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Afternoon, I am transferring information from Safety Data Sheets to an inhouse CoSHH data sheet. When its asking for the STEL / WEL infomation, the data sheet has various limits for the different chemicals within the substance, however the CoSHH sheet only has space for 1, would you use the highest exposure limit? thanks in advance.
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Rank: Super forum user 
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Hi CM I think it is time you revisited the in house COSHH sheet! If you have a mixture containing A,B and C together with X,Y and Z some of the components may have risks that are similar, so either addititive in terms of the risk to the person exposed or "synergistic" where the risk might be greater than simply each risk element together. If additive there is an equation you can use to work out the notional exposure limit for the mix based on how much of each component you have. But some components may present an entirely different nature of risk. So, just picking one of a selection of exposure limits aint going to work.
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 2 users thanked peter gotch for this useful post.
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Rank: Super forum user 
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The answer is in the title COSHH sheet - the regulations are about controlling Substances, problem is very few of us deal with pure substances and are often faced with trying to control mixtures of multiple hazards. As Peter said you need to change the sheet as you will need to note all the substances that present hazard from the product under evaluation.
Different susbstances have not only different values STEL/LTEL but separate requirements such as biological monitoring (Lead, isocyanates) - you will never properly address the potental hazards picking a single higehst airborne exposure value. Then you have to consider that for some substances e.g. Respirable Crystaline Silica (RCS) the level is quite low at 0.1mg/m3
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2 users thanked Roundtuit for this useful post.
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Rank: Super forum user
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The answer is in the title COSHH sheet - the regulations are about controlling Substances, problem is very few of us deal with pure substances and are often faced with trying to control mixtures of multiple hazards. As Peter said you need to change the sheet as you will need to note all the substances that present hazard from the product under evaluation.
Different susbstances have not only different values STEL/LTEL but separate requirements such as biological monitoring (Lead, isocyanates) - you will never properly address the potental hazards picking a single higehst airborne exposure value. Then you have to consider that for some substances e.g. Respirable Crystaline Silica (RCS) the level is quite low at 0.1mg/m3
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2 users thanked Roundtuit for this useful post.
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Rank: Super forum user 
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No, I wouldn't pick one of the exposure limits based on any arbitrary criterion.
If indeed you picked the highest one it wouldn't make any sense anyway. In general the lower the limit the more dangerous the substance is when airborne. But picking the lowest limit would be no guide to which is the worst constituent in practice. That's because how much of the constituent gets into the air depends on its volatility.
The form you are using appears to be intended for single substances, and not for formulations. If I was forced to use such a form I would try to enter some text in there explaining it is a formulation in which multiple constitutents have exposure limits.
And in general, any COSHH form which basically involves copying information across from the safety data sheet is basically a waste of time.
So given the chance I would replace the COSHH form with something that actually supported me in carrying out an intelligent risk assessment.
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2 users thanked Kate for this useful post.
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Rank: Super forum user
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What everybody else has said but let’s look more deeply: how does knowing a particular WEL/STEL help? In the first instance none really. All it confirms is that the substance or mixture of substances pose a airborne risk to users. So then apply they hierarchy of controls(starting with the best first): - Look at a process that does not create an airborne risk
- Eliminate the airborne risk by substituting the hazardous substances for something non-(or less) hazardous
- Or fully enclose the process so that the users are never exposed to the hazardous substance
- Or partially enclose the process using some form of LEV
- Or rely on dilution ventilation
- Or limit the exposure time to the hazardous substance
- Or rely on RPE
If you adopt controls 1 to 3 then the WEL/STEL in not important as the exposure should be zero. If you adopt other methods these reduce the exposure but not eliminate it completely so you need to test the users exposure levels which is where the WEL/STEL becomes relevant. Do you need additional controls to keep with in the WEL/STEL (and other things like the biological monitoring guidance values)? Your COSHH form should reflect this process, because as we keeping say risk assessment is a process not a form.
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1 user thanked A Kurdziel for this useful post.
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