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

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.

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?

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

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!!!!

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?

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.

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

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.

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.