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Acute Exposure Guideline Levels (AEGLs)
AEGLs are exposure guidelines that are meant to protect nearly all members of the general public when they are exposed to a toxic chemical.
This page discusses the following topics:
What are AEGLs?
AEGLs estimate the concentrations at which most people--including sensitive individuals such as old, sick, or very young people--will begin to experience health effects if they are exposed to a toxic chemical for a specific length of time (duration). For a given exposure duration, a chemical may have up to three AEGL values, each of which corresponds to a specific tier of health effects.
The three AEGL tiers are defined as follows:
All three tiers (AEGL-1, AEGL-2, and AEGL-3) are developed for each of five exposure periods: 10 minutes, 30 minutes, 60 minutes, 4 hours, and 8 hours. The table below shows how the chlorine AEGL values vary with exposure duration.
Final AEGLs for chlorine (in parts per million)
| 10 minutes | 30 minutes | 60 minutes | 4 hours | 8 hours |
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| AEGL-1 | 0.50 | 0.50 | 0.50 | 0.50 | 0.50 |
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| AEGL-2 | 2.8 | 2.8 | 2.0 | 1.0 | 0.71 |
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| AEGL-3 | 50 | 28 | 20 | 10 | 7.1 |
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Typically, the AEGL values will be different for each exposure duration (such as the AEGL-3 values in the table above). This is because the physical effects are typically related to dose (that is, concentration over exposure duration). However, in some cases, the AEGL values will be the same for all durations. This situation usually occurs at the AEGL-1 level (as in the table above), because it is a threshold for detection or mild effects; some effects (for example, whether people will be able to smell the chemical) depend only on concentration--not the length of time people are exposed.
How are AEGLs chosen?
AEGLs are developed by the National Advisory Committee of the National Research Council. The committee established detailed guidelines for developing uniform, meaningful emergency response standards for the general public.
AEGLs represent the best public guidelines available to date. Each AEGL is developed independently by a team of scientists who assign priority to current data from human and animal studies. The process is exhaustive and the guidelines are thoroughly reviewed. As part of the development process, interim AEGL values are established and then evaluated thoroughly (sometimes over several years) before the final AEGL values are approved by the committee. To find out more about the AEGL development process, select the link titled AEGL Program at the bottom of this page.
What substances have AEGLs?
As of mid-2007, 31 substances have final AEGLs and nearly 100 substances have interim AEGLs. To see the current list of substances with AEGLs, select the link titled AEGL Program at the bottom of this page. You can also search for a specific substance on the CAMEO Chemicals site (by selecting the link at the bottom of this page) to find response recommendations and chemical data (including final AEGLs).
According to the AEGL Program site, the development committee's goal is to define AEGLs for "chemicals that could potentially cause dangerous inhalation exposures to persons through accidental releases to air or by means of a terrorist action." The committee has established priority lists that include hundreds of these industrial and weaponized chemicals. Many of the industrial chemicals on the list are extremely hazardous substances (EHSs) listed in Title III of the Superfund Amendment and Reauthorization Act (SARA).
How should AEGLs be used?
AEGLs should be used to help protect the public when there has been a chemical release that is short-term in duration.
AEGLs estimate how the general public would react to a release of this nature, so they can be used to identify areas where a hazard exists if the toxic gas concentration is exceeded for the specified exposure duration. For example, in areas with concentrations above the AEGL-1, most people would detect the chemical and may experience temporary, mild effects. On the other hand, in areas with concentrations above the AEGL-2, most people would experience significant, but not life-threatening, health effects.
Each defined chemical has AEGL values for five exposure durations, and you should use the duration that is appropriate for your release.
AEGLs should not be used as:
- Guidelines for workers who are routinely exposed to chemicals for longer durations. In such cases, you should use workplace exposure limits (such as the Threshold Limit Value) because they contain safety factors specific to this type of exposure.
- Guidelines for members of the public who are exposed to background chemical releases for longer durations. In these types of air quality issues, values such as the National Ambient Air Quality Standards (NAAQS) should be used rather than emergency response guidelines.
How does ALOHA use AEGLs?
In ALOHA, you can choose AEGLs as your Levels of Concern (LOCs) when modeling a toxic chemical release--if AEGLs have been defined for that chemical. (A toxic LOC is the value above which the toxic gas concentration might be high enough to harm people.) ALOHA allows you to specify up to three toxic LOCs. So, you can choose the AEGL-1, AEGL-2, and AEGL-3 values to generate a threat zone plot where yellow, orange, and red zones indicate areas where the those values were exceeded at some point after the chemical release began. (To determine how long the LOC was exceeded at a particular location, read the Ask Dr. ALOHA article on working with the concentration graph.)
If final AEGLs are available for the chemical you are modeling, ALOHA will provide the AEGL values with a 60-minute exposure duration as the default toxic LOCs. Even though AEGLs are available for five exposure durations, only the 60-min AEGLs are provided in ALOHA because it models the release for 60 minutes from your start time.
Note: If your release has a short duration and ALOHA's concentration graphs show that the predicted exposure durations are short at all points in the threat zone, you may want to use the 10-min or 30-min AEGL values instead of the 60-min AEGLs included in ALOHA. Read the Ask Dr. ALOHA article on choosing toxic LOCs (to learn how to enter your own LOCs) and the article on working with the concentration graph (to learn how to use this graph to consider exposure durations). You can look up the AEGL values for all durations on the CAMEO Chemicals site by following the link below.
Where else can I find information on AEGLs?
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- AEGL Program Read all about AEGLs on this Environmental Protection Agency site, which contains a list of current AEGLs and details about AEGL development. [leaves OR&R site]
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- CAMEO Chemicals Search the CAMEO chemical database online and find final AEGLs for specific chemicals. At this separate Office of Response and Restoration site, you can also print customized reports with response recommendations and find out how chemicals would react if they mixed. [leaves OR&R site]
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