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Assessment of Exposure-Response Functions for Rocket-Emission Toxicants Appendix B DEFINITIONS OF CURRENT EXPOSURE GUIDANCE LEVELS Emergency Response Planning Guidelines (ERPGs) are developed by the American Industrial Hygiene Association. Definitions of ERPG-1 (mild effects), ERPG-2 (serious effects), and ERPG-3 (life-threatening effects) are provided in the box in Chapter 1. ERPGs are intended to protect "nearly all individuals" from each effect level. In establishing ERPGs, acute toxicity data as well as possible long-term effects from a single acute exposure are considered. Adjustments, based on informed judgment, can be made for the increase susceptibility of sensitive subgroups in the general population (EPA 1987, Appendix D). Immediately Dangerous to Life and Health (IDLH) values are used by the National Institute for Occupational Safety and Health (NIOSH) as respirator selection criteria (first developed in the mid-1970s). The Occupational Safety and Health Administration (OSHA) defines an IDLH as: "An atmospheric concentration of any toxic, corrosive or asphyxiant substance that poses an immediate threat to life or would cause irreversible or delayed adverse health effects or would interfere with an individual's ability to escape from a dangerous atmosphere" (29 CFR 1910.120). A joint effort was called the Standards Completion Program (SCP), whereby NIOSH and OSHA cooperated to develop draft standards (NIOSH 1978). The definition of an IDLH that was developed during the SCP considered the ability of a worker to escape a building. Although egress from a particular worksite could occur in much less than 30 min in most cases, as a margin of safety, IDLHs were based on effects
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Assessment of Exposure-Response Functions for Rocket-Emission Toxicants 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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Assessment of Exposure-Response Functions for Rocket-Emission Toxicants fetus is considered. Personnel are expected to have appropriate protective equipment available and to have planned escape routes, but EEGLs are not based on the availability of the protective equipment or escape routes (NRC 1986). Short-Term Public Emergency Guidance Levels (SPEGLs) are suitable concentrations for single, short-term, emergency exposures of the general public (NRC 1986). SPEGLs are developed at the request of the U.S. Department of Defense for emergency situations in which the public might be involved. Sensitive populations, such as children, the aged, and persons with serious, debilitating diseases (NRC 1986), are considered in SPEGLs. Acute Exposure Guideline Levels (AEGLs) are under development by the U.S. Army and U.S. Environmental Protection Agency. There are likely to be three levels of AEGL: Below AEGL-1, exposure levels might produce mild odor, taste, or other mild sensory irritations in the general population, including sensitive individuals. Below AEGL-2 but above AEGL-1, exposure levels might cause notable discomfort in the general population. Below AEGL-3 but above AEGL-2, exposure levels might cause irreversible or other serious long-lasting effects or impaired ability to escape. Above AEGL-3, exposure levels might cause life-threatening effects or death in the general population, including sensitive individuals. The AEGL definitions might not be final. ACGIH Threshold Limit Values (TLVs) are based on available information from industrial experience, from experimental human and animal studies, and when possible, from a combination of the three. The basis on which the values are established might differ from substance to substance; protection against impairment of health might be a guiding factor for some values, whereas reasonable freedom from irritation, narcosis, nuisances, or other forms of stress might be the basis for others. Health impairments under consideration are those that shorten life expectancy, compromise physiological function, impair the capability to resist other toxic substances of disease processes, or adversely affect reproductive function or developmental processes (ACGIH 1986). ACGIH TLV Time-Weighted Averages (TWAs) are defined as time-weighted-average concentration limits for a normal 8-hr workday, with
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Assessment of Exposure-Response Functions for Rocket-Emission Toxicants a total of 40 hr per week. Nearly all workers can be exposed repeatedly, day after day, to these concentrations without adverse effects (ACGIH 1986). ACGIH TLV Short-Term Exposure Limits (STELs) are 15-min timeweighted-average concentrations for a normal 8-hr workday and 40-hr workweek. All workers should be able to withstand up to four exposures per day of concentrations as high as the TLV-STEL with no ill effects if the TLV-TWA is not exceeded. TLV-STELs are applied to supplement the TLV-TWA when there are recognized acute effects from a substance whose toxic effects are primarily chronic in nature (ACGIH 1986). ACGIH TLV Ceiling (C) limits are airborne concentrations that should not be exceeded in the workplace under any circumstances. Ceiling limits can supplement other limits or stand alone. For chemicals with TLV-TWA values for which ACGIH could not find sufficient toxicity data to derive TLV-STELs or TLV-C values, ACGIH recommends that five times the TLV-TWA be used in place of the TLV-C and that only three short-term exposures to that level for up to 30 min per day be allowed (ACGIH 1986). OSHA Permissible Exposure Limits (PELs) are workplace exposure standards listed in the General Industry Standards for Toxic and Hazardous Chemicals (29 CFR 1910, Subpart Z). Most of the PELs are based on ACGIH TLVs. PELs for many chemicals are simply 8-hr time weighted-average (TWA) concentrations that should not be exceeded in an 8-hr workday. For other chemicals, ceiling concentrations and maximum peak concentrations are given in addition to the 8-hr TWA concentrations. The maximum peak concentrations apply to specific exposure durations (e.g., 5-min maximum peak concentrations in any 2hr period). The concentrations should never exceed the maximum peak and should fall between the ceiling and the maximum peak concentrations for the duration indicated. The majority of OSHA PELs were adopted from the ACGIH TLVs available in 1971. PELs are enforceable by law (EPA 1987). NIOSH Recommended Exposure Limits (RELs) are 8-hr or 10-hr TWA or ceiling concentrations (EPA 1987).
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Assessment of Exposure-Response Functions for Rocket-Emission Toxicants REFERENCES ACGIH (American Conference of Governmental Industrial Hygienists). 1986. Threshold Limit Values and Biological Exposure Indices for 1986-87. American Conference of Governmental Industrial Hygienists, Cincinnati, Ohio. EPA (U.S. Environmental Protection Agency). 1987. Technical Guidance for Hazards Analysis: Emergency Planning for Extremely Hazardous Substances. Prepared in cooperation with the Federal Emergency Management Agency, Washington, D.C., and U.S. Department of Transportation, Washington, D.C. U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response, Washington, D.C. Available from NTIS, Springfield, Va., Doc. No. PB93-206910. NIOSH (National Institute for Occupational Safety and Health). 1978. The Standards Completion Program Draft Technical Standards Analysis and Decision Logics. U.S. Department of Health and Human Services, National Institute for Occupational Safety and Health, Cincinnati, Ohio. NIOSH (National Institute for Occupational Safety and Health). 1994. Documentation for Immediately Dangerous to Life or Health Concentrations (IDLHs). U.S. Department of Health and Human Services, National Institute for Occupational Safety and Health, Division of Standards Development and Technology Transfer , Cincinnati, Ohio. Available from NTIS, Springfield, Va., Doc. No. PB94-195047. NRC (National Research Council). 1986. Criteria and Methods for Preparing Emergency Exposure Guidance Level (EEGL), Short-Term Public Emergency Guidance Level (SPEGL), and Continuous Exposure Guidance Level (CEGL) Documents. Washington, D.C.: National Academy Press.
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