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Using a filter bypass leakage test for aerosol sampling cassettes.
Appl Occup Environ Hyg 2002 Sep; 17(9):593-597
The plastic two- and three-piece cassettes commonly used for collection of personal samples of airborne dust may be prone to bypass leakage if the cassettes are not properly assembled. The filter is clamped into place in the cassette by pressing together the base and the ring or cap of the cassette. If pressure is insufficient, or the base and mating piece are not aligned properly, air can flow through the inside of the cassette and around the filter (see Figure 1).(1) If too much pressure is used, the cassette can crack, also producing bypass leakage. This air flow can carry particles and con- tribute to loss of the particle mass that should have been collected on the filter, thus resulting in an underestimate of worker exposure. Press-fitted cassettes continue to be widely used. Anecdotal indications of leakage have cropped up from time to time, but the issue has not been dealt with satisfactorily. Van den Reever and Tieman(2) presented data on cassettes using a pressure drop measurement to indicate leakage. The average pressure drop for a specific cassette/filter combination was measured for a number of "good" cassettes; any decreased pressure drop observed for the assembled cassettes was attributed to bypass leakage. l Establishment of this baseline pressure drop when assembling only a few cassettes has been cumbersome, and a more direct measure of leakage is deemed.
Air-samplers; Air-sampling-techniques; Respiratory-function-tests; Aerosol-sampling; Dust-collection; Aerosols
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Issue of Publication
Research Tools and Approaches: Exposure Assessment Methods
Applied Occupational and Environmental Hygiene
Page last reviewed: April 12, 2019
Content source: National Institute for Occupational Safety and Health Education and Information Division