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HYDROFLUOROCARBON-404A 73 EXPOSURE GUIDANCE LEVELS FOR HFC-404A The Navy proposes to use the same exposure guidance levels for HFC-404a that were set for CFC-12 and CFC-114 (1-hr EEGL of 2,000 ppm, 24-hr EEGL of 1,000 ppm, and 90-day CEGL of 100 ppm), but did not provide an adequate rationale for doing this. To evaluate the validity of the proposed guidance levels, the subcommittee reviewed the available toxicity data on HFC-404a to determine what levels would be adequately protective of submariner health. A comparison of those results is presented below. Submarine Exposure Guidance Levels for HFC-404a Exposure Level NRC's Calculated Levels Navy's Proposed Levels 1-hr EEGL 12,900 ppm 2,000 ppm 24-hr EEGL 4,300 ppm 1,000 ppm 90-day CEGL 800 ppm 100 ppm 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 (ACGIH 1999) to calculate Threshold Limit Values (TLVs) 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 of the liquid mixture eventually evaporates). In that case, when the percent composition by weight of the liquid mixture is known, the exposure guidance levels can be determined using the following equation: The letter f stands for the fraction of each particular component. The component's corresponding TLV or, for the purposes of this report, exposure guidance level is expressed in units of milligrams per cubic meter (mg/m3) (see Table 4-5). Using this equation, exposure guidance levels for HFC-404a were calculated using the EEGLs and CEGLs that were derived by the subcommittee for HFC-143a, HFC-125, and HFC-134a (see the following pages for calculations).
