EPA memo re: asbestos assessment and Superfund advantages, Jan 2002

NYC 9/11 Public Portal Document

AHER4 TEM clearance test not sensitive enough to detect hazardous levels of asbestos

The first, and fatal problem in using the AHERA TEM test is that it is quite insensitive. It caimot detect airborne asbestos at levels that are shown to cause excessive cancers.

First, it is necessary to explain a very confusing way in which the results of the AHERA TEM test are reported. There are three different ways to express the results, using one or all of the following units of measure:

structures per square millimeter (s/mm^) structures per milliliter (s/mL) structure per cubic centimeter (s/cm^)

The “structures per square millimeter” unit is the value the laboratory gets first, before converting it to structures per milliliter. The lab needs to use the volume of air pulled across the filter to make this conversion. Since a “milliliter” is the exact same volume as a “cubic centimeter,” the last two units are identical and used interchangeably. See my December 19 memo for a more detailed explanation.

EPA has been giving test results using the “structures per square millimeter” units. EPA will typically describe results as “below 70 structures per square millimeter” or however much was detected above 70. But what does 70 s/mm? mean? This is not a SAFE level. This is only the lowest level that the method can detect. This 70 structures per square millimeter (s/mm’)level is equivalent to 0.02 structures per milliliter (s/mL):

The 0.02 s/mL (which is equivalent to 70 s/mm^) level is not a safe level. It is only the lowest level that the method can detect because of the method background (there is asbestos in the cellulose filters used to collect the air). The EPA has determined that a concentration of asbestos in air that is 0.0004 s/mL will result in an increased risk of cancer of 1 in ten thousand." An elevated cancer risk of over 1 in ten thousand is the action level, or trigger, for EPA to declare an imminent and substantial endangerment to public health under CERCLA, as explained in Section 4 of this memo. Thus, the AHERA TEM clearance text can only tell if the air has 50 times the safe level (or 10 times the safe level if it is assumed that only 20% of the asbestos is in the hazardous size range called “PCM-equivalent.”).

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