Closed-face filter cassette (CFC) sampling-guidance on procedures for inclusion of material adhering to internal sampler surfaces.

The sampling and analytical methods published in the NIOSH Manual of Analytical Methods (NMAM)(1) represent state-of-the-art methods for assessing worker exposures to toxic chemicals. Aerosol sampling methods generally specify the collection of workplace air samples using samplers containing filters such as 37-mm closed-face cassettes (CFCs). NIOSH considers that all particles entering CFCs, as well as some other samplers, such as the Institute of Occupational Medicine (IOM) sampler, should be included as part of the sample whether they deposit on the filter or on the inside surfaces of the sampler. This matter has been discussed in detail in the section on “Sampler Wall Losses” of NMAM Chapter O(2) and has also been specifically addressed in a gravimetric method promulgated by the Occupational Safety and Health Administration (OSHA).(3) The most accurate measure of occupational exposures therefore includes all aerosol particles entering workplace air samplers, both for gravimetric analysis and for analytes such as metals and metalloids. Hence, following sampling, i.e., during sample preparation and analysis, procedures should be used to account for material adhering to the internal surfaces of air sampling cassettes.