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Suggested Citation:"TOXICOKINETICS." 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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Page 28

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HYDROFLUOROCARBON-23 28 Common name: HFC-23 Chemical name: Trifluromethane Synonyms: Freon 23, Genetron 23, fluoroform, HC-23, fluoryl, Arcton 1, carbon trifluoride, halocarbon 23, methyl trifluoride, R 23, FE-13 CAS number: 75-46-7 Structural formula: HCF3 Description: Colorless gas Molecular weight: 70.01 Boiling point: -82.03°C at 760 mm Hg Melting point: -155.2°C Density and specific gravity: 0.670 g/mL at 25°C Vapor pressure: 686 psig at 25°C (77°F) Vapor density: 2.4 (Air = 1.0) Flash point and flammability: Nonflammable Solubility: 0.10 wt% in water Autoignition: 765°C (1409°F) Octanol and water partition coefficient: Kow = 0.64 Conversion factors: 1 mg/m3= 0.35; 1 ppm = 2.86 mg/m3> TOXICOKINETICS Ewing et al. (1990) studied the use of HFC-23 in nuclear magnetic resonance spectroscopy as a gaseous indicator of cerebral blood flow in cats. HFC-23 at a concentration of 600,000 ppm was rapidly absorbed from the lungs and the arterial blood concentration reached a plateau within 3 or 4 min after initiation of the exposure. Likewise, HFC-23 was rapidly eliminated from the blood upon termination of the exposure. It was also rapidly taken up by the brain, with the brain uptake lagging the arterial blood uptake by about 2 min. Similar findings were demonstrated with 670,000 ppm by Detre et al. (1990) in the rat.

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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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