On Wiping the Interior Walls of 37-mm Closed-Face Cassettes: An OSHA Perspective

Abstract

As early as 1976, Occupational Safety and Health Administration (OSHA) methods for analyzing metal samples collected using 37-mm polystyrene closed-face cassettes specified that any loose dust be transferred from the cassette to the digestion vessel, that the cassette be rinsed, and that, if necessary, the cassette be wiped out to help ensure that all particles that enter the cassette are included along with the filter as part of the sample for analysis. OSHA analytical methods for metal analysis were recently revised to explicitly require cassette wiping for all metal samples. This change was based on policy that any material entering the collection device constitutes part of the sample and on OSHA Salt Lake Technical Center research showing that invisible residue on the cassette walls can significantly contribute to the total sample results reported. OSHA procedures are consistent with guidance given in the NIOSH Manual of Analytical Methods. This guidance concludes that internal deposits in sampling cassettes should be included in the analysis and that one way to accomplish this would be to wipe or wash the internal surfaces of the cassette and include the material along with the filter for analysis.

Aerosolisation of Escherichia coli and associated endotoxin using an improved bubbling bioaerosol generator

“…Significantly lower reproducibility for endotoxin concentrations was found when only the results for endotoxins collected on filter were considered. This can be explained by the variability and random nature of the quantity of deposits on the inner walls of the cassette during sampling (Demange et al, 1990;Hendricks et al, 2009).…”

Criteria for the Collection of Useful Respirator Performance Data in the Workplace

“…The amount of mass on the cassette walls did not correlate with mass on the C i filter (R 2 = 0.001). Nonetheless, more recent studies of cassette wall losses for routine workplace samples, i.e., the equivalent of C o samples in workplace studies, have lead OSHA to conclude “… wall deposits can often be a large and inconsistent fraction of the total sample.” (54, p. 734) The OSHA authors also noted that it is not possible to apply a correction factor to account for wall losses. As a result, OSHA’s laboratory now requires that internal cassette walls for all metal samples be wiped, and any mass collected included in the analytical result.…”

Comparison of a Wipe Method With and Without a Rinse to Recover Wall Losses in Closed Face 37-mm Cassettes used for Sampling Lead Dust Particulates

“…Collected particles will adhere to the internal surfaces of the closed faced cassettes during sample collection, transport, and handling (Baron 1998). Several methods have been proposed to account for this wall loss, including rinsing (Ashley et al 2001), wiping (Hendricks et al 2009), within-cassette dissolution (Fabriès 1985; Harper and Ashley 2012), and an internal capsule fused to the filter that could be digested with the filter (Harper and Ashley 2013). …”