Skip directly to search Skip directly to A to Z list Skip directly to navigation Skip directly to page options Skip directly to site content

Immediately Dangerous To Life or Health (IDLH) Values

May 1994
Immediately Dangerous to Life or Health Concentrations (IDLH)


This publication documents the criteria and information sources that have been used by the National Institute for Occupational Safety and Health (NIOSH) to determine immediately dangerous to life or health (IDLH) values. IDLH values were originally determined for 387 substances in the mid-1970's as part of the Standards Completion Program (SCP), a joint project by NIOSH and the Occupational Safety and Health Administration (OSHA), for use in assigning respiratory protection equipment. NIOSH is currently evaluating the scientific adequacy of the criteria and procedures used during the SCP for establishing IDLH values. In the interim, the IDLH values have been reviewed and, (if appropriate) revised. In this document, IDLH values are listed with the basis and references for the current values as well as with the original IDLH values and their documentation (as paraphrased from the SCP draft technical standards).


Special appreciation is extended to the following individuals from the Division of Standards Development and Technology Transfer: Crystal L. Ellison for locating the references and verifying the information used during the Standards Completion Program to determine the original IDLH values; Rosmarie T. Hagedorn, Marsha A. Striley, and B. JoAnne Hamons for typing the numerous drafts of this document; Vanessa L. Becks for assistance in page design; and Laurence D. Reed, Ralph D. Zumwalde, Robert W. Mason, and G. Kent Hatfield for their technical reviews and comments.


Mention of the name of any company or product does not constitute endorsement by the National Institute for Occupational Safety and Health.