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Construction term · Glossary

Confined Space

Verified vs OSHA sources · 2026-10-05

A space that is large enough for a worker to bodily enter, has limited or restricted means of entry or exit, and is not designed for continuous occupancy. If it also contains — or could contain — a serious hazard (a hazardous atmosphere, engulfment material, an entrapping configuration, or any other recognized serious hazard), it becomes a permit-required confined space (PRCS).

29 CFR 1926.1202

Also known as: confined space, permit-required confined space, PRCS

Confined Space at a glance

  • Three-part test: enterable + limited entry/exit + not designed for continuous occupancy.
  • Becomes permit-required (PRCS) if it has a hazardous atmosphere, engulfment, entrapment, or other serious hazard.
  • Hazardous atmosphere: oxygen below 19.5% or above 23.5%, or flammable gas/vapor above 10% of its LFL.
  • Atmosphere must be tested before entry — in order: oxygen, then flammables, then toxics.

In plain English

A tank, vault, manhole, pit, or similar spot you can climb into but that's hard to get out of and isn't meant for working in all day. If the air could go bad or you could get trapped or buried, it's a “permit-required” space with strict entry rules.

What the rule says

“Confined space means a space that: (1) Is large enough and so configured that an employee can bodily enter it; (2) Has limited or restricted means for entry and exit; and (3) Is not designed for continuous employee occupancy.”
29 CFR 1926.1202

In context

A concept governed primarily by OSHA's construction standards, 29 CFR Part 1926 — the rules that apply on jobsites rather than the general-industry 1910 set.

29 CFR 1926

Where this is written in OSHA's rules

Example

A crew needs to enter a storm-drain vault. It's a confined space — you can enter it, the only way in is a manhole, and no one works there continuously. Before entry, a calibrated meter reads oxygen, then flammable gas, then toxics: it shows 18% oxygen, below the 19.5% minimum, making it a hazardous atmosphere and a permit-required space. Entry is prohibited until it's ventilated and re-tested, with an attendant and rescue plan in place.

Why it matters

Confined spaces cause some of the deadliest events in construction — and a large share of victims are would-be rescuers who rush in. OSHA's confined-space standards are frequently cited, and the requirements (testing, permits, an attendant, rescue) exist precisely because “it looked fine” has killed many workers.

Confined space vs. permit-required confined space

Every permit-required space is a confined space, but not every confined space needs a permit. A plain confined space just meets the three-part test; it becomes permit-required (PRCS) only when a serious hazard — bad atmosphere, engulfment, entrapment, or another recognized danger — is present or possible.

Confined space vs. permit-required confined space (PRCS)

TypeDefining featureEntry controls
Confined spaceEnterable, limited exit, not for continuous occupancyBasic precautions
Permit-required (PRCS)The above + a serious hazard (atmosphere, engulfment, etc.)Permit, testing, attendant, rescue plan

Confined Space: frequently asked questions

What are the three criteria for a confined space?
It must be (1) large enough to bodily enter, (2) have limited or restricted means of entry and exit, and (3) not be designed for continuous employee occupancy (29 CFR 1926.1202).
What makes a confined space 'permit-required'?
A serious hazard: a hazardous atmosphere (oxygen below 19.5% or above 23.5%, or a flammable atmosphere above 10% of the LFL), material that could engulf the entrant, a configuration that could trap or asphyxiate, or any other recognized serious safety or health hazard.
In what order do you test the atmosphere?
Oxygen first, then flammable gases and vapors, then potential toxic air contaminants — using a calibrated direct-reading instrument, before anyone enters.

Related terms

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Governing OSHA standards

More Construction terms

29 CFR 1910

The part of Title 29 of the Code of Federal Regulations that contains OSHA's General Industry standards — the default rulebook for most American workplaces (manufacturing, warehousing, healthcare, etc.) that aren't covered by the construction, maritime, or agriculture standards. It includes core rules like Hazard Communication (1910.1200) and the permissible exposure limits (1910.1000). Several 1910 standards are cross-referenced into construction via Part 1926.

29 CFR 1926

The part of Title 29 of the Code of Federal Regulations that contains OSHA's Construction standards — the “Safety and Health Regulations for Construction.” It governs construction, alteration, and repair work, with construction-specific rules for fall protection (Subpart M), scaffolds (Subpart L), excavations (Subpart P), electrical (Subpart K), and more. Where a task isn't addressed in 1926, some general-industry (1910) standards apply by reference.

Anchor Point

The secure attachment point a personal fall arrest system (PFAS) ties off to — the “A” in the ABC of fall arrest. Under 29 CFR 1926.502(d)(15), a non-engineered anchorage must support at least 5,000 pounds per attached worker; alternatively, it can be an engineered anchorage designed and supervised by a qualified person with a safety factor of at least two.

Atmospheric Testing

Measuring the air in a confined space (or other hazardous atmosphere) with a calibrated direct-reading instrument before and during entry. OSHA requires testing in a set order — oxygen first, then flammable gases and vapors, then potential toxic contaminants — and defines the acceptable ranges: oxygen 19.5%–23.5%, flammables below 10% of the LEL, toxics below their exposure limits.

Benching

An excavation cave-in protective system that cuts the sides into a series of horizontal steps (benches), usually with vertical or near-vertical faces between levels. It's one of OSHA's accepted protective systems under Subpart P — but it is NOT permitted in Type C (the least stable) soil.

Competent Person (Excavation)

The competent person OSHA's excavation standard (Subpart P) requires on every trenching job — someone trained in soil classification and protective systems, who can identify cave-in and other hazards AND has authority to remove workers and correct problems. They must inspect the excavation daily before work starts, throughout the shift, and after any rain or event that could increase the hazard.

Controlling Employer

Under OSHA's Multi-Employer Citation Policy (CPL 02-00-124), the controlling employer is an employer with general supervisory authority over a worksite — including the power to correct safety and health violations itself or to require others to correct them. This is typically the general contractor or construction manager. A controlling employer can be cited for a hazard at the site even if none of its own employees are exposed, because it has a duty to exercise reasonable care to prevent and detect violations by the other employers on site.

Crane Operator Certification

OSHA's requirement (29 CFR 1926.1427) that construction crane operators be certified — by an accredited crane-operator testing organization or an employer's audited program — for the equipment type they run. The certifying body may issue by type, or by type and capacity (1926.1427(d)(1)(ii)(B)); capacity alone is not mandatory. Certification is one part: the employer must also train the operator and separately evaluate their ability to operate the specific equipment safely.

Sources & verification

Reviewed by HazComFast against eCFR, OSHA.gov, NIOSH, and the Federal Register. Last reviewed 2026-10-05. This glossary is general information, not legal advice; OSHA State-Plan states (e.g. California, Michigan) may adopt stricter requirements.

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