Ralph, since OSHA regulates MC as a carcinogen, the standard is quite specific about the monitoring requirements and it often takes more than a single sample to demonstrate exposures below the standard. Also, there are two different exposure levels, in addition to the PEL that need to be monitored. The Action Level, which for MC is 12.5ppm TWA 8hour, is one mark that needs attention and is the level that triggers additional requirements. The other measurement that needs to be performed is the STEL (short term exposure limit) of 125ppm, taken over a 15 minute sampling time. All sampling and analytical methods also have specific requirements for confidence limits around each sample.
From: DCHAS-L Discussion List [mailto:dchas-l**At_Symbol_Here**med.cornell.edu] On Behalf Of Ralph Stuart
Sent: Friday, April 15, 2016 8:21 AM
Subject: Re: [DCHAS-L] Spray booths for select carcinogens
>Methylene chloride is an IARC Group 2A potential human carcinogen. As such, it becomes a "particularly hazardous substance" under the OSHA lab standard and according to the standard, must be handled in a "containment."
>Is a spray booth considered a "containment?"
Potentially, if it is able to keep the worker exposure levels below PEL of 25 ppm. The good news is that you can document the containment or lack thereof pretty straightforwardly by sampling the workplace during use of the methylene chloride.
Let me know if you have any questions about this.
Ralph Stuart, CIH, CCHO
Chemical Hygiene Officer
Keene State College
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