IDLH (immediately dangerous to life or health)

What it means

IDLH includes delayed threats, not only immediate ones, and anything that would prevent unaided escape. The respiratory protection standard says all oxygen-deficient atmospheres shall be considered IDLH (1910.134(d)(2)(iii)).

For IDLH atmospheres, 1910.134(d)(2)(i) requires a full facepiece pressure demand SCBA with at least a 30-minute service life, or a full facepiece pressure demand supplied-air respirator with an auxiliary self-contained air supply.

Example

A pit reads 17% oxygen. That's oxygen deficient, so under 1910.134 it's treated as IDLH: an air-purifying respirator is not allowed, and entry would need an SCBA or an airline respirator with an escape bottle.

Where it appears on the exam

• ASP: ASP11 Domain 6, Industrial Hygiene and Occupational Health

  Practice: Respiratory Protection, Permit-Required Confined Spaces

• CSP: CSP11 Domain 1, Advanced Application of Safety Principles

  Practice: Confined Spaces and Lockout/Tagout, PPE Hazard Assessment and Selection

• CHST: CHST5 Domain 1, Hazard and Risk Identification and Control

  Practice: Confined Spaces in Construction

Questions

Can you use an air-purifying respirator in an IDLH atmosphere?

No. 1910.134(d)(2)(i) requires a full facepiece pressure demand SCBA or a full facepiece pressure demand supplied-air respirator with an auxiliary self-contained air supply.