Memorandum on asbestos wipe sampling and cancer risk estimation, December

NYC 9/11 Public Portal Document

Reporting 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 posted 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/milliliterunless you have die volume of air sampled from the original lab sheet. This is because you need the air voltune to convert fibers/miUimeter to fibers/milliliter, and this volume is not always the same. Any level reported as structures/square millimeter will always be much higher than die structures/milliliter, usually by a factor of at least 100.

The “70 structures or less” AijT®A clearance standard for air

In die World Trade Center disaster, EPA has said that it is using the 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 the munber of analyses (and I costs) by stating that if die average loading on the five samples collected inside the abatement does not exceed 70 structures.mnf, the samples are 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, this 70 stfuctures/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 “pm” with the Greek “ p ” or as “ um”.

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