Rank: Forum user
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Hello everyone
I was wondering if anyone can help. I am a bit confused as to how a zone classification (0,1,2) is arrived at. When accessing the zone do you take into account issues such as forced extraction etc or should the zone be assessed as though the extraction was not in place? An example of this could eb an area where highly flammable liquids are being decanted from one vessel to another with the flammable liquid being exposed to the open atmosphere. Should the zone be identified taking into account the operation of the extraction, i.e if it has been established that with extraction it is unlikely that the LEL will be reached.
Cheers
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Rank: Forum user
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Hi
I sat a course for this for the past 2 days and i still struggle with it..
read BSEN 60079/10 that should hopefully help you
also if you are a member of Energy institute download document EI15 This is about zoning.
hope that helps
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Rank: Super forum user
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KC, I have conducted just a few DSEAR assessments, some for dust and some in areas where acetone liquid/vapour is present.
Zone classification should take into account how the hazardous material is contained and controlled.
e.g. if the acetone is being piped through a work area, then if the pipe is maintained well, and in normal circumstances it won't leak, then that area would not be classified as hazardous - but it would be a recommendation to have a system in place that alerts if the pipe ever leaked which would produce a hazardous environment.
Similarly a work area with a good extraction system in place, maintained well, you could say when decanting small quantities of acetone only the decanting area could be zoned, likely as a Zone 1. But in the event of a spill AND a ventilation failure the situation would change and you might not want unprotected electrical equipment running, so maybe a wider area should be zoned.
It's all down to risk assessment.
An example: consider a well-ventilated area where acetone (from 5 litre 'dip-tanks') is used to clean parts, even if 10kg of acetone is evaporating every day the acetone release approaches less than 0.1% of the LEL.
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Rank: Super forum user
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In the first instance undertake your zoning based on normal operations and the ventilation present.
As other have said the 2 methods of assessment are available to follow BS60079-10 or EI/IP 15 3rd edition. Decide which one you want to use.
Obviously you need to consider what happens if the extraction fan fails - a warning alarm etc might be needed.
Hazardous area zoning isn't an exact science, but you should understand the definitions used for the different types of zones.
IP15 also considers the occupancy factor for the area.
Your hazardous area extent and type then dictates what electrical rating of equipment is required, (if any) in the classified areas. And other control of ignition sources.
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Rank: Forum user
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Thanks for the replies folks but I still am not sure what it should be. Basically should I class the area as say zone 1 as it is possible that an atmosphere could exist for a short time such as if the extraction fails or do I take into account the extraction and assume that the LEL can't be reached and as such regard as zone 2 or not a zone at all?
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Rank: New forum user
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Hi,
I worked for British Airways, this topic is a minefield.
If budget allows get a qualified external accredited company to carry your zoning.
I don't mean this in a bad way, if you are not suitably qualified why would you even consider attempting to zone a DSEAR classified area.
Transfer the risk onto a qualified company who specialise in DSEAR zoning.
Once you get the zoning classification you can then concentrate on the risk assessments knowing they are correct as you have the correct zone information and backed up and certificate from an accredited company.
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Rank: Super forum user
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DSEAR and hazardous zoning is not 'a minefield' - its actually quite straight forward.
I would use IP/EI 15 Pt 3 - that standard gives good guidance on time a flammable atmosphere is likely to be present and then helps you decide on the grade of release - 'continuous', 'primary' or 'secondary'
A release should be regarded as continuous grade if it is likely to be present for more than 1 000 hours per year and primary grade if it is likely to be present for between 10 and 1 000 hours
per year. A release likely to be present for 1 to 10 hours per year and for short periods only should be regarded as secondary grade.
IP 15 also gives a methodology for classifying and grouping the flammable substances you are working with. This affects the size/extents of the hazardous area.
I have done loads of hazardous area classification and DSEAR assessments, its all easy enough.
For decanting from an open vessels to another open vessel (bad practice by the way) - you are likely to have Zone 0 inside the vessel/can, then Zone 1 for a 1m radius from the vessel and then Zone 2 for a further 2m distance in all directions.
Also see HSG140
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Rank: Forum user
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Thanks again but I feellike we are going round in circles here. I appreciate that there are many aspects to DSEAR, best practice etc but the main point o fmy question is this: Do I take account of the ventilation system when deciding what zone I should class the area as i.e should I disregard the extraction/ventilation as this is one of the control methods. For example an area where flammable liquids are being mixed but there may some release of flammable vapour to the atmosphere during the process. Do I rate the zone as if there was no extraction or do I take account of the extraction which should ensure that the LEL of the liquid is not achieved.
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Rank: Super forum user
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KC, pardon me but we have answered your question!!! The whole point of your extraction is to create a safer zone!! So it is a factor in your assessment!!!!
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Rank: Super forum user
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The guidance from HSE may be of some use, although it is in context of Laboratory operations, i.e. ranging from small scale (~50 ml) to medium scale (~2.5 litres) to large scale ( up to 200 litres) pilot plant.
http://www.hse.gov.uk/el.../atex/classification.htm
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Rank: Super forum user
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I have to agree with John at #26.
Your question has been answered.
In normal operation, your ventilation fan/forced ventilation SHOULD be taken into account when classifying the hazardous area.
What happens after hours or in the case of fan failure?
I assume all cans/vessels are closed with tight lids outside of normal working hours and the ventilation fan is turned off? If not, they should be.
I would assume if the fan fails during normal operation, it would get noticed quite quickly as there are people working in the area and/or it would be linked to a failure alarm and filling operations would stop until the fan is repaired or alternative ventilation is provided?
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Rank: Forum user
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Thanks to everyone for your comments. I see what John W and others are saying in that say zone 2 definition is "A place in which an explosive atmosphere consisting of a
mixture with air of dangerous substances in the form of gas,
vapour or mist is not likely to occur in normal operation but, if it
does occur, will persist for a short period only. " If the environment within the zone is such that with the extraction running that the LEL is not reached then OK I can see why this is likely to be a zone 2. But why then do I see ATEX approved electrical fittings suitable for zone 1 in a spray booth which has LEV capable of reducing the vapour down to a level below the LEL? Not trying to be awkward etc I am just a bit confused.
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Rank: Forum user
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Hi KC,
I am no expert but have worked in the area of DSEAR and ATEX for some years. It is important to understand that although related they cover 2 different things. DSEAR is about protecting people in zoned areas whereas ATEX is about the equipment used in zoned areas. So irrespective of the zone whether it be 0, 1 or 2 you will need ATEX approved equipment. The key to it is understanding the codes on the label on the equipment. In essence, once a zoned area is defined then you need to purchase the correct ATEX equipment to work in that area. Each piece of ATEX equipment has a label which defines amongst other things what zoned area it is designed to be operated within. As mentioned previously if you are not comfortable doing the zoning then get an expert. However, a very simple principle to possibly follow is as follows
Zone 0 - inside of a vessel containing a flammable substance e.g. Storage tank
Zone 1 - anywhere between 1 and 2 metres in all directions around the Zone 0 area
Zone 2 - for an enclosed building you may include the rest of the area or for an external area possibly go to 10 metres
The above is not meant to be definitive just some of the principles I have come across in the past.
Hope this helps.
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Rank: Super forum user
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Its because hazardous area classification is not certainty - its probability!! If the conditions are met, it becomes less likely there will be the potential for a hazardous flammable concentration to form.
However, where there are open vessels or paint spraying taking place etc then its very likely that there will be a hazardous cloud present - simply by the nature of the activity.
Hence why you need to have Zone 1 or Zone 0 electrical equipment or ideally no electrical equipment in places such as paint spraying booths.
Having the correctly rated electrical equipment then protects people in the area - which is why understanding the ATEX equipment classification system is important and also the fault tolerance of the equipment e.g. Cat 1, 2 or 3.
Also rating for the correct gas group and equipment group and method of protection that the electrical equipment uses e.g. 'ia', 'd' etc etc
The extent of your hazardous area and the type of Zone - 0,1, 2 etc dictates the rating of the required electrical equipment and where it should be installed - if necessary.
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Rank: Super forum user
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I presume that you may have referred to The spraying of flammable liquids (HSG 178) from HSE
http://www.hse.gov.uk/pubns/priced/hsg178.pdf
http://books.hse.gov.uk/...alogueCode=9780717614837
The HSE Books webpage highlights in its update that, "While the technical content of this guidance remains substantially correct, some of the legislation referred to has been superseded..........."
Paragraphs 38 to 41 are specific:-
Para 38
Hazardous area classification is not easy. For spray areas, the zones depend on where the spray gun may be used, the level of ventilation, the output of the spray gun, the flashpoint of the spray and its vapour density. The maximum flammable concentration may be determined using an explosimeter or by calculation.36 It is suggested that if the maximum flammable concentration in normal operation is between 0% and 25% LEL then the area should be regarded as zone 2. If it is above 25% LEL in normal operation then the area should be regarded as zone 1.
Para 39
In many cases a qualitative or ‘common-sense’ assessment will be sufficient. For example, everywhere in range of the spray gun should be considered as zone 1. For spray booths, the simplest approach is to regard the whole booth interior as zone 1, and to exclude all electrical equipment and other sources of ignition. Adequate lighting of the interior of the booth may be achieved either by using protected lighting, or by allowing light from an overhead fitting to shine through half-hour fire-resistant glass panels sealed into the top of the booth
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Rank: Forum user
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On a slightly different tack, what do you feel about spray booths where light fittings are behind Georgian wired glass e.g in ceiling or wall panels in the booth. In my view I have always regarded the interior of the booth as being zone 1 and as such this mode of lighting is not appropriate for a zone 1 environment, yet booth manufacturers still supply booths this way. Where I have seen this I have asked for the appropriate ATEX light fittings etc to be installed.
I would welcome your views on this.
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Rank: Super forum user
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This is normal practice for spray booths - quite obviously good lighting is essential - but by placing outside as described, is inherently safer and cheaper - as the lights don't need to be ATEX rated as they are not inside the hazardous/flammable area because of the physical separation provided by the wired glass vision/lighting panels.
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Rank: Forum user
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Ian thanks for your comments. In the past I have been happy to OK light sources behind GW glass which are outside the 2m zone e.g there is GW glass in the roof of a spray boooth but the actual fitting is 2m above this. However where the light fitting is directly in the booth and is only segregated from the vapour by GW glass and mastic or rubber seal I have not been comfortable with this. My main concern is that this would not be to ATEX zone one requirements and if vapour was to get into the fitting or the light fitting bulb exploded the spark etc could travel to the vapour and cause a fire/explosion. However looking at Jays comments taken from HSG178 para 39 "Adequate lighting of the interior of the booth may be achieved either by using protected lighting, or by allowing light from an overhead fitting to shine through half-hour fire-resistant glass panels sealed into the top of the booth" The proble is it doesnt state if the light fitting can be directly above the 30 minute rated glass or if it must be several metres away.
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Rank: Super forum user
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Its a while since I have been in a garage/paint booth. From memory external lights are positioned directly on the separating wired glass. You would need multiple failures to still get a problem, which is probably not a credible failure mode.
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