Differences between AEGLs, ERPGs, and TEELs
There are subtle difference in the definitions of AEGLs, ERPGs, and TEELs and major differences in how they are developed and issued. Differences in their definitions include:
- AEGLs and TEELs pertain to the “general population, including susceptible individuals,” but ERPGs pertain to “nearly all individuals.”
- AEGLs and TEELs are defined as the level “above which” certain health effects are expected, while ERPGs are defined as the level “below which” certain health effects are not expected.
- ERPGs refer to exposure durations of 1 hour (with shorter periods for some chemicals). AEGLs are developed for five time periods (i.e., 10-minutes, 30-minutes, 1-hour, 4-hours, and 8-hours); the PAC database includes the AEGL 1-hour value. TEELs will be standardized on 1-hour in the near future.
AEGLs and ERPGs are developed through a rigorous review of primary sources of toxicological information, and the values eventually assigned to each chemical are individually peer reviewed. ERPGs are formed using a weight of evidence approach. AEGLs are typically based on the results of a single key study. Both of these processes are painstaking and time-consuming. Additionally, AEGLs are subject to a public comment period and a further review by the National Academy of Science before being considered final.
To produce limits in a more timely fashion while maintaining high quality, TEELs are derived from secondary data sources using a peer-reviewed algorithm. These sources are either existing exposure limits designed to prevent adverse effects in humans or experimentally derived toxicity parameters. It is important to emphasize that TEELs are considered temporary; they are approximations of potential values and are subject to change whenever new or better information becomes available.
Additional information and reference links for AEGLs, ERPGs, and TEELs:
The U.S. EPA's AEGL Program has developed AEGLs to describe the risk to humans resulting from once-in-a-lifetime, or rare, exposure to airborne chemicals. The National Advisory Committee and National Research Council Committee on AEGLs are developing these guidelines to help both national and local authorities, as well as private companies, deal with emergencies involving spills, or other catastrophic exposures. The AEGL Program web site provides information on the scientific and policy work in developing AEGLs.
AEGL Chemicals provides a searchable database of AEGL values, as well as a compiled listing of AEGL values.
Because there can be a time lag between the release of new AEGLs and their incorporation in a revised PAC data set, please consult the AEGL website for the latest information on new AEGL releases.
The AIHA Emergency Response Planning Committee develops guidelines for responding to potential releases of airborne substances for use in community emergency planning. ERPGs are air concentration guidelines for single exposures to agents and are intended for use as tools to assess the adequacy of accident prevention and emergency response plans, including transportation emergency planning, community emergency response plans and incident prevention and mitigation. The AIHA Emergency Response Planning Committee website provides information on the development of ERPGs.
ERPGs Levels for Select Chemicals (a PDF file) provides the official listing of ERPG values.
Because there can be a time lag between the release of new ERPGs and their incorporation in a revised PAC data set, please consult the ERPG website for the latest information on new ERPG releases.
In the early 1990s, the DOE Office of Emergency Operations recognized that ERPGs existed for only a limited number of chemicals (AEGL development did not start until later in the decade.) As a result, the DOE Office of Emergency Operations asked SCAPA for its recommendations on appropriate substitutes so that DOE facilities could conduct appropriate emergency preparedness hazard analyses (EPHAs) and perform consequence assessments. TEELs, first referred to as Alternative Guidelines Limits, were initially released in October 1992 and included values for approximately 65 chemicals. Today there are well over three thousand chemicals for which TEELs are used to provide one or more PAC values.
The TEELs Method and Practices Handbook details the specific methods used to derive TEEL values. It also presents background information, sample calculations showing how TEELs are derived, and quality assurance measures used in the TEEL derivation process. A list of useful reference documents related to TEELs is provided by SCAPA.