38314009 very good presentation atex icheme

Equipment Use in Explosive Atmospheres

Equipment Use in Explosive Atmospheres within the Pharma, Bio and Fine Chemical

Industries

Authors

Eur Ing Keith Plumb FIChemE and Neil Graham MIChemE

Presented by

Eur Ing Keith Plumb FIChemE


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We are striving to avoid this!


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Overview

• Definitions

• Can an explosive atmosphere be formed?

• Carrying out a Hazardous Area Classification

• Equipment selection

• Residual risks

• Additional measures


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Standards Used in this Presentation

1. IEC 60079-0:2009 Explosive atmospheres – Part 0: Equipment – General Requirements

2. IEC 60079-10-1:2009 Explosive atmospheres – Part 10-1: Classification of areas –Explosive gas atmospheres

3. IEC 60079-10-2:2009 Explosive atmospheres – Part 10-2: Classification of areas – Combustible dust atmospheres

4. IEC 60079-14: 2008 Explosive atmospheres. Electrical installations design, selection and erection

5. EN 1127-1:2007 (E) Explosive atmospheres. Explosion prevention and protection. Basic concepts and methodology

6. EN 13463-1:2009 Non-electrical equipment for use in potentially explosive atmospheres Part 1: Basic methods and requirements


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Explosive Atmospheres

• Explosive atmosphere− A mixture with air, under atmospheric conditions of flammable

substances in the form of gas, vapour, mist dust, fibres or flyings which, after ignited, permits self-sustaining flame propagation.

• Atmospheric conditions− Conditions that include variations in pressure and temperature above

and below reference levels of 101.3 kPa and 20°C, provided that the variations have negligible effect on the explosive properties of the flammable materials.

Note: The standards do not apply to conditions other that atmospheric conditions.


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Relevant Substances – IEC 60079-10-1

• Flammable liquid− A liquid capable of producing a flammable vapour under any foreseeable

operating conditions.

− Generally a liquid that is being used close to or above its flash point

• Flammable gas or vapour− A gas or vapour which, when mixed with air will form a flammable

atmosphere.

− Gas or vapour that is close to or within the limits of the lower and upper explosive limits.

• Flammable mist− Droplets of liquid, dispersed in air so as to form a flammable atmosphere.

In general the droplets need to be smaller than 50 microns.

− This can apply to liquids below their flash point but the concentration of sub 50 micron droplets must be great enough to allow ignition.


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Relevant Substances – IEC 60079-10-2

• Combustible Dusts

− Finely divided solids, 500 microns or less in nominal size, which may be suspended in air, may settle out of the atmosphere under its own weight, can burn or glow in air and may form explosive atmospheres with air at atmospheric pressure and normal temperatures.

• Combustible Flyings

− Solid particles, including fibres, greater than 500 microns in nominal size, which can be suspended in air, may settle out the atmosphere under their own weight, can burn or glow in air, and may form explosive mixtures with air at atmospheric pressure and normal temperatures.

• Dust Layers

− A layer of dust, which is not likely to form a dust cloud, but may ignite due to self heating or exposure to hot surfaces or thermal flux and cause a fire hazard or over heating of equipment. The ignited layer may also act as an ignition source for explosive atmosphere.


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Workplace Risk Assessment

FG or CD present?

Yes

No

Explosive atmosphere cannot be created

END

START

FG = Flammable Gas, Vapour or Liquid

CD = Combustible Dust or Flyings

Can process be changed to eliminate FG and/or

CD?

Yes

Residual risk of

ignition?

Carry Out Hazardous Area

Classification

Select appropriate equipment to minimise

sources of ignition

No

No

Can oxygen be exclude from the process

equipment?

Provide system to eliminate oxygen

Change process to eliminate FG and/or CD

Yes

Mitigate consequences by providing explosion relief, suppression etc.

NoYes


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Is it likely that there will be a flammable gas, vapour or liquid and/or a combustible dust or

flyings present?

To check this you need to know the properties of the process materials

being used.


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Overview of Likelihood of Explosive Atmosphere

• Are flammable gases, vapours or mists (FGs) and/or combustible dusts or flyings (CDs) used or created as part of the process?

• Can these be dispersed by some form of release, including spillage?

• Is it credible that a mixture with air in the explosion range can be formed?− This is determined by flash points plus lower and upper explosive limits

for FGs and minimum explosive concentration for CDs.

• Is the sufficient material to cause injury or damage.

• See EN 1127-1 for more details


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Fire and Explosion Pentagon

Dispersion

Fuel

Ignition Source

Oxidant

Confinement


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Flammability/Combustibility Properties

• Flammable liquids, vapours and gases (FGs)− Flash points, lower explosive limit and upper explosive limit are

frequently available from literature, material safety data sheets etc.

• Flammable mists− Testing and simulation will be required to find out if it conceivable that

a flammable mists can be created.

• Combustible dusts and flyings (CDs)− Some literature information on minimum explosive concentrations is

available that is indicative but not suitable for design, e.g. BIA-Report 13/97 “Combustion and explosion characteristics of dusts”.

− Combustibility properties are highly susceptible to the dust/flyings physical properties.

− Laboratory testing of the actual dust/flyings being used is normally required.


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Explosion Data – LactoseImpact of Particle Size

R2 = 0.6926R2 = 0.1764

1

10

100

1000

10000

0 50 100 150 200 250Mean Particle Size - µm

Min

imum

Ignitio

n E

nerg

y -

mJ

1

10

100

1000

Min

imum

Explo

siv

e C

onc -

g/m

3

Minimum Ignition Energy

Minimum Explosive Concentration

Source: BIA-Report 13/97 Combustion and explosion characteristics of dusts


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Explosion Data – LigniteImpact of Moisture Content

R2 = 0.3329

200

300

400

500

600

700

800

900

1000

1100

1200

5 10 15 20 25 30 35

Moisture Content % by Weight

Min

imum

Ignitio

n E

nerg

y -

mJ



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Minimum Explosive Concentration in Context

• The Minimum Explosive Concentration (MEC) measures the minimum quantity of material that must be evenly distributed in air before the dust will explode.

• If the MEC is high then a more concentrated dust cloud must be generated before an explosive atmosphere will be present.


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Minimum Explosible Concentration More Details

• Typical MEC for dusts is 30 to 60 g/m3 or greater− A 25 watt light bulb can be just be seen through a two metre coal dust

cloud with a concentration of 40 g/m3.

− It would be difficult to read a newspaper in typical explosive dust cloud.

− It is quite difficult to create a cloud this concentrated that will last more than a few minutes unless you are doing it as part of your process or you have poor housekeeping.

• By way of comparison the typicaloccupational exposure limit forpharmaceutical powders is− 1 – 10,000 g/m3 or less

− There is a 1,000 to 1,000,000 folddifference!


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Quantity of Flammable Material

• Is a Hazardous Area Classification (HAC) required where only small quantities of materials exists?− A risk assessment is always required but not necessarily an HAC.

• The UK Health and Safety Executive advice suggests:− Flammable liquids.

1. If equipment is above the 2 litre scale an HAC should be considered.

2. Above 50 litres an HAC is normally required.

− Flammable gases

1. Low pressure odorised gases with small bore pipework do not normally need a formal HAC.

2. High pressure non-odorised gases normally require a formal HAC.

− Combustible dusts - For quantities of 25 kg or less where the only way to create a dust cloud is to drop a bag of powder then a formal HACwould not normally be required.


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Can the process be changed to eliminate the flammable gas, vapour

or liquid and/or a combustible dust or

flyings?


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Change the Process

• The best way to approach the problem of explosive atmospheres is to eliminate them by changing the process.

• At the small scale changing to a less hazardous material may eliminate the need for a full Hazardous Area Classification.

• Chemical Engineers need to be involved in the early stages of develop to reinforce the need to eliminate FGs and/or CDs.

• If FGs and/or CDs cannot be eliminated then their inventories must be kept to a minimum.


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Carry Out Hazardous Area Classification

Using

StandardIEC 60079

Part 10-1“Classification of areas – Explosive gas

atmospheres”

Part 10-2“Classification of areas – Combustible

dust atmospheres”


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Hazardous Area Classification

1. Record physical properties on a data sheet.

2. Identify all of sources of release and tabulate the result.

3. Identify the grade of release.

4. Note the operating temperature and pressure and plus level of housekeeping

5. Note the level of ventilation associated with each source of release.

6. Identify the zone for each source of release.

7. Calculate the size of each zone.

8. Plot the zones on the plan and elevation of the equipment.


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Step 1. Record Information on Data Sheet

• Data table for gases, vapours and liquids− Gases, vapours and liquids data sheet

• Data sheet for dusts and flyings− Dust and flyings data sheet

Part 10-1 Page 53.pdf

HACD Dusts.pdf


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Step 2 – Identify the Source of Hazard

• Historically standards have used 2 methods

−Generalized method; this involves making judgments about quite large areas of plant

• e.g.. 'blanket' zone 2 inside building, 1m zone 1 around vents, zone 0 inside vessels

−Source of hazard method; each release point is analyzed to determine the distance at which the concentration of the flammable falls below the LEL (by a margin).

• Hazardous area classification standards IEC 60079-10-1 and IEC 60079-10-2 use the source of hazard method

• Generalized method tended to be conservative (hence expensive) but could fail to identify small high hazard points such as rotating equipment glands.


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Step 2. Indentify all sources of release and tabulate them.

• Sources of release table− Sources of release table

Part 10-1 Page 54.pdf


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Step 3. Identify the Grade of Release

• Continuous Grade Release− Continuous or is expected to occur frequently or for long periods

(typical ~ 1000+ hrs/annum)

− E.g. Inside processing equipment

• Primary Grade Release− Expected to occur periodically or occasionally during normal operation

(typically~ 10 – 1000 hrs/annum)

− E.g. Loading powders or solvents into vessel without LEV

• Secondary Grade Release− Not expected to occur in normal operation and, if it does occur, is likely

to do so only infrequently and for short period.

− Typically < 10 hr/yr and a persistence of max 1 hour

− E.g. Equipment joints or spillage

Note 1. Layers, deposits and heaps of combustible dust must be considered as any other source which can form an explosive atmosphere.

Note 2. "Normal operation" means the situation when installations are used within their design parameters.


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Step 4. Note operating temperature and pressure and level of housekeeping

• Operating pressure and temperature− Important for calculation of the size of gas or vapour zone.

• Level of Housekeeping

− Relevant to the type of dust zone and the presence of dust layers

− Three levels are defined:

1. Good – Dust layers are kept to negligible thickness irrespective of degree of release.

2. Fair – Dust layers are not negligible but are short lived (less than one shift)

3. Poor – Dust layers are not negligible and persist for more than one shift.


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Step 5. Note type, degree and availability of ventilation

• Required for calculating the size of the gas/vapour zone and for assessing the size of a dust zone.

• Natural versus artificial – general or local

• Degree of ventilation− High (VH) – Can reduce the concentration of a release virtually instantly.

− Medium (VM) – Can control the concentration of a release and maintain a stable zone boundary.

− Low (VL) – Cannot control the concentration of a release nor prevent long persistence.

• Availability of ventilation− Good – present virtually continuously (min. 0.5 m/s for natural ventilation)

− Fair – expected to be present during normal operation

− Poor – not fair or good but discontinuities are not expected to occur for long periods


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Step 6. Identify the Hazardous Zones

• Zone 0 for Gases and Zone 20 for Dusts

− A place in which an explosive atmosphere is present continuously, or for long periods or frequently.


− A place in which an explosive atmosphere is likely to occur in normal operation occasionally.


− A place in which an explosive atmosphere is not likely to occur in normal operation but, if it does occur, will persist for a short period only.

Notes:1. Layers, deposits and heaps of combustible dust must be considered as any other source which can form an explosive atmosphere.2. "Normal operation" means the situation when installations are used within their design parameters.


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Source of Release VersusHazardous Zone

• Traditionally there was a simple relationship

Gas Dust

− Continuous Grade Zone 0 Zone 20

− Primary Grade Zone 1 Zone 21

− Secondary Grade Zone 2 Zone 22

• But

− Ventilation has an impact on the gas zone

− Housekeeping has an impact on the dust zone

− Consequences of an explosion also has an impact


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Impact of Ventilation on Gas Zones

Grade of Release

Degree of Ventilation

High Medium Low

Availability of Ventilation

Good Fair Poor Good Fair Poor G,F or P

Continuous NH Zone 2 Zone 1 Zone 0Zone 0

+Zone 2Zone 0

+Zone 1Zone 0

Primary NH Zone 2 Zone 2 Zone 1Zone 1

+Zone 2Zone 1

+Zone 2Zone 1 or

0†

Secondary NH NH Zone 2 Zone 2 Zone 2 Zone 2Zone 1 or

0†

Notes

1. NH = Non-hazardous

2. “+” symbol indicates surrounded by

3. “†” There will be a Zone 0 if the ventilation is so weak and the release is such that in practice an explosive gas atmosphere exists virtually continuously i.e. approaching a no ventilation condition.


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Impact of Housekeeping on DustZones

• Housekeeping has an impact on thickness and the persistence of dust layers.

• Dust layers are important because:

− A dust layer can be raised into a cloud and acts as a source of release. This is a particular problem when small primary explosion raises dust and cause a much larger secondary explosion.

− Dust layers can be ignited by heat flux from equipment and act as a source of ignition.

• Dust layers from primary and secondary grades of release can be there continuously with poor housekeeping.

• A secondary grade release with a high deposition rate can lead to thicker layers than a primary grade release with a lower deposition rate if housekeeping is not adequate.


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Consequences of an Explosion

• Traditional Hazardous Area Classification does not take into account the consequence of an explosion.

• In a true risk assessment the consequences would be taken into account and this is now being recognised.

• Two examples of changes that could be made− The use of Zone 1 equipment in a Zone 2 to allow this equipment to be

used even in event of a prolonged gas release.

− The use of Zone 2 equipment in Zone 1 because the amount of flammable material available is small and the equipment is in a remote secure location that is normally unmanned.


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Step 7. Calculate the Size of Each

Zone


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Step 7a – Calculate the Size of Each Gas Zone

• The size and shape of the zone is influenced by− mass released (total and rate)− if a liquid is released, the fraction of the liquid flow that vaporizes− dispersal parameters e.g. buoyancy, ventilation/wind effects

• Industrial experience was enshrined in various codes and guidelines but these were shown to give quite widely varying predictions1.

• The work of Cox, Lees & Ang hoped to help progress from the empirical, experienced based methods towards more rigorous, quantitative methods.− 'The dispersion of leaks by ventilation is difficult to model and more

work needs to be done in this area...”

• IEC 60079-10-1 attempts to provide a rigorous, quantitative method but fails to do so.− “This standard is not based on any rigorous science” 2

1. See figs 3.1, 3.2, 3.3 'Classification of Hazardous Locations'; A.W. Cox, F.P. Lees, M.L. Ang2. Pers comm. UK Health and Safety Executive


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Extracts from IEC 60079-10-1

• Section 5.4 states:

− "The extent of the zone depends on the estimated or calculated distance over which an explosive atmosphere exists before it disperses to a concentration in air below its lower explosive limit with an appropriate safety factor. When assessing the area of spread of gas or vapour before dilution to below its lower explosive limit, expert advice should be sought“

• Section B.5.2.3 states:

− "In the open air an assessment should be made on the basis of the site layout and site features. Estimates of Vz [hypothetical volume] should be made based on the result of using an appropriate modeling tool e.g. from CFD analysis"


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IEC 60079-10-1 Annex B

• Annex B outlines a method for determining the type of zone by– estimating the minimum ventilation rate required to prevent significant

build up of an explosive gas atmosphere

– calculating a hypothetical volume, Vz, which allows determination of the degree of ventilation

– estimating the persistence time of the release (for transient releases)

– determining the type of zone from the degree of ventilation and the grade of release (table B.1 in the standard)

• The method is not intended to determine the extent of the hazardous areas (though standard is not clear on this).


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IEC 60079-10-1 Annex B Continued

• Section B.5.2.2 states:– "The hypothetical volume Vz gives a guide as to the volume of flammable

envelope from a source of release but that envelope will not normally equate to the volume of the hazardous area. Firstly, the shape of the hypothetical volume is not defined and will be influenced by ventilation conditions (see B.4.3 and B.5). The degree and availability of ventilation and possible variations in these parameters will influence the shape of the hypothetical volume. Secondly the position of the hypothetical volume with respect to the release will need to be established. This will primarily depend on the direction of ventilation with the hypothetical volume biased in the down-wind direction. Thirdly, in some situations, account must be taken of the possibility of varying directions of ventilation and the buoyancy (or relative density) of the gas or vapour."

• Calculation of Vz by the method outlined in Annex B is necessary to evaluate the type of zone but does not provide sufficient data to delineate the zone. Vz is merely a measure of ventilation effectiveness.

• It is important to note that work by the Health and Safety Laboratories in the UK suggests Vz could overestimate the volume of the hazardous area by as much as 1000 times.


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Example – Degree of Ventilation

• Release characteristics– Flammable material: Toluene

– Molecular mass of Toluene: 92 kg/kmol

– Source of release: Failure of flange gasket

– Lower explosive limit LEL: 0.046 kg/m3 (1.2 vol%)

– Grade of release: Secondary

– Safety Factor k: 0.5 for secondary grade

– Release rate (dG/dt)max 2.8 x 10-6 kg/s

• Ventilation characteristics... (indoor situation)– No. air changes, C: 1 per hour (2.8 x 10-4 per sec)

– Quality factor, f: 5 equates to impeded air flow

– Ambient temperature, T: 20 deg C

– Temperature coefficient (T/293 K): 1

– Building (room) size, V0: 10m x 15m x 6m = 900 m3


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Example Continued

(dV/dt)min = (dG/dt)max x T = 2.8 x 10-6 x 293k x LEL 293 0.5 x 0.046 x 293

= 1.2 x 10-4 m 3/s

Evaluation of hypothetical volume Vz:

Vz = f x (dV/dt)min = 5 x 1.2 x 10-4 = 2.2 m3

C 2.8 x 10-4

Calculate the time of persistence:

t = -f/C ln((LEL x k)/X0) = -5/1 ln((1.2 x 0.5)/100)

= 25.6 hr

Calculate the theoretical minimum volumetric flow rate of fresh air to dilute the release:


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Example - Conclusion

• The hypothetical volume Vz is greater than 0.1m3 but less than the room volume V0 (900 m3).

• In this case the degree of ventilation may be considered as medium with regard to the source of the release and area under consideration. Therefore a secondary grade of release would equate to Zone 2

• However the flammable atmosphere would persist therefore the concept of Zone 2 may not be met.


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Zone Sizing

• Standard IEC 60079-10-1 does not give the zone sizing – a very unsatisfactory situation.

• The examples given in IEC 60079-10-1 can be used to give a judgemental zone sizing. An example is covered later.

• Standard IP15 for may be used for zone sizing as could computation fluid dynamics.

• The Health and Safety Execute the safety agency for the UK government has done some research into this problem and will be issuing some guidelines in the near future.

HSL CFD.doc


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Step 7b. Assess the Size of Each Dust Zone

• Zone 20

− A zone 20 is generally inside contained equipment that determine size of the zone.

− If a Zone 20 exists outside equipment you have got a serious housekeeping and GMP problem.

• Zone 21

− The size will depend on the dust properties and ventilation.

− Good exhaust ventilation will down grade this to a Zone 22.

− A distance of 1m from the source with a vertical extension to a solid floor is usually adequate.

• Zone 22

− A distance of 3m from the Zone 20 or Zone 21 as appropriate, extending down to a solid floor is usually adequate.

− Mechanical barriers such as walls may limit the extent.

− The presence of dust layers may extent the Zone 22 or turn a Zone 22 into a Zone 21


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Step 8. Plot the Zones on the Plan and Elevation of the Equipment


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Gas Zoning Example

• A fixed process mixing vessel, situated indoors, being opened regularly for operational reasons. The liquid is piped into the vessel through all welded pipework flanged at the vessel.


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Gas Zoning ExamplePrincipal factors which influence the type

and extent of the zone.

• Ventilation− Type Artificial

− Degree Low inside vessel; medium outside vessel

− Availability Fair

• Source of release Grade of Release− Liquid surface within vessel Continuous

− The opening of the vessel Primary

− Spillage or leakage of liquid close to vessel Secondary

• Product− Flashpoint Below process and ambient temperature.

− Vapour density Greater than air.


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Example Dimensions

Process Liquid

Zone 0

Zone 1

Zone 2

a a

b

e

cd dc

Taking into account the relevant parameters, the following are typical values which will be estimated for this particular example.

a = 1m horizontally from the source of releaseb = 1m above the source of releasec = 1m horizontallyd = 2m horizontallye = 1m above grade


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Dust Zoning Example 1

Bag emptying station with no LEV within a building

Bag emptying station with LEV

Zone 20

Zone 21

Zone 22See plan views

Part 10-1 Pages 18 and 19.pdf


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Bag Emptying Station with no LEV Within a Building

• Zone 20− Inside the hopper because an explosive dust/air mixture is present

frequently or even continuously.

− The size of the zone is determined by the hopper.

• Zone 21− The open manway is a primary grade of release.

− Zone 21 exist around this manhole extending 1 m from the edge of the manhole and extending down to the floor.

• Zone 22− Accidental spillage of the bag could cause a dust cloud to extend beyond

the Zone 21

− Zone 22 extends 3m from the edge of the Zone 21 so in effect fills the whole of a room


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Bag Emptying Station with LEV

• Zone 20− Inside the hopper because an explosive dust/air mixture is present

frequently or even continuously

• Zone 21− There is no Zone 21 in this case due to the dust extraction system

• Zone 22− The open manhole is a secondary grade of release. There is no escape

of dust in normal circumstances because of the dust extraction system in a well designed extraction system, any dust released will be sucked inside. Consequently, only a Zone 22 is defined around the manhole extending for 3m from the edge of the manhole and extending down to the floor.


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Dust Zoning Example 2

Cyclone and filter with clean outlet outside building

Zone 20

Zone 21

Zone 22


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Dust Zoning Example 2 Continued

• Zone 20− Inside the cyclone because an explosive dust/air mixture is present

frequently or even continuously.

• Zone 21− The dirty side of the filter is a Zone 21, if only small amounts of dust enter

the filter from the cyclone in normal operation. If this is not the case, the dirty side of the filter is Zone 20.

• Zone 22− The filter clean side may contain a dust cloud if a filter element fails. This

zone includes the ducting.

− The Zone 22 extends around the outlet of the ducting and extends down the ground (not shown in diagram).

− The size of the Zone 22 (in plan) around the outlet will depend on the process and properties of the dust. The expected minimum size would be 1m and the 3m is a reasonable maximum.


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Questions on Hazardous Area Classification


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Select Appropriate Equipment for the

Zone Identified


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Equipment Definitions

• Electrical Equipment – IEC 60079-0− Items applied as a whole or in part for the utilization of electrical energy

including amongst others, items for generation, transmission, distribution, storage, measurement, regulation, conversion and consumption of electrical

energy and items for telecommunications.

• Non-electrical Equipment – EN 13463-1− Currently only applies in Europe. However, non-electrical equipment is very

relevant to pharma, bio and fine chemicals.

− Machines, apparatus, fixed or mobile devices, control components and instrumentation thereof and detection or prevention systems, which separately or jointly are intended for the generation, transfer, storage, measurement, control or conversion of energy and/or the processing of material and which are capable of causing an explosion through their own potential sources of ignition.

− Simple apparatus with no moving parts, e.g. containers or pipes on their own are not considered equipment.


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Sources of Ignition

• Electrical Equipment− Assume that without protective or preventative measures, electrical

equipment will be an effective source of ignition i.e. a source of ignition that is capable of igniting the FGs and/or CDs where they are present.

• Non-Electrical Equipment− Analyse the potential ignition sources to see if there are any effective

ignition sources.


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Ignition Sources – Non-Electric Equipment

1. Does the equipment have a related ignition source other than static electricity?− Yes - Some form of preventive or protective measures may be

required. See question 2 below.

− No – Non-electrical equipment where the only source of ignition is static electricity is not covered by the ATEX directive. Protection against static electricity is required – covered later.

2. Are there effective ignition sources that can ignite the explosive atmosphere present?

− Yes – Some form of preventive or protective measures will be required.

− No – Equipment is safe to use.

atexguidelines_june2009_en Own Source of Ignition.pdf

BS EN 13463_1_2009 Pgs 9 and 10.pdf


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Equipment Providing Preventive or Protection Measures

1. Select equipment that is compliant with IEC or EN Standards and certified to be compliant.

2. Consider if there are any residual risks.− If residual risks exists then further preventive or protective measures

will be required. See later.


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EU ATEX Marking

0999 II 2 G

CE Mark

Notified Body reference number

EU Explosive Atmospheres Symbol

Equipment Group I or II

Equipment Category 1, 2 or 3

x

Group II only G = Gas, vapour or mist D = Dust or flyings


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IEC MarkingGases, vapours and mists

Ex d IIB T6 Gb - 40oC<Tamb<+50oC

Explosion protection symbol

Type of protection code

Gas Group

Temperature class reference to ambient of -20 to +40oC unless indicated

Certified ambient temperature range

Explosion protection level


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IEC MarkingDust and Flyings

Ex tb IIIC T125°C Db IP66

Explosion protection symbol

Type of protection code

Dust Group

Maximum surface temperature reference to ambient of -20 to +40oC unless indicated

Ingress Protection

Explosion protection level


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Marking Non- Electrical Equipment –EN 13463-1

II 2 G d IIA T4

Equipment Group I or II

Equipment Category 1, 2 or 3

Group II only G = Gas, vapour or mist D = Dust or flyings

Protection concept

Gas group

Temperature class

Notes:1. The “Ex” symbol is not used with non- electrical equipment2. Dust groups IIIA, IIIB and IIIC are not used with non-electrical equipment.3. The temperature class can be replaced by the maximum surface temperature in °C


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Electrical Equipment Groups

IEC 60079-0 EU Directive 94/9/EC IEC 60079-10-X

Explosion Protection Level

GroupEquipment

GroupEquipment Category

Zones

MaI I

M1NA

Mb M2

Ga

II

II

1G 0

Gb 2G 1

Gc 3G 2

Da

III

1D 20

Db 2D 21

Dc 3D 22

Ma, Mb, Group I, M1 and M2 apply to coal mining only


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Non - Electrical Equipment Groups

EN 13463-1 EN 60079-10-X

Equipment Group Equipment Category Zones

IM1

NAM2

II

1G 0

2G 1

3G 2

1D 20

2D 21

3D 22

Group I, M1 and M2 apply to coal mining


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Protection ConceptElectrical Equipment

Gases, Vapours and Mists

Code Protection Concept Zone

d Flameproof 1

pxb/pybpzc

Pressurised12

q Powder Filled 1

o Oil Filled 1

e Increased Safety 1

iaibic

Intrinsic Safety012

nAnLnRnC

Non-sparkingEnergy limited

Restricted breathingEnclosed break

2

mambmc

Encapsulation012

Dusts and Flyings


tatbtc

Enclosure202122

p Pressurised 21/22

iaibic

Intrinsic Safety202122

mambmc

Encapsulated202122


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Protection Concept Non-Electrical Equipment

Gases, Vapours, Mists, Dusts and Flyings


fr Flow restriction 2/22

d Flameproof 1/21

c Constructional safety 1/21

bControl of ignition

sources1/21

p Pressurisation 1/21

k Liquid immersion 1/21


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Material Groups

Gases, Vapours and Mists1 Dusts and Flyings

IIA MIE > 0.20 mJ IIIA Combustible flyings

IIB2 MIE 0.05 – 0.20 IIIB3 Non-conductive dustsElectrical resistivity > 103Ωm

IIC2 MIE < 0.05 IIIC4 Conductive dustsElectrical resistivity < 103Ωm

1. Group II subdivisions are also based on maximum experimental safe gap. See IEC 60079-12 and IEC60079-20

2. Equipment marked IIB can be used for IIA and IIB gases. Equipment marked IIIC can be used for IIA and IIB gases.

3. Equipment marked IIIB can be used for non-conductive dusts and combustible flyings.

4. Equipment marked IIIC can be used for conductive and non-conductive dusts and combustible flyings.


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Temperature ClassesGases and Vapours

Temperature Class of Materials in Use

Minimum Ignition Temperature of Gas or

Vapour °C

Allowable Temperature Classes of Equipment

T1 >450 T1 – T6

T2 >300 T2 – T6

T3 >200 T3 – T6

T4 >135 T4 – T6

T5 >100 T5 – T6

T6 >85 T6


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Equipment Surface Temperature Dusts

1. Layers− If, the layer thickness is controlled and frequently removed before

thermal effects occur

• Hopefully the case in a GMP facility

− Then apply the rule, Tmax T5 – 75 , where:

• Tmax is maximum surface temperature of the apparatus when tested in a dust free test method.

• T5 is the minimum ignition temperature of a 5 mm dust layer

2. Clouds− For clouds apply the rule, Tmax 2/3 TCl, where:

• TCl is the ignition temperature of a dust cloud

For more details see IEC 60079-14


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Ingress Protection

Dust Water – Protected Against

IP5X Dust Protected IPX4 Splashing water

IP6X Dust Tight IPX5 Water Jets

IPX6 Powered Water Jets

IPX7 Temporary Immersion

IPX8 Continuous Immersion


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Equipment Selection Examples


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Example 1 – Ethanol Pump

• Process

− Batch transfer of the contents of a measuring head tank to a process vessel.

• Hazards Area Classification

− Inside the pump is a Zone 1 because air can enter the pump at the start and end of each transfer.

− Outside the pump there is small Zone 1 around the single mechanical seal because of the small leakage across the seal face.

− Outside the pump there is a large Zone 2 due to the possibility of seal failure and leakage from pipe joints.

Head Tank

Process Reactor

Transfer Pump


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Ethanol Properties

Flash Point 14°C

Low Explosion Limit 3.3%

Upper Explosion Limit 24.5%

Minimum Ignition Energy 0.65 mJ

Apparatus Group IIA

Auto Ignition Temperature 363°C

Temperature Class T2


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Equipment Selected

Location Inside Pump Outside Pump

Zone 1 1 2

Electrical or Non-electrical

Non-electrical Electrical Electrical

Category Required 2 2 2 or 3

IEC or EN Standard Marking

pc IIA† T2‡ Ex pc IIA T2 GbEx pc IIA T2 Gb orEx pc IIA T2 Gc

EU ATEX Marking II 2 G II 2 GII 2 G orII 3 Gx

PC = Protection Concept e.g. d, e, fr etc.

† IIB or IIC would also be acceptable

‡ T3 to T6 would also be acceptable

x x

Pump analysis in EN 13463-1

BS EN 13463_1_2009 Pgs 52_53.pdf

BS EN 13463_1_2009 Pgs 52_53.pdf

BS EN 13463_1_2009 Pgs 52_53.pdf


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Zone 0 Issues

• Although in this example the pump does not contain a Zone 0, the air space in the head tank and the process reactor would each create a Zone 0.

• LEV extract fans can frequently contain a Zone 0

• There are no non-electrical equipment protection concepts that are suitable for Zone 0. To overcome the problem two independent protection concepts need to be used.

• Later on we examine an alternative approach to this problem.


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Example 2 Milling Dry Lactose

• Dry milling of lactose down stream of a fluid bed dryer discharging into an IBC, no solvent.

• Connections− Clamped joint on outlet from dryer

− Clamped joint on the inlet to the IBC

• Containment− Fully contained pipe work

− Mill has a purged mechanical seals

− Located in a room with HVAC

• Cleaning− WIP after milling

− Dismantled for full clean


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Product Properties – Dust Example

Lactose Based Dry Granules

Minimum Explosive Concentration MEC1 60 g/m3

Minimum Ignition Energy (fines)1 10 mJ

Resistivity2 1 x 1012 Ωm

Apparatus Group (Resistivity > 1 x 103 Ωm) IIIB

Minimum Ignition Temperature Layer T51 450oC

Minimum Ignition Temperature Cloud TCl1 420oC

1. BIA Report 13/97 Combustion and explosion properties of dusts

2. M. Murtomaa, E. Laine, Electrostatic measurements on lactose-glucose mixtures, J. Electrostat. 48 (2000)


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Analysis

• Sources of Release− MEC will be exceeded inside the mill Continuous Grade Zone 20

− No dust outside the mill unless there ismal operation and and dust cloud Secondary Grade Zone 22will be quickly remove by the HVAC

• Probability of the Mill acting as an ignition source− EN 13463-1 states that single impacts between metal parts need not

considered as potential ignition sources when:

• the impact velocity is less than 1 m/s and sparking metals are avoided.

• or less than 15 m/s and less than 150 J with non-sparking metals (Cu, Zn, Sn, Pb some brasses (CuZn) and bronze (CuSn). Standard Text

− Austenitic stainless steel is not a major sparking risk because it is not easily oxidised. However, unless the impact speed is less than 1 m/s then there is a potential ignition source.

− Since the is MIE low, friction and static electrical discharge are also potential ignitions sources.

BS EN 13463_1_2009 Pgs 19 and 20.pdf


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Assessment of Risk versus MIE

MIE mJ Recommended Action1

500Low sensitivity to ignition. Earth plant and equipment when ignition energy is at or below this level.

100 Consider earthing personnel when energy is below this level.

25 The majority of incidents occur when MIE is below this level.

10High sensitivity to ignition. Consider restrictions on high resistivity non-conductors when MIE is below this level.

1Extremely sensitive to ignition. Precautions should be as for flammable liquids and gases when MIE is below this level.

1. J Barton, Dust Explosion Prevention and Protection – A Practical Guide, IChemE

MIE is low on the scale shown in this table so static electricity is likely to be a significant problem.


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Surface Temperature Required

• Layer Ignition Temperature− Tmax 450 – 75oC Tmax 375oC

• Cloud Ignition Temperature− Tmax 2/3 x 420oC Tmax 280oC

• Select the lower temperature from above, therefore surface temperature of equipment must be less than 280oC


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Properties of Dusts - Reminder

• The analysis in this example is based on data book information, any actual analysis needs to be based properties of actual material.

• Particle size and moisture content will have an an impact on the material properties. Material tested needs to be at the moisture content leaving the dryer and the particle size leaving the mill.


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Equipment Selected

Location Inside Mill Outside Mill

Zone 20 22

Electrical or Non-electrical

Non-electrical Electrical

Category Required 1 3

IEC or EN Standard Marking

pc1/pc2† T125°C Ex pc IIIB T125°C‡ Dc IP65

EU ATEX Marking II 1 D II 3 Dx

PC = Protection Concept e.g. d, e, fr etc.

† pc1/pc2 indicates two independent methods of protection

‡ T125°C is a common surface temperature specification

x

ATEX Guidelines Mill Example

atexguidelines_june2009_en Mill Example.pdf


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Zone 20 Issues

• In this lactose milling example, the mill contained a Zone 20.

• Zone 20s are common is solids handling equipment because air is frequently present during operations.

• There are no non-electrical equipment protection concepts that are suitable for Zone 20. To overcome the problem two independent protection concepts need to be used.

• Later on we examine an alternative approach to this problem.


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Questions on Equipment Selection


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Once compliant electrical and non-

electrical equipment has

been selected, is there a residual

risk of explosion?


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Assessment of Residual Risks

• EN 1127-1 lists the following possible ignition sources.− Hot surfaces, mechanical sparks, flames and hot gases, electrical

sparks, stray electrical currents and cathodic corrosion protection, static electricity, lightning, electromagnetic waves, ionising radiation, high frequency radiation, ultrasonics, adiabatic compression and chemical reaction.

• Effective ignition sources - whether a possible ignition sources becomes an effective ignition sources depends on:1. Properties of FGs and/or CDs e.g. minimum ignition energy, and

minimum ignition temperature.

2. Energy of ignition sources.

3. When ignition source occurs, normal operation, expected malfunction or rare malfunction.

• Scale of anticipated effect of explosion− Inventory of FGs and/or CDs

− Maximum explosion pressure, rate of pressure rise and deflagration constant KG or KSt.


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Sources of IgnitionFrom Accident Reports

Stactic Electriity

8.5%

Unknown

17.0%

Welding

4.2%

Self-Ignition

6.0%

Hot Surfaces

4.8%

Flames

7.9% Smoldering Nests

12.7%

Electrical Equipment

3.2%

Mechanical

Sparks/Friction

32.7%

Other

3.0%

BIA Report 11/97

DustsStactic Electriity

22.0%

Pyrophoric Iron

Sulphide

10.0%

Hot Surfaces

12.0%

Welding and Open

Flames

22.0%

Adibatic Compression

10.0%

Electrical Arc and

Sparks

8.0%

Mechanical

Sparks/Friction

8.0%

Vehicle Ignition

8.0%

Gases

Fire and Explosion Incident Analysis May 2005 Canadian Upstream Oil and Gas Industry


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Sources of Ignition for Dust Explosions - Percentages

Equipment

IgnitionSource

Silos and Bunkers

Dust Collectors

and Separators

Mills and Crushers

Conveying Systems Dryers Mixers Polishers Sieves and

Classifiers

Mechanical Sparks and Mechanical Heating 17.2 41.0 71.3 45.5 1.8 46.1 86.4 12.5

Smouldering Nests 30.2 10.5 0 9.1 27.8 0 0 6.3

Electrostatic Discharges 2.6 9.5 3.7 16.7 9.3 34.6 0 12.5

Fire 6.0 4.8 1.3 0 0 3.9 0 12.5

Self Ignition 2.6 6.7 3.7 4.5 16.7 0 0 6.3

Hot Surfaces 10.3 0 3.7 4.5 16.7 0 0 0

Welding and Cutting 7.8 0.9 0 3.0 1.8 3.9 0 0

Electrical Equipment 3.5 0.9 0 0 0 0 0 0

Unknown 18.1 20.9 12.5 13.6 20.4 11.7 13.6 50.0

Other 1.7 4.8 3.7 3.0 3.7 0 0 0

Reference: BIA Report 11/97


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Sources of IgnitionAnalysis of Accident Report Data

• Electrical equipment is not a large problem perhaps due to existing electrical standards.

• Mechanical friction is a problem but should be covered by selecting compliant equipment.

• Mechanical sparks, static electricity and smouldering nests (dusts only) are a problem.

• The major sources of ignition for dusts depend on the type of equipment.

• Some of these sources are difficult to eliminate and maybe there during normal operation.

• Some ignition sources such as welding need to be controlled by procedures such as hot work permits.


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Residual Ignitions Sources

• Static sparks have sufficient energy to ignite FGs and most CDs – see table on next slide.

− Even if Ex compliant equipment is purchased, static electricity can still be a problem due to the process.

• Mechanical sparks from stones or tramp metal− Where the speed is greater than 15 m/s mechanical sparks can ignite

gases and vapours plus mists, dust and flying where the minimum ignition energy is low – typical < 10 mJ

− Where the minimum ignition temperature is low the sensitivity to mechanical sparks is greater.

• Smouldering nests can be:− transferred from item of equipment to other items;

− created by self heating dusts or liquid soaked in porous materials.

• Hot surfaces need to be reviewed since they may be part of process.


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Maximum Theoretical Static Electricity Spark Energies

ObjectStatic Electricity Spark Energy (mJ) at Various Voltages

10 kV 20 kV 30kV

Single Screw 0.05 0.2 0.45

100 mm Flange 0.5 2 4.5

Shovel 1 4 9

50 Litre Drum 0.5 – 5 2 – 20 4.5 - 45

Funnel 0.5 – 5 2 – 20 4.5 - 45

200 Litre Drum 5 -15 20 – 60 45 – 135

Person 5 -15 20 – 60 45 – 135

Reaction Vessels 5 – 50 20 -200 45 - 450

Road Tanker 50 200 450

Reference: R. K Eckhoff, Dust Explosions in the Process Industries, 3rd Edition, Gulf Professional Publishing


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Additional Measures to Reduce Residual Risk

• Reduce risk of static electricity generation− Earth/ground all equipment.

− Reduce the speed of material transfer.

− Make equipment linings conductive i.e. ≤ 109Ω surface resistance and ≥ 8 mm to avoid propagation brush discharges.

− Allow time for the charge in non-conductive liquids and dusts to dissipate

− Change the process to use conductive solvents or the relative humidity of dust handling processes.

• Protect against stones and tramp metal.

• Investigate ways to prevent self heating.

• Review welding and hot work procedures

• Eliminate hot surfaces that are hotter than the acceptable surface temperature for FGs and/or CDs. This may require insulation and high levels of maintenance.


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Anticipated consequences of

an explosion


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Explosion Consequences

• Material inventory− A high material inventory can increase the consequences of an explosion.

− Poor housekeeping can lead dust layers forming increasing the rise of major secondary explosion resulting from a minor primary explosion.

• Equipment connectivity− An explosion can spread between items of equipment and turn a smaller

incident into a much larger one.

• Equipment location− Normally manned versus normally unmanned

− Local to versus remote from occupied premises

• Explosion severity− Maximum explosion pressure and maximum rate of pressure rise KG or KSt

Where KG or KSt= dp/dt ∛vessel volume. A high KG or KSt indicates the likelihood of a severe explosion.

− Deflagration versus detonation. Detonations are much more severe than deflagrations.


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Explosive Properties – Gases and Vapours Max Explosion Pressure and KG

Gas/Vapour

Maximum Explosion (Deflagration) Pressure

Bar g

KG

bar m/s

Dimethyl Formamide 8.4 78

Ethanol 7.0 78

Hydrogen 6.8 550

Isopropanol 7.8 83

Methanol 7.5 75

Toluene 7.8 94

Examples not to be used for designSource: NFPA 68


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Impact of Temperature and Pressure on Maximum Explosion Pressure

• Maximum explosion pressure decreases with the temperature at the start of the explosion.

Pmax (T) = Pmax (T0) T0/T T in degrees K

• Maximum explosion increases with the pressure at the start of the explosion

Pmax (p) = Pmax (p0) p/p0 p in bar abs


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Explosive Properties - Dusts Max Explosion Pressure and Kst

Substance Particle Size m

Moisture Content %

w/w

Max Explosion (Deflagration) Pressure bar g

Kst

Bar m/s

Acetylsalicylic Acid 400 0.1 7.8 157

Lactose 70 0.1 6.7 50

Lactose 220 0.0 4.8 16

Magnesium Stearate <10 (St2)

Maize Starch 11 5.4 8.6 143

Methyl Cellulose 37 10.1 209

Sugar 17 0.4 8.5 116

Sugar 275 0.1 3.9 11

Sorbitol 52 0.2 7.2 74

Examples not to be used for design

Source: BIA-Report 13/97 Combustion and

explosion characteristics of dusts


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Explosion Data – LactoseImpact of Particle Size

R2 = 0.5355

R2 = 0.4532

0

5

10

15

20

0 50 100 150 200 250

Mean Particle Size - mm

Max

imu

m E

xplo

sio

n P

ress

ure

- B

ar

0

10

20

30

40

50

60

70

80

90

100

Kst

- b

ar m

/s

Maximum Explosion Pressure

KSt



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Explosion Data – StarchImpact of Moisture Content

R2 = 0.8217

R2 = 0.8999

0

5

10

15

20

0 2 4 6 8 10 12 14 16 18

Moisture Content %

Max

imu

m E

xplo

sio

n P

ress

ure

- B

ar

0

20

40

60

80

100

120

140

160

180

200

Kst

- b

ar m

/s

Maximum Explosion Pressure

KSt



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Explosion Severity

Dust Explosion Class KstBar.m/s

Characteristics

St 0 0 No explosion

St 1 1 – 199 Weak/moderate explosion

St 2 200 – 300 Strong explosion

St 3 >300 Very strong explosion

Dust explosions are classified as follows:

There is no agreed comparable system for gases and vapours but KG can be used to give a indication of explosion severity.


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Deflagration versus Detonation

• All previous references to explosions are for deflagrations

• A detonation is defined as a supersonic combustion wave – a deflagration is subsonic.

• A detonation needs to be initiated by a high explosive or a chemical initiator except for highly reactive gases such as hydrogen, acetylene and carbon disulphide.

• A deflagration can change suddenly to a detonation as a result of increased turbulence, this can occur along long pipes or ducts.

• Detonations are more destructive than deflagrations due to the higher maximum pressure.

• The shock wave created by a deflagration to detonation transition is even more destructive due to the high pressures created 50 bar g


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Residual Risk Still Unacceptable?

If the some or all of the following conditions exist:

1. All potential ignitions sources cannot be eliminated.

2. The FGs and/or CDs have low minimum ignition energies or low minimum ignition temperature.

3. There is at least one Zone 0 or Zone 20.

4. The consequences of an explosion are high.

Then it is very likely that additional preventative or protective measures will be required.


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Can oxygen be excluded from

the process equipment?O2


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Yes, oxygen can be excluded.

• Inert Gas Blanketing – Prevents an internal explosion by reducing the oxygen concentration− This is the preferred approach to residual risk elimination associated

with explosion within equipment since it prevents an explosion.

− Oxygen concentration must be lowered sufficiently to prevent an explosion – the limiting oxygen concentration is a property of the FG or CD.

− Nitrogen or carbon dioxide are the most appropriate for pharma, bio and fine chemicals.

− Extra precautions are required since inert gases are also asphyxiants.


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No, oxygen cannot be excluded

• In this case other protective measures are required. These protect the equipment but do not prevent an explosion.− Explosion suppression – uses an inert material to suppress an explosion.

Sodium bicarbonate is frequently used.

− Explosion venting – vents the explosion so the pressurein the equipment remains low. The location of the explosionvent is a particular problem since a large amount of burningmaterial is ejected. New flameless venting systems maybe useable for certain applications.

− Explosion proof – equipment is design to withstandthe max explosion pressure without deforming

− Pressure shock resistant equipment - the equipment is design to withstand the maximum explosion pressure but some equipment deformation is permitted.

• These measures are not suitable for high KG or KSt materials i.e. > 200 bar m/s.

• These measures are not suitable for detonations.

Flameless Venting.pdf


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Additional Measures - Mitigate Consequences

• Reduce the inventory of FGs and CDs.

• Change the process so that materials with lower maximum explosion pressure, KG or KSt are used.

• Automate the process or find other ways to reduce the number of personnel in close proximity to the process.

• Move the process to a location where there are few people.

• Provide explosion quench systems between items of equipment to prevent the spread of explosion and to prevent a deflagration turning into a detonation.

• Provide blast proof walls and room explosion vents – this is a particular requirement where Kg or KSt is high and/or detonation is likely e.g. hydrogen.

The previous additional measures apply to explosions within equipment. The following measures apply to all explosions.


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Note on Hybrid Mixtures

• Hybrid mixtures consist of a mixture of gas or vapour and dust.

• Hybrid mixtures are not covered by the standards.

• A hybrid mixture provides fuel from two sources and therefore the an explosion can occur when the concentration is below both the LEL and MEC.

• The addition of just 0.5 vol% of methane can cause the MIE of a dust to more than halve.

• The addition of 1% methane can cause the rate of pressure rise to double and 7% methane causes a ten times increase.

• The best safety precaution is to change the process to eliminate hybrid mixtures.


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Workplace Risk Assessment

FG or CD present?

Yes

No

Explosive atmosphere cannot be created

END

START

FG = Flammable Gas, Vapour or Liquid

CD = Combustible Dust or Flyings

Can process be changed to eliminate FG and/or

CD?

Yes

Residual risk of

ignition?

Carry Out Hazardous Area

Classification

Select appropriate equipment to minimise

sources of ignition

No

No

Can oxygen be exclude from the process

equipment?

Provide system to eliminate oxygen

Change process to eliminate FG and/or CD

Yes

Mitigate consequences by providing explosion relief, suppression etc.

NoYes


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References

1. BIA Report 11/97 Dokumentation Staubexplosionen – Analyse und Einzelfalldarstellung2. BIA Report 13/97 Combustion and explosion properties of dusts.3. Fire and Explosion Incident Analysis May 2005, Canadian Upstream Oil and Gas Industry 4. M. Murtomaa, E. Laine, Electrostatic measurements on lactose-glucose mixtures, J.

Electrostat. 48 (2000)5. IEC 60079-0:2009 Explosive atmospheres – Part 0: Equipment – General Requirements6. IEC 60079-10-1:2009 Explosive atmospheres – Part 10-1: Classification of areas –

Explosive gas atmospheres7. IEC 60079-10-2:2009 Explosive atmospheres – Part 10-2: Classification of areas –

Combustible dust atmospheres8. IEC 60079-14: 2008 Explosive atmospheres. Electrical installations design, selection and

erection9. EN 1127-1:2007 (E) Explosive atmospheres. Explosion prevention and protection. Basic

concepts and methodology10. EN 13463-1:2009 Non-electrical equipment for use in potentially explosive atmospheres

Part 1: Basic methods and requirements11. J. Barton, Dust Explosion Prevention and Protection – A Practical Guide, IChemE12. R. K. Eckhoff, Dust Explosions in the Process Industries, 3rd Edition, 2003, Gulf Process

Publishing.13. Guidelines on the application of Directive 94/9/EC, 3rd Edition, June 2009, European

Commission – Enterprise and Industry14. A.W. Cox, F.P. Lees, M.L. Ang, 'Classification of Hazardous Locations'; IChemE


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Many thanks for listening

I will now answer further questions

38314009 very good presentation atex icheme

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