NYC-WTC_000199812

NYC 9/11 Public Portal Document

was unsuccessful because of the high particulate loadings on the filters. Examination of the unsatisfactory TEM specimens prepared from these filters indicated that much of the material on the filters was gypsum and cement dust. It was found that the gypsum and the water-soluble components of the cement dust could be removed from the surfaces of the filters by a water extraction treatment. After this treatment, specimens suitable for TEM analysis for asbestos were obtained by using the preparation procedures of ISO10312. TEM data recorded according to ISO 10312 allows for results to be compared with known TEM and phase contrast microscopy (PCM) exposure criteria. The TEM fiber counting data was interpreted to derive the concentrations of asbestos structures greater than 0.5 pm, asbestos fibers and bundles longer than 5 pm, and PCM-equivalent asbestos fibers and bundles (fibers and bundles longer than 5 pm with widths greater than 0.25 pm).

5.1.3 Results

Tables 6 through 13 present the results of the TEM analyses for asbestos in the air samples collected at 46 -Warawi-Stfa6t. The maximura concentration ofchryscrtife Structures* greater than 0.5 pm observed under the passive conditions of the air sampling indoors was 0.12 structure/mLs with an upper 95% confidence limit of 0.16 structure/mL. The maximum mean airborne concentration of chrysotile fibers longer than 5 pm observed under the passive conditions of the air sampling indoors was 0.018 fiber/mL, with an upper 95% confidence limit of 0.034 fiber/mL. The maximum mean airborne concentration of PCM-equivalent chrysotile fibers observed under the passive conditions of the air sampling indoors was 0.010 fiber/mL, with an upper 95% confidence limit of 0.023 fiber/mL. No amphibole fibers were detected in any of these indoor samples. Only one asbestos fiber was detected in the sample collected outdoors. This fiber was a chrysotile fiber longer than 5 pm (but too narrow to be PCM- equivalent), and corresponded to an upper 95% confidence limit of 0.012 structure/mL. No asbestos fibers of any size were detected on the open field blank, corresponding to an upper 95% confidence limit of 0.007 structure/mL for an assumed air volume of 1200 liters. It must be appreciated that these are the airborne asbestos concentrations measured in samples collected under passive conditions and that airborne asbestos concentrations would become

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NYC-WTC_000199834