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OSHA confined spaces (Subpart AA) for the CHST

Toe Board editorial teamSources checked 3 min read

Confined spaces kill the people who go in and the people who go in after them. The CHST blueprint lists working in confined spaces in Domain 1, and rescue and response in Domain 2. Subpart AA (29 CFR 1926.1200 to 1926.1213) is the construction rule. This guide gives the structure in our own words.

Check anything you rely on against your own licensed code book and the edition your AHJ enforces.

Where Subpart AA sits in the blueprint

Confined spaces are item 6 in the Domain 1 knowledge list, with emergency response items in Domain 2 (19.9%). Domain 1 is 36.6% of the CHST. Expect scenario questions about who does what.

The sections to know

  • 1926.1203 holds the general requirements: a competent person evaluates the site for confined spaces and permit spaces, workers are told about them, and entry is controlled.
  • 1926.1204 requires a written permit space program where entry will happen.
  • 1926.1205 and 1926.1206 cover the permitting process and the entry permit.
  • 1926.1207 requires training.
  • 1926.1208, 1926.1209 and 1926.1210 set the duties of the authorized entrant, the attendant and the entry supervisor.
  • 1926.1211 covers rescue and emergency services, which must be arranged before entry.
  • 1926.1212 covers employee participation.

Subpart AA also includes provisions for controlling contractors, who coordinate when more than one employer is on site.

Try one question

Question 1 of the free 10-question check on CHST. No signup.

Question 1 of 10 · free checkUntimed

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?

Choose an answer to begin

Atmospheric hazards

The usual testing order is oxygen first, then flammable gases and vapors, then toxic gases. The test comes before entry, and monitoring continues while people are inside. The definitions in the subpart set the oxygen range that counts as a hazardous atmosphere. Use your own copy for the figures.

Who does what

  • Entrants know the hazards, use the equipment and leave when told or when something changes.
  • The attendant stays outside, counts who is inside, keeps communication and calls for rescue. The attendant does not enter to rescue.
  • The entry supervisor checks that conditions are right, signs the permit and ends entry when needed.

Common mix-ups

  • Permit space and confined space differ. A permit space is a confined space with a recognized hazard. Not every confined space needs a permit.
  • Rescue is planned before entry. Calling for rescue after someone is down is too late.
  • The attendant stays out. Entering to help adds a second victim.
  • Testing is repeated, because atmosphere can change once work starts.

How to practice

Write the three roles on a card with one duty each. Then work questions that describe an entry and ask who failed which duty, or what the first action is.

Related guides: excavations (Subpart P), since trenches can become confined spaces, and health hazards.

Practice it

Take the free 10-question check. It covers the four CHST domains, needs no signup and explains every answer, so you see whether this subpart is a weak spot. The CHST study guide shows where it fits in a six-week plan.

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Sources

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Facts checked 24 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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Study guideOSHA fall protection (Subpart M) for the CHSTStudy guideOSHA excavations (Subpart P) for the CHSTStudy guideOSHA scaffolds (Subpart L) for the CHSTStudy guideOSHA electrical (Subpart K) for the CHSTStudy guideOSHA cranes and derricks (Subpart CC) for the CHSTStudy guideOSHA ladders and stairways (Subpart X) for the CHSTStudy guideOSHA health hazards: silica, lead and noise for the CHSTStudy guideOSHA recordkeeping (Part 1904) for the CHST