WTC environmental health assessment draft, May 2002

NYC 9/11 Public Portal Document

The Tier I level for refractory ceramic fibers (RCF) in settled dust was based on Millette’s (full name & reference?) K factors, which are empirical relationships between concentrations of asbestos fibers in settled dust and indoor air, Millette developed the K factors by studying matched air and dust samples taken from various homes, at varying levels of activity in the home. The Tier I level was based on the K factor for a worst case scenario of a high level of activity. Although K factors are based on activity data for asbestos, they are believed to be protective for larger RCFs that are less airborne. In addition, although K factors are not rigorous enough to rely upon for a firm health decision, they are used here only to define what might constitute elevated fiber counts, that would need to be addressed as a near-term concern. This approach ma.y overestimate potential exposures, but as such, is protective.

The Tier I level for RCF in indoor air was based on the American Conference of Governmental Industrial Hygienists’ (ACGIH) threshold limit value (TLV) of 0.2 f/cc. ThatTLV is based on plural and lung function abnormalities and a potential for carcinogenic effects after long term exposures. Although quantitative risk estimates specific to RCF are not available, RCF is expected to be intermediate in its toxic effects between other forms of fibrous glass and asbestos. Therefore, in the face of uncertainty, the conservative approach was taken to set screening values for RCF similar to those for asbestos.

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CONFIDENTIAL, CITY_21MC100_003423804 SUBJECT TO PROTECTIVE ORDER NO. 2, SEPT. 2008

NYC-WTC_000176175