EPA memorandum on carpet asbestos testing, June 2002

NYC 9/11 Public Portal Document

APPENDIX B : ASBESTOS AIR CONCENTRATIONS AND RISKS

Table B gives the cancer risks for exposures to asbestos at different air concentrations. There are 3 different calculations that you must do before using this chart.

1. Estimate the air exposure

From Appendix A, you can estimate the air exposure using the settled dust level. As an alternative, you can use an actual measured air level. Note that the AHERA TEM clearance test level of 70 structures per square millimeter is the same as 0.01 PCM-equivalent f/mL, and is given directly on Table B.

2, Convert the air levels to “PCM-eauivalent fibers per milliliter”

The “PCM equivalent” fraction of asbestos fibers are those asbestos fibers at least 5 micrometers (nm) long, with a width greater than 0.25 p.m, and an aspect ratio greater than or equal to 3 to 1. These are fibers small enough to be inhaled deeply into the limgs (“respirable size”), but also large enough to be retained by the lungs. It is believed that fibers shorter than 5 pm can be engulfed by macrophages and carried out of the lungs, and do not contribute to cancer.

The older studies upon which the EPA risk assessment levels are based used analytical methods which could only detect the larger, PCM-equivalent fibers. Presumably, the smaller asbestos fibers were also present in the populations addressed by these early studies as well. Thus, it would be incorrect to directly compare newer studies where all sizes of fibers are detected with older studies where only the larger fibers were detected. The way to make the studies comparable is to convert the newer studies data to PCM-equivalents, the units used in the older studies. When the PCM-fraction is unknown for transmission electron microscopy (TEM) levels, a good rule of thumb is to divide by at least 2, if not 4 or more.

3. Convert the 70-year exposure risk level to shorter exposures

If an exposure is for a shorter period of time than 70 years, multiply the risk level by the firaction of 70 years exposure. For example, if a person is only exposed for 35 years, 24 hours per day, multiply the risk by >2 (multiply by 0.5). If the person is only exposed for 1 year, multiply by 1/70 (multiply by 0.014).

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