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NYC 9/11 Public Portal Document

As shown in Table 15.0, the comparison of these results suggest that no conclusive difference could be observed.

Overall, the samples collected using the aggressive technique had a slightly higher percentage of samples below the detection limit (80 percent vs. 69 percent) than the samples collected with the modified-aggressive technique, while the samples collected using the modified-aggressive technique had a lower average concentration (0.00045 S/cc) than the samples collected using the aggressive technique (0.00071 S/cc).

5.9 Filter Overloading

As mentioned above, there were many instances where the filters from the asbestos air samples were overloaded with particulate material and could not be analyzed, which resulted in invalid asbestos air results and required additional cleaning events. During the study, the use of an air filtration device was added to the cleaning method for the third cleaning in an attempt to reduce the airborne particulate matter as both previous air sampling events resulted in overloaded filters. This occurred twice. In both cases, there was no overloading of the filters and valid asbestos air results were received. This prompted an evaluation to determine if there was a noticeable reduction in overloading filters with particulate matter when an AFD was used during the cleaning event. The data for all of the units in the building were used to see if there was a difference in the percentage of units with at least one overloaded filter when an AFD was used.

Table 16.0 presents a comparison of the percentage of units, including residential, common spaces, and commercial spaces, with asbestos air samples that could not be analyzed due to the filter being overloaded with particulate matter, and indicates whether or not an AFD was used. The data suggest that using an AFD during cleaning may offer a slight advantage for reducing the potential for overloading a filter with particulate matter.

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