EPA memo re: wipe sampling and cancer risk at WTC,

NYC 9/11 Public Portal Document

Re Ing TEM air measurements in either “structures/square millimeter” or “structures/milliliter”

To complicate things further, in the WTC disaster, EPA’s web site’’ has only been reporting TEM measurements in the units of “structures/square millimeter” ( s/mm’), which IS NOT THE SAME as “structures/milliliter ( s/mL )”. The actual lab sheets, which were obtained by a ’freedom of Information Act request and pos ted at the New York Environmental Law and Justice Project web site“ gave the asbestos levels in both units.

The “structures/mm’" unit refers to the number of structures on a given area of a filter through which the air drawn. There is no easy way to convert “structures/square millimeter” to “fibers/millilitei”unless you have fire volume of air sampled from the original lab sheet This is because you need the air volume to convert fibers/miHimeter to fibersZmilliliter, and this volume is not always the same. Any level reported as structures/square millimeter will always be much higher than the structures/milliliter, usually by a factor of at least 100.

The “70 structures or less” AHERA clearance standard for air

In the World Trade Center disaster, EPA has said that it is using die level of 70 or fewer asbestos structures/square millimeter standard required by the Asbestos Hazard Emergency Response Act (AHERA). This 70 or fewer structures does not correspond to any level found to be related to health effects. Instead, it is the equivalent to detecting 4 structures in 10 IBM grid openings in a filter through which air has been drawn.

The AHERA “Standard” for clearance is - “A response action is determined to be completed by TEM when the abatement area has been cleaned and the airborne asbestos concentration inside the abatement area is no higher than concentrations at locations outside the abatement area.” The 70 structures criterion is an intermediate standard designed to reduce die number of analyses (and costs) by stating that if the average loading on die five samples collected inside the abatement does not exceed 70 structures.mnf, the samples a’-e below filter backgrounds and there is no need to analyze the five outside samples and perform the “Z-test.”

The filters used to collect the asbestos in air are always contaminated with low levels of asbestos. The fibers found as background on the filter were present without any air being drawn through the filter. Thus, diis 70 structures/square millimeter corresponds roughly to a general laboratory method background level of 0.02 structures/milliliter.

“cc” and “mL” are the same thing, “um” and “um” are the same thing

Milliliters (mL ) are the same as cubic centimeters ( cc ). Air concentrations are sometimes reported using cubic centimeters instead of milliliters, as in “fibers/cc” or “fibers/mL”.

Micrometers are abbreviated either as “gm” with the Greek “ g ” or as “ um”.

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