NYC-WTC_000232959

NYC 9/11 Public Portal Document

Each of the particulate air sample fractions was analyzed for crystalline minerals (quartz, cristobalite, tridymite, calcite, portlandite, gypsum, mica, and halite). X-ray diffraction analysis (XRD) identifies a mineral by the unique diffraction pattern given off when the x- ray strikes its surface. The diffraction pattern serves as a “fingerprint” to identify the mineral present.

Other air samples were screened for fibers using phase contrast microscopy (PCM) to count the total number of all fibers present. If the concentration of total fibers was higher than the maximum concentration of fibers found in the comparison homes (0.003 fibers per cubic centimeter of air) the sample was re-analyzed for asbestos by transmission electron microscopy (TEM). Additionally, scanning electron microscopy (SEM) was used to look for SVF if the PCM fiber counts was higher than 0.003 fibers per cubic centimeter (f/cc) and if the settled surface dust sample from that area contained SVF.

Settled Surface Dust Samples

The composition of settled surface dust reflects particles and fibers that have been tracked into an area or that were present in the air and have with time, deposited on surfaces. Settled surface dust was collected indoors using a specialized vacuum cleaner. Outside settled surface dust was collected by scooping any visible dust-type material into a container. As with the air samples, the settled surface dust samples were analyzed to assess the presence of fibers and minerals. The analysis performed does not allow the determination of what size particles are present in the dust. The composition of the settled surface dust was evaluated to determine if, on the basis of its composition, it could be an irritant if it became airborne or came in contact with skin or eyes during cleaning activities.

The dust samples were analyzed for the presence of asbestos and SVF using polarized light microscopy (PLM). PLM can distinguish between fiber types by their unique appearance and color when viewed under different wavelengths of light. In addition, TEM analysis was conducted on all dust samples that showed asbestos content by PLM as less than 1%. TEM analysis is very specific, can detect smaller fibers of asbestos, and is subject to less interference than PLM.

The dust samples were also analyzed for mineral content using XRD as described previously for the air samples. For the dust samples, the mineral and the fiber results are expressed as a percent, indicating the weight percent each component represents in the portion of the dust sample analyzed. The different analytical techniques, XRD and microscopy (PLM, TEM, SEM), help to characterize what was in the settled surface dust; however the results from the two methods each performed on a portion of the dust collected, cannot simply be added together to “sum up” what was in the dust. XRD results are based upon the weight of the dust sample analyzed. While, PLM, TEM, and SEM results are based on the surface area viewed under the microscope.

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