Law Department notice on WTC document preservation, Oct 2001

NYC 9/11 Public Portal Document

Screening Level Chloro-methane .4 ppm [1] Region 2 [2]

2.6 ppm [3] Region 2 [2] 1,4 Dioxane .5 ppm [3] Region 2 [2] Ethanol 45 ppm American Conference of Government Industrial Hygienists Threshold Limit Ethyl­ 2.5 ppm [1] Region 2 [2] benzene Freon 22 140 ppm Not Identified Rropylene simple asyphyxiant Styrene 2.3 ppm [1] Region 2 [2] Alpha methyl .Ippm [1] Region 2 [2] styrene Tetrahydro-furan .9 ppm [3] Region 2 [2] Toluene 1.1 ppm [1] Region 2 [2] Xylenes 1 ppm ATSDR Minimum Risk Level x 10. Represents screening level for chronic (over 365 days) exposure. Used to identify contaminants of potential concern. Acetaldehyde .05 ppm [1] Region 2 [2] 1.3 ppm [3] Region 2 [2] Formaldehyde .04 ppm ATSDR Minimum Risk Level for acute exposure. Represents screening level for acute (1 - to 14-day) exposure to identify a potential concern. .35 ppm [3] Region 2 [2] Acrolein .0001 ppm [1] Region 2 [2]

Notes:

[11 = Represents risk of non-cancer disease based on a 1-year continuous exposure at screening level. The hazard quotient represents the ratio of the potential exposure to the substance and the level at which no adverse health effects are expected. If the quotient is greater than 1, then adverse health effects are possible. For WTC's response, the screening level established equals a hazard quotient of 10. [2] = Region 2 developed the screening level using ERA'S “Hazard Evaluation Handbook: A Guide to Removal Actions," and toxicity criteria from ERA'S Integrated Risk Information System database. [31 = Represents a 1-in-10,000 increased lifetime risk of cancer based on a 1-year continuous exposure at the screening level.

80 Report No. 2003-P-00012

NYC-WTC_000145600