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Suggested Citation:"HFC-404A." National Research Council. 2000. Submarine Exposure Guidance Levels for Selected Hydrofluorocarbons: HFC-236fa, HFC-23,and HFC-404a. Washington, DC: The National Academies Press. doi: 10.17226/9815.
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SUMMARY 5 relatively nontoxic in laboratory studies and because similar HFCs, such as HFC-23 and HFC-134a, have been shown to have low toxicity in humans, the subcommittee recommends that tests be conducted with humans to determine whether HFC-236fa affects performance skills, such as motor coordination and alertness. HFC-23 The subcommittee believes that data on HFC-23 support a 1-hr EEGL of 20,000 ppm, a 24-hr EEGL of 5,000 ppm, and a 90-day CEGL of 500 ppm. The basis for the 1-hr EEGL was a human exposure study in which subjects were intermittently exposed to HFC-23 (eight exposures of 3 min each with 2-min intervals of exposure to air only). The NOAEL for the study was 200,000 ppm. To account for the discontinuous exposure, the NOAEL was divided by a factor of 10, resulting in a 1-hr EEGL of 20,000 ppm. For the 24-hr EEGL, a developmental toxicity study was used. Although such a developmental study is not necessarily the most appropriate study for deriving a 24-hr exposure guidance level, when considering the all-male population aboard submarines, that study had the most relevant exposure duration (a total of 90 hr), and no maternal or fetal effects were observed at the highest dose tested of 50,000 ppm. The NOAEL was divided by a factor of 10 to account for interspecies differences, resulting in an exposure guidance level of 5,000 ppm. The basis for the 90-day CEGL of 500 ppm was a 90-day continuous exposure study in dogs, in which the NOAEL was 5,000 ppm. That value was divided by an uncertainty factor of 10 to account for interspecies variability. HFC-404A HFC-404a is a gaseous mixture of three halocarbons—52% HFC-143a, 44% HFC-125, and 4% HFC-134a. The subcommittee believes that the most appropriate way to calculate exposure guidance levels for HFC-404a is the method used by the American Conference of Governmental Industrial Hygienists to calculate threshold limit values for special cases when the exposure of concern is a liquid mixture and the atmospheric composition is assumed to be similar to that of the original material (i.e., on a time-weighted- average exposure basis, all the liquid mixture eventually evaporates). In this case, when the percent composition by weight of the liquid mixture is

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As part of the effort to phase out the use of stratospheric ozone-depleting substances, such as chlorofluorocarbons (CFCs), the U.S. Navy is considering hydrofluorocarbons (HFCs) as replacements for the CFC refrigerants used aboard its submarines. Before using the HFCs, the Navy plans to set emergency exposure guidance levels (EEGLs) and continuous exposure guidance levels (CEGLs) to protect submariners from health effects that could occur as a result of accidental releases or slow leaks.

In this report, the Subcommittee on Exposure Guidance Levels for Selected Hydrofluorocarbons of the National Research Council's (NRC 's) Committee on Toxicology independently reviews the scientific validity of the Navy's proposed 1-hr and 24-hr EEGLs and 90-day CEGLs for two of the candidate refrigerants-HFC-236fa and HFC-404a. In addition, the subcommittee reviews the the EEGLs and CEGL for HFC-23, one of the combustion products of HFC-236fa. This NRC report is intended to aid the Navy in using HFCs safely.

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