NYC-WTC_000196150

NYC 9/11 Public Portal Document

****J)RAFT****

Regardless of which account is most accurate or even if the two accounts actually emerged about the same time resulting in the final definition of asbestos containing material, neither account indicates that the derivation of the 1% rule was in a manner that employed considerations of human health. The 1% rule is not based on health.

Two main short-comings of the 1% rule exist.

► The 1% rule is not derived from a risk assessment or any other type of health based analysis.

► The 1% rule does not insure that asbestos air levels will be at levels that are protective of human health.

The second point is not well documented in the literature. But two personal communications o' indicate this is a major problem with the 1% rule. OSHA (personal communication with Dan Krane, OSHA) has examined over 6000 work places in which asbestos existed in bulk material between 0% and 1 %. Four percent of these work places had asbestos air levels at or above the OSHA permissible exposure limit (PEL) of 0.1 f /cc. The measurements were point determinations and not 8 hour time weighted averages (TWA). But had the exposures continued for 8 hours, 4 % of the work places would have exceeded the PEL even though materials in these work places did not exceed 1% asbestos w/w.

The second indication of the limits of the 1% rule comes from Libby, Montana (personal communication with Chris Weis, EPA). Preliminary data from investigations into different types of activities show that tilling the soil in gardens with < 1% detectable levels of asbestos resulted in air levels close to the OSHA PEL.

Conclusion: Tlie 1% rule has the advantage of being a legally enforceable level and precedence for its use is available. However the rule is not health based and may not provide adequate protection from airborne asbestos under a variety of conditions. Because of these limitations great care should be used in using any type of w/w percentage as guidance to protect human health. If percent determinations have to be made, they should be used only to confirm the presence or absence of asbestos or to recommend clean-up followed by further air testing. . A possible guideline is suggested below.

Interpretation of bulk and air samples: The following table provides a general guide for determining public health actions based upon sampling of both bulk material and indoor air. The table integrates the Environmental Assessment Workgroup multi-agency recommendations for reoccupation of residences in lower Manhattan (see attachment 1). It is important to note that the ultimate decision criteria for reoccupation is the ambient air level of asbestos. Bulk asbestos determinations are useful for (1) determining the potential for recontaminating ambient air and (2) for determining the type of further sampling needed.

In general the sampling and resampling strategy encompasses testing of bulk material and clean up until such a time that further clean up will not lower bulk asbestos levels. Confirmation is

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NYC-WTC_000196151