average of the two values. However, given the Navy's stated goal of having a reasonable yet protective fiber standard, the subcommittee concludes that the adoption of the OSHA PEL of 1 f/cm3 would have been more conservative. Alternatively, the Navy could have derived its own occupational exposure standard by conducting a risk assessment based on a rigorous scientific review of existing toxicological and epidemiological data.

In January 1999, the Navy policy for establishing occupational exposure standards was changed. That resulted in the adoption of the ACGIH TLV of 1 f/cm3. The subcommittee believes that lowering the standard from 2 to 1 f/cm3 is appropriate on the basis of available toxicological and epidemiological data and is in accord with other national and international occupational health limits for MVF.

The subcommittee concludes that 1 f/cm3 might not be protective for RCF or for some other MVF that are particularly biopersistent. The subcommittee recommends that the Navy consider setting separate exposure standards for the more biopersistent fibers.

Information Gaps and Recommendations for Future Research

Future research efforts should focus on identifying and monitoring the health effects associated with different fiber types. Animal models that are most appropriate for human health risk assessment of MVF should be identified. The development of short-term screening assays to predict long-term effects should encourage the testing of new fibers for health effects. Epidemiological studies should look not only at workers engaged in the manufacture of MVF, but also at those involved in their installation, maintenance, and removal. Data on the latter types of exposure are available for RCF but are less robust for other MVF, especially with regard to exposures during MVF removal. Monitoring studies of workers exposed to new, used, or stressed fibers would add considerably to the understanding of the health effects of both short-term and long-term exposures to these fibers.

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