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Posted By Anthony Brearley
Good afternoon, I wonder if anyone can help me?
I have conducted a series of personal dust samples, and had them tested for cobalt. Now I know how much cobalt is on the disc, and how long the pump was running for, and the volume of air per minute through the pump.
The first sample was 74 microgram (or 0.074 milligram) in 378 minutes (6.3 hours). The calculation I have tells me that the wt on the disc divided by the sum of litres of air (1.9) times the duration of test (378)divided by a 1000 (in order to get the amount of cubic metres) gives a result of 0.10303 mg.m3
My question is.... is that the airborne concentration as quoted as the EH40 guideance of 0.1 mg.m3 TWA 8 hours?
I'm at a point where I don't know if I should by working the value up to 8 hours from 6.3 hours, or taking it back to a single hour?
I would be greatful for any assitance that may be offered.
Anthony.
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Posted By Coshh Assessor
What you need is the average exposure to the dust throughout an 8-hour period. How you get at this depends on how the exposure to dust varies over that period. For the period that wasn't measured, would there have been no exposure to dust (in which case you can calculate as if the dust was collected over the 8 hour period), or would there have been the same exposure to dust (in which case you can use the result you have calculated as the 8 hour exposure without correction)?
But whether the result comes in just over or just under the WEL, it is still a cause for concern.
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Posted By Anthony Brearley
Thank you for your reply.
The company makes hardmetal components and one person operating the mixing process, which puts him at greatest risk of exposure. However this exposure does differ over any working day. He is required to fill and empty the mixing vessel which only takes a short while, and then spends a longer proprotion of the day working with the powder.
It was impractical to test specific exposures as the time varies too greatly. It 'seemed' more appropriate to have him wear the monitor whilst doing the high risk and general work. Due to not wishing for a contamination issue, I was the only person to fit the monitor over the 4 working periods between rest breaks, hence the shorter than 8 hour test.
From what you're saying it looks like I should be classing this as 6.3 h made up to 8 hours, giving a daily exposure of 0.1308 mg.m3?
Perhaps I'll have to investigate breaking the day down into high and low risk exposures?
Anthony.
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Posted By Ian Dale
Just a small point regarding significant figures. Quoting the results to five figures after the decimal point is not justifiable given the range of errors associated with the analytical measurements - far better just to leave it at 0.10 mg/m³.
Ian Dale
Occupational Health
Glasgow
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Posted By Coshh Assessor
If he was on a break in a cobalt-free atmosphere at other times and not exposed to the dust, then his average exposure over 8 hours is less than what you calculated for 6.3 hours.
The total amount of dust you would have collected if you had continued collecting during the breaks is just the same as what you actually collected. But the time would have been longer. Same total dust, longer time gives a lower average concentration of dust.
So you replace the 6.3 hours in the calculation with 8 hours, and you'll get a smaller result, not a bigger one.
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Posted By Paul Leadbetter
Or the sampling errors.
Anthony
If the sampling period (6.3 hours) represents the working time over a nominal 8 hour shift (with remaining time being breaks in what I hope is a clean area), then the result should be multiplied by 6.3/8 (to give 0.08 mg/m3)to get the result that you would have got had the worker worn the sampler for the whole 8 hours (including breaks). Given the day-to-day variation typically found in occupational exposures to hazardous substances, it is possible that, had you sampled on another day or on another person, the result may well have been above the WEL. Therefore, do not take your one result as an indication that the WEL has not been exceeded. If you are sampling within your company, repeat samples will enable you to get a clearer picture of the situation. If you are sampling at a client, you may not have the luxury of repeat sampling, of course, unless the client is prepared to pay for it.
Paul
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Posted By Anthony Brearley
Thank you all for your help.
As an example of my confusion, I initially did the calculation without converting l/min to m3... giving an answer to 0.0001.. I realised something was wrong whilst my boss thought his prayers had been answered.
What was done was an attempt to check the daily dust levels for three days and then follow that with a cobalt in urine biological test, aiming for some kind of correlation between all the results.
I put the sampler at head height near the blokes main machine, and that sample was considerably cleaner. That alone seems to indicate that although the personal sample is still high, it's probably more to do with specific short term tasks.
I actually work at the company so I see everything on a daily basis, although HS was only given to me as a sideline so to speak.
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Posted By Paul Leadbetter
Anthony
Well done for the biological monitoring but you may find little correlation with the air monitoring results if, for example, there is significant exposure by ingestion.
Do the short-term tasks to which you refer include brushing up? I have carried out personal monitoring in a powder metallurgy plant and just about all of the exposure came from dry brushing the floor at the end of the shift.
Paul
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Posted By Anthony Brearley
We operate a system of dry vac and wet mopping. The (predicted?) main exposure is loading the raw powder and then unloading the mixing vessel the following morning.
The calculation for the background sample gave an exposure of 0.01 mg/m3, so applying a certain amount of logic, it must be the bulk handling that causes the biggest exposure.
I'm beginning to feel that personal hygiene is having a bigger impact than my boss wishes to accept, especially as the operator uses a P3 disposable mask when doing the bulk handling.
Thanks for everyones comments on this.
Anthony.
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Posted By Paul Leadbetter
Anthony
Did the biological monitoring indicate that there had been absorption, then, as a P3 mask, if properly used, should protect the operator from significant inhalation?
Paul
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Posted By Biggles473
Anthony,
Without trying to hijack your thread my company are trying to source some air sampling equipment foer mainly sugar dust, can you or anyone else recommend a manufacturer or equipment for this?
It won't be a constant sampling perhaps only once per year across 8 units.
Thanks,
Biggles473
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Posted By Anthony Brearley
Hello Paul Leadbetter,
The biological testing did show a high level of cobalt in the urine sample. The UK only has guidelines (as confirmed by previous tests done on our behalf by the Health and Safety Laboratory. The level in this test was over three times the anticipated result for exposure to the UK 0.1mg/m3 8 h TWA.
The dust sample and the biological sample are not backing one another up, hence why I think that hygiene is a bigger factor.
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Posted By Anthony Brearley
Hello Flic,
Thank you for the link, I've had a quick scan through, and at one point it says a person can become contaminated through skin contact (we use gloves and barrier creams) which was ruled out by the HSE and HSL people when they visited.
I'm definantly going to have a more careful read of that document.
Anthony.
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Posted By Anthony Brearley
Hello Biggles,
We used a Casella pump with a fairly standard sampling head which takes 25mm filter paper discs.
My boss is trying to get some information from Casella CEL about a new pump, but they're not returning his calls for some reason.
I know there must be others out there, but it's knowing what to type into Google!
Anthony.
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