Very Good Presentation - ATEX IchemE

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

Equipment Use in Explosive Atmospheres

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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 Carry Out Hazardous Area Classification

START

Select appropriate equipment to minimise sources of ignition

No

FG or CD present?

Yes

Can process be changed to eliminate FG and/or CD?

Residual risk of ignition?

FG = Flammable Gas, Vapour or Liquid CD = Combustible Dust or Flyings Yes

Can oxygen be exclude from the process equipment?

No No Explosive atmosphere cannot be created

Yes Yes

No

Provide system to eliminate oxygen

Change process to eliminate FG and/or CD

END

Mitigate consequences by providing explosion relief, suppression etc.

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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 Confinement

Dispersion

Fuel

Equipment Use in Explosive Atmospheres

Oxidant

Ignition Source www.integpharma.com

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 – Lactose Impact of Particle Size 1000

Minimum Ignition Energy Minimum Explosive Concentration

1000

100

100 R2 = 0.1764

R2 = 0.6926

10

10 1

Minimum Explosive Conc - g/m3

Minimum Ignition Energy - mJ

10000

1 0

50

100

150

200

250

Mean Particle Size - µm Source: BIA-Report 13/97 Combustion and explosion characteristics of dusts

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Explosion Data – Lignite Impact of Moisture Content Minimum Ignition Energy - mJ

1200 1100 1000 900

R2 = 0.3329

800 700 600 500 400 300 200 5

10

15

20

25

Moisture Content % by Weight

30

35

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

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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 typical occupational exposure limit for pharmaceutical powders is − 1 – 10,000 g/m3 or less − There is a 1,000 to 1,000,000 fold difference!

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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 HAC would 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 Standard IEC 60079 Part 10-1 “Classification of areas – Explosive gas atmospheres”

Part 10-2 “Classification of areas – Combustible dust atmospheres” Equipment Use in Explosive Atmospheres www.integpharma.com

Hazardous Area Classification 1. 2. 3. 4. 5. 6. 7. 8.

Record physical properties on a data sheet. Identify all of sources of release and tabulate the result. Identify the grade of release. Note the operating temperature and pressure and plus level of housekeeping Note the level of ventilation associated with each source of release. Identify the zone for each source of release. Calculate the size of each zone. 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

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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

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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, − −

Note 1. Note 2.

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

is likely

Layers, deposits and heaps of combustible dust must be considered as any other source which can form an explosive atmosphere. "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, long periods or frequently.

•

Zone 1 for Gases and Zone 21 for Dusts

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

•

or for

in normal

Zone 2 for Gases and Zone 22 for Dusts

− 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. Equipment Use in Explosive Atmospheres www.integpharma.com

Source of Release Versus Hazardous 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 Degree of Ventilation High

Grade of Release

Medium

Low

Availability of Ventilation Good

Fair

Poor

Good

Continuous

NH

Zone 2

Zone 1

Zone 0

Primary

NH

Zone 2

Zone 2

Zone 1

Secondary

NH

NH

Zone 2

Zone 2

Fair

Poor

G,F or P

Zone 0 Zone 0 Zone 0 +Zone 2 +Zone 1 Zone 1 Zone 1 Zone 1 or +Zone 2 +Zone 2 0† Zone 1 or Zone 2 Zone 2 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. Equipment Use in Explosive Atmospheres www.integpharma.com

Impact of Housekeeping on Dust Zones • •

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”

1. 2.

2

See figs 3.1, 3.2, 3.3 'Classification of Hazardous Locations'; A.W. Cox, F.P. Lees, M.L. Ang 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 Calculate the theoretical minimum volumetric flow rate of fresh air to dilute the release: (dV/dt)min =

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

x 293 x 293

= 1.2 x 10-4 m 3/s Evaluation of hypothetical volume Vz: Vz = f x (dV/dt)min C

=

5 x 1.2 x 10-4 2.8 x 10-4

= 2.2 m3

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 Equipment Use in Explosive Atmospheres www.integpharma.com

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.

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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 Example Principal factors which influence the type and extent of the zone.

• Ventilation

− Type − Degree − Availability

Artificial Low inside vessel; medium outside vessel Fair

• Source of release

− Liquid surface within vessel − The opening of the vessel − Spillage or leakage of liquid close to vessel

Grade of Release Continuous Primary Secondary

• Product

− Flashpoint − Vapour density

Below process and ambient temperature. Greater than air.

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Example Dimensions 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 release b = 1m above the source of release c = 1m horizontally d = 2m horizontally e = 1m above grade

d

c

a

a

b

c

d

Zone 0 Zone 1 Zone 2

Process Liquid e

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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 See plan views

Zone 22

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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 frequently or even continuously

mixture is present

• 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 Equipment Use in Explosive Atmospheres www.integpharma.com

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 Equipment Use in Explosive Atmospheres www.integpharma.com

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 relevant to pharma, bio and fine chemicals.

equipment is very

− 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 own are not considered equipment.

or pipes on their

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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 ignition sources.

to see if there are any effective

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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.

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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

x

II 2 G Group II only G = Gas, vapour or mist D = Dust or flyings Equipment Category 1, 2 or 3 Equipment Group I or II

EU Explosive Atmospheres Symbol Notified Body reference number CE Mark

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IEC Marking Gases, vapours and mists

Ex d IIB T6 Gb - 40oC 103Ωm

Electrical 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. Equipment Use in Explosive Atmospheres www.integpharma.com

Temperature Classes Gases 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 thermal effects occur

−

•

Hopefully the case in a GMP facility

Then apply the rule, Tmax

• •

2.

is controlled and frequently removed before

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

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.

Head Tank

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.

Transfer Pump

Process Reactor

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Ethanol Properties Flash Point

14°C

Low Explosion Limit

3.3%

Upper Explosion Limit Minimum Ignition Energy Apparatus Group Auto Ignition Temperature Temperature Class

24.5% 0.65 mJ IIA 363°C T2

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Equipment Selected Location

Inside Pump

Zone

1

1

2

Electrical or Nonelectrical

Non-electrical

Electrical

Electrical

Category Required

2

2

2 or 3

IEC or EN Standard Marking

pc IIA† T2‡

Ex pc IIA T2 Gb

EU ATEX Marking

x

II 2 G

PC = Protection Concept e.g. d, e, fr etc. † IIB or IIC would also be acceptable ‡ T3 to T6 would also be acceptable

Outside Pump

x

II 2 G

Ex pc IIA T2 Gb or Ex pc IIA T2 Gc

x

II 2 G or II 3 G

Pump analysis in EN 13463-1

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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

Minimum Ignition Energy (fines)1 Resistivity2 Apparatus Group (Resistivity > 1 x 103 Ωm)

60 g/m3

10 mJ 1 x 1012 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 − No dust outside the mill unless there is mal operation and and dust cloud will be quickly remove by the HVAC

Continuous Grade

Zone 20

Secondary Grade

Zone 22

• 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.

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Assessment of Risk versus MIE MIE mJ

Recommended Action1

500

Low 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.

10

High sensitivity to ignition. Consider restrictions on high resistivity nonconductors when MIE is below this level.

1

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

MIE is low on the scale shown in this table so static electricity is likely to be a significant problem. 1. J Barton, Dust Explosion Prevention and Protection – A Practical Guide, IChemE Equipment Use in Explosive Atmospheres www.integpharma.com

Surface Temperature Required • Layer Ignition Temperature − Tmax

450 – 75oC

• Cloud Ignition Temperature − Tmax

2/3 x 420oC

Tmax

375oC

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 Nonelectrical

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

x

II 1 D

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

II 3 D

ATEX Guidelines Mill Example

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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 Equipment Use in Explosive Atmospheres www.integpharma.com

Once compliant electrical and nonelectrical 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 Ignition From Accident Reports Gases

Dusts Stactic Electriity 22.0%

Hot Surfaces 12.0%

Stactic Electriity 8.5% Flames 7.9%

Smoldering Nests 12.7%

Hot Surfaces 4.8%

Welding and Open Flames 22.0%

Self-Ignition 6.0% Welding 4.2%

Pyrophoric Iron Sulphide 10.0%

Unknown 17.0%

Adibatic Compression 10.0%

Mechanical Sparks/Friction 8.0%

Vehicle Ignition 8.0%

Electrical Arc and Sparks 8.0%

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

Mechanical Sparks/Friction 32.7% Other 3.0%

Electrical Equipment 3.2%

BIA Report 11/97

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Sources of Ignition for Dust Explosions - Percentages Equipment Ignition Source

Dust Silos and Collectors Mills and Conveying Bunkers and Crushers Systems Separators

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 Equipment Use in Explosive Atmospheres www.integpharma.com

Sources of Ignition Analysis 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 Object

Static 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

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

50

200

450

Shovel

Road Tanker

Reference: R. K Eckhoff, Dust Explosions in the Process Industries, 3rd Edition, Gulf Professional Publishing Equipment Use in Explosive Atmospheres www.integpharma.com

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 incident into a much larger one.

and turn a smaller

• 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 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

Gas/Vapour

Source: NFPA 68

Examples not to be used for design

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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

300

Very strong explosion

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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O2

Can oxygen be excluded from the process equipment?

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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 pressure in the equipment remains low. The location of the explosion vent is a particular problem since a large amount of burning material is ejected. New flameless venting systems may be useable for certain applications. Explosion proof – equipment is design to withstand the 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.

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Additional Measures - Mitigate Consequences The previous additional measures apply to explosions within equipment. The following measures apply to all explosions.

• 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.

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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 Carry Out Hazardous Area Classification

START

Select appropriate equipment to minimise sources of ignition

No

FG or CD present?

Yes

Can process be changed to eliminate FG and/or CD?

Residual risk of ignition?

FG = Flammable Gas, Vapour or Liquid CD = Combustible Dust or Flyings Yes

Can oxygen be exclude from the process equipment?

No No Explosive atmosphere cannot be created

Yes Yes

No

Provide system to eliminate oxygen

Change process to eliminate FG and/or CD

END

Mitigate consequences by providing explosion relief, suppression etc.

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References 1. 2. 3. 4. 5. 6. 7. 8.

9. 10. 11. 12. 13. 14.

BIA Report 11/97 Dokumentation Staubexplosionen – Analyse und Einzelfalldarstellung BIA Report 13/97 Combustion and explosion properties of dusts. Fire and Explosion Incident Analysis May 2005, Canadian Upstream Oil and Gas Industry M. Murtomaa, E. Laine, Electrostatic measurements on lactose-glucose mixtures, J. Electrostat. 48 (2000) IEC 60079-0:2009 Explosive atmospheres – Part 0: Equipment – General Requirements IEC 60079-10-1:2009 Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas atmospheres IEC 60079-10-2:2009 Explosive atmospheres – Part 10-2: Classification of areas – Combustible dust atmospheres IEC 60079-14: 2008 Explosive atmospheres. Electrical installations design, selection and erection EN 1127-1:2007 (E) Explosive atmospheres. Explosion prevention and protection. Basic concepts and methodology EN 13463-1:2009 Non-electrical equipment for use in potentially explosive atmospheres Part 1: Basic methods and requirements J. Barton, Dust Explosion Prevention and Protection – A Practical Guide, IChemE R. K. Eckhoff, Dust Explosions in the Process Industries, 3rd Edition, 2003, Gulf Process Publishing. Guidelines on the application of Directive 94/9/EC, 3rd Edition, June 2009, European Commission – Enterprise and Industry 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

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