NYC-WTC_000230857

NYC 9/11 Public Portal Document

Submitted to American Industrial Hygiene Association. October 2, 2001

analysis unit using both the secondary and back-scattered modes. Using the back- scattered electron (BE) mode, the sample was examined for particles that contained heavy elements. This procedure is useful in locating particles containing toxic metals such as lead and cadmium. Using the secondary electron (SE) mode, the sample was examined for particles that were consistent with asbestos fibers. X-ray elemental analysis (energy dispersive spectrometry (EDS)) was performed on each particle located for further study by either the BE or SE scans. The fine (small) fraction of the samples were qualitatively analyzed with analytical electron microscopy (AEM) using a JEOE 1200, 100 kV scanning transmission electron microscope (STEM), equipped with a Noran EDS x-ray analysis system.

Airborne asbestos analysis was performed by Scientific Eaboratories, Inc. in the following manner. The TEM air sample analysis method chosen for this specific application was the modified EPA Eevel n analysis Method following Yamate et al. (1984), chosen in order to provide the greatest flexibility in sample preparation and analysis. Heavy non-asbestos particulate loading encountered in many WTC air samples precludes analysis under the lower loading limitations of the EPA AHERA protocols which are optimized for clearance testing in essentially particle free atmospheres. Indirect preparation methods were applied when the Eevel II loading limitations were exceeded and the non-asbestos particulate obscured short, thin asbestos fibers (USEPA,, 1990). The possibility of bundle dispersion into single fibrils was expected to be of minimal impact due to the already highly dispersed nature of the asbestos aerosols observed in the WTC air samples (see figures 7 & 8). The air sample filters were gently collapsed using a DME/acetic acid/Dl water solution with mild heating on a slide warmer. The collapsed filters were subjected to the AHERA/EPA Level II calibrated plasma ashing procedure prior to deposition of a thin carbon support film. The carbon film covered, collapsed filter was placed onto a 200 mesh locator grid (Emicron, Inc.) and placed in a Jaffe wick DME bath followed by an acetone rinse, Jaffe wick bath in order to remove the remaining MCE filter. The resulting direct preparation sample was analyzed by AEM in a JEOE 100-CX II TEM, equipped with an IXRE EDS x-ray analysis system. A total of 10 grid openings (5 on each of two grids) were analyzed. When the non-asbestos particulate loading was excessive, the particulate on a 1/4 segment of the filter was resuspended in DI water using mild agitation in a low power sonicator bath and an aliquot of the suspension was refiltered onto a 0.1 pm pore size MCE filter. The dried, indirect filter preparation was prepared as described previously.

PCM was performed on a portion of the original filters following the NIOSH 7400 method, Issue 2, 1994. The filters were collapsed using a VAP 300 acetone vaporizer (BGI Inc, Waltham, MA) and covered with a cover slip after application of a drop of triacetin. The prepared samples were analyzed on a calibrated Olympus CH-2 Phase Contrast Microscope at 400X. A total of 100 fields of view or 100 fibers in a minimum of 20 fields of view were counted on each sample. All fibers > 5pm long with an aspect ratio >3:1 were counted and assumed to be asbestos.

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