INTRODUCTION
The National Research Council’s Committee on Toxicology recommends emergency exposure limits (EELs), short-term public limits (STPLs), and short-term public emergency limits (SPELs—formerly called public emergency limits, or PELs) for a variety of chemicals of concern to its sponsoring agencies. The definitions and applicability of these limits and the criteria used to establish them were originally outlined in two documents prepared by the Committee (National Research Council, 1964, 1971). In a revision of these documents (National Research Council, 1979), the Committee summarized the principles used to establish exposure limits for short durations. The Committee has also recommended continuous exposure limits (CELs) in response to specific sponsor requests.
This document is one in a series prepared by the Committee that form the basis of the recommendations for EELs and CELs for selected chemicals. Since the Committee began recommending EELs and CELs for its military sponsors (U.S. Army, Navy, and Air Force), the scope of its recommendations has been expanded in response to requests by the U.S. Coast Guard and the National Aeronautics and Space Administration. The CELs grew out of a Navy request for exposure limits for atmospheric contaminants in submarines. The EELs and CELs have been used as design criteria by the sponsors in considering the suitability of materials for particular missions (as in a submarine or a spacecraft) and in assessing the habitability of particular enclosed environments. They are recommended for narrowly defined occupational groups and are not intended for application in general industrial settings or as exposure limits for the general public. These recommended values do not take into consideration the possible effects of exposure of hypersensitive persons.
The EEL is defined as a ceiling limit for an unpredictable single exposure, usually lasting 60 min or less, and never more than 24 h—an occurrence expected to be rare in the lifetime of any person. It reflects an acceptance of the statistical likelihood of the occurrence of a nonincapacitating, reversible effect in an exposed population. It is designed to avoid substantial decrements in performance during emergencies and might contain no uncertainty factor.
The CEL is recommended in specific situations where there may be exposure to a chemical continuously for up to 90 d. It is defined as a ceiling limit designed to avoid adverse health effects, either immediate or delayed, and to avoid degradation in crew performance that might endanger the objectives of a particular mission. Because human data on continuous exposures are rarely available, uncertainty factors might be used, the magnitude depending on the judgment of the Committee.
REFERENCES
National Research Council, Ad Hoc Committee of the Committee on Toxicology. 1964. Basis for Establishing Emergency Inhalation Exposure Limits Applicable to Military and Space Chemicals. Washington, D.C.: National Academy of Sciences. [5 p.]
National Research Council, Committee on Toxicology. 1971. Basis for Establishing Guides for Short-Term Exposures of the Public to Air Pollutants. Washington, D.C.: National Academy of Sciences. [15 p.]
National Research Council, Committee on Toxicology. 1979. Criteria for Short-Term Exposures to Air Pollutants. Washington, D.C.: National Academy of Sciences. [15 p.]
