ventilation fumehood

8/3/2019 Ventilation FumeHood

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How To

Select The

Right

LaboratoryHood System


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Foreword

This booklet has been developed to serve as an aid inselecting a laboratory fume hood ventilation system.

The information is intended to be unbiased andgeneric in nature, compiled with help from experi-enced architects, laboratory consultants, engineersand laboratory hood users.The basic understandingof hood systems you gain from reviewing this book-let should prove valuable to you as you discuss yourneeds with safety officers, engineers and hoodmanufacturers.

Our Method

The table of contents outlines the various issues thatare addressed in this booklet. As you read throughthe material, remember you are selecting a labora-tory hood system. A fume hood does not functionalone.A variety of factors external to a hood influ-ences its performance. Likewise, a hood and theapplications performed inside it can also affect itssurroundings. When selecting a fume hood, youmust consider the whole picture the laboratoryspace, the buildings ventilation system, the hoods

location in the room, to name a few.While this booklet will raise the questions neces-

sary to identify your specific hood requirements, itmay not answer those questions. Only you, yoursafety officer or industrial hygienist, and a qualifieddesign consultant can identify your laboratorysunique challenges.

We want this document to expand and improveover time. If you have suggestions for additions orimprovements to this guide, please write LabconcoCorporation, 8811 Prospect Avenue, Kansas City,MO 64132. Call 800-821-5525 or 816-333-8811. Ore-mail [email protected].

Table of Contents

Selecting The Proper EnclosureWhat is a Laboratory Fume Hood? 3

Laboratory Exhaust Systems and

Types of Laboratory HoodsConstant Air Volume (CAV)Conventional, 3

By-Pass, High Performance, Auxiliary-Air,Reduced Air Volume (RAV)

Variable Air Volume (VAV) 5

Special Application Laboratory fume HoodsPerchloric Acid Hoods 5Radioisotope Hoods 6Distillation and Floor-Mounted Hoods 6

Not All Enclosures are Laboratory Fume HoodsDuctless Carbon-Filtered Enclosures 6Canopy Hoods 7

Downdraft Hoods 7Biological Safety Cabinets and Other 7

HEPA-Filtered EnsclosuresClean Benches 8Glove Boxes 8

Laboratory Hood SpecificationsHood Size 9Liner Material 9Sashes 10Explosion-Proof vs. Non Explosion-Proof Hoods 10Lighting 10Service Fixtures 11Electrical Receptacles 11Americans with Disabilities Act Requirements 11Hand-Operated, Positive 12

Energy Control (HOPEC IV)Performance and Installation Considerations

Face Velocity and Containment Issues 12Proper Techniques for Hood Use 13

Ventilation System Components and AccessoriesRemote Blowers 13Blower Sizing 14Air Volume 14Static Pressure Loss 14Integral Motor/Blowers 14

Airflow Monitors 15Exhaust Air Treatment 15Ductwork 16Base Cabinets 16Work Surfaces 16By-Pass Blocks 17Sash Stops 17Sash Position Alarms 17Fire Extinguishers 17

Renovating Existing LaboratoryFume Hoods and Ductwork 17

Planning Laboratory Space

Laboratory Layout 17Sufficient Room Air 18Energy Conservation 18Noise Control 18

Conclusion 18

Laboratory Safety Standards 19

General References 21

Glossary 22

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Selecting The Proper Enclosure

What is a Laboratory Fume Hood?

A laboratory fume hood is a ventilated enclosurewhere harmful or toxic fumes or vapors can be han-dled safely. The purpose of the hood is to capture,contain and remove contaminants, preventing theirescape into the laboratory. This is accomplished bydrawing contaminants within the hoods work areaaway from the operator, so that inhalation and con-tact are minimized.

Airflow into the hood is achieved by an exhaustblower that pulls air from the laboratory room intoand through the hood and exhaust system. Thispull at the opening of the hood is measured as facevelocity. A baffle, air foil and other aerodynamicallydesigned components control the pattern of airmoving into and through the hood. Contaminatedair within the hood is then diluted with room airand exhausted through the hoods duct system to theoutside where it can be adequately dispersed at anacceptably low concentration.

Laboratory Exhaust Systems andTypes of Laboratory Hoods

All laboratory fume hoodsoperational airflow canbe described as one of two types: conventional andby-pass.Conventional hoods were developed firstand have been, for the most part, replaced withby-pass hoods, which have superior performance

features.High performance, reduced air volume andauxiliary-air hoods are variations of the by-passhood. High performance, auxiliary-air and reducedair volume hoods are variations of the by-pass hood.

Hoods use one of two kinds of exhaust systems:constant air volume or variable air volume.

Constant Air Volume (CAV)

Conventional

The conventional hood is a basic enclosure with aninterior baffle, movable front sash but no air foil.The conventional hood generally operates at a con-stant exhaust volume with all of the exhaust airentering the hood through the sash opening.Closing the sash increases the speed of the airthrough the sash opening so that high face velocitiesare to be expected with the sash in the nearly closedposition (Figure 1).

The conventional hoods performance dependslargely on sash position. With the sash in the nearclosed position, high velocity air passing through thesash opening can damage fragile apparatus, disturbinstrumentation, slow distillation rates, cool hotplates, disperse valuable sample materials or result inturbulence inside the hood.

By-Pass

The by-pass hood generally operates at a constantvolume and is designed so that as the sash is closed,the air entering the hood is redistributed, therebyminimizing the high velocity air streams encoun-tered in conventional hoods. The by-pass openingsabove the sash and below the air foil reduce fluctua-

tions in face velocity as the sash is raised or lowered(Figure 2). Therefore, the face velocity in by-passhoods does not generally reach levels that might bedetrimental to procedures. By-pass type hoods com-prise the majority of hoods in the market.

3

Left to right: ProtectorClassmateLaboratory Fume Hood on

Protector Storage Cabinets, ProtectorPremierLaboratoryHood on Protector Storage Cabinet and ProtectorXStream

Laboratory Fume Hood on Protector Storage Cabinets

Figure 1. Conventional hood with sash open and nearly closed

ExhaustExhaust

RoomAir

RoomAir


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High PerformanceA variation of the by-pass hood, the high perfor-mance hood is the newest generation of fume hoodsthat rely on containment-enhancing features thatmaintain safety while saving energy. These designfeatures,which vary by manufacturer, include sashstops or horizontal-sliding sashes to restrict the sashopening; sash position and airflow sensors that con-trol the opening and closing of mechanical rear baf-fles; small fans to introduce air that operates as abarrier in the operators breathing zone; or a combi-

nation of aerodynamic and anti-turbulence elementssuch as a dual baffle system with a pattern of vari-able-sized slots to provide laminar flow through thehood. (Figure 3). Sometimes called low flowhoods, these hoodsimproved containment allows

them to operate at face velocities as low as 60 feet perminute (fpm), thus conserving energy and providingan alternative to auxiliary-air hoods in air-starvedlaboratories, where room supply air is not adequate.

Due to their increased level of sophistication, theinitial cost of high performance hoods is slightlyhigher than traditional by-pass hoods. However, theenergy savings realized from operating these hoods

at 60 fpm instead of 100 fpm can average more than$2000 per year, depending on hood size and sashopening.

Auxiliary-Air

A variation of the by-pass hood, the auxiliary-airhood offers a means of providing up to 50% of theair for the hood exhaust from outside the laboratory,and limits the volume of tempered air removed from

the laboratory (Figure 4). This hood type hasmany names including induced air, add-air andmake-up air.

Auxiliary-air hoods were designed for air-starvedlaboratories and energy savings. When properlyapplied, they can provide energy savings by limitingthe volume of heated or cooled room air exhaustedby the hood. The level of savings depends on thedegree to which the auxiliary air must be tempered.

Certain negative aspects of auxiliary-air hoods

should be considered. Because two blowers and twoduct runs are required, initial equipment and set-upcosts are higher than average. Since an oversized aux-iliary-air system may overpower the exhaust system,auxiliary-air systems require careful balancing toprevent undesirable turbulence at the face of thehood. In addition, temperature extremes, caused byuntempered auxiliary air, can adversely affect thehoods containment ability and cause user discom-fort. Finally, the auxiliary air should be clean, dryand tempered properly so it does not interfere with

analytical work being done in the hood.

Reduced Air Volume (RAV)

A variation of the by-pass hood, the RAV hood usesa by-pass block to partially obstruct the by-passopening above the sash to reduce the air volumeexhausted thus conserving energy. It is used in

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Figure 3. Protector XStream high performance by-passairflow design

Upper By-PassOpening

Upper DilutionAir Supply

Front Sash

Containment-Enhancing

Sash Handle

Ergonomic Air Foilwith Clean-Sweep

Openings

Lower By-PassOpening

ExhaustExhaust

RoomAir

By-PassOpening

RoomAir

Figure 2. By-pass hood with sash open and closed

By-PassOpening

ExhaustExhaust

RoomAir

AuxiliaryOutside

Air

AuxiliaryOutside

Air

RoomAir

Figure 4. Auxiliary-air hood with sash open and closed


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conjunction with a sash stop that limits the height-the sash may be opened during normal use so thatthe hood demands less air volume to achieve safevelocity (Figure 5). Since these hoods use less air vol-ume than by-pass hoods of the same size, theyrequire smaller blowers, which can be another costsaving advantage.

RAV hoods should be used with caution. Thesash stop should be overridden only when loadingor cleaning the hood; never while in use. If the sashstop is disengaged and the sash raised while the hoodis in use, the face velocity could drop to an unsafelevel.An airflow monitor is recommended.

Variable Air Volume (VAV)

Variable air volume (VAV) hoods vary the amountof room air exhausted while maintaining the facevelocity at a preset level.VAV hoods alter the exhaustvolume using various methods. One method utilizesa damper that opens and closes based on airflow andsash position. Another method involves varyingblower speed to meet air volume demands. When

multiple hoods share one common exhaust blower,both methods may be utilized.

Fume hoods with VAV systems generally includea modified by-pass system with by-pass block thatensures that sufficient airflow is maintained toadequately contain and dilute fumes even at low sash

positions (Figure 6).VAV hoods have electronics that allow them to beconnected to the laboratory buildings heating, venti-lation and air conditioning (HVAC) system for mon-itoring hood exhaust air and controlling laboratoryair supply from a central location.

Although initial start up costs may be higher dueto building alterations, VAV hoods can offer energysavings over traditional constant volume hoods. Atthe same time, they offer consistent airflow regard-less of sash position. In addition, most VAV systemsfeature monitors/alarms that alert the operator tounsafe airflow conditions.

Special ApplicationLaboratory Fume Hoods

Some hood exhaust systems accommodate specialprocedures. Below are descriptions of a few of themany special purpose hoods on the market.

Perchloric Acid Hoods

Perchloric acid hoods are dedicated for use with per-chloric acid only. Organic materials should not beused in a perchloric acid hood because an explosionmay occur when perchloric acid reacts with organicmaterials.Industrial Ventilation: A Manual of

Recommended Practice states that these hoods beconstructed of nonreactive, acid resistant and rela-tively impervious materi-als such as Type 316stainless steel, Type 1unplasticized polyvinylchloride (PVC) or inor-ganic ceramic-coatedmaterial. Hoods used forthese applications haveintegral work sur-faces, radiused interi-ors, and a drain foreasy and thoroughcleaning.Washdownfeatures arerequired since

the hood andduct systemmust be thor-oughly rinsedafter each use toprevent theaccumulation of

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ExhaustExhaust

RoomAir

By-PassBlock

RoomAir

SashStop

By-PassBlock

Figure 5. Reduced air volume hood with sash stop and by-pass

block shown with sash open to sash stop position and sash closed

ExhaustExhaustDamper

RoomAir

By-PassOpening

RoomAir

By-PassBlock

By-PassBlock

By-PassOpening

Figure 6. Variable air volume hood with damper control andmodified by-pass

Damper

By-PassOpening

By-PassOpening

Figure 7. Perchloricacid hood withwashdown system


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potentially reactive perchloric salts. (Figure 7).Horizontal duct runs and sharp turns should beavoided so that washdown residue drains thorough-ly. Each perchloric acid hood requires its own dedi-

cated exhaust system with washdown capability.Radioisotope Hoods

Hoods used for radioactive applications feature inte-gral work surfaces and radiused interiors to facilitatedecontamination. Liner materials, such as Type 304stainless steel, should be impermeable to radioactivematerials. Cupsinks are sometimes provided in theintegral work surface, however local codes that dic-tate the safe disposal of radioactive effluents shouldbe observed. These hoods should be sturdy enough

to support lead shielding bricks in instances wherethey are required. They should also be installed tofacilitate the use of high efficiency particulate air(HEPA) or carbon filters in the ductwork. The labo-ratorys safety officer should determine which, if any,filters are required to trap the radioactive materialsemitted during a particular application.

Distillation and Floor-Mounted Hoods

Distillation and floor-mounted hoods are construct-ed with additional interior height and depth to

accommodate large apparatus. Distillation hoods

typically mount on a platform instead of a base cabi-net or bench. A California hood is a type of distilla-tion hood with sash entry on both sides (Figure 8).Floor-mounted hoods permit roll-in loading ofheavy or bulk apparatus. Although formerly knownwalk-in hoods, the operator should never standinside a floor-mounted hood while fumes are beinggenerated.

Not All Enclosures AreLaboratory Fume Hoods

There are many enclosures designed to protect theoperator from exposure to potentially hazardoussubstances. Other enclosures function to protect thesamples contained inside. Although in some

instances they may look similar to fume hoods, thesecontainment devices have different modes of opera-tion and different uses.

Ductless Carbon-Filtered Enclosures

As the name implies, ductless enclosures are not con-nected to an exhaust system. They rely on filters totrap vapors and fumes before air is recirculated tothe room. The filters are usually made of speciallytreated or activated carbon media that treat oradsorb chemical fumes including certain organic sol-

vents, ammonia, acids and formaldehyde. Filter typesand capacities can vary widely between manufactur-ers. Since these enclosures recirculate filtered air backinto the laboratory, they often have a built-in mecha-nism to alert the user to unsafe concentrations ofchemicals detected in the exhaust area of the filters.

Filtered enclosures can provide a practical solu-tion for laboratories where ducting may not be feasi-ble. Since they are portable, they may be sharedamong laboratories and stored out of the way whennot in use. Since they do not require ducting, they

can be placed on adjustable height base stands andeasily lowered for use by wheelchair-bound individu-als. Due to the cost of replacing saturated filters,these enclosures are recommended for applicationsinvolving only small quantities of chemicals. Sincedifferent filters may be required for different chemi-

6

ProtectorXL Floor-Mounted Laboratory Fume Hood

Figure 7. California hood with front and back sashes


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cals, the enclosures are generally restricted to repeti-tive applications and procedures involving a limitednumber of chemicals. Carbon-filtered enclosures arenot recommended for highly toxic or carcinogenic

materials. Careful and regular monitoring by a safetyofficer is essential to the safe operation of theseenclosures.

Canopy Hoods

Canopy hoods are designed to remove steam, heat orodors from large or bulky apparatus such as ovens,steam baths or autoclaves.Vapor removal is most

efficient when the canopy is mounted no more than12above the equipment being ventilated. Because itis inefficient and ineffective in containing fumes, thecanopy hood is not recommended for ventilatinghazardous substances.

Downdraft Hoods

Like fume hoods, downdraft hoods draw air into theface of the hood. Unlike fume hoods, the blower isusually mounted below the hood work area so that

air is pulled down through a mesh work surface andthen exhausted to the outside (Figure 9). Downdrafthoods are used for applications involving heavierthan air gases and materials such as dusts and pow-ders. In some cases, these materials are recovered forreuse.

Biological Safety Cabinets and OtherHEPA-Filtered Enclosures

Although often referred to as hoods, Class II bio-logical safety cabinets are not fume hoods. Biologicalsafety cabinets are designed to contain hazardousparticulates such as bacteria and viruses and oftenrecirculate cabinet air back to the laboratory.Biological safety cabinets use HEPA filters to trapparticles while any gaseous materials pass throughfreely. When exhausted to the outside, they canaccommodate trace amounts of toxic chemicals and

radionuclides. If the work involves infectious or car-cinogenic agents and personnel and product protec-tion are required, then a biological safety cabinet isprobably the enclosure of choice. Other HEPA-fil-tered enclosures, including Class I enclosures thatprovide only personnel protection, are designed forapplications including weighing powders or handling

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Protector360 Filtered Enclosure on Mobile Base Stand

Canopy Hood

Figure 9.A downdraft hood designed forremoving powders generated by grindingmetals or plastics


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asbestos. For an in-depth discussion on HEPA-fil-tered enclosures including Class II safety cabinetsand Class I enclosures, request the publication,Personnel and Product Protection: A Guide to

Biosafety Enclosures, by calling 800-821-5525 or816-333-8811 or downloading it fromwww.labconco.com.

Clean Benches

Clean benches are devices that use a blower to forceroom air through a HEPA filter, and over a work sur-

face. This vertical or horizontal laminar flow of fil-

tered air protects the work from particulate contami-nation. The major limitation of clean benches is thatthey provide only product protection; the operator isconstantly exposed to any aerosols generated by the

work being performed. Consequently, hazardousmaterials should never be handled in a clean bench.Clean benches were developed as part of cleanroom technology and are widely used in the elec-tronics and pharmaceutical industries. They havealso been successfully used in research laboratoriesfor tissue culture and media preparation, and in hos-pitals and pharmacies for drug preparation.

Glove Boxes

Glove boxes consist of a sealed chamber with glove

ports and gloves for handling materials inside, aviewing window for observing, and transfer chamberor door for loading and unloading. Because theyprovide a physical barrier between the operator andthe substances inside, glove boxes are appropriate forapplications that require the greatest protectionagainst inhalation of substances used within them.Glove boxes for hazardous materials such as low levelradioisotopes and carcinogens filter the chamber air

prior to exhausting it through a duct system to theoutside. Other glove boxes used for containingatmosphere-sensitive materials may or may not be

ducted to the outside.

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PurifierDeltaSeries Class II, Type A2 Biological SafetyCabinet on Telescoping Base Stand

PurifierHorizontal Clean Bench on TelescopingBase Stand

ProtectorStainless Steel Controlled AtmosphereGlove Box on Mobile Base Stand


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Laboratory Hood Specifications

Hood Size

The working space inside a laboratory hood is

defined as that part of the hood interior where appa-ratus is set up and vapors are generated. This spacenormally extends from behind the plane of thesash(es) to the face of the baffle, and up from thework surface 34" to 48". The working space requireddetermines the width of the hood needed. OSHA 29CFR-1910 recommends laboratories provide an aver-age of 2.5 linear feet of hood space per person.

Laboratory hood sizes are commonly expressed

by the outside width and not by working space. Themost common hood widths are 3, 4, 5, 6 and 8 feet.Custom designed fume hoods may have widths upto 24 feet. The actual working space is approximately

5" to 12" less than the expressed exterior width ofthe hood.

Liner Material

The liner material selected should be durable andresist chemicals, heat and open flame. A descriptionof common liner materials and their characteristicsis shown (Table 1). The best liner material for a hoodshould be determined by the applications, types and

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Liner Stain Moisture Chemical Heat Flame OtherMaterial Resistance Resistance Resistance Resistance Spread Index* Comments

Epoxy-coated Good Very good Good Very good 5 Care must be takensteel to avoid damaging

coating since corrosionmay occur in damagedareas. Inexpensive.

Epoxy resin Good Excellent Excellent Very good ** Not easily modified.Brittle, requires carein handling. Expensive.

Molded Good Excellent Excellent Very good 25 Excellent light reflectiveFiberglass properties.Moldablereinforced to eliminate seams andpolyester crevices. Easily

(FRP) modified. Moderatelyexpensive.

Fiberglass Good Excellent Excellent Very good 25 Good sound-dampeningreinforced qualities. Heavy.composite Inexpensive. Easilypanel modified.

Glass Fair Fair Very good Excellent 0 Good sound-dampeningreinforced qualities. Heavy.cement Inexpensive. Easily(GRC) modified.

Poly- Very good Excellent Excellent Poor ** Easily modified.propylene Expensive.

Polyvinyl Very good Excellent Excellent Poor. 20 Easily modified.chloride except for Will distort Well-suited for sulfuric(PVC) some solvents at 160 F and hydrofluoric acid

digestions. Expensive.

Phenolic Good Excellent Excellent Very good 25 Excellent light reflec-composite tive properties. Well-panel suited for corrosive

materials. Moderatelyexpensive.

Stainless Good Excellent Good resistance Excellent 0 Primarily used forsteel to a wide range, special applications(Type 316 subject to attack involving perchloricor 304) by some acids acid or radioisotopes.

Heavy. Difficult tomodify. Expensive.

Tempered Excellent Excellent Excellent Very good 0 Good for teachingSafety demonstrations. Cannot

Glass be field modified. Re-quires frequent cleaningto maintain transparency.Heavy. Expensive.

** Contact manufacturer

* The lower a materials flame spread index, the greater its flame-retarding capabilities. The index varies with the thickness of materials and other factors. NFPA 45 Standard on FireProtection for Laboratories Using Chemicals states that m aterials of construction should have flame spreads of 25 or less. The flame spread index is determined using ASTM E84 test method,which compares the surface flame spread and smoke development measurements of a particular material to those obtained from tests of standard calibration materials at the opposite ends ofthe spectrum - m ineral fiber cement board (flame spread index = 0) and select grade red oak flooring (smoke spread index = 100). The test specimen surface, 18" wide x 24" long, is exposedto a flaming fire for 10 minutes.Flame spread over its surface is measured and recorded. Test results are presented as the computed comparisons to the standard calibration materials.

Table 1. Common Liner Materials and Their Characteristics


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concentrations of chemicals that will be handled inthe hood and exhaust system. Laboratory hood efflu-ents may be classified generically as organic or inor-ganic chemical gases, vapors, fumes or smoke and

qualitatively as fume acids, alkalis, solvents or oils.Hood liners are subject to attack from such effluentsby: (1) corrosion (the destruction of metal or othermaterial by chemical or electrochemical action),(2) dissolution (a dissolving action to whichcoatings and plastics are subject), and (3) melting(occurs with certain plastics and coatings at elevatedoperating temperatures). The effect of any deconta-mination materials on the hood liner should alsobe considered.

Working temperatures inside the work spacealso affect the selection of liner materials. Certaincodes and insurance underwriters have flame andsmoke spread rating requirements that establishprescribed limits to applicable materials. Most localenvironmental authorities have codes that incorpo-rate standards based on National Fire ProtectionAssociation (NFPA) Standard No. 45, Fire Protectionfor Laboratories Using Chemicals.

Sashes

Sashes provide some physical protection from splash-es and reactions, and are transparent to allow viewing.Sashes rise vertically, slide horizontally or combineboth horizontal and vertical characteristics in a designknown as a combination A-stylesash (Figures 10, 11and 12). Sash configuration selection is a matter ofpreference.Vertical rising sashes are the most popularand allow large apparatus to be loaded in the hood.Horizontal sliding sashes allow the operator to reacharound both sides of the sash while using the sash as ashield. Because the sash opening is smaller, they con-serve energy by limiting the volume of air exhausted.

Tempered safety glass is the most common and

economical choice for sash material. Polycarbonatesashes are recommended when hydrofluoric (HF)acid is used since this material does not fog or etchwhen exposed to HF fumes.

Explosion-Proofvs. Non Explosion-ProofHoods

An explosion-proof hood may be required for pro-tection when specific concentrations of flammable orexplosive materials are to be used. An explosion-

proof hood is defined by most manufacturers as alaboratory hood equipped with specially designedelectrical components, such as explosion-proof lightfixtures. Explosion-proof does not mean that thehood is capable of containing or withstanding anexplosion. Rather it means that electrical compo-nents are designed to eliminate sparks and preventthe escape of flame or heat that could ignite flamma-ble materials. An explosion-proof hoods electricalcomponents, such as explosion-proof switches,receptacles and internal wiring, are supplied and

installed on site by a licensed electrician in order tomeet all state and local codes. In addition to thecomponents on the hood, the electrical apparatusused inside the hood should also be explosion-proofby design. The National Electrical Code can providedetails about specific explosion-proof components.

Lighting

Light fixtures come in either vapor-proof or explo-sion-proof styles (Figure 13). Vapor-proof light fix-tures are usually fluorescent, installed outside the

hood liner and protected from the hood interior by a

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Figure 13. Explosion-proof light fixture protects incandescentbulb with globe and sealed housing

Figure 10. Hood with vertical-rising sash Figure 11. Hood withhorizontal-sliding sashes

Figure 12. Hood with combinationA-stylesash


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transparent, impact-resistant glass shield. Access forreplacing or cleaning should be from the exterior,whenever possible. Explosion-proof lights are nor-mally incandescent bulbs protected by a specially

reinforced fixture mounted in the hood.Service Fixtures

Utility services include connections to gases, air,water and vacuum (Figure 14). If service fixtures arerequired, they should be installed to allow the con-nection of service supply lines either on the hooditself or the work surface supporting the hood. All

service valves should be accessible for maintenanceand should be corrosion resistant if located insidethe hood. The plumbing tubing should be of theproper material to satisfy local code requirements.For example, some states require gas service connec-tions to be made with black iron pipe or brass tub-ing. For safety and convenience, all service fixturesshould be remotely controlled from outside the hoodand clearly identified.

Electrical Receptacles

If electrical receptacles are required, they are usuallylocated on the hood exterior, away from the corro-

sive effects of the fumes inside the hood structure(Figure 15). Provisions should be made so that allelectrical wiring is isolated and physically separatedfrom vapors handled within the hood.

Americans with Disabilities Act Requirements

Employers, except very small businesses, must com-ply with the Americans with Disabilities Act (ADA),the federal law that went into effect on January 26,

1992, prohibiting discrimination against disabledindividuals in employment. Fume hoods and acces-

sories are available with features that meet therequirements of the ADA. Switches, controls andwritten instructions should be located where theycan be seen and reached by a seated person. ADAStandards for Accessible Design specifies that forwardreach should be a maximum of 48 inches high andside reach a maximum of 54 inches high. To allow aperson in a wheelchair to work comfortably, ADAalso specifies that work surface height should be from28 to 34 inches above the floor and knee clearanceunderneath should be at least 27" high, 30" wide and19" deep. Audible alarms must have an intensity and

frequency that can attract the attention of individualswho have partial hearing loss. The ADA Standardstates that audible emergency alarms shall produce asound that exceeds the prevailing equivalent soundlevel in the room or space by at least 15 dB or exceedsany maximum sound level with a duration of 60 sec-onds by 5 dB, whichever is louder.

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ProtectorXL Laboratory Fume Hood on Manual Hydraulic LiftBase Stand may be lowered to accommodate wheelchair-boundusers. Hoods on adjustable base stands require special modifica-tions to incorporate flexible ducting, wiring and plumbing

Figure 14. Components of a gas service fixture

Hose connector

Brass tubing

Remote control knob

Figure 15. Duplex electrical receptacle


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Hand-Operated, Positive EnergyControl (HOPEC IV)

HOPEC IV is a hood design developed by a labora-tory planner in response to the ADA, OSHA labora-

tory standard and other ergonomic concerns. TheHOPEC IV hood is suitable for use by wheelchair-bound users as well as non-disabled users. The sashviewing area is taller than traditional benchtophoods, which permits mounting the hood in either ahigh or low position while maintaining usable access.The air foil, which may be an obstacle to users of tra-ditional hoods, includes a spill trough.

For energy efficiency, the sash is a combinationhorizontal/vertical-rising to reduce airflow require-ments and sash stops limit the sash opening heightto 50%. The sash stop in combination with a by-passblock reduce the total amount of air exhausted fromthe hood. To further limit the sash opening, theupper 6" of the sash is stationary so that energy con-servation does not compromise visual accessibility.

Safety features include a digital airflow monitorto alert the user to low velocity conditions, a sashpocket to prevent laboratory exposure to contami-nated interior sash surfaces as the sash is raised, a

highly-visible yellow air foil with integral trough tocontain spills, and an interior depth of approximate-ly 30 inches to allow fume-generating materials to beplaced deep within the hood while still allowing ade-quate room for procedures.

Performance andInstallation Considerations

Face Velocity and Containment Issues

The laboratorys degree of exposure to toxic contam-inants is an important consideration when selectinga fume hood. The concentration of contaminants inthe actual breathing zone of the operator should bekept as low as possible. Two fume hood issues thatimpact the concentration of contaminants are facevelocity and containment.

Regulatory compliance agencies and other advi-sory groups have established guidelines relating tothe exposure limits of various chemical reagents.These exposure limits are identified as American

Conference of Governmental Industrial Hygienists(ACGIH) Threshold Limit Values (TLV) orOccupational Safety and Health Administration(OSHA) Permissible Exposure Limits (PEL).Threshold Limit Values refer to airborne concentra-tions of substances and represent conditions underwhich it is believed workers may be repeatedlyexposed day after day without adverse effect.

Until recently, general thinking was that the lowerthe TLV number, the higher the face velocityrequired to ensure adequate protection for the oper-

ator. Face velocity is still regarded as an importantparameter for assessing a hoods performance.However, present views focus on containment ratherthan face velocity alone. The emergence of high per-formance hoods is evidence of this trend. Highervelocity is not necessarily better. A face velocity thatis too high can cause turbulence within the hoodand actually decrease the hoods ability to containcontaminants. Refer to Laboratory VentilationStandards on page 19.

Factors that affect the performance level of the

laboratory hood that are not easily monitored bysimple measurement of face velocity include: 1) typeand location of air supply; 2) location of laboratoryhood in relationship to the laboratory itself; 3) airdisturbances caused by overhead air diffusers, heatregisters, fans, open windows or doors, or personnelmovement; 4) hood sash configurations; 5) locationof the worker in relation to the hood; 6) location andtypes of emission sources; 7) apparatus loaded orstored in the hood; 8) use of apparatus such asmachine tools, grinders or centrifuges that generateaerosols and/or high velocity particles; and 9) ther-mal drafts due to extreme temperature conditions.

Because of these external demands, the AmericanSociety of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Standard 110-95was developed to demonstrate the laboratory hoodsability to contain and exhaust contaminants releasedinside the hood.

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ProtectorXL HOPEC IV Laboratory Fume Hood onADA-compliant ProtectorStandard Storage Cabinets


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ASHRAE Standard 110-95 is a performance test,not a performance specification. It describes how toevaluate a hoods performance, but it does notspecify the performance level required. It remains the

responsibility of the user, industrial hygienist, safetyofficer or applications engineer to specify the perfor-mance level requirement for a laboratorys individualsituations.

ASHRAE Standard 110-95 gives a relative andquantitative determination of the efficiency of thehood to capture contaminants under a set of strictconditions. This test is used to evaluate hoods, bothin the manufacturers facility (as manufactured,AM), and on site (as installed, AI, or as used, AU).Briefly, ASHRAE Standard 110-95 is a three-part test.First, the average face velocity is calculated. The sashopening is divided into one-foot squares.Velocityreadings are taken in each grid area and averaged.

Second, the hood is tested for its ability to con-tain fumes. Titanium tetrachloride, which emits awhite smoke, is released at prescribed locations with-in the hoods interior and work surface. Smoke isobserved and any air movement toward the face ofthe hood and any areas of no air movement arenoted. Titanium tetrachloride is also passed underthe air foil and any smoke flowing out the front isnoted.

In the final part of the test, a tracer gas is releasedat an established rate and at various positions withinthe hood. The gas is monitored in the breathing zoneof a mannequin placed at various positions in frontof the hood. Based on the average exposure in thebreathing zone, a performance rating is determined.The complete standard is available from ASHRAE.

It is recommended that laboratory hoods betested at the time of installation to verify the AMtest results. Initial testing provides a baseline forfuture maintenance checks. Hood performance

should be monitored and maintained as part of thelaboratorys chemical hygiene plan.

Proper Techniques for Hood Use

Containment and efficient removal of fumes areenhanced when the operator follows proper hoodprocedures.Apparatus should be placed at least sixinches inside the hood. Large apparatus that canobstruct airflow should be elevated on blocks toallow fumes to pass under them. The hood shouldnot be used as a storage cabinet; equipment in the

hood should be kept to a minimum so airflow is notcompromised. Finally, the sash should be closed asmuch as possible when work is being performedinside the hood. The Industrial Ventilation Manualmay be referenced for a complete list of recommen-dations for proper operator techniques.

Ventilation System Componentsand Accessories

The laboratory hood is just one component of a

complete fume ventilation system. At the same timea hood is selected, a blower, ductwork, base cabinetand work surface must also be selected (Figure 16).Air supply must be determined as well.A laboratoryfume hood may, as appropriate, also include an air-flow monitor, filtration system and fire extinguisher.

Remote Blowers

Of all the additional components needed, the bloweris the most crucial to the performance of the hood.Fume hood installations utilizing remote blowers arethe most common type.Since the entire duct lengthis under negative air pressure, any leakage in the ductis drawn in and contained rather than pushed outinto the building environment. The exhaust blower ispositioned in a penthouse or on the buildings exteri-or, usually on the roof, where noise is less noticeable.

By creating suction within the ductwork, blowersdraw air from the laboratory room, through thehood and out the duct system.

Centrifugal type blowers are popular becausethey are more efficient and less noisy than others.Belt-driven impellers have greater flexibility than

13

Figure 16. Typical components of a hood ventilation system

Zero PressureWeathercap

Blower TransitionAdapter

RemoteBlower

Manual Duct Damper

Fume Hood

Work Surface

Base Cabinet

Flexible Duct Connection

ThermoplasticDuct

Female DuctCoupling

90 Elbow


14/24

direct-dr ive impellers because the sheavescan be adjusted to vary the air volume. Blower com-ponents are constructed from a variety of materials.To resist corrosion from chemical fumes, impellers

and housings may be made of various types ofmetal, fiberglass or plastic. For weather-proofingwhen roof-mounted, blowers have protective hous-ings. Blowers used to exhaust potentially flammablematerials should be explosion-proof, meaning thatthey are designed to prevent generation of a spark.

In addition to centrifugal blowers, other exhaustdevices are available including air ejectors (Figure17). An air ejector creates suction by venturi methodto draw fumes through the ductwork. Air ejectors aresuitable for use with highly corrosive fumes, such asperchloric acid, because the blower wheel nevercomes into contact with the fumes. Air ejectors areconsiderably more expensive and noisier than cen-trifugal type blowers.

Blower SizingTo provide the optimum face velocity and air volumefor the laboratory hood, the blower must be sizedproperly. Although horsepower and revolutions perminute (RPM) are important blower specifications,blower selection should be based on the air volumethe hood will exhaust and the total static pressureloss of the entire system.

Air Volume

The air volume passing through the hood is general-ly equal to the area of the sash opening multiplied bythe average velocity desired. For example, if 100 feetper minute (fpm) is required and the hood has asash opening of 7.5 square feet, then the hoods airvolume is 750 (7.5 x 100) cubic feet per minute(CFM).

Static Pressure Loss

At any given exhaust volume, the hood has a uniquestatic pressure loss usually expressed in inches ofwater. The manufacturer can provide this static pres-sure loss information. In addition, the ductworkcomponents (duct, elbows, reducers, weathercaps)and filters in the system have static pressure losses

based on the volume of air passing through them,which is often expressed as equivalent resistance infeet of straight duct. To determine the total pressureloss in the ductwork, the equivalent resistance in feetof straight duct for all the components in the systemis totaled. This total equivalent feet provides amethod to calculate the static pressure loss at specificair volumes. The static pressure loss of the ductworkis added to the static pressure losses of the hood andany filters for the total static pressure loss of the sys-tem.

Integral Motor/Blowers

Some fume hoods are available with blowers builtdirectly into the hood superstructure (Figure 18).These hoods are relatively easy and inexpensive toinstall. However, a built-in blower should not beused for corrosive or highly toxic applications since it

14

Labconco Fiberglass Blower, a centrifugal blower with belt-driven impeller

STACK WASH

LINE

OPTIONAL

DAMPER

OPTIONAL

WASH RING

STACK

DRAIN

LINE

Figure 17.Air ejector installed with washdown system

Stack Wash Line

Optional Damper

Optional Wash Ring

Stack Drain Line


15/24

causes positive air pressure in the duct system, andany leaks could push contaminants out of the duct-work. This type of hood may be noisier since theblower is closer to the user. Long duct runs, too, mayprohibit its use since these blowers are sized to fit anarrow range of static pressure requirements. Themanufacturer can provide duct length parametersfor its laboratory hoods with built-in blowers.

Airflow Monitors

American National Standards Institute (ANSI)Standard Z9.5 recommends the use of an airflowmonitor, a device that gives warning (by a visible oraudible signal, or both) when the airflow through thehood has deviated from a predetermined level.Whenmounted in an easily accessible area, monitors mayhave locking devices to prevent tampering by unau-thorized personnel. Other monitors include a remote

alarm signal and/or automatic auxiliary-air/exhaustblower interlock that shuts off the auxiliary-air blow-er should the exhaust blower fail.

Exhaust Air Treatment

Depending on the hazard level associated with thelaboratory operation, and the degree of pollutionabatement required, treatment for the hoods efflu-ents may be necessary.Treatment methods includefiltering, wet scrubbing and incineration, each effec-tive for a specific range of materials. No universaltreatment exists.

Dry media filters (95% efficient by ASHRAEStandard 52-68 Test Method) or HEPA filters(99.97% efficient by DOP Test Method) may berequired to meet specified design criteria (Figure 19).The filter assembly may include a prefilter for cap-turing coarse particles and a filter enclosure arrangedfor easy access.For removing gaseous organic com-pounds, activated carbon filters are often satisfactory.Many filters are not suitable for collecting radioiso-topes. Consult a reputable filter manufacturer for

specific recommendations.For convenient handling, replacement and dis-

posal with minimum hazard to personnel, the filtershould be: (1) located outside the laboratory areaunless it is an integral part of the hood; (2) beforethe remote exhaust blower; and (3) installed in spacethat provides free, unobstructed access. The filtershould be located on the suction side of the exhaustblower and as close to the laboratory as possible tominimize the length of contaminated ductwork.Some installations will require shut-off dampers and

hardware for filter decontamination in the ductwork.A damper is often added to filtered hoods to balanceairflow because HEPA filters vary and change in air-flow resistance as they load during use.

The filter housing should provide for easy trans-fer of the contaminated filter to a disposal site.Depending on the nature of the work, the filter may

15

Figure 18. Hood with integral motor/blower

Figure 19. HEPA filter with housing designed for in-lineconnection to duct system

GuardianDigital Airflow Monitor


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need to be treated as hazardous waste. Local codesshould be consulted for regulations on disposal.

Fume scrubbers are another type of device placedin the hood or in the fume duct system to remove

particulates and soluble contaminants from exhaustair. Scrubbers use water or chemical sprays toremove particulates and to neutralize and diluteacids or alkaline materials (Figure 20). Scrubbersmay have a filtering system to trap particulates.

Ductwork

Ductwork includes fume pipe, male and femalecouplings, elbows, reducers and exhaust dischargestacks (weathercaps). Round diameter duct made ofrigid materials offers the least static resistance.Likethe liner material of a laboratory hood, duct materialmust be resistant to the fumes exhausted through it.Ductwork made of unplasticized polyvinyl chloride(PVC) is a popular choice because it is rigid, highlyresistant to both acid and solvent vapors and,because it is extruded, comes in round diameters.

Stainless steel and coated steel are used when veryhigh temperatures are anticipated and because theyoffer fire protection. Fiberglass provides highstructural strength and corrosion resistance.Localcodes should be consulted for duct materialrecommendations.

Base Cabinets

Most laboratory hoods are designed to rest on abench-high base stand or cabinet with a work sur-face. Existing casework may be used as long as it pro-

vides adequate depth and height for the structuralsupport of the hood. Base stands that allow the usersto be in the sitting position may be preferable for

persons with limited mobility. Specialty base cabinetsare available that store acids, solvents, vacuumpumps or supplies. If base cabinets are vented into alaboratory hood, they will be ventilated only if thehood is operating continuously. Chemical storagecabinets that need ventilation can be more effectivelyand economically ventilated with a separate, contin-uously running exhaust system than by connectingthem to a laboratory hood.

Work Surfaces

The work surface, the slab or platform that supportsthe hood, should be made of a chemical-resistantand heat-resistant material com-patible with the applica-tion. Most are

designedwith a dished

surface to containspills. Popular choices

include molded epoxy resins,aluminum silicate, natural stone and other compos-

16

Flow In

To Drain

Scrubbing Section

Mesh Packing

Out

Round PVC pipe withfemale coupling

90-Degree PVC elbow

Figure 20. SwirlawayFume Scrubber utilizing water sprayProtectorSolvent Storage Cabinet

SpillStopper

Work Surface


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ite materials. Specialty hoods, such as those for per-chloric acid and radioisotope applications, havebuilt-in work surfaces.The smooth one-piece designof built-in work surfaces improves and simplifies

decontamination procedures. Built-in work surfacesrequire a structural support underneath them.

By-Pass Blocks

As described earlier, by-pass hoods are designed sothat as the sash is closed, the constant volume of airentering the hood is redistributed to by-pass open-ings, which helps reduce the potential for extremelyhigh face velocities. By-pass blocks partially obstructthe by-pass openings above the sash of the hood toreduce the air volume demanded. When used with a

sash stop, a by-pass block can conserve conditionedroom air and maintain face velocity.

Sash Stops

A sash stop is a device to restrict the sash openingheight during normal working conditions.Maintaining the sash in a lowered position can

reduce the exhaust volume demand so hoods withsash stops may utilize small blowers. This practicegenerally requires a by-pass block.

Sash Position Alarms

To encourage users to keep the sash lowered, a sashposition alarm provides audible and/or visual warn-ing when the sash is raised above a designated level.

Sash position alarms may be used alone or in con-junction with a sash stop.

Fire Extinguishers

Hoods can be scenes of fires due to the nature ofsome experiments. Some hood manufacturers offerautomatic fire extinguishers that mount inside or

adjacent to the hood and discharge at pre-deter-mined temperature set points, providing around-the-clock protection.

Renovating Existing LaboratoryFume Hoods and Ductwork

While the changes may be subtle to the untrainedeye, modern laboratory fume hoods are much moreefficient at capturing fumes than earlier models.Hoods can now be tested according to ASHRAE 110-95 and their performance levels compared to others.The addition of air foils at the front lip of the benchand other aerodynamic components have reducedturbulence and loss of containment from the hood.

It is usually not possible to retrofit older hoods tobring their performance up to todays standards. Theaddition of necessary components to an older hoodis an expensive custom exercise that requires exactingengineering and design knowledge.

When replacing or adding to existing ductwork,extreme caution is required to avoid exposure to con-taminants. In particular, ductwork exposed to per-chloric acid can be potentially explosive and shouldonly be removed by personnel experienced in han-dling these substances. Anytime an exhaust system ismodified, testing should be done to ensure that thechanges have not affected fume hood performance.

Planning Laboratory Space

Whether adding one hood to an existing laboratoryor installing hundreds in a new facility, planning iscrucial. Because each hood affects the rooms ventila-tion and traffic flow, the whole picture must be con-sidered including the laboratory space, the buildingsventilation and the hoods location in the room. Thefirst and most imperative step taken should be to

consult a qualified laboratory ventilation expert whocan provide helpful advice through the planning,selection and installation phases.

Laboratory Layout

In determining the amount of space necessary forthe laboratory, a layout of all essential laboratoryequipment should be made. The hood should alwaysbe located so that exit from the laboratory will notbe impeded in the event of a fire or explosion withinthe hood structure itself. The hood should also be

located away from high pedestrian traffic lanes in thelaboratory to avoid disruptions to the airflow enter-ing the hood. Cross currents from room ventilationshould also be avoided, as they distort the flow of airessential to the safe operation of the fume hood. Ifventilation components are in place, an attemptshould be made to position the hood out of their

17

Sash Stop

Glass Sash

Sash Stop

Sash Handle


18/24

influence (Figure 21). Some redirecting or blockingmay be necessary. Hoods should not be installed in alocation where it is likely to be affected by anotherpiece of equipment, such as a biological safety cabi-net or another fume hood. If possible, the hood sidewall should be at least one foot away from the roomwall to allow access to service connections.

Sufficient Room Air

A fume hood should not be installed without firstconsidering whether the laboratorys supply air sys-tem will be able to replace all of the air exhausted.For proper hood operation and user safety, theremust be sufficient room air available for exhaustingto achieve the face velocity required. The NationalFire Prevention Association (NFPA) Code 45 calls forreplacing the laboratory with slightly less than theamount of air exhausted from the hood. This nega-tive pressurization causes a slight inflow of air intothe laboratory from corridors and non-laboratoryspaces that helps to keep contaminants from spread-ing throughout the building.

In general laboratory situations,PrudentPractices for Handling Hazardous Chemicals inLaboratories states that the room air should betotally replaced at least 4-12 times an hour. Special

laboratory functions may require an even greaternumber of air exchanges to ensure personnel safety.Open windows are not a substitute for a properlydesigned make-up air system.

Air changes per hour or air changes perminute, however, are not a basis for ventilation cri-teria when environmental control of hazards, heatand/or odors is required. The required ventilationdepends on the problem, not on the size of the roomin which it occurs. The laboratorys safety officershould establish design criteria for room air changes.

Energy Conservation

For every 300 cubic feet per minute of air exhausted,approximately one ton of refrigeration is required.With energy resources becoming scarcer and more

expensive every day, conservation is a high priority.Several methods to reduce the energy consumed by ahood have been developed.

High performance hoods may be safely operated

at lower face velocities, and thus lower air volumes,to conserve energy. Variable air volume hoods usedampers or variable speed blowers to decrease thevolume of air exhausted when demand is low, suchas at night. Reduced air volume hoods function withby-pass blocks and sash stops that reduce the maxi-mum sash opening areas thus lessening the airvolume requirements.Auxiliary-air hoods canreduce the hoodsdemand for room air by replacinga portion of the conditioned air exhausted with sup-plemental air from outside the laboratory. Properuser training can enhance energy conservation as well.

Noise Control

According to OSHA Standard 29 CFR Part 1910.95,the action level for providing personal protectionagainst the effects of noise exposure is an average of85 decibels or greater during an 8 hour workday.Following certain guidelines ensures that the noise inthe laboratory created by a laboratory hood ventila-tion system never approaches the permissible noiselevel. The hood should be aerodynamically designedto reduce the noise created by air passing through it.Properly sized duct components installed with theminimum number of elbows reduces air movementnoise. Installing the blower outside the laboratory,preferably on the roof, keeps the single largest sourceof noise away from the workplace. Sturdily con-structed hoods and vibration-isolating componentssuch as flexible duct connections minimizevibration noise.

Conclusion

The purpose of the preceding discussion was to pre-sent important factors to consider when selecting alaboratory fume hood ventilation system. Space limi-tations kept discussions brief. The General Refer-ences that follow offer sources of in depth informa-tion on the factors presented in this booklet.Labconcocan also provide technical assistance and help withlaboratory planning. Our sales engineers and prod-uct specialists combine their expertise to help solveend userslaboratory ventilation problems.You canreach us at 800-821-5525, 816-333-8811 or

[email protected].

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Figure 21. Laboratory layout showing hood located away fromexits and potential airflow disruptions

Casework

Alternate HoodLocation

Block register opening facing hood

Air SupplyRegister

Air SupplyRegister

Hood

Airflow

Corridor


19/24

Laboratory Safety Standards

Federal Register 29 CFR Part 1910.1450

National Research Council Recommendations

Concerning Chemical Hygiene in Laboratories (Non-mandatory) from Prudent Practices.

Fume hoods should have a continuous monitoringdevice.

Face velocities should be between 60-100 linear feetper minute (lfpm).

Average 2.5 linear feet of hood space per person.

Federal Register 29 CFR Part 1910.95

Occupational noise exposure

Protection against exposure to noise must be

provided when average noise levels are at or above85 dB during an 8-hour workday.

Occupational Safety & Health AdministrationU.S. Department of Labor200 Constitution Avenue, NWWashington, DC 20210(800) 321-6742www.osha.gov

Industrial Ventilation-ACGIH

Fume hood face velocities between 60-100 lfpm.Maximum of 125 lfpm for radioisotope hoods.

Duct velocities of 1000-2000 fpm for vapors, gasesand smoke.

Stack discharge height 1.3-2.0 x building height.

Well designed fume hood containment loss


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ASTM E84-01 Standard Test Method for SurfaceBurning Characteristics of Building Materials

Determines the relative burning behavior of the mater-ial by observing the flame spread along the specimen.

Measures flame spread and smoke development.Material is exposed to flaming fire for 10 minutesand the results measured and recorded.

Results are compared to the indexes of mineralfiber cement board (flame spread and smokedevelopment of zero) and red oak flooring (smokedevelopment of 100).

ASTM International100 Barr Harbor DriveP.O. Box C700West Conshohocken, PA 19428-2959(610) 832-9585www.astm.org

UL 1805-Standard for Laboratory Hoods andCabinets

Hood interior constructed of nonflammable, corro-sion and chemical-resistant materials.

Counterbalanced sash of non-shattering material.

Shielded by-pass opening.

Dished work surface to contain spills.

No air recirculation.Integral blower wheel of nonsparking materials.

Externally mounted electrical receptacles, light fix-tures and service fixture controls.

No indication of reverse flow or backflow whentested with sash at full, 2/3 and 1/3 open positionsat flow rate recommended by the manufacturer.

UL 61010-1 (formerly 3101-1) Electrical Equipmentfor Laboratory Use

Specifies the general safety requirements for electrical

equipment.

Based on International ElectrotechnicalCommission (IEC) Publication 61010-1 with differ-ences noted for U.S. use.

Tests for protection against electrical shock,mechanical hazards, spread of fire, radiation, liber-ated gases, explosion and implosion.

Tests for resistance to shock, vibration, impact, heat,moisture and liquids.

Underwriters Laboratories Inc.333 Pfingsten RoadNorthbrook, IL 60062(847) 272-8800www.ul.com

CAN/CSA Standard C22.2 No.1010.1-92 SafetyRequirements for Electrical Equipment forMeasurement,Control and Laboratory Use

Specifies general safety requirements for electrical

equipmentDesign and methods of construction should pro-vide adequate protection to the operator and thesurrounding area against shock or burn, mechanicalhazards, excessive temperature, spread of fire fromthe equipment, gas liberation, explosion or implo-sion.

Canadian Standards Association5060 Spectrum WayMississauga, OntarioL4W 5N6

CANADA(800) 463-6727www.csa.ca

CE Marking

Established in 1993 to standardize the EuropeanCommunitys electrical directives into a single set ofregulations. Indicates an electrical apparatus conformsto all safety and other directives/specifications presentlyrequired by the Council of European Communities.

Electrical safety.

Electromagnetic emissions testing interferencesignals being output by the product.

Electromagnetic immunity testing the productdoes not respond to outside electromagnetic inter-ference signals.

European Unionwww.europa.eu.intEuropean UnionDelegation of the European Commission to theUnited States

2300 M Street, NWWashington, DC 20037(202) 862-9500www.eurunion.org

ADA Standards for Accessible Design

Federal law revised in 1994 that prohibits discrimina-tion based on disability by public accommodations andin commercial facilities.

Forward reach should be a maximum of 48 incheshigh.

Side reach should be a maximum of 54 inches high.

Work surface height should be from 28 to 34 inchesabove the floor.

Knee clearance should be at least 27" high, 30" wideand 19" deep.

Audible alarms should exceed prevailing equivalentsound level by at least 15 dB.

20


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U.S. Department of JusticeCivil Rights DivisionDisability Rights Section NYAV950 Pennsylvania Avenue, NW

Washington, DC 20530(800) 514-0301www.ada.gov

General References

American Conference of Governmental IndustrialHygienists.Industrial Ventilation, A Manual of

Recommended Practice, 24th Edition.Cincinnati, OH: 2001.

American Conference of Governmental IndustrialHygienists. Documentation of the Threshold LimitValues and Biological Exposure Indices, Pub#0100DOC. 7th Edition, Cincinnati, OH: 2002.

ASHRAE Standards Committee.ASHRAE Standard110-1995 - Method of Testing Performance of

Laboratory Fume Hoods (ANSI Approved). Atlanta:ASHRAE Publications Sales Department, 1995.

British Standards Institution.Laboratory Fume

Cupboards. BS7258-1, 2, 3 & 4. London: 1994.

DiBerardinis, L. et al. Guides for Laboratory Design:Health and Safety Considerations. 3rd Edition,Wiley-Interscience,2001.

Fleming, Diane O., Tulis, Jerry I., Richardson, J. andVesley, Donald.Laboratory Safety: Principles andPractices. 2nd Edition, American Society forMicrobiology, Washington, D.C.: 1995.

Furr, A. Keith, Editor. CRC Handbook of LaboratorySafety, 5th Edition. CRC Press, 2000.

Lewis Sr., Richard J.Rapid Guide to HazardousChemicals in the Workplace. 4th Edition, Wiley-Interscience, 2000.

McDermott, Henry.Handbook of Ventilation forContaminant Control, 3rd Edition. AmericanConference of Governmental and IndustrialHygienists, 2001.

National Fire Protection Association. NFPA 45 -Standard on Fire Protection for Laboratories UsingChemicals. Quincy, MA, 2000.

National Institutes of Health,NIH Guidelines for theLaboratory Use of Chemical Carcinogens. NIHPublication No. 81-2385, National Institutes ofHealth, Bethesda, MD, 1981.Rayburn, Stephen R. The Foundations of LaboratorySafety, A Guide for the Biomedical Laboratory.Springer-Verlag, New York: 1990.

Schilt, Alfred A. Perchloric Acid and Perchlorates.The G. Frederick Smith Chemical Company,Columbus, OH: 1979.

Scientific Equipment & Furniture Association.Laboratory Fume Hoods Recommended Practices,SEFA 1-2002, Garden City, NY, 2002.

U.S. Department of Justice,28 CFR Part 36: ADAStandards for Accessible Design. Washington, DC: 1994.

U.S. Department of Labor, Occupational Safety andHealth Administration. 29 CFR Part 1910.1450,Occupational Safety and Health Standards:Occupational exposure to hazardous chemicals in labo-

ratories. Washington, DC: 1996.

U.S. Department of Labor, Occupational Safety andHealth Administration, 29 CFR Part 1910.95,Occupational Safety and Health Standards:Occupational noise exposure. Washington, DC: 1996.

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22

Glossary

access opening That part of the fume hood through whichwork is performed; entrance or sash opening.

activated carbon filter A filter containing activated carbonmedia designed to trap gaseous organic compounds byadsorption or absorption.

air ejector An air-moving device that creates suction byventuri method to draw fumes through the ductwork to theatmosphere. An alternative to a blower.

airflow monitor A detection device mounted on a fume hoodthat alerts the operator to low airflow levels.

air foil Curved or angular member(s) at the fume hood

entrance that helps to control the pattern of air moving intothe hood.

air volume Quantity of air normally expressed in cubic feetper minute (CFM).

auxiliary air Supply or supplemental air delivered to afume hood to reduce room air consumption; make-up airor add air.

auxiliary-air hood A fume hood designed with a means ofproviding supplemental air for the hood exhaust thereby

reducing room air consumption.

baffle Panel located across the fume hood interior backwhich controls the pattern of air moving into and throughthe fume hood.

biological safety cabinet Safety enclosure with HEPA filter(s)that provides containment for airborne particulates such asinfectious or carcinogenic agents; laminar flow biohazardhood. This enclosure is not a fume hood.

blower Air moving device, sometimes called a fan, consistingof a motor, impeller and housing.

by-pass Compensating opening that maintains a relativelyconstant volume exhaust through a fume hood, regardless ofsash position, and that functions to limit the maximum facevelocity as the sash is closed.

by-pass block Device that partially obstructs the by-passopening above the sash of a by-pass hood, reducing the airvolume demand.

by-pass hood A fume hood designed with openings aboveand below the sash to minimize fluctuations in face velocityas the sash is raised or lowered.

California hood A fume hood used to house distillationapparatus that can provide visibility from front and back orall sides, with horizontal-sliding access doors along the length

of the assembly. The hood, when connected to an exhaustsystem, contains and carries away fumes generated within theenclosure when doors are closed or when the access openingis limited.

canopy hood Suspended ventilating device used to exhaustheat, steam and odors. This device is not a fume hood.

capture velocity The air velocity at the hood face necessary toovercome opposing air currents, and to contain contaminatedair within the fume hood.

clean bench An enclosure that directs HEPA-filtered airvertically or horizontally over the work area providingproduct protection. This enclosure is not a fume hood anddoes not provide personnel protection.

constant air volume (CAV) hood A fume hood that main-tains a consistent exhaust volume. Conventional, by-pass,high performance auxiliary-air and reduced air volume hoodsare examples of CAV hoods.

conventional hood A basic fume hood with an interior baffleand movable front sash.

cross draft A flow of air that blows into or across the face ofthe hood.

damper Device installed in a duct to control airflow volume.

dead air space Area inside a fume hood with no air movement.

distillation hood A fume hood that provides a work surfaceapproximately 18 inches above the room floor, to accommo-date tall apparatus.

downdraft hood An enclosure designed for applicationsinvolving heavier than air materials in which the blower ismounted below the work surface so that air is pulled downthrough a mesh surface before being exhausted to the outside.This enclosure is not a fume hood.

duct Round, square or rectangular tube or pipe used toenclose moving air.

ductless carbon-filtered enclosure An enclosure that housesfilters to trap certain chemical fumes and vapors.

ductwork Duct and all the components necessary to connectpieces of duct together including adapters, reducers, elbowsand couplings.

effluent Waste material (fumes, particles, smoke) discharged

to the atmosphere.

explosion-proofDescription for hoods or other devices withspecially designed electrical components that totally containand isolate electrical sparks from fume exposure so they can-not generate a fire or explosion.


23/24

face Front or access opening of a fume hood.

face velocity Speed of air moving into a fume hood entranceor access opening, usually expressed in feet per minute (fpm).

fan Air moving device, usually called a blower, consisting of amotor, impeller and housing.

fume scrubber An exhaust treatment device that uses wateror chemical sprays to remove particles and to neutralize anddilute acids.

glove box A leak-tight chamber with glove ports and glovesfor handling materials inside, a viewing window for observ-ing, and a transfer chamber or door for loading and unload-ing. This enclosure is not a fume hood.

HEPA filter High-efficiency particulate air filter. A disposableextended-pleated dry-type filter with a minimum particleremoval efficiency of 99.9% for thermally generatedmonodisperse DOP smoke particles with a diameter of 0.3micron.

high performance hood A fume hood with containment-enhancing features that permit the hood to operate at lowerface velocities to conserve energy.

HOPEC IV Hand-Operated, Positive Energy Control. Fumehood design with features that promote safety, energy

efficiency and ADA compliance.

laminar flow Name applied to clean bench or biologicalsafety enclosure that uses a smooth directional flow of air tocapture and carry away airborne particles.

liner Interior lining used for side, back and top enclosurepanels, exhaust plenum and baffle system of a fume hood.

make-up air Supply or supplemental air delivered to a fumehood to reduce room air consumption; auxiliary air or add air.

manometer Device used to measure air pressure differential,usually calibrated in inches of water.

modified by-pass system A method used by some variable airvolume hoods whereby when the sash is lowered to a certainlevel, air volume is no longer reduced and some air volumeenters through by-pass openings to maintain a volume greatenough to adequately dilute and transport fumes.

negative air pressure Air pressure lower than ambient.

positive air pressure Air pressure higher than ambient.

reverse airflow Air movement from inside the hood towardthe face of the hood.

reduced air volume (RAV) hood A fume hood that uses asash stop and by-pass block to reduce the air volume demandso that a smaller blower can be utilized and energy savingsrealized.

room air That portion of the exhaust air taken from the room.

sash Movable transparent panel set in a fume hood entrance.

sash stop Device that restricts the height the sash can be raised.

service fixture Item of laboratory plumbing mounted on orfastened to laboratory furniture or fume hood intended to con-trol the supply of piped gases and liquids for laboratory use.

static pressure Air pressure in a fume hood or duct, usuallyexpressed in inches of water.

static pressure loss Measurement of resistance created whenair moves through a duct or hood, usually expressed in inchesof water.

threshold limit value-time weighted average (TLV-TWA)The time-weighted average concentration for a normal8-hour workday or 40-hour work week, to which nearly allworkers may be repeatedly exposed, day after day, withoutadverse affect as established by OSHA.

transport velocity Minimum speed of air required to supportand carry particles in an air stream.

variable air volume (VAV) hood A fume hood that alters theexhaust volume based on demand, while maintaining a facevelocity within a preset range.

velocity pressure Pressure caused by moving air in a fumehood or duct, usually expressed in inches of water.

floor-mounted hood A full-height fume hood, designed toaccommodate tall apparatus and to permit roll-in of instru-ments and equipment.

weathercap Device used at the top of an exhaust stack toprevent rain from entering the stack end.

work surface The slab or platform, usually dished to contain

spills, that supports the hood and rests atop a base cabinetor bench.

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Labconco Corporation

8811 Prospect Avenue

Kansas City, MO 64132-2696 U.S.A.

800-821-5525 / 816-333-8811

Fax: 816-363-0130

E-mail: [email protected]

Home Page: www.labconco.com

ventilation fumehood

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