In 1991, the Environmental Protection Agency (EPA) and the Agency for Toxic Substances and Disease Registry (ATSDR) asked the National Research Council (NRC) to provide technical guidance for establishing community emergency exposure levels for extremely hazardous substances (EHSs) pursuant to the Superfund Amendments and Reauthorization Act of 1986. In response to that request, the NRC published Guidelines for Developing Community Emergency Exposure Levels for Hazardous Substances in 1993. Subsequently, Standing Operating Procedures for Developing Acute Exposure Guideline Levels for Hazardous Substances was published in 2001; it provided updated procedures, methods, and other guidelines used by the National Advisory Committee (NAC) on Acute Exposure Guideline Levels (AEGLs) for hazardous substances for assessing acute adverse health effects.

Using both these reports, the NAC--consisting of members from the EPA, the Department of Defense (DOD), the Department of Energy (DOE), the Department of Transportation (DOT), other federal and state governments, the chemical industry, academia, and other organizations from the private sector--developed AEGLs for approximately 270 EHSs. In 1998, EPA and DOD requested that the NRC independently review the AEGLs developed by NAC. In response to that request, the NRC organized within its Committee on Toxicology the Committee on Acute Exposure Guideline Levels, which prepared this report.

This report, Twenty-First Interim Report of the Committee on Acute Exposure Guideline Levels: Part B, summarizes the committee's conclusions and recommendations for improving AEGL documents for several chemicals and chemical classes not mentioned in Twenty-First Interim Report of the Committee on Acute Exposure Guideline Levels: Part A.