29 CFR 1910.146: OSHA Permit-Required Confined Spaces

Regulatory citation: 29 CFR 1910.146 (general industry); 29 CFR 1926 Subpart AA (construction)

What Are OSHA's Permit-Required Confined Space Requirements?

The Permit-Required Confined Spaces standard, found at 29 CFR 1910.146 for general industry, governs entry into spaces that are large enough for an employee to enter, have limited means of entry or exit, and are not designed for continuous occupancy, when those spaces also contain or have the potential to contain a serious hazard, such as a hazardous atmosphere, engulfment risk, or an internal configuration that could trap or asphyxiate an entrant.

Construction work involving confined spaces is governed by a separate, though similarly structured, standard at 29 CFR 1926 Subpart AA.

What Makes a Space "Permit-Required"

Not every confined space requires a permit. A space becomes permit-required when it contains, or has the potential to contain, one or more of the following: a hazardous atmosphere, a material with engulfment potential, an internal configuration that could trap or asphyxiate an entrant, or any other recognized serious safety or health hazard.

Core Requirements Under 29 CFR 1910.146

1. Confined Space Identification and Evaluation

Employers must identify all permit-required confined spaces in the workplace and inform employees of their existence and location, typically through signage and a written inventory.

2. Written Permit Space Program

Employers who allow entry into permit-required confined spaces must develop a written program detailing procedures for safe entry, including hazard identification, control measures, and entry permit procedures.

3. Entry Permits

Before entry, a written permit must be completed, documenting the specific space, identified hazards, control measures in place, atmospheric test results, and authorized entrants, attendants, and supervisors.

4. Atmospheric Testing

The space must be tested for oxygen content, flammability, and toxic contaminants before entry, and often continuously monitored throughout the duration of entry.

5. Attendant and Entry Supervisor Roles

A trained attendant must remain outside the space throughout entry, maintaining communication with entrants and prepared to initiate rescue procedures if necessary, while an entry supervisor authorizes and oversees the entry.

6. Rescue and Emergency Services

Employers must arrange for rescue and emergency services, whether through a dedicated in-house rescue team or a coordinated external service, and ensure that service is capable of responding appropriately to the specific space and hazards involved.

Common Confined Space Compliance Mistakes

Misclassifying a Space as Non-Permit-Required

Underestimating a space's hazard potential, particularly for infrequently entered spaces, is a common and serious compliance failure.

Inadequate Atmospheric Monitoring

Testing the atmosphere once before entry, without continuous monitoring where conditions could change, leaves entrants vulnerable to hazards that develop after entry begins.

Attendant Leaving Their Post

Confined space attendants leaving their position, even briefly, undermines one of the standard's most critical safety controls, since the attendant is often the only reliable means of initiating a timely rescue.

Unverified Rescue Service Capability

Employers sometimes assume local emergency services can perform confined space rescue without confirming that capability in advance, which can cause dangerous delays during an actual emergency.

Example: Confined Space Entry in Practice

A wastewater treatment facility requires periodic entry into an underground holding tank for inspection and maintenance. The facility has classified this tank as a permit-required confined space due to the potential for hazardous atmosphere buildup. Before each entry, the entry supervisor completes a written permit, atmospheric testing confirms safe oxygen and gas levels, a trained attendant remains at the entry point with continuous communication to the entrant, and the facility has a pre-arranged agreement with a local rescue service specifically trained and equipped for confined space rescue in this type of tank configuration.

Frequently Asked Questions

What makes a confined space "permit-required" under OSHA?

A confined space becomes permit-required under 29 CFR 1910.146 when it meets the basic definition of a confined space, large enough for an employee to bodily enter, having limited or restricted means of entry or exit, and not designed for continuous human occupancy, and additionally contains or has the potential to contain one or more serious hazards. These hazards include a hazardous atmosphere (such as oxygen deficiency, flammable gases, or toxic contaminants), material with the potential to engulf an entrant (such as grain, sand, or liquid), an internal configuration that could trap or asphyxiate someone due to converging walls or a downward-sloping floor, or any other recognized serious safety or health hazard. Spaces that meet the basic confined space definition but don't contain any of these additional hazard characteristics are classified as non-permit confined spaces, which carry fewer procedural requirements, though employers must still evaluate and document why a space doesn't require a permit if questioned.

What has to be on a confined space entry permit?

An entry permit for a permit-required confined space must document several specific pieces of information before entry is authorized: the specific space being entered and the purpose of the entry, the date and authorized duration of entry, the names of authorized entrants and the entry supervisor, the specific hazards identified within the space, the measures taken to isolate the space and control those hazards, atmospheric test results along with the name of the person who conducted the testing and when, the communication procedures and equipment to be used between entrants and the attendant, and the rescue and emergency services arranged for that specific entry. The permit must be completed and signed by the entry supervisor before entry begins, and must be posted at the entry point or otherwise made available to entrants during the entry. Once the entry is complete or the permit's authorized duration expires, the permit must be canceled, and any conditions that arise during entry that weren't already covered must halt entry until the permit is updated or a new one is issued.

Who is responsible for confined space rescue?

Employers who allow entry into permit-required confined spaces must ensure that rescue and emergency services are available and capable of responding appropriately to the specific hazards present in that space, whether through a dedicated in-house rescue team or a coordinated arrangement with an external rescue service. Simply assuming local emergency responders can perform confined space rescue isn't sufficient; the standard requires employers to evaluate a prospective rescue service's ability to respond in a timely manner and to have the specific equipment and training needed for confined space rescue scenarios, which differ significantly from general emergency response. If an in-house rescue team is used, those team members must be trained and equipped to the same standard as authorized entrants, plus additional training specific to rescue procedures, including practice rescue exercises using mannequins or volunteers from representative confined spaces at least annually. Employers must also ensure a means of summoning rescue services is available at all times during entry, since delays in initiating rescue are often the deciding factor in whether a confined space incident results in a survivable outcome.

How is atmospheric testing conducted for confined space entry?

Atmospheric testing for permit-required confined space entry must be conducted using calibrated, direct-reading instruments capable of testing for oxygen content, flammability or combustible gases, and any toxic contaminants that could reasonably be expected to be present based on the space's history and configuration. Testing must occur in a specific sequence, oxygen levels first, since both combustible gas readings and some toxic gas sensors can be affected by oxygen concentration, followed by flammability testing, and finally toxic contaminant testing. Initial testing must be completed before entry begins, and depending on the specific hazards and how likely conditions are to change during entry, continuous or periodic monitoring throughout the entry period may also be required, particularly in spaces where work activities themselves could generate or disturb hazardous atmospheres, such as welding or the disturbance of settled residues. All testing results must be documented on the entry permit, along with the identity of the person who performed the testing and the specific instrument used, supporting both real-time safety decisions and post-entry compliance documentation.

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