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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 (NRC, 1964, 1971). In a revision of these documents (NRC, 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 a request by the National Aeronautics and Space Administration. The CELs, in particular, 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.

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 use of uncertainty factors will depend on the specific compound in question and on the type of effect produced by the compound.

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 data on continuous exposures are rarely available, uncertainty factors might be used, depending on the judgment of the Committee.

Table 1 summarizes the EELs and CELs for selected chemicals previously recommended by the Committee and revised recommendations made on the basis of information presented in this report.



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Emergency and Continuous Exposure Limits for Selected Airborne Contaminants, Volume 1 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 (NRC, 1964, 1971). In a revision of these documents (NRC, 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 a request by the National Aeronautics and Space Administration. The CELs, in particular, 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. 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 use of uncertainty factors will depend on the specific compound in question and on the type of effect produced by the compound. 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 data on continuous exposures are rarely available, uncertainty factors might be used, depending on the judgment of the Committee. Table 1 summarizes the EELs and CELs for selected chemicals previously recommended by the Committee and revised recommendations made on the basis of information presented in this report.

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Emergency and Continuous Exposure Limits for Selected Airborne Contaminants, Volume 1 TABLE 1. Emergency and Continuous Exposure Limits Compound Duration of Exposure Recommended Exposure Limita Previous Current Acetone 60 min 15,000 8,500   24 hr 2,000 1,000   90 d 300 200 Acrolein 10 min — 0.1   60 min 0.2 0.05b   24 h 0.1 0.01b   90 d 0.1 0.01 Arsine 60 min 1.0 1.0   24 h 0.1 0.1   90 d 0.01 — Carbon disulfide 10 min 200 200   30 min 100 100   60 min 50 50 Chloroform 60 min 200 100   24 h 30 30   90 d 3 1 Fluorine 10 min 15 15   30 min 10 10   60 min 5 7.5 Mercury vapor mg/m3 24 h 2 mg/m3 0.2 mg/m3 90 d 0.01 mg/m3 0.01 Methane 24 h 5,000 5,000   90 d 5,000 5,000 Ozone 60 min 1 1   24 h 0.1 0.1   90 d 0.02 0.02 Sulfuric acid mg/m3 10 min 5 mg/m3 5 mg/m3 30 min 2 mg/m3 2 mg/m3 60 min 1 mg/m3 1 appm, unless otherwise stated. bTentative recommendation.

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Emergency and Continuous Exposure Limits for Selected Airborne Contaminants, Volume 1 REFERENCES National Research Council, Ad Hoc Committee, 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, Assembly of Life Sciences, Board on Toxicology and Environmental Health Hazards, Committee on Toxicology. 1979. Criteria for Short-Term Exposures to Air Pollutants. Washington, D.C.: National Academy of Sciences. [15 p.]

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