NYC-WTC_000234515

NYC 9/11 Public Portal Document

CONFIDENTIAL

FOR INTERNAL USE ONLY

Considerations

1. Asbestos fibers are an inhalation hazard and there has been no direct correlation reported between settled dust and airborne levels. It can be inferred that higher settled dust levels have the potential to lead to higher airborne levels, but without a direct correlation, these levels would be based on supposition. The use of aggressive (e.g. air circulating fans during sampling) TEM air samples would be more appropriate in determining public risk.

2. The screening values are set with 1,000 17cm’ or the background. The background level using microvac sampling is unknown. For practical purposes the screening value is therefore being set at 1,000 f/cmc

The basis of the 1,000 17cm’ appears to be the analytical sensitivity for the ASTM microvac sampling methodology. (ASTM D5755 §16.8- “An analytical sensitivity of approximately 1000 asbestos structures/ cm’ [calculated for the detection of a single asbestos structure] has been designed for this analysis”). This is parallel to the discussions and criticisms of the current standards.

When determining the background, the presence of inplace ACM and the history of ACM usage in the building must be obtained. Of particular concern, the clearance for re-occupancy after an asbestos project has not included microvac sampling. We do not know what level will be found at these sites when compared to buildings constructed without ACM.

From time to time, there has been an interest in determining the background levels in New York City. Some background air samples have been collected during past emergency incidents. The Department had plans to perform the necessary research with a background air monitoring study about ten years ago but the contract and funding fell through.

From time to time, USEPA and DEP have received requests for the information from research groups starting a project, therefore some data may be available through outreach. In addition, the asbestos rules require background air sampling prior to the start of an asbestos project. It is conceivable that a research group may obtain these background air sample results.

3. The ASTM D5755 document indicates the following limitations: 5.1.1 This test method does not describe procedures or techniques required to evaluate the safety or habitability of buildings with ACM or compliance with federal, state or local regulations or statutes. 5.1.2. At present, a single relationship between asbestos containing dust and potential human exposure does not exist.

CITY_21MC100_003235213

NYC-WTC_000234515