Chain of custody form for DEP environmental samples, 2001

NYC 9/11 Public Portal Document

5.11 Observations

5.11.1 Review of Personal Monitoring Data

In addition to evaluating the efficiency of various cleaning methods, the study assessed the potential for exposure to workers during the actual cleaning procedures. This was accomplished through the collection of personal monitoring data (approximately 500 samples) while cleaning was taking place. These samples, which measured airborne levels of asbestos, lead and silica, provide insight, although limited by the scope of the pilot program, into the potential exposures incurred by residents during cleaning activities.

All air samples (103) that were analyzed by phase contrast microscopy (PCM) were below the Occupational Health and Safety Administration’s (OSHA) Permissible Exposure Limit (PEL) for asbestos of 0.1 free. The PEL represents a time-weighted average over a 40 hour work week, and is intended to protect workers from adverse health effects. Although PCM analysis is the required analytical procedure for compliance with OSHA PEL for asbestos, EPA conducted an additional analysis of samples using transmission electron microscopy (TEM) for all samples that were greater than 1/10 the OSHA PEL (64 samples). This follow up analysis by the more powerful transmission electron microscope determined that very little of the fibrous material identified by PCM was actually asbestos. PCM cannot distinguish asbestos from other non­ asbestos fibers (e.g., fibrous glass), whereas TEM has that ability.

Personal air monitoring results (44 samples) for lead were all below the OSHA PEL of 50 (J-g/m^. The PEL represents a time-weighted average over a 40 hour work week, and is intended to protect workers from adverse health effects. No individual sample exceeded 1 P-g/m^.

Personal air monitoring results (97 samples) for crystalline silica (quartz) were, with one exception, below the OSHA PEL of 100 gg/m^. The PEL represents a time-weighted average over a 40 hour work week, and is intended to protect workers from adverse health effects. The quartz concentration in the sample that exceeded the PEL was 108 gg/m^. Only 19 of the 96 samples were above the approximate detection limit of 5 gg/m’.

Asbestos, lead and crystalline silica (quartz) are substances that have been identified as WTC contaminants of potential concern in the indoor environment. The personal monitoring data obtained during the study, within the range of contamination found in the building’s apartments, that the use of personal protective equipment (e.g., respirator, gloves) during cleaning activities (vacuuming, wet wiping) was not necessary.

5.11.2 Final Observations

EPA’s position remains that individuals concerned about the presence of WTC-related dust should use HEPA vacuums and wet wiping to remove the dust from their dwelling spaces. Depending on the amount of dust deposited, repeated cleanings may be necessary.

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