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Posted By Alias
Hi all,
I once understood all this but I'm so far away from uni right now I would appreciate some help, it's a tall ask but I need to know this by tomoro afternoon if poss please.
Carbon Monoxide 8 hour TWA is 30ppm, STEL is 200ppm. If my exposure time is not 8 hours but 3 and a half hours, can I actually expose my workers to up to 68ppm per hour as long as the STEL of 200 is not reached or the 240ppm over the 3 and a half hours?
I am not doing the monitoring another company is but I am suspicious of whether he is competent in what he is saying.
Thank you in anticipation.
Emma.
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Posted By Smurfer An exposure of 68ppm over 3.5 hours is 30ppm as an 8hr TWA: (68*3.5)/8=29.75 So it appears you have been given the correct info...so long as exposure to CO for the rest of the day (24hrs) is 0. This document might be of help to you: http://www.hse.gov.uk/coshh/calcmethods.pdf
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Posted By Merv Newman
Must be the holiday season. Poor Emma had to wait a whole 29 minutes before getting a decent answer. Tut.
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Posted By Smurfer
I've been on holiday from lunchtime today!! - must be really sad to have checked the forum out later on this afternoon.... in-between packing the car up!
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Posted By Adrian Watson
Dear Emma,
Smurfer is right with the calculations. The trouble is how can you guarentee that the exposure period is 3.5 hours? Furthermore with the revisions to COSHH in 2004 you are not likely to be meeting the principles of control.
Contact me by email if you want to chat about this.
Regards Adrian Watson
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Posted By Alias
Thank you ever so much guys, I got a double ego boost as they were my calculations, the figures he gave made no sense to me so I wanted to work it out for myself and at least I now know I do understand, I just didn;t want to be all gung-ho and assume I knew best.
I really appreciate the response!
The activity causing the CO is only 3.5 hours long so after that we should have no problem as the area is very well ventilated and fumes usually clear within seconds. It's a one off unique event and we have contingencies in place if the fumes build up.
Thanks again, gotta love this forum :D
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Posted By Robert K Lewis Adrian is bang on the money here. Any company quoting STELs and /or MELs to you is not in touch with COSHH 2004. There are now WELs and I don't have my new EH40 to hand but you need to check with this. As a holding operation ask the company to explain its understanding of COSHH 2004, I rather suspect they might need an hour or two. In the meantime if your calculated figure exceeds the WEL then something must be done. Even if it doesn't reach the WEL you still have to be able to demonstrate that the best practicable means have been used and that levels are as low as reasonably practicable. There is a guidance on the HSE website for these processes. - search under COSHH 2004 Try this link http://www.hse.gov.uk/coshh/index.htmit should be on this page as COSHH esentials Bob
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Posted By Alias
I'm not sure I follow that TWA and STEL are no longer relevant, I have 2005 copy of EH40 in front of me and for CO is still states STEL is 200 and TWA is 30 so where does WEL come into it?
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Posted By Paul Leadbetter
All occupational exposure limits in the UK are now Workplace Exposure Limits (WELs); these have replaced MELs and OESs.
All previous MELs and many OESs are now WELs and, like MELs, WELs must not be exceeded. WELs can either be long-term exposure limits (LTELs) with a reference period of 8 hours or short-term exposure limits (STELs) with a reference period of 15 minutes. Some substances will have an LTEL, some will have an STEL and some will have both depending on their properties and their health effects.
Time-weighted averaging (TWA) is applied to both LTELs and STELs as that is inherent in the way that they are measured (over a period of time).
Paul
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Posted By Alias
Thanks Paul, so I am still able to use both those terms without soundling like the local village idiot :D
Cheers, Emma.
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