What does IDLH mean under OSHA?
In the respiratory protection standard, 29 CFR 1910.134, IDLH means an atmosphere that poses an immediate threat to life, would cause irreversible adverse health effects, or would impair a person's ability to escape. Other standards, including 1910.146 and 1910.120, define it in their own words.
By Cairn. Updated . Sources: eCFR text as of October 27, 2026.
The legal definitions
Respiratory protection, 29 CFR 1910.134
“Immediately dangerous to life or health (IDLH) means an atmosphere that poses an immediate threat to life, would cause irreversible adverse health effects, or would impair an individual's ability to escape from a dangerous atmosphere.”
Permit-required confined spaces, 29 CFR 1910.146
“Immediately dangerous to life or health (IDLH) means any condition that poses an immediate or delayed threat to life or that would cause irreversible adverse health effects or that would interfere with an individual's ability to escape unaided from a permit space.”
Hazardous waste operations, 29 CFR 1910.120
“IDLH orImmediately dangerous to life or health means an atmospheric concentration of any toxic, corrosive or asphyxiant substance that poses an immediate threat to life or would cause irreversible or delayed adverse health effects or would interfere with an individual's ability to escape from a dangerous atmosphere.”
The official text of this definition runs "or" and "Immediately" together, and the quotation keeps it that way.
Where it applies
- 29 CFR 1910.134, Respiratory protection 20 paragraphs use the term. Read the text on eCFR.
- 29 CFR 1910.146, Permit-required confined spaces 4 paragraphs use the term. Read the text on eCFR. Not the same definition: 29 CFR 1910.146(b) defines IDLH for permit spaces in its own words, quoted above.
- 29 CFR 1910.120, Hazardous waste operations and emergency response 10 paragraphs use the term. Read the text on eCFR. Not the same definition: 29 CFR 1910.120(a)(3) defines IDLH for hazardous waste operations in its own words, as an atmospheric concentration of a toxic, corrosive or asphyxiant substance. Quoted above.
In the enforcement record
Federal and state-plan agencies issued 57,190 cited violations under 29 CFR 1910.134, Respiratory protection, from January 2016 through September 10, 2026. The section ranks 3rd among the 248 sections of 29 CFR cited at least 50 times. This is the count for the whole section, not for the term alone.
Cairn data, October 2026 snapshot.
See the full record for 29 CFR 1910.134Sources
- 29 CFR 1910.134, Respiratory protection. eCFR, text as of October 27, 2026.
- 29 CFR 1910.146, Permit-required confined spaces. eCFR, text as of October 27, 2026.
- 29 CFR 1910.120, Hazardous waste operations and emergency response. eCFR, text as of October 27, 2026.
- Cairn data, October 2026 snapshot. Cairn analysis of the OSHA enforcement record.
Written by Cairn, updated . The quoted text is copied from the sources above. A test compares each quotation with a stored copy of the source, and a separate script compares that copy with the live sources. This page explains the law and is not legal advice.