Standard Test Method for Sampling and Counting Airborne Fibers, Including Asbestos Fibers, in the Workplace, by Phase Contrast Microscopy (with an Option of Transmission Electron Microscopy)

Importancia y uso:

5.1 Users of this test method must determine for themselves whether the practices described meet the requirements of local or national authorities regulating asbestos or other fibrous hazards (for example, the test method must be used within the parameters set out in Appendix A of the U.S. OSHA asbestos standard when used for determining compliance with the Permissible Exposure Limit in the U.S.).

5.2 Variations of this test method have been described by the Asbestos Research Council in Great Britain (10), the Asbestos International Association (AIA) (RTM 1), HSE (11), WHO (7), NIOSH (NIOSH 7400), OSHA (OSHA ID 160), and ISO (ISO 8672); where the counting rules of the latter three methods differ, this is noted in the text.

5.3 Advantages: 

5.3.1 PCM is a technique that enhances the visibility of particles. This test method is specific for fibers. Non-fibrous particles are excluded from the analysis.

5.3.2 The technique is inexpensive, but requires specialized knowledge to carry out the analysis for total fiber counts, at least in so far as the microscopist is often required under regulations to have taken a specific training course (for example, NIOSH 582, or equivalent12).

5.3.3 The analysis is quick and can be performed on-site for rapid determination of the concentrations of airborne fibers.

5.3.4 Measurements acquired by this technique were used by OSHA in determining an exposure-dose relationship (29 CFR Parts 1910, 1915, and 1926), so that measurements obtained by this technique can be compared to OELVs that have been based on that risk assessment.

5.4 Limitations: 

5.4.1 The main limitation of PCM is that fibers are not identified. All fibers within the specified dimensional range are counted. Differential fiber counting may sometimes be used to discriminate between asbestos fibers and fibers of obviously different morphology, such as cellulose and glass fiber. In most situations, differential fiber counting cannot be used to adequately differentiate asbestos from non-asbestos fibers for purposes of compliance with regulations without additional positive identification. If positive identification of asbestos is required, this must be performed by polarized light or electron microscopy techniques, using a different portion of the filter.

5.4.2 A further limitation is that PCM will not detect the finest asbestos fibers, which may be thinner than 0.02 μm in diameter. In addition, fibers shorter than 5 μm are excluded, by definition. However, this test method is compatible with the methods used to determine concentrations for the exposure axis of the dose-response relationship used in risk assessments that established OELVs. Therefore, this test method is appropriate for use in demonstrating compliance with OELVs.

5.4.3 Where calculation of fiber concentration provides a result exceeding an OELV, non-compliance can be assumed unless it can be proven that the fibers counted do not belong to a member or members of the group of fibers regulated.

Subcomité:

D22.07

Referida por:

D7712-18, D7712-18

Volúmen:

11.07

Número ICS:

13.040.30 (Workplace atmospheres)

Palabras clave:

air monitoring; asbestos; fibers; membrane filter method; phase contrast microscopy; sampling and analysis; workplace atmospheres;