Confined Spaces in Construction (Subpart AA) vs General Industry (1910.146): Don't Cite the Wrong Standard

Confined space work on a construction site is governed by 29 CFR 1926 Subpart AA (sections 1926.1201–1926.1213) — not the general industry standard 1910.146. OSHA wrote a separate construction rule, effective August 3, 2015, because construction sites are multi-employer, fast-changing environments that the older general-industry rule did not address. Applying or citing 29 CFR 1910.146 to a construction confined space is applying the wrong standard. And note a separate trap that runs the other way: trenches and excavations are excluded from Subpart AA outright by 1926.1201(b)(1) — not just their cave-in protection, but the whole job, atmosphere included. Excavations live under 29 CFR 1926 Subpart P.

Confined space work on a construction site falls under 29 CFR 1926 Subpart AA, sections 1926.1201 to 1926.1213, not the general industry standard 1910.146, and trenches and excavations are excluded from Subpart AA entirely because Subpart P governs them, atmosphere included.

Getting the citation right is not pedantry. It changes which duties apply, who is responsible on a multi-employer site, and whether a citation survives review. This guide gives you the section-by-section map, the construction-only requirements, two worked scenarios, and a checklist so you never reach for the wrong rule.

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The core distinction in one table

A frequent error is reaching for 1910.146 out of habit because it is the older, more familiar permit-required confined space rule. For construction work, Subpart AA controls, and a construction confined-space citation reads 1926.12xx.

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Subpart AA, section by section

Subpart AA mirrors the concepts of 1910.146 but renumbers them and adds construction-specific duties. Knowing the section numbers lets you read a citation correctly and write a defensible program.

If you only memorize four numbers, make them 1926.1203 (general requirements + coordination), 1926.1204 (program), 1926.1206 (equipment), and 1926.1211 (rescue) — those carry the core duties.

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What Subpart AA adds that 1910.146 does not

OSHA built Subpart AA around the reality of construction: multiple employers move in and out of the same space, conditions change hour to hour, and the crew that opens a vault is often not the crew that enters it. Compared to general industry, Subpart AA adds or strengthens these duties:

• A controlling contractor as the information hub. Under 29 CFR 1926.1203(h), the controlling contractor (not the host) is the primary point of contact for confined space information and coordinates entry among multiple entry employers. 1910.146 has a host-employer/contractor exchange, but nothing as structured as the construction controlling-contractor role.
• Mandatory, bidirectional information exchange. Before entry the controlling contractor must pass hazard information to each entry employer; after entry, each entry employer must report back the hazards confronted and lessons learned, and the controlling contractor relays that to the next employer. (1926.1203(h)(1)–(5).)
• Continuous atmospheric monitoring. Subpart AA requires continuous monitoring of atmospheric hazards unless the employer shows that continuous equipment is not commercially available or that periodic monitoring is frequent enough (1926.1204(e)(2)). 1910.146 leans more on periodic testing.
• Spaces that cannot be isolated. Where isolation is infeasible because the space is large or part of a continuous system, such as a sewer, the employer tests before entry to the extent feasible, continuously monitors entry conditions where entrants work, and provides an early-warning system that continuously monitors for non-isolated engulfment hazards (1926.1204(e)(1)(i)–(iii)), a construction-specific provision driven by sewer, vault, and manhole work.
• Competent-person site evaluation. A competent person must evaluate the worksite for confined spaces before work begins (1926.1203(a)).

These provisions exist because, on a construction site, the conditions in a space can be created by another employer's work happening at the same time.

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Permit-required vs non-permit confined spaces

Both standards distinguish a plain confined space from a permit-required confined space (PRCS).

A confined space has all three of these traits (1926.1202):

1. Large enough to enter and perform work, and
2. Limited or restricted means of entry or exit, and
3. Not designed for continuous human occupancy.

It becomes a permit-required confined space if it also has any one of:

• A hazardous or potentially hazardous atmosphere;
• Material with the potential to engulf an entrant;
• An inwardly converging configuration or sloping floor that could trap or asphyxiate; or
• Any other recognized serious safety or health hazard.

Before entering a permit space under Subpart AA, the employer must, among other things: identify and evaluate hazards; develop and document the written program and entry procedures; test and (where feasible) continuously monitor the atmosphere; provide attendants and an entry supervisor; verify rescue capability; and complete an entry permit signed by the entry supervisor. The framework resembles general industry in concept, but the legal citation and the coordination duties differ — which is exactly why the right standard matters.

Atmospheric testing order matters. Test in the sequence oxygen first, then flammables (LEL), then toxics (1926.1204(e)(3)). An out-of-range oxygen reading invalidates the combustible-gas sensor's accuracy, so a wrong order can mask a real hazard.

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Worked example 1: a sanitary-sewer manhole on a road job

A utility contractor must enter a 12-foot sewer manhole to repair a pipe joint. The general contractor (GC) holds the prime contract.

• Which standard? Construction → 1926 Subpart AA, not 1910.146.
• Is it a permit space? Yes. The manhole is large enough to enter, has restricted egress, is not designed for occupancy, and a sewer carries an atmospheric hazard (H₂S, methane, oxygen deficiency) plus an engulfment risk from flow. That triggers the full PRCS program (1926.1204).
• Who coordinates? The GC is the controlling contractor (1926.1203(h)). The GC must pass known hazards to the utility sub before entry and collect the sub's post-entry report.
• Monitoring? Continuous atmospheric monitoring is feasible with a 4-gas meter, so it is expected (1926.1204(e)(2)). Test oxygen → LEL → toxics (1926.1204(e)(3)); if the line cannot be isolated, provide an early-warning system for engulfment (1926.1204(e)(1)(iii)).
• Rescue? Arrange rescue before entry (1926.1211). Manholes typically require non-entry retrieval (full-body harness + retrieval line to a tripod/davit) unless the configuration makes it infeasible.

A citation here would read, for example, 29 CFR 1926.1204 or 1926.1211 — never 1910.146.

Worked example 2: a deep excavation with a "confined" feel

A crew is working in a 9-foot-deep, narrow trench to tie in a storm line. It feels like a confined space, and there is some standing water.

• Which standard for the cave-in risk? 1926 Subpart P (1926.650–.652) — sloping/benching/shoring/shielding and the daily competent-person inspection. The trench's protective system is not a Subpart AA matter.
• Could Subpart AA also apply? No — and this is stronger than most people assume. 29 CFR 1926.1201(b)(1) states that Subpart AA "does not apply to … construction work regulated by subpart P of this part (Excavations)." It is a flat exclusion, not a hierarchy: you do not layer a confined-space permit on top of an excavation. (Paragraphs (b)(2) and (b)(3) exclude Subpart S underground construction/caissons and Subpart Y diving.)
• So who covers the bad air? Subpart P does, in its own right. 29 CFR 1926.651(g) governs hazardous atmospheres in excavations: where one could reasonably be expected — near landfills, fuel storage, sewers, or running engines — the atmosphere must be tested before employees enter an excavation more than 4 feet deep (1926.651(g)(1)(i)), workers may not be exposed to more than 20% of the lower flammable limit (1926.651(g)(1)(iii)), and adequate precautions such as ventilation must be taken. The duty does not vanish with the exclusion — it simply lives in a different subpart, with different section numbers on the citation.
• Practical answer: an excavation is cited under Subpart P for everything — cave-in protection and atmosphere. Reaching for a Subpart AA permit is the mirror image of the 1910.146 mistake. See our trenching and excavation safety guide and the Excavation & Trench Safety hub.

This two-example split is the heart of the "don't cite the wrong standard" problem: construction confined space = 1926 Subpart AA; excavation = 1926 Subpart P for everything, including its atmosphere; general industry = 1910.146.

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Common mistakes and myths

• "Confined space is always 1910.146." No — for construction it is 1926 Subpart AA. 1910.146 is general industry only.
• "A deep trench is a confined space." No. 1926.1201(b)(1) excludes construction work regulated by Subpart P from Subpart AA outright — cave-in protection and the excavation's atmospheric duties (1926.651(g)) are Subpart P matters. Don't fold an excavation into your confined-space permit.
• "The host employer runs coordination." On construction, the controlling contractor is the central coordinator (1926.1203(h)), and the duty is bidirectional.
• "Periodic atmospheric checks are enough." Subpart AA expects continuous monitoring where feasible (1926.1204(e)(2)). A single pre-entry reading is rarely sufficient for sewer/vault work.
• "We'll call 911 if something goes wrong." Rescue must be arranged and verified before entry (1926.1211); relying on an untrained or unprepared public service for permit-space rescue is a deadly gap. The employer must evaluate a rescue service's ability to respond in time and its proficiency for the hazards (1926.1211(a)).
• "Reclassification means no permit ever." A PRCS can be reclassified to a non-permit space only after eliminating all hazards (not just controlling them with ventilation). If you rely on continuous forced-air ventilation, you are using alternate entry procedures (1926.1203(e)), and the space is still a permit space; reclassification requires a competent person's determination under 1926.1203(g).

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Penalties: getting it wrong is expensive

Confined-space failures can be cited as serious or willful, and a willful violation that meets OSHA's egregious criteria can be cited instance by instance (CPL 02-00-080). Under 29 CFR 1903.15(d), the 2026 maximums are:

These amounts are unchanged from 2025 — there was no inflation adjustment for 2026. Construction confined-space citations are written under 1926 Subpart AA; a citation mistakenly written under 1910.146 invites a challenge that the wrong standard was applied. For the standard's own page, see Permit-Required Confined Spaces in Construction — 1926.1204.

Multi-employer note. A controlling contractor cited on a multi-employer site is held to a reasonable-care standard for a subcontractor's confined-space violation — not strict liability (OSHA Directive CPL 02-00-124; Acosta v. Hensel Phelps, 909 F.3d 723, 5th Cir. 2018). Document your coordination and information exchange to meet it. See the multi-employer worksite citation doctrine.

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Don't-cite-the-wrong-standard checklist

• Confirm the work is construction → use 1926 Subpart AA (1926.1201–.1213)
• Do not apply 1910.146 to construction confined spaces
• A competent person evaluates the site for confined spaces before work (1926.1203(a))
• Identify the controlling contractor as the confined-space information hub (1926.1203(h))
• Exchange hazard info before and after entry among host, controlling, and entry employers
• Classify each space: confined vs permit-required (1926.1202)
• For permit spaces: written program (1204), permit (1205), equipment (1206), attendant + supervisor (1209/1210)
• Test the atmosphere in order O₂ → LEL → toxics (1204(e)(3)); continuously monitor atmospheric hazards (1204(e)(2))
• Arrange and verify rescue before entry (1926.1211)
• Handle excavations entirely under Subpart P — cave-in protection and atmosphere (1926.651(g)); Subpart AA is excluded by 1926.1201(b)(1)

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What to do next

1. Confirm jurisdiction first. Construction? It's 1926 Subpart AA. General industry? 1910.146. Cave-in? Subpart P. Write that on the permit.
2. Designate and document the controlling contractor and the information-exchange flow before mobilization.
3. Generate compliant entry permits with the Confined Space Entry Permit Generator — atmospheric log, attendant/entrant roster, rescue plan, and the entry-supervisor signature block.
4. Don't forget hot work inside the space — combine your permits with the Hot Work Permit Generator.
5. Train to the right standard (1926.1207). Background reading: Safety Permits hub — confined space & hot work · Confined Space Entry Permit: OSHA Requirements · Digital Permits for Hot Work and Confined Space.

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Sources & verification (read on the eCFR, October 6, 2026): 29 CFR 1926 Subpart AA (1926.1201–1926.1213), including 1926.1201(b)(1)–(3), 1926.1203(a), (e), (g) and (h)(1)–(5), and 1926.1204(e)(1)–(3); general industry 1910.146; excavations 29 CFR 1926 Subpart P, including 1926.651(g)(1); multi-employer policy OSHA CPL 02-00-124 and Acosta v. Hensel Phelps (5th Cir. 2018); egregious policy CPL 02-00-080; penalty maximums per 29 CFR 1903.15(d) (2026). This is general guidance, not legal advice; State Plans may impose requirements at least as effective as the federal standard — verify your state's rules.