ASTM D 7201 : 2025

1.1This test method2 describes the determination of the concentration of fibers, expressed as the number of such fibers (f) per cubic centimeter (millilitre) of air, using phase contrast microscopy and optionally transmission electron microscopy to evaluate particulate material collected on a membrane filter in the breathing zone of an individual or by area sampling in a specific location.

1.2The fibers determined by this test method are specified by geometry according to counting rules and are limited to those visible under specified conditions of phase contrast microscopy resulting in a determination of concentration (index) that may be compared to workplace risk assessments based on similar methodology. Phase contrast microscopy as embodied in this test method does not distinguish fibers of asbestos from fibers of other materials visible under the same conditions. If it is desired to restrict the count of fibers only to those of asbestos and it is suspected that fibers of other materials are present, the optional procedure by transmission electron microscopy (Appendix X1) can be used on a separate portion of the filter to modify the phase contrast microscopy result according to the proportion of asbestos fibers.

1.3Workplaces are considered those places where workers are exposed to airborne fibers including asbestos. The current test method may be used as a means of monitoring occupational exposure to asbestos fibers when asbestos fibers are known a priori to be present in the airborne dust. The test method gives an index of airborne fiber concentration and can be used to demonstrate compliance with an occupational exposure limit value (OELV) at least as low as 0.01 f/mL. This test method may be used in conjunction with electron microscopy (see Appendix X1) for assistance in identification of fibers. This test method may be used for other materials such as fibrous glass, or man-made mineral fibers by using alternate counting rules (see Annex A3).

1.4This test method specifies the equipment and procedures for sampling the atmosphere in the breathing zone of an individual and for determining the number of fibers accumulated on a filter membrane during the course of an appropriately-selected sampling period. The test method may also be used to sample the atmosphere in a specific location or room of a building (area sampling), where this may be helpful in assessing exposure to workers handling fiber-containing products.

1.5The ideal working range of this test method extends from 13 fibers/mm² to 1300 fibers/mm² of filter area. For a 1000-L air sample collected on a 25 mm diameter filter, this corresponds to a concentration range from approximately 0.005 f/cm³ to 0.5 f/cm³. However, when this test method is applied to sampling the presence of other, non-asbestos dust, the level of total suspended particulate may impose an upper limit to the volume of air that can be sampled if the filters produced are to be of appropriate fiber loading for fiber counting. The lower working range is based on a count of 20 fibers (assuming a background on filter of no more than 4 fibers) in 200 graticule fields.

1.6Users should determine their own limit of detection (LOD) using the procedure in Practice D6620. The LOD is a function of fiber background on the filter, which ideally should not exceed 2.5 f/mm² (2 fibers per 100 graticule areas or 4 fibers per 200 graticule areas). Filters with higher background cannot be used if the aim of measurement is to determine compliance with an OELV of 0.01 f/mL.

1.7If this test method yields a fiber concentration that does not exceed the OELV for the particular regulated fiber variety, no further action may be necessary. If the fiber concentration exceeds the OELV for a specific fiber variety, and there is reason to suspect that the specific fiber variety is mixed with other fibers not covered under the same standard or regulation, the optional method specified in Appendix X1 may be used to recalculate the concentration based on the proportion of the fibers counted that are of the regulated variety.

1.8The mounting medium used in this test method has a refractive index of approximately 1.45 (triacetin 1.43; Euparal 1.48). Fibers with refractive indices in the range of 1.4 to 1.5 will exhibit reduced contrast, and may be difficult to detect.

1.9The minimum width of fibers visible under this test method will be determined by several factors. Theoretical and experimental studies have shown that visibility should be possible for fibers of chrysotile having width of 0.15 μm or greater (2), and for amphibole fibers (for example, crocidolite and amosite) having width of 0.05 μm or greater (3).

1.10The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.11This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For specific precautionary statements, see Section 7.

1.12This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.