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About Acute Exposure Guideline Levels (AEGLs)

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Acute Exposure Level Guidelines (AEGLs) are used by emergency planners and responders worldwide as guidance in dealing with rare, usually accidental, releases of chemicals into the air. AEGLS are expressed as specific concentrations of airborne chemicals at which health effects may occur. They are designed to protect the elderly and children, and other individuals who may be susceptible.

AEGLs assigned 1, 2 or 3 according to severity of effects

AEGLs are calculated for five relatively short exposure periods – 10 minutes, 30 minutes, 1 hour, 4 hours, and 8 hours – as differentiated from air standards based on longer or repeated exposures. AEGL “levels” are dictated by the severity of the toxic effects caused by the exposure, with Level 1 being the least and Level 3 being the most severe.  

All levels are expressed as parts per million or milligrams per cubic meter (ppm or mg/m3) of a substance above which it is predicted that the general population could experience, including susceptible individuals:

Level 1

  • Notable discomfort, irritation, or certain asymptomatic non-sensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure.

Level 2

  • Irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape.

Level 3

  • Life-threatening health effects or death.

Below AEGL Level 1

Airborne concentrations below the AEGL-1 represent exposure levels that could produce mild and progressively increasing but transient and non-disabling odor, taste, and sensory irritation or certain asymptomatic, non-sensory effectsWith increasing airborne concentrations above each AEGL, there is a progressive increase in the likelihood of occurrence and the severity of effects described for each corresponding AEGL.

AEGL values represent threshold levels for the general public. As mentioned, that includes susceptible subpopulations, such as infants, children, the elderly, persons with asthma, and those with other illnesses. However, it is recognized that individuals, subject to unique or idiosyncratic responses, could experience the effects described at concentrations below the corresponding AEGL. 

AEGLs are developed under formal guidance 

In 2001, the National Academies published procedural guidance or "Standing Operating Procedures" to make development of AEGLs systematic, consistent, documented and transparent to the public.

Read the Standing Operating Procedures (SOP) of the National Advisory Committee on Acute Exposure Guideline Levels for Hazardous Substances 

Important information for users of AEGLs

Users of the AEGLs should first determine if there are legally enforceable standards that apply to the situation. Other organizations may also have recommended levels of exposure that more appropriately apply to the scenarios under evaluation. 

There may be situations in which it is desirable to use AEGLs values for other exposure scenarios. To determine if an AEGL applies to a particular situation, consult the chemical-specific AEGL technical support document that contains a comprehensive review of all identified acute toxicology data on the subject chemical and the basis for the development of the AEGL values. 

Find chemical-specific AEGL technical support documents.