NYC-WTC_000219925

NYC 9/11 Public Portal Document I Search - 1 Result - APPENDIX A TO SUBPART E - INTERIM TRANSMISSION EL... Page 36 of 38

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. "Outside" means outside the abatement area, but not necessarily outside the building. EPA reasons that an asbestos removal contractor cannot be expected to clean an abatement area to an airborne asbestos concentration that is lower than the concentration of air entering the abatement area from outdoors or from other parts of the building. After the abatement area has passed a thorough visual inspection, and before the outer containment barrier is removed, a minimum of five air samples inside the abatement area and a minimum of five air samples outside the abatement area must be collected. Hence, the response action is determined to be completed when the average airborne asbestos concentration measured inside the abatement area is not statistically different from the average airborne asbestos concentration measured outside the abatement area.

The inside and outside concentrations are compared by the Z-test, a statistical test that takes into account the variability in the measurement process. A minimum of five samples inside the abatement area and five samples inside the abatement area and five samples outside the abatement area are required to control the false negative error rate, i.e., the probability of declaring the removal complete when, in fact, the air concentration inside the abatement area is significantly higher than outside the abatement area. Additional quality control is provided by requiring three blanks (filters through which no air has been drawn) to be analyzed to check for unusually high filter contamination that would distort the test results.

When volumes greater than or equal to 1,199 L for a 25 mm filter and 2,799 L for a 37 mm filter have been collected and the average number of asbestos structures on samples inside the abatement area is no greater than 70 s/mm<2> of filter, the response action may be considered complete without comparing the inside samples to the outside samples. EPA is permitting this initial screening test to save analysis costs in situations where the airborne asbestos concentration is sufficiently low so that it cannot be distinguished from the filter contamination/background level (fibers deposited on the filter that are unrelated to the air being sampled). The screening test cannot be used when volumes of less than 1,199 L for 25 mm filter or 2,799 L for a 37 mm filter are collected because the ability to distinguish levels significantly different from filter background is reduced at low volumes.

The initial screening test is expressed in structures per square millimeter of filter because filter background levels come from sources other than the air being sampled and cannot be meaningfully expressed as a concentration per cubic centimeter of air. The value of 70 s/mm (2) is based on the experience of the panel of microscopists who consider one structure in 10 grid openings (each grid opening with an area of 0.0057 mm (2) to be comparable with contamination/background levels of blank filters. The decision is based, in part, on Poission statistics which indicate that four structures must be counted on a filter before the fiber count is statisticallyy distinguishable from the count for one structure. As more information on the performance of the method is collected, this criterion may be moddified. Since differnet combinations of the number and size of grid openings are permitted under the TEM protocol, the criterion is expressed in structures per square milimeter of filter to be consistent across all combinations. Four structures per 10 grid openings correspondds to appropriately 70 s/mm <2>.

B. Sample Collection and Analysis

1. A minimum of 13 samples is required: fivee samples collected inside the abatement area, five samples collected outside the abatement area, two fieidd blanks, and one sealed blank.

2. Sampling and TEM analysis must bee done according to either thee mandatory or nonmandatory protocols in Appeendex A. At least 0.057 mm (2) of filter must be examined on blank filters.

http://lexis/research/retrieve?_m=el35f2ca3d266867e53d261df3205722&_fintstr=FULL(S... 02/04/2002 CITY_21MC100_012558700

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