NYC-WTC_000230857

NYC 9/11 Public Portal Document

Submitted to American Industrial Hygiene Association. October 2, 2001

Findings

The particle size distribution of the surface residue at two locations, #6 and #10, are presented in Table 2. The data describe a residue that is dominated by very small particles with larger particles consisting primarily of mineral wool (fiber) aggregates.

The composition of the settled residue is presented in Table 3 and Table 4. The residue from both locations is uniform in its composition reflecting both the effect of fire and force applied to building materials and contents. Of note is the presence of small chrysotile asbestos bundles, both with and without attached binder.

The asbestos content determined by visual estimation and point counting is presented in Table 5. Asbestos was not observed in three samples, locations 3, 8 and 9. These locations are on a line approximately due north of WTC Building #7. All specimens on the 45° and 90° radians were found to contain asbestos by at least one analyst (see figure 6). The point counting method produced a range of positive values from <0.25 - 0.75%. This range is consistent with the compositional description provided by the particle characterization and not inconsistent with the visual estimation.

Airborne asbestos concentrations within two building structures that are damaged but standing and repairable are presented in Table 6. The transmission electron microscopy/ energy dispersive spectrometry (AEM) analysis detects a dominance of small, thin asbestos fibers less that or equal to 5 microns (<5 jam) in length. Some longer fibers are also present but are generally one order of magnitude lower in concentration. Airborne asbestos concentrations measured by light microscopy are generally higher than concentrations reported using electron microscopy for fibers greater that 5 microns (>5 |am). The opposite relationship is found between airborne asbestos concentrations measured by light microscopy and those reported using electron microscopy for fibers less than or equal to 5 microns (<5 (tm). Comparisons for air samples which could be prepared and analyzed by both direct and indirect analysis indicates that for this matrix and set of circumstances the apparent asbestos fiber concentration may increase by as much as a factor of 10 for samples undergoing indirect preparation.

Discussion

Health risks associated with inhalation exposure to asbestos fibers have been an area of emphasis for public health practitioners for many decades (Lehman, 1936; Gilson, 1962; Landrigan, 1999; Anttila, 1993; Hillerdal, 1999; Kamp, 1999). During that time, toxicologists and epidemiologists conducted risk assessments and developed exposure criteria to manage and reduce known risk to appropriate levels for workers and the general population. In some cases these criteria have been promulgated by various governmental agencies as exposure limit standards. To evaluate worker and general population exposure to all airborne asbestos fibers, specialized laboratory methods have been used (Yamate, 1984; AHERA, 1987). As with all analytical methods, the various asbestos analytical methods have specific useful applications and limitations (Verma, 1995; Dement, 1990). Not all methods are suited to all applications and care must be

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