Which of the following is a regulation commonly cited for confined spaces in the US?

• A. AFMAN 91-203 Chap. 23 (USAF)
• B. ANSI Z117.1
• C. 29 CFR 1910-146 (OSHA)
• D. AFI 48-151

Answer: (C)

In the US, the binding rules for confined spaces come from OSHA, specifically the permit-required confined spaces standard. This regulation, codified as 29 CFR 1910.146, sets the enforceable requirements for recognizing, evaluating, and safely entering confined spaces. It defines what counts as a permit-required space, requires an entry permit with hazard evaluation, atmospheric testing, space isolation, ventilation, and rescue planning, and mandates training for workers involved. Because it is an actual federal regulation with nationwide enforcement (and adopted by states with OSHA-approved plans), it is the regulation most commonly cited for confined-space safety across industries.

ANSI Z117.1, while widely used as a respected standard for best practices and a practical reference for safe entry procedures, is not itself a regulatory mandate. AFMAN 91-203 and AFI 48-151 are military-specific manuals; they apply within their particular DoD contexts rather than serving as the general nationwide regulatory framework for confined spaces.