that might occur as a consequence of a 30-min exposure (NIOSH 1994).

The criteria used to determine the adequacy of existing IDLHs were a combination of those used during the SCP and a new method developed by NIOSH (tiered data preference). Acute lethal animal data could be used but would be time adjusted to a 30-min exposure period according to the formula:

Adjusted LC50 (30 min) = LC50(t) × (t/0.5)1/n

where LC50(t) is an LC50 determined over t hours and n is a constant determined empirically (NIOSH 1994).

EPA Levels of Concern (LOC) are the "concentrations of an extremely hazardous substance (EHS) in air above which there may be serious irreversible health effects or death as a result of a single exposure for a relatively short period of time" (EPA 1987). For purposes of the December 1987 Technical Guidance for Hazard Analysis, Emergency Planning for Extremely Hazardous Substances, EPA defined LOCs as 1/10 of NIOSH IDLH levels.

Emergency Exposure Guidance Levels (EEGLs) are concentrations of substances in the air that may be judged by the U.S. Department of Defense to be acceptable for the performance of specific tasks during rare, emergency conditions, lasting 1 to 24 hr (NRC 1986). The EEGL should allow personnel to continue to perform tasks necessary to take care of the emergency conditions and to allow self-rescue. Therefore, the EEGL should not impair judgment, interfere with performance of tasks in response to the emergency, or cause irreversible harm to the personnel. The EEGL may, however, cause transient adverse effects, such as increased respiration rate, headache (but not debilitating headache), mild central-nervous-system effects, or irritation to the eyes or upper respiratory tract. An EEGL is acceptable only during an emergency, when some discomfort or risk must be taken to avoid greater risks, such as fire, explosion, or massive releases of toxic material (NRC 1986).

The calculation of an EEGL is based on the exposure population being military personnel who are healthy and relatively young. Women are included; thus, the potential toxicity of the exposure material to the



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