NYC-WTC_000199812

NYC 9/11 Public Portal Document

hand-picked from the centrifugate and identified by both polarized light microscopy (PLM) and transmission electron microscopy (TEM), and then their dimensions were measured. On mounted point counting filters, amphibole fibers can be classified only on the basis of morphology, birefringence, and optical sign. Accordingly, on the point counting filters, discrimination between amosite and actinolite/richterite asbestos is not possible. Numerically, these amphibole asbestos fibers were infrequent, and did not contribute to the point counting data. The amount of amphibole asbestos on the point counting filters could be quantified, however, by measuring the dimensions of the fibers. The weight percent of amphibole asbestos was calculated from the dimensional measurements made on both the fibers hand-picked from the sediment and the amphibole asbestos fibers observed during the point counting. The weight percent of chrysotile was calculated from the weight of hand-picked fibers and the results of the point counting.

5.3.3 Results

Table 22 presents the summary results of the analyses of samples of exterior dust and debris. The material collected from the roof of the automobile contained 0.67% chrysotile by weight, and the material collected from the roof outside the Sth Floor loft at 45 Warren Street contained 1.05% chrysotile by weight. Fibers hand-picked from the centrifugates showed that actinolite asbestos and richterite asbestos were present in both of these samples, amosite was present in the sample collected from the roof outside the Sth Floor loft at 45 Warren Street, but no amosite was detected in the sample collected from the roof of the automobile on Church Street. During point counting of filters to determine the presence of chrysotile in these two samples, amphibole asbestos fibers were observed. Because most of the amphibole asbestos hand-picked from these two samples was actinolite/richterite asbestos, it is reasonable to conclude that the fibers on the corresponding point counting filters are also primarily actinolite/richterite asbestos. Based on this assumption, the concentration of actinolite/richterite asbestos in the sample collected from the roof of the automobile on Church

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NYC-WTC_000199855