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Temporary Emergency Exposure Limits (TEELs)
TEELs are temporary guidelines designed to predict the response of members of the general public to different concentrations of a chemical during an incident.
This page discusses the following topics:
What are TEELs?
TEELs estimate the concentrations at which most people will begin to experience health effects if they are exposed to a toxic chemical for a given duration. (Sensitive members of the public--such as old, sick, or very young people--are not covered by these guidelines and they may experience adverse effects at concentrations below the TEEL values.) TEELs are used in similar situations as the 60-minute AEGLs and ERPGs. However, in situations where the concentration varies over time, the TEEL developers recommend using a conservative 15-minute time-weighted average concentration. A chemical may have up to four TEEL values, each of which corresponds to a specific tier of health effects.
Each TEEL includes four tiers, defined as follows:
Note: Because the TEEL-0 tier is essentially a no effects threshold, it is often ignored for emergency response and planning purposes. ALOHA treats TEELs as a three-tiered guideline (TEEL-1, TEEL-2, and TEEL-3), which can be compared in a general way to the AEGL and ERPG tiers. ALOHA does not include TEEL-0 values.
How are TEELs chosen?
TEELs are derived by the U.S. Department of Energy Subcommittee on Consequence Assessment and Protective Actions (SCAPA) according to a specific, standard methodology. The TEEL methodology uses available levels of concern and manipulates current data using a peer-reviewed, approved procedure in order to establish the TEELs.
AEGLs and ERPGs, on the other hand, are derived from extensive reviews of animal and human studies. Recognizing that AEGLs and ERPGs are better public exposure guidelines, the TEEL methodology prescribes replacing the TEEL value with those values when they become available. The 60-minute AEGL value is used preferentially, followed by the ERPG value.
However, the extensive review process for AEGLs and ERPGs that enhances the quality of those values also increases the amount of time it takes for chemicals to be defined under each hazard classification system. As of mid-2007, only 31 substances have final AEGLs and just over 120 chemicals have ERPGs.
TEELs can be derived relatively quickly for almost any chemical; as a result, TEELs are available for thousands of chemicals. TEELs can provide a useful reference when no other public exposure guidelines are available.
What substances have TEELs?
As of mid-2007, more than 3,000 chemicals have TEELs. To find current TEEL values, select the link titled TEEL Database 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 TEELs).
How should TEELs be used?
TEELs should be used to help protect the public when AEGLs or ERPGs are not available and there has been a chemical release that is short-term in duration.
TEELs estimate how nearly all of the public (except for sensitive individuals) 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 a given duration. For example, in areas with concentrations above the TEEL-1, most people would detect the chemical and may experience temporary, mild effects. On the other hand, in areas with concentrations above the TEEL-2, most people would experience significant, but not life-threatening, health effects.
TEELs 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 TEELs?
In ALOHA, you can choose TEELs as your Levels of Concern (LOCs) when modeling a toxic chemical release--if TEELs have been defined for that chemical and they have not been superseded by ERPGs or AEGLs. (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 TEEL-1, TEEL-2, and TEEL-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.)
For chemicals defined under the TEEL classification system, ALOHA will provide the TEEL values as the default toxic LOCs until either ERPG or final AEGL values are established. TEELs are interim values that are superseded by ERPGs and AEGLs when those become available. Therefore, TEEL information is not included in ALOHA once the chemical is defined under either of the other guidelines.
Where else can I find information on TEELs?
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- TEEL Program Read all about TEELs on this Subcommittee on Consequence Assessment and Protective Actions (SCAPA) site, which contains TEEL resources and details about TEEL development. [leaves OR&R site]
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- TEEL Database Search for TEEL values in a database on this Department of Energy site. [leaves OR&R site]
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- TEEL Tables Download tables for all of the TEELs in several different formats on this Department of Energy site. [leaves OR&R site]
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- CAMEO Chemicals Search the CAMEO chemical database online and find TEELs 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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