VOC sampling locations table for Ground Zero area, Jan 2002

NYC 9/11 Public Portal Document

of 70 S/mm’ was evaluated as being statistically distinguishable from the count that would come from a blank filter. That background count is about one-fourth the standard, or 17.5 S/mm^. The AHERA rule specifies that children would be allowed back into a school that has been undergoing asbestos abatement (removal and/or encapsulation) if the TEM readings were consistently below the count of 70 S/mm^. This would be evidence that the concentration was similar to background readings. Alternately, an abatement area could be deemed suitable for occupation if samples taken within the area were statistically similar to samples simultaneously taken outdoors in an asbestos-free environment. Details of these procedures are provided in the Final Rule, as cited above.

It should be noted that this standard is not health based, but rather technology based. It is also noted that the technology has improved since 1987, such that current filters often have much less than 17.5 S/mm’, sometimes close to 0 S/mm^. Therefore, 70 S/mm^ would be much higher than blanks and represents more than just a statistical elevation above background, above. Finally it is noted that while the AHERA standard was originally intended as an indoor ‘clearance’ standard, it is being used to evaluate outdoor exposures in this assessment.

The current OSHA PEL is also used in this assessment to evaluate air concentrations of asbestos measured using the PCM method. The PEL for occupational exposures to asbestos is 0.1 free by PCM averaged over an 8-hour day (OSHA, 1994). This standard is relevant for the comparison of exposure of rescue and other workers at the WTC site with current workplace standards. EPA also collected air samples analyzed for fibers by the PCM method that may be used for this purpose.

IV,e.3. Background Air Concentrations for Asbestos ATSDR’s Toxicological Profile for Asbestos (ATSDR, 1999) provides a summary of background asbestos levels. Because the health effects data regarding inhalation exposure to asbestos are usually expressed in terms of PCM free, ATSDR chose to convert ambient air data reported in units of ng/m^ or TEM free to units of PCM free. ATSDR’s summary included these crude assumptions: 1 PCM free is equal to 60 TEM f/cc and also approximately equivalent to a mass concentration of 30,000 ng/m\ (Note, however, that there was not sufficient analysis available for this current report to suggest applying these factors to asbestos measurement data for the WTC data.)

On this basis, the following summaries are excerpted from the profile (specific references supplied in ATSDR, 1999). It should be noted that these “background” data are derived from settings where no identified asbestos materials are present, as well as other settings, such as buildings containing asbestos materials where there may have been some local releases.

Data from several studies indicate that in urban areas, most ambient air concentrations range from 3*10’® to 3*10"* PCM free, but they may range up to 3*10'’ PCM free as a result of local sources. In another investigation, the median concentration in U.S. cities has been estimated to be 7*10'® PCM free.

A recent analysis of monitoring data for asbestos in ambient air worldwide estimated rural and urban levels at about PIO’^ TEM fZcc (2*10 ’ PCM f/cc) and 1*10"^ TEM f/cc (2*10"''’

DRAFT-DO NOT QUOTE OR CITE 89 October 2002

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