Before developing AEGLs for individual chemicals, the NAC developed the guidelines document Standing Operating Procedures for Developing Acute Exposure Guideline Levels for Hazardous Substances (referred to as SOP), which documents the procedures, methods, criteria, and other guidelines used by the NAC in the development of AEGLs. The information contained in SOP is based on guidance provided by the National Research Council in its guidelines report (NRC 1993). SOP was reviewed by the National Research Council AEGLs committee and published by the National Research Council (NRC 2001).

In addition to reviewing AEGL documentation developed by the NAC, the National Research Council committee is charged to identify guidance issues from time to time that may require modification or further development on the basis of the toxicologic database for chemicals reviewed. The committee provides the following recommendation to the NAC for updating and improving SOP and TSDs.

“Mechanism of Toxicity” is Section 4.2 of the TSD as a subsection of Section 4, “Special Considerations.” In light of the review of methylene chloride, in which the mechanism of toxicity is key to understanding the data and the development of the AEGL values, the committee recommends the following change to SOP: make “Mechanism of Toxicity” Section 2, “Mechanism of Toxicity,” and renumber the later sections (such as Section 3, “Human Toxicity Data”).