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SUMMARY 2 236fa and HFC-404a that it established for two chlorofluorocarbons (CFC-12 and CFC-114): a 1-hr EEGL of 2,000 parts per million (ppm), a 24-hr EEGL of 1,000 ppm, and a 90-day CEGL of 100 ppm. The Navy also proposes to apply those guidance levels to HFC-23, a combustion product of HFC-236fa. HFC-23 is formed when escaped HFC-236fa is passed through a submarine's carbon monoxide and hydrogen burners. STATEMENT OF TASK The National Research Council (NRC) was asked to conduct an independent evaluation of the Navy's proposed exposure guidance levels for HFC-236fa, HFC-23, and HFC-404a. The NRC assigned this task to the Committee on Toxicology (COT), which convened the Subcommittee on Exposure Guidance Levels for Selected Hydrofluorocarbons, a multidisciplinary group of experts. The subcommittee was asked to review the available toxicity data on the three HFCs and to determine the scientific validity of the Navy's proposed EEGLs and CEGLs. The evaluation was to include an assessment of the relevance of animals studies for evaluating risks to humans, the completeness of the data base, the target organs of toxicity, and the appropriateness of the methods used to derive the guidance levels (e.g., correctly adjusting for exposure durations and the use of uncertainty factors). The subcommittee was asked to review the three HFCs only in the context of use aboard submarinesâvessels with male personnel only. The subcommittee was also asked to identify any deficiencies in the data base on each HFC and to make recommendations for future research. Although products other than HFC-23 are formed during combustion of HFC-236fa or HFC-404a, HFC-23 was the only combustion product the subcommittee was asked to consider. APPROACH TO THE STUDY The subcommittee conducted a critical analysis of the available toxicity data on each of the HFCs and used the data to calculate possible EEGLs and CEGLs according to the guidelines outlined in the NRC's 1986 report Criteria and Methods of Preparing Emergency Exposure Guidance Level (EEGL), Short- Term Public Emergency Guidance Level (SPEGL), and Continuous Exposure Guidance Level (CEGL) Documents. The subcommittee also reviewed the Navy's toxicity assessments of the HFCs and used information provided in a 1996 report of
