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Posted By Robert S Woods
Is it unusual for results from air monitoring using Draeger tubes and those from passive diffusion badges to inconstant?
I have had a monitoring exercise carried out and the results from the Draeger tubes recorded 400ppm (extremely high) for xylene and toluene but analysis of the passive diffusion badges stated that exposure was below detectable limits.
Recommendations were that further long term monitoring should be carried out.
Any advice or information on the above results; reason for the anomaly between the two sets of results and recommended type of future monitoring would be appreciated.
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Posted By Mike
Robert
What was the actual reported detection limit, was it a very brief exposure and which badge was used? To get an amount of xylene at 400 ppm for the lab to report with confidence you would need the following exposure times: 3M 3500, 1 min.; SKC 575, 2 mins; Draeger ORSA, 4 mins.
I don't mean to imply that badge results are valid at exposure times this short, but they would give something to report with a confidence of about +/- 50%. The three examples above were never validated below 30 mins exposure and they are not ideal for monitoring compliance with a 15 min STEL for example.
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Posted By Robert S Woods
Mike,
They operatives wore them for a substantial part of their shift approx 6hrs
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Rank: Guest
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Posted By Mike
Robert
I assume that you used the Draeger 10/a which takes about a minute for a reading. If you believe from your own observations that personal exposure was significant over 6 hours then the gas detector tube results (more than one?)and diffusion badge results cannot be reconciled. Time to go back to the test lab. Are they accredited ? Anything that interferes with the xylene Draeger tube to give a false positive should show up in the analysis of the badges and be reported. Sorry I can't be any more help.
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Posted By Descarte
Call me a suspicious individual, but we sometimes found personal purposely making our instruments give a false reading, by throwing dust on a filter, by putting tubes in a puddle of chemical or by sitting in their diner hour (where time was recorded on the meter) and banging a microphone/dosimeter to show an exposure level of 100dBA in the canteen.
I guess you may need to ask yourself the question, is it reasonably foreseably that they could have practically been exposued to these concentrations during their normal work, AND also note that the Drager tube is a one off sample at one point during the 6 hour day, unless you by chance (or planned) happen to be monitoring the worst point/task for exposure then it would not show the same as the average / cumulative badges.
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Posted By Robert S Woods
Descarte,
We have one reading on the dust monitoring survey where an employee (if the readings were to be believed was exposed to 79 mg/m3 (all other measurements were 3-4mg/m3). He would have been lucky to see the work piece at those foggy levels. One for the wood dust chuckers I think.
The spray booths have excellent LEV, but there can be 5 people spraying at any time some of which is not done directly in front of the LEV. Measurements were taken 1 minute and ten minutes after spraying ceased. Readings for toluene were at 100ppm and 50ppm respectively. Knowing the place and working practices I would have to rely on the Draeger readings rather than the badges.
I just wonder what info the monitoring company gave the employees: these badges measure your exposure. Employee thinks; stick it in my pocket and I won’t have any, so no need for PPE.
Maybe the truth will come out when they have to wear air fed masks. “Hey we don’t need these cos the badges can’t have shown any chemicals.” How do you know? “Err, I just do”.
Next time I’ll make sure I’m on site when the survey is carried out.
Bob
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