Ortiz L W, Ettinger H J, Fairchild C I
Am Ind Hyg Assoc J. 1975 Feb;36(2):104-12. doi: 10.1080/0002889758507217.
A laboratory proficiency testing program has been initiated by NIOSH to permit standardization of asbestos counting procedures by various state agencies. This has required preparation of multiple membrane filter samples containing "identical and predictable" concentrations of asbestos fibers, with consistent particulate backgrounds. A technique to filter liquid (toluene) suspensions was developed to provide chrysotile asbestos standards ranging from 200 to 1,500 fibers/mm-2 of filter area, with an aluminum oxide particulate background. Details of the necessary techniques are described. To evaluate variations inherent in preparing these "identical" samples and to estimate variations between different counters, extensive replicate fiber counting was performed. Count data from several counters at a single facility show that this liquid suspension filtration technique provides reproducible asbestos standards as measured by optical microscopy with a coefficient of variation of plus or minus 20% with the maximum individual variations of plus or minus 50%.
美国国家职业安全与健康研究所（NIOSH）启动了一项实验室能力验证计划，以使各个州机构的石棉计数程序标准化。这需要制备多个含有“相同且可预测”浓度石棉纤维且颗粒背景一致的膜滤器样品。开发了一种过滤液体（甲苯）悬浮液的技术，以提供每平方毫米过滤面积含200至1500根纤维的温石棉标准样品，并带有氧化铝颗粒背景。文中描述了所需技术的详细信息。为了评估制备这些“相同”样品时固有的变化，并估计不同计数者之间的差异，进行了大量的重复纤维计数。来自单个机构的多个计数者的计数数据表明，这种液体悬浮液过滤技术提供了可重现的石棉标准样品，通过光学显微镜测量，变异系数为正负20%，最大个体变异为正负50%。
