Harper Martin, Lee Eun Gyung, Slaven James E, Bartley David L
Exposure Assessment Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, 1095 Willowdale Road, MS-3030, Morgantown, WV 26505, USA.
Ann Occup Hyg. 2012 Jul;56(6):645-59. doi: 10.1093/annhyg/mer123. Epub 2012 Mar 28.
The US Occupational Safety and Health Administration (OSHA) and Mine Safety and Health Administration do not regulate cleavage fragments of amphibole and serpentine minerals as asbestos, even when particles meet the dimensional criteria for counting under standard phase-contrast microscopy methods. The OSHA ID-160 method cautions that discriminatory counting is difficult and should not be attempted unless necessary and no procedure is provided for differentiation. A standard published by the American Society for Testing and Materials (ASTM International D7200-06) includes an attempt to codify a procedure but recognizes that the procedure should be validated in an inter-laboratory study. The US National Institute for Occupational Safety and Health has carried out such a study with multiple laboratories using slides made from riebeckite and crocidolite, grunerite and amosite, tremolite and tremolite asbestos, and actinolite and actinolite asbestos using two different measurement aids (graticules). The asbestos fibers had dimensions consistent with those reported for air samples from actual amphibole asbestos operations, and the cleavage fragments were also dimensionally consistent with those found in non-asbestos mining and milling operations. The procedure for discriminating asbestos fibers from other mineral particles in the ASTM Standard calls for the recognition of characteristics supposedly common to asbestos. For the asbestos fibers created in this study, these characteristics were found not to be common and generally a function of length. More importantly, different laboratories did not recognize these features consistently. Laboratories were much more consistent in measuring dimensions, but excessive overlap in the lengths of asbestos fibers and cleavage fragments rendered length a poor criterion for discrimination. The ASTM discrimination procedure as written could not be supported on the basis of this study. Width was a much more consistent parameter for distinguishing the asbestos and non-asbestos fibers in this study and inclusion of aspect ratio, while considered important by some researchers, did not refine the discrimination further. The ability of the majority of microscopists in this study to discriminate fibers and cleavage fragments through measurement of particle widths was determined and found to be within limits of uncertainty typical for air sampling measurements. A width criterion might be a very simple and useful aid where discrimination between asbestos and non-asbestos fibers in fiber counting by phase-contrast microscopy is required for further investigation. Recognition of asbestos features can also be retained as excessive recognition by some laboratories will lead to a conservative decision for additional investigation.
美国职业安全与健康管理局（OSHA）以及矿山安全与健康管理局并不将闪石和蛇纹石矿物的解理碎片作为石棉进行监管，即便这些颗粒符合标准相差显微镜法计数的尺寸标准。OSHA ID - 160方法警示称，进行区分计数很困难，除非必要且没有提供区分程序，否则不应尝试。美国材料与试验协会（ASTM International D7200 - 06）发布的一项标准尝试编纂一种程序，但也认识到该程序应在实验室间研究中得到验证。美国国家职业安全与健康研究所已与多个实验室开展了这样一项研究，使用了由钠闪石和青石棉、铁石棉和铁石棉、透闪石和透闪石石棉以及阳起石和阳起石石棉制成的载玻片，并使用了两种不同的测量辅助工具（目镜测微尺）。石棉纤维的尺寸与实际闪石石棉作业空气样本报告的尺寸一致，解理碎片的尺寸也与非石棉采矿和研磨作业中发现的一致。ASTM标准中区分石棉纤维与其他矿物颗粒的程序要求识别石棉假定共有的特征。对于本研究中产生的石棉纤维，发现这些特征并不常见，且通常是长度的函数。更重要的是，不同实验室对这些特征的识别并不一致。实验室在测量尺寸方面更为一致，但石棉纤维和解理碎片长度的过度重叠使得长度成为一个糟糕的区分标准。基于这项研究，所编写的ASTM区分程序无法得到支持。在本研究中，宽度是区分石棉纤维和非石棉纤维更为一致的参数，虽然一些研究人员认为长宽比很重要，但它并没有进一步优化区分效果。通过测量颗粒宽度来区分纤维和解理碎片的能力在本研究中被大多数显微镜工作者所确定，并且发现其处于空气采样测量典型的不确定度范围内。在通过相差显微镜进行纤维计数时，如果需要进一步调查石棉纤维和非石棉纤维之间的区分，宽度标准可能是一个非常简单且有用的辅助手段。对石棉特征的识别也可以保留，因为一些实验室的过度识别将导致做出进行额外调查的保守决定。
