Permit-required confined space: what it means for the CHST
A confined space is big enough to enter and work in, has limited ways in and out, and is not designed for someone to stay in. It becomes a permit-required confined space when it also has, or could have, a serious hazard: a hazardous atmosphere, material that could engulf someone, a shape that could trap them, or another serious hazard.
Two tests, in order
First ask whether the space is confined at all: enterable, limited entry and exit, not built for continuous occupancy. Manholes, vaults, tanks, crawl spaces, pits and some attics qualify. Then ask whether it holds a hazard that makes it permit-required. The construction standard is 29 CFR 1926 Subpart AA, and the definitions are in 1926.1202.
A hazardous atmosphere under the rule includes oxygen below 19.5 percent or above 23.5 percent, flammable gas above 10 percent of its lower flammable limit, and toxic contaminants above their limits. The common testing order is oxygen first, then flammables, then toxics, because many flammable gas sensors need oxygen to read correctly.
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Emergency Preparedness, Incident Investigation, and Response
On a building under construction, what is the longest allowed travel distance from any point of the protected area to the nearest fire extinguisher?
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Who does what
- A competent person evaluates the site for confined spaces and permit spaces before work starts, under 1926.1203. See competent vs qualified person.
- The entry supervisor checks the permit's conditions, signs it and can cancel entry.
- The attendant stays outside, keeps count of entrants, keeps contact and summons rescue. The attendant does not go in to rescue.
- Authorized entrants know the hazards and get out when told or when something changes.
Rescue must be arranged before entry, under 1926.1211. A permit also lists other permits needed for the work, such as a hot work permit.
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Not every space stays a permit space
Subpart AA lets an employer use alternate procedures where ventilation alone keeps the only hazard, the atmosphere, under control, or reclassify a space as non-permit when every hazard is eliminated. Both have conditions and records. Read 1926.1203 for them in your own copy.
Common mix-ups
- Confined does not mean permit-required. Many confined spaces have no serious hazard.
- A hazard can come from the work. Welding, coating or running an engine inside can create the atmosphere hazard.
- Testing once is not enough. Conditions change, so monitoring continues.
- The attendant does not enter.
On the CHST exam
Confined spaces sit in the hazard and risk identification and control domain, 36.6% of the CHST, and rescue planning touches the emergency preparedness domain.
Practice it
The confined spaces guide maps every Subpart AA section. Trenches are covered separately in excavation protective systems, and every term in this set is in the CHST terms glossary.
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Sources
Show the list
- 29 CFR 1926 Subpart AA, Confined Spaces in Construction, OSHA.
- CHST Examination Blueprint (CHST5, V.2022.04.12), Board of Certified Safety Professionals.
Facts checked 26 October 2026 against the sources listed above. If something has changed, tell us and we will correct it within 2 business days.
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