Re-occupancy recommendations for 170 Broadway, Sep 2001

NYC 9/11 Public Portal Document

FEB-25-2002 18:05 HYG I ENET I CS NYC 212 244 8505 P.09/21

Ms. Peggy Nash September 27, 2001 Page 2

Sainole Data and Disc

Please refer to copies of the attached analytical laboratory's report for the results of the sampling conducted. In summary, the levels of measured airborne fibers present during the sampling period were low, and did not approach or exceed any applicable, enforceable industrial exposure limits as set by governmental agencies.

At the present time, there are no non-industrial indoor air quality standards, or permissible exposure limits for airborne asbestos. However, a generally accepted airborne fiber concentration for "Clean Air" subsequent to asbestos abatement activities in commercial buildings in New York City is 0.01 fibers per cubic centimeter (f/cc). This 0.01 f/cc concentration is also referred to as a "Reoccupancy Criteria" by the NYC Department of Environmental Protection.

Subsequent to the environmental cleaning, the airborne fiber concentration was found to be below this (0.01 floc) value on all floors at 170 Broadway.

With regards to sampling analysis, optical Phase Contrast Microscopy (PCM) is a standard analytical method to assess airborne fiber concentration. This method does not distinguish between asbestos and non-asbestos fiber types, and only those fibers wider than 0.25 micrometers, greater than 5 micrometers in length, and with a length-to-width (aspect) ratio equal to or greater than 3:1 were counted. Because of these limitations, fiber counts by PCM typically provide an "index" of the total concentration of particulates in the ambient air of an occupied building.

If you have any questions or comments regarding the information presented herein, please feel free to contact Hygienetics at (212) 244 - 3443.

Very tr ly yours,

Laurence M. Jare Project Director

(attachment)

2060.033

NYC-WTC 000105741