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Process for Developing Acute Exposure Guideline Levels (AEGLs)

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The process to develop Acute Exposure Guideline Level (AEGLs) values is the most comprehensive ever used to determine short-term exposure limits for acutely toxic chemicals. AEGL values are developed through the National Advisory Committee for Acute Exposure Guidelilne Levels for Hazardous Substances (NAC/AEGL Committee), which is a federal advisory committee.  When the NAC/AEGL Committee's federal advisory committee charter expired in October 2011, the current process was developed to finalize interim AEGLs.  

The objectives of the process are:

  1. Development of scientifically valid AEGL values for use in chemical emergency planning, prevention and response programs.
  2. Comprehensive identification of published and unpublished information sources used to set AEGLs.
  3. Sharing resource burdens by stakeholder members.
  4. Adoption of consistent emergency planning both domestically and internationally.
  5. Transparency of program methods (Standard Operating Procedures or SOPs) and information through public participation at meetings and by commenting on Federal Register notices.
  6. Inclusion of National Academies (formerly National Academy of Science [NAS]) as the final peer reviewer of AEGL values and methods.

Original process to develop AEGLs (1996 to October 2011)

The process consists of four basic stages, and they are identified according to the review level and concurrent status of the AEGL values: (1) draft AEGLs, (2) proposed AEGLs, (3) interim AEGLs, and (4) final AEGLs.

See a diagram of the original AEGL development process  

Stage 1: Draft AEGLs

  • This first stage begins with a comprehensive search of the published scientific literature. Attempts are made to mobilize all relevant unpublished data through industry-trade associations and from individual companies in the private sector.
  • A more detailed description of the published and unpublished sources of data and information used is provided in Section 2.3 of Standing Operating Procedures (SOP) for Developing Acute Exposure Guideline Levels (AEGLs) for Hazardous Chemicals addresses search strategies.
  • The data are evaluated by following the National Academies Standing Operating Procedures. Selected data are used as the basis for the derivation of AEGL values and the supporting scientific rationale.
  • Data evaluation, data selection, and development of a technical support document (TSD) are all performed as a collaborative effort among the staff scientists at the organization drafting the TSD, the chemical manager, and two chemical reviewers. This group is called the AEGL Development Team.
  • Specific NAC/AEGL Committee members are assigned to a AEGL Development Team for each chemical under review. The product of this effort is a TSD that contains draft AEGLs.
  • The draft TSD is subsequently circulated to all other NAC/AEGL Committee members for review and comment prior to a formal meeting of the committee. Revisions to the initial TSD and the draft AEGLs are made up to the time of the NAC/AEGL Committee meeting scheduled for formal presentation and discussion of the AEGL values and the documents.
  • At the committee meeting, the committee deliberates and, if a quorum is present, attempts to reach a consensus or a two-thirds majority vote to elevate the draft AEGLs to "proposed" status. A quorum of the NAC/AEGL Committee is defined as 51 percent or more of the total NAC/AEGL Committee membership. If agreement cannot be reached, the committee conveys its issues and concerns to the AEGL Development Team and further work is conducted by this group.
  • After completion of additional work, the chemical is resubmitted for consideration at a future meeting. If a consensus or a two-thirds majority vote of the committee cannot be achieved because of inadequate data, no AEGL values will be developed until adequate data become available.

Read the ​Standing Operating Procedures (SOP) for Developing Acute Exposure Guideline Levels (AEGLs) for Hazardous Chemicals

Stage 2: Proposed AEGLs

  • Once the NAC/AEGL Committee has reached a consensus or a two-thirds majority vote on the AEGL values and supporting rationale, they are referred to as Proposed AEGLs. These are published in the Federal Register for a 30-day comment period. Following publication, the committee reviews the public comments, addresses and resolves relevant issues, and seeks a consensus or a two-thirds majority vote of those present on the original or modified AEGL values and the accompanying scientific rationale. The AEGL values are then classified as "Interim AEGLs."

Stage 3: Interim AEGLs

  • The Interim AEGL status represents the best efforts of the NAC/AEGL Committee to establish exposure limits, and the values are available for use on an interim basis by federal and state regulatory agencies and the private sector.
  • The interim AEGLs, the supporting scientific rationale, and the TSD, are subsequently presented to the NAS Subcommittee for its review and concurrence. If concurrence cannot be achieved, the NAS Subcommittee will submit its issues and concerns to the AEGL Committee for further work and resolution.

Stage 4: Final AEGLs

  • When concurrence by the NAS Subcommittee is achieved, the AEGL values are considered "Final AEGLs" and published by the NAS. Final AEGL values may be used on a permanent basis by all federal, state and local agencies, and private organizations. It is possible that new data will become available from time to time that challenges the scientific credibility of final AEGLs. If that occurs, the chemical will be resubmitted to the NAC/AEGL Committee and recycled through the review process.

Current process to develop AEGLs  (November 2011 to present)

  • By 2011, the AEGL program had successful addressed all but five of the 329 chemicals listed in the AEGL Chemical Priority Lists, an important milestone. Budget constraints resulted in redirecting funding towards the finalization of AEGL values through the NAS Subcommittee. As a result, the NAC/AEGL Committee was eliminated for future work on the AEGL program. 
  • The new process focuses on finalizing Interim AEGL chemicals through the NAS with the limited resources available. The following paragraphs describe the changes to the development process of AEGLs.
  • Procedure to address NAS comments that would not result in changes to AEGL Interim Values:
    • The AEGL program did not change the approach to handle NAS comments that do not result in a change in AEGL values. Currently, the AEGL program receives technical support from a contractor that is responsible for making revisions to the AEGL technical support documents. As in the past, the contractor made changes to the documents per the recommendations of the NAS Subcommittee and prepared the response to comments. The contract project officer (in this case the AEGL Program manager), reviewed and approved the changes and response to comments. The revised technical support documents were submitted to the NAS for publication.
  • Procedure to address NAS comments that would result in changes to AEGL Interim Values:
    • Under the old process, NAS recommendations resulting in changes to AEGL values were debated and approved by the NAC/AEGL Committee. The contractor then responded to NAS comments for a particular AEGL chemical and the response was taken to the NAC/AEGL Committee for its deliberation and approval. Under the new current process, the NAC/AEGL Committee is no longer available. The new approach is presented below.
    • The current approach engages the federal stakeholders, but in a different way. Under this process, the contractor addresses the NAS comments and revises the document and prepares a response to comments. Next, the response and the revised technical support document are sent to the federal stakeholders for a 2-week review. After consensus, the response and the revised technical support document are sent to the NAS. If consensus cannot be reached, the differences are written and presented to the NAS for their resolution. Note that changes to the documents are not posted on the AEGL website until they are finalized by the NAS.