NYC-WTC_000164840

NYC 9/11 Public Portal Document

Asbestos

Tier Action Asbestos (settled dust) Asbestos (indoor air) Screening Basis Screening Basis Value Value I Aggressive > 100,000 Risk-based > 0.0004 f/cc * Risk-based cleaning. If levels f/cm2 screening level screening level persist, take for residential for short term additional action to setting (E-04 x 1 exposures (< = reduce exposure. y) 1 yr) may result in exposures which contribute to long-term risk.

II Maintain 10,000 to Risk- based NYC *Risk- based recommended 100,000 f/cm2 screening level background to screening level cleaning methods. for residential 0.0004 f/cc * for residential Consider additional setting (E-04 x setting (E-04 x monitoring 30 yr) 30 yr).

III No further action <or = <or = NYC required. background or background 1000f/cm2 * f/cc = fibers (greater than 5 micrometers long) per cubic centimeter of air. Note that fibers and structures are used interchangeably in this report.

For asbestos in indoor air, the Asbestos Hazard Emergency Response Act (AHERA) standard of 70 structures per square millimeters (S/mm2), as measured by Transmission Electron Microscopy (TEM) analysis, has been used since the 1980s to confirm effective abatement of asbestos­ containing material in schools. The standard represented the highest detectable level of background contamination on blank filters at the time (in the 1980s), not a risk-based analysis.

In order to develop risk-based benchmarks for this report, the AHERA standard was compared to a risk-based approach called Phase Contrast Microscopy (PCM). PCM was used for airborne asbestos analysis in most of the occupational epidemiology studies that provide robust dose­ response data on asbestos-related carcinogenesis. AHERA’s TEM fiber counts were converted to structures that would be visualized had the analysis been done by PCM. It should be noted that the correlation between total PCM fiber and TEM fiber counts is very uncertain and is likely to vary from one venue to another; therefore, no standard conversion factor exists for these two measurements.

The process for estimating cancer risk based on the AHERA standard includes 1) harmonizing the standard (TEM counts) with the dose-response metric (PCM counts); 2) converting units of measurement from fibers per unit area of filter paper to fibers per unit volume of air; and 3)

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