Submarine Exposure Guidance Levels for Selected Hydrofluorocarbons: HFC-236fa, HFC-23,and HFC-404a (2000)
Chapter: Emergency Exposure Guidance Levels
an NRC (1986) report, and a brief description is provided below. Additional guidance is provided in two other NRC reports (NRC 1992, 1993).
Emergency Exposure Guidance Levels
An EEGL is defined as a ceiling guidance level for single emergency exposures usually lasting from 1 to 24 hr—an occurrence expected to be infrequent in the lifetime of a person. “Emergency” connotes a rare and unexpected situation with potential for significant loss of life, property, or mission accomplishment if not controlled. An EEGL can also be set for much shorter periods, such as 1-min or 5-min exposures. An EEGL specifies and reflects the subcommittee's interpretation of available information in the context of an emergency.
An EEGL is acceptable only in an emergency, when some risks or some discomfort must be endured to prevent greater risks (such as fire, explosion, or massive release). Even in an emergency, exposure should be limited to a defined short period. Exposure at the EEGL might produce temporary discomfort, such as eye or upper-respiratory-tract irritation, headache, or increased respiratory rate. The EEGL is intended to prevent irreversible harm. Even though some reduction in performance is permissible, it should not prevent proper responses to the emergency (such as shutting off a valve, closing a hatch, removing a source of heat or ignition, or using a fire extinguisher). For example, in normal work situations, a degree of upper-respiratory-tract irritation or eye irritation causing discomfort would not be considered acceptable; during an emergency, however, such irritation would be acceptable if it did not cause irreversible harm or seriously affect judgment or performance. The EEGL for a substance represents the subcommittee's judgment based on evaluation of experimental and epidemiological data, mechanisms of injury, and, when possible, operation conditions in which emergency exposure might occur, as well as consideration of DOD goals and objectives.
The EEGL is generally calculated on the basis of acute toxicity end points. However, even brief exposure to some substances might have the potential to increase the risk of cancer or other delayed effects. If the substance under consideration is carcinogenic, a cancer risk assessment is performed with the aim of providing an estimate of the exposure that would not lead to an excess risk of cancer greater than 1 in 10,000 exposed persons. The acceptable risk selected for military exposures is based on considerations of policy and objectives of DOD.
