0.208 10.73 Bu ty l Alcohol n 74 29 343 1.4 11.2 0.8 2.6 117 0.797 0.256 0.323 18.01

1.7 10.9 0.8 2.8 110 0.797 0.256 0,323 14.80 Buty l Alcohol - - mo 74 28 427 @ 100°C. @ 100oC. Bu ty l Cellceolve 118 60 244 . . . . . . . . 0.902 4.07 171 0.898 0.184 0.203 . . . . Buty l Propiovate 130 32 427 . . . . . . . . 0.9 4.5 146 0.897 0.167 0.186 . . . . Camphor • 152 66 466 . . . . . 1.0 5.2 209 0.996 0.160 0.160 Carbon Disulphide 76 - 3 0 100 1.3 ~ " 1.3 2.6 46 1.295 0.415 0.320 31'.5 ;) Cellosolve ( E thy l Cellceolve) 90 40 238 2.0 15.7 0.931 3.10 135 0.928 0.249 0.270 9.34 Cellosolve Acetate 132 81 370 1.7 0.975 4.72 156 0.974 0.172 0.176 9.93 Chlorobensene-mono 113 32 638 1.3 ' 7~1 1.1 3.9 132 1.097 0.234 0,214 17.77

100°C. @ 150aC. Cottonseed Oil (Refined) . . . . 252 343 . . . . 0.9 . ' . 0.899 . . . . . . . . . . . . Cresol m or p 108 94 559 '1~i" . . . . 1.0 . . . . '2"()2" 0 .998 0.223 0.223 20.04

@ 150°C. Cyclohexane 84 - 2 0 260 1.3 8 0.8 2.9 82 0.728 0.229 0.286 17.38 Cyelohexanone 312 44 420 1.1 . . . . 0.9 3.4 156 0.899 0.218 0.242 19.57

@ lO0°C. Cymene-para 134 48 436 0 .70 . . . . 0.9 4.0 176 0.899 0.163 0.182 23.13

@ IO0*C. Denatured Alcohol 16 399 ........ 0.8 1.0 80 0,798 0.415 0.520 .... Dibutylphthalate o "27"8 157 403 .... 1.0-[- .... 360 0.998 Dichlorobenzene ortho 147 66. 648 "2'.2 ' 9.2 1.3 5.1 180 1.297 0.212 0.1~3 '9.41 Diethyl Ketone 86 . . . . . . . . . . . . 0.816(a) . . . . 102(a) 0.813 Dimethyl Formamlde 73 " "5'8" 445 2.2 . . . . 0.9 2.5 153 0.899 0.298 0.332 1"3".~

@ 100°C. Diox~ne - - 1,4 0.274 13.41

(Diethylene Dioxide) 88 12 180 2.0 22 1,0-J- 3.0 101 0,998 0.274 Ethy l Acetate 88 --4 427 2.5 9 0.9 3.0 77 0.899 0.246 0.273 9.60 0 . 7 9 8 0 . 4 | ~ 0 . ~ 2 0 9 . 2 4

0.6,c~g 0.2~4 E t h y l Alcohol 46 13 423 4.3 19 0.8 1.6 # 7 8 O..~! fa ! I .~4 lz ,~ . l ~ : , h o ~ 7 ~ - ~ 1so |:~ 4 8 0 . 7 2 .6 , . . , ~

. , t o o . . , , . , ~ -

t ~ bJ

bJ

O

I °

01

C)

A Moloouhtr F ~ C Ign . W ~ h t (a) Point T m ~ .

Deg.-C 60 ~-%?" 19b E t h y l M e t h y l E t h e r

@

E t h y l Prop iona ta 102 12 477 Ethy l en e Dichlor ide 99 13 413 Gasol ine - 4 3 257 Hexane n " "86" - 2 2 234 Kerosene . . . . 38 229 Linseed Oil - - R a w . . . . 222 343 M e t h y l Aceta te 74 - 10 502 M e t h y l Alcohol 32 11 464 M e t h y l Carb i to l 120 94 M e t h y l Ceilosolve 76 40 "2"88" M e t h y l Cellosolve Aceta te 118 50 M e t h y l E t h e r 40 Gas "350 M e t h y l E t h y l Ketone 72 - 6 516 M e t h y l Lactate 104 50 385

M i n e r a l Sp i r i t s No . 10 . . . . 40 245

N a p h t h a (V .M. & P. Regu la r ) . . . . - 6 232 N a p h t h a l e n e 128 78 526 Ni t robenco l 123 88 482

N i t roe than e 75 28 414 N i t r o m e t h a n e Co) 61 35 (o. c.) 418 N i t rop rop an e - - 1 89 49 (o. c.) 420 Ni t rop ropane - - 2 89 39 (o. c.) 428 Paraffin 0 i l . . . . 228 Pe t ro leum E t h e r (See Benzine) . . . . < --18 "2"88 P ropy l Aceta te - - Leo 102 4 460 P ropy l Alcohol n 60 15 371 P ropy l Alcohol - - iso 60 12 399 P rope l E t h e r - - iso 102 - 2 8 443 P y n d i n e 79 20 482 Rosin Oil . . . . 130 342 Soy Bean Oil . . . . 282 445 Te t rach lo roe thane (sym) 168 To luo l 92 "' 5' "536" T u r p e n t i n e 35 253 Viny l Ace ta te " "8(} 12 427 Xylene (Xylo l ) 106 17 464

D lo. Llmlt~

%E~y V o l u m e Lower U p p e r

2.0 10.1 1.9 11 6.2 16 1.4 7.6 1.2 7.5 0.7 5

3 . i ib" 7.3 30

"3.~. i s 1 . 8 10 2.2 . , .

@ 100*C. 0.8 . . .

@ 100*C. 0 .92 6.0 0.9 5.9 1.8 . . . 93°C.

4.0 . . . 7.3 . . . 2.6 . . . 2.6 . . .

' i . i gi~i 1.8 8 2.1 13.5 2.0 12 1.4 21 1.8 12.4

0.8 2.6 i3~4 1.0 0.0

No te : C o l u m n J gives the cubic mete rs of a i r rendered bare ly explosive b y 1 l i ter of so lvent . However , for mos t pract ica l calculat ions, th is value is close enough to the ac tua l v o l u me of the vapor -a i r mix ture .

*For final required safety vent i la t ion va lues in each pa r t i cu la r oven operat ion these f igures are mul t ip l i ed b y the fol lowing.factors as they app ly (see 410 and 420 of tex t and ca lcula t ions examples Appendix C):

(1) T e m p e r a t u r e - - Vo lume Convereiov (see tab le - - 400-10) .

E. I~' ¢~ 14 ]t 8Dec t~. Vl~ lpor B O ~ Kg. CU. ~lete~

Grav i t y Den~iW P o i n t Per Per Li ter

. . 10 0.698 0 . ~ 7 0.9 3.5 99 0.899 0.213 1.3 3.4 84 1.297 0,318 0.8 3 --1 38 - -204 0.798 0.221 0.7 3.0 69 0.698 0.194

< 1 . 0 . . . . 151 --301 . . . . . . . . 0.9 316 o.9 21d 80 6.sbi~ o.287 0.8 I . I 64 0.798 0.604 1.035 4.14 193 1,033 0.209 0,966 2.62 124 0.964 0.306 1.005 4.07 143 1.004 0.205

• 1.6 - -24 . . . . o.8 2.5 80 0.798 6.b25 1.1 3.6 145 1.097 0.254

0.8 3.9 149 0.798 0.169

0.75 3.73 100 --160 0.748 0.167 1.1 4.4 218 1.097 0.207 1.2 4.3 211 1.198 0.232

1.1 2.6 114 1.097 1.1 2.1 101 1.097 (J.435 1.0 3.1 131 0.998 0.268 1.0 3.1 120 0.998 0.268

0.9 3.5 90 0.899 0.213 0.8 2.1 97 0.798 0.316 0.8 2.1 83 0.798 0.316 0,7 3.5 69 0.698 0,166 1.0 2.7 115 0,998 0.307 1.0 . . . . <300 0.998 . . . . 0.9 . . . . 0.899 . . . . 1.0 (a) '1"4'(~ (a) 1.593 0.9 3 1 i ' 111 0.899 (J.24i <1 149 o.9 3~6' 72 6.si~i~ 6.~9 0.9 3.7 144 0.899 0.202

ot %'at~or remlerL~i ~ V Per K g .

Li te r of ~o lven t Lol,9~Ug~ ~p lo~ lve pe r

13.56 0,237 11.01 0.245 5.09 0.275 15.56 0,275 15.98

6.3~9 s.s9 0.756 7.66 0.202 . . . 0.317 . . . 0 .204 . . .

0.231 11.27

0.214 20.96

0.223 o.188 2£~ 0.193 12.63

ti.39~ g.~2 0.268 10.03 0,268 10.03

0.335 i7.89 0.237 11.63 0.396 14.75 0.396 15.51 0,238 11.69 0,308 16.75

6.~7 ~i.3~ 0.225 19.99

(2) S t a n d a r d fac tor of safety of 4 for cont inuous process ovens. (3) L .E.L. Correc t ion factor for ba tch ovens be tween 121 C., and 260 C.,

mu l t i p ly by 1.4 (see 420-2) .

(4) The m a x i m u m n u m b e r of l i ters of solvent evapora ted per un i t of t ime on the bas is of m a x i m u m possible loadinge.

,a> " H a n d b o o k of C h e m i s t r y " N i n t h Edi t ion - - 1956 - - Lange.

b ) Classified as a po ten t ia l ly explosive chemical .

O

oo

t , J

b ~

2.264 COMMITTEE ON OVENS AND FURNACES OF-37 ~-..,

110., In Appendix B, add new " T a b l e of P r o p e r t i e s of C o m m o n l y U s e d F l a m m a b l e .L iqu ids in M e t r i c U n i t s . "

111. In Appendix C, delete " A p p l i c a t i o n of E x a m p l e s for C o n t i n u o u s O v e n s , " and insert tt~Jollowing " E x a m p l e s C, D, a n d E : "

Example C . For a C o n t i n u o u s L i q u i d So lvent Paint O v e n

T . . . . . . . e---~ oven has a 21~ million Btu /hour burner system and the r u s u l r e c t g t ~ - t t t ~ u , . . • .

heating process is intended to evap.orate 1 4 g a h o n s o f ~luol from a dipped liquid finish' on sheet steel products being oagea at ,~-uu .

When this calculation for 70 ° F equivalent volume is shown ' to be more than one-third of the volume determined for the removal of chemical by-products (from 410-1, 2, or 3), the minimum exhaust volume for the oven will be the sum of the two computations adjusted for thermal expansion as per 400-10. When the combustion products are shown to be less than one-third of the volume determined for removal of chemical byproducts, the minimum oven exhaust volume shall be based on the volume determined for removal of-chemical by. products only with adjustment for thermal expansion as per 400-10.

a. The exhaust indicated for combustion products is: (refer tO Paragraph 410-4).

2,250,000 _ 395 SCFM (70 ° F condition) 95 x 60

b. Ventilation for solvent vapors is: (refer to Paragraph 410-2).

14 gph x 10,000 = 2,331 SCFM 60

c. The adjustment for thermal expansion is based on item B only:

2,331 x 1.62 = 3,776 CFM (at 400 ° F)

Example D. For a Cont inuous P o w d e r Coat ing O v e n .

This direct gas fired oven has a 2 million Btu /hour burner system being used to fuse an organic powder finish on steel products at 4506 F. Seven thousand square feet (7,000 sq. ft.) of surface is to be covered hourly to a depth of 3 with a powder intended to provide 135 square feet of 1 rail coating per pound.

a. T h e exhaust indicated for combustion products is: (refer .to Paragraph 410-4). 5'

• .2,000~000 _ 351 SCFM " • f 95 x 60

b. T h e amount of powder to enter the oven is:

7000 x 3 -- 156 lb. per hour 135

c.- Ventilation for constituents released from powders will be: (Refer to Para- graph 410-3).

156 × 0.09 x 360x 4 = 337 SCFM 60

O F _ O ~ . " RI~VISION8 'gO NFP?, NO. 8 0 A 2 2 6 5

d. The adjus tment for thermal expansion is based on the sum of a and b :

(351 + 337) x 1.72 = 1182 C F M (at 450 ° F)

Example E. For a Con t inuous P o w d e r Coat ing O v e n .

This 450 ° F, electrically-heated oven is required to cure 156 pounds of powder m r hour as in Example "D":abov6. However , there are no combustion products r~ be considered. Accordingly, the venti lat ion rate for constituents released ~rom powders will be: . . . . "

: 156 x 0.09 x 360 x 4 ' = 337 8 C F M a. -,'~. 60

b. The adjustment for':thermal expansion will .be:

"' 337 x 1.72 = 580 CFM (at 450T)

If this is adecjuate to avoid undesirable fume spill at oven work openings, no additional ventilation will be required..

112. In Appendix D, 1, third line, change "1 :,: . . . . p s i g " to " 0 , 5 p s i g . "

113. Locate Figure 26 in Appendii D, following Fig: 24 . .

ATMOSPHERIC ~ ~1 INSPIRATOR ~ I I I

APPROVED ELECTR CALLY .~ / . ,~ INTERLOCKED SUPERVISING COCK I[ I 1 "

APPROVED MANUAL. ~ 1 1 OPENING SAFETY SHUTOFF VALVE W,TN END SWITCH i . ~

G ~ PRESS.RE ~ . ^ I I • . - , •

G A S A T , P S , . . " ~S ~TEIRPSI~; ~ BLEED T A P FOR LEAKAGE TEST OF

. . . . . SAFETY SHUTOFF VALVE

P I P I N G (MULTI-BURNER SYSTEM WITH HIGH PRESSURE

ATMOSPHERIC INSPIRATORS)

(Cut continued on page 0F-39)

2266 COMMITTEE ON OVENS AND FURNACES O ~

OT

/

VENT FAN INTERLOCK 120V. AC

--r-- COCK SWITCH CONTACTS _L. CLOSE WHEN COCK IS

GAS PRESSURE . . . . . . . AND OTHER / J I, ; . . . . ,NTERLOCKS ~ H I-4 I

END SWITCH ON . . L - SAFETY SHUTOFF ~ -r-~. / VALVE-CLOSEO / ONLY WHENVALVE ,L OPEN i F

COMMON~

A P PR OV E D TIMER (TIME DELAY SWITCH \

TTIMER LOAD CONTACT ICLOSED AT END OF

_J_. PURGE PERIOD APPROVED

~ .-" MANUAL OPENING SAFETY SHUTOF~ 'VALVE (WITH ENP, SWITCH)

WIR ING (DETAILS WILL VARY DEPENDING ON TYPE OF BURNER 8CONTROLS USED)

Fig. 26. Safety Control System Piping and Wiring, Electric Interlock Type Supervismg Cock.

114. Delete Appendix 1 and replace with a new Appendix I as follows:

APPENDIX I.

MAINTENANCE CHECK LISTS

1. Responsibility An essential safety aid is an established maintenance program which insurts

that the equipment is in perfect working order. The equipment manufactu.rer shall imnress upon the user the need for adequate operational checks arid main. tenance 'and shall issue complete and clear maintenance instructions. The final "responsibility of establishing a maintenance program which insures that the equipment is in perfect working order shall rest with the user.

2. Check Lists The user's ooerational and maintenance program shall include" any listed

procedures, which are applicable.to.his furnace and that may be reerCaOtmnm:ln~ bv his imurance underwriter and lals eqmpment suppner. An opt ,, maintenance check list is essential to the safe operation of the equipment.

m ~ v x s x o ~ s T o NFPA NO. 8 6 A 2267

GAS - - ~ ~ - - - ~ T O BURNER(S) COCK COCK ®

H

~c~--~IN. PIPE CAP (~ RUBBER HOSE (~) ~ -" =-'~ v

OUICK TEST S E T - U P ' ~ W A T E R

M e t h o d 1 U s i n g S u p e r v i s o r y

Ga8 Cock

SAFETY SHUT-OFF ~, VALVE O ~ STANDARD GAS COCK ( ~

M e t h o d 2 GAS - - ' TO BURNER (S) Us/ng Standard • ~s IN. COCK (~)__<~BLEEDTAP(~

Gas Cock ~/. IN PIPE CAP ~ ru~ =GRADUATED GLASS ° " ~J ~ CYLINDER(IOOcc OR

v ~ / LARGER) RUBBER HOSE(~ - - ¢ ~ . ~ . ; /

ACCURATE TEST S E T - U ~ • ~ - - W A T E R

Fig. 27

N o ~ To FIotnw 27. 1. Main gas safety shutoff valve may be manual-opening, automatic-

dosing or automatic-opening, automatic-dosing, to smt the firing method used.

2. For bleed tap, ~ - i n c h O.D. copper tubing or pipe shall be used.

3. Supervisory cock shall be located downstream as close as practical to outlet of safety shutoff valve.

4. Standard gas cocks shall be used.

5. Bleed tap outlet should be capped (or plugged) except while making tightness checks of safety shutoffvalve.

6. A standard gas cock shall be installed downstream as close as practical to outlet of safety shutoff valve.

7. Lengths of rubber hose shall be as short as possible.

Teat Procedure The safety shutoff valve shall be closed and the valve indicator shall be

observed to make sure it is closed.

Supervisory cock 3 (method 1) or s tandard gas cock 6 (method 2) shall he dosed.

Pipe cap 5 shall be removed and rubber hose 7 shall be attached to outlet of bleed tap 2.

2268 Cock 4 shall be opened so as to vent any gas trapped in piping, between

valve 1 and cock 3 (method I) or between valve 1 and cock 6 (method 2~. Then outlet end of hose shall be held just beneath the surface of some water

. " er tin can bottle, etc.) to observe if any bubbles appear in a small contain ( . . . . . . If no bubbling occurs, safety shutoff valve may be reported "bubbleught ."

If bubbling occurs and continues, safety shutoff valve has leakage and should be immediately cleaned a n d overhauled, or r?placed..Howeveriliit may ,he desirable to measure accurately the leagage rate oezorenana as ~o ows: (a) a graduated glass cylinder shall be fille.d wi.th water and inverted in a l~--g e container of water; (b) end of hose snan ne mshaziea in e n a o z cylmaer, and the amount of time required (seconds) to "displace any given n u m b e r of cubic centimeters of water; (c) the valve leakage rate (cubic centimeters per second) is determined by dividing cubic centimeters of water displaced by seconds re. quired; (d) if leakage rate exceeds 8.0 cc/sec., which corresponds to 1.0 cu. ft . /hr. , valve should be immediately cleaned and overhauled, o r replaced.

Important. At newly installed equipment, if this test discloses valve has leakage, it may indicate that fuel gas piping was not properl)" cleaned out so as to be free of weld particles, pipe chips, etc. In such cases the pipelirle and valve should be cleaned out and the test xepeated.

A. Maintenance of Gas Equipment ~.i,

I. General. These recommendations are prepared for maintenance of gas

~i.q uipment. Special types of equipment command special attention. A preven,

ve maintenance program should be established and followed. This program should include adherence to manufacturer 's recommendations. In this program a minimum maintenance schedule should include inspection and action on the recommendations given in the following paragraphs.. An adequate supply of repair parts should be maintained. 2. Burners and Pilots. Burners and pilots should be kept clean and in proper operating condition. Burner refractory parts should be examined at frequent regular intervals to assure good condition. 3. Flame Safeguard Equipment. When automatic flame safeguards are used, a complete shut-down and restart should be made at frequent intervals to check the components for proper operation. 4. Other Safeguard Equipment. Accessory safeguard equipment, such as manual reset valves with pressure or vacuum switches, high temperature limit switches, draft control, shut-off valves, air flow switches, door switches and gas valves, should be operated at frequent regular interv~ils to insure proper functioning. If.inoperative, they should be repaired or replaced Promptly.

When fire checks are installed in air-gas mixture piping to prevent flashbacks from traveling further upstream, thepressure loss across the fire cheeks should be measured at regular intervals . .When ex/:essive pressure loss is found, screens should be removed and cleaned. Wa te r type backfire checks should be inspected at frequent regular intervals and liquid leyel maintained.

All safety shutoff valves should be checked for leakage and proper operation at frequent regular intervals. Two procedures f o r making these tests are out. lined in Fig. 27. 5. Auxiliary Devices. A necessary par t .o f the g.as equi'pment maint.en~a_u ~ should be the proper maintenance of auxdmry de~ces. ~vlamtenance lnsrruj fifions as supplied by the manufacturers o! these aevices snoum oe ionoweu. Gas combustion equipment, including blowers, mechanical mixers, control valves, temperature control instruments, air valves, and air filters, should be kept clean and should be examined at frequent regular.intervals. Necessary repairs and replacements should be made promptly. "

0F--42 REVISIONS TO NFPA NO. 8 6 A 2269

6. Regulators and Zero Governors. Regulator and zero governor vents and impulse or control piping and tubing should be kept clear. Regulator valves wl~ch operate improperly should be cleaned, repaired, or replaced promptly.

7 Piping. A necessary part of the gas equipment maintenance should be the p~oper maintenance of the gas piping system. I t is recommended that gas - 'n ine be inspected and tested for leakage at regular intervals in accordance

" " . • , , . ~ , " , . , .

the fans.

8. Standby or Substitute Fuels Systems. Standby or substitute fuel e.qluipment and systems for gas equipment should be kept in good operating condition and tested periodically.

B. Maintenance of Electric Furnaces and Equipment

1. General . A program of regular inspection and maintenance of electric furnaces is essential to the safe operation of that equipment. Recommendations of the manufacturer should be rigorously followed and a long trouble free furnace life will result. Suitable spare, parts should be stocked to insure replacement quickly a~ needed.

\

2. Hea t ing Elements. The heating elements should be inspected at regular intervals and any foreign contamination removed. Repair is essential if elements are dislodged or distorted to touch alloy hearths or furance components so that grounding Or shorting can occur. Element terminals Should be periodically checked and tightened since loose connections cause arcing and oxidation which can result in burnout of the terminal.

3. Insulat ion-and Refractory MaterialS. Furnace linings re.quire attention when protective atmospheres are used to be sure that excesszve carbon has not been deposited. Grounding or shorting of the elements can occur unless recommended burnout procedures are followed. Cracked or broken refractory element supports must be replaced as required.

4. Thermocouples . A regular replacement program should be established for all control and safety thermocouples. Effectwe life of thermocouples varies depending on the environment and temperature and these factors must be considered in setting u p a replacement schedule.

5. Atmosphere Furnaces. Many electric furnaces use specially prepared atmospheres and they may be either inert or combustible depending on the application. Safety devices are provided to prevent introduction of combustible atmospheres unless the furnace is at suitable temperature or has been properly purged with an inert gas. Protective devices include pressure switches, safety shutoff valves, interlocks, solenoid valves and those components should be tested on a once a week schedule by instituting a failure which would demon- strate correct functioning'of the system. Safety shutoff valves should be checked for leakage. The same maintenance principles apply in the case of atmosphere gases of the flammable type as apply for fuel fired furnaces.

6. Auxiliary and Control Devices. Contactors require periodic checking of contacts and replacement when pitting due to arcing could result in welding of the contacts and uncontrolled application of power to the furnace. All cbn- trol components including pyrometers and relays require periodic checking to assure proper operation or control accuracy. Instructions provided by the manufacturer of each control component should be followed with care.

2270 COMMITTI~,E ON OVV'N~ AND- FUI'LNAcv'S , OF--4~ ' . /

7. Voltage. The voltage supplied to electric furn,, aces must b c ~ t a i n e d within reasonable limits to insure agatnst, overmaomg ox c.ontrola;~aCcs and. transformers. Under voltage can result m operatmnaJ lamure ot r ys anti solenoid valves.

8. !Water Cooling. If components are water cooled it is important to fr¢. quendy check the flow and temperature of the cooling water.

9. Interlocks. Periodic checks of all safety interlocks are essential. Hig h frequency generators must have functioning door interlocks to prevent oper. ators entering the enclosure with any power on and these safety d eyi'ceS must be checked frequently.

V g N T TO , , . A T M O S P H E R E

~ ; $ 0 L E N 'OI0 L O W G,AS V A L V E . P R S S S U R E

, /SWLTeH HIGH OAS + R E $ S D R I [ 0 P E R A + t O N A L p R E S S U R E

P L U G P UANUA c o c k L

V E N T TO ':'" COCK

• . A T M O S P N E R E

+ $ O L E N O I O V A L V E

• R E G U L A T O R S A F [ T Y ' S H U T ' O F F ~ V A ~ Y E

¢OCR Low A i m s COMSU+TION

S W I T C H . , .

O A S SUPf fLY ~ S A F E T Y S H U T OFF V A L V [ $ I N T E R R U P T E D P I L O T • ,

Fig. 28. Typical double safety shutoff valve and vent arrangement.

C. Suggested Operational and Maintenance Check List

I. Continuous Check List (a) Check for proper inlet air-gas ratios. (b) Check atmosphere gas for proper flow and pressure. (c) Check for proper operating temperatures. (d) Check sight drains or gages, or both,+for proper water flow and water

temperature. (e) Check combustion chamber visually to make sur.e i t is incandescent. (f) Check pilots or spark plugs, or both, for proper main burner ignition. (g ) Check burners for proper ignition and combustion characteristics. (h) Make sure atmospheric burners or pilots, or both, are protected from

improper drafts. . (i) Check for proper operation of ventilating equipment. (j) Check control and auxiliary equipment for abnormal temperatures.

2. Regular Shift Cheek List • (a ) Take necessary gas anal .yses; if automa.tic . .g~ an alyze,.rsL_a~e u:sed maa~:

sure the manual and automaUc reamngs comcme. ~xccm~u,,,,~ , ~ - . , , - , - gas analyzers.

(b) Standardize or balance instruments. ' (c) Check valve motors and control valves or dampers for free, smooth aetioa

and adjustment. • (d) Check hand valves, manual damp.ers, secondary air openings or ad-

justable bypasses, or both, for proper posmons.

0 F - 4 4 . " ' REVISI'ONS TO NFPa~NO. 8 6 A 2271,

(e) Check all pressure swishes for proper pressure settings. ~+: s h ~ .Ch~.k blower, compressors and pumps, for unusual bearing noise and

vmrauon; it v-be£t dnven, check belt tension and belt fatigue. " 3. Weekly Check c a ~ , Make sure flame-sensing devices are in good condition, properly lo-

and free of foreign deposit. Gh~e~k) Test thermocouples and lead wire for shorts and loose connections.

the protection tubes for cracks and proper immersion. (c) Check setting and operation of low temperature limit device. (d) Test visible or audible alarm systems, or both, for proper signals. (e) Check ignition spark el~trodes and check proper gap.

4. Monthly Check (a) Test interlock sequence of all safety equipment. Manually make each

interlock fail, noting that related equipment closes or stops as specified by the manufacturer.

(b) Test main gas hand valves and safety shutoff valves for tightness of desure.

(c) Test pressure switch settings by checking switch movements against pressure settings and comparing with actual impulse pressure.

(d) Inspect ~lfelectrical switches and contacts; clean ff necessary. (e) Test all amplifier a~ad thermocouple fail-safe devices, m~king Certain

that the instrument drives in the proper direction. (f) Clean the air blower filter. " . = . , ;~. - " -: ,+~ (g) Clean water, gas compressor and pump s t r a i n e r s . . . (h) Clean. fire check screeus and valve sea~, and test 'for freedom of Value

movement. (1) Inspect burners and pilots; clean if necessary. • - (j) Check ignition cable and transformers . . . . . . (k) Check all orifice plates, air-gas mixers, flow indicators, n~eters, gages,

and pressure indicators; and clean or repair, if necessary." : (1) Test automatic or manual turn-down equipment. (m) Test l~ressure relief v~yes; clean if necessary. • ' (n) Inspect air, water, fuel gas, atmosphere gas, reaction gas, and impulse

piping for leaks..

5. Periodic Check List "' The frequency of maintenance of thefollowing will depend on the recom-

mendatious of the. equipment manufacturer: (a) Inspect the: retort tubes, brick, coolers, refrigerators, driers, and other

accessories and r~palr if necessary. (b) Lubricate the instrumentation, valve motors, valves, blowers, com-

pressors, pumps, and Other components. (c) Test instrumentation, clean slidewires, check amplifier tubes and battery. (d) Test flame safeguard units. (e) Burn out carbon in reaction tubes. (f) Clean humidifiers. (g) Check for plugging of hot pipes, tube bundles and jacketed p ipes .

2 2 7 2 coM *T E o . O ENS A.D

Part H of the report, prepared by the Sectional Committee on Class B Electric and Fuel-Fired Furnaces, proposes revisions for

NFPA No. 86B-1971.

Part II has been submitted to letter ballot of the Committee, but results were not available at the time oJ printing of the Technical Committee Reports. Results of balloting will be announced at the Annual Meeting• "

Part II

Proposed Revisions to Standard for

Industrial Furnaces

NFPA No. 86B - - 1971

1. In lO0-3(a),first line, delete "For the purpose of this standard,".

2. Add a new lO0-3(c) as follows:

(c) "Authority Having Jurisdiction" is the organization, offi.ee, or individual responsible for "approving" eqmpment, an mstanauon, or a procedure.

NOTE: The phrase "authority having jurisdiction" is used in NFPA ds in a broad manner since jurisdictions and approval agencies vary standar .... . • " " " ri

as do their responsibihues. Where pubhc safety Is primary, the autho ty havin~ Jurisdiction" may be a federal, state, local, or oth.cr regional dc- p~tm°cnt or individual such as a fire chief, fire marshal, ch~cx ox a nrc prevention bureau, labor department, health department, building official, electrical inspector, or others having statutory authority. For insurance purposes, an insurance inspection department, rating bureau, or other insurance company representative may bc the "authority having jurisdiction."

In many circumstances, the property owner or his delegated agent • • * • • . , , n o assumes the role of the "authortty having jurisdiction,, at gover .

mcnt installations, the commanding officer, or a departmental official may be the "authority having jurisdiction."

3. Add a new lO0-3(d) asJollows:

(d) "Operators" are the individuals responsii)le for the light-up, operation, shutdown, and emergency handling of the specific installation, consisting of the atmosphere gas generator and/0r furnace and the associated equipment through or into which the atmosphere gas flows.

REVISIONS TO NFPA NO. 8 6 B 2273

4. Add new 100-6 as follows:

100-6. Operator Training.

(a) It is fully recognized that the most essential safer considera tion is the selection of alert and competent operators. ~Yheir knowl- edge and training are vital to continued safe operation.


(c) Regular operators shall receive scheduled retraining to main- rain a high level of proficiency and effectiveness.

(d) Operators shall have access to operating instructions at all times. An outline of these instructions shall be posted in a suitable location.

(e) Operating instructions shall be provided by the equipment manufacturer. These instructions shall include schematic piping and wiring diagrams. All instructions shall also include:

1. Light-up procedures. 2. Shutdown procedures. 3. Emergency procedures. 4. Maintenance procedures.

(f) Operator training shall include: 1. Combustion of air-gas mixtures. 2. Explosion hazards.

3. Sources of ignition and ignition temperature. 4. Atmosphere gas analysis. 5. Handling of flammable atmosphere gases. 6. Handling of toxic atmosphere gases. 7. Functions of control and safety devices.

8. Purpose and basic principles of the gas atmosphere generators.

5. In l~-2(a) , delete the second sentence starting with "Where base- rnent . . . . " in the third line.

6. Delete 200-2(b) and replace with the Jollowing :

(b) Special consideration shall be given when using fuels with a specific gravity greater than air. Class B furnaces may be located

2274 o. ov--47

below grade where consideration has been given to ventilation and the ability to safely provide the required explosion relief.

7. In 200-3, add "(See Article 200, Section E.)."

8. Revise D., 200-4, and 200-5 to read as follows:

D. Location in Regard to Stock, Processes, and Per~nnel

200-4. Stock and Processes. Class B furnaces should be well separated from valuable stock, important power equipment, important process equ!pment, and fire protection facilities, in order to minimize interrupuon of production, and to provide protection in the event of accidents.

200-5. Personnel. (a) Furnaces shall be located to minimize exposure to groups of persons from the possibility of injury from fire, explosion, or asphyxiation and toxic materials.

(b) Furnaces shall not adjoin personnel assembly areas, such as recreational areas, locker rooms, lunchrooms, etc., and shall not obstruct personnel travel to exitways.

9. At the end of 200-6(a), add "(See NFPA Nos. 30, 33, and 34.)?'

10. Delect Section E of Article 100, and replace with the following:

E. Floors and Clearances

200-7. Class B furnaces shall be located for ready accessibility, with adequate space above, and on all sides, to permit inspection and maintenance. The space above, below and around the.equipment shall be properly ventilated to keep temperatures at combustible floors, ceilings and walls below 160°F.

200-8. (a) Furnaces shall be located on, or above, noncombustible floors. If such a location is not possible, then one of the following procedures shall be employed.

1. Remove combustible floor members and replace with a mono- lithic concrete slab which extends a minimum of 3 ft. beyond the outer extremities of the furnace or generator.

2. Provide air channels between the floor and the equipment (perpendicular to the axis of the equipment) and/or noncombustible insulation. This shall be adequate to prevent surface temperatures of floor members from exceeding 160°F.

-48 R E V I S I O N S T O N F P A NO. 86B 2275

(b). Where electrical wiring will be present in the channels of certam types of floors, the wiring shall be installed in accordance with Article 356 of the National Electrical Code (NFPA No. 70 - - 1971).

(c) Floors beneath oil burners shall be provided with a non- conabustible, nonporous surface to prevent the floors from becoming oil soaked.

200-9. Where furnace stacks penetrate combustible walls, floors or roofs, clearances and insulation shall be provided to prevent surface temperatures of combustible members from exceeding 160°F.

200-10. Combustible stock, stock fixtures, equipment, etc., shall not be located near any furnace or high temperature ducts or stacks.

I1. Revise Article 210 to read as follows:

ARTICLE 210. CONSTRUCTION OF FURNACES

A. General

210-1. Furnaces and related equipment shall be built in a substantial manner with due regard to the fire hazard inherent in equipment operating at elevated temperatures, the hazard to operators from high temperatures, open flames and mechanical equipment and the need of ensuring reliable, safe operation over the expected maximum life of the equipment.

B. Materials

210-2. (a) Furnaces shall be constructed of noncombustible materials.

(b) Furnace structural supports and conveyors shall be designed with adequate factors of safety at the maximum operating temperatures, consideration being given to the strains imposed by expansion.

(c) Adequate facilities for access shall be provided to permit proper inspection and maintenance.

(d) Burners and heating elements of all types shall be substantially constructed or guarded to resist mechanical damage from falling work, trucking, or other mechanical hazards inherent in industrial use.

(e) Where refractory materials are used, they shall be supported so that they will not fall out of place.

2276 COMMITTEE ON OVENS AND FURNACES 0 ~

(f) Corrosion resistance. Where subject to corrosion; metal parts shall be adequately protected.

(g) •Accessibility and mounting of controls. Provision shall be made for the rigid attachment of control devices. Combustion safe. guard mounts shall be arranged so that the electrode or other flame detecting element is correctly positioned. Valves and control panel shall be so located that all necessary observation and adjustment may be readily made.

(h) :EXteriors of furnaces which operate ~;f temperatures in excess . . . . . . . . . . . nf 16N°F shnuld be ~guarded by_ locati0n',.guard rails, shields . . . . . of insula. tion to prevent accidental contact with 'personnel. All parts of equipment operating at elevated temperatures shall be installed in accordance with Article 200, Section E, Floors and Clearances.

(i) Bursting discs i or panels, mixer openings, or'other parts of the furnace from which flame or hot gases may be discharged S.hould be located or guarded to prevent injury to personnel. -

(j) -Properly located observation ports shall be provided to permit the operator to observe the lighting of individual burners.

(k) .Devices such as relief valves, open sight drains, and water • flow switches from water cooling systems shall b e designe d an d in-

stalled for ready 0bseryation by operator.

12. Revise Article'220 to read as follows:

ARTICLE 220. FURNACE E X H A U S T sYSTEMS

220-1. The need for a furnace chimney or furnace exhaust system for removal of products of combustion, heat, toxic gases, ':and other objectional gases Will depend on the heating process, tylSe of combustion, hazard to personnel, and all applicable air pollution control r e g u l a t i o n s . . ~: . . . .

220-2. When furnace venting is requ!red, care shall be'exercised so that excess draft is not imposed upon the furnace by.the draft hood, barometric damper, or exhaus t .hood. . . • • "

220-3. Before exhausting products of combustion directly into the area in which the furnace is located,"the following factors regarding the ability of the building ventilation system to dilute these vapors and gases shallbe considered:

(a) The quantity of the contaminants discharged into the area must not be too great o r the air volume necessary for dilution will be impractical.

--REVISIONS TO NFPA,NO. 8 6 B 2277

(b) Workers must not be expo.sed to. concentrations of harmful contaminants in excess of the established threshold limit values.

, . . . . . - . : ,

, ,on~ In all cases where.contaminants are exhausted from a fur- Z~e and related equipment, into a room, the room should have ~chanical ventilation consistingof an air intake system bringing II1 ill air from the outside and an exhaust system exhausting an equal amount of air to the outside. The suppler air'should be uniformly distributed wi thin the area, and the exhaust duct should be arranged to enmmate" all pockets and' dead air areas at either floor or ceiling levels, depending on the type of contaminant being evolved.

220-5. Furnaces and related equipment requiring outside exhaust of flue gases or other combustion by-products may use direct connected, dilu.tion,.or.recuperative-type exhaust systems. Size, insulation and auxiliary equipment employed shall be suitable for the maximum temperature and volume of gases to be discharged under peak conditions. The design shall otherwise conform to Articles 200-9 and 210-2(h). "

13. Revise Sections A and B of Article 230 to read as follows:

,A. General , • '~

230-1. Adequate facilities for access shall be provided to permit proper inspection and rhaintenance.

230-2, When such openings are •intended to permit persons to climb inside for inspection and cleaning , there should be provided such additional equipment as ladders, Steps,' arid grab-rails to permit safe and easy access and egress.

B. Mountings

230-3. Mountings for aux'fliary equipment , such as control instruments and safetydevices, shall provide protection against damage by heat, vibration, and mechanical hazards.

14. Revise 240-I to read,as fol/ows:

240-1. Hydraulic systems for furnace door operation, lifts for work loads, and conveyor systems sliould not use petroleum or other dom- bustible hydraulic fluids. The use of fire resistant hydraulic fluids is recommended.

2278 COMMITTEE ON OVENS AND FURNACES O F . . ~

75. Revise 240-2 to read as foUows:

240-2. When petroleum oils or other combustible fluids must be used, the system shall be designed to minimize the possibility of fluid release which may result in a fire or explosion.

/6. Delete 310-2(c) and replace with the following:

(c) The maintenance of an adequate air supply to fuel-air rnixers for reliable combustion throughout the burner operating range.

77. Revise 310-2(0 to read as Jollows:

(f) A stable pilot flame either manually or spark ignited, if required. (See 510-7.)

18. In 3/Od(a), second line, change "should" to "shall."

19. In 310-11(a), first line oJ second paragraph, change "should" to "shall".

20. In 310-22(a), after "control devices," in the seventh line, delete the remainder oJ the sentence and replace with the JoUowing : "or obstructions which will change overall manifold pressure during operation will be permitted between the blower discharge and the burner or burners." .

21. In 310-24(a), second line, change "burner" to "mixer".

22. In 310-26(e),first line, insert "combustion" before "blowers."

23. In 320-1, third line, change "convertible" to "dual fuel".

24. In 320-5(c), title, delete "Oil burners should include:".

25. In 320-5(d), second line, change "should" to "shall."

26. In 320-6(a)2., third line, change "should" to "shall".

27. Revise Fig. 17 as JoUows:


OUPLE

:TRIC TING MENTS

tMINALS BOXES

Fig. 17. Electric Furnace

2280 COMMITTEE ON OVENS AND FURNACES

28. Revise 330-1(c) to read as Jollows:

b INDUCTION HEATER - - a heating system by means of whirl ~-) . . . . . . arr,,in~ conductor induces the transfer of electri"

~1. I . . I . t l t v ~ - . A l L T M 7 ~ •

energy to the work by eddy currents. (See Arucle 665 of NFP A N0. 70 - - 1971.) z"

29. In 330-7(a), first and second t;,.o delete. "which .operate at te peratures in excess of 160°F, ' ' , and in the second line change "Should,, to "shall".

30. In 330-8(c), second line, delete."ad+quately".

3t. In 330-8(d), third line, change "should" to "shall".

32. Delete 330-11 and replace with the foUowing:

330-11. -Installation. High frequency induction equipment heating systems shall .not be installed, in hazardous locations. (See Article 665 of NFPA No. 7.0 - - 1971.) , . :

! ,

33. Revise 330-12(b) to read as foUows: . " ,

(b) Combustible electrical insulation shall. 'l~e reduced to a m i n i m u m . . Transformers should be of the dry or noriflammable liquid type. Dry transformers should be in compliance with NEMA T R 27-4.03, 150°C rise insulation.

34. Revise 330-13 to read'as follows:

330-13. Controls for Induct ion Heating Systems ~hall be as required in Article 665 of NFPA No. 70 - - 1971.

35. In 330-76(a), first line, change "should" to "shall".

36. In 330-76(bi, second line, change '"to" to "will": ."

37. In 330-16(c), first line, change "should" to "shall", and in the second line place a period after '%upply" and delete" the iemainder of the paragraph.

38. Revise 330-18(c) to read as Jollows:

(c ) Provision shall be made for securely positioning with respect to the pouring spout when discharging metal.

REVISIONS T O ' N F P A NO. 86B 2281

39. In 330-19, second and fifth lines, change "should" to "shall".

_ ~r=,, 330-20, fourth hne," change "if unsafe conditions should" to ~" ould unsafe conditions", ~and in the fifth hne change "should" to ~h ,, ,,shall •

41. Delete Chapter.4.

,¢~ In 500-1, in the fourth line after "at all.", delete the remainder of ~O-l(c) and all of 500-1(d), and replace with the following:

Safety device's shall be properly designed and installed where prescribed in this standard. Safety devices shall not be shorted out or by-passed in the systems. All safety devices, including the oven or furnace, shall be inspected and maintained in accordance with the typical maintenance check list in Appendix I . Where Sl~_ial maintenance and inspection procedures are required due to the nature of the equipment plant management and the authori ty having jurisdiction shall prescribe the time interval at which t h e . equipment and controls shall be tested for service.reliability-based on recommendations of the equipmentmanufacturer.

43. In 510-1, se~pnd line, insert "(high and low)" after "switches",

44. In 510-2,fourth and fifth lines, replace "can usually be considered as" with "is", change "should" to "shall" in the tenth and thirteen lines, and add a new paragraph as follows:

On continuously Operating furnaces, i.e., those that are not shut down for long periods of time, the safety shutoff valves may be installed so that they can be readily'tested while'the furnaces are in operation.

45. Add a "new 510-3 as follows:.

510-3. Safety shutoff valve tightness test. Apermanent and ready means for making tightness checks of all main burner gas safety shutoff valves shall be provided. (See Appendix C.)

Renumber 510-3 through 510-9 as 51054 through .510-10, respectively.

46. In new M0-5(c),fifth line, change "should',' to "shall."

47. In new 510-7, in the first line of "Caution" under "Separate Gas Cock At Each Automatic Fire Check", change "should" to "shall".

2 2 8 2 coMM, E , oN o.,EN A,.,

48. Relocate Article 530to be new Appendix F, and provide a new Article 530 as foUows:

ARTICLE 530. COMBUSTIBLE GAS. INDICATORS

AND c o N T R O L L E R S

A. General

530-1. (a) ' Continuous vapor .concentration indicators and controls are devices which measure and indicate, directly or in. directly in percentage of the lower explosion limit, theconcentration of a flammable vapor-air mixture., xney may oe ot me portable or fixed location continuous operating type. T h e continuous indicators are mostly used throughout the period of operation of a proee~ wherein flammable vapor is evolved. In addition to indicating or recording concentrations to aid in safe and efficient process control, they can be arranged through suitable controls automatically to sound an alarm, open or close .dampers, start or stop motors, con. veyors, and ventilating fans, when the concentratioh of a flammable vapor-air mixture has reached a,predetermined dange rous level.

(b) When a continuous vapor concentration indicator and controller is arranged to shut down or operate auxiliary equipment a t -a predetermined dangerous level of vapor' Coricentration, the operation point shall be set to not exceed 50 percent 0.f the lower explosive limit.

530-2. These devices are ordinarily used witia continuous process ovens and dryers or coating machines evaporating relatively large amounts of flammable liquids where the character of the process ts such that evaporation rates may fluctuate widely or the normal working vapor concentration level is unusually high. Ovens connected to solvent recovery systems are frequently equipped with these instruments.

530-3. Only approved devices should be used and plans covering the application of the instrument to the process in question should be •submitted to the authority havingjurisdict ion-~ " " "

530-4. Flammable vapor cOnCentration indic~itors shall be used to test flammable vapors having a flash point below 70°F unless it is possible to mainthin the sampling line and measuring assembly at the temperature of the vapors, so that condensation will not occur.

. . , . ,

530-5. Maintenance of continuous flammable vapor indicat0n and controls shall be done periodically, through a maintenance service by the instrument, manufacturer or equivalent. Properly

R E V I S I O N S T O N F P A NO. 86B 2283

g~ace d personnel, competent to make necessary daily adjustments cordance with the manufacturer's exact instructions or equiva-

. . . . hall be macte responsible for reliable operation. A reliable au ~le~-'L:l~'~.~ means for checking indicator calibrations frequently is imperatxve. It sh6uld ben0ted that some flammable vapor indicators are designed for use on specific materials, and that new calibrations must be made for each change in material tested. Maintain- Lag sampling lines clean and airtight and prompt renewal of filaments when necessary are essential.

49. In 550-6(c)i delete the last sentence starting "Where cond i t i ons . . . " .

50. In 550-10(a)(4c), add the following:

At continuous-line burners, including those composed of a limited number of individual radiant burners or line-burner sections located

adjacent to one another, supplied from a common burner ifold and having reliable flame propagation between the con-

secutive individual burners without special external flame-propagation devices, the length of burner supervised by a single approved combustion safeguard shall not be more than 50:ft. At.burners where the total length exceeds 20 ft., the trial-for-ignition periods should be automatically limited to not more than 15 seconds after fuel is available at the burner head. i(See Fig: 18.)

At continuous-line burners composed of a number of individual radiant-cup burners that are not located directly adjacent to one another but are supplied from a common burner manifold and have reliable flame-propagation devices, the maximum number of individual burners in a group supervised by a single approved corn- bastion safeguard shall be 50. The total distance of the single-flame path from the first burner ignited to the last in the group, where the flame-sensing element should be located, shall not exceed 50 ft., the individual burners should not b e spaced more than 30 in., the trial-for-ignition periods should be automatically limited to not more than 15 see., and it is not necessary during lighting-off to prove the pilots before permitting the main safety shutoff valves to be energized and opened. (See Fig. 19.)

51. In 550-10(b)4, add a new "Exception (a)" as follows:

The following are exceptions to 550-10:

Exception (a): Multiple burners where combustion safeguards Jot each burner are too numerous to be practical, but continuous line-burner type pilots for groups of burners (see Section 310-11) can be used: An approved prac- &ally instantaneous combustion safeguard shall be provided at the far end of each line-burner type pilot, away from the pilot fuel source, with sensing

21284 element located at the junction oJ the flame paths oJ both pilot and last tnain burner. The pilot safety shutoff valve must be initially •opened b~ a manual momentary push button.

Reletter " E x c e p t i o n s (a), (b) , a n d (e)" as " E x c e p t i o n s i ( b ) , (e),

ar/d (d ) " , respectively.

52. Add new Figures 18, 19, and 20 in 550-10(b) asJollows:. : .

1. Approved main gas safety shutoff valve. Manual-opening automatic- closing valve or automatic-opening automatic-closing valve, to suit firing method used.

2. Permanent and ready means for making periodic checks • of main gas safety shutoff valve. . ~,~ ~ ~ •

3~ Approved piloi gas safety shutoff valve.

41 Pilot flame-sensing element. Wired into s~ifety-control circuit so that it is automatically cut out of combustion safeguai'd's flame-detecting circuit at end of trial-for-ignition period. (Flame rod shown, but a photocon- ductive cell maybe used.)

. • , J §

5. Main flame-sensing element. Wired into combustton safeguard flame-detecting circuit. ' Unlike pilot flame-sensing element 4, it is not cut out but remains in the flame-detecting circuit" during lighting-off and firing. (Flame rod shown, but a photoconductiveceil may beused.)

Fig; 18. Example of appl ica t ion of an approved combustion safeluard supervising a pilot for a continuous l ine bu rne r dur ing l ighting o~" and the m a i n f lame a lone d u r i n g f ir ing. ,

REVISIONS TO NFPA NO. 8~B 2285

RADIANT CUP BURNERS • , ( ~ - - ~ (SHOULD NOT EXCEED 50 . . . . . ~ ~j; PILOT GAS CUP BURNERS PER B U R f q E R ~ " ~ ' : ~ * ~ = ~ ' ~ P - - GRQUP) ~ RILOT'~./~r m .~,:

FLAME P R O P A G A T ~ (sHOULD NOT EXCEED SOFT) . . . ~ ~ -

I. Approved main gas!safety shutoff valve. Manual-opening automatic- dosing valve or automatic-opening automatic-closing_ Valve, to suit firing method used-: .

2. Permanent and ready means for making periodic tightness checks of main gas safety shutoff Valve.

3. Approve d pilot gas safety shutoff valve.

4. Main flame-sensing elemeni~ (Flanie rod Shown, but a photocon- ductive cell may be used.)

Fig. 19. Example of application of an approved combustion safeguard suaervising a group of radiant-cup burners having reliable flame-pro a- ~ i o n characteristics from one to the other by means of flame-propagatr~n devices.

ONE GROUP OFL~NE BURNERS (OTHER GROUPSPROT ECTEO LIKEWISE)

I~1 I~1 BURNERS I~1 CONTtNUOUS - I,~l J ~ l ~ l ~ / PREM,XEO 161 I~1 / \ l ~ l LiNE PILOT~ PILOT AS

/ UR~_~NER GAS

\FL . . , SENS,NG , .. / I E \ ~o.E Ps, oR OVER)

I. Approved main gas safety shutof f valve. !V[anual-opcning automat ic - closing yalve or automatic-opening automatic-closing valve, to suit firing method used.

2. Permanent and. ready means for making periodic tightness checks of main gas safety shutoff valve.

3. Approved pilot gas safety shutoff valve.

Fig. 20. Example of application of:an.approved combustion safeguard mpervisin~ a continuous line pilot for a group of line burners during llghting-o~ and firing. - ;

2286 COMMITTEE ON OVENS AND FURNACES

53. Revise old Figure 18 and renumber as Fig. 21.

, l o t ~ ~ ~ ~ £:ZZ22Z ~u"

".,'=~'~=': I'~-.11 ~t~...~,.'N-W v i i " r , • ,,~',,

~~~~__------LIT~_ -~-Z~J_ L'llr~ L ~ 1 - - - Y " , i ~ ~ " ~ . - - a . . . ,

¢- c 0 - ~ _ ~ / " G . . , / I I ~ I ~ ' / s ' p . t 0 o ~ k I I /c~,!..qp,..,e,,,-. a , n ~

M,',nS,fetyShut.dl r/ Sulx'rvising(rMl)CKk Whe~severatlxn'nema~.iUPl~m~ ~ St ̀ . . . . VaWe Man~ Reset for lelkaqe tell Of 0~ zero ~ utearl ,scgvri~ • ~ .,, l r ~ $1fet$ 5hui:.of f VaNI :rap, Mlar and i .~Nr v,s,mJ ( EM~ ( Vi~.'~"

Cock It ~ burner, to plrn~i~ individual li~dlng,

Fig. 21. Supervising Cock and Gas Safety Control System.

54. Move old Figure 19 to Appendix A following Fig. 26, and renumber as Fig. 27.

t~HOT COMMONweal"

. / VENT FAN INTERLO~ _ ~ |20V. AC- APPROVED

COCK SWITCH CONTACTS TIMER (TIME _ L CLOSE WHEN COCK IS DELAYSWITCH]

GAS PRESSURE . . . . . . / I.,I..V ~¢. I~, AND OTHER ~ - i~ INTERLOCKS ~ H I - 4 I -

TTIMER LOAD CONTACT iCLOSEO AT END OF

END SWITCH ON - - I - - _1--PURGE PERIOD SAFETY SHUTOFF jFT- " ~ VALVE-ClOSED / I ONLY WHENVALVE. ,L OPEN "r -

WIRING (DETAILS WILL VARY DEPENDING ON TYPE OF BURNER BCONTROLS USED)

--¢_

APPROVED / MANUAL OPENING

SAFETY SHUTOFF VALVE (WITH ENO SWITCH)


56. Move old Figure 20 to Appendix C, renumber as Fig. 29, and locate following B, 9.

56. Revise 550-17 to read as follows:

~50-11. Safety Shutoff Valves. (See 510-2). (a) When the main heating system input of the furnace is greater than 400,000 Btu's per hour, an approved safety shutoff valve shall be provided in the main gas line to the burner. A second approved safety shutoff valve shall be provided downstream from the first safety shutoff v~ve. An appropriately sized normally open electrically operated

ve shall be provided in a vent line between the two safety shutoff valves. The vent line pipe shall be run to a safe location, preferably outdoors, and shall be accessible for inspection.

Thesafety shutoff valves shall be arranged to close and the vent valve shall be arranged to open in the event of failure of combustion air, excessive combustion air pressure, flame failure, excessive temperature, excessive gas pressure, too low a gas pressure and failure of electric current.

When recireulating and/or exhaust fans are used and are essential to the proper operation and safety of the furnace, the failure of the recirculating fan and/or exhaust fan shall also close the safety shutoff valves and open the vent valves.

(b) When gas pilot systems are piped up stream from the main line gas burner safety shutoff valves and the pilot system capacity is greater than 400,000 Btu's per hour, this same double safety shutoff valve system with a vent valve shall be used.

(c) When the main heating system input of the furnace is 400,000 Btu's per hour or less, a single approved safety shutoff valve without a vent line may be used in place of the double safety shutoff valve and vent valve system described in 550-11(a) and 550-11(b).

1. Spring load solenoid valves may be used as the primary safety shutoff valve with fuel flow up to 400,000 Btu's per hour, or as the secondary safety shutoff valve with the double safety shutoff valve and vent system described in 550-11 (a) provided :

a. The seating force of the spring is a minimum of five pounds, exclusive of "dead weight" of the assembly and fuel pressure exerted.

b. Their use does not necessitate any abnormal settings of either the high or low gas pressure switches to counter any

2288 COMMITTEE ON OVENS AND FURNACES O F f a l

transient pressure fluctuations created by sudden operatio~ of the valve.

a°

b.

C.

2. Other solenoid valves, not meeting the above specifications may be used when all three of the following conditions prevail:

The flow is less than 150,000 Btu's per hour.

The valve size and pipe size is ~/~ inch or less.

The gas pressure is five (5) Psig, or less.

(d) The attention of the operator shall always be required before restart.

(e) A leak test facility shall be provided downstream of each safety shutoff valve. See Fig. 28 in Appendix C for proper location and procedure.

(f) Vent lines where specified above shall be as follows:

1. For fuel line diameters larger than 8 inches, the vent pi.pe shall be at least 15 percent of the cross sectional area of the mare gas pipe. If the main line is less than 3/~ inchs, then the vent line shall be equal to the cross sectional area of the main line.

2. Vent valve ports shall have a cross sectional area equal to the specified vent line.

3. Vent lines should have a maximum length of 40 feet and discharge to outside atmosphere. If longer runs are unavoidable, or an unusual number of fittings are necessary, an increase in vent size may be necessary.

4. Manifolding of vent lines should be avoided. If manifolding is absolutely necessary, then the cross sectional area of the manifold pipe must be equal or greater than the sum of the cross sectional areas of all individual vents involved.


. See Figure 29 in Appendix C.

VENT PIPE SIZE TABLE

FULL LINE VENT LINE

DIAMETER DIAMETER

up tO 11~ ' ' ~4"

2" 1 "

2½" 174" Y' l ~ "

3½- ~½,, 4" 2"

4 ½ " 2"

5" 2"

s½" 2½" 6" 21~ ''

6 ½ " 3"

7" 3"

7 ½ " 3"

8" 3 ½ "

57. In 550-15, in the first line of the fourth paragraph, change "should" to "shall".


59. In 550-29, in the fourth line of "Exception (a)", change "should" to "shall".

60. In 550-31,fourth line, change "should" to "shall".

61. In 560-1, in the second and sixth lines, change "should" to "shall", and add at the end oJ the paragraph "(See Appendix A.)".

2290 COMMITTEE ON OVENS AND FURNACES O ~

62. In 560-3(a)4, in the seventh line of the second paragraph, insert "heating system" between "main" and "disconnect".

63. In 560-3(c), second line, change "should" to "shall".

64. In 560-4, third line, change "should" to "shall".

65. In 560-5,first line, change "should" to "shall".

66. In 560-6, first line, before "excess" insert "Where a furnace is subject to damage, an", and change "should" to "shall".

67. In 560-9, sixth line, change "should" to "shall".


69. In 560-13, in the third and fifth lines, change "should" to '.'shall".



72. In 6~.4, second line, change "should" to "shall".

73. In Appendix A, 1, under both "Low Pressure Gas or Atmospheric System" and "High Pressure Gas System", change "1 psig" to 0.5 psig".

74. Provide a new "Appendix F" (former Article 530) as foUows:


A P P E N D I X F.

GAS COMBINATION S A F E G U A R D S -

cOMBUSTIBLE GAS ANALYZER TYPE FOR MANUALLY LIGHTED BURNERS

fhis equipment is intended for use on large manually lighted, gas-fired in. . .~.,~1 heating equipment such as heat treating furnaces. It is designed to

az~v"'~l continuous!y the gaseous products of combustion and to indicate and °- -'..,4 ,~rcent combustibles and percent oxygen (optional) present in the sampled ~ . " ~ t ' z ~ ithportant that sample point(s) be located so that the sample to the g ~--~h,--er aecuratelv renresents the total flue as or atmos here assin that gasa~"~'7- . _ - ~ _ g . . P P g _~rticular sectaon ann to respond to gas concentration claanges at the burners aspP"Tromptly as possible. Temperatures at the sampling point should not exceed 1200"1~.

The "percent combustibles" indication may be considered the safety control function'of the equipment. During a firing cycle, a dangerous condi/ion maY result, for example, from a deficiency of air; however, such a circumstance ,ormally would cause a gradual increase in the amount of combustibles in the :r0ducts of incomplete combustion. The equipment is designed to provide an al'utomatic warning signal at 1 percent and a danger signal at 2 percent combustibles. Provision is made for shutting off the fuel supply at the 2 percent no/at. (The 2 percent value is well below the danger level regardless of the type lad gas.) Similarly, this equipment may be used to detect a dangerous internal atmosphere at the time of burner light-off.

The "percent oxygen" indication, when employed, is intended to provide the operator with information on which to judge the efficiency of combustion. No automatic signal indication is required for the oxygen analysis.

This equipment usually consists of a Sampling System, Analyzer and Recorder. It is not instantaneous in response to composition changes of the monitored gases. From the pick-up point, the sample gas travels through tubing which may be 25 feet long. After reaching the actual analyzing equipment, the gas is passed through a catalytic combustion chamber. A change in gas composition causes a change in electrical characteristics of a Wheatstone bridge circuit which is automatically compensated by mechanical movement of a slide wire resistor. This motion not only results in a continuous recording of conditions but also results in snap switch actuation for signaling purposes if the specified 1 and 2 percent limits are reached. It is recognized that this series of operations involves a time delay which may be in the order of 10-20 seconds depending somewhat on the concentration of combustibles in the sample. However, because unsafe combustion is usually the result of gradual changes in conditions, the speed of response in a well engineered system can be sufficiently fast, and with sufficient safety factor to warn of danger except for a sudden loss of flame. The good judgment of well-trained operators is a necessary element, especially while the combustion chamber is heating up.

In order to derive the full benefits of the equipment, each application must be individually engineered and inspected by the manufacturer of the device or an authorized representative. It is expected that such engineering will also require the cooperation of the manufacturer of the associated gas firing equipment.

2292 FOREWORD 8 ~

Par t H I of the report prepared by the Sectional Committee on Class C and Vacuum Furnaces, proposes amendments and recom. mends official adoption of NFPA No. 86C-T-1972.

Pa r t H I has been submitted to letter ballot of the Committee, but results were not available at the time of printing of the Technical Committee Reports. Results of balloting will be announced at the Annual Meeting.

Tentative Standard for

Industrial Furnaces Using

A Special Processing Atmosphere

NFPA No. 86C-T -- 1972

Foreword

The standard for the location, design, and construction of ovens and furnaces is set forth under classifications as follows:

Class A ovens or furnaces are those operating at approximately atmospheric pressures and temperaturs not below 1400 ° F (760 ° C) where there is an explosion hazard from either, or a combination of, the fuel in use; or f lammable volatiles from material in the oven or catalytic combustion system; i.e., f lammable volatiles from paints and other finishing processes such as dipped or sprayed material, impregnated material, coated fabrics, etc.

Class B ovens or furnaces are those operat ing at or above atmospheric pressure and temperatures exceeding approximately 1400 ° F (760 ° C).

Class C furnaces are those which utilize a special processing at- mosnhere and operate at approximately atmospheric pressure. Tem'peratures may range from ambient to over 5000 ° F (2760 ° C) and any type of heating system ma.y be used. This furnace classification includes the special processing atmosphere generators.

Class D furnaces are vacuum furnaces which operate at temperatures above ambient to over 5000 ° F and at pressures below atmosphere, using any type of heating system. These furnaces may include the use of special processing atmospheres.

2293 I N D U S T R I A L F U R N A C E S - - S P E C I A L A T M O S P H E R E

C H A P T E R 1. GENERAL

A R T I C L E 100. G E N E R A L I N F O R M A T I O N

100ol. Scope. (a) This standard refers to Class C industrial furnaces and atmosphere generators, only, and shall apply to new installations, major alterations, or extensions to existing equipment.

(b) Within the scope of this standard, a Class C furnace shall be any heated enclosure, operating at approximately atmospheric pressure, which utilizes a special processing atmosphere within the furnace.

100o2. Definitions. (a) For the purpose of this standard, BATCH I~oCESS FURNACaZS include all furnaces into which the work is introduced all at one time.

(b) CONTINUOUS PROCESS FURNACES are furnaces into which the work charge is more or less continuously introduced.

(c) OPERATORS are the individuals.responsible for the light-up, operation, shutdown, and emergency handling of the specific i~stallation, consisting of the atmosphere gas generator and /o r furnace and the associated equipment through or into which the atmosphere gas flows.

(d) AUTHORITY HAWNO JURISmCTION: The "authori ty having • * * " n " " " ' " jurisd~cuo is the orgamzatton, office, or individual responsible for "approving" equipment, an installation, or a procedure.

NOTE: The phrase "authority having jurisdiction" is used in NFPA standards in a. broad manner since jurisdictions and "approval" agencies vary as do their responsibilities. Where public safety is primary, the "authority having jurisdiction" may be a federal, state, local, or other regional department or individual such as a fire chief, fire marshal, chief of a fire prevention bureau, labor department, health department, building official, electrical inspector, or others having statutory authority. For insurance purposes, an insurance inspection department, rating bureau, or other insurance company representative may be the "authority having jurisdiction."

In many circumstances, the property owner or his delegated agent assumes the role of the "authority having jurisdiction," at government installations, the commanding officer, or a departmental official may be the "authority having jurisdiction.'"

100-3. Approvals , Plans, a n d Specifications. (a) Before new equipment is installed or existing equipment remodeled, complete plans and specifications shall be submitted for approval to the authority having jurisdiction. Plans shall be drawn to an indicated scale, and show all essential details as to location, construction, heating equipment, fuel piping, heat input, and safety control wiring diagrams. The plans shall include a list of equipment giving manufacturer and type number.

2294 GENERAL

I,I CONTROL C IRCUIT VOLTAGE'

~ r u s [ O SWITC H

I .... - - ° * 1 O FLAME SUPERVISION O N,C, CONTACT OF FLAM(~ CONTROL SUPERVISION CONTROL TO ALARM SILI[NC[R SWITCH ALARM

OPI[N WITH FLAME PRESENT Jv o

VENTILATING " I v AIR FAN STARTER DOOR

~'~f LOW INTERLOCK LIMIT ~. s w r r c N . ~ SWITCH : ~ •

o---t o

, . . . . . .s G . , • . . ~ 1 • / J [ xcI~$S LOW HIGH LOW

T[MPERA7 UR[ I PILOT " PRESSURE SWITCHI[B COMBUSTION t START

. . . . . A:.%:~°oW ~ BUTTON ,~:,: ,O.

AT END OF PURGING-- IS Sl[C i

. . . . . OMPL*T*A,, " % / ' P*L Y'LV . . . . o . ,oR o . k_=_L. 25 . . . . . ,

. . . . . , . | - - I - ' - - - TO CLOSE ONLY WHI[N £ , , ] SAFETY SHUT R . . . . . . . , MOTORS A . **.0 ~ . ~ CN[RGIZ[O WITH POWER' N O CONTACTS OF' PLAMI[ OF'F' VALVI~

SUPI[RVISION CONTROL

c L o ; , ;,:7:':.;.'o:'~';*,,s L ' o ~ ' " ~ MOTOBIZ[B ~ - I

I I BLOCKING VALVIr L . . ~ , , I ~ _ , . j

VENT VALV[

Fig. ! . Typical "ladder-type" schematic diagram

(b) Any deviation from this standard will require special per- mission from the authority having jurisdiction.

(c) Wiring diagrams and sequence of operations for all safety controls, including "ladder type" schematic diagrams, shall be provided (see Fig. 1).

100-4. Electrical. All wiring in and around furnaces and generators shall be in accordance with the National Electric Code (NFPA No. 70) and as described in Fig. 1.

100-5. Operator Training (a) It is fully recognized that the most essential safety considera-

tion is the selection of alert and competent operators. Their knowl- edge and training are vital to continued safe operation.


2295 INDUSTRIAL FURNACE8 ~ SPECIAL ATMOSPHERE

Regular operators shall receive scheduled retrainin to main- (c) high level of proficiency and effectiveness, g

t ~ l a

(d) Operators shall have access to operating instructions at all ti~es. An outline of these instructions shall be posted at the furnace.

Operating instructions shall be provided by the equipment cturer. These instructions shall include schematic piping

and wiring diagrams. All instructions shall also include:

1. Light-up procedures.

2. Shutdown procedures.

3. Emergency procedures.

4. Maintenance procedures.

(0 Operator training shall include:

1. Combustion of air-gas mixtures.

2. Explosion hazards.

3. Sources of ignition and ignition temperature.

4. Atmosphere gas analysis.

5. Handling of flammable atmosphere gases.

6. Handling of toxic atmosphere gases.

7. Functions of control and safety devices.

8. Purpose and basic principles of the gas atmosphere generators.

2296 L O C A T I O N . A N D C O N S T R U C T I O N

CHAPTER 2. LOCATION AND CONSTRUCTION

ARTICLE 200.: L o c A T I O N OF FURNACES, GENERAToR~ AND RELATED EQUIPMENT '

: A. General

200-1. Furnaces, generators, and related eqdipment shall located with consideration to the possibility of fire resulting from overheating, molten metal, ignition of quench oil, ignition of hr. draulic oil, overheating of material in tile furnace, l'etc.; or fro~ escaping fuel or processing atmosphere, with, the resulting possibility of building and equipment damage and injury to personnel. " "

: • g,

B. Grade Location x

200-2. (a) Class C furnaces and special atmosphere generators should be located at or above grade to make .maximum use of natural ventilation and to minimize restrictions to adequate expl0. sion relief.

(b) Special consideratiofi shall be given when a flammable spee. ial atmosphere is used or when using fueLs wi th a specific gravity greater thah air. When basements, or other Confining areas, must be used, additional consideration must fie given to ventilation and the ability to safely provide the required explosion relief.

C. Structural Members of Buildings /

200-3. Class C furnaces and generators shall be located so that there will not be any adverse temperature effect on bUilding strut. tural members.

D. Location in Regard to Stock, Processes, and Personnel

200-4. Stock and Processes. Class C furnaces and special atmosphere generators should be well separated from valuable stock, important power equipment, important process equipment, and fire protection facilities, in order to minimize interruption of production, and to provide protection in the event of accidents.

200-5. Personnel. (a) Furnaces and generators shall be located to minimize exposure to groups of persons from the possibility of injury from fire, explosion, or asphyxiation.

(b) Furnaces shall not adjoin personnel assembly areas, such as recreational areas, locker rooms, lunch rooms, etc., and shall not obstruct personnel travel to exitways.

2297 10 INDUSTRIAL FURNACES - - SPECIAL ATMOSPHERE

~ . Finishing Operations. Class C furnaces and generators be safely located and protected from exposure to flammable

liquid dip tanks, spray booths, flow coaters, or storage and mixing rooXns or areas. The hazard is particularly severe when vapors from dipping operations may flow by gravity to heating units at, or near, floor level. ,' ' '

E. Floors and Clearances < . . .

~00-7. Class C furnaces and generators shall be located for ready a-ccessibility, with adequate spacc abovc, and on all sides, to permit inspection and maintenance. The space above, below and around the equipment shall be properly ventilated to kccp temperatures at combustible floors, ceilings and walls below 160 ° F.

200-8. (a) Furnaces" and generators shall bc located on, or above, noncombustible floors. If such a location is not possible; then one of the following procedures shall be employed:

I. Remove combustible floor members and.replace witha mono- lithic concrete slab which extends a minimum of 3 ft. beyond the 0utcr extremities of tbe furnace or gcneratoi'...

2. Provide air channels between the floor and theequipment .~msdrpcndicular to the axis.of the equipment) and/or noncombustible

ation. This shall bc adequate to prevent surface temperatures of floor members,from exceeding. 160 ° F . : .

(b) Where electrical wiring will be present, in the channels of certain types of floors, the wiring shall beinstal led ' in accordance. with Article 356 of the National Electric Code (NFPA No. 7 0 - 1971).

(c) Floors beneath oil burners shall be provided with a noncombustible, nonporous:~urface - to prevent the floors from becoming 0il soaked.

200-9. Where furnace or generator ducts or stacks penetrate combustible walls, floors or roofs, clearances and insulation shall be provided to prevent surface temperatures of combustible members from exc~d ing 160 ° F.

200-10. C0mbustible stock, stock fixtures, equipment, etc., shall not be located near any furnace or generator or high temperature ducts or stacks. '

2298 LOCATION AND CONSTRUCTION

ARTICLE 210. CONSTRUCTION OF FURNACES AND GENERATORS

' A. G e n e r a l

210-1. Furnaces and related equipment shall be built in a sub,tan. tial manner with due regard totthe fire hazard inherent in equip. ment Operating at elevated temperatures, the hazard to operators from high temperatures, open flames and mechanical equipment and the need of ensuring reliable, safe operation over tl~e expected maximum life of the equipment.

B. M a t e r i a l s • C

210-2. (a) Furnaces shall be constructed of noncombustible materials . . . . . ~

(b) Furnace structural supports and conveyors shall be. designed with adequate factors of safety at the maximum operating tempera. tures, consideration being given to the strains imposed/by expansion.

(c) Adequate facilities for access shall be provided, to permit proper• inspection and maintenance. . ,,

(d).Burners and heating elements of'all types shall.be substantially constructed or guarded to resist mechanical damage from falling work, trucking, or. other mechanical hazards, inherent in industrial use.

(e) Where-refractory materials are used, they shall' be supported so that they will not fall out of place. .

(f) Corrosion resistance. Where subject to corrosion, metal parts shall be adequately protected.

(g) Accessibility and moUnting of Controls. Provision shall be made for the rigid'attachment of con'ti'ol devices. Combustion safeguard mounts shall be arranged so that the electrode or other flame detecting element is correctly positioned. Valves and control panel shall be so located tha t all necessary observationl)and adjustment may be readily made.

(h) Parts of furnaces which operate at temperatures in excess of 160 ° F should be guarded by location, guard rails, shields or insulation to prevent accidental contact with personnel. All parts of equipment oper~tting at elevated tempera'tures sffall I~e installed in accordance witfi Article 200,. Section E, Floors and Clezir~inces.

(i) Bursting discs or panels, mixer openings, or other parts of the furnace from which flame or hot gases may be discharged should be located or guarded to prevent injury to personnel.

.2'299 1~ INDUSTRIAL FURNACE ~ SPECIAL ATMOSPHERE

wit0 ) Properly located observation ports shall be provided to per- the operator to observe . the lighting of individual burners

&) Devices such as 'relief valves; open sightdrains and water flo~'switches from water cooling systems shall be designed and installed for ready observation by operator.

A RTIC LE 220. FURNACE AND G E N E R A T O R E X H A U S T SYSTEMS

220-1- The need for a furnace chimney or furnace exhaust system for removal of products of combustion, heat, toxic gases, and other 0bjectional gases will depend on the heating process, type of combustion, hazard to personnel, and all applicable air pollution control regulations.

220-2. When furnace venting is required, care shall be exercised so that excess draft is not imposed upon the furnace by the draft hood, barometric damper, or exhaust hood.

220-3. Before exhausting products of combustion directl)~ into the area in which the furnace is located, the following factors regarding the ability of the building ventilation system to dilute these vapors and gases shall be considered :

(a) The quantity of the contaminants discharged into the area must not be too great or the a i r volume necessary for dilution will be impractical. ,

(b) Workers must not be exposed to concentrations of harmful contaminants in excess of the established threshold limit values.

220-4. In all cases where contaminants are exhausted from a furnace and related equipment into a room, the room should have mechanical ventilation consisting of an air intake system bringing in air from the outside and an exhaust system exhausting an equal amount of air to the outside. The supply air should be uniformly

, distributed within the area, and the exhaust duct should be arranged to eliminate all pockets and dead air areas at either floor or ceiling levels, depending on the type of contaminant being evolved.

920-5. Furnaces and related equipment requiring outside exhaust of flue gases or other combustion by-products may use direct con- netted, dilution, or recuperative-type exhaust systems. Size, insula-

,ti0n.and auxiliary equipment employed shall be suitable for the maximum temperature and volume of gases to be discharged under peak conditions. The design shall otherwise conform to Articles 200-9 and 210-2(h).

2300 ,.ocA~xoN AN]) CONSTRUC~XON 86C-I~

ARTICLE 230. ACCESS, MOUNTINGS, AND AUXILIARY EQUIPMENT

A. General

230-1. Adequate facilities for access shall be provided to permit proper inspection and maintenance. 230-2. When such openings are intended to permit persons to climb inside for inspection and cleaning, there should be provided such additional equipment as ladders, steps, and grab-rails to permit safe and easy access and egress.

B. Mountings

230-3. Mountings for auxiliary equipment, such as control in. struments and safety devices, shall provide protection against dam. age by heat, vibration, and mechanical hazards.

C. Ladders or Steps"

230-4. Where ladders or steps are needed to reach valves or other controls, they shall be noncombustible and provided as a permanent part of the installation.

D. Auxiliary Equipment

230-5. Auxiliary equipment such as conveyors, racks, shelves, bas. kets, and hangers shall be noncombustible and designed to facilitate

cleaning.

ARTICLE 240. FURNACE HYDRAULIC SYSTEMS

240-1. Hydraulic systems for furnace door operation, lifts for work loads, and conveyor systems should not use petroleum or other combustible hydraulic fluids. The use of fire resistant hydraulic fluids is recommended. 240-2. When petroleum oils or other combustible fluids must be used, the system shall be designed to minimize the possibility of fluid release which may result in a fire or explosion.

240-3. All components of the hydraulic system shall conform to the standards of the National Fluid Power Association and/or ANSI Standards in the B-93 series. 240-4. Drawings for fluid power diagrams should fgllow ANSI Standards Y14-17, 1966, and Y-32.10, 1967.


CHAPTER 3. HEATING SYSTEMS

ARTICLE 300. GENERAL REQUIREMENTS

500-1. Scope. (a) For the purpose of this standard the term ,,furnace heating system" shall include the heating source and associated ductwork and circulating fans used to convey heat to the furnace or work therein.

(b) Other heating systems such as coal or other solid fuel firebox and firing equipment, and hot oil or other liquid circulating systems are not included in this section.

(c) The source of heat may be internal, i.e., within the furnace, external, i.e., outside the furnace and the means of transfer of heat may be direct, i.e., t.he products of combustion enter the furnace and contact the work in process, or indirect if the products of combustion do not contact the materials in process.

(d) The transfer of heat into and throughout the furnace may be by convection, radiation, or conduction; als6 combinations of these means.

$00-2. Control Equipment. For control equipment requirements, including combustion safeguards, air flow switches, time relays and temperature controls, see Chapter 5.

300-3. Fuel Supplies. For the handling of fuel supplies up to the point of connection with the furnace, see Section C, Articles 310 and 320 of this standard and the following NFPA standards: Oil Burning Equipment (No. 31), Liquefied Petroleum Gases (No. 58) and Gas Piping and Gas Equipment on Industrial Premises (No. 54A).

300-4. Electrical Equipment . Electrical installation shall be in accordance with the National Electrical Code (NFPA No. 70) and as described hereafter.

ARTICLE 310. GAS HEATING SYSTEMS

A. General

310-1. Scope. This section includes heating systems fired with natural gas, commercial manufactured gas, mixed gases, liquefied petroleum gases, and producer gas.

2302 . H E A T I N G SYSTEMS ' 86~.~1~

310-2. Gas burners and associated mixing and control equ:- ment shall be of a proper type for safe operation and constructioa suitable for:

(a) The Btu content and specifiC gravity of the gas used.

(b) The operating pressures available. (c) The maintenance of an adequate air supply to fuel-air

mixers for reliable combustion throughout the burner operating range.

(d) In the case of excess air burners, a correct air-gas ratio for the particular burner shall be maintained througl~/out the turno down,range. Sufficient air and gas pressures or mixture pressure8 depending onthe type of burner shall be maintained throughout the turndown range so that safe conditions of pressure aiad secondary air will prevail in the combustion space.

(e) The use of safety interlocks. See chapter 5, Safety Control Equipment.

(f) A stable 'pilot flame, either ima'nually or sparl~ ignited, if required. (See 510-7).

(g) Temperature exposure, air movement and flame propaga. tion as may prevail. "

. . •

. . B. Installation of Fuel Gas Systems.-

310-3. A description of the types of commercial gashes, the prop. erties of these gases, and a glossary with interpretation of terms as they apply to gas combustion systems and equipment i s found in the Appendix. "

C. Gas Piping and Valves

310-4. Other Standards Applicable. (a) Gas piping and valves for natural and manufactured gases shall be installed in accordance with the following paragraphs. Where high pressure services (above 0.5 psig) are utilized, the installation requirements shall comply specifically to the following paragraphs and to the applicable provisions of the Standard for Installation of Gas Piping and Gas Equipment on Industrial Premises and Certain Other Premises (NFPA No. 54A).

(b) Installation of liquefied petroleum gas storage and handling systems used to supply furnace.heating systems shall b e m a d e in accordance with the Standard for Liquefied .Petroleum Gases (NFPA No. 58). ': :

2303 ~6~__1~ INDUSTRIAL FURNACES - - - SPECIAL ATMOSPHERE

. • 0 - 5 . Pipe Material . Gas piping shall be so constructed :and "tared in accordance with t h e Standard for Installation of Gas los

~ and Gas Equipment' on Industrial Premises and Certain er Premises (NFPA No. 54A). -

510-6. Size of Piping. Piping shall be of a size and so installed as to provide a supply of ga#. sufficient to meet the maximum denaand at the point of use.

510-7. Emergency M a n u a l Shutoff Valves. Manua l ly operated shutoff valves, operated separately from any automatic valve, shall be provided to permit turning off the fuel in emergency and shall be located so that fires, explosions, etc., at furnaces will not prevent access to these valves.

$10-8.. Pressure Regulator. Where a pressure regulator or governor is used. as part of a furnace heating system, including gas mixing blowers and gas mixing machines, the air space of the diaphragm or bellows housing shall be vented outdoors, or to a safe location unless construction does not require a vent. The vent is not required when the diaphragm discharges through a restricted orifice into spacelargeenough so that escaping gas would not present a hazard (not to be used on high pressure gas lines or an LP-Gas System). Also, the vent is not required for regulators having the diaphragm space connected to discharge piping from mixers through a restricted orifice. The foregoing does not apply to zero governors or loaded ra t io regulators .

• D. B u r n e r s a n d M i x e r s

510-9. General . There are numerous variations, combinations, and trade names for mixers and burners. ' A "description and definition of the various types of 'burners and mixers may be found in the Appendix.

~10-10. Bu r ne r Air Adjustment shall be fixed or provided with a locking device which will prevent accidental change of setting and shall be so located that adjustments may be readily made.

310-11. Mult ip le Port Burners . (a) Burners having many individual ports shall maintain a stable flame over the entire length (or surface) of the burner under all draft conditions which may arise in the operation of the furnace. They shall light easily, flash across the entire bui'ner surface and not blow off or flash back when the burner is at operating temperatures.

Such burners • must be carefully maintained and shall be so located that foreign material cannot enter ports.

2 3 0 4 , , s6 17 (b) Multiple port burners shall be so designed that ignition of

ort Shall result rapidly from the ignition of ~o ~as from every p . . . . . . . . ~ at an sin le I3ort when gas is supplied to the,burner at me nighest Y g . and lowest rates of the control devlce.

(c) When "modulating" or "proportional" control 'is used, the low rate must bc set so that burners will light dependably over their entire length or area from the ignition source pro,~idcd.

310-12. Tunnel , Nozzle Mix or Torch Burners shall be so con. structed t ha t ' a stable' flame condition without tendencY to flash back or blow o f f will be maintained over the entire range of turn. down and finder all operatifig Conditi0ns Wliich may be encountered in furnace operations. : ' : .i ~

Where a number of nozzle burners are supplied from a single inspirator, the provisions of 310-14;.Grouped Burners, shall apply. . - . .

310-i3. Special Burne r Types . Specialized burner"designs shall ignite reliably over the entire area of the burner from a single ignition source~ Stable flame conditions wi~out flash back or blow off shall be maintained over the entire range of turfidown. Ex. amples of special bur~er types "~e radiafit and luminous wall burners. , < 310-14. Groupe d Burners . When.a number o f separate burners having" a sin'gle mixing inspirator" are supplied, such ~ 4nspirators shall be ~capable of inspirating all air needed for combustion and shall be installed in accordance with Section E governing, propor. tioning burners.

310-15. Educt ion Burners . When an atmospheric inspirafing burner fires into a combustion, space maintained, a t less than atmospheric~ pressure, i t shall operate reliably under normal draft conditions a n d controls shall be~provided to shut off the burner in event of suction failure. : '

310-16. Tu r ndown . The burner shall maintain stable operation over the entire operating range and shal.1 ignite reliab!yr ore the entire-burner (at low flame) from the pilot location. Stops to limit the travel Of automatic control devices shall be provided. The use of cocks or val~es provided with fixed bypasses where manual control is used, is recommended.: ; :

, " " t : "

E. Automatic Proportioning Systems

310-17. General . For definitions and ~ descriptions of tl~e various types of proportioning mixers, burners, inspirators, etc., see Air pendix. .:

2305 8 1 ~ INDUSTRIAL F U R N A C E S - - SPECI A L A T M O S P H E R E

~10-18. Gas Burner Systems shall be equipped with a proportioning device or other device which will insure a correct gas-air ratio over the entire range of turndown. (See 310-2(c) and 2(d)

• t O - 1 9 Burner Limitations ( a ) In an single gas mixing burner assembly when only one burner is used, no valve or control device except a fixed orifice for balancing purposes shall be inserted in piping between the proportioning device and any firing point.

(b) The burner head, tip or line burner shall maintain a stable flame when supplied with correct gas-air mixture over the full range of turndown.

(c) Line burners (including" blast tip burners, radiant types, ,,i~rared buruers," and other grouped burners) shall light over their entire length when an ignition source is applied to any point on the burner over the entire operating range of the burner. Line burners shall not be used where ports may be subject to obstruction without adequate protection to eliminate the possibility of such obstruction.

(d) All burners shall be regulated to light reliably.

$10-20. Proportioning Inspirators. (a) Valves or other obstructions shall not be installed between a proportioning mixer and burner except a fixed orifice for purposes of balancing.

(b) Each proportioning inspirator shall have a gas adjustment consisting of a fixed, replaceable orifice or an adjustable orifice. When an adjustable orifice is :used, the adjustment screw shall be protected against tampering.

(c) The gas-air adjustment shall be provided with a device for locking in place.

310-21. Proport ioning Mixers. (a) Valves or other obstructions shall not be installed between a proportioning mixer and burner except a fixed orifice for purposes of balancing.

(b) Each proportioning mixer shall be equipped with an adjustment means for setting the air-gas ratio which shall be equipped with locking no other means of effectively securing the setting.

310-22. Mixing Blowers. (See Appendix A, 2 for definition.)

(a) The blower shall be equipped with a gas control valve at its entrance so arranged that gas is admitted to the air stream entering the blower in proper proportions for correct combustion

2 3 0 6 • v '

b the type of burner or burners employed; the .said gas control s~t~all be of either the "zero governor" or "mechamcaJ rauo valve,, types which control the gas and air adjustments simultaneously, and no valves, control devices, or other obstructions ,which Will change overall manifold pressure during operation, will be permitted between the blower discharge a n d the burner or burners.

(b) An approved safety shutoff valve of the manual opening, automatic' closing type shall be installed in the gas supply connee. tion to each mixing blower which will shut off the gas supply automatically when the blower is not in operation and in the event Of gas pressure failure (see Article 510).

(c) Proper gas-air mixtures shall be supplied to. the burner over the entire turndown range.

( d ) The total length of air-gas mixture pipe from a mixing blower to the farthest removed gas burner inlet on the manifold shall be as short as possible.

(e) The size or sizes of pipe used in fabricating an ~air-gas mix. ture manifold shall conform with the instructions of t h e manufacturer of the mixing blower; but, in any event, the diameter of main manifold shall be at least the size of the discharge of the mixer.

(f) Only mixing blowers having a" static delivery .pressure of 10 inch w.c. or less and otherwise meeting the definition should be so classed; blowers of higher pressure being subject to the ~limitatiom of gas mixing machines under 310-27.

(g) The air-gas control or ratio valve on the inlet of a mixing blower shall be equipped with a permanent but adjustable limit stop to assure that a minimum mixture pressure can be established in the'field to suit the requirements of the burners, the manifold, and the combustion environment.

(h) Mixing blowers should not be used with manufactured gas or other fuels containing more than 10 per cent hydrogen.

310-23. Pressure-Loaded Regulktor Systems usually involve a "Zero Governor" which is cross-connected by means of an Impulse Line to a source of varying pressure for which compensation is desired. Examples include (1) Proportioning Mixers w i t h sealed-in nozzles, with varying furnace pressure, and (2) Nozzle Mixing Burners with single (air) valve control.

(a) If a shutoff valve or an adjustment device is installed in the impulse line, it shall be done only at the direction of the equipment manufacturer.

2307 f

0 INDUSTRIAL FURNACES - - SPECIAL ATMOSPHERE

510-24. Mechanical Air-Gas Propor t ion ing ' Va l ve s consist of (1) an air valve and (2) an adjustable gas valve and are essentially an interlocked Two Valve System with one valve in the ai~ line and the other in the gas line.

The two valves may depend upon approximately equivalent inlet pressures and flow characteristics for maintaining proper gas-air ratios throughout the range, or their movement may be synchro- nized by adjustmen~ of a flexible cam to give desired gas-air ratios at multiple positions in the range.

(a) I f any adjustment device is located downstream from the Air-Gas Valve it shall be done only at the direction of the mixer manufacturer and should be protected against tampering.

F. Gas Mixing Machines

310-25. General. Any combinat ion o f proportioning control devices, blowers or compressors which supply mixtures of gas and air to burners where control devices or other obstructions are installed between the mixing device and burner is defined as a "gas mixing.machine ' ' . and the provisions of 310-26, 310-27, and 310-28 shall a p p l y .

NOTE: The essential difference between the mixing devices used with automatic proportioning burners, Section E, .and the gas mixing machines is the provision of a proportioning valve which responds to changes in rate of gas delivery controlled at any point between the machine andburner . There are several distinct types of gas mixing devices which come within the scope of this section and may supply premixed, gas within the explosive range or with only part of the air required for complete combustion.

A gas mixing machine usually comprises a pressure regulator or "zero governor" which reduces the gas supply pressure ot atmospheric and. a proportioning valve and compressor.

Gas mixing machines may deliver g~-air mixtures which are not within the explosive range, additional combustion air being secured at the burner, either from a burner mixre or directly from the combustion space. They also may supply mixtures within the explosive range and, when so installed, means to prevent flash backs occurring in piping containing the flammable mixture or to prevent damage if flash back should occur should also be provided.

310-26. Nonexplosive Mix tu res (outside flammability limits). Gas mixing machines supplying gas-air mixtures which are above the upper explosive limit shall be installed as follows:

(a) A stop or other means shall be provided which will prevent effectively adjustment of the machine within or approaching the explosive r~inge .

(b) The machine should be located in a large, well-ventilated

2308 HEATING SYSTEMS 86~.~

area. I f the machine is in a small detached building or cut-off room, explosion vents shall be provided in the ratio of I square foot of vent area to each 20 cubic feet of room volume (see NFp/~ No. 68, Guide for Explosion Venting).

The choice of location varies considerably in individual installations. In large, well-ventilated manufacturing areas there is relatively little chance of leakage accumulating in dangerous proportions and, under such conditions, the machine may well form an integral part of a furnace heating system.

In considering small rooms where dangerous gas-air mixtures could be formed, the machine is better located in a detached building or in small room cut off by concrete walls bonded into the floor and ceiling and provided with explosion relief vents to outdoors. Entrance to this room should be directly from outdoors.

(c) When gas mixing machines are installed in well-ventilated areas, the type of electrical equipment shall be governed by the National Electrical Code requirements for general service condi. tions unless other hazards in the area prevail.

When gas mixing machines are installed in small detached buildings or cut-off rooms, the electrical equipment and wiring shall be installed in accordance with the National Electrical Code requirements for hazardous locations (Article 500, Class I, Di- vision 2).

(d) Machines should, if practical, be constructed so that in the event of an explosive mixture forming and flash back resulting that the machine casing will not be ruptured.

(e) Air intakes for gas mixing machines and blowers using compressors or blowers should be taken from outdoors wherever practical.

310-27. Explosive Mixtures (within" flammability limits). Gas mixing machines supplying gas-air mixtures within the explosive range shall be installed in accordance with paragraph 310-26 b, c, and e, and the following paragraphs shall also apply.

(a) Automatic fire checks and safety blowouts shall be provided as called for in 510-6.

(b) Burners used with explosive mixtures shall be designed with port areas and length of gas passage through each port such that the possibility of backfire is largely eliminated. When necessary to secure stability of operation, water-cooled burners may be used.

310-28. Controls for gas mixing machines shall include interlocks and safety shutoff valve of the manually opening automatic closing type in the gas supply connection to each machine arranged to automatically shut off the gas supply in event of air and/or gas supply failures. (See Article 510.)


C.. Furnace Heat ing Systems

310-29 . General. Furnace heating systems are of two general typeS, direct fired and indirect fired.

510-30- Direct Fired shall mean any heating system in which the b~rners fire within the work chamber. Such a system may have multiple burners (see Fig. 2).

510-31. Indirect heating systems are so arranged that the products of combustion do not enter the work chamber, heating being accomplished by radiation or convection from tubes or muffles.

(a) RADIANT TUBES are defined as tubular elements open at one or both ends, constructed gas-tight of suitable heat-resistant ~aaterial, and capable of withstanding explosion pressure from ig-

CROSS SECTION NOIUIONTAL. Sll CTION

kfracfory Burner ~ " 1~lo4:k

Governorlblve ~ . . ( ~ e r n o r

H F.u.~k,tUh -El- Sum •

I I I I . : • ...~1"~117P Inser~

TYPICAl- PIPING, olRtC.¥ IHTtRNAL-FIREo MULTISURNIK FUIIIIA~I

Fig. 2. Typical piping, direct fired multlburner furnace.

2310 H~.ATXNO SYST~,MS 86C--23

nition of fuel-air mixtures. The" tube has an inlet and/or burner arrangement where combustion is initiated, a suitable length wl~ere combustion occurs, and an outlet for the combustion products formed. The fuel-air mixture can be mixed before, during, or after introduction into the tube. The introduction can be accomplished

To Prod.Of Comb. E~haust Sy~fem

i

CROSS SECTION

~ / / / / / / / / / / / / / / / / I " [ / / ] r R a a i a " t ' v ~ b c s ~

h . ~ , / / / / / / / / / / / / . . ' ~ , ' / / / / / , / / /

~.::-,~:.. ::~-.'~'..',,'..h ~'. .~:. :,~..'~¢:..,-.--

HORtZONTP, L SECTIOI~

E, , mLl~ _RawGast.~fromDiafra~LmCoatrolVatveWh;chlsLoaded oucror. .~ l l~ l I / " : - ~ From"~ rSupplyL ineTo [.d.uc4or.

• IIl~[I I V / / / A T~mperature~ntrollerRe~.ulatesEducf0r / / I I \ L L - . . ~ , / / / t l ~ ~rPressure

• TYPICAL INDIRECT IRTERNAL-FIRED RAI)IkNT-TUEE FUflH~CE(CAR-80TTOM TYPE)

Fig. 3. Typical Indirect fired radiant- tube furnace (car-bottom t ype )

I

~ llrs

I - - (~ROSS SECTION - -

Muffl0"fylx jntGrnM fil~cl meN,burner furnace.

Fig. 4. Muff le-type internal-fired multiburner furnace.


ttnder high pressure, under slight pressure, or under suction. Ig- nition can be accomplished at either the inlet or the outlet of the tube.

Radiant tubes can be located in the actual heating chamber of the furnace or remotely in another chamber. In the latter instance, heat transfer is accomplished by recirculation of heated gases (see Fig. 3).

(b) MUFFLES are enclosures within a furnace which separate the products of combustion from the work and from any special atmosphere which may be required for the process. Burners may be used for direct-firing of the space within the furnace but outside the muffle, or heating of the muffle may be by indirect means using radiant tubes or external furnace heaters (see Fig. 4).

ARTICLE 320. OIL-FIRED HEATING SYSTEMS

A. General 520-1. Scope. This section includes furnace heating systems fired with fuel oil and the oil burning portions of combination systems of oil and other fuels. When dual fuel heaters are used, this section shall apply to such heaters when fuel oil is being used.

B. Fuel Oil

320-2. Fuel oil as used in this Standard shall mean Nos. 2, 4, 5 or 6 in accordance with Tentative Specifications for Fuel Oils, ASTM D396-63T.

C. Fuel Supply 320-3. The installation of fuel storage tanks, piping, and valves shall be in accordance with the NFPA Standard for the Installa- tion of Oil Burning Equipment (No. 31).

D. Oil Burners 320-4. (a) Burners and control devices shall be acceptable to the authority having jurisdiction (see 500-1).

(b) Adequate safety protection shall be provided to prevent spillage to the building floor or to the inside floor of the combustion chamber.

320-5. Oil burners shall be of a type suitable for the service intended, as follows:

(a) Oil shall be delivered by the burner in a readily combustible condition, by proper preheating to a gas or vapor, or by atomization using preheating if necessary.

2312 HEATING SYSTEMS 86C--25

(b) Proper methods of main burner ignition in their order of preference for safety are gas pilots, electric ignition and manual ignition (see 510-7).

(C) OIL BURNER TYPES: 1. Air or stream atomizing: oil divided into a fine spray by an

atomizing agent, such as steam or air. 2. Rotary: oil atomized by centrifugal force, such as applied

by a whirling cone or plate. 3. Pressure atomizing: oil under high pressure forced through

small orifices. 4. Vapor: oil vaporized by heat.

(d) COMBINAaUON - - GAS AND OIL BURNERS. This type unit shall conform in safety, design and operating characteristics with the requirements specified for gas or oil burners as would be the case if they were not being used in combination.

320-6. Fuel Burning Equipment

(a) MAIN BURNER 1. The atomizing equipment for oil burners shall be designed

for convenient removal, cleaning and maintenance. 2. If an oil burner is equipped with a single atomizer and if

provisions for clearing the passages of the atomizer into the furnace are included, such clearing should be done after a normal shutdown with the pilot ignited and the fan operating.

3. Clearing of the oil passages of the atomizer into the furnace immediately after a safety shutdown shall be prohibited.

(b) ATOMIZING MEDIUM FOR OIL BURNERS

1. When the fuel is to he atomized with the assistance of another medium, this atomizing medium shall be supplied free of contaminants that could cause an interruption of service.

2. The atomizing medium shall be provided at the pressures required for proper operation.

3. Provisions shall bc made to insure that fuel cannot enter the main air and atomizing medium line during or after operation.

320-7. Oil Burner Controls. See Chapter 5.

E. Furnace Heating Systems - - Oil Fired

(See 310-29, 30 and 31)

2313 ~ 2 6 I N D U S T R I A L F U R N A C E S ~ S P E C I A L A T M O S P H E R E

ARTICLE 330. E L E C T R I C H E A T I N G SYSTEMS

A. General

$~0-1. Scope. This section includes all types of heating systems where electrical energy is used as the source of heat.

$30-2. Definitions. The following definitions apply to the several types of electrical heating systems included under Article 330.

(a) R~SXSTANCE HVArSR - - any electric heater in which heat is prt)duced by current flow through a resistive conductor.

(b) INVUC~ON H~ATSR - - a heating system by means of which a current-carrying conductor induces the transfer of electrical energy to the .work by eddy currents. (See Article 665 of NFPA No. 70-1971).

MM VENT

:RE

FLAM CURT~

ATMOSPHE! VENT

S

.S S

Fig. 5. Electric furnace.

2 3 1 4 . A xNo .. .S6C,-27

(c) ARe AND SKULL CASTING FURNAGES - - the passage of an electric current between either a pair of electrodes or between electrodes and t h e w o r k Causing an arc which releases energy in the form of heat.

(d) PLASMA ARC FURNACE ~ the passage of an electric cu.rrent between either a pair of electrodes or between electrodes and the work causing an arc which releases energy in the form of heat under the influence of an ionized gas such as argon.

330-3.:Control Equipment . For control equipment requirements, including air flow interlocks, time "relays and temperatur.e switches, see Chapter 5. "

• - . . • , . .

. . ; : ' . .

3 ~ - 4 . Electrical Installation. All par ts0f : the electrical installation shall be in accordance with the NationalElectrical C °de-

B. Resistan~ce Heating Systems

330-5. General . The following paragraphs appl~' to resistance heating systems. ' T h i s category includes; b u t is fi6t: limited to, metallic resistors, refractory metals, cermet, silicon carbide, carbon, metal sheath, and quartz lamp heat, sources.

330-6. Enclosure. (a) All parts of heaters operating within a furnace a t elevated temperatures and all energized parts shall be protected to prevent accidental Contact, by work in process and metal objects.

(b) Unenclosect el'ectric heatih.~ systems shall ha;ce the electric elements insulated and/or shlelde~l to prevent injury to personnel and ~ property.

(c ) Furnaces, shells, and chambers containing heaters'shall be grounded. - - . . . . .

330-7. Protection to Personnel. (a) Parts of furnace heaters shall be so guarded by location or

enclosure as to prevent accidental contact with personnel.

330-8. Construction. (a) Resistance 'heaters of all types shall be located, protected, and constructed to'resist damage from falling work, or other mechanical hazards inherent in industrial use.

.,2315 8 6 C ~ 2 8 INDUSTRIAL FURNACES - - SPECIAL ATMOSPHERE

(h) Where refractory materials or insulators are used, they shall be supported so that they will not fall out of place.

(c) Corrosion Resistance~ Where subject to corrosion, metal parts shall be protected.

(d) Accessibility and Mounting of Controls. Provision shall be made for the rigid attachment of control devices. All control devices shall be located so that all necessary observation and adjustment may be readily made.

(e) All parts of" equipment operating at elevated temperatures shall be installed in accordance with Article 200, Section E, Floors and Clearances.

350-9. Controls for Resistance Heaters. Refer to Chapter 5.

C. Induction Heating Systems

330-10." General. The following paragraphs apply to induction heating systems. This type of heating shall be designed and installed in accordance with the National Electrical Code (NFPA No. 70) with special reference to Article 665.entitled, Inductive and Dielec- tric Heating Equipment: ~ . . . . :"

To prevent spurious radiation cause d by this type of equipment and to ensure that the frequency spectrum is utilized equitably, the Fedbral Communications Commission (FCC) has established rules (FCC, Part 18) which governthe use of industrial heating equipment of this type operating above 10 kHz.

330-11. Installation..High frequency induction equipment heating systems shall not be installed in hazardous locations. (See Article 665 of NFPA No. 70-1971).

330-12. Construction. (a) Frames, enclosures, and shelves shall be of noncombustible construction and shall be sufficiently strong to resist" physical damage.

(b) '~ Combustible electrical insulation shall be reduced to a minimum. Transformers should be of the dry or nonflammable liquid type.. Dry transformers should be in compliance with NEMA TR27-4:03, 150 ° C rise insulation.

(c) Protection shall be installed to prevent overheating of anv part of the equipment, in accordance with the National Electrical Code.

2316 HEATING SYSTEMS 86C~29

(d) When water cooling is used for transformers, capacitors. electronic tubes, spark gaps, or high-frequency conductors, cooling coils and connections shall be arranged so that leakage or condensa. tion will not damage the electrical equipment. The cooling-water supply shall be interlocked with the power supply so that loss of water will cut off the power supply. Parallel water paths should have their own pressure or flow interlock.

(e) When forced ventilation, by motor-driven fans is necessary, the air supply shall be interlocked with the power supply. Non. combustible air filter shall be provided at the air intake.

330-13. Controls for Induction Heating Systems shall be as required in Article 665 of NFPA No. 70-1971.

D. Plasma Arc Furnaces

330-14. General. A plasma arc installation will in general consist of a furnace, an ionizing gas supply system, water cooling, a high current low voltage power supply, and a control system which integrates the system operation and protects the eqmpment and operating personnel.

330-15. Construction. (a) Furnace shell, control enclosure and power supply enclosure shall be made of noncombustible material and sufficiently strong to resist physical damage. Crucible and insulation material shall be compatible with required process temperatures.

(b) Furnace support arms and/or frame shall be strong enough to securely support the furnace in all possible loading, heating, and pouring positions.

330-16. Controls. (a) Furnace controls shall be located so that the operator can give attention to the electrical features of the furnace operation. An ammeter and voltmeter are essential. Also recommended are a gas flow meter and water flow meter, with operating and emergency controls convenient to the operator.

(b) Exterior furnace and control enclosure surfaces shall be grounded. Other safety control.equipment will be as required in Chapter 5 where applicable.

(c) The cooling water supply shall be interlocked with the power supply.

2317 3 0 I N D U S T R I A L F U R N A C E S - - S P E C I A L A T M O S P H E R E

(d) Provisions should be included for positioning and securely clamping molds to prevent moving with respect to the pouring spout during operation.

(e) Provisions shall be provided for tilting furnace to pouring position without exposure to sparks or molten metal.

(f) Since .the arc .generated radiates intensely at various wave lengthS, particularly m the ultra violet, eyes and skin surface of the furnace operator, and other personnel near the furnace shall be oroperly protected. Clothing and eye protection normally associ- ~tea with electric are welding has been found to be adequate. Sight glasses should have, in addition to the usual heavy-duty high temperature glass, a filter lens in a range of No. 6 to No. 10.

2318 SAFETY'CONTROLEQUIPMENT

CHAPTER 5. SAFETY CONTROL EQUIPMENT


" A. G e n e r a l :

500-1. (a) For safety of personnel a n d protection of pro-perry against fire or explosion, careful consideration shall be ~ive-nst n to all hazards peculiar to each individual project. All furnaces heated With combustible fuels shall be provided with adequate safety dt~vices to guard against these hazards. I t is also essential tl~t all auxiliary apparatus in close proximity to the furnace shall safeguarded properly to avoid additional hazards.

(b) Adequate safety devices shall be used which will provide:

1. sufficient preventilation

2. control of fuel combustion 3. overtemperature protection where furnace is self-destructive

(c) Proper inspection and maintenance of safety devices shall be performed to insure that protection against the hazard is avail. able at all times. Partial protection caused by failure of any one safety device could be more dangerous than no protection at all. Safety devices shall be properly designed and installed where prescribed in this standard. Safety devices shall not be shorted out or by-passed in the systems. All safety devices, including the oven or furnace, shall be inspected and maintained in accordance with the typical maintenance check list in Appendix L Where special maintenance and inspection procedures are required due to the nature of the equipment plant management and the authority having jurisdiction shall prescribe the time interval at which the equipment and controls shall be tested for service reliability based on recommendations of the equipment manufacturer.

B. F u e l H a z a r d s

500-2. Since a source of ignition will inevitably be present, any accumulation of flammable gases from unburned or incompletely burned fuel gas or oil in a furnace that may come within the explosive range may result in an explosion and serious fire.

(a) In order to cope with the fuel hazard, it is necessary to recognize three different conditions when operating a fuel gas or fuel oil heating system and these are discussed in 500-3, 4 and 5:

500,3. Light ing Off. Before torches, sparks, or other ignition sources are introduced, and until all burners are properly lighted, the operator shall exercise every precaution, backed up by such

2319 3~ INDUSTRIAL" FURNACES ~ - SPECIAL ATMOSPHERE

autonaatic safety controls as are practical, to eliminate or to avoid producing dangerous unburned fuel-air accumulations.

~n~dPnd . Firing. (a) Safety requires burning of the fuel before it beyond its normal combustion zone at the burner. The mixer urner assembly must proportion the particular fuel and air

~ p e r l y throughout the combustion zone, to the correct concen- ~a-t~on, and the mixture velocity through the combustion zone must be neither too high',, causing extinguishment by blowoff, nor too low, causing flame to flash back or "go out," at any firing rate within the turn.down range. :It is thus obvious that good burner- gfixer design and proper application to the particular heating equip- meat operating conditions will be one of the main factors in safety during "firing.". •

(b) Air for combustion i s obtained from the primary and-or secondary air.supplied at the burner, Total or partial failure of combustion a i r supply 'can result in unstable flame which/may lead to flame failure, and introduc.tion of unburned fuel into the combustion chamber. When too little combustion air is supplied, the result is an overrich mixture and incomplete combustion. The resultant'flammable incomplete products of combustion are passing out of those parts of the system at temperatures high enough for prompt ignition, may later' become diluted with air down into the explosion range in the furnace and after a dangerous accumulation has' built up, ignition from a number of sources may produce an explosion. Overrich combustion may also produce rapid smothering and extinguishment of the burner flame, and the flammable products o f incomplete Combustion followed by raw gas may likewise become explosive when diluted b); air later or in another part of the system, Therefore, it is essential that precau- tions be taken to cut off the fuel in event of failure of combustion air.

(c) Liquid fuels, suchas fuel off, must be broken up into fine globules by atomization for easy ignition and quick complete combustion. This can be accomplished by ejecting the liquid fuel at high pressure, as well as by directing a steam or air jet into the oil stream or by other means. Improper oil temperature preventing proper flow, partial obstructions in burner tips, and loss of oil or atomizing medium pressures can cause improper atomization. Failure to atomize properly will usually result in unstable flame Which can lead to flame failure. Other factors leading to flame failure are stoppage of'fuel supply by improperly closed fuel valve: or other pipe obstruction, and presence of a slug of water in a fuel oil line.

2320 ' ' S A F E T Y C O N T R O L E Q U I P M E N T "

500-5. Shut t ing Down. A dangerous accumulation of unburned fuel may occur in a furnace and heating system following a shut. down if any manual fuel valves are left open or leaking and/or safety shutoff valves arc not tight closing. Subsequent ignition by hot refractory or ignition source when. starting up may produce an explosion. All fuel valves including individual burner-valves shall be: closed. When practical, all safety devices should be shut down.

ARTICLI~ 510. SAFETY C O ~ R O L S ' FOR FUEL=FIRED FURNACES

510-L Fuel safety controls, are devices such as safety shutoff valves;, flame i detection'.units, pressure switches, combustible gas detectors, flowmeters, firechecks, reliable ignition• sources, and supervisory cocks. See Appendix A for a description of the items not described below.

510-2. Safety Shutoff Valves are;n~rm~iliy ~'~l~s~d (closed when de-energized) automatic valves installed in the fuelpiping to shut off the fuel in the event of unsafe Conditions or during shutdown periods. The Safety shutoff valve 'is the/,Key Unit" of'all the safety controls used to protect against the explosion or fire hazards which ~:ould result from accidental interruiJfion to,various services or op. erations, such as flame' failfire, failure Of fuel pressure, failure of combustion a i r pressure, failure of e.xhaust or recirculation fans, exees~iv~e temperatures, or power failure. C0mponent parts of a safety' shutoff valve shall be~of material ~snitable for the fu~l handled and the design of the valve such as to assure pgsigiVe shutoff under the maximum operating presstire Of the fuel handled. Safety shutoff valves shall be of such design that they cannot be readily by- passed or blocked in the open position. A safety' shutoff valve should' 'be reserved for, safety shut6ff servite only, and,not subjected ,to 'the ' additional wear "and" te~ir of temperature i=bntrol 0i~era~0n. See" Appendix A-for types' of safe'ty .~hdtoff ~,alves.

On continuously operating furnaces, i.e., those that are not shut down for long periods of time, the safety "shutoff Valves may be installed so that they can be refidily tested while the furnaces are in. operation.

510-3. Safety Shutoff" Valve Tightness Test. A permanent and ready means for making tightness checks of all main burner gas safety shutoff valves shall be provided: (See Appendix (3).

510-4. F lame Detect ion Devices detect the presence or absence of flame and areused to interrupt the fuel supply in event.of flame outage. Flame detection devices may be based on:

1. Flame rectification and conductivity by" burning gases.

2321 ~6 .~34 INDUSTRIAL FURNACES - - SPECIAL ATMOSPHERE

2. Ultra-violet radiation produced by burning gases.

3. Infrared radiation produced by burning gases. Nolm: Not recommended for refractory furnaces.

A complete description of these devices may be found in Ap- pendix A.

510-5. Pressure 'L imi t or Supervisory Switches shall be provided to prove fuel, atomizing medium and combustion air pressures are within design l!mits for the burner or furnace. These pressure limit or supervisory switches are, but not necessarily limited to:

(a) HIGH GAS PRESSURE SWITCH. A pressure activated device arranged to effect a safety shutdown of the burner or burners or prevent the burner or burners from starting in the event of abnormally high gas pressures. The attention of qualified personnel shall be required before restart.

(13) Low GAS PRESSURE' SWITCH. A pressure, activated device arranged to effect a safety shutdown of the burner or burners or prevent the burner or burners from starting in the event of abnormally low gas pressure. The attention of qualified personnel shall be required before restart.

(c) Low OIL PREssuRE SWITCH. A pressure activated device arranged to effect a safety shutdown of the oi1 burner or burners or to prevent .it: or them from starting when" the oil pressure falls below that recommended by the burner manufacturer. The attention of qualified personnel should be required before restart.

(d) ATOMIZING MEDIUM PRESSURE SWITCH. A pressure activated device arranged .to effect a safety shutdown or to prevent the oil burner or burners from starting in the event of inadequate atomizing medium pressure. Differential pressure sensing between the atomizing medium and oil is the preferred supervisory method when system design permits.

(e) COMBUSTION AIR PRESSURE SWITCH. A pressure activated device arranged to effect a safety shutdown or to prevent the burner or burners from starting in the event the combustion air supplied to the burner or burners falls below that recommended by the burner manufacturer.

510-6. Flowmeters. Properly calibrated flow meters are available to monitor proper flow rates of air and combustible gases for special processing.

510-7. Automatic Fire Checks and Safety Blowouts. Auto- matic fire checks a n d safety blowouts (sometimes called backfire

2322 SAFETY CONTROL EQUIPMENT 8 6 ~

preventers) shall be provided in piping systems distributing flana. mable air-gas mixtures from gas-mixing machines (as requir~ in 310-27) to protect the piping and the machines in event of ex. plosions in accordance with the following recommendations:

AUTOMATIC FIRE CHECKS. Automatic fire checks shall be in. stalled upstream as close as practicable to the burner, inlets f01- lowing the fire-check manufacturer's instructions. Two basic methods arc generally used. One calls for a separate' fire check at each burner, the other a fire check at each group of burners.

The second method is generally more practical if a system con. sists of many closely spaced burners.

SAFETY BLOWOUT DEVICES. Safety blowout device (or back. fire preventer) shall bc provided near the outlet of each gas-mixing machine where the size of the piping is larger than 2½ in. IPg or equivalent, to protect the machine in event of an explosion passing through an automatic fire check.

The manufacturer's instructions shall bc followed when installing these devices. Acceptable safety blowouts arc available from some manufacturers of approved gas-mixing machines. They incorporate the following components and design features:

I. Flame arrcstcr.

2, A blowout disk, 3. Provision for automatically shutting off the supply of air-

gas mixture to the burners in event of a flash back passing.through an automatic fire check.

SEPARATE GAS COCK AT EACH AUTOMATIC" FIRE'. CHECK. A separate manually operated gas cock shall be provided at cach automatic fire check for shutting off the flow of air-gas mixture through the fire check after a flash back has occurred. The cocks shall be located upstream as close as practicable to the inlets of the automatic fire checks.

Caution. These cocks should not be reopened after a flash back has occurred until the fire check has cooled sufficiently to prevent reignition of the flammable mixture and has been properly reset.

510-8. Pilots. A reliable ignition source for the main burner is one of the best safety controls. Properly constructed pilot burners of adequate capacity and properly located to insure ignition of the main burner, reduce the hazard associated with burning of fuel. :

1. FIXED PREMIXED PILoTs FOR MANUAL-LIGHTED~FURNACES. The main burners of gas- and oil-fired manual-lighted furnaces should have fixed premixed pilots. These pilots shall have suf-

2323 INDUSTRIAL FURNAC E S - - SPECIAL ATMOSPHERE

~den tlv large capacities to insure ignition of the main burners, their flames shall be stable even during substantial fluctua-

~allO ~ in draft or back pressure. • Each pilot-mounting assembly be designed and installed so that the pilot cannot be moved

out of the position and will furnish reliable ignition for the burner.

Exception (a): The main burners of gas- and oil-fired manual-lighted f~.naces do not requ#e premixed pilots but may be ignited by gas- or oil.fired portable burner pilots or by oil-soaked swabs placed in proximity to" the burner nozzles by the burner man, provided approved combustion safeguards are wired into the safety-control circuit as described under Combustion Sofeguards, Section 550-10, or they are indirect-fired with radiant tubes. Exception (b): The main burners of gas- and light (Aros. 1, 2, and 4) oil-fired manual-lighted furnaces do not require premixed pilots but may have direct electric ignition; if the burner design makes premixed pilots impractical.

2. FIXED PREMIXED PILOTS FOR SEMIAUTOMATIC,LIGHTED F U R - NAC~S. The main burners of gas- and oil-fired semiautomatic- lighted furnaces should have fixed premixed pilots.- These pilots shall have sufficiently large capacities to insure ignition of the main burners, and their flames shall be stable even during substantial fluctuations in.draft or back pressure. Each pilot-mounting assembly shall be designed and installed so that the pilot cannot be moved out of the position and it will furnish reliable ignition for the burner.

Exception (a): The main burners of light (Aro. 4 or lighter) oil- fired semiautomatic-lighted furnaces do not require premixed pilots but may have direct electric ignition if the design of the burners makes gas pilots impractical.

Exception (b): The main burners of gas-fired semiautomatic-lighted furnaces do not require premixed pilots but may have direct electric ignition if the number of burners or their design makes premixed pilots impractical.

Exception (c): The main burners of oil-fired automatic- and semiautomatic-lighted furnaces do not require premixed pilots but may have oil-fired portable burner pilots. Such pilots should have sufficiently large capacities to insure provision of reliable ignition for the main burners, and their flames should be stable even under conditions of substantial fluctuations m draft or back pressure.

$10-9. T h e Supervising Cock is a special approved cock i n - eorporating in its design means for positive interlocking with a main fuel safety shutoff valve so that before the main fuel safety shutoff valve can be opened all individual burners supervising cocks must be in the full closed position. Proper application of super-

2324 86c--37 SAFETY CONTROL EQUIPMENT

vising cocks in a.safety control system will minimize the type of ex. plosion which .could result where one or more standard burner cocks are accidentally left open when the main fuel supply is turned on and there is a delay in applying a properignition source. For application and detailed description, see Section 550-10, Exception 4(c) and Appendix A-6. '

510-10. Programming Combustion Safeguard. A program. ruing combustion safeguard i s comprised of a flame-de~cting assembly, an ignition-timing assembly, and one or more. name. sensing elements. The flame-detecting assembly and the 4g;nition. timing assembly are usually in the same enclosure and comple- ment each other.

This device may be wired into a safety-control circuit .so that in ~ addition to providing flame-failure protection during firing, it will' also furnish protection against fuel explosions during lighting- off by automatically limiting the pilot-flame-establishing ~ period and/or the trial-for-ignition period. For example, it may be arranged so that it will activate the electric'ignition automatically and determine the length of time it..is on and when the pilot and the main fuel safety"shutoff valves can be opened. Further, a programming combustion safeguard may provide other features such as timed preventilation period and a timed post-firing-purge p e r i o d . .

Apl3roved programming combustion safeguards may be of either the recycling or the nonrecycling type, depending on whether or not they automatically make one attempt to re-ignite and prove a pilot flame before permitting the main fuel safety shutoff valve to be reopened following accidental flame failure during firing.

The nonrecycling type causes all fuel to be shut off and the electric ignition to be .de-activated in event the pilot f lame is not proved at the end of the pilot-flame establishing period o r the main flame is not established and proved at the end of the trial- ignition period, or if accidental flame failure occurs during firing. In all theseevents, the attention of an operator is required before the next pilot-flame-establishing period or trial-for-ignition period can start.

The recycling type causes all fue l to be shut off and the electric ignition to be de-activated in event the pilot flame is not proved at the end of the pilot-flame-establishing period or the main flame is not proved at the end of the trial-for-ignition period. The attention of an operator is required before the next pilot-flame- establishing period or trial-for'ignition period can start. In case of accidental flame failure during firing, this device causes the main fuel safety shutoff valve to be tripped closed, but it' automatically

2325 C ~ - 3 8 I N D U S T R I A L ' F U R N A C E S - - S P E C I A L A T M O S P H E R E

recycles, that is, it makes one attempt to re-ignite and prove the presence of the pilot f ame before permitting the main fuel safety shutoff valve to be reopened. "If the pilot is not ignited during this attempt, it causes fuel to the pilot to be shut off and the electric ig~i'tion to be de-activated. The attention of an operator is required I~efore the next pilot-flame-establishing period or trial-for-ignition period can start. :

Appro~(ed programming combustion safeguards of either the recycling or the nonrecycling type provide the following desirable li~hting-off programs:

(a) GAS MAIN BtmNER. A pilot flame is proved by the combustion ~feguard pri0i-'to r permitting the main gas safety shutoff valve ~;0 open, and'where' an interrupted or expanding pilot is used, the trial-for-igniti0n:'peri0d is limited to 15 seconds and the pilot-flame'~tablishing ~.~ riod to 15 Seconds.

(b) Om MAIN BtmNP-R.' When a pilot flame is proved by the combustion safeguard prior to permitting, the main oil safety shutoff valve tO open, the trial-for-ignition period is limited to 30 seconds when using heavy oil and 15 seconds .when using light oil. With either direct~electric ignition or an.unproved pilot, the trial- for-ignition period is limited to 15 seconds. The pilot-flame-establishing period is limited to 30 seconds when using heavy oil and 15 seconds when using light oil.

ARTICLE! 520. TEMPERATURE CONTROLLERS

520-1. (a) Temperature controllers are devices'.which measure the temperatureautomatically and control the-hea t input of the burner. -. Excess temperature controllers-are similar units designed to cut off the Source o f heat if t h e temperature controllers fail to operate properly. On failure of the primary sensing element, the controller shall fail safe.

(b) Excess temperature limit 'switches shall be arranged to cut off the fuel ~upply when the temperature exceeds a safe limit; they shall not 'AUtomatically retpen' the'fuel valve or turn on the power. The device shall be suitable for the atmosphere in which the thermal element is located, "and temperature service to which it will be subjected, its design :shall be such that eventual failure at the end of its service life will not close the electric circuit causing it to "fai l" unsafe. The exact location of the thermal- element in the heatingsystem shall be carefully chosen so as to supervise that temperature Which most directly affects safety.

2326 "' S A F E T Y C O N T R O L E O U I P M E N T 86C~39

ARTICLE •530, , c o M B u S T I B L E G A S I N D I C A T O R S

: AND C O N T R O L L E R S

A. General 530-1. (a) Continuous vapor concentration indicators a n d con. trois are devices which measure and indicate, directly or indirectly in percentage of the lower explosion limit, the concentration of a flammable vapor-air mixture. They may be of the portable or fixed location continuous operating type. T h e continuous indicators are mostly used throughout ~the period of operation of a process wherein flammable •vapor is evolved., In addition to indicating or recording concentrations t o a id in safe and efficient process control, they can be arranged through sfiitable controls automatically to sound an a l a rm, open or close .dampers, s tar t or stop motors, conveyors, and ventilating fans, When the concentration of a flammable vapor-air mixture has reached a predetermined dangerous level.

(b) When a continuous vapor concentration indicator and controller is arranged to shut down'or operate auxiliary equipment at a predetermined dangerous level of vapor concentration, the operation point shall'be set to not exceed 50 percent of the lower explosive limit.

530-2. These devices are ordinarily used with continuous process ovens and dryers or coating machines evaporating relatively large amounts of flammable liquids where the character of the process is such that evaporation ra tesmay fluctuate widely o r t h e normal working vapor concentration level is unusually high. Ovens connected to solvent recovery Systems are frequently equipped with these instruments.

530-3. Only approved devices should be used and plans covering the application of the" instrument to the process in question should be submitted to the authority having jurisdiction.

530-4. Flammable vapor concentration indicators shall be used to test flammable vapors having a flash point below 70 ° F. unless it is possible to maintain the sampling l ineand measuringassembly at the temperature of the vapors, so that condensation will not occur.

530-5. Maintenance of continuous" flammable vapor indicators and controls shall be done periodically, through a maintenance service by the instrument manufacturer or equivalent. Properly trained personnel, competent ' to make necessary daily adjust° ments in accordance with the manufacturer's exact instructions or equivalent shall be made responsible for reliable operation.

2.327 ~ 6 ~ 0 INDUSTRIAL FURNACES - - SPECIAL ATMOSPHERE

A reliable auxiliary means for checking indicator calibrations frequently is imperative. I t should be noted that some flam- r~able vapor indicators are designed for use on specific materials, and that new calibrations must be made for each change in material tested. Maintaining sampling lines clean and airtight and prompt renewal of filaments when necessary are essential.

A R T I C L E 540. GENERAL APPLICATION OF SAFETY CONTROLS

A. General 540-1. Safety controls are provided to aid the operator and to

rOtect against various conditions which could result in a fire and losion such as:

1. Accumulations of dangerous mixtures of unburned fuel or flammable vapors with air.

2. Ventilation, reeireulation, or exhaust system failures. 3. Combtisti0n air failure. 4. Abnormal fuel pressures and fuel failure. 5. Ignition and flame failure. 6. Electric power failure. 7. Excessive temperatures.

B . Operating Procedure In general, to provide protection against fuel hazard, the oi 3-

erating procedure of operators and application of safety control equipment shall cover the following:

540-2. Light ing Off. (a) First, all fuel valves shall be checked for closure before any main valve is opened; and second, to remove any possible accumulation of fuel leakage during shutdown, furnace shallbe preventilated before introducing an ignition source.

(b) A reliable ignition source shall be provided before the main burner fuel is supplied. I t shall be kept in place until stable flame is obtained over the entire burner.

(c) Before fuel can be turned on, the fuel supply pressure and necessary air supply for reliable combustion shall be present.

540-3. F/r/ng. (a) In event of flame failure with furnace under 1400 ° F. the fuel shall be shut off immediately. When applicable, flame failure combustion safeguards should be used to provide automatic fuel.shutoff on flame failure (see 510-2 and 550-5).

2328 . SAFETY CONTROL EQUIPMENT ,-' 8 6 ~ 1

(b) I n event of excess furnace temperature; the main burner fuel should be shut off with manual restart required and shall sound an alarm . . . .

540-4. Shutt ing Down. ( a ) A l l fuel valves, including'individual l~urner cocks, shall be closed. :

(b) When practical, all safety devices should be tested' during the shutting down operation.

ARTICLE 550. SPECIFIC APPLICATION ()F SAFETY .CONTROLS

A. General

550-1. Application of safety controls and safeguards to protect against fuel hazards in furnaces shall be provided in accordance with the following sections. The safety control circuit shall be arranged So that proper operating sequence is obtained. All electrical wiring shall be in accordance with the National Electrical Code and a8 described hereafter. ":' ~ "

550-2. Operation. A manua l system of lighting of pilots and burners shall be accomplished by trained personfiel. A programmed combustion safeguard system shall be used for semiautorfiatic con. trol which governs the sequence o f events in the lighiing off and shutting down of the burner. See 510-9'for details of aprogrammed combustion safeguard. .

550-3. Power. Safety control circuits shall be single phase, one side grounded, with all breaking contacts in the "Hot" ungrounded, fused (or circuit breaker) protected :line~ which shall n0t .exceed 120 volts potential. Where possible this control circuit and its "non-furnace mounted control andsafe ty componen.ts" should be housed in a reasonably dust-tight panel or cabinet, protected by partitions or secondary barriers from electrical controls employed in the higher Voltage furnace power system. Related instruments may or may not be installed in the same control cabinet.

The door providing" access to this 'control enclosure may include means for meehanical'interlock.-.with the main" disconnect device required in the furnace power supply circuit (see 560-3). Tem- peratures within this control enclosure should be limited to 125 ° F. for suitable operation of plastic components, thermal elements, fuses, and various mechanisms as may be employed in the control circuit.

550-4. Pilots (does. not apply to radiant.tubes - - see550-14). (a) Gas pilots should be provided for. ignition of main gas and

oil burners. These pilots shall be:

2329 I N D U S T R I A L F U R N A C E S ~-- S P E C I A L A T M O S P H E R E

1. Stable Under all operating conditions of the equipment. 2. Properly sized to give a reliable ignition of the main burner. 3. Properly posltioned'to give a smooth lightoff of the main

burner. 4. Fixed in position in relation to the main burner. ()b Ignition . . . . . of pilot burners may be either manual or electrical

If manual lgnmon is employed, either a supervising cock system or a flame detection system shall be provided to insure that the fuel to the main "andpi lot burners is shut off before ignition can be attempted.

(c) Ignition of pilot burners shall not be attempted unless the furnace is in the preventilated condition relating to fan operations, open doors, and full open dampers.

(d) Where main burners operate continuously, and/or flame supervisory equipment is provided, interrupted pilots may he em- nloved. Continuous burning pilots may be used where main burner orpe'rations so dictate..

(e) Spark ignition of main gas and oil burners is.permitted provided that the burner is provided with proper combustion safeguard equipment (see 550-10).

550-5. If several flame, failure combustion safeguard systems are used to monitor a multiple burner heating system having only one safety shuttff valve, the combustion safeguard system shall be so interconnected tha t a flame failure of any burner will result in the shutting off of all fuel to the heating system. When multiple safety shutoff valves are used for individual burner or zone control, the combustion ,~afeguard controlling the burner(s) shall be interconnected so that flame failure will result in shutting off fuel to the burner or zone involved.

550-6. Purg ing Cycle or Prevent/lat/on. (a) Ventilation for an appropriate time is required for a l l furnaces in which fuel can accumulate during a shutdown period. Radiant tube systems may or may not require ventilation controls.

(b) Only furnaces with natural ventilation shall have an electrical interlock arranged so that furnace doors must be open fully before burners can be lighted or heat can be turned on.

(c) Where preventilation is required, an approved time delay relay shall be arranged in the safety control circuit and set so as to require operation of exhaust and recirculating fans for sufficient time to provide a minimum of four complete furnace volume air changes with fresh air before the burner ignition system may be operated or fuel turned on. Distribution of fresh air introduced into the furnace during the preventilation period should be such that all internal areas of the furnace are purged.

2330 SAFETY CONTROL EQUIPMENT 8 6 ~

(d) Furnace doors and/or dampers in fresh air inlets or safety exhaust outlets may require limit switch interlocks, to insure that before the t ime delay relay can be energized, doors or damperg must be opened sufficiently to inovd the amount of air required for preventilation within ~ reasonable time period. These switcltc8 may be shunted after the completion of the preventilation purge by suitable bypass switches, such as a fuel low-cutout pressure switch or extra "flame-on" contact of a Combustion safeguard.

550-7. Combustion Air Blowers shall be interlocked i n the safety control circuit so that they cannot be started until the preventila. tion purge' period has been completed, unless provision ts made by the addition of a second supervised valve to minimize the leak. age when the aspirating effect of a blower can increase the leakage of gas through the burners during the purge period.

B. Safety Control Apl~licati-on - - Direct Fired Gas Heating Systems

550-8. Theseheat ing systems are defined in 310-30. Each furnace equipped with a gas-fired (direct fired) heating system shall be provided with the control devices and safety control circuit with proper operating sequence as covered in 550-9 to 550-13 inclusive.

550-9. Venti lat ion Controls shall be as outlined in 550-6.

550-10. Combust ion Safeguards. In general, each burner should be equipped with an approved instantaneous (flame seining) coin. bnstion safeguard (510:3) arranged through suitable approved safety shutoff valves to shut off fuel to the burner and its pilot in the event of flame failure.

NOTE: Combustion safeguards are recommended' on multi.purpose m~ti- burner furnaces which process different ty~e~= ot worg reqmrm.g operaung temperatures both above and below 1400 F. This. also appnes to mose zones of a multizone furnace where zone operating temperatures are under 1400 ° F.

It is recognized that properly applied and applicable combustion safeguards can also give valuable protection on higher temperature furnaces during the initial lighting-off and warm-up periods where temperatures can be under 1400 ° F. for considerable lengths of time.

The flame-sensing element of the combustion safeguard should be located so as to prove the pilot flame and monitor at the inter- section of the main and pilot burner flame paths, so that prompt reliable ignition by the pilot is assured before the main fuel valves can be opened. In addition, these approved combustion safeguards shall be wired into the safety control circuits to provide an acceptable sequence of operation during lighting off, firing, and re- lightitlg as follows:

2331 I N D U S T R I A L F U R N A C E S ~ S P E C I A L A T M O S P H E R E

(a) Gas-fired semiautomatic •lighted furnaces with f ixed gas pi lot&

1. Before permitting the main gas safety shutoff valves to be e~ergized and opened, the existence of a gas pilot flame should be proven at locations where they will reliably ignite the main burners.

2. T h e main burners shall be immediately ignited by the pilots even when they are reduced to a minimum flame that will barely hold the flame-sensing relay of the combustion safeguard in the energized (flame) position.

3. There shah be no automatic recycling after accidental flame failure; all fuel shaH be shut off (safety shutoff valves tripped closed) and electric ignition deactivated.

4. The pilot flare e establishing period and/or the main burner trial for ignition period shall be automatic~ly lindted to 'not more than 15 seconds unless the authority having jurisdiction grants, an extension. If the authority having jurisdiction considers such an extension, the following conditions must be met:

(4a) A written jnstification must be submitted for the extension. (4b) The time period shah not exceed 60 seconds.

(4c) An extension for the timing will be granted only after it has been determined that no more than 25 per cent of L.E.L. is the maximum permitted under the most extreme operating conditi~ns.

At continuous-line burners, including those composed of a limited number of individual radiant burners or line-burner sections located directly adjacent to one another, supplied from a common burner manifold and having reliable flame propagation between the consecutive individual burners without special external flame-propagation devices, the length of burner supervised by a single approved combustion safeguard shall not be more than 50 ft. At burners where the total length exceeds 20 ft., the trial-for-ignition periods should be automatically limited to not more than 15 seconds after fuel is available at the burner head.

At continuous-line burners composed of a number of individual radiant-cup burners that are not located directly adjacent to one another but are supplied from a common burner manifold and have reliable flame-propagation devices, the maximum number of individual burners in a group supervised by a single approved combfistion safeguard shall be 50. The total distance of the .single-flame path from the first burner ignited to the last in the group, where the flame-sensing element should be located, shah not exceed 50 ft., the individual burners should not be spaced more than 30 in., the trial-for-ignition periods should be auto- maticaHy limited to not more than 15 sec., and it is not necessary

2 3 3 2 : s6c. - S A F E T Y C O N T R O L E Q U I P M E N T " ,

during lighting-off to prove the pilots before permitting the main safety shutoff valveto be energized and opened. • "

(b) Gas-Fired Manual Lighted Furnaces.. : 1.' At main, gas burners ignited by pilots or portable torches, the

existence of the pilot or torch flames should be proven at loeati0~ where they will reliably ignite the rr~in burners before perr~.tting the main gas safety shutoff valves to he energazea ana openea.

2. There should be no automatic re~.yeling after accidental flame failure.

3. The pilot flame establishing or main burner trial-for-ignition periods shall be automatically limited to not more than 15 seconds.

4. When using fixed pilots, the 15 second flame establishing period shall apply to pilot, ignition only. When using portable torches, the 15 second: trial-for-ignition period shall apply to main burner ignition only . . . . .

Exception (a)." Multiple burners where combustion" safeguards for each burner are too numerous to be practical, but continuous line-burner type pilots for groups of burners (see Section 310-11) ca n be used: An approved practically instantaneous combustion safeguard shall be provided at the fur end of each lirie-burner type pilot, away from the p_ilot fuel source, with sensing element locatea at the junction OJ the flame paths of both pilot and last main burner.. The pilot safety shutoff valve must be initially opened by a manual momentary push: button. Exception (b): Where two burners, which will reliably ignite one from the other, are used, i't shall be permissible to us'e a single approved instantaneous combustion' safeguard supervm'ng one of the burners; the supervised burner shall burn continuously at a firing rate at all times sufficient to reliably ignite, the unsupervised burner. Exception (c): Burner for direct ftred gas heating" iystems which supply a furnace at a fuel rate not exceeding 150,000 Btu-hr may be equipped with heat actuated combustion safeguards Or safety pilots. (See Article 570.) For srAall equipment under constant attenaance, approaching in size the "hoitsehold gas range, or very small laboratory test furnace, combustion safeguards may be omitted, subject to approval of the authority having jurisdiction. Exception (d): In general, for greatest security, all burners should be protected with combustion safeguards as outlined in the foregoing sections. When this is impracticable the maximum practical protection should be

furnished by providing a reliable continuous pilot at each burner, and-or operating burners on high-low flame; and by installing devices (pressure

• switches and safety shutoff valves) (See Article 510) to assure, where practical, closure of all individual burner Cocks before the main burner safety shutoff valve can be opened, and to shut off all gas in case of

. high and low gas pressure and low air pressure, where a#pressure is


necessary for operation of burners and controls, subject to the approval o.f the authority having jurisdiction.

A method of assuring closure af all individual gas burner cocks before the main bur.nff, gas safety shutoff valve can be opened is the supervising cock and gas safety control system. A typical piping and wiring arrangement, using the pneumatic type supervising cock is

~n'~t~w~7-Fat,77rwr~rrrj-a ~*h~.tto~ l?ilo~*,l[l~p;r t©.7:,.:. 7 - - . L q_L__ / L . ~ k

M l i ; n r r n l l c e ~Jl o

i~ l . I f o r s e v e n l l " ~ ~ , ~ l - ' ! '~!~ j~l~Jl Ir~:,,~ ,-~,'~-,-,:~ I " - - ' - L o w - A I r - .~ ? ' i _a. - - i • ! . ' ~ W l t C h ' ~ ' I v

It . . . . s-,. j l . , ¢ , t : - -< \ / - C ! . . . .

• . , v i . ~ l i m a i l , . l i e i l o t l e l l k i q e t e s t o f t h r t l l l n h o n l i l l ~ ~ - I { : l _ l l l l l d O r i f i c e

; ; ' Co/t , t i~:h ~ , , -4 { i - o ' ~ ' 9 / " , ~, i n d l v l d u l l I i g h i i n t .

llg~ 61 Supervising Cock and Gas Safety Control Syitem.

illustrated in Fig. 6. (See ~10-8 / ~ details ~ ~upervising Cock.) The number and location af pressure switches, arrangement of tubing anti other details "will vary with the individual installation. In the illustration, t ~ main burner safety shutoff valve cannot be opened until all supervising cocks are closed, combustion air pressure is normal, and normal gas press~re present in the pilot burner manifold. Power failure, loss o£ kombustion air, and~or gas pressure failure during normal firing will shut and lo'ck ~ Out the main burner and pilot safety shutoff valves. Once the initial check has been completed and the main burner safety shutoff valve is opened, the low gas pressure switch downstream from the safety shutoff valve shunts the checking pressure switch so that, after lighting the pilots, the supervising cocks can be opened to light off.

A typical piping and wiring arrangement for the electric interlocking type.supervising cock is also illustrated in Fig. 7. The main burner safety shutoff valve cannot be opened until all supervising cocks are closed (cock switch, conta#ts in series are all closed), ventilation

Sans operating,,prevkatilation purge completed ano(.other interlocks

~50-11. Safety Shutoff~'Valves. (See 510-2.) (a) When 'the main heating system input of the furnace is greater than 400,000 Btu's'ner hour, an approved safety shutoff valve shall be provided,in the main gas line to the burner. A second approved safety shutoff valve shall be provided in the main gas line to the burner. A second approved

2334 s6¢ 7 SAFETY CONTROL EQUIPMENT

safety shutoff valve shall be provided downstream from the first safety shutoff valve. An appropriately sized normally open elec. trically operated valve shall be provided in a vent line between the two safety shutoff valves. The vent line pipe shall be run to a safe location, preferably outdoors, and shall be accessible for inspection.

The safety shutoff valves shall be arranged to close and the vent valve shall be arranged to open in the event of failure of COns. bustion air, excessive combustion air pressure, flame failure, ex. cessive temperature, excessive gas pressure, too low a gas pressure and failure of electric current.

When recirculating and/or exhaust fans.are used and are es. sential to the proper operation and safety of the furnace, the failure of the recirculating fan and/or exhaust fan shall also close the safety shutoff valves and open the vent valves.

(b) When gas pilot systems are piped up stream from the main line gas burner safety shutoff valves and the pilot system capacity is greater than 400,000 Btu's per hour, this same double safe~ shutoff valve system with a vent valve shall be used.

(c) When the main heating system input of the furnace is 400,000 Btu's per hour or less, a single approved safety shutoff valve without a vent line may be used in place of the double safety shutoff valve and vent valve system described in 550-11 (a) and 550-11 (b).

1. Spring load solenoid valves may be used as the primary safety shutoff valve with fuel flow up to 400,000 Btu's per hour, or as the secondary safety shutoff valve with the double safety shutoff valve and vent system described in 550-11 (a) provided:

a . . T h e seating force of the spring is a minimum of five pound~ exclusive of "dead weight" of the assembly and fuel prea. ure exerted.

b. Their use does not necessitate any abnormal settings of either the high or low gas pressure switches to counter any transient pressure fluctuations created b y sudden operations of the valve.

2. Other solenoid valves, not meeting the above specifications may be used when all three of the following conditions prevail:

a. The flow is less than 150,000 Btu's per hour. b. The valve size and pipe size is a/~ in. or less. c. The gas pressure is five (5) Psig, or less.

(d) The attention of the operator shall always be required before restart.

(e) A leak test facility shall be provided downstream of each safety shutoff valve. See Fig. 15 in Appendix A for proper 10- cation and procedure.

2335 8 I N D U S T R I A L F U R N A C E S ~ S P E C I A L A T M O S P H ~ . R ~

(0 Vent lines Where specified above shall be as follows:

1. For fuel line diameters larger than 8 in., the vent pipe shall be at least 15 percent of the cross sectional area of the main gas pipe. I f the main line is less than 3~ in., then the vent line shall be equal to the cross sectional area of the main line.

2. Vent valve ports shall have a cross sectional area equal to the specified vent line.

3. Vent lines should have a max imum length of 40 feet and discharge to outside atmosphere. I f longer runs are unavoidable, or an unusual number of fittings are necessary, an increase in vent size may be necessary.

4. Manifolding of vent lines should be avoided. I f manifolding is absolutely necessary, then the cross sectional area of the manifold pipe must b e equal or greater than the sum of the cross sectional areas of all individual vents involved.

5. See Figure 17 in Appendix C.

V e n t P i p e S i z e T a b l e FUEL LINE VENT LINE DIAMETER DIAMETER

up to 1~ in. ~ m. 2in. 1 m. 2 ~ In. 1~4 In. 3 3~ 4 4 ~ 5 S~ 6 6 ~ 7 7~

m . l ~ m . m. 1~ m. In. 2 m . 111. 2 In. 113. 2 m . m. 2~ m. m. 2~ m. In. 3 In. In . 3 In. In. 3 In.

8 m . 3 ~ m.

550-12. Excess T e m p e r a t u r e Limi t Switches of the Fall Safe Type (see 520-f(b) ) should be provided and suitably interlocked with the safety control circuit so that all main burners controlled by the circuit will be shut off in event of excessive temperatures in the furnace, and shall sound an alarm. They shall not automatically rtopen the fuel valve. These controls shall be in addition to any normal temperature control devices used.

550-1& Auxil iary Interlocks. (a) Interlocks shall be provided for protection of the furnace. Some items that should be considered are:

1. Water-cooled walls, rolls, fan bearings, etc. 2. Conveyors. 3. Doors.

2336 . . . ,qAFETY C O N T R O L E Q U I P M E N T , . 8 ~ _ ~ . ~

(b) An audible and/or visible alarm shall be provided in the safety•circuit to give warning of unsafe conditions and interruption of the Safety circuit by these interlocks.

C. Safety Control Application - - ' IndirectFired Gas Heating Systems

.. 7 Using Radiant Tubes , . i" '.

550-14.i T h e e systems are defined.in 310-31 (a)...Each ~d ian t tube heating system or combination of systems (when two or more are combined into a single processing l inewith ~ common :combustion system), shall have ~ e following sfifeguards, as covered in 550-15 th rough 5 5 . 0 - 2 1 . . , - ,. . ' " . . . . .

550-15. The main fuel supply shall be supervised bymeans of suit. able pressure switches. Both automatic and manual reset types are acceptable. Switches shall b e arranged to detect abnormally high or low fuel pressure. "J.They shall be interlocked with a safety shut. off valve to stop the fl6w'of •fuel when abnormal pressure occurs. The low pressure switchshall be set below, but still within the operable range of the cOinbustion system. The high pressure switch shall be set above, but still,within, the operable range of the com. bustion system.

The safety shutoff valve: Used in the main fuel supply line shall be a manually opened, automatically closed,type. This valve shall be properly interlocked to shut down upon any.abnormal operating condition or failure of the safety control circuit.

A leak test facility shall ~- be provided downstream of the fuel supply safety shutoff valve.

• * " " " ~ ° n Pilots should be piped upstream of the mat gas safety Shutoff valve with a separate safety shutoff valve and low gas pressure switch. If the •manufacturer decides to locate pilot supply line d0wnstr~arfi~ 0f t hema in gas safety •shutoff valve,• means shall be provided to prevent the introdficti0n .of-gas to. the main burners prior to energizing 'pilot valve: ' ' : " ' :: ....

550-16. On units util~ing a pressurized combustion air'stipply, a suitable pressure switch shall be provided to supervise this silpply. Both automatic and manualreset- types are 'acceptable." The low pressure setting shall .be:~within ,the, 9pesa~ble range.;%of~ the combustion system. This switch shall be interlocked.to'shut 9if" the main flow of fuel when low air pressure is detected. This switch shall be satisfied before the safety shutoff valve can be opened. . .

On combustion sy.~terns requiring pressure reduction, a high pressure combustion air switch shall also be provided. I t shall be

2337 I N D U S T R I A L F U . R N A C E S ! S P E C I A L A T M O S P H E R E

i~terlocked to shut off main flow of fuel when excessive air pressure is detected. This setting-shall be above but still within Operable range of the combustion system.

Radiant tube installation employing pull-through or induced draft for induction of combustion air shall provide suitable interlocks to close fuel valve upon loss of adequate combustion air.

550-17- Purging of Radiant Tube-Type Heating Systems. Pre- igni'tion purging of radiant tube-type heating systems is not re- -~--nhired{h°wever' special conditions may require purging of furnace work chamber. ~ ,

550-18. Flame Supervision and Burner Ignition. Flame supervision of the radiant tube( biirners ' i s not required; however, a suitable meansof.ignition shall be provided. Initial ignition can be manual or automatic. Subsequent ignition can he by auxiliary pfii]ot, by continuous jself-piloted burner, or by direct spark ig-

tion. . . . . ~,

550-19. F lue Product Venting. A suitable collecting'and venting s~.. tem for t h e rad!ant tube-type heating systems shzill be pro- vldea oy me user. t h e system shall be of sufficient capacity.to render the total unburned input capacity, of the radiant tubes noncombustible. ~. .

The flue venting products system is to be considered as part 'of the plant exhaust system.. ~ •

550-20. An Excess Temperature Limit Switch or switches should be provided as outlined in 550-12. ' ~

550-91. Auxiliary "interlocks shall be provided as outlined :in 550-13.

D . Safety C~ntrol Appllcati0'n '--- Indirect Fired Gas Heating.Systems

' ~ . , ' , , , . - - Muffle Type

550-99. T.hese heating systems are defined in 310-31 (b). Each muffle furnace gas heating system shall be equipped with control devices and safety control circuit with proper operating sequence as covered in 550-23 through 550-27.

550-93. Ventilation Controls shall be as outlined in 550-6.

550-94. Combustion Safeguards shall be provided on the burners as outlined in Section 550-10.

2 3 3 8 • SAFETY CONTROL EQUIPMENT 86C-51

550-25. Safety Shutoff Valves shall be provided for indirect fired internal nonexplosion resisting heating systems as outlined in 550-11. 550-26. An Excess Temperature Limit Switch shall be pro. vided as outlined in 550-12.

550-27. Auxiliary Interlocks shall be provided as outlined in 550-13.

E. Safety Control A p p H c a t i o n ~ Oil Fired Heating Systems

550228. For description of these heating systems refer to Article 320 through 320-7. Control devices shall be in accordance with'the NFPA Standard for Oil Burning Equipment (No. 31) and approved By the authority having jurisdiction. Each furnace equipped with an oil fired heating system shall be provided with-control devices and safety control circuit with proper operating sequence, as coy. ered in 550-29 through 5 5 0 - 3 3 . .

550-29. Ventilation Controls shall be as outlined in. 550-6.

Exception (a): Prfoentilation of an indirect heating system is not required when the oil burners are of the aspirating type which utiliz~ air pressure to create a suction and draw oil fiom a reservoir. The fan used to draw products of combustion out of the radiant tubes should be interlocked with the furnace ventilation controls and will, therefore, operate during the furnace preventilation period.

550-30. Combustion Safeguards. In general, oil burners shall be equipped with approved instantaneous combustion safeguards to supervise burner flames and to prevent dangerous accumulations of unburned fuel and air mixtures in the furnace work chambers in the event of accidental flame failure,

Combustion safeguards" shall be wired into safety-cofit/ol circuits to provide an acceptable sequence of operations during lighting off, firing, and relighting as follows:

(a) Heavy-oil-fired semiautomatic lighted furnaces (Nos. 5 and 6 oil) with fixed gas pilots.

I. At main oil burners having fixed gas or 0if" pilots, prove the existence of the pilot flames at locations whcre thcy will rcliably ignite thc main burncrs before permitting the main oil safcty shutoff valves to be energized and opened.

2. The pilot flame establishing or main burncr trial-for-ignition periods shall be automatically limited to 3Oscconds.


3. The safety lshutoff valves shall be interlocked with the following devices to detect:

(a) Low oil temperature (b) Low fire start (c) Low oil pressure

(d) Supervision of atomizing medium

4. There shall be no automatic recycling following accidental flame failure. -'

(b) Light oil-fired semiautomatic lighted furnaces (Nos. 1, 2, and 4 off) .

1. At llght-oil burners having fixed gas pilots, prove the existence of the pilot flames at locations where they will reliably ignite the main burners before permitti~ag the main oil safety shutoff valves to be energized and opened.

2. The pilot flame establishing or main burner trial-for-ignition periods shall be automatically limited to 15 seconds.

3. T h e safety shutoff valve shall be interlocked with the following devices to detect:

(a) Low fire start

(b) Low oil pressure

(c) Supervision of atomizing medium..

4. There should be no automatic recycling after flame failure.

(c) Oil-fired manual-lighted furnaces with pilots or portable torches.

1. At main light and heavy oil fired burners ignited by pilots or portable torches, the existence of the pilot or torch flames should be proven at locations where they will reliably ignite the ma in burners before permitting the main oil safety shutoff valves to be energized and opened.

2. There should b e no automatic recycling after accidental flame failure.

3. The pilot flame establishing or the main burner trial-for-ignition periods shall be automatically limited to 30 seconds when using "heavy oil" and 15 seconds when using "light oil."

4. When using fixed pilots, the flame establishing period shall apply to pilot ignition only. When using portable torches, the. flame establishing period shall apply to main burner ignition only.

2340 SAFETY CONTROL EQUIPMENT

Exception (a): Subject to the approval of the authority having juris. diction, direct supervision of the off flame by a combustion safeguard may not be required when a continuous burning reliable gas pilot flame ignition source is provided for an oil burner, providing that the pilot

flame is supervised by an approved instantaneous combustion safe. guard (see 510-3) arranged to shut off the furl to the main burner and pilot in event of pilot flame failure through suitable approved safety shutoff valves. The safety control circuit should be so arranged that the fuel safety shutoff valve cannot be opened until the combustion safeguard senses a strong pilot flame. Exception (b): When two oil burners will reliably ignite on.from each other, it may be permissibleto use a single approved instantaneous combustion safeguard supervising one of the burners, provided that the supervised burner burns continuously at a firing rate at all times suffident to reliably ignite the unsupervised burner. Exception (c): Combustion safeguards may be omitted on radiant tube burners (see 550-16).

550-31. Safety Shutoff Valves (see 510-2). Each oil heating system shall be provided with an approved safety shutoff valve or valves for shutting off fuel to the burner or burners being protected. An approved safety shutoff valve shall also be provided on the gas pilot lines to the burners, if gas pilots are used. These valves shall be arranged to close in event of failure of ventilation, air flow, flame failure, failure of fuel pressure, failure of atomizing air or steam pressure (if used), and failure of electric current. For small furnaces not equipped with mechanical ventilation, the safety shutoff valve, in addition to the foregoing shall, be connected so that it will close when the furnace is shut down and require opening of the furnace before it can be reopened.

550-32. Excess Temperature Limit Switch shall be provided as outlined in 550-12.

550-33. Auxiliary Interlocks shall be provided as outlined in 550-13.

ARTICLE 560. SAFETY CONTROL APPLICATION FOR ELECTRIC FURNACES

A. General 560-1. Safety control application for furnaces lacking fuel hazards shall provide protection from excess temperatures, loss of secondary systems (cooling, material handling, etc.) essential, to normal operation of the furnace. Controls and arrangement shall be as outlined in the safety control application for electric furnaces. Instruments shall be of the fail-safe type. (See Appendix A).

2341 INDUSTRIAL FURNACEs ~ SPECTAv. ATMOSPHERE

B. Safety Control Application for Electric Furnaces 560-2- For a description of these systems refer to Article 330. Each fm-nace., or heat processing system (including resistance, induction, dectric arc or plasma device) shall be nrov ;.4=-~ ---:" . . . . . . . . • ~. , u ~ wl t r i m e IOUOwlng conU'ol oewces and safety contro I circuits for proper operation.

560-8. Heating Equipment Controls. (a) Electric heating equipment of other than the portable type shall be equipped with a main disconnect device, capable of de-energizing the entire heating system under load to provide safety for secondary measures ne- cheitated by one or more of the following conditions:

1. A system short circuit not cleared by supplemental branch circuit protection.

2. Excess furnace temperature. 3. Failure of normal operating controls. 4. Complete or partial loss of power such as single phasing of

a multiple phase power system.

The interrupting capacity of the main disconnect device (See Ap- pendix D) shall be adequate to clear the maximum fault current capability of the immediate power supply system (fault current shall be determined from the voltage and impedance of the furnace power supply circuit, not from the summation of the operating load c'urrents). Other disconnect means in this power supply circuit may be used as the heating equipment "main heating system disconnect" provided furnace operation can be terminated without affecting operation of other essential equipment. Automatic versus supervised operation of the "main disconnect" shall be governed by the furnace size, design characteristics and the potential hazards involved.

NuO~l: W h e n o.pe~ation of a mult iple phase "ma in disconnect" is to be m~ . aay SUl~rvisea, e a c h phase of the power supply circuit should be eqmppecl to snow electrical potent ial on the protected or load side, as an indication of in tended operation, par t ia l or complete loss of power.

Portable furnaces may be equipped with main disconnect devices to meet the above requirements, but if not, the power supply circuit to the furnace shall be so equipped. Supplemental electrical con- trois (contactors, circuit breakers, relays, signaling devices, etc.) shall be provided in accord with safety, temperature control, branch circuit and auxiliary system requirements.

(b) The capacity of all electrical devices used to control energy for the heating load shall be selected on the basis of continuous duty load ratings when fully equipped for the location and type of service ~ roposed. This may require de-rating some components as listed Y manufacturers for other types of industrial service, motor control,

etc., and shown in Table I.

2342 SAFETY CONTROL EQUIPMENT

T ~ L E I

Control Device

Resistance Type Heating Devices

Rating in % Permissible of Actual Current in %

Load of Rating Fusible Safe W Switch

(% rating of Fuse employed) 125 80

Individually Enclosed Circuit Breaker 125 80

Circuit Breakers in Enclosed Panel- boards 133 75

Magnetic Contactors 0-30 Amperes 111 90

30-100 Amperes 111 90 150-600 Amperes 111 90

No~: The above applies to "maximum load" or open ratings for safety switches, circuit breakers, and industrial controls approved under current NEMA standards.

(c) All controls, using thermal protection or trip mechanisms, shall be so located or protected as to preclude faulty operation due to abnormal temperatures or other furnace hazards.

560-4. Ventilation Controls. When removal of by-product vapors is essential to the safe operation of the furnace, controls and interlocks shall be provided as outlined in 550-6.

560-5. Material handling or positioning controls should be arranged for proper sequence of operation with other furnace (special atmosphere and safety controls), and also to assure emergency action as may be needed in the event of malfunction of the material handling system.

Exception: It is permissible to install provision .for operating conveyors manually or by means of a constant pressure pushbutton .for the purpose of removing material from the .furnace in event o.f malfunction in the automatic system.

560-6. Where a furnace is subject to damage, an excess furnace temperature limit control should be provided for annunciation and interruption of power supply to the furnace heating system.

Manual reset shall be provided to prevent automatic restoration of power.

2343 I N D U S T R I A L F U R N A C E S ~ S P E C I A L A T M O S P H E R E

These controls shall be in addition to any normal operating tevaperature control devices.

c~c60.7. Branch circuits and branch circuit protection for all electrical uits in the furnace heating system shall be provided in accord-

with the National Electrical Code (NFPA No. 70).

~60-8. Main Disconnect to Power. See Appendix D.

2 3 4 4 A OSPaEw a .N aATOaS 86P -

~ GAS. A T M O S P H E R E GENERATORS A N D B U L K STORAGE SYSTEMS

ARTICLE 600. GENERAi~: '

600-1. This• chapter covers special processing atmosphere generat. ing and bulk storage equipment, only. Ovens and furnaces are covered in other chapters.

While liquid fuels for atmosphere generation are not covered, the same basic principles of safety and operating procedures will apply.

600-2. Atmosphere generators and auxiliary equipment must he properly selected and operated.

(a) Responsibility for selection shall rest with the person or agency authorizing the equipment.

(b) Responsibility for observing the operating, instructions shall rest with the person or agency operating the eqmpment.

600-3. Provision shall be made.to safely dispose of unwanted atmosphere gas at the point of discharge from the generator. Depending upon: the specific local circumstances and the analysis of the atmosphere gas, this shall be accomplished by one of the following:

(a) provide a vent line, properly controlled by Valves, to permit venting of the unwanted atmosphere gas to a safe place outside the building, or

(b) arrange a suitable method for completely burning the atmosphere gas and properly disposing of the combustion products.

6 0 0 - 4 . The electrical power for the safety control circuit shall be single phase with one side grounded. All safety circuit breaking contacts shall be in the ungrounded line. The maximum nominal voltage shall not exceed 120 volts and the ungrounded line shall be protected against circuit overload.

600-5. (a) Water cooled equipment shall have valvin.g provided on the cooling water inlet. Piping shall be arranged to insure that equipment jackets are maintained full of water.

(b) For open water cooling systems, the water shall be discharged to an open sight funnel with no valves in the discharge piping.

(c) For closed water cooling systems, the water shall be discharged through individual sight flow indicators. A relief valve shall be installed on such systems to relieve obstructed discharge lines.

2345 ~ ' - 5 8 INDUSTRIAI, FURNACES - - SPECIAL ATMOSPHERE.

ARTICLE 610. EXOTHERMIC GENERATORS

610-1. Definition. Exothermic generators are those that Convert a fuel gas to a special atmosphere gas by burning, completely or partially, the gas with air in a controlled ratio.

The combustion reaction is self-supporting and gives off heat (i.e., exothermic). The usual combustion range is from 60 percent to |00 percent aeration. In exothermic generators the air-gas corn- bastion products become the atmosphere gas, and therefore the gaS~cOUS constituents.supplied to exothermic generators will simply be ailed gas and air.

610-2.. Protective Equipment. :Protective equipment shall be selected and applied for the gas and air'separately, and interlocks shall be provided; .The protective devices shall shut down the system, which wouldrequire manual resetting after any. utility (gas, air, power) or mechanical failure.-Observation ports shall be provided to permit ready viewing of burner operation under all firing conditions. . . . . . - -

(a) Required Protective Equipment shall include: ,

1. A safety shutoff valve in the gas supply piping, arranged to dose in case of abnormally low gas pressure/abnormally high gas pressure, loss of air supply, power failure, or flame failure. A manual operation shall be required to open this valve.

2. A low gas pressure device in the gas supply piping. This device shall close the safety shutoff valve, and shut off the air.supply or mechanical mixer in casd of abnormally low gas pressure.

3. A high gas pressure device in the gas supply piping, when the system is such that abnormally high gas pressures may create a dangerous situation. This device shall close the safety shutoff valve, and shut off the air supply or mechanical mixer in the case of abnormally high gas pressure.

4. A low pressure device in the air supply piping coming from an air blower or compressed air line. This device shall close the safety shutoff valve, and shut off the air supply in case of abnormally low air .pressure.

5. A suitable device to shut off the air from a remote supply in case of power failure, abnormally low or abnormally high gas pressure at the generator.

6. A flame safeguard device to shut off the safety shutoff valve and air supplyor mechanical mixer .when a flame failure occurs.

2 3 4 6 s6c s9 GAS ATMOSPHERE GENERATORS

7. Certain conditions and designs may preclude the preferred main flame supervision under all operating conditions. Under these special conditions, continuous pilot supervision, with dual flame sensors for both pilot and main flame, or a combination of supervised continuous pilot wi th generator chamber discharge temperature monitoring, could be considered acceptable alternates.

8. Flow indicators, meters of differential pressure devices on the gasr and air supply piping, or a test burner with suitable flashback protection in the air-gas mixture line, to aid a trained operator in checking the air-gas ratio.

9. A manual cock or valve on the downstream side of the safety shutoff valve, with a tap in between to permit periodic checking of the tightness of closure of the safety shutoff valve.

10. An automatic fire check installed in the air-gas mixture line. as close as practicable to the generator burner inlet, whenever a mechanical mixer employing an atit6matic constant air-gas ratio device is used. Actuation of the fire check shall close the safety shutoff valve in the gas-supply line and stop the mechanical mixer.

11. A manual shutoff valve, designated as "main "gas" shutoff valve in the gas supply line, located directly upstream from the safety shutoff valve. This valve shall be readily accessible to the operator for emergency and normal shutdown.

12. A reliable method-of ignition for each:burner. Main burner ignition shofild be by a supervised, interrupted gas pilot. If direct ignition of main burner is required, trial for ignition should not exceed 15 seconds. ..... "

13. 'An atmosphere gas vent. (See "600-4.)

(b) Supplementary Protective EqUipment may be applicable and the following should be considered :'

1. Visible and/or audible alarm devices to indicate abnormal conditions. '

2. High temperature limiting devices.

3. Cooling water failure protective devices.

4. Gas analyzing devices.

: 5. A supervisory cock system.

6. A preignition purge timer.

610-3. Opera t ingProceduree . Operating instructions shall be followed during light-up, operation, normal shutdown, and emergency

2347 ~ 0 I N D U S T R I A L F U R N A C E S - - S P E C I A L A T M O S P H E R E

shutdown. Of prime concern in the case of generator shutdown is the equipment in-which-the atmosphere gas is being used. Protec- tion of this equipment, and the process material depending upon it, may require quick action by a competent operator. Operatmg instructions shall include the following:

(a) Light-up Procedure.

1. Make certain that all gas valves are closed and the sir supply b off.

2. Make certain the atmospher e gas header is closed to points of use.

3. Make certain the atmosphere gas vent line is opened to a safe point of discharge.•

4. Energize electrical circuits.

5. Purge generator with air as required by the manufacturer.

6. Activat e cooling equipmen L •

7. Establish reliable ignition at each burner. : ,

8. Light each burner immediately When it is sfipplied an air-gas mixture. In the event of lighting difficulty, shut off all fuel valves and purge the system thoroughly after each lighting attempt.

9. Check each burner for satisfactory operation..

10. Vent the atmosphere gas to a safe location' until proper generator temperature and atmospheregasanalysis are obtained.

(b) Shutdown Procedures.

1. Open the atmosphere gas vent line to a safe point of discharge.

2. Close the atmosp.hcre gas header to•points of use.

3. Close the "main gas" shutoff valve and check the operation.

4. Close all remaining gas and air valves immediately.

5. Turn off cooling equipment when safe to do so according to the manufacturer's instructions.

6. De-energize the electrical equipment when it is no longer required.

(c) Utility Failure Procedures. The equipment and associated circuits shall be arranged to shut down the unit automatically in case of flame failure or supply failure of gas, air, or electrical power. This type of shutdown shall be immediately followed by the shutdown procedure in 610-3(b).

2348 aa~ ATMOSPHERE OENERATORS 8 6 ~

(d) Emergency Procedure. Plant safety personnel should recog. nize the hazards that can occur in end use equipment and should develop methods for meeting these emergencies.

ARTICLE 620. ENDOTHERMIC GENERATORS

620-1. Endothermic generators a ~ those that require the addition of heat to complete the reaction ot the gas and air generating the atmosphere. This standard includes the types of atmosphere generators in which the atmosphere being generated is separate at all times from the heating combustion products or other medium. The separation may be effected by use of retorts, tubes, pipes, or other special vessels. To simplify this standard, all gas used in the reaction with air to make the atmosphere will be called "Reaction Gas," and all air used in this reaction will be called "Reaction Air." Gas burned with air to supply heat will be called "Fuel Gas," and all air used with the fuel gas will be called "Fuel Air." The atmosphere produced in the generator from heating the mixture of "Reaction Gas" and "Reaction Air" will be called "Atmosphere Gas."

It should be noted that the Reaction Gas and the Fuel Gas may or may not be the same type of gas.

620-2. Protective Equipment. In general protective equipment will be selected and applied for

the reaction gas and fuel gas separately. In some cases the reaction gas and fuel gas will be interlocked.

Under some conditions, the same device may serve both reaction gas and fuel gas. The protective devices shall shut down the system which would require manual resetting after any utility (gas, air, power) or mechanical failure. Observation ports shall be provided to permit ready viewing of burner operation under all firing conditions.

(a) The required protective equipment for the reaction section of endothermic generators shall include at least the following:

1. A safety shutoff valve in the reaction gas supply piping arranged to close in case of abnormally low gas pressure, abnormally high gas pressure, loss of air supply, low generator temperature (see 620-2.(a)9), or power failure. A manual operation shall be required to open this valve.

2. A low pressure device in the reaction gas supply piping. This device shall close the safety shutoff valve and shut off the reaction

2349 2 INDUSTRIAL FURNACES ~ SPECIAL ATMOSPHERE

air supply in case of abnormally low reaction gas pressure at the l ~ e r .

3. A high pressure device in the reaction gas supply piping when the system is such that abnormally high gas pressure may create a dangerous situation. This device shall close the safety shutoff valve and shut off the reaction air supply in case of abnormally high reaction gas pressures at the mixer.

4. A low pressure device in the reaction air supply piping coming from an air blower or compressed air line. This device shall close the safety shutoff valve and shut off the reaction air supply in case of abnormally low reaction air pressure. If an air blower has its impeller mounted on the blower motor shaft and supplies a single generator, a starter interlock contact may be permitted instead of the low air pressure device.

5. A suitable device to shut off reaction air from a remote supply in case of power failure, abnormally low or abnormally high reaction gas pressure at the mixer.

6. An atmosphere vent. (See 600-4.)

7. A manual cock or valve on the downstream side of the safety shutoff valve, with a tap in between, to permit periodic checking of the safety shutoff valve closure tightness.

8. A manual shutoff valve, designated as "main gas" shutoff valve, in the reaction gas supply line, located directly upstream from the safety shutoff valve. This valve shall be readily accessible to the operator for emergency and normal shutdown.

9. A generator temperature control to prevent flow of reaction air and reaction gas unless the generator is at proper temperature. The minimum generator temperature shall be specified by the generator maufacturer.

(b) Supplementary protective equipment may be applicable to the reaction section and the following should be considered:

1. Automatic fire check protection.

2. Visible or audible alarm devices, or both, to indicate abnormal conditions.


4. Gas analyzing devices.

5. Flow indicators, meters, or pressure gauges on the reaction gas and reaction air supplies.

2,350 GAS ATMOSPHERE GENERATORS

(c) Protective, equipment for the heating section of. units fired with atmospheric gas burners shall include at least the following:

1. A safety shutoff valve in the fuel gas supply piping arranged to close in case of abnormally low fuel gas pressure, abnormalh, high fuel gas pressure, or power failure. A manual operation s~l~ -be required to open this valve..

2. A low pressure device in the fuel gas'supply piping to close the safety shutoff valve in case of abnormally low fuel gas pressure.

3. A high pressure device in the fuel gas supply piping when the system is such that abnormally high fuel gas pressures may create a dangerous situation. This device will close the safety shutoff valve in case of alAn0rm~illy l~igh fuel gas pressure.

4. A manual cock or. valve on downstream side of the safety shutoff valve with a tap between these valves to permit periodic checking of the tightness of closure of the safety shutoff valve.

5. A manual shutoff valve, designated as "main gas," in the fuel gas supply line, located directly upstream from the safety shutoff valve. This valve shall be readily accessible to the operator for emergency and normal shutdox4n.. : : .,.:

6. A reliable method 'of ignition for each burner.

. (d) Supplementary protective equipmen t may be applicable to the heating section of endothermic generators fired with atmospheric gas burners, and the following should be considered:

1. Visible or audible alarm devices, or both, to indicate abnormal conditions. : f •


3. Flame safeguard devices.

4. A supervisory cock system.

e. Protective equipment for the heating secuon of :units fired with blast-type gas burners shall inc.lude at least the following:

1. A safety shutoff valve in the fuel gas supply piping arranged to close in ease 6f abnormally lbw fuel gas pressure, abnormally high fuel gas pressure, loss of fuel air supply, or power failure. A manual operation shall be required to open, this valve..

2. A low pressure device in the fuel. gas supply .piping. This device shall close the safety shutoff valve, And shu'toff the fuel air supply or mechanical mixer in case of abnormally low fuel gas pressure. " • :.

2351 ~______.~ INDUSTRIAL FURNACES ~ SPECIAL ATMOSPHERE

$ A high pressure device in the fuel gas supply piping when the ~stem is such that abnormally high fuel gas pressures may create a dangerous situation. This device shall close the safety shutoff valve, ond shut off the fuel air supply or mechanical mixer in case of ab- ~'ormallY high fuel gas pr~sure. " -

4. A low pressure device in the fuel air supply piping coming from an air blower or compressed air line. This device shall close the safety shutoff valve, and shut off the fuel air supply in case of loss of fuel air pressure;

5. A manual cock or valve on the downstream side of the safety shutoff valve with a tap beween these valves to permit periodic checking of the tightness of closure of the safety shutoff valve.

6. Automatic fire check protection in the fuel gas and air mixture suoply line as close as practicable to the burner or burners whenever a- ~n'echanical mixer employing an automatic constant air-gas ratio device is used. Actuation of the firecheck shall close the safety shutoff valve in the fuel gas l i neand shut off the mechanical fuel gas and air mLxer.

7. A manual shutoff valve, designated as "main gas" in the fuel gas supply line, located directly upstream from-'the safety shutoff valve. This ~valve shall be readily accessible to the operator for emergency and normal shutdown.

8. A reliable method of ignition for each burner~

(f) Supplementai'y :protective equipment may be applicable to the heating section of endothermic generators, fired with blast type gas burners, and the following should be considered:

1. Visible or audible alarm devices, or both, to indicate abnormal conditions.


3. Flame Safeguard devices.

4. Sup~rvisory cock systems.

5. A suitable device to shut off fuel gas from remote supply i n case of power failure, abnormally low or abnormally high fuel gas pressuresat the generator.

(g) Protective equipment for the heating section of units fired with oil burne ~ shall include at least the following:

1. A safetyshutoff valve in the fuel oil supply piping arranged to close in case of low oil pressure, low atomizing medium pressure, loss

2352 GAS ATMOSPHERE GENERATORS 8 6 ~

of combustion air supply, low oil temperature (for preheated oils3 flame failure (when flame supervision is provided), and power failure'. A manual operation shall be required to open this valve.

2. A low pressure device in the fuel oil piping.. This de~ce shall close the safety shutoff valve and shut off the atomtzmg memum and combustion air supply in case of abnormally low fuel oil pressure.

3 A low ressure device in the atomizing medium supply pipin~ • P • • . . ~ "

This device shall close the safety shutoff valve m the fuel oil .p.lpmg, and shut off the combustion air supply in case of aonormally low atomizing medium pressure.

4. A low pressure or flow monitoring device in the combustion air supply piping. This device shall close the safety shutoff valve in the fuel oil piping and shut off the atomizing medium in case of abnormally low combustion air pressure or flow.

5. A low temperature device in the fuel oil piping of preheated oils. This device shall close the safety shutoff valve and shut off the atomizing medium and combustion air supplies in case of abnormally low fuel oil temperatures.

6. A manual shutoff valve on the fuel oil supply piping• This valve shall be readily accessible to the operator for emergency and normal shutdown.

7. A reliable method of ignition for each burner.

(h) Supplementary protective equipment may be applicable to the heating section of units fired with oil burners, and the following should be considered:

I. Flame safeguard devices.

2. High oil temperature limiting device.

3. High generator temperature limiting device.

4. A suitable device to permit shutoff of fuel oil from a remote supply in case of power failure or abnormal operating conditions.

(i) Protective equipment for the heating section of units heated electrically shall include at least the following:

1. A main disconnect device, capable of de-energizing the entire heating system under full load. This device shall de-energize the heating system in case of complete or partial loss of power, excess generator temperature, or failure of normal operating controls.

The interrupting capacity of the main disconnect device (see Appendix D) shall be adequate to clear the maximum fault current

2353 ~...~-~6 INDUSTRIAL FURNACES ~ SPECIAL ATMOSPHERE

capability of the immediate power supply system (fault current shall ~.~ determined from the voltage and impedance of the furnace power u ~ - - " " n o~,oDlY-~. _ c~rcmt, . ot from the summation. . of the operatin_ g load cur-

_,o~ Other disconnect means m this Dower sunnlv circuit ma be re-~/. _ , . . ,, . _ - r r , Y ~sed as me heating eqmpment roam disconnect" provided furnace ~oeration can De terminated without affecting operation of other ~csse' ntial equipment. Automatic versus supervised operation of the ,,main disconnect" shall be governed by the furnace size, design characteristics and the potential hazards involved.

No~..: When operation of a multiple phase "main disconnect" is t o be manuaUy supervised, each phase of the power supply circuit should be enuipped to show electrical potential on the protected or load side, as an

~ . • . . .

indicauon of mtended operatmn, partml or complete loss of power.

2. A generator temperature limiting device. This device shall yen the main heating system disconnect device in case of ab-

normally high generator temperature. NoTz: The entire electrical installation shall conform to the requirements

of the National Electrical Code, NFPA No. 70.

620-5. Operating Procedures.

Operation instructions shall be followed during light-up, operation and normal and emergency shutdown. Of prime concern in the case of atmosphere generator failure is the equipment in which the atmosphere gas is being used. Protection of this equipment and the process material depending upon it may require quick action by a competent operator. The operation of endothermic generators requires careful coordination of the Fuel Gas heating section with the Reaction Gas atmosphere gas section. Operating instructions shall include the following:

(a) Light-up procedure for heating sections of endothermic generators fired by atmosphere or blast gas burners, or oil burners.

1. Make certain that all Fuel valves and Reaction Gas valves are closed and the Reaction Air supply is off.

2. Make certain the atmosphere gas header is closed to points of use.

3. Make certain the atmosphere gas vent line is opened to a safe point of discharge.

4. Energize electrical circuits.

5. Establish reliable ignition at each burner.

6. Light each burner immediately when it is supplied a fuel-air- mixture. In the event of lighting difficulty, shut off all fuel valves and purge the system thoroughly with air after each lighting attempt.

2354 GAS A T M O S P H E R E G E N E R A T O R S

7. Check burners for satisfactory operation.

(b) Operating instructions for reaction gas ,start-up for e~. dothermic generators. •

When the :retort operating temperature is reached , check to be sure the atmosphere gas vent line is open to a safe point of dischar~o and the atmosphere gas header is closed to points of use The u~t • t should now be ready to produce atmosphere gas. At this point the operating instructions based upon the manufacturer's design shall be followed. This is important because each manufacturer has de. veloped procedures applicable to this particular design and general instructions cannot be listed. •

(c) Temporary Shutdown Procedure.

1. Open the atmosphere gas'vent tO a safe point of discharge.

2. Close the atmosphere ga s header to points of use.

3. Close the "main gas" reaction gas shutoff valve and check the operation of reaction gas and reaction air safety devices.

4. Close all of the remaining reaction gas and reaction air valves immediately.

' (d) Permanent Shutdown Procedure. Follow the steps for temporary shutdown a n d a d d the.following: - .

1. Close the '"main fuel" shutoff valve and check the operation of the safety devices.

2. Close all of the remaining fuel air, fuel, and atomizing medium valves immediately. :. ....

3. De-energize the electrical equipment when its use is no longer required. . . .

(e) Utility Failure Procedure.

The equipmentand associate circuits shall be arranged to shut down the unir automatically in case of supply• failure of fuel, air, or power. This type of shutdown shall 'be followed immediately by the shutdown procedures of 620-3.(c) and 620-3,(d).

(f) Emergency Procedure.

• Plant safety personnel should recognize the. hazards that can occur in end use equipment and should develop methods for meeting emergencies. ..

2355 ~..~____ 8 INDUSTRIAL FURNACES ~ S P E C I A L A TMO SPH ERE

ARTICLE 630. AMMONIA DISSOCIATORS

£aO-1. Definition. An ammonia dissociator is a heated vessel in .~i-ch ammonia is broken down into its component parts (25 per- ce"'tn nitrogen and 75 percent hydrogen) by temper-ature in the presence of a suitable catalyst.

650-2. Construction. Ammoniadissociators shah be designed and constructed to withstandthe maximum pressures possible upon failure of regulat on at operating temperatures, taking into consideration all pressure relief venting. All equipment, components, valves, fittings, etc., must be suitable for ammonia service.

650-5. Protective Equipment (a) Protective equipment for the dissociation vessel shall include:

1. A relief valve in the high pressure ammonia supply line, ahead of the pressure reducing regulator. Relief is to be set at 100 percent of design pressure of the ammonia supply manifold.

2. A relief valve in the low pressure ammonia line, between the high pressure reducing regulator and the dissociation vessel. Relief is to be set at 100 percent of the design pressure of the dissociation vessel.

3. A high temperature limiting device to shutoff the heat source when temperatures exceed the designated temperature rat ing of * the vessel.

4. A manual shutoff valve between the pressure reducing regulator and the dissociator. This valve shall be readily accessible to the operator for emergency and normal shutdown.

5. An atmosphere gas~vent. (See 600-3.)

(b) Protective equipment for the dissociator heating system shall conform to the requirements for endothermic generators, as outlined in Article 620.

(c) Operational.equipment shall be provided as recommended by the manufacturers. Consideration should be given to the following:

1. A high pressure gauge in the ammonia supply line- ahead of the high pressure reducing regulator.

2. A low pressure gauge in the ammonia supply line after the high pressure.' reducing regulator.

3. A suitable flow measuring device.

2356 GAS ATMOSPHERE GENERATORS

4. A reducing regulator valve in the ammonia supply line, set tr) reduce the high ammonia pressure to that required by equipment design.

5. A suitable pyrometer for dissociator temperature control within manufacturers recommended limits.

(d) Supplementary protective devices that should be considered are:

1. A visible and/or audible alarm to indicate abnormal or un. safe conditions.

2. A suitable temperature control device to prevent introduction of ammonia to the dissociation vessel if the unit is not up to opcrat. ing temperature.

3. A suitable safety shutoff valve in the ammonia supply line to the generator, arranged to close automatically when abnormal Con- ditions of pressure and temperature are encountered.

ARTICLE 640. BULK ATMOSPHF_~RE GAS STORAGE SYSTEMS

640-1. Construction.

All storage tanks and cylinders shall comply with local, ~tate, and federal codes relating to Pressures and type of gas. NFPA standards shall also be followed.

Vessels, controls and piping shall be designated to maintain their integrity under maximum possible pressures and temperatures.

640-2. Location.

Locations for tanks and cylinders containing flammable or toxic gases shall be selected with adequate consideration given to exposure to buildings, processes, personnel, and other storage facilities. Tables of distances specified in the various NFPA standards shall be followed.

640-3. Storage systems shall comply with the following NFPA standards:

(a) Liquefied petroleum gas systems shall be in accordance with the Standard for Liquefied Petroleum Gases, NFPA No. 58.

(b) Gas piping shall be in accordance with the Standard for Installation of Gas Piping and Gas Equipment on Industrial Premises, NFPA No. 54A.

2357 INDUSTRIAL FURNACES ~ SPECIAL ATMOSPHERE

re) Hydrogen storage systems shall be in accordance with the St~lard for Gaseous Hydrogen Systems at Consumer Sites, NFPA No. 50A.

[d) Oxygen storage systems shall be in accordance with the St~lard for Bulk Oxygen Systems at Consumer Sites, NFPA No. 50.

N~(~)A Processing atmosphere gas storagc systems not covered by an standard (i.e., Anhydrous Ammonia) shall be installed in

~ ccordance with recommendations from the supplicr and all applic- bte local, state and federal codes.

NOTS: Special reference is made to the ANSI Standard K-61-1 "Storage and Handling of Anhydrous Ammonia."

ARTICLE 650. MAINTENANCE

650-1. Responsibility.

An essential safety aid is an established maintenance program which determines that the equipment is in perfect working order. The equipment manufacturer shall impress upon the user the need for adequate operational checks and maintenance and shall issue complete and clear maintenance instructions. The final responsibility of establishing a maintenance program which determines that the equipment is in perfect working order shall rest with the user. Maintenance on gas atmosphere generators and associated equipment shall be undertaken only under the jurisdiction of a supervisor familiar with the safety and proper functioning of the equipment.

650-2. Check Lists.

The user's operational and maintenance program shall include any listed procedures which are applicable to his generator and that may be recommended by the authority having jurisdiction and his equipment supplier. An operational and maintenance check list is essential to the safe operation of the equipment. (See Appendix E.)

2 3 5 8 I RoDo oN AND R ovA,

CHAPTER 7. CLASS C FURNACES WITH ZONEs ABOVE AND BELOW 1400 ° F ATMOSPHERE

INTRODUCTION AND REMOVAL BY BURNING

ARTICLE 700. GENERAL INFORMATION

700-1. Scope. Procedures for "burn in" and "burn out" of in- direcdy heated atmosphere type furnaces having zones both above and below 1400 ° F, but where "burn in" and "burn out" proce. dures of flammable atmosphere gas may be safely used.

700-2. Type of Furnaces. The three general types of furnaces covered in this chapter (see Fig. 7) are as follows:

TYpE I. All zones within furnace chambers above 1400 ° F., having vestibules with doors. (Vestibule chamber utilized to prevent air infiltration into furnace chamber proper.)

TYpE II . All zones within furnace chambers abo~,e 1400 ° F., having vestibules without doors.

TYpE III . Batch-type furnace where temperature indication is below 1400 ° F, upon the introduction of a new load, having vestibules with doors and separate cooling section. See Typical Sketch 3.

ARTICLE 710. ATMOSPHERE INTRODUCTION AND REMOVAL

710-1. Introduction of flammable atmosphere gas into furnace Type I.

(a) Furnace temperature must be above 1400 ° F. (b) Pilots at outer doors and effluent lines (flammable at-

mosphere vent) should be lighted.

(c) All outer doors are open. (d) All inner doors are open. (e) Introduce flammable atmosphere gas into furnace and observe

that ignition takes place. (f) Close inner doors. A reliable source of ignition is required in

vestibule to ignite flammable gas fed into the vestibule. When gas leaving furnace chamber is ignited, the air in the furnace chamber has been replaced by the flammable gas atmosphere.

2,359 ~ INDUSTRIAL FURNACES ~ SPECIAL ATMOSPHERE

T Y P E Z

T Y P E "!'1" I I

/ / / / / / / X .

~ . 1 4 0 0 ° r

g / / / / / / / / ×

G O O L

T Y P E TI'I"

Figure 7. Types of Furnaces

2360 INTRODUCTION AND REMOVAL BY,BURNING

(g) Turn on flam'e curtain burners. .~.

(h) Close outer doors. ':Y~

(i) When flame appears at vestibule effluent lines, a vestib,., purge is indicated. (See furnace manufacturer's instructions ~e further processing.) " " ur

710-2. Removal of flammable'a~mosphere gas from furnace Type I.

(a) Make certain furnace temperature is above 1400 ° F.

(b) Open all outer doors and shut off f ame curtain (see rnanu. facturer's instructions).

(c) Open all inner doors to allow air to enter furnace chamber and burn out the gas (see manufacturer's instructions).

(d) Shut off the flammable atmosphere gas supply to furnace.

(e) Follow the manufacturer's instructions for further shutdown procedures. • ...... " ""':' ",,

710-3. Introduction of flammable ~ atmosphere g~ into furnace Type II.

(a) Furnace temperature must be above" 1400 ° F.

(b) Pilot burners at charge <and discharge vestibules should be lighted. _

(c) If flame curtain burners are provided, these shouidbe lighted.

(d) Introduce flammable atmosphere gas into furnace and observe that ignition takes place.

(e) When flame appears at both vestibule openin'gs, the air within the furnace and vestibules has been replaced by flammable atmosphere gas. (See :furnace' manufacturer's instructions for further processing.)

7 1 0 4 . Removal of flammable atmosphere, gas from furnace Type II. ~ " " " "~'," " ~'

(a) Make certain furnacetemperature, is above 1400 ° F.

(b) Shut off any flame curtains. ~,,,

(c) Shut off the flammable a'tm6sphere gag supply to furnace.

(d) If vestibules are equipped with any baffles or curtains which would hinder the entrance of air for burnout, special provisions shouldbe made for allowing air to enter furnace chamber.

2361 4 INDUSTRIAL FURNACES ~ SPECTAT. A T M O S P H E ~

t 5 Introduction of flammable atmosphere gas into furnace _0" ;~T.

(a) Furnace temperatur e must be above 1400 ° F.

(b) Pilot burners at outer doors and effluent lines should be l i g h t e d . .

.!

(c) Open outer doors.

(d) Open" all inner doors--furnace chamber and cooling c h a m b e r . .

(c) Introduce flammable atmosphere gas into furnace chamber and observe that-ignition takes place.

(f) Close ffirnac'e door. A reliable source of ignition is required in vestibule to ignite the flammable gas fed into the vestibule. (See furnace manufacturer's instructions.) When gas leaving furnace chamber is ignited, the air in the furnace chamber has been replaced by the flammable gas atmosphere.

(g) Provide reliable source of ignition of flammable atmosphere gas inlet in cooling section and introduce-gas atmosphere into the cooling sectaon. Observe that ignmon takes place and continues,

(h) Remove ignition source from cooling section and close cooling chamber door only. (See manufacturer's instructions.) Make certain a reliable source of ignition is available to ignite flammable atmosphere gas fed to vestibule from cooling chamber.

(i) When .flame . appears at cooling: Chaml~er openings the air within cooling chamber has been replaced by flammable atmosphere gas.

(j) Flame curtains shall be mr ned on and outer door closed. (See manufactur, er's instructions.)

(k) When flame appe~s at vestibule effluent line, the air within the vestibule has been replaced by flammable atmosphere gas. (Follow furnace manufacturer's instructions for further processing.)

710-6. Removal. of flammable atmosphere gas from furnace Type III~ ,

(a) Make certain furnace temperature is above 1400 ° F.

(b) 0pen inner door to cooling chamber. . "

(c) Open outer door.

(d) Shut off flammable gas to cooling chamber only.

2362 INTRODUCTION AND REMOVAL BY BURNING 8~__.~

(e) Shut off flame curtain.

(f) Open inner door to furnace chamber.

(g) Shut off flammable atmosphere gas supply: to furnace chamber. " . . . . .

(h) When all burning inside of furnace, cooling chamber, and furnace vestibule has ceased, the flammable atmosphere gas has been replaced by a i r . .

, , .

(i) Follow furnace manufacturer's instructions for further shut. down proccdur~ ..... - . . . .- -'.

,710-7. Emergency Procedures in case of interruption of flammable atmosphere gassupply. ~ .~

: ( a ) . Furnace Types I, II 'and III. : Incase an inert purge g~is Supply is not available, follow standard burnout procedures immediately. If purge gas is available introduce this gas into the same:chamber~at rate sufficient to provide positive pressure. Purge is compiete when all cl4ambersare below 4 percent total combustible. ' "

710.-8: Emergency. Procedures in case of interrtll~tion of electrical lJower supply. Furnace Types i~ 'II and I I I .

(a) An inert gas supply should be utilized for purgingif available or some provisions shall be made for ~ ~

1. auxiliary electrical power or 2. mechanical means for opening doors, where applicable, to

i.mmediately effect burnout procedures. . ~

710,9. The following safety equipment shall be provided'for furnace Types I, II and III in conjunction With the flammable ~atmosphere gas system.- ~ ' .~, ,~

(a) Safety shutoff valve in the flammable atmosphere gas supply line to the furnace. This valve shall bc .energized when furnace temperature is above 1400°F. Operators attention shall bc required.

(b) Low pressure switch to assure that flammabl'c atmosphere gas supply is available. Loss .of pressure shall shut off the. safety shutoff .valve and sound an alarm.

' ,., t '

(c) Safety interlock with furnace temperature controller- • extra contact to-close at 1400 ° F.

2363 INDUSTRIAL FURNACES~ SPECIAL ATMOSP~RE

In case of the batch furnace, Type III, a bypass of the temperature contact after the initial gas introduction is required, such as an twosphefe'-flow switch

(d) Pilot burners at outer, door curtain burner and vent lines - - ctn:tain burner pilots shall be supervised with an approved com- bt~tion safeguard interlocked to prevent automatic opening of v~tibule door, shutoff gas t ° curtain burner, and alarm operator.

(e) Manual, shutoff valves and petcocks for checking tightness of safety shutoff .valves.

(f) Provisions sh~tll [Je made for explosion relief in vestibule.

(g) Audible.. and/or visual alarms to indicate normal and ab- norinal condmom.

2,364 ALL ZONES ABOVE 1400 ° F

• ' C H A P T E R 8 '

S P E C I A L A T M O S P H E R E F U R N A C E S A L L ZONEs A B O V E 1400" F

+ .

ARTICLE 800. GENERAL

800-i. This chapter covers controls and procedures relating to the admittance and removal of special processing atmospheres + for furnaces ,having no vestibules, and all zones• operating, in excess of 1400 ° F. All furnaces are considered to be either electrically heated or indirectly heated. '

• . ~ . + ' . ~ +

ARTICLE 810. ATMOSPHERE INTRODUCTION

810-1. Nonflammable processing atmospheres may be introduced into the furnace chambers at any. time providing there is positive assurance regarding the analysis of the atmosphere. I t is reeom. mended that all atmospheres supplied by generating equipment, which could generate a flammable atmosphere upon malfunctioning, be introduced and removed in accordance with 810-2.'

810-2. Flammable processing atmospheres should be introduced and removed under .definite control, a n d procedures must provide proper, sequencing. Because of the explosion potential when using flammable atmospheres, the following procedural guide should be used:

(a) Specific operating instructions shall be provided by the furnace manufacturer. These instructions shall be ~onveniently posted for ready use by operators at a l l times. -

(b) Procedure for the introduction of flammable, processing atmospheres. ".

1. All furnace zones shall • be operating above 1400 ° F~ 2. If flame curtains are provided at entrance and exit openings,

the curtain burner pilots shall be ignited. Operator shall determine the pilots safely ignite the curtain burners.

3. Pilots shall be ignited a t all atmospherevent lines.

4. When provided, doors shall be opened. , 5. After determiningthe atmosphere gas supply is adequate, the

atmosphere gas may be introduced. When a positive •ignition of the atmosphere gas is established, the doors (when provided)'should be closed. . ; .~

2365 ~ INDUSTRIAL FURNACES - - SPECIAL ATMOSPHERE

6. Gontinue the flow of atmosphere gas. When flame appears at e~trance and exit openings, and at all effluent vent lines, the air 1~ been replaced by the flammable atmosphere gas.

7. Refer to manufacturer's instructions for processing procedure.

ARTICLE 820. A T M O S P H E R E R E M O V A L

890-1- Pr°cedur-e~ : f o r the "removal of flammable processing atmospheres. . . - :~-, - ,r~,

(a) All furnace zones shall be operating above 1400 ° F.

(b) When doors arelprovided, these shall be opened to the extent dictated by the furnace manufacturer. . ....

(c) ~'3ae flammable atmosphere gas supply ia-/ay now be shut• off2 The furnace manufacturer's instructions shall be followed regarding the speed of shutoff. .i--~, ....... . v " -J - . : : . . . :

(d) When flame is no longer visible inside the furnace the atmosphere gas l"/as been'replaced by air. Manual valves slaall be dosed at all:points of: atmosphere in t roduct ion. .This will insure against an unsafe condition developing because of malfunctioning or leaking of electric or pneumatic valves..

" ' , ' , . 2 " . 7 " " . " . "

A R TIC LE 830. EMERGENCY PROCEDURES

830-1. Procedure for emergency situations.

(a) Upon loss of the furnace heating system, the flammable atmosphere gas may be safely removed in accordance with 820-1, as long as all furnace zones are above 1400 ° F.

(b) If any furnace zone drops below 1400 ° F., the flammable atmosphere gas supply fails, or there is a power failure to the furnace, the furnace operator shall initiate one of the following:

1. A nonflammable gas should be introduced, at a rate equal to that of the flammable atmosphere, and the flammable atmosphere shut off. A complete purge of the furnace shall be determined by analyzing the furnace atmosphere less than 4 percent combustibles. The nonflammable gas supply must be adequate in volume to complete the purge.

2. A normal "burn out" of the flammable atmosphere gas (820-1) may be used if the furnace zones are all above 1400 ° F.

2,366 ALL ZONES ABOVE 1400 ° F

ARTICLE 840. PROTECTIVE EQUIPMENT

840-1. Protective devices shall be installed and interlocked as described in the following sections.

(a) A safety shutoff valve shall be provided on the-atmosphere supply pipe to the furnace.

(b) An atmosphere gas supply monitoring device shall be provided to permit the operator to visually determine the adequacy of atmosphere gas flow at all times.

(c) A sufficient number of furnace temperature monitoring devices shall be provided to determine temp.eratures in all zones. These shall be interlocked to prevent opening of the atmosphere gas supply safety shut-off valve until all zones are at or above 1400 ° F.

(d) An automatic safety shut-off valve shall be provided for each curtain burner gas supply. This shall be interlocked to prevent opening of the valves when the furnace is under 1400 ° F.

(e) Audible and/or visual alarms shall be provided to alert the furnace operator of abnormal furnace conditions.

(f) Manual door opening facilities to permit operator control in the event of power failure.

2367 0 INDUSTRIAL FURNACES ~ SPECIAL ATMOSPHERE

CHAFI'ER 9. FURNACES ABOVE AND BELOW 1400 ° F BURN-IN AND B U R N - O U T N O T P E R M I T T E D

A R T I C L E 900. G E N E R A L

900-1. Scope. The two general types of furnaces covered are fuel fired or electrically heated contmuous, semi-batch or batch furnaces having none, one or two vestibules attached to the furnace chamber(s) wherein:

TYpE I - All furnace zones can be heated above 1400 ° F before hatroduction and removal of f lammable atmosphere gas, but all or part. of the furnace zones normally operate below 1400 ° F. Burn-in and burn-out procedures can normally be used; however, emergency conditions require inert gas purge.

TYPE I I - - All or part of the furnace zones operate below 1400 ° F., and cannot be heated to 1400 ° F., or the furnace is a batch-type and the flammable atmosphere gas must be introduced and removed below 1400 ° F., using the inert gas purge procedures.

A R T I C L E 910. TYPE I FURNACE

910-1. Introduction of Flammable Atmosphere Gas, Type I Furnace.

A supply of flammable atmosphere gas of an acceptable analysis shall be available and the entire furnace heated to an operating temperature above 1400 ° F.

Make sure the emergency inert gas storage system contains sufficient purge gas. The stored pu rgegas must be free of oxygen and contain less than 4 percent total combustibles. Furnace doors or covers are closed and vestibule doors are open (if provided).

(a) Make certain all f lammable atmosphere gas, flame curtain, etc., valves are closed.

(b) Make certain that all furnace zones are above 1400 ° F.

(c) Be sure the gas pilots at doors or cover and at the effluents are burning.

1. Provide reliable ignition sources to ignite flammable a tmosphere gas flowing from furnace into vestibule(s).

(d) Turn on the flammable atmosphere gas:

2368 BURN-IN AND BURN-OUT NOT PERMITTED

1. Open the main and secondary flammable atmosphere gas valves to the supply headers.

2. Open the valves to all furnace chamber inlets and observe that ignition takes place.

WARmNO: The operator must make sure that reliable ignition sources are at both the charge and discharge ends of the furnace and ' that the flammable atmosphere gas ignites when passing from the furnace into the vestibule(s).

(e) When the flammable atmosphere gas burns steadily in each vestibule at the furnace outlets:

1. Open the main and secondary hand valves to the fuel gas flame curtain system (if provided).

2. Open fuel gas hand supply valve to the flame curtain (if provided) at the discharge vestibule. Make sure flame curtain is operating properly.

3. Close discharge vestibule door (if provided).

(f) At the charge vestibule (if provided), repeat step (e).

(g) Reset the temperature controllers to the required operating temperatures. Flammable atmosphere gas flow must be sufficient to maintain a positive pressure at all operating temperatures.

(h) Admit secondary process atmosphere or enriching gases as required.

Removal of flammable Atmosphere Gas, Type I

910-2. Furnace.

(a) Remove all work from furnace, if required.

(b) Turn off secondary process or enriching atmosphere gases.

(c) Increase the temperature in all zones to above 1400 ° F.

(d) When all zones have reached 1400 ° F, open charge vestibule door and turn off flame curtain (if provided).

1. Allow flammable gas in vestibule to burn out.

(e) Repeat step (d) for discharge vestibule (if provided). WARNINO" The operator must make sure tha t reliable ignition sources

are at both the charge and discharge ends of the furnace and that the flammable atmosphere gas ignites when passing from the furnace into the vestibule(s).

(f) Turn off the main and secondary flammable atmosphere ga~ valves.

2369 8 6 ~ 2 INDUSTRIAL F U R N A c E s ~ SPECIAL ATMOSPHERE

(g) Close all remaining flammable atmosphere gas valves.

(h) Open furnace charge and discharge doors or cover to burn out the atmosphere.

(i) Follow manufacturer's instructions for further shutdown procedures.

910-5. Emergency Shutdown, Type I Furnace (a) Electric power and/or flammable atmosphere gas failure(s).

1. In case of an electrical power failure the following will stop: In. Heating system

lb. Flammable atmosphere gas system

lc. Secondary process atmosphere gas system ld. Pumps, etc., (if provided).

le. Automatic cycle (if provided).

2. The emergency inert gas standby system shah be immediately actuated to purge the furnace at a rate to maintain a positive pressure in all chambers.

2a. The operator shall immediately check and be sure purge flow is sufficient to maintain positive furnace pressure.

3. If the electric power failure occurs with all of the vestibule doors (if provided) closed, this is the way to leave the furnace. If ,.ither of the vestibule outer doors (if provided) are open - - l eave t ~]3Cl].

3a. Operator must make sure that a reliable ignition source is at the open ends of the furnace and that the flammable atmosphere ~s ignites when passing from the furnace to the open vestibule(s).

4. Close all flammable atmosphere gas valves to the furnace.

5. Close all the fuel gas valves to the furnace.

6. When analysis in all of the furnace chambers indicates the atmosphere in the furnace is below 4 percent total combustibles on two consecutive readings, the purge is completed. Restart furnace per Section 910-1.

(b) Heating system failure during normal operation with flam- nlable atmosphere gas in furnace.

1. The automatic cycle where provided shall be stopped.

2. Find and correct the failure.

2.370 BURN-IN AND BURN-OUT NOT PERMITTED . . . . 8 ~

2 a . Relight the furnace per manufacturer's instructions • out shutting off any atmosphere Valves, or opening any doorsWltth~ t are closed . . . .

3. If heating system failure cannot be corrected: 3a. The atmosphere gas must be purged from the furnace fol.

lowing same procedures: for power and/or flammable atmosphere failures. Reference 910-3 - - Part A.

ARTICLE 920. TYPE II FURNACE

920-1. IntroduCtion of Flammable. Atmosphere; Gas, Type lI Furnace

A supply of flammable atmosphere gas. and process inert purge gas of an acceptable analysis shall be available. The process inert purge gas must be free of oxygen and contain less than 4 percent total combustibles. The processing inert gas requirements shall not deplete the adequacy of the emergency purge gas Supply. Make sure the emergency inert gas storage system contains sufficient purge gas. The stored purge gas must • be free of oxygen and contain less than 4 percent total combustibles.

Furnace doors or cover are closed and vestibule doors are open (if provided).

(a) Make certain all flammable.atmosphere gas, flame curtain, etc., valves are closed.

(b) Open the process inert purge gas supply to all furnace chambers making sure rate will maintain a positive furnace pressure.

(c) After the process inert purge gas has been flowir~...into the furnace for sufficient time and at a rate to maintain a posture pressure, take analysis of al l furnace chambers, Ot must be less than 1

percent on at least two different readings.

(d) After the furnace has been purged toless than 1 percent Os:

1. Make sure the gas pilots at doors or Cover and at the'effluents are burning.

la. Provide reliable ignition sources "to ignite flammable atmosphere gas flowing from furnace into vestibule(s).

2. Open the main and secondary flammable'atmosphere gas supply valves to the furnace. ~

2371 ~ _ _ _ _ INDUSTRIAL F-URNACI~.S ~ SPECIAL ATMOSPHERE

3. Admit the flammable atmosphere gas. W , ~ o : The operator must make sure that reliable ignition sourc~

are at both t h e c ~ . ~ " and discharge ends of the furnace and that the a~mmable atmosphere gas igpi tes-when passing from the furnace into the~ fives bule(s).

(c) Shut off process inert purge gas supply.

(f) When the flammable atmosphere gas burns steadily in each vesti" "bulc (if provided) at the furnace outlets: .

I. Open the main and secondary hand valves to the fucl gas flame curtain system (if provided). .. , .'~,

2. Open fuel gas hand supply valve to the flame curtain (if provided) at the discharge vestibule. Make sure flame curtain, is operating properly.. °

3. Close discharge vestibule door (if P r0vided).

(g) At the charge vestibule (if provided): repeat, step (f).

(h) Flammable-atmosi~here gas flow 'must be sufficient to main- rain a posmve pressure at all operating temperatures.

(i) Admit secondary process atmosphere 9 r enriching gases as required. '~ i

920-2. Removal of Flammable: Atmosphere Gas, Type H Fur- l lace.

(a) Remove all work from furnace, if requi~d. ':

(b) Turn off secondary process or enriching atmosphere gases.

(c) Open charge vestibule door and turn off flame curtain (if provided).

1. Allow flammable atmosphere gas i n vestibule to burn out.

(d) Repeat step (c) for discharge vestibule (if provided). WARNmo: The operator must makomure that reliable ignition sources

are at both the charge and discharge ends of the furnace and that the flammable atmosphere ,gas ignites when ~passing from the furnace-into the vestibule(s).

(e) Turn on the process inert purge gas supply hand valves to the furnace, making sure flow rate will maintain a positive furnace pressure.

(f) Close all the flammable atmosphere gas supply valve(s) to the furnace.

2372 BURN-IN AND BURN-OUT NOT PERMITTED 8 ~

(g) After completing the above:

1. Begin sampling the furnace atmosphere until the total cons. bustibles in all the furnace chambers are below 4 percent total com. bustibles.

(h) Turn off the process inert gas supply to the furnace.

(i) Open furnace charge and discharge doors or cover.

1 . Make sure all atmosphere gas valves are closed.

(j) Follow manufacturer's instructions for further procedures.

920-3. Emergency Shutdown, Type H Furnace.

(a) Electric power and/or flammable atmosphere gas failure(s).

1. In case of an electrical power failure, the following will stop:

la. Heating system lb. Flammable atmosphere gas systems lc. Secondary process atmosphere gas system ld. Pumps, etc. (if provided) le. Automatic cycle (if provided).

2. The emergency inert gas standby system shall be immediately actuated to purge the furnace at a rate to maintain a positive pressure in all chambers.

2a. The operator shall immediately check and besure purge flow is sufficient to maintain positive furnace pressure.

3. If the electric power failure occurs with all of the vestibule doors (if provided) closed, this is the way to leave the furnace. If either of the vestibule outer doors (if provided) is open - - leave open.

3a. Operator must make sure that a reliable ignition source is at the open ends of the furnace and that the flammable atmosphere gas ignites when passing from the furnace to the open vestibule.

4. (]lose all flammable atmosphere gas valves to the furnace.

5. Close all the fuel gas valves to the furnace.

6. When analysis of furnace indicates the atmosphere in all furnace chambers is below 4 percent total combustibles on two con- aecutive readings, the purge is completed. Restart furnace per Section 920-1.

(b) Heating system failure during normal operation with flammable atmosphere gas in furnace.

2373 ~ I N D U S T R I A L F U R N A C E S ~ S P E C I A L A T M O S P H E R E

1. The automatic cycle should be stopped (if provided).

2. Find and correct the failure.

2a. Restart the furnace heating system per manufacturer's instructions without shutting off any atmosphere valves, or opening ~ y doors that are closed.

3. If heating system failure cannot be corrected:

3a. The atmosphere gas must be purged from the furnace following same procedures for power and/or flammable atmosphere failures. (See Section 920-3(a).)

ARTICLE 930. PROTECTIVE EQUIPMENT

950-1. Protective devices for Type I furnaces shall be installed as described in the following sections:

(a) Provide heating system safety controls as outlined in Chap- ter 5.

(b) A safety shutoff valve shall be provided in the flammable atmosphere gas supply pipe to the furnace.

(c) A flammable atmosphere gas supply monitoring device shall be provided to permit the operator to visually determine the adequacy of flammable atmosphere gas flow at all times.

(d) A sufficient number of furnace temperature monitoring devices shall be provided to determine temperatures in zones. These shall be interlocked to prevent opening of the flammable atmosphere gas supply safety shutoff valve until all zones are at, or above, 1400 ° F. Temperature monitoring devices shall be provided with flammable atmosphere gas flow bypass device to permit operating furnace below 1400 ° F after initial introduction of atmosphere.

(e) An automatic safety shutoff valve shall be provided for flame curtain gas supply. This should be interlocked in the same manner as flammable atmosphere safety shutoff valve as noted in item four (4) above.

(f) Pilot burners at outer door curtain burner and vent lines - - curtain burner pilots shall be supervised with an approved combustion safeguard interlocked to prevent automatic opening of vestibule door, shut off gas to curtain burner, and alarm operator.

(g) Audible and/or visual alarms shall be provided to alert the furnace operator of abnormal flammable atmosphere flow condi-

2374 s6c 3

tions detected by monitoring devices, thus giving the operator the necessary time to actuate emergency shutdown procedures.

(h) The emergency inert gas purging system shall consist of:

1. ASME coded storage tank(s) sized to hold a minimum of five furnace volumes (scf) of inert gas which is free of oxygen and con. tains less than 4 percent total combustibles.

2. Tank pressure monitoring devices to indicate abnormal low or high tank pressure.

3. ASME tank relief devices sized, constructed and tested in accordance with the ASME Boiler and Pressure Vessel Code, Sec- tion 8 --Division I. "

4. Operator's actuation station having necessary hand valves, regulators, relief valves, flow and pressure monitoring devices.

5. Separate furnace inlets for introduction of emergency inert gas.

6. Audible and/or visual alarms to alert operator of abnormal tank pressures, and abnormal purge flow rate.

7. Gas analyzing equipment for assuring furnace is purged.

930-2. Protective devices for Type II furnaces shall be installed and interlocked as described in the following sections:

(a) Provide heating system safety controls as outlined .in Chap- ter 5.

(b) Process inert purge and flammable atmosphere gas supply monitoring devices shall be provided to permit the operator to visually determine the adequacy of prgcess inert purge and flammable atmosphere gas flow at all times.

(c) An automatic flame curtain safety shutoff valve shall be pro- dded for flame curtain gas supply. This should be interlocked so that the flammable atmosphere supply must be established prior to opening flame curtain safety shutoff valve.

(d) Pilot burners at outer door curtain burner and vent l i ne s - curtain burner pilots shall be supervised With an approved combustion safeguard interlocked to prevent automatic opening of v~estibule door, shut off gas to curtain burner, and alarm operator.

(e) Audible and/or visual alarms shall be provided to alert the furnace operator of abnormal process inert purge and flammable atmosphere flow conditions detected by monitoring devices, thus giving the operator the necessary time to actuate emergency shutdown procedures.

2375 8 . . ~ 8 8 INDUSTRIAL FURNACES ~ SPECIAL ATMOSPI~ER~

(f) A safety shutoff valve shall be provided in the flammable atmosphere gas SUlSply pipe to the furnace. This valve shall be interlocked with the flammable atmosphere gas supply and shall require manual opening. Further, this valve shall be interlocked with a process purge gas timer so that it can only be opened after the process purge gas flow has been established and allowed to flow for the proper time. For other required devices see 930-2. Closure of this safety shutoff valve shall be immediately followed by introduction of inert gas purging.

NOTE: The purge timer recommended in this section shall not be considered a substitute for the atmosphere analysis recommended in other sections.

(g) Emergency inert gas purging system shall consist of:

1. ASME coded gas storage tank(s) sized to hold a minimum of five furnace volumes (scf) of inert gas which is free of oxygen and contains less than 4 percent total combustibles.

2. Tank pressure monitoring devices to indicate abnormal low or high tank pressure.

3. ASME tank relief, devices sized, constructed and tested in accordance with the ASME Boiler and Pressure Vessel Code, Sec- tion 8, Division I.

4. Operator's actuation station having necessary hand valves, regulators, relief valves, flow and pressure monitoring devices.

5. Separate furnace inlets for introduction of emergency inert gas.

6. Audible and/or visual alarms to alert operator of abnormal tank pressure, and abnormal purge flow rate.

7. Gas analyzing equipment to assure that the furnace is purged.

2376 B E I ~ TYPE FURNACES s6e. 9

CHAPTER 10. CLASS C BELL T Y P E FURNACES

A R T I C L E 1000. G E N E R A L I N F O R M A T I O N

1000-1. Scope. (a) This chapter gives procedures for introduction and removal of flammable atmosphere from directly and indirectly heated bell type furnaces operating at temperatures above and be'- low 1400 ° F.

(b) Within the scope of this chapter bell type furnaces shall he only furnaces wherein the heating bell and /o r retort is lifted from a stationary insulated base which supports the work to be processed.

1000-2. T y p e s of Bell Furnaces . There are two general types of bell furnaces covered within this standard. They are further classified according to their mode of operation.

TYPE A. Bell Furnaces with Retort.

TYPE A-I. Indirectly h e a t e d - - o p e r a t i n g above and below 1400 ° F. Where the heat source is in a space between an outer bell

a n d inner bell (retort). The inner bell enclosed Lhe work. (See Fig. 8.)

TYPE B. Bell Furnaces without Retort.

TYPE B-I. Directly heated operating above and below 1400 ° F. Where the work is exposed to the radiant heat source and an inner bell (retort) is not used.

TYPE B-II . Directly heated operating above 14000 F. Same as Type B-I except that the furnace operates above 1400 ° F:

The temperature of the furnace when the flammable atmosphere is introduced is most important. For Type A-I and B-I the procedures are for introduction and removal of flammable atmosphere at furnace temperatures below 1400 ° F (see Article 1010). For Type B-II the procedures are for introduction and removal of flammable atmosphere at temperatures at or above 1400 ° F, (see Article 1020).

CAUTION: Flammable atmosphere gas shall not be introduced into a Bell Furnace until either an inert gas purge has been completed or until

• o F the furnace work chamber temperature ts at least 1400 .

NOTE l : These furnaces may or may not have a circulating fan. .The method of sealing the inner bell (retort) and/or outer heating bell vanes. Seals may be water cooled "O" tings, water cooled packings, uncooled gaskets, or sand seals. The outer heating bell may be raised by factory crane, or may employ its own heating bell "Lift and Roll-Away" mechanism. Variations also exist in the method of atmosphere piping,

2377 86D-90 INDUSTRIAL FURNACES ~ SPECIAL ATMOSPHERE

measurin, g the flow. of atmosphere and controlling th~ atmosphere. For nroper__, mstructmn m. these .areas refer to the manufacturers specific m-" strucuons for a particular umt.

NoTE 2: For details concerning heating systems for classes A-I, B-I, and B-II Bell Furnaces, see Chapters 3, 4, and 5.

Zell 36

Guide I~

rBell d Retort)

Diffuser

Shroud)

Water Co and Drall Trough

n o [ U I I 110 / Heat Exchanger

Atmosphere Outlet

Fig. 8

Atmosphere Inlet

2378 BELL TYPE FURNA.CES 86G-91

ARTICLE 1010, P R O C E D U R E F O R P U R G I N G " FURNACES BELOW 1400 ° F

1010-1. .Procedures for Introduction of FlammalSle Atmosphere Into A Type A-I Bell Furnace.

(a) Purge of initial room air by means of an inert gas and/or vacuum pumps is required prior to the introduction of a flammable atmosphere. Furnace may operate above and below 1400 ° F.

1. Starting Con/:lition:'Furnace base is loaded with work. Both the base and work load are cold. The inner bell is not in position over work load.. " ~

i a . i f furnace is equipped with a fan, check the cleai, ance between the fan blades and the combination work 'support and fan diffuser fixture. Make sure that the support fixture/fan diffuser has not been shifted out of its proper position during the~previous unload/reload operations or that" interferences were dreated by any other causes.

lb. Atmosphere gas valves on all bases which do not have a charge:and: retort in position and the atmosphere gas valve on all bases which ha~-e "an unpurged retort in position are to be closed. All lines shall be marked with the type of gas in the line at the manually operated valves. " . . . .

lc. Place cold inner bell (retort) over work and seal to furnace base. (Follow the manufacturer's instructions for establishing a proper seal.) If the seal is of the water-cooled oil-type, make sure liquid levels are proper, tha t oil seal pump is running, and cooling water flowing. If the seal is of the water-cooled gasket or " O " ring- type, make sure cooling water is flowing. (Follow the manufacturer's instructions for establishing proper water~ flow rates, liquid levels, and /o r proper seating.) . ' -

ld. Check the liquid level in manometers and /o r bubbler bottles on the vent line and light the effluent gas pilot(s).

le. Where used, follow the manufacturers instructions for establishing cooling water flow to circulating fan bearings, start fan bearing lubricators and start the circulating fan.

2. Inert Purge: Turn on •control power, open manual valve in inert purge gas supply line and establish proper flow-rate whereby starting to fill the retort. When flow is established through the bubbler or seal pot the retort pressure is establishedand the" inert gas flow should be continued• until a minimum•of five furnace volume changes have been completed. The effluent atmosphere leaving the retort should now be checked with an oxygen analyzer.

2379 860--92. INDUSTRIAL FURNACES ~ SPECIAL ATMOSPHERE

The inert gas flow should be continued until an oxygen analysis indicates that the oxygen within the retort is below 1 percent by volume of the inert gas. When this point is reached the inert purge can be considered completed.

(Alternate) Vacuum Purffe: Turn on control power, start the vacuum pumping equipment following the manufacturers instructions. In vacuum purging, the initial room air within the retort is PranUmped' but with a :mechanical pump to a vacuum generally in the

gc of 100 microns (1 X 10 -1Torr )

3. Open the flammable atmosphere supply valve to,the base and adjust flow thru flowmeter to furnace retort.

N0xz: T h e i n e / t ' p u r g e system shall be wired in such a m a n n e r t ha t w h e n t h e control valve in the iner t gas line is open then the f l ammab le gas line is closed and vice versa.

4. Means of measuring flow ratc of atmosphere and/or vacuum prcssurcs'sl~'all be. provided. If uscdi the manometers, or bubblcr bottles should be checked for indication of proper pressure.

5. This stationary base with load and inner bell is.now ready to procced with. thc heat treating cycle. The outer heating bell may be placed over the inner bell (retort) and heat applied. See the manufacturers' instructions. ' ' :

1010-2. Removal of Flammable Atmosphere From ~ Type A-1 Bell Furnace. Purge by means of inert gas is required.

(a) Remove outer heating bell f rom over inner bell' (retort). (Follow manufacturer's instructions.)

(b) After the work has coded sufficiently, under process atmosphere and can be exposed to room air, the inner bell .(retort) may be removed from the stationary furnace base after the following procedur e :

1. Close the flammable gas safety shutoff va lve . When this happens the automatic valve in the inert gas line will automatically open admitting inert gas into the retort . .Continue to purge for a minimum of five 'volume changes and unti l the tot/fl combustible content is less than 4 percent by volume.

2. Stop pilot flame at effluent vent line (if Used).

3. Stop circulating fan, (if used)i "wait . until fan stops.

4 . Release any" mechanical clamping devices which hold the inner bell (retort) to 'the stationary furnace base.

(c) Remove the cold inner bell (retort) from over the work.

2380 BELL TYPE FURNACES 86e-ga

(Follow the manufacturers' instructions.) If the seal is of the Water cooled oil type, stop flow, stop oil seal pump, stop running and cooling water if flowing.

(d) Shut off inert purge gas flow.

1010-3. Procedure for the Introduction of a Flammable Atmo- sphere into a Directly Heated Type B-I Bell Furnace without inner bell (retort), operating above and below 1400 ° F. A purge of the initial room air within the bell by means of an inert gas or. vacuum pumps is required prior to the introduction of a flammable atmosphere. An inert gas purge is required for removal of the flammable atmosphere. The furnace may operate above and below 1400 ° F.

(a) Starting Condition: Furnace stationary base loaded with work. Outer heating bell not over work.

1. I f furnace is equipped with circulating fan, cheek clearance between fan blades and combination work-support fan-diffuser fixture. Operate fan for a short period of time to assure it is operating properly.

2. Check outer heating bell to base seal, making sure foreign objects have not fallen into liquid seals or across mechanical seals.

3. Check atmosphere valves. Atmosphere valves on all bases which do not have a work load under process are to be closed. All atmosphere lines at manual valves shall be properly marked or coded with the type of gas in the line.

(b) Place outer heating bell over work and seal it to the stationary base. (Follow the manufacturer 's instructions for sealing and connecting the outer heating bell to the base for proper operation.)

1. Water-cooled oil seals. Establish proper cooling water flow, start oil seal pump and check liquid levels.

2. Establish proper cooling water flow to Such devices if furnace is so equipped, such as: circulating fans, mechanical seals, atmosphere outlet pipes, etc. (Follow manufacturer 's instructions.)

3. Check liquid level in the manometer or bubbler bottle on the vent line or light the effluent gas pilot where used.

(c) Inert Purge: Turn on control power. Open manual valve in inert purge gas supply line and establish proper flow rate, thereby starting to fill the retort.' When flow is established through the bubbler or seal pot, the retort pressure is established and the inert gas flow shall be continued until five furnace volume changes have been completed. The effluent atmosphere leaving the retort should now be checked with an oxygen analyzer.

2:381 86G--94 INDUSTRIAL FURNACES b SPECIAL ATMOSPHERE

The inert gas flow should be continued until an oxygen analysis indicates that the atmosphere within the bell is below 1 percent by volume of the inert gas. When this point is reached the inert purge can be considered completed.

(Alternate) Vacuum Purge: Turn on control power. Start the vacuum pumping equipment following the manufacturer's instructions. In vacuum purging the initial room air within the heating bell is pumped Out with a mechanical pump to a vacuum generally in the range of 100 microns (0.1 mm Hg).

(d) Open the flammable atmosphere supply valve to the base and adjust flow through flow meter to the furnace.

NOTE: The iner t gas purge system shall be wired in such a manne r tha t when the control valve in the inert gas line is open, the flammable gas line is closed, and vice versa.

(e) Means of measuring flow rate of atmosphere and vacuum pressure shall be provided.

(f) I f used, the manometers, or bubbler bottles should be checked for indication of proper pressure.

(g) The furnace is now ready for the heat treating cycle and may be started. (See manufacturer's instructions.)

1010-4. Removal of Flammable Atmosphere from a Type B-I Bell Furnace. Type B-I without inner bell (retort) operating above and below 1400 ° F.

(a) Close the flammable gas safety shutoff valve. When this happens the control valve in the inert gas line will automatically open admitting inert gas to the heating bell. Continue to purge for a minimum of five volume changes and until the total combustible content is less than 4 percent by volume.

(b) After work a'nd furnace has cooled sufficiently, the heating bell may be removed from the base after the following procedures:

1. Stop circulating fan, (if used). Wait until fan stops.

2. Stop fan lubricator (if used).

3. Stop pilot flame at end of vent line (if used).

4. Release any mechanical clamping devices which hold the bell to the stationary furnace base.

(c) Remove the bell from the base. (Follow manufacturer's instructions.)

(d) Shut off inert purge gas.

2 3 8 2 BEL, RNAC S

1010-5. Emergency shutdown for Type A-1 and B-1 Furnaces.

(a) Emergency safety purge system. An emergency safety purge system, completely independent of the normal inert purge system, shall be provided. It shall be designed to immediately purge the flammable atmosphere gas from the retort of the Type A-1 Furnace, or the heating bell of the Type B-1 Furnace, when an emergency situation occurs, such as electric power failure or failure of both the flammable and normal purge gas supply.

(b) The stored purge gas must be free of oxygen and contain less than 4 percent total combustibles.

(c) In case of electric power failure the following will stop:

1. Heating system

2~ Flammable atmosphere system

(d) The normal inert purge gas system shall be immediately actuated to purge the flammable gas from the retort of the Type A-I, or the heating bell of the Type B-I Furnace.

1. If electric power failure also causes failure of the normal inert purge system the emergency safety purge system shall immediately be actuated.

(e) In case of failure of the normal inert purge system while purging a flammable gas from either the Type A-1 or B-1 Furnace, the emergency safety purge system shall be immediately actuated.

(f) The flow of emergency inert safety purge gas shall be at a rate to maintain a positive pressure in the retort of the Type A-I Furnace or the heating bell of the Type B-I Furnace.

(g) Close all flammable atmosphere gas valves to the furnace.

(h) When analysis of the effluent atmosphere indicates the atmosphere within the furnace is below 4 percent total combustibles on two consecutive readings, the purge is completed.

(i) The emergency safety purge gas can be shut off.

(j) Correct failure to heating or normal inert purge system.

2383 ~ 6 ~ 9 6 INDUSTRIAL FURNACES - - SPECIAL ATMOSPHERE

A R T I C L E 1020. P R O C E D U R E F O R P U R G I N G FURaNACES O P E R A T I N G A T O R ABOVE 1400 ° F

1020-1. Procedure For Introduction of a flammable Atmosphere Into a Type B-II Bell Furnace. A purge by means of an inert gas or vacuum purge pumps is recommended prior to the introduction of a flammable atmosphere.

However, if the flammable atmosphere gas is not introduced until after the heating bell is at or above 1400 ° F, an inert or vacuum purge is not required.

If inert purging is used follow Section 1010.

(a) Furnace stationary base loaded with work. Outer heating bell not over work.

1. I f furnace is equipped with circulating fan, check clearance between fan blades and combination work-support fan-diffuser fixture. Operate fan for a short period of time to assure it is operating properly.

2. Check outer heating bell to base seal, making sure foreign objects have not fallen into liquid seals or across mechanical seals.

3. Check atmosphere valves. Atmosphere valves on all bases which do not have a work load under process are to be closed. All atmosphere lines at manual valves should be properly marked or coded with the type of gas in the line.

(b) Place outer heating bell over work and seal it to the stationary base. (Follow the manufacturers ' instructions for sealing and connecting the outer heating bell to the base for proper operation.)

1. Water cooled oil seals. Establish proper cooling water flow, start oil seal pump and check liquid levels.

2. Establish proper cooling water flow to such devices if furnace is so equipped, such as: circulating fans, mechanical seals, a tmosphere outlet pipes, etc. (Follow the manufacturers' instructions.)

3. Check liquid level in the manometer or bubbler bottle on the vent line.

(c) Turn on furnace power and bring temperature of the furnace to 1400 ° F or greater.

(d) Light the effluent gas pilots at all vents where gas may be discharged from the furnace.

(e) Open the flammable atmosphere supply valve to the base

2 3 8 4 B E L L TYPE FURNACES 86C,--97

and adjust flow through the flowmeter. Means of measuring flow rate of atmosphere shall be provided.

(f) (If used) manometers or bubbler bottles shall be checked for indication of proper pressure.

N . . . . . of 1400 ° F or ,,rrJater t h roughou t the entire furnace OTE: A ~emperatui~ 9 7 - - • • is required for positive ignition of the f l ammable gas upon be ing in t roduced into the furnace.

(g) Continue the flow of flammable atmosphere gas. When a flame appears at all effluent vents the initial room air within the bell furnace will have been replaced with the flammable atmosphere gas.

(h) The bell furnace is now ready to proceed with t he balance of the heat treat cycle. (See manufacturer's instructions.)

1020-2. Removal of Flammable Atmosphere From a Type l~-II Bell Furnace.

Purge by means of an inert gas is recommended. However if the flammable atmosphere gas is to be removed with the furnace bell at or above 1400 ° F then the following burn-out procedure of the flammable gas may be followed.

(a) Before the bell has cooled "below 1400 ° F the following procedures (1 through 7) shall be completed.

1. Where required, ignite pilots or torches and place in position or have ready for ignition of the flammable atmosphere gas at the heating bell to stationary base seal as soon as the seal is broken.

2. Turn off heat source.

3. Stop circulating fan, if used. Wait until fan stops.

4. Release any mechanical clamping devices which hold the heating bell to the stationary base.

5. Gradually lift the heating bell off the base and as sooh as the heating bell breaks its seal with the stationary base the flammable atmosphere gas should ignite or be ignited at the base of the heating bell.

NOTE: Th i s step is required to prevent the .po~.ible,formation of a n o ~ plosive mix tu re inside the Bell F u rnace after tt rms oeen r e m o v e a zro the base.

6. Close the flammable atmosphere gas inlet valve.

7. Complete shutdown of cooling water flow, circulating fan lubricator, etc., following the manufacturer's instructions.

2385 INDUSTRIAL FURNACES - - SPECIAL ATMOSPHERE

1020-3. Emergency shutdown. Type B-II Furnace.

()a Emergency safety, purge: An emergenc, y inert safet, y p u r g e system shall be provided. It should be designed to Immediately vurge.the flammable atmosphere from the heating bell when an ena" ergency situation occurs, such as'. electric power failure.

(b) In case of electric power failure the following will stop: a. Heating system

b. Flammable atmosphere gas system

c. Heating bell hoisting equipment.

(c) The emergency inert gas standby system shall be immediately actuated to purge the flammable gas from the heating bell.

(d) The emergency inert gas flow shall be at a rate to maintain a positive pressure in the heating bell.

NoTs: Opera to r s shall immedia t e ly check and be sure the emergency purge gas flow is sufficient to maintain a positive heating bell pressure.

(e) Close all flammable gas manual valves to the furnace.

(f) When analysis of the effluent atmosphere indicates the atmosphere within the heating bell is below 4 percent total combustibles on two consecutive readings, the purge is complete.

(g) Shut off the emergency inert gas flow.

A R T I C L E 1030. P R O T E C T I V E EQ~UIPMENT

1030-1. Protective devices shall be installed and interlocked as described in the following sections:

(a) A safety shutoff valve shall be provided on the flammable atmosphere supply pipe to the furnace.

(b) An atmosphere gas supply monitoring device shall be provided to permit the operator to visually determine the adequacy of atmosphere gas flow at all times.

(c) A sufficient number of furnace temperature monitoring devices shall be provided to determine temperature in all zones. These shall be interlocked to prevent opening of the atmosphere gas supply safety shutoff valve until all zones are at, or above, 1400 ° F., when inert gas or vacuum purging of the initial room air within the retort or bell is not employed.

2386 BELL TYPE FURNACES

(d) Audible" and/or visual" alarms should be prowdedvk to alert the furnace operator of abnormal furnace temperature or atmosphere flow conditions detected by the monitofi_ng devices as recommenderl ga'ving the operator the opportunity to safely perform any requ'tred-' shutdown procedure.

(e) Emergency Safety Purge: An emergency inert safety purge system, completely independent of the normal inert purge syste% shall be provided. It shall be designed to immediately purge the flammable atmosphere gas from the furnace whenan emergency situation occurs, such as power taaure or nammame ana normal inert purge supply failure.

2387 ~__.~ 1 0 0 INDUSTRIAL FURNACES ~ SPECIAL ATMOSPHERE

CHAPTER 11. INTEGRAL QUENCH FURNACES


A. General

1100-1. (a) The heat treat furnace, having an integral quench tank, is a special furnace design which permits maintenance of the ,.ork under flammable and/or nonflammable atmosphere from the time the work enters the furnace until it has been quenched and removed from the furnace.

(b) The heat treat furnace, having an integral quench, is generally an assembly which consists of a Class C furnace, to which is added an enclosed quench tank. Work withdrawn from the heat section is immediately immersed in a quench medium and then removed from the furnace.

(c) The integral quench section consists of a gastight quench vestibule and a quench tank. An additional cooling chamber may be provided, and is elevated above the quench tank or located to one side of the quench.

(d) The atmosphere used will depend on the metallurgical requirements of work being processed.

(e) The integral quench tank may utilize any combination of heating and cooling depending on the metallurgical requirements of the work to be processed.

B. Hazards

1100-2. The heat treat furnace, having an integral quench tank, utilizing a combustible liquid, presents an unusually severe fire hazard.

(a) Three basic types of furnaces are covered in this chapter (see Fig. 9).

TYP~ I - - dunk-type elevator quench

TYPE II - - dunk-type elevator quench with under oil transfer TYPE II I - - bottom chute-type quench

NOTE: Th i s s t anda rd does not cover salt q u e n c h tanks or cent ra l q u e n c h medium cooling systems.

(b) The integral quench tank, using a combustible liquid, may be subject to the introduction or accumulation of water from a number of sources which, when exposed to the heat released from quenching of work, flashes to steam. The resulting increase in volume causes overflow of the quench tank, or over-pressurization of the quench vestibule, and expulsion of the quench medium.

2388 INTEGRAL QUENCH FURNACES 86~.~10 l

TYPE I OUNK TYPE ELEVATOR QUENCH

/ / " / / " T ' O I L LEVEL

" r ~ l l DUNK TYPE ELEVATOR QUENCH WITH UNDER OIL TRANSFER

I

I"YPEIII. BOTTH CHUTE TYPE QUENCH

Figure 9. Integral Quench Furnaces

2389 ~.~ I 0 2 I N D U S T R I A L F U R N A C E S ~ S P E C I A L A T M O S P H E R E

C. Quench Vestibule 1100"5. (a) The quench vestibule shall be gastight and shall be constructed of noncombustible materials with due regard to the fire a~d explosion hazards inherent to such equipment. Attention to ~echanical_ functions and corrosive conditions is vital to ensuring reliable, sate operation.

(b) The quench vestibule's design and size are dependent upon end use. If the quench vestibule doubles as atmosphere gas cooling chamber, forced cooling is normally required, provided by either ~¢ater- or oil-filled jackets, plate coils, or tubing tracing. (See 1100-4.)

(c) The intermediate door between furnace and quench should close the opening to serve as an insulated baffle to block heat loss to the quench vestibule.

(d) Emergency or service openings shall be provided with gastight closures.

(e) All external load and unload doors shall be properly fitted with adequately sized and stable pilots.

(f) The quench vestibule shall be supplied with adequate atmosphere gas supply to maintain safe conditions during the entire process cycle.

(g) An effluent line (flammable atmosphere vent) shall be provided to control pressure equilibrium in chamber and be so located that operators will not be exposed to injury upon pressure erup- tion. A stable adequately sized pilot shall be provided at the effluent line to ignite the vented gases.

(h) If the quench tank is provided with a "quick dump" valve, means shall be provided to immediately open the outer quench vestibule door upon operation of the dump valve. (See Par. 1100-7(0.)

D. Cooling Chamber Design 1100-4. These recommendations are intended to cover any design utilizing water as a cooling medium, where, by means of leakage or condensation, the quench medium is exposed to an accumulation of water.

(a) Although hot rolled steel plate has been used for many years with water cooling, it is not to be recommended as corrosion is continuous and its physical state difficult to determine. When hot rolled steel plate is used, oil or other compatible coolant shall be used in place of water. If quench medium temperature is excessive for

2,390 II~Pl~.oRAL QUEIgCH I~ACF-~ 86~1~0 ~

d acket coolin a se arate heat exchanger should be employed desire j g, P . . . . . . If a:water-cooled exchanger is employed, the quench oil ctrculatia~

m should be installed on the inlet side of the heat exchanger a ~ U p . . . . . . . P~ ,,;,~,,~-h " m nres~sure should always exceed that of the Cool. -,,~ -t . . . . . . medtu ~ : , Kagwater. ' . . . . . . . . . . -. . • : . . . .

(b) Jacketed stainless steel plate may b e used, w i th water as a coolant, to eliminate the hazards of corrosion o f hot rolled steel.

ever. unless all of the stainless steel is of. the. stabilized tm~ How , . . . . -,~-, such as Columbinm or .Tt tamum or. the lowcarbonL-ser les type, corrosion can take place faster than m hot rolled steel ctue to carbide precipitation in the steel at the welds. If used, 'a careful study should be made as to compatibility of materials and welding techniques employed. ":~

(c~ Steel:plate" coils, iattacKed by thermo, contact cement to the external surfaces of the quench.chamber, f~ib~icated of hot roiled steel platei have-produced: acceptable heat t r ans fe r /and careful attention given to the design of the junction of the upper and lower chambers minimizes the possibility of water leak into the quench reservoir. - " . , . : : ~.. - . . . . ' .

Steel plate coils can be used with either water or oil type coolants, although the eventual plugging of the pass'ages with rust and rain. drai '/[eiJbdiscan' be anticipated /vhen w~/ter is used as a coolant. The hse of stainless steel plate coils, while a more expensive construction meth,od.., will considerably reduce the possibili.ty of plugging of the:water passages.- • ~ . . . . . -~' '"

"" (d) . Serpentine ~6ilformed from a r i o n c o t r b s i v , e ' , t u b i h g : material brazed or "welded' to tile exterior surfaces 0 fa -cool ing cfiamber, fabricated of hot rolled steel plate, have"prOduced 'Acceptable heat transfer.. When'careful attention is given.to the.;design of the junction of the upper and lower quench vestibule, the possibility of a water leak into the quench tank, is m in imized . . .

E . E l e v a t o r D e s i g n ~

1100-5. (a) The elevator's function is to immerse the work charge into the quehch medium with minimum splash: '~At termination of

t e d uerich cycle; the elevator is raised :to dr/iin position at the t 'm q ._. , . . . . . -. ~ hearth level. " " ~ . . . . . . . . . .

(b) The elevating-mechanism shall be substantially supported by structural members to hand le the maximum'rated:ioads.

", (c) " Elevator guides or ways'Shall~be provided~.t6 .in~ure unifom Stabilized m6vement of the elevator in the confined areas of the quench tank. " ' : ' '

2391 ~ 6 ~ 1 0 4 INDUSTRIAL "FURNACES - - SPECIAL ATMOSPHERE

(d) Tray guides a nd / o r stops shall be provided to insure tray is properly positioned on the elevator.

• , , . . ~ ,

F'. Protective Features

1100-6. (a) Automatic temperature controls shall be installed in pressure-type water'cooling and oil-cooling systems to insure the desired jacket temperature.

(b) External door operation shall be interlocked so that it cannot be opened unless the elevator has reached its maximum quench l~sition, or on outage of flame curtain pilot, except through action of manual over-ride in emergencies.

(c) The admittance and maintenance of protective atmosphere within the upper quench chamber shallconform to Chapters 7 and 8.

G. Lower Quench Chamber or Tank

1100-7. (a) The quench tank shall be designed and constructed to contain the quench medium capacity at the expected operating temperature and With maximum work load volume.

(b) The' quench tank Shall be tested for lehks prior to use.

(c) The quench tank shall be designed and operated with a maximum quench medium level, when elevator and work load are sub- merged, of not less than six (6) inches below door or any opening into the furnace. -,

(d) The quench tank shall have sufficient capacity to quench a maximum gross load with a maximum, temperature rise that will not exceed 50 °- F below the flash point and cooling capabilities to recover quench medium temperature between minimum design quench cycles. .

(e) The" quench tank shall be provided with an adequately sized overflow directed to a safe location outside of the building or to a salvage tank. Overflow shall be trapped or otherwise arranged to prevent loss of qimneh chamber atmosphere gas and prevent syphon effect. " . . . .

(f) A quench tank shall be equipped with drain piping, so located and sized to permit draining of the. contents within five minutes. Drain piping, shall,be.trapped a n d directed to a safe location outside the building or tO a salvage tank. The drain shall be provided with a quick opening valve, readily accessible to the operator. (See Par. l100-3(h).)•~ ,.

1. Overflow Drains

2392 s6 % 1o5 • l a . Quench tanks of over 150 gallons in liquid capacity or

10 s uare feet in liquid surface area shall b~ equipped with a Droh , q; . . . . . . n^,,, nin e leading to a safe location outside b'ux ~" emy trappeu uw. .u ,~ ~, ~, ~ , "1 .

ings. Smaller quench tanks should also be so equipped, Where practicable. The discharge of~ the-over"flow pipe should be go located and arranged that if the entire combustible contents of the quench tank is overflowed through overflow pipe by application of water during fire fighting, property will not be endangered. The size of the overflow pipe should be sufficient to conduct the maximum rate of flow of water eKpeCted to be''applied to the liquid surface of tile qu'ench tank from automatic sprinklers or from'other sources in the event of fire.

lb. Overflow pipes shall be of sufficient capacity to overflow the maximum delivery of quench tank liquid fill pipes, bat shall not be less than 3'in. in diameter, and shall be increased in size depend. ing upon the area of the liquid surface and the length and pitch of pipe. : ~

lc. If the liquid surface area of quench tank is 75-150 square f~et, diameter of overflow pipe should be not less t han 4 in . ; if I50-225 square.feet, not less than 5 in., if 225-325 square feet, not less than 6 inches.

ld. o n la~'ge qtiench t~inks,' multiple overfl6~' connections are preferable' to a single large pipe, provided the aggregate cross- sectional area is equivalent. " '• ~ le. Overflow pipes shou ld ' be , connec t ed to-quench tanks through a flared outlet where the accumulation of 'caked or dried material may clog the overflow opening.

If. Piping connections on drains and overflow lines shall be designed so as to permit read~, access for inspection and cleaning of interior. " ' .-.

lg. The bottom of the overflow connection shall"b~ riot less than 6 in. below the.top of the, tank. , ,/•,. , " "

. . . . . . ~ . • i ~ ' ~ ' ' = : "

" 2." Botto m Drains . . . . . • 2a. Quench tanks over 500 gallons in liquid capacity shall

be equipped with bottom drains automatically and /or manually arranged to quickly drain tank in event of fire, unless the viscosity o f the liquid-at,, noi-mal atmospheric temperature makes this impractical , l~Ianual operation shal lbe from a safely accessible location. Where gravity flow is not practicable, . automatic'pumpsshall be required. ' -

2b. Such drain shall be trappecl and discharge to a closed properly ventilated salvage tank or to a safe location outside which will not endanger property.

2393 ~ . ~ - - 1 0 6 INDUSTRIAL FURNACES ~ SPECIAL ATMOSPHERE

2c. According to tank capacity the diameter of bottom drain shall be not less than the following:

500 to 750 g a l l o n s - 3" 750 to 1,000 g a l l o n s - 4"

1,000 to 2,500 gallons - - 5" 2,500 to 4,000 gallons - - 6"

Over 4,000 gallons - - 8"

H. Quench Medium Cooling Systems

1100-8. Quench medium tanks generally utilize a cooling system to maintain tl~e general quench medium at.an operating temperature to reduce the quantity of quench medium required. Three basic cooling systems are in general use, consisting of:

(a) Internal cooler, where heat transfer medium is circulated through heat exchanger within quench tank.

(b) External cooler, where quench medium is withdrawn from quench tank, circulated through a water-cooled heat exchanger, and returned.

(c) External cooler, where quench medium is withdrawn from quench tank, .circulated through an air-cooled heat exchanger, and returned.

Water shall not be used as a cooling: medium within a quench tank utilizing a combustible liquid quench medium.

J. Internal Tank Cooled Heat Exchanger

1100-9. The heat exchanger should be constructed of noncorrosive materials.

(a) The heat exchanger shall be subjected to.a minimum pressure test of 150 percent of maximum designed working pressure after installation in quench tank. The heat exchanger should be subjected to similar test prior to being placed in service, and at periodic intervals thereafter, to ascertain that it is free of leaks.

(b) The he'at exchanger shall be.located within the quench tank in such a manner as not to be subject to mechanical damage by the elevator or load tobe quenched.

(c) The cooling medium flow should be controlled b y an automatic temperature control.

(d) If it is possible to .completely close off the internal heat exchanger, a pressure relief shall be provided, terminating in a safe location.

2394 • INTEGRAL QUENCH FURNACES 8 6 ~

' K. External Water-Cooled HeatExchanger

1100-10. Tubes of the heat exchanger which are exposed to con. tact with water should be Constructed of noncorrosive materials.

(a) The heat exchanger, after, fabrication, shall be subjected to a minimum pressure test of ,150 percent of the maximum design working pressure. The heat exchanger should be subjected to sirai. lar test prior to being placed in service, and at periodic intervals thereafter, to ascertain that it is free' of leaks.

(b) The pressure of the quench ,.medium through the heat exchanger shall be greater, than the ,water pressure applied.

L . External Air-C0oled System

1100-11. External air-cooled heat exchangers installed out-of-doors Shall b'~'structurally reinforced to wlthstand anticipated wind forces without damage at elevation at which it is mouhted.

(a) External air-cooled heat exchangers installed out-of-doors or which utilize supplemental water cooling shall be of materials suitably protected against corrosion.

• M. Quench Tank Protective Features

1100-13. Quench Tank ' (a) Quench reservoir shall be equipped with a reliable quench medium level indicator. If of the sight glassl type, thelevel indicator shall be of heavy duty construction and protected from mechanical damage.

(b) Quench tanl~ shall be equipped with a low level device arranged to sound an alarm, prevent start of quenching and shut off heating medium in case of'a low level~condition.' ' "

• (c) Excess temperature limit Control Shaft be provided, and suitably interlocked to automatically shut Off ~ 'thel quench heating medium, and shall require operator, attention in case of excessive quench medium temperature. Excess ~temperature limit shall be interlocked to prevent St~/rt of quenching in case of excessive quench medium temperature. Audible and/or visual alarms shall be provided.

(d) When agitation of the quench medium is required to prevent overheating, then the agitation shall be interlocked tO prevent quenching until, agitator has been started.

(e) When a combustible liquid quench medium is used, a water detector shall be provided for the quench tank to sound an audible

2395 ..~108108 I N D U S T R I A L F U R N A C E S ~ S P E C I A L A T M O S P H E R E

~ata~en and interlocked to'prevent quenching in the.event that water t of the quench medium, exceeds 0.35 percent by volume.

1100-14" External Water-Cooled Heat Exchangers , (a ) The oil pressure through the heat exchanger shall be main-

rained greater than the water pressure.

(b) It it is possible to completely close off the external heat ex- ¢han.ger, a pressure relief shall be provided, terminating in a safe locauon . . . . . .

1100-15. External Air-Cooled System a) An external heat exchanger installed out-of-doors shall be vided with lightning protection if located in an exposed, rooftop

lPo~t ion • . , . .

(b) i f th e air-cool.ed heat. exchanger is installed in a rooftop location, ,it shall be installed in a eurbed~or diked area, drained to a safe location outside' of the building, ,

N , ' Q u e n c h T a n k Hea t ing Controls

1100-17, Fuel-Fired Immersson'" . . . . . Heaters;~ ~

(a) Fuel-fired immersion burners ~ shall have fuel supplies and pilots and main burne/'s installed and protected in accordance with Chapter V~ " " ~

(b) Burner control .systems shall be interlocked with quench medium agitation or recirculating system to prevent localized overheating of the quench medium .

(c) T h e immersion tubes shall be installed so that the entire tube within the quench tank'is covered with quench medium at all times. The inlet and the 'outlet shall be through the top of the quench tank.

(d) A quench level and excess temperature supervision shall be interlocked to shut off immersion heating, during normal operations.

1100-18. Electric Immersion Heaters. (a) Electric heaters shall be of a sheath type construction.

(b) Heaters shall be installed so that the hot sheath is fully sub- merged in the quench medium at all times.

(c) The quench medium shall be supervised by:

1. A temperature controller arranged to maintain quench medium at proper temperature and interlocked to shut off the im, mersion heating,when excess temperature is detected.

2 3 9 6 • FI. pRo EcT o Fo. F ..AcE 86c,

2. A quench medium level control interlocked to Shut off the immersion heating when low level is detected.

(d) The electrical control system shall be interlocked with the quench medium'agitation or recirculation system to prevent localized overheating of the quench medium.

CHAPTER 12. FIRE PROTECTION FOR FURNACE AREAs

ARTICLE 1200. SPRINKLER AND SPRAY SYSTEMS

A. General

Furnaces can present fire hazards to the surrounding area in which they will be installed. Consid etzation /'nust be given to providing fixed fire extinguishing systems toprotect against-such hazards as overheating, spillage of molten salts or metals, quench tanks, ignition of hydraulic oil, escape of fuel, etc. It is the responsibility of the user-to consult with the authorit3/:having.jurisdiction concerning the necessary~requirements for such protectton..

B. Automatic Sprinkler Systems

i200-1. Automatic" sprinkler installations shall conform to the NFPA Standard for the Installation of Sprinkler Systems (No. 13) for hazardous locations.

C. Water Spray Systems

1200-2. Water spray systems shall be fixed Systems, automatic in operation and conforming to the NFPA Standard for Water ° Spray Fixed •Systems for Fire Protection (No. 15).

/

ARTICLE 1210. PORTABLE PROTECTION EQUIPMENT

1210-1. Extinguishers. Approved portable extinguishing equipment shall be provided near the furnace, and related equipment. Such installations shall be in accordance with the NFPA Standard on Portable Fire Extingifishers (No. 10).

1210-2. Small Hose Streams. When small hose streams are required, they shall be in accordance with NFPA Standard for the Installation'of Standpipe and Hose Systems, NFPA•No. 14.

2397 ~ - - 1 1 0 I N D U S T R I A L F U R N A C E S - - S P E C I A L A T M O S P H E R E

ARTICLE 1220. MAINTENANCE OF FIRE P R O T E C T I O N E Q U I P M E N T

1220-1- Inspection. All fire protection equipment shall be inspected and maintained at regular intervals, in accordance with NFPA standards.

1220-2. Records of inspection and tests shall be kept on forms prepared for this purpose and brought to the attention of management.

1220-3. Testing shall be done by responsible men familiar with the operatio~a and maintenance of this type of fire protection equipment.

1220-4.:,Ouilets. Sprinkler heads and outlets of other extinguishing equipment .shall be kept clean and free of deposit under a regular inspectio n program. - '

2398 OF TERMS 86C-111

APPENDIX A. GLOSSARY OF TERMS.

1. Gas-Air Proportioning and Mixing Systems for Combustion. Low PRESSURE .GAS OR "ATMOSPHERIC'" SYSTEM (Gas pressure less than

I psig). A system using the momentum of a je t of low pressure gas to entrain from-the atmosphere a portion of the air required for combustion.

HIOH PRESSURE GAS SYSTEM (Gas pressure 1 psig*.or higher) . ASYo~Stl:~e using the momentum of a jet of high pressure gas to entrain trom the a p ere all, or nearly all, of the air required for combfistion.

Low PRESSURE AIR SYSTEM (Air pressure up to 5 pRig). A systemusing the momentum of a jet of low pressure air to entrain gas to produce a combustible mixture, i

• .HIoR PpogssuPog A~R SYSTEM (Air pressure 5 prig O r h i g h e r ) . A system using the momentum of a jet of high pressure air to entrain gas, or mr and gas to produce a combustible mixture.

SuoTioN SYSTEM. A system applying suction to a combust ion.chamber to draw in the air and /o r gas necessary to produce the desired combusuble mixture.

TwO VALVE SYSTEM. A system using separate contt'ol ~of air a n d gas both of which are under pressure. The valves, controlling the air and gas flows, may or may not be interlocked.

M E C ~ m A L SYSTEM. A system which proportions air and gas a n d . me- chanicaily compresses the mixture for combustion purp.~es~ ~ c e n t r ~ r nuxmg unit may be used or individual appliances may e a c u , . . . . . . . . . . . . . . . .

2. Mixers and Mixing Devices. MIXER, GENERAL. A device for mixing gas and air in any desired proportions.

MANUAL MIXER. A mixer tha t requires manual adjustments to maintain the desired air/gas ratio as rates of flow are changed.

AUTOMATIC MIX1gR. A mixer that automatically maintains within its rated capacity a substantially constant air /gas ratio at varying rates of flow. All types defined below can be designed to fit this classification.

GAS JET MIXER OR ATMOSPm~. RIC INSPIRATOR M ' x z R - A mixer using the kinetic energy of a je t of gas issuing trom an onnce to enurea all or part of the air required for combustion.

(a) The term "Atmospheric Inspirator (venturi) Mixer" shall mean ~ y mixer in which par t or all of the combustion air (primary air) is drawn in by the iuspirating effect of a ~as jet entering the inspiratur, the remaining combustion air (secondary air'~, if needed, being supplied from the atmosphere in which the burner is located. See Fig. 10.

as for the "et is available at the spud at pressures below.l prig, the .(b) I f g ,,J re atmos heric insplrator" mixer; it at ] pug rmxer ts defined as . low .pressu . p " " " r.--

or above, the mixer is designated "h~gh pressure atmospheric msplrato AIR JET MIXER. A mixer using the kinetic energy of a stream of air issuing

from an orifice to entrain the gas required for combustion. In some cases, this type of mixer may be designed to entrain some of the air for combustion as wel las the gas. *Equipment Will not function satisfactorily at pressures less than I prig.

2399 86G--112 INDUSTRIAL FURNACES - - SPECIAL ATMOSPHERE

pamARY Am. All air supplied through the burner, including atomizing and combustion air.

SBCOh'DARY AiR. secondary air is all of the air that is intentionally allowed to enter the furnace, but which does not pass through the burner nozzle.

E Secondary Air _-~ . ~ e q i s t e r ./Primary

InsRirator Body / Air ' - - ~ (Venturi)/ Spud ~

. . . . _ . . . . . . . /__ x, , Ga.

r

_ r Burner _L Mixer _ F L . J - I -

Fig. 10. Atmospheric Inspiring Burner Mixer.

ZERO GOVERNOR. Also called "atmospheric regulator." A diaphragm- type regulator that maintains th6 fuel-gas pressure at atmospheric or zero gage pressure.

MEC.I"IANICAL. MIXER. A .mixer usin~ mechanical means to mix gas and air, aeglecUng entirely any kmeuc energy m the gas and air, and compressing the resultant mixture to a pressure suitable for delivery to its point of use. Mixers in this group utilize either a centrifugal fan or some other type of mechanical compressor with a proportioning device on its intake through which ~as and

~ drawn by the fan or compressor suction. The proportioning device may oc automauc or reqmre manual adjustment to maintam the desired air/gas ratio as rates of flow are changed.

PROPORTIONAL Mmmo BURNER. (a) The term "proportioning system" (automatic proportioning systems)

shall mean a combination of one or more burner tips, nozzles or other firing heads and a proportioning device intended to supply a gas-air mixture to the firing point in proper proportions for combustion. Similar devices with additional controls to permit operation with control devices between burner and proportioning device are governed, by 310-20 and 310-21.

(b) The term "proportioning inspirator" shall mean an inspirating tube ~which, when supplied with gas, will draw into the gas stream all the air necessary for combustion. , • :

(c) .The term "proportioning mixer" (Fig. 11 ) shall mean a mixing device compnse~a oI an inspirator which, when supplied with air, will draw into the air stream all the gas necessary for combustion and a gas governor, zero regulator, 0~ ratio valve which reduces incoming gas pressure to approximately atmos-

pher ic .

(d) The term "mixing blower" shall mean a motor-driven blower to produce air-gas mixtures for combustion through one or more gas burners or nozzles on a single zone industrial heating appliance or on each control zone of a multi-zone installaiion. Blower shall be equipped with a gas control valve at its air entran, ce so arranged that gas is admitted to the air stream entering the

2 4 0 0 GLOSSARY OF TERMS 86C--II__..3 blower in ro er roportions for correct combustion by the type of burner or buyers e: l ed ; th0 said control vaive beln of either the "zero ove o , or mechanical "ratio valve" type which controls the gas and a.tr adjustments simultaneously. No valves, control devices or omer oostrucuons should be installed between the blower discharge and the burncr or burners.

~ | ' NSPIRATOR

. I V TUBE

• c ~ _ J i l L , , , x T u ~

~JtC~ AIR CONTRO L

' Fig. 11. Typical Proportioning Mixer.

3 . B u r n e r s . . ' , :

BURNER, GENERAL. ' A device for the finial:release of air/gas, or oxygen/gas mixtures, or air and gas separately into .the combustion zone.

ATMOSPHERIC BURNER. A burner u s e d i n the Low Pressure Gas or "At- mospheric" system which requires secondary air for coml31ete combustion.

BLAST BURNER. A burner delivering a combustible mixture under pressure, normally above 0.3 in. w.c. to the combustion zone. '*

PRESSURE BURNER. Same as Blast Burner. SmOLE PORT BURNER. A burner having only one discharge opening or port

MULTWORT BURNER. A burner having two or more separate discharge openings or ports. These ports may be either flush or raised.

I_aNE BURNER. A burner whose flame is a continuous "line" from one end to the other. Normally applied to a blast burner~

PIpE BURNER. General term covering any type of atmospheric or blast burner in the form of a tube or pipe with ports or tips spaced ove r its length.

RIBBON BURNER. A burner havin~ many small closely spaced ports usually made up by preying corrugated metal ribbons in a slot or other shaped opening.

OPEN PORT BURNER. Any type of burner that fires acr.o~ a gap .into opening in the furnace or combustion chamber wall and m not sealea m the wall.

. . o . f ExcEss AIR BURNER. A nozzle mmmg burner.dellvenng a. fixed volumceu~ air and a variable volume of gas such that complete comvusuon ol gas occ at all rates of firing, to provide a relatively uniform flow of air and products regardless of firing rates

2401 86~114 INDUSTRIAL.FURNACES - - SPECIAL ATMOSPHERE

TUNNEL BUP.NER. A burner sealed in the furnace wall in which combustion takes place mostly in a, refractory tunnel or tuyere which is really part of the burner- ~ ' : . ' . ;"

FLA~E RETAIniNG NOZZLE. Any burner nozzle with built-in features to hold the flame at high mixture pressures.

BLAST TIP. A small metallic or ceramic burner nozzle so made that flames will not blow away from it,, even with high mixture pressures.

NOZZLE MIXmO BumqEt~. A burner in which the gas and air are kept separate until discharged from the burner into the combustion chamber or tunnel. Generally used with low pressure gas (up to ~ psig or 14 in. w.c.) and low pressure air (up to 5 psig). . .

IL~IANT BURNER. A 'burner designed to transfer a significant part of the combustion heat in the form of radiation from surfaces of various shapes which

, are usually of refractory material.

LumiNous FLAME BURNER." A :burner which discharges nonturbulent parallel strata of air and gas to produce an extended flame of high luminosity.

R/NO BURNER. There are twq' types - -

(a) A form of atmospheric burner made with one or more concentric rings. (b) A form of burner used in firing boilers consisting of a perforated vertical

gas ring with air admitted generally through the center of the ring. Combustion air may be supplied by natural, induced, or forced draft.

MULTIJET BURNER. A form of burner which geneially, consists of gas mani- folds with a large number of jets arranged to fire horizontally through openings in a vertical refractory plate. These openings are of various shapes -~- round, square, cmverleafed, etc. Combustion air may be supplied by natural , induced, or forced draft . . Complete assemblies combining burner, refractory plate, wind box, blower,- and controls are generally known as Forced Draft Boiler Burners.

ENCLOSED COMBUSTION 'BugNER." A burner' which cot/fines the combustion in a small chamber of mifiiature furnace and only the high teml>drature com- pletdy combusted gases, in the form of high veloci/y jets or Streams, are used for heating.. ~

DIAPHRAOM BURNER. A burner which utilizes a porous refractory diaphragm as the port so that the combustion takes place ovdI the entire area of this refractory diaphragm. " " . . . . . .

' - • • v

GAs-OIL BURNER. A burner designed to hum gas and oil simultaneously.

DUAL "FUEL BURNER." A burner designed to burn either gas or oil, but not both together . . . . . . ,

COMBINATION GAS AND OIL BURNER~ 'A burner which can burn either gas or oil or both together.

PREMIXED BURNER. A burner that utilizes a positive and dependable air- gas mixer to furnfih the air needed for complete combustion of the fuel supplied to the burner independently of the concentration or pressure of the atmosphere inside the enclosure where t h e burner fires. ~ The zero governor inspirator raix~ er, high-pressure (gas plessure 1.0 psi or higher) atmospheric inspirator on~ser, mixing blower, and the approved gas-mixing machine are illustrative

SUCh a mLxer.

PowEa BURNER. A gas burner in which either gas or air or both are supplied at pressure exceeding, for gas, the line pressure, and for air, atmospheric pres-

2 4 0 2 o,,

sure; this added pressure is appl ied at the. burner. ,.Examples .ar.e gas burner8 havin zero governor inspirator mixers, ttaose s u p p n e a oy m m m g mower or

g • • • - , - : - ~ and those sunvlied with air by a blower, com. approvea gas-lmxmg m a c n , , ~ , --- - - pressor, o: forced-draft fan.

Other examples are oil b u r n e p of the .pressure-ato .mi~ng _WCreSUaCh as..the oil-pressure atomaz.mg burner ~atso call.ea, mecnamcai p~o~zon t~d~ora t~ burner) , air a tomizmg burner, s team atormzmg burner , and h ---7- cup burner .

LuMInous WALL BURNER. A porous refractory liner to permit-gas-air mix. tures to flow t h r o u g h - - forming a luminous wall.

• . urner of either the atmospheric or nozzle mixia~ RADIANT TYPE BURNER A b . . . . . . . a ~ " ; t in a tube of given len th °

w o e sneciauy aesignea to provluc a ,u, ,s - , , . . . . . h _ u g to ~s~ure~substandally uniform rad iauon f rom the tube surface.

4. Ign i t ion Systems. MANUAL-LIGHTED INDUSTRIAL HEATINO EQUlP~NT. Gas- or oR-fired equip.

ment such as a furnace or oven where fuel to the main burner(s) can be turned on only by h a n d and is manually or semiautomatically ignited under the super. vision of the burner man (see Manual- igni ted Burner and Semiautomatic. ignited Burner below). Once ignited, firing of the main burner(s) may be high-low or 'modula ted .

ignited Burner below). Firing of the m " ~ " " lated to off, or on-off.

matic-li h ted except that on each l ight ing-o- , p,x~. ~5 - ' i , r . . . . f rom c~g~ condit ion, fuel to t h e main b u r n e r ( s ) c a n be tu rnea on omy Dy nane and is manually, o r semiautomatically ignitex.t, under the l supe.rvi.sion of the burner m a n (see Manual- igni ted BtTrner and SemiautomaUc-:gn:tetl Burner below). Once ignited, firing of the n/ain burner(s) may be high-low, modulated

to, off, or on,off. M ~ A L - m s r r ~ BURNER- A burner ignited by a por table gas-or oil-burner

torch or by. an oR-soaked-swab torch, p laced in proximity to the burner nozzle

by. the b~maer man. Au-r0MA~zc-zoNrr~ Bumcsg. • A burner ignited by. direct electric ignition,

or by. an electric-ignited or continuous pilot.- S~.MIAUTOMATIO.IGNITED BURN.ER. A burner ignited by direct electric ig-

nition or by. an electric-ignited pilot, electric ignition being manually, activatea.

DmageT EL~CTmC IoNrr~o~. Ignit ion of an oil f l a m e ( a n d in some cases a gas flame) by. an electric-ignition source such as a high-voltage spark or hot wire.

PROVED LOW-Fmag-ST~T INTeRLOCk. A burner start in which a control sequence insures that a high-low or modula ted burner is in the low-fire (firing rate not exceeding 33% o f the m a x i m u m ) pos.i " ' started, as for example by. m.e.a~, o , an e n a s , w ~ n a ~ e ~ ' o n t r o f c i r c u i t . of the modula t ing motor, w m c n is w ~ u m~u ~,,~ ° -1

Hzoa-LOW Fmmo. Provision for two firing rates, high and low, according

to load demand . MODULATED F m m o . Provision:for gradually, varying the firing rate between

high-fire and low-fire, according to load demand .

2403 860-116 INDUSTRIAL FURNACES - - SPECIAL ATMOSPHERE f

Btu~sR TmtNDOWN. The ratio of maximum to minimum burner fuel-input rates.

j . Pilots.

CONTn~UOUS PILOT. A ~ilot that burns without turndown thrmaghout the cadre period that the heating equipment is in service whether or not the main burner is firing.

I~TsaMrrFENT PILOT. J A p i lo t which burns during lighting-off and while the main burner is firing, a n d w h i c h is shut off with the main burner.

brr~auPTm~ PILOT. A pilot which burns during the entire pilot-flame- establishi~..g period .and/or trial-for-ignition period, and which is cut off (in- t~rrupten) at the enci of this period(s) or during firing.

ExPANDmO PILOT. A pilot that burns at a set turndown throughout the cndre period t ha t the heating equipment is in service whether or not the main burner is firing. During lighting-off, it is expanded (burns without turndown) w ignite the main burner reliably.

P a o v ~ PILOT. A pilot flame-supervised by a combustion safeguard which se~ses the presence of the pilot flame and which is located where i t will reliably ig~'tc the mare burner before permitting the main-burner fuel safety shutoff valve to be opened.

6. Safety Controls. , .

FUEL SAFETY SHUTOFF" VALVES. An approved fuel (~as or oil) safety shutoff valve is held open by electric energy or by pressure (oiJ, gas, air, or atomizing medium) or by both. It is serf-closing by means of a spring and /o r dead weight within 5 seconds after the holding medium is cut off. Approved valves are available in two different types, manuai-opening and automatic-opening. Both types can be opened only after the holding medium is applied. They arc so enclosed that they cannot be bypassed readily or blocked open. Block- ing the valve-operating handle of the manual-opening valves does not prevent valve closure when the holding medium is cut off. All approved fuel safety shutoff valves, except the direct-acting l~ackless solenoid type, have a me- chanically actuated indicator to show whether the valve is open or shut. The valves arc available equipped with an end switch that is open when the valve is closed and closed when the valve is open. The end switches having reverse operation are als0 available. End switches may be wired into safety-control carcuits for interlocking purposes or i n t o a l a r m or signal circuits.

COMBUSTION SAFEOUARD. The term "combustion safeguard," except where supplemented by the words "gas-analyzer type," means a safety control responsive directly to flame properties; it senses the presence of flame and causes fuel to be shut off in event of flame failure.

This device in its simplest form, often called nonprogramming, comprises a flame-detecting assembly and one or more flame-sensing elements. I t may be wired into a safety-control circuit so that during lighting-off it must prove the presence of the pilot flame at a location where the pilot will reliably ignite the main burner before permitting the main fuel safety shutoff valve to be energized and opened. During firing, it supervises the main flame alone or the pilot and main i~lames simultaneously. In event of accidental flame failure during firing it causes all fuel to be shut off and the electric ignition to be deactivated. The ~ttention of an operator is necessary before the next pilot-flame- establishing period or trial-for-ignition period can start. Because of this operating characteristic, a n0nprogramrning combustion safeguard is often further classified as nonrecyeling.

2404 ~ o ~ OF TERMS 86C-117

This device is also avail~tble in a more complex form, often called program. ruing which is the same as the nonpro am ng excep at, te " r 2 niti?o timing assembly as well as a flame-aetecung assemmy ~ s ' mmmg Combustion Safeguard below).

Approved combustion safeguards, either programming.or ononprogramming, have a flame-failure response time of not m o r e m a n 4 seconos. Atso, they may have a flame-failure contac t tha t can be wired irito ;flame failure alarm and signal circuits. They usually have a built-in safe-start check, a safety feature that prevents lighting-off if t h e flame-sensing relay is in the unsafe (flame present) position duc to component failure within thexcombustion safe, guard or to the prese/ace of actual or simulated flame.

COMBUSTION SAFEGUARDS, GAs-ANALYzER TYP ~'- This equipment is intended rimarily for use on manual-lighted, g'as~-fired industrial heating equipment such

P . . . . . . . ; ..... it- in rounds of steam per hour) and type of burner as large hOllers. ~izc t.t;,xpa~ y t-, r do not affect application. It samp~les continuously the gaseous p oducts of com- bu~stion, and indicates and records per cent of combustibles and oxygen (optional) in the sampled gases. It is important th.ar sample point(s) be located so that the sample to the gas analyzer accurately represcn.ts the tot.al, ttuc gas or atmosphere passing that partmular secuon,, and_ so that ,t intricates gas condentration changes at the ourners as prompuy as pt~,~lo,~.

The per cent of combustibles indication is the safety-control function of the equipment. During a firing cycle, a dangerous condition may result, for ex~ ample, from a deficiency of air; such a deficiency would normany cause a graGuai increase in the amount of combustibles in the products of incomplete combustion. The equipment provides an automatic warning signal at 1 % and a dan er signal at 2 % combustibles: I t shuts off the fuel supply at the2d% point.

g _ , . . . . . . . t._ -~'-~er level xeirardless Of .the k" of fuel he 2 % vmue m Well oelow t t l ¢ U a A l ~ 0 I *

g(T/.) This equipment may also be used t o detect .a dangerous internal atmosphere at the time of burner light-off. : '" ' "

The per cent of oxygen indication, when employed, provides information on which to judge emcieney of combustiGn. This makes possibl e more eco- nomical operation of boilers.

• This eauivment usually consists.of a sampling system, analyzer, and recorder. I t s response" to composition :changes of monitored gases is not instantaneous. From the pickup point, t h e sample gas travels through ~ tub ing ' t ha t may bc 25 feet long. • After reaching the analyzing equipment, the gas.is passed through a catalytic combustion chamber.

This series of operations involves a time delay that may 13e 10 to 20 seconds, dependin~ somewhat on the concentratibn .of combustibles i n the sample. However~'because unsafe combustion is usually the result of gradual changes in conditions, the speed of response in a well-engineered system is sufficiendy fast and with sufficient safety factor to warn of danger. • " . .

In order to derive the full benefits of ' tbe equipment, each application must be individually engineered and inspected by the manufacturer of. the device or an authorized representative.

SAFE-START CHECK. A"checking circuit incorporated i n a safety-control circuit usually built into the combustion-safeguard)"that prevents lighting-off if the fl~me-seusin~ relay of the combustion safeguard is in the unsafe (flame- present) position d~ue to component failure within the combustion safeguard or the presence of actual or simulated flame.

SUPERVISED FLAME. A flame Whose presence or absence is detected by a combustion safeguard. '

PmOT-FLAUE-ESTAeLISmNG PER1GD. The interval"of time during lighting off in which a safety-control circuit permits the pilot fuel safety shutoff valve

2405 18 INDUSTRIAL FURNACES - - SPECIAL ATMOSPHERE

to be open before the combustion safeguard is required to prove the presence of the pilot flame. •

T~AL-FOR-IoNrrIoN PERIOD. That interval of time during lighting-off in ~hich a safety-control circuit permits the main-burner fuel safety shutoff valve to be open before the combustion safeguard is required to supervise the

burner flame alone. The FM cock safety-control system i s a positive and dependable method of

oreventing fuel explosions during lighting-off periods in mult iburner gas- ~ d equipment such as manual- and semiautomatic-lighted boilers, and direct-intern~-fired .furnac.es, ovens,_ and dryers. The system is designed to prevent O l?en ng ot the ~ gas salety shutoff-valve unless all the individual bamer valves supphea with fuel through the safety valve are proved to be dosed- This is accomplished by using fuel gas or combustion air as a checking medium. The system may be pneumatic-electric or pneumatic alone.

7. Properties of Fuel Gases. The following definitions and tables are for information only and indicate

the properties of typ!cal commercial gases.

CO~gRCIAL M A N U F A ~ GAS shall mean in this standard a mixture of gases usually composed of various proportions of some of the following gases:

(a) Coal gas, formed bydis t i l la t ion or cracking of bituminous coal. (b) Coke-oven gas, produced in a similar manner as a by-product in manu-

facture of coke. (e) C~bure t ed water gas, formed by flowing steam through incandescent

carbon. It has a low heat content which is increased by bringing the hot gas into contact with oil so that some of the oil is broken down or "cracked" into a gas. ~ product, . called carbureted water gas, is sometimes mixed with coke oven gas.

(d) Oil gas, made by "cracking" petroleum oils, is used occasionally in manufactured gases.

NATU~L GAS shall mean in this standard, a mixture of gases, principally methane and ethane obtained from gas wells and from which less volatile hydrocarbons such as propane and butane have been removed, leaving a mixture of gases which will remain in the gaseous state at all pressures and temperatures encountered in the distribution "system.

LIQUEFIED PETROLEUM GASES~ -

(a) T h e term "liquefied petroleum gases" as used in this s tandard shall mean and include any material which is composed predominandy of any of the following hydrocarbons, or mixtures of them: propane, propylene, butanes (normal butane or iso-butane), and butylenes.

The composition of liquefied petroleum ~ases varies, but in all the established grades the predominant compounds ar~e propane and butane (isc~butane and normal butane). Under moderate pressure, the gases liquefy, bu t upon relief of the pressure arc readily converted into the gaseous phase. Advantage of this characteristic is taken by the industry, and for convenience, the gases arc shipped and stored under pressure as liquids. When in the gaseous state, these gases present a hazard comparable to any flammable natural or manufactured gas, except that being heavier than air, ventilation requires added attention. The range of combustibility is slightly narrower and lower than that 0fnatural gas. When below 30°F., butane is a liquid and the hazard is similar to that of a flammable liquid. Propane is liquid at atmospheric pressure at temperatures below minus 44°F. Flash vaporization takes place at temperatures above the boiling points (butane above 30°F. ; propane above minus 44°F.).

2406 (b) Installation of liquefied petroleum gas storage and handling systems

used to supply oven heating systems shall be made in accordance with th. NFPA Standard for Liquefied Petroleum Gases (No. 58). - - ~

• Of li i uefied etroleum gases and a i r a r e distributed by 13ubllr c) Mixtures q p . - - ~ , , t ~ ; H ~ thrnu~rh fzs systems for use in place of commercial manufactured ~a~ or"na'tural~-g-as°~'n~r-na~-satisfactoriiy be ~Jsed in equipment designed for use w]~ those gases. Such mixtures shall be conside~d equiv~ent of commercial .manu. facturcd gas or natural gas except that provision Shoulct t3e maae for ventxlation based on these mixed gases being heavier tttan mr. .

PRODUCER G~s. (a) Producer gas shall mean in this s tandard any gas formed by blowing

air through incandescent coal, coke, or charcoal. Such gases often contain solid particles and carry liquids which cause d i~cal ty in burner operation. Special design is needed and automatic control is often difficult.

(b) The use of producer gas for heating systems should bc restricted to equipment under constant supc.rvision ot a quaJmco operator, ri.ans i o r p .to. ducer gas equipment, distribuU.on .syste.n~. ,.an.o. oven n e a u n g s y s t c ~ snould bc submitted to the authority rtavmg junsmcuon zor approva l I ne use ol other types of gases is recommended . . . . . . . "

• low *.e . mixture may lgmtc and continue to burn. I ms is amo re~errco une auto- ignition temperature. When burners supplied with 'a~gas-air mixture in the flammable range are heated above the auto-ignition temPerature, flash backs

Mumm [] i m m l l I l m m m n n m m m l ~

/ / F " r / ~ ' ~ l

/ / 1 t II I .,~.Z

\

\

,~.',r \'%" ,.

P~e q LS"

IqlJl&~r KIN PLqatJSV Of TDla I~T~L JlO~RIlIOfT ~ amJ~JtTK e081uWl0M

lun~l,um V l B ~ ) I ~ I r ~ ~ a t .

Fig. 14. The rate of flame propagation is defined in Appendix A. Values are given in .the above graph.

:2407 120 INDUSTRIAL FURNACES - - SPECIAL ATMOSPHERE

WaucY occur." I n g e n e r a l ; such temperatures range from 870°F. to 1300°F. A h higher t.empera .tu.~. is needed to ignite gas dependably. T he temperature

-oessary ~s sngnuy mgner tor natural uas than for manufactured ases but n g ~ . . ~ o g " ' for safety with manufactured gas, a temperature of about 1200 F IS needed ~ d for natural gas, a temperature of about 1400°F. is needed.

FLA]~g PROPAGATION AND "EXPLOSIVE RANOE. The term "ra te of flame

~rop agation" means the speed at which a flame progresses through a com-

ustible.g.as-ai.r mi.'xture under the pressure, temperature, and mixture conditions existing m the comt~nsuon space, burner, or piping under consideration.

For any combustible gas, the range of its concentration in air within which flame is propagated is known as the explosive range" or as the limits of flam- n~ability. The lowest flammable concent ra t ion is the lower explosive limit. Within the range, the maximum rate of flame vrova~ation occurs When the combustible gas and air are mixed in proportio'ns'for complete combustion or oRen with the'gas at a slightly higher concentration (see Fig. 12) .

Properties of Typical Commercial Gases T A B L E H-

Gas ' B t u ' P e ~ Cu. Ft.

Limits of Explosive Range Per Cent in

Air by Volume Lower Upper

Cu. Ft. ol Specific Air Required Gravity To Burn

Compared 1.0 Cu. Ft. To Air - - 1.0 of Gas

Natural (High Btu type) Natural (High methane

type) Natural (High inerrt type) coke Oven Carbureted Water (Heavy oil with

blow i 'un) Carbureted Water (Gas oil) Oil Gas (Pacific Coast ) Coal Gas Water Gas (Blue gas) Producer Gas (Anthracite) Producer Gas (Bituminous) Propane Butane

1115

960

I 0 0 0 575

530

530

• 496 536

287

136

153 2 5 0 0

3200

4 .6

4 .0

3 .9 5 . 0

6 .4

4 .5 5 .6

6 .9

20.7

16.8 2 .4 1 .9

14.5 .64 10.6

15.0 .56 9 . 0

14.0 .76 9.4 28.0 " .44 5.1

• 37.5 .70 4.1 •

3 7 ; 7 .•67 4.5

2 9 . 6 .47 4 .0 30.8 .47 4 .9

69.5 .57 2.1

73 .7 .86 1.1

61.0 .86 1.2 9 .5 1.52 24.0 8 .5 1.95 31.0

The rate of flame propagation has practical significance in the design and operation of gas burners. If the velocity of the. mixture at the burner diminishes,

2408 ~ , o ~ oF T~.RMS 86C-121

the tendency of the f lame to flash back into the burner body is increased. Conversely, if the gas velocity leaving the bu rne r is m u c h grea te r than the rate of f lame propagat ion , the f lame m a y be blown away f r o m the burner. For this reason, a. bu rne r which has been usea on a m a n u t a c t u r e a gas, with a relatively h igh rate Of f lame propagat ion , m a y not be suitable for na tu ra l gas or

• ' a low rate For tuna te ly , the relat ion between bu rne r discharge bi~tane which has " - . . . . . . n e i t % r ~ " velocity" a n d f lame p r o p a g a u o n rate ts no t c n u c m , so tna t n variation in the .rate of flow nor changes in mix ture a d j u s t m e n t over a fairly wide range will cause the f lame to blow away f rom the bu rne r or to flash back.

8. Ventilation Equipment Definitions. AIR FLOW SWITCHES are devices ac tua ted by the flow of air in a duc t system.

Air flow switches instal led in duc ts hand l ing vapor- laden air shall be located on the. suct ion side of fans to min imize condensed deposit on moving parts.

(a) V a n e type air flow switches consist of a vane or paddle m o u n t e d on a movable a rm. T h e vane is so located t ha t a differential pressure or air flow agains t the vane will cause the vane a r m assembly to move and . actuate a switch contact .

(b) D i a p h r a g m type air flow switches consist general ly of a d i aph ragm with one side open to room pressure a n d the other connec ted_ to . th .eexhaus t or vent i la t ion duct . M o v e m e n t of the d i a p h r a g m by a pressure amerent ia l will ac tua te a switch contact .

ROTATmNAL SwrrCHES for vent i la t ion inter locking are devices which are usual ly dr iven di recdy by the fan wheel or fan motor shafts. W h e n the speed of the fan shaf t or dr ive motor reaches a cer ta in p rede te rmined ra te - - which will give a safe m i n i m u m air flow - - a swi tch con tac t wil lclose.

LIMIT SWXTCHES for use on oven doors or venulauon, sys tem dam.pers, cons m basically of a lever and sui table connec t ing m e c n a m s m to a swttcn contact. By swinging the door or d a m p e r to a p rede te rmined position, usual ly .wide open, w h e r e i t m o v e s t h e lever, the switch con tac t is made . L imi t switches are used mosdy for safe l ight ing-off sequence to insure the doors or dampe r s will be wide open or posi t ioned for prevent i la t ion before electric-ignition or fuel will be m a d e avai lable for l ight ing up burners , ol: power is avai lable for energiz ing electric heaters.

ELECTRICAL VENTILATION INTERLOCKING m e a n s a fan t ha t is too(or driven by direct shaf t or a t least- two Vee belts, is interlocked wi th the safety control circuit , by energiz ing the circuit f rom the load side of an overcur ren t protected s tar ter for the fan motor , t h rough an ex t r a con tac t of the starter, a suitable relay or t ransformer .

PREVENTILA~ION Tnaz DELAY RELAY. A t ime delay relay for preventi lat ion consists of a switch which is closed au tomat ica l ly after a preset u m e inteeTtoM usual ly measu red by a t iming device. Such a relay s h o u m t)e axrang o reset ins tant ly to the s tar t ing position when the cu r ren t supply is interrupted.

9. Fuel Safety Contro ls . ELECTRIC, MANUAL-OPENING AUTOMATIC CLOSING SAFETY SHUTOFF VALVES

can be ovened only after the valve solenoid coil is energized and m u s t be 'opened manual ly , by means of a sui table " f r ee -hand le . " De-energiz ing the valve solenoid coil au tomat ica l ly closes the valve.

ELEc~,c OPE~x.o, AUTO.^~C CLOSX~. S^.=~.Y S"VoyF V~L~s_~°P~v automat ica l ly on energizing the .va lve a c t u a u n g aevtce, ana .c tose a u t o m a u ~ y on de-energiz ing the a~tuat ing device.

2409 86C-122 INDUSTRIAL F U R N A C E S - - SPECIAL ATMOSPHERE

MECHANICAL, PRESS(IRE-OPERATED SAFETY SHUTOFF VALVES must be opened vaanually but automatically shut off the fuel supply if the fuel and/or air pressure necessary for proper atomization or combustion falls below predetermined values. These pressure settings are usually the minimum values for stable combustion and safe operau.'on. I- These valves must be reopened manually but will rcclosc when the hand ts removed unless the fuel and/or air pressure has been restored to above the set point.

10. Flame Detection Devices.

ELECTRICAL CONDUCTIVITY DETECTORS employ an electrically insulated rod of temperature resistant material that extends into the flame being supervised. A voltage is impressed across the rod to a ground connected to the nozzle of the burner. The electrical current passing through the flame is amplified and calibrated for high and low cutoff points. The current thus produced within the prescribed range maintains an electrical circuit through the relay.

Tm~ INFRARED AND ULTRAVIOLET RADIATION DEVICES are based on the variation of the electrical conductivity of a crystalline material as a function of radiant euergy of specific wave lengths. The current passing through the detector cell is amplified to control a relay.

PHOTOELECTRIC COMBUSTION SAFEGUARDS are mounted outside the firebox and sighted on the flame being supervised. They depend on the radiation (light) from the flame striking a light-seusitive cell. When enough light in- tcmlty m present, sufficient current will .flow in the cell (phototube). This minute current, is amplified electronically and will then actuate suitably arranged relays to make or interrupt the power to a fuel safety shutoff valve in event of presence or absence of flame, respectively, and actuate an alarm (if provided) on flame failure. The photoelectric combustion safeguard is suitable for use on the usuat highly radiant oil flames; it is not generally used on gas flames owing to the scant radiation intensity of properly proportioned gas flames which are "non-luminous." This type of combustion safeguard is practically instantaneous in operation.

RAmANT-HEAT-ACTUATED T ~ E COMBUSTION SArEOUAt~VS are mounted outside the firebox and sighted on the flame being supervised. They depend on the radiant heat from a luminous flame being absorbed on a "black" body, such as a diaphragm or a bimetal coil, thus causing expansion and contraction to make or break an electrical contact , in the presence or absence of flame, respectively. This opens or doses thc safety shutoff valve and actuates an alarm if one is provided. Thesc radiant-heat-actuated devices are designed principally for use on oil flames only. Due to the time required for heat transfer, and for interrupting the safeguarding circuit (five to thirty or more seconds), they are not considered sufficiently responsive for use on industrial ovens or heaters. Further, the diaphragm type has a slip clutch for quick response which makes it unsuitable for modulating or "high-low" flames ,as a slight reduction in flame intensity would cause the contacts to open, resulting in false shutdowns.

HEAT-ACTUATED COMBUSTION SAFEGUARDS operate by the heating of a thermal element such as a liquid-filled bulb, or. bimetal helix by the burner or pilot fame; and the resultant movement or expansion closes a switch contact. Loss of flames causes contraction of the bimetal or reduction in confined fluid pressure, thus opening the switch contact. Electric safety shutoff valves and alarms are powered through these contacts.

(a) These devices are not usually well suited to supervising industrial size burner flames owing to their relatively s low response or inability to furnish direct main flame supervision.

2410 GLOSSARY OF TERMS 86C-123 1 TO Burner

Flere~C~)uptinq A [ ' ~ ---

5pec;al Narrow / K~wa~

Copper TublncJ

Invlrted Ket/ stainless steel wi~)

HsndlerivetedtokeL] ~ - I I Imdequipped w i t h / I | querter-turn Stops. L.J

Supervising Cock (F.M. Cock)

Fig. 13

!

(b) One type of metall ic-element, heat-actuated, combustion safeguard, which has a small built-in pilot, compares favorably in speed of response to the radiant -heat -ac tuated combustion safeguard; however, its small pilot is easily deflected by drafts giving false operations. The liquid-filled-bulb type usually has an excessively slow response when subjected to the relatively high temperatures near industrial size main burners (40 sec. to 5 rain.). Neither the metallic e lement nor the liquid-filled-bulb types will withstand for a reasonable time the high temperatures usually adjacent to industrial main burners, hence they ordinarily supervise only gas pilot flames and frequently an auxiliary gas pilot flame. They should not be used in oil flames or in industrial size main gas burners.

(c) The bimetallic helix (stack switch) type is used with oil burners. Its response is considered too slow for good protect ion against explosion hazard for industrial size oil burners.

THERMOCOUPLE OPERATED COMBUSTION SAFEGUARDS consist of a the rmo- couple with its hot junct ion in a g ~ pilot flame. The heat from the flame generates a minute electric current m the thermocouple which may open a magnetic gas valve or actuate a relay. Since high ambient temperatures will

2411 ~C-124 INDUSTRIAL F U R N A C E S - SPECIAL ATMOSPHERE

~.ovide an.excessively long response t ime and shor t thermocouple life, this type b fcombus t lon safeguard is no t suitable for supervis ing industr ial size gas burners . [11' ' general , . . . . they are suitable only for supervis ion of gas pilot f lames in smal l ~urner msta l la tmns .

i L Pressure Switches.

DIAPHRAGM-OPERATED PRESSURE ~WITf~HES are used for low pressures, gen- e.rally not exceeding several pounds pe r square inch. T h e d i a p h r a g m sui table for the fluid being handled bears aga ins t a lever control l ing a switch contact . A spring, with tension ad jus tmen t for pressure setting, provides coun te r th rus t

the d i a p h r a g m .

BELLOW-OPERATED PRESSURE SWITCHES are used for h igher pressures a n d are general ly s imilar in opera t ing pr inciple to the d i a p h r a g m type, except that a flexible meta l bellows replaces the d i aph ragm.

12. Supervis ing Cocks.

PNEUMATIC TYPE. The p n e u m a t i c type supervis ing cock is a special approved cock similar to the usual bu rne r gas cock, except tha t it has two side outlets which furnish a smal l i n d e p e n d e n t . p a s s a g e w a y which is opened only

• after the ma in gas passage is comple te ly closed. T h e key way width is na r row enough in respect to the size and propor t ions of the ma in gas ports to ensure positive closure of the ma in gas way before opening the side outlets. This par - t icular type of supervis ing cock is no t sui table for fuel oil. (See Fig. 13).

In app ly ing p n e u m a t i c supervis ing cocks on mul t i -gas burner systems, the side ports are connec ted in series wi th copper tubing to ad jacent cocks, so that when the gas passages of all cocks are closed a new cont inuous passage- way is provided th rough all the closed supervis ing cocks. O n e end of the line of tub ing is connec ted to the ma in gas line on the ups t r eam side of the ma in

Fig. 14.

2 412 ,~Loss.,-RY oF TE~Z~S 86C--1~2~

TO [ U A N I G °

*ePROVEOs.U~.O, VALv["A"bAL ~ • . l l . . o . . , , _ , , , , , , , .

,,,,,,~.;;;,,..°, ..... E] ~ Er~ : )

. "

GAS I S G. 'qI--,-BLEE° TAP FOR LEAKAGE T(S' f "

.OR 0VIR ~ q l - - , - OF SAFETY SHUT'-OFF VALVE "

PIPING ' - MULYI-BUflN[R SYSTEM WiTH HiGH "

PRESSURE AYMOSPHERI¢ INSPIRATOGS

/ VENT FAN INTERLOCK - -

GAS PRESSURE - AND OTHER , ,~ INTERLOCKS

END SWITCH ON SAFETY SHUTOFF~' VALVE-CLOSED / ONLY WHEN VALVE OpEN

COMMON d

12OV AC APPROVED

COCK SWITCH CONTACTS TIMER (TIME -- CLOSE WHFN COCK iS DELAY SWITC

CLOSED ~

"TTIMER LOAD CONTACT ICLO5ED AT END OF

--I~ PURGE PERIOD :.

WIRING (DETAILS WILL VARY DEPENDING ON TYPE OF BURNER ~CONTROLS USED)

-T-_

APPROVED / MANUAL OPENING

SAFETY SHUTOFF: ,/ALVE (WITH END SWITCH)

Fig. 15. . Safety control system piping *and wiring, electric interlock type supervising cock.

2413 12~ INDUSTRIAL F U R N A C E S - SPECIAL ATMOSPHERE

burner safety shutoff valve; or where combustion air is used, it can be connected to the combustion air line downstream from the main blast gate. The other end of the line of tubing beyond all supervising cocks is connected to a checking pressure switch and terminates in a bleed orifice which must be unob- strructed at all times. By properly interlocking the checking pressure switch with the main burner safety shutoff valve, the arrangement requires complete d0sure of the individual burner supervising cocks before the main burner safety shutoff valve can be opened. (For application see Section 550-10, Exception c.)

ELECTRIC INTERLOCKING TYPE. The approved electric interlocking type supervising . . . . . cock basically consists of a conventional straight-through cock with a specxal built-in swRch assembly protected against tampering, and arranged so that switch contacts are closed only when the cock is in the fully closed position. This type of supervising cock is suitable for. both gas or oil fuels. (See Fig. 14.) The switch contacts of all cocks are wired in series in the safety control circuit so that all supervising cocks must be closed before the main fuel safety shutoff valve can be opened. (For application and further description see Sections 510-8 and 550-10, Exception (c).)

13. Electrical Definitions.

For simplicity, general guides for this section of definitions include only those essential to the proper use of this standard. In general, NEC definitions will be the same as definitions in the latest revision of ANSI Standard C-42 series, "Defi- nitions of Electrical Terms," and are so identified by an asterisk*.

GUARnEn. Covered, shielded, fenced, enclosed or otherwise protected, by means of suitable covers or casings, barriers, rails or screens, mats or platforms, to remove the liability of dangerous contact or approach by persons or objects to a point of danger.

INTERRUPTINO CAPACITY: Devices intended to break current shall have an interrupting capacity sufficient for the voltage employed and for the current which must be interrupted. ,

CIRCUIT IMPEDANCE AND OTHER CHARACTERISTICS: The overcurrent protective devices, the total impedance and other characteristics of the circuit to be protected shall be so selected and coordinated as to permit the circuit protective devices used to clear a fault without the occurrence of extensive damage to the electrical components of the circuit. This fault may be assumed to be between two or more of the circuit conductors; or between any circuit conductor and the grounding conductor or enclosing metal raceway.

VEN~LATED:* Provided with a means to permit circulation of air sufficient to remove an excess of heat, fumes or vapors.

DUSTEROOF:'* So constructed or protected that dust will not interfere with its successful operation.

BRANCYH CIRCUIT ---:' INDIVIDUAL: A branch circuit that supplies only one utilization equipment.

2414

Appendix B

TYPICAL m.-,n,u , , 'OB~ ,,.'~,m[nAC1L" NO.

WAM! OF ~ p ~ ~! .rn :==-- m" v.. . . , ,;

APPENDIX B Achtptod from Form No. 23. Factory Mutual Engineering Division

FURNACE DESIGN CHECK LIST FOR ACCEPTANCE

I °'*" I _. . . . PART A - PLANS

Armn~ ~ • No.)

NAME OF MANUFAC'~u-~ER

JC2TK 18TAT!

DRAwuv.,~4 ~ ] T ~ It.u. Jtwk

INSTALLA-

TION

RATED H E A T

I N P U T

SIZE (EXTERNAl. IN I~F. )

L O C A T I O N O F

E Q U I P M E N T

N*~TS OF

_ D I ~ NO. ~ UAUlf

I NO, OF ~T8

B'FU/HR. [ ~ G A S B'I1J/CU, l 'F. [~FUELO:LNOo GALS/IO ~]ELECI1UC

w ~ ruu~::- OPID~ATING TEMP.

NO. OF iq,l~m OR 6'~ms

KW

olr ~J

mt

tl

F U E L S H U T - O F F

• F I R E P R O T E C T I O N

OF OIL QUENCH *

T A N K

~ C C ~ L E ~ EVENT OF FIRE

• , , 0 - D 5EPARAT sr -~,~.~ao T E ~ A ~ L , ~ L/kilT 8WITCH MIUT8 OFF HEAT

81~ FOR

. , u [ ] - ! -7 Op

A U T O . T I C ', AOTOXATIC A , , , o , , , c [ ] o,E. [ ] w A , n m , . , . [ ]

] I r O T l a ,

HEAT TREAT"JNG MBTALB

T Y P E . O F . ~ . w h y s M c s ~ ~ L s Avuo~mms [ ] wn~ mPzc~L mm~r ATMO~ZZ~

' W O R K ~ ZrOTSES.

H E A T I N G

.1 ~ . . . M E N T

I M E T H O D O F ILICHTING O N

METHOD OF FIRING

M I X E R

T Y P E

TYPB OF ~ I iZA m.,E1~ns Elm I,OCATIml

ND. OIP P ~ F m

• . W l

[ • D m J K C T

:B NO, OF MAW B I ~ I I I Z ~

I D ~ []~ D ~ D ~ ~ D °,, ' I~RCH D ~

1~, l ~ O ' r

~C~IR

I F ~ D ~ ( M F I L & T F P m

, j

, - L

PROTEL'TION

AGAINST

FuEL

EXPLOSION

P R O T E C T I O N

A G A I N S T

S P E C I A L

TYPICAL FURNACE DESIGN CHECK LiST FOP, Ar, f~EPTAItt',F.. . . . . . [ ] TOP [ ] ~ M

] TIMED PREVENTILATION BY - W~)E OPEN - " EXE. A RECIRCULATING FANS baN. . .

PILOT-FLAME ESTABLL~nu~, ~ • . ~TRIAL-FOR-i~s~1ON PERIOD I~AUTOMATICALLY LIMITED

MEANS PROVIDED FOR

L--.J ~O~J~ CLO~E D [ 8HUT-OFF VALVE TIGHTNESS

~ ~ N O OD AUTOMA ALLY LIMITED . . . . ' ]O|LTEMP. ~I~s~LOCK ] p VED W. 8E~ SET J~R ~. YES "OF . [] ~NO []YES []NO ~ INT~OR LOCK

~ A ~ c~r-o~r A~rO~CALLY,- sz0~m~ ~ U A L O ~ E ~ O . TO a ~ E , O. e ~ L ~ E o~

- ~ OD!OR SCANNER LOCATION INSURES PILOT IGNITES MAIN FLAME

~7 FUEL FLA~IE " " PRESSURE [] ( ~ ' - ~ , ~ ! o n ~ e z u a r d )

MANDATORY PURGe AFTER FLAME FA/LURE

. . . . .

MAIN SAFETY SHUT-OFF VALVe |PS. . IN. " PILOT SAFETYS~ 'T , .OFeVALVE " LoS,

COMBUSTION SA FEOUARD . ~ ' ] Pk ~ ustE SWITCHES i AUTOMATIC F/RE CHECI~

ATMOSPHERE i11~ Tb~s~Lm ON INTO:.

[] HEATED WORK SECTION [] COOL~qG SECTION ,e COOLING ~ECTION, EXPLAIN HOW HAZARD AVOID~

IN.

wHmq ATMOSPHERE TURNED ON ATMOSPHERE INTERLOCKEI) WFFE FURNACE TEMPERATURE

"P" ~C~vi~sa ~nu, -s unnmu ON O~l CONTROLLER

smn.TmO o e e A ' J ~ O S p ~ [""] ms~l, oAs [ ] "BURN- [ ] NO IoNrrIoN SOURCE WmLE FmmACE • PURGE OUT" ATMOSPHERE EXPLO6/VE

IF LATTER CASE, IS CHECK FOR GAS Ro~,-~Losrvm A T ~ O S P ~ ~ [ ] ANALYZ~ [--'] S " ~ ' a Tssr [ ] ~ , ~ . v o L ~ u ]

SAMPLE w~ASI/RE t i NONE

ATMOSPHERE

EXPLOSION ~ ° I

dO ~ ~ F ~ r Y SR~UF-OFF VALVKE

~: h',...",AT,~ j.. i s ~ C l m r 8

pART A ACCgPTgD A8 8~DM~TTKJ~ [ ]

BY

V I m T I ~ T O O U ' t D 0 0 m I D r r u . Q ~ B R ~ T O R H U R l e R ST

D ' ~ FI--- ~ ' ' ~ ' D ' - - " , E) ' ~ " E3 , ' ' ' A ' ° ' " AT Gn4KRATOR

8U~C~T TO ANY ~ 1 ~ ' ~ n --v~ilr~TKD [ ] I DATr

FOR

PART B - MANUFACTURER'S INSPECTION & TEST ( ~ p t e ~ t ~

ADJ. VOR ~FABLE BURNERS ['-I UOBYIm [--~ .~r~'m~ ~, ~"~ ~/rr Mp" c°~m°L - [ ~ Low FZ.Am~

SAFETY [ ] Anaurr~ [ ] Tm'l"~ rob pnoen n~p~lQs~ CONTROLS

• 1"7"1 AppUCA'nON IFOR A ~ ' ~ - T ~ C K " ~ I~]~TKD OH ~ITI~OL PANKL :NSTRUC'nONS -1 ~ ° ~ A'"

i ~ 1 ~ K I I P -

SIGNATURES

~ART B j~-~C~VTi~ 8U~IKCT TO A r r CRAUe~J~J m u ~ T i D

BY

[ ] PRI3~TKD OP~RA'I~NG DrSTRUG'TtOI~ LEFT '

DATE

1~8 G'mJTOMKR DATB

leOR

PART C*- FIELD KX~cMINATION OF COMPLETED INSTALLATION

e~w,- ~ g, Tal

t,~

7~

2419 ~ 6 ~ 1 3 ~ INDUSTRIAL FURNACES ~ SPECIAL ATMOSPHERE

APPENDIX C.

MAINTENANCE CHECK LISTS

t. Besponsibility

An essential safety aid is an established maintenance program which insures that the equipment is in perfect working order. The equipment manufacturer

impress d up~l~ the user the need for adequate .operational checks and main- t~ance an . s. . Lssue comp!ete and clear maintenance instructions. The fina/ responsibility of estabhshing a maintenance program which insures that the equipment is in perfect working order shall rest with the user.

2 . Check The user's o~,rational ..and maintenance program shall include any listed

proce.d.ures, wmcn are appficable to.his fu.rnace and that may be recommended his insurance .under~. lter andhis eqmpment suppfier. An operational and

maintenance caeca/rot m essential to the sate operauon of the equipment.

SAFETY SHU~.TOFF.~.~.~I"I"I"I"I"I"~sBLEEO TAP (~)

GAS ~ ~ ]J[Z]5.---~TO BURNERIS) Method !

~IN. COCK .(~--~[~F" COCK ( ~ . " UsingGasSUpervisory.cock

- IN.PIPE C A P . ®

RUBBER HOS((~) ~ -" =-" ~ : r'-~h •

QUICK TEST • S ~ ' - ~ ' ~ W A T E R

SAFETY SHUT-OF_ :~ VALVE (~ ; STANDARD GAS COCK (~

~ - - ~ T O BURNER IS) Method 2 OAS-~ ' / ' " "

Using Standard ~e IN.COCK (~)__,~]...]~BLEEDTAP~ H ~

r ~ ' ~.~/LARGER) • RUBBER HOSE(~) --~".~- t - ~ i /

. ~ ~

ACCURATE TEST S E T - U ~ WATER

Fig. 16.

24x0 ' : . , MAINTENANCE CHECK LIST 86C~-13~ NOTES TO FIOURE 16

1. Main gas safety shutoff valve may be manual-opening, automatic. closing or automatic-opening, au tomat ic -c los ing , to suit the firing method used. - "

2. For b leed tap, t~-inch O.D. copper tubing, or pipe shall be used.

3. Supervisory cock shall be located downst ream as close as practical to outlet of safety shutoff valve. . .

4. S tandard gas cocks shall ~ u s e d . . , . " . . . . .

5. Bleed tal~ outlet shoulci be chpped (or plugged) except while making tightness checks of-safety shutoff valve.

6. A s tandard gas cock shall be installed downstream as close as practical to outlet of safety shutoff valve.

• 7. Lengths of rubber, hose shall be,as short as possible. , '

Test Procedure

The safety shutoff valve shall be closed and the valve indicator shall be observed to make sule it is closed.

"" Supei'visory co~k 3 (method 1 ) or s t anda ld gas Cock 6 (method 2)shal l be closed.

Pipe cap 5 shall be removed and rubber hose 7 shall be. a t tached to oudet of bleed tap 2. • . . . . . .

C ~ k it shall be o p e n e d s o as to vent any gas t rapped in p ip ingbe tween valve1 and cock 3 (method 1) or between valve 1 and cock 6 (method 2). Then outlet end of hose shall be held just beneath the surface of some Water in a sma l l contaner (tin can, bottle, e t c . ) t o observe if any bubbles appear . I f no bubbl ing occurs, safety shutof f valve may be reported "bubble t igh t . " . . . . .

I f bubbl ing occurs and continues, safety shuioff valve has leakage and should be immediately d l eaned and overhauled, or replaced. However, it may be desirable to measure accurately the leakage rate beforehand as follows: (a) a graduated glass cylinder shall be filled With water and inverted in a large container of water ; (b) end of hose shall be installed in end Of cylinder, and the a m o u n t o f time required (seconds) to displace any given number of cubic centimeters of water; (c) the valve leakage rate (cubic centimeters per second) is determined by dividing cubic cend- mdters of water displaced 'by secdnds reqlaired; (d ) if leakage rate exceeds 8.0 cc/sec. , Which • corresponds to 1.0 cu. f t /hr . , "valve should be immediately cleaned and overhauled, or replaced.

Important. At newly installed equipment , if this test discloses valve has leakage, it may indicate t ha t fuel gas piping was not properly cleaned out so as to be free of weld particles, pipe chips, etc. In such cases the pipline and valve should be cleaned out and the test repeated.

2421 ~ 1 3 4 INDUSTRIAL F U R N A C E S - - SPECIAL ATMOSPHERE

:~ A. Maintenance of Gas Equipment

I General. Th.ese recommendations are prepared for maintenance of gas ~,uipment. SpeclaJ types of equipment command special attention. A preven~ ~ . maintenance program should be established and followed. This program ,~0"~d include adherence to manufacturer's recommendations. In this program "-~;, imum maintenance schedule should include inspection and action on the a,,c"~'mmendatioos given in the following paragraphs An adequate supply of repair parts should be maintained.

2 Burners and Pilots. Burners and pilots should be kept clean and in proper 0~erating condition. Burner refractory parts should be examined at frequent ~mlar intervals to assure good condition.

3. Flame Safeguard Equipment. When automatic flame safeguards are used, a complete shut-down and restart should be made at frequent intervals to check the components for proper operation.

4. Other Safeguard Equipment. Accessory safeguard equipment, such as manual reset valves with pressure Or vacuum switches, high temperature limit switches, draft controls, shut-off valves, air flow switches, door switches and gas valves, should be operated at frequent regular intervals to insure proper functioning. If inoperative, they should be repaired o r replaced promptly.

When fire checks are installed in air-gas .mixture piping to prevent flashbacks from traveling further upstream, the pressure, loss across the fire checks should be measured at regular intervals. Whefi excessive pressure loss is found, screens should be removed .and cleaned. Water type backfire checks should be inspected at frequent regular intervals and liquid level maintained.

All safety shutoff valves should b e checked for leakage and proper operation at frequent regular intervals. Two procedures for making these tests are outlined in Fig. 26.

5. Auxiliary Devices. A necessary part of the gas equipment maintenance should be the proper maintenance of auxiliary devices. Maintenance instructions as supplied by the manufacturers of these devices should be followed. Gas combustiofi equipment, including blowers, mechanical mixers, control valves, temperature control instruments, air valves, and air filters, should be kept clean and should be examined, at frequent regular intervals. Necessary repairs and replacements should be made promptly.

6. Regulators and Zero Governors. Regulator and zero governor vents and impulse or control piping and tubing should be kept clear. Regulator valves which operate improperly should be cleaned, repaired, or replaced promptly.

7. Piping. ~A necessary part of the gas equipment maintenance should be the p.ro.per maintenance of the gas piping system. It is recommended that gas piping be inspected and tested for leakage at regular intervals in accordance with provisions of 4.21.6 of NFPA No. 54A. Air piping should be kept in- ternally clean to prevent accumulation of dust, lint, and grease in air jets and

valves. Where conditions warrant, filters should be installed at the intake to the fans.

8. Standby or Substitute Fuels Systems. Standby or substitute fuel equipment and systems for gas equipment should be kept in good operating condition and tested periodically.

2422 ~ , A , , ~ . N A , , ~ 01t'Z.0K L I S T 8 6 ~ 1 ~ ~

B . M a i n t e n a n c e o f Electric Furnaces and E q u i p m e n t

L Genera l . A program of regular inspection and maintenance of electric furnaces is essential to the safe operatton o f that eqmpment. _KbueC~e~nfida,~0m of the manufacturer should be rigorously touowea ana a zlong .u~uD. ~ furnace life will result. Suitable spare parts should be stocgea to msure rePtacemeat dluickiy as needed.

2. Hea t ing Elements. The h.eadn, g elements, should.be, ins p~ut.~ a t _regular intervals and any foreign con tammauon removea- KeP alr ls ~ecom_U ~_emeatB are dislodged or distorted to tOUCh aimy near ms of_~mmactt.~2 ~ . n ~ ,9 tha t grounding or shortua, g can occur. J~.e.mem termm- .,~ ,u_u~(da~o._-~_ ~ . y checked and tightened since loose connecuons cause arcing anu u~ u Wmcll Can result in burnout of the terminal.

q I - su la t lon a n d Refractory Materials . Furnace linings re.quire attention • ~'. " - - - : -- - ~ - ~ - t - e r e s are used to be sure that excesstve caroon has

W ~ t ~ l ' l p r o t e c U V U i £ 1 . u l ~ l J u . . . . . .

not been deposited. Ground~g or shorUng ot th,~_ee_mmentsCanenOCCr~raeUm~ recommended burnout proceaures are tOllOWea. ~ritts]gcu ua u . u : .~,,,~t.vory element supports must be replaced as required.

4, Thermocouples . A regular replacement program should i~e, est.ablished for all control and safety thermocouples. Effecuve life of thermocouples varies depending on the environment and temperature and these factors must be considered in setting up a replacement schedule.

5 . A tmosphere Furnaces. Many electric" furnaces use specially prepared atmospheres and they may be either inert or combustible depending on the application. Safety devices are provided to prevent introduction of combustible atmospheres unless the furnace is,at sui.table temperature or has be. en properly nurtr "th an inert gas Protecuve oevmes mcmae pressure switches, sate~ r__oed wl . _ ., . shutoff,valves, mterlocks solenmd valves and these components snoma ~e tested on a once a week schedule by instituting a failure which would demon- strate correct functioning of the system. Safety shutoff valves should be checked for leakage. The same maintenance p/ incipl~ apply in the case of atmosphere gases of the flammable type as appty xor reel nreo turnaces. - , ' "

6." Auxiliary a n d Control Devices. Contactors require periodic checking of contacts and replacement when pitting due to arcing could result in welding of the contacts and uncontrolled application of pow6r to the furnace. All con. trol components including pyrometers and relays require periodic checking to

~ . i O L U N O l O LOW GAS • V LYE PIl lUUUU|

A RWITOH

PREUSURE OpEI~AYIUNAI. • ' PRESSUUII

8W|VGR VALVE REGULA'rOII p~us /

• " " COCK ~ •

• A'lrldo UPHIIBI~ " . . ' / tartly sauT-orr f~ ~ suPnz

REou,,,oR "~ r" l /~ ~ , . . . , , . , E . . o . . . , "

¢0¢K " / - ' L o w AIR ¢OMSURTION

SWIYGH .

GAS SUPPLY ~ $AF[Ty SHUT-OF~ yALV[S INy~RR~P?~D PILOT • ' ' t . , • .

Fig. 17. Typical double safety shutoff valve and vent arrangement.

2423 86~136 INDUSTRIAL FURNACES - - SPECIAL ATMOSPHRE

a.cure proper operation or control accuracy. Instructions provided by the ~aanufacturer of each control component should be followed v, ath care.

7. Voltage. T h e voltage supplied to electric furnaces must be maintained ~thin reasonable l imits to insure against overloading of control devices and wando.rmers. Under voltage can result in operational failure of relays and solenoid valves.

8. Water Cooling. If components are water cooled it is important to fre- quendy check the flow and temperature of the cooling water.

9. Inter locks. Periodic checks of all safety interlocks are essential. High frequency generators must have functioning door interlocks to prevent operators entering the enclosure'with any power on and these safety devices must be checked frequently.

C. Suggested.Operational and Maintenance Check List

I. Continuous Check List '

(a) Check for proper inlet air-gas ratios.

Cv) Check atmosphere gas for proper flow and pressure.

(c) Check for proper operating temperatures. •

(d) Check sight drains o r gages, or both , for proper water flow and water temperature.

(e) Check combustion chamber visually to make sure it" is incandescent.

(f) Check pilots or spark plugs, o r both, for proper, main burner ignition.

(g) Check burners for proper ignition and combustion characteristics.

(h) Make sm:e atmospheric burners or pilots, o r both, are protected from improper drafts.

(i) Check for proper operation of ventilating equipment.

(j) Cheek control' and auxiliary equipment for abnormal temperatures.

, 2. Regular Shift Check List

(a) Take necessary gas analyses; if automatic gas analyzers are used make sure the manual and automatic readings coincide. Recalibrate automatic gas analyzers.

(b) Standardize or balance instruments.

(c) Check valve motors and control valves or dampers for free, smooth action and adjustment.

(d) Check hand valves, manual dampers, secondary air openings or adjustable bypa~es, or both, for proper positions.

(e) Check all pressure switches for proper pressure settings.

(f) Check blowers, compressors and pumps, for unusual bearing noise a n d shaft vibration; if V-belt driven, check belt tension and be l t fatigue.

3. WeeHy Check List ' "

(a) Make sure flame-sensing devices are in good condition, properly located, and,free of foreign deposits. -.

2424 MAINTENANCE CHECK LIST 86C-137 (b) Test thermocouples and lead wire for shorts and loose conncctio~

Check the protection tubes for cracks and proper immersion. (c) Check setting and operation of low temperature limit:device.

• (d) Test visible or audible alarm systems, or both,, for proper signals.

(e) Check ignition spark'electrodes and check proper gap.

4. Month ly Check List (a) Test interlock sequence Of all .safety equiisment. ManuallYimake each__

interlock fail., noting that related eqmpment closes or stops as spec fled by the manufacturer.

Co) Test main gas hand valves and safety shutoff valves f'or tightness 0f closure.

(c) Test pressure switch-settings by checking switch movements agai~t pressure settings and comparing with actual impulse pressure.

(d) Inspect all electrical switches and contacts; dean if necessary.

(e) Test all amplifier and thermocouple ffiil-safe devices, making, certah that the instrument drives in the proper direction.

(f) Glean the air blower filter. (g) Glean water, gas compressor and pump strainers. (h) Clean fire check screens and valve seats, and test for nreedom of valve

movement. ~ • (i) Inspect burners and pilots;clean ff necessary. '~:

(j) Check ignition cable and transformers. (k) Check all orifice plates, mr-gas mixers, flow indicators, meters, gageg

and pressure indicators; and clean or repair, if necessary.

O) Test automatic or manual turn-down equipment.

(m) Test pressure relief valves; clean if necessa/y. " : " (n) Inspect air, water, fuel gas, atmosphere gas, reaction gas, and impulse

piping for leaks. J

5. Periodic C h e c k L i s t The frequency of maintenance o f t h e following will depend on the recom.

mendations of the equipment.manufacturer: (a) Inspect the retort tubes, brick, coolers, refrigerators, driers, and other

accessories and repair if necessary. . ~ (b) Lubricate the instrumentation, valve motors, valves, blowers, com-

pressors, pumps, and other components. ' . • "'(c) Test instrumentation, clean slidewires, check amplifier tubes and battery.

• . . . :

(d) Test flame safeguard units.

(e) Burn out carbon in reaction tubes. • , - •

(f) Clean humidifiers. . . . . . . (g) G~ncck for plugging of hot pipes, tube bundles and jacketed pipes.

2 4 2 5 ~ 6 ~ 3 8 INDUSTRIAL FURNACES - - SPECIAL ATMOSPHRE

APPENDIX D .

MAIN DISCONNECT TO PowER SUPPLY SYSTEM

Manual switches, powered (electrical opening, manual closing) switches, ,lastic case circuit breakers, and steel case circuit'breakers are "among the ~eviccs used to provtde the "mare dmconnect" function. The use of switches will require the proper selection of fuses to handle the normal equipment load current, some .short term. ove.rcurrent for starting motors and .an interrupting capacity s..umcmnt,to e.xungulsn an arc as may be caused by a short, circuit fatflt, rqauonat r.aectrmai Lame requirements for Class " H " fuses should be followed for current ratings up to 600 amperes and for Class " L " fuses above 600 amperes. Typical current ratings and interrupting capacities for 600-volt class fuses and circuit breakers are as follows: .

Identification.- ,. ~ T~r~e Name

plastic Case Breakers* !- ¢ ,

A. Std. Industrial Duty. 70--2,500 I~ High Interrupting Capacity with

CMrrent Limiting F/Jses " , 100-1,600

Steel Case • : Air Circuit Breakers 100-4,000

Typical Current Limiting - - Tim~ Delay - - Fuses

Fusctron .1- 600

Low Peak I - 600

Limitron 600-6,000

~ . C a p ,'" 600-6,000

High Interrupting Capacity - - Pressure Switches

Manually and Electrically Operated Types 800-4,000

Symmetrird Current Carrying Interrupting Capacity-Amperes Capacity-RMS

22~000 to 65,000

200,000

• 14,000 to 85,000

100,000

200,000

200,000

200,000

200,000

The above symmetrical interrupting capacities may be increased by a factor of 1.3 when equipment is operated at 480 volts, or for asymmetric fault currents at 600 volts.

*Available with numerous optional features for furnace protection from ground faults~ short-circult faults, over-temperature, single/or multiple phase power failure.

For proper selection of "main disconnect" equipment it is necessary to know: (a) The full load-operating current and voltage of the equipment to be

served.

(b) The impedance of the furnace power supply system including its tram- former.

2426 APPENDIX E 86Cc'1..~

APPENDIX E.

ATMOSPHERE GENERATOR OPERATIONAL AND MAINTENANCE CHECK LIST

E1 Continuous Check List 1. Check for proper inlet air-gas "ratios. 2. Check atmosphere gas for proper flowand pressure.

3. Check for proper operating temperatures.~ 4. Check sight drains or gages, or both, for proper water flow and water

temperature. = 5. Check combustion chamb~er visually to make sure it is incandescent.

6. Check pilots or spark plugs, or both, for proper main burner ignition.

7. Check burners for proper ignition and combustion characteristics. 8. Make sure atmospheric burners or pilots, or both, are protected fr0~

improper drafts, 9. Determine proper disposal of unwanted atmosphere gases.

a. Check proper ignition of flammable atmosphere gas. . b . Make sure area contains less than 0.01 percent carton m/~noxide (CO).

10. Check for proper operation of ventilating equipment. 11. Check control and auxiliary equipment for abnormal temperatures.

E2 Regular Shift Check L'~t ~ . • • 1 Take nece - gas anai ses; if autom c the manu~ai and automatic reactmgs comcme. ~ , ~ o- analyzers. . '" 2. Standardize or balance instruments. 3. Check valve motors and control valves or dampers for frec,-smooth action

and adjustment. 4. Check hand valves, manual dampers, secondary air openings or adjustable bypasses, or both, for proper positions. 5. Check all pressure switches for proper pressure settings. : 6. Check blowers, compressors and pumps, for unusual bearing noise and shaft vibration; if V-belt driven, check belt tensio n and belt fatigue.

7. Check for damaged explosion heads.

E3 Weekly Check List 1. Make sure flame sensing ddviCes are in good C °ndition properly located, and free of foreign deposits, 2. Test thermocouples and lead wire for shorts and loose connections. Ched

• the protection tubes for cracks'and proper immersion. 3. Check setting and operation of Reaction Gas low-temperature limit devic~

4. Test visible or audible alarm s~tems, or both, for proper signals.

5. Check ignition spark electrodes and check proper gap.

2427 ~ 1140 INDUSTRIAL FURNACES - - SPECIAL ATMOSPHERE

~4 Monthly Check List

! Test interlock sequence of all safety equipment. Manually make each inter- 10c.k fail, noting that related equipment closes or stops as specified by the ~anufacturer.

2. Test main gas hand valves and safety shut-off valves for tightness of closure.

3 Test pressure switch settings by checking switch movements against pressure ~ttings and comparing with actual impulse pressure.

4. Inspect all electrical, switches and contacts; clean if necessary.

5 Test all an~plifier and thermocouple fail-safe devices, making certain that ~e instrument drives in the proper direction. 6. Clean the air blower flter.

7. Clean water, gas compressor and pump strainers.

8. Clean firecbeck screens and valve seats, and test for freedom of valve ~ovement.

9. Inspect burners and pilots; clean if necessary.

10. Check ignition cable and transformers.

II. Check all orifice plates, air-gas rnixers,'flow indicators, meters, gages, and pre~ure indicators; and clean or repair, if necessary.

12. Test automatic or manual turndown equipment.

13. Test pressure relief va lve; c!ean if.necessary.

14. Inspect air, water, fuel gas, atmosphere gas, reaction gas, and impulse piping for leaks.

E5 Periodic Check List

The frequency of maintenance of the following will depend on the recommendations of the equipment manufacturer:

I. Inspect the retort tubes, brick, coolers, refrigerators, dryers, and other accessories and repair ff necessary.

2. Lubricate the instrumentation, valve motors, val~,es, blowers, compressors, pumps, and other components:

3. Test instrumentation, clean slidewircs, check amplifier tubes and battery. 4, Test flame safeguard units. . . "

5. Burn out carbon in reaction tubes. 6. Clean humidifiers.

7. Check for plugging of llOt pipes, tube bundles and jacketed pipes.

2428 86C-141 ,, APPENDIX F, :

APi'ESnlX V.

Gas Combustion Safeguards - - Combustible Gas Analyzer T y p e for Manual ly Lighted Burner's

This equipment is intended for use on large manually' iighted, gas-fired in. dustrial heating equipment such as heat treating furnaces. I t is designed to sample continuously the gaseous products of combustion and to indicate and record percent combustibles and percent oxygen (optional) present in the sampled gases. I t is important that sample point(s) be located so that the sample to the gas analyzer accurately represents the total flue gas or atmosphere passing that particular section and to respond to gas concentration changea at the burners as promptly as possible. Temperatures at the sampling POint should not exceed 1200 F. ,

The "percent combustibles" indicat ion may be considered the safety con. trol function of the equipment. During a firing cycle, a dan.gero.us condition may result, for example, from a deficiency of air; however, such a clrcurnstance normally would cause a gradual increase in the amount of combustibles in the products of incomplete combustion. The equipment is designed to provide an automatic warning signal at 1 percent and a danger signal at 2 percent combustibles. Provision is made fc>r shutting off the fuel supply at the 2 percent point. (The 2 percent value is well below the danger level regardless of the type fuel gas.) Similarly, this equipment may be used to detect a.dangerous internal atmosphere at the time of burner light-off.

The "percent oxygen" indication, when employed, is intended t o provide the operator with information on which to judge the efficiency of combustion. No automatic signal indication is required for the oxygen .an~ysis. ,

This equipment usually consists o f a Sampling System, Analyzer and Re- corder. I t is not instantaneous in response to composition changes of the monitored gases. From the pick-up point, the sample gas travels through tubing which may be 25 feet long. After reaching the actual analyzing equipmen~ the gas is passed through a catalytic combustion chamber. A change in gas composition causes a change in electrical characteristics of a Wheatst0ne bridge circuit which is automatically compensated by mechanical movem.ont of a slide wire resistor. This motion not only results in a continuous rccommg of conditions but also results in snap switch actuatiofi for signaling purposes if the specified 1 and 2 percent limits are reached. I t is recognized that this series of operations involves a time delay which may be in the order of 10-20 seconds depending somewhat on the concentration of combustibles in the sampl~ However, because unsafe combustion is usually the result of gradual changa in conditions, the speed of response in a well engineered system can be sufficiently fast, and with sufficient safety factor to warn of danger except for a sudden 10~ of flame. The good judgment of well-trained operators Is a necessary elemenh especially while the combustion chamber is heating up.

In order to derive the full benefits of the equipment, each application must be individually engineered and inspected by the manufacturer of the device or an authorized representative. It is expected that such engineering will als0 require the cooperation of the manufacturer of the associated gas firing equip- meat.

2228 - national fire protection association · 2228_ report of committee on ovens and furnaces...

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