Submarine Exposure Guidance Levels for Selected Hydrofluorocarbons: HFC-236fa, HFC-23,and HFC-404a (2000)
Chapter: Special Considerations
In estimating the EEGL for a substance that has multiple biological effects, all end points—including respiratory, neurological, reproductive (in both sexes), developmental, carcinogenic, and other organ-related effects—are evaluated, and the most important is selected. If confidence in the available data is low or if important data are missing, appropriate uncertainty factors are used and the rationale for their selection is stated. Generally, EEGLs have been developed for exposure to single substances, although emergency exposures often involve complex mixtures of substances and thus have a potential for toxic synergism. In the absence of other information, guidance levels for complex mixtures can be developed from EEGLs by assuming as a first approximation that the toxic effects are simply additive—thus implying a proportional reduction in EEGLs for each of the constituents of a mixture.
Continuous Exposure Guidance Levels
The CEGL is a ceiling guidance level set to prevent adverse health effects, either immediate or delayed, of prolonged exposures and to prevent degradation in crew performance that might endanger the objectives of a particular mission as a consequence of continuous exposure for up to 90 days. In contrast with EEGLs, CEGLs are intended to provide guidance for exposures under what is expected to be normal operating conditions in a submarine for periods of up to 90 days. Some conditions, such as slight headache, which might be acceptable for short periods under emergency conditions would not be permissible for long-term exposures. Because long-term exposures are repeated or continuous, detoxification and excretion are of special importance as they relate to the potential of the chemical to accumulate in the body.
Special Considerations
One important consideration that is commonly used in establishing exposure guidance levels for the general public is variability among humans in sensitivity to the effects of chemicals. A default uncertainty factor of 10 is typically used to protect susceptible individuals. However, the subcommittee believes that using an uncertainty factor to account for intraspecies variability is not necessary because the submariner population is all male, young (18-30 years of age), and healthier than the general population, having passed rigorous physical and psychological examinations.
