Glossary / Exposure limits
Immediately dangerous to life or health (IDLH)
Immediately dangerous to life or health (IDLH) describes an atmosphere that poses an immediate threat to life, would cause irreversible adverse health effects, or would impair a person's ability to escape. OSHA's respirator standard defines the term, and NIOSH publishes IDLH values for many chemicals that are used mainly to select respirators for emergencies and unknown conditions.
Explanation
NIOSH publishes IDLH values for many chemicals. They were developed to guide respirator choice, and the underlying idea is whether a worker whose respirator failed could still get out safely. They are not exposure limits for normal work, and they are generally much higher than the PEL, REL or TLV for the same chemical.
OSHA's respirator rule, 29 CFR 1910.134(d)(2)(i), requires the most protective equipment in IDLH atmospheres: a full facepiece pressure-demand SCBA certified by NIOSH for a minimum service life of 30 minutes, or a combination full facepiece pressure-demand supplied-air respirator with an auxiliary self-contained air supply. Air-purifying respirators are not among the permitted options for working in an IDLH atmosphere; respirators provided only for escape must be NIOSH-certified for escape. Where the employer cannot identify or reasonably estimate the exposure, the atmosphere must be treated as IDLH, and oxygen-deficient atmospheres are treated as IDLH too (with a narrow exception in the rule).
Under 29 CFR 1910.134(g)(3), work in an IDLH atmosphere requires at least one employee outside the atmosphere who is trained and equipped for rescue, plus communication and a rescue plan. This is part of emergency response and Confined space programs. The IDLH is not a safe level for anyone to enter, and values for some chemicals reflect effects such as escape-impairing irritation, not only lethality.
Because IDLH figures depend on the research available, some chemicals have none. The SDS may list the IDLH in Section 8, or it may be absent. In that case assume the worst until measured.
What to do and watch for
- Treat unknown atmospheres as IDLH until tested.
- Use an SCBA or equivalent in IDLH conditions, with a standby rescue team.
- Never use an IDLH value as a working exposure target.
Where it appears on an SDS
- Section 8: Exposure controls / personal protection. May include the NIOSH IDLH value among the exposure parameters.
- Section 5: Fire-fighting measures. Firefighting advice on protective equipment and breathing apparatus is relevant to IDLH conditions.
SDS content and wording vary by supplier. This page is general reference and does not replace the current SDS for your product.