Validation of Sorbent Sampling Methods for Methylene Chloride

Abstract

The Occupational Safety and Health Administration (OSHA) is currently examining the possibility of reducing the permissible exposure limit (PEL) for methylene chloride from 500 ppm to 25 ppm. Air sampling equipment that is validated for use with the existing standard requires reevaluation before it can be used reliably at the new standard. Three sorbent sampling methods (two sample tubes and one diffusive sampler) in process of validation at the higher concentration were reevaluated for use at the lower concentration. A sample tube containing a carbon molecular sieve (Anasorb CMS) passed laboratory validation over the appropriate concentration range (2.5–50 ppm). The other sample tube, containing a special synthetic charcoal (Anasorb 747), can be used effectively, although sample migration takes place on storage so that the two sections must be separated prior to transport or storage. The diffusive sampler containing coconut charcoal passed full National Institute for Occupational Safety and Health protocol validation over the same concentration range, although it had fallen short of full validation at the higher PEL concentration because it became saturated at high loadings.