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HYDROFLUOROCARBON-236FA 25 divided that value by an uncertainty factor of 10 to account for interspecies differences, yielding a value of 2,000 ppm. The Navy's proposed 24-hr EEGL of 1,000 ppm is half this value and is thus an adequate exposure guidance level. In its evaluation of the Navy's proposed 90-day CEGL of 100 ppm for HFC-236fa, the subcommittee used the 14-week study in rats (Valentine 1996). On the basis of transient decrements in alerting response, a NOAEL of 20,000 ppm was determined. The subcommittee divided that value by a factor of 10 to account for interspecies differences to yield a value of 2,000 ppm. Because the study involved a discontinuous exposure regimen, the subcommittee multiplied that value by 1/4 (to account for exposure for 6 hr per day) and by 5/7 (to account for exposure five times per week), which yielded a value of about 350 ppm. The Navy's proposed 90-day CEGL of 100 ppm is below that value, and, therefore, the subcommittee concludes that the Navy's CEGL is adequately protective of health for prolonged exposures. The subcommittee noted that a developmental toxicity study in rats (Munley 1995) reported reduced weight gain and decrements in alerting response in the dams at 20,000 ppm, the same concentration as the NOAEL identified in the 14-week toxicity study. Because the purpose of this project was to establish exposure guidance levels for use on submarines, vessels that have no female crew members, the subcommittee did not use the developmental toxicity study as the basis for calculating the 24-hr EEGL or 90-day CEGL. However, if HFC-236fa is considered for use on vessels with female personnel, those values might have to be reconsidered on the basis of maternal toxicity. RECOMMENDATIONS Uncertainties exist with regard to the effects that HFC-236fa might have on human performance. End points of narcosis and decrements in alerting response have been observed in laboratory animals, but it is unclear whether human performance would be affected similarly. Because HFC-236fa was relatively nontoxic in laboratory studies and because human studies have been conducted with other HFCs, such as HFC-23 and HFC-134a, the subcommittee recommends that tests be conducted with humans to determine whether HFC-236fa affects performance skills, such as motor coordination and alertness.
