【国外标准】 Standard Test Method for Turner and Newall (T and N) Wet-Length Classification of Asbestos (Withdrawn 2021)

5.1 This test method provides a simple procedure for obtaining information on the fiber length distribution of suitable asbestos fiber. The use of relatively low cost apparatus, small test specimens, and a short test period, enhance the usefulness of this test method.5.2 Normally, results obtained by this test method are reproducible under comparable laboratory conditions. However, close agreement cannot be expected unless all deviations from the procedure, however minor, are avoided. Moreover, results for longer fiber grades are influenced to a greater extent by differences in fiber length distribution, and characteristics, than are those for shorter grades.5.3 This test is suitable for specification acceptance and manufacturing control.5.4 It is assumed that all undersized fibers, and only those, will pass through any given sieve aperture. However, this idealized condition is not normally achieved. Thus, results should not be misconstrued as true length distribution data.1.1 This test method covers the operation of the Turner and Newall (T and N) wet sieving classifier for asbestos,2 and a procedure for the determination of fiber length distribution and fines (defined in Terminology D2946) content of milled asbestos fiber (−74 μm [200 mesh]) sieve described in Specification E11.1.2 For purposes of estimating length distribution, the test is limited to samples free from excessive quantities of non-fibrous particles or contaminants. Quantities exceeding 0.05 g retained in any given length fractions are considered excessive.1.3 For comparisons between different fiber grades, only those specimens which have approximately the same degree of fiberization as determined by Test Methods D2752/D2752M will give completely meaningful results.1.4 This test method is not applicable to ultrafine grades of asbestos powders which contain little or no fibers retained on a 74-μm [200 mesh] sieve. This method is restricted to Quebec Standard3 grades 4A to 7D inclusive as determined by Test Method D3639/D3639M.NOTE 1: This is an alternative procedure to Test Method D2589/D2589M.1.5 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.1.6 Warning—Breathing of asbestos dust is hazardous. Asbestos and asbestos products present demonstrated health risks for users and for those with whom they come into contact. In addition to other precautions, when working with asbestos-cement products, minimize the dust that results. For information on the safe use of chrysoltile asbestos, refer to “Safe Use of Chrysotile Asbestos: A Manual on Preventive and Control Measures.”41.7 This 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 and health practices and determine the applicability of regulatory limitations prior to use. For a specific hazard statement, see 1.6.