WTC environmental health assessment draft, May 2002

NYC 9/11 Public Portal Document

2) Nleasuremeiit lieporting Units* Conversion from to f/cc

To accommodate a quantitative risk assessment paradigmrthe AIIERA standard must also be convcTted-from f/mrn2 todfcc. As per the AIIERA sampling criteria (i.c., sample volume of 1,200 L, filter diameter of 25 mm), the standard of 70 f/mm2 converts to 0.022 f/cc as demonstrated below 70 f X 385 mm2 (effective filtorarea of 25 mm filter) 1,200 Lx 1,000 cc/L

3) WTC Screening Levels

The draft risk-bascd screening analysis for WTC assumes an upper bound (continuous) exposure cstiinatc of one year duratronT ased on the IRIS inhalation unit riskrof 2.3 &-1 per (f/cc), excess lifetime cancer risk of 1 E-O*!- (onc-in-ten thousand) for a 70 year exposure duration equates to an asbestos concentration of .0004- f/cc. Adjusting the exposure duration to l~ycar at a 1 E-O^ cancernsk (target nsk used for WTC screening values) yields an airborne asbestos concentration of 0.028-f/cc.

Conclusion

The above analysis indicates that continuous exposure to 70 f/iiiiiiZ (under the worstxasc assumption that all fibers ^5 uni) for a one year exposure duration wouW-restrit4rriess-tht^ onC“in ten thousand- exceasdifetimc cancer risk.

It is worth noting that the unit (f/nmi2 to f/cc) conversion of the AIJJLilxA standard is a function of sample volume. The relationship is inverse. That is, the lower the sample volume the higher the asbestos concentra sufficiently less than 1,200 L, the AIIERA standard of 70 fymm2 would-convert to an airborne asbestos concentration-thatexcecds the one year, nsk-based value of 0.028 f/cc. However, of greater importance to note is that^to datcHess than 2 %'~of the samples have exceeded the- AIIER-A standard of 70 f/mm 2 and that the vast majority (approximately 80 -”90%) of fibers (from all sampling results) have been 5 um in length.

In conefusion, when taken in its totality (i.c., individual sample results, 1ength distribution of counted fibers, sample volume), The WTC airborne asbestos sampling data demonstrates that exposure to ambient air for a one year exposure duration is-below WTC risk-based screening levels?

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CONFIDENTIAL, CITY_21MC100_003423800 SUBJECT TO PROTECTIVE ORDER NO. 2, SEPT. 2008

NYC-WTC_000176171