ing Bayliss et al. (1976) and Enterline et al. (1987). OSHA was also concerned with potential carcinogenic effects of refractory ceramic fibers (RCF). In evaluating the existing exposure level, the Navy reviewed the scientific data on MVF but concluded that neither 3 f/cm3 nor 1 f/cm3 was necessarily scientifically justified. It selected a standard of 2 f/cm3 because this it was more stringent than the NIOSH REL but not as stringent as the OSHA PEL (Krevonick 1998). The Navy selected an exposure level that was the average of the two existing occupational exposure limits.

In January 1999, the Navy revised its Occupational Safety and Health Program Manual, changing the occupational exposure limit for MVF to the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) of 1 f/cm3 (CNO 1999). The Navy then requested that the subcommittee address several questions concerning the selection and adoption of the original 1995 standard of 2 f/cm3 and the appropriateness of the newly established standard of 1 f/cm 3. These questions were: Are there any studies in the scientific literature that the Navy should have considered that would have justified an exposure standard of more than or less than 2 f/cm3? Is the process that the Navy used to adopt the 2-f/cm3 standard appropriate for MVFs? Does the subcommittee feel that the reduction in the exposure standard from 2 to 1 f/cm3 is justified on the basis of current scientific evidence?

The subcommittee believes that the Navy did not fail to consider any specific scientific studies that would have justified selecting an exposure standard that was higher or lower than 2 f/cm3 when it adopted this standard in 1995. However, the subcommittee does not consider the method used by the Navy to adopt the 2-f/cm 3 standard to be justifiable on the basis of the exposure limits given by OSHA and NIOSH, nor was it scientifically defensible. The Navy could have chosen to adopt one of the existing exposure limits (that is, NIOSH or OSHA), as stated in the Navy Occupational Safety and Health Program Manual (CNO 1994). If the Navy had elected to use an existing limit, it should have considered selecting the more conservative exposure limit of 1 f/cm3. This exposure limit would be more protective of workers, particularly in light of the toxicological data that suggested the carcinogenic potential of RCF (Davis et al. 1983; Mast et al. 1995a; Mast et al. 1995b; McConnell et al. 1995). Alternatively, if the Navy intended to derive a new exposure standard, a risk assessment based on a rigorous scientific evaluation of the toxicological and epidemiological data should have been conducted to

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