OSHA 29 CFR 1910.146

29 CFR 1910.146 is the federal OSHA standard for permit-required confined spaces in general industry. It sits in Subpart J (General Environmental Controls) and applies to every general industry employer whose workers enter confined spaces.

A confined space has three defining characteristics: it is large enough for a worker to bodily enter and perform work, it has limited or restricted means of entry or exit, and it is not designed for continuous human occupancy. Think storage tanks, process vessels, silos, vaults, pits, and manholes.

A confined space becomes permit-required when it contains or has the potential to contain one or more of these hazards:

• A hazardous atmosphere (toxic, flammable, or oxygen-deficient/enriched)
• A material that could engulf the entrant (grain, sand, water)
• Inwardly converging walls or a floor that slopes downward and tapers to a smaller cross-section, trapping the entrant
• Any other recognized serious safety or health hazard (moving parts, electrical, thermal)

Before any worker enters a permit space, the employer has a series of obligations under 1910.146(c) and (d). These are not optional.

• Evaluate the workplace to determine if any spaces are permit-required confined spaces
• Inform exposed employees about the existence, location, and danger of permit spaces by posting danger signs or using another equally effective means
• If employees will not enter permit spaces, take effective measures to prevent unauthorized entry
• If employees will enter, develop and implement a written permit space program
• Make the written program available to affected employees and their representatives
• Review the program at least annually, using cancelled permits, to ensure it protects entrants

If a contractor is bringing workers into permit spaces at your facility, you must inform the contractor about the permit spaces, the hazards, your experience with them, and any precautions or procedures you have in place. The contractor must do the same in return. This two-way communication requirement under 1910.146(c)(8) and (c)(9) is one of the most commonly cited provisions during multi-employer site inspections.

Atmospheric testing is the most critical step before any confined space entry. 1910.146(d)(5) requires testing before entry and continuous or periodic monitoring during the entry. The testing must follow a specific order: oxygen first, then combustible gases, then toxic gases.

The reason for this order matters. Combustible gas sensors need adequate oxygen to read accurately. If you test for LEL before confirming oxygen levels, you could get a false low reading and walk into a flammable atmosphere. Always test O2 first.

A 4-gas monitor is the standard tool for pre-entry testing because it covers all four measurements in one device: O2, LEL, H2S, and CO. The instrument must be calibrated according to the manufacturer's instructions and bump-tested before each day of use.

The entry permit is the written authorization that documents conditions and controls for a specific confined space entry. Under 1910.146(f), the permit must include these elements at minimum:

• Identity of the space to be entered
• Purpose of the entry
• Date and authorized duration of the entry
• Names of authorized entrants (or a system to track who is inside)
• Names of current attendants and the entry supervisor
• Hazards of the permit space
• Measures used to isolate the space and eliminate or control hazards (lockout/tagout, purging, inerting, ventilation)
• Acceptable entry conditions (atmospheric test results)
• Results of initial and periodic atmospheric tests, including the names or initials of testers and the testing equipment used
• Rescue and emergency services available and how to summon them
• Communication procedures between entrants and attendants
• Equipment required (PPE, testing instruments, communications, lighting)
• Any additional permits issued for hot work or other operations

The entry supervisor signs the permit before entry begins. The permit must be posted at the entry point or otherwise made available to entrants. When the entry is complete or conditions change beyond what the permit allows, the permit is cancelled. Cancelled permits must be retained for at least one year to facilitate the annual program review.

1910.146 defines four distinct roles for permit space entry. Each person must be trained in their specific duties before they participate in an entry.

Entry Supervisor

The person responsible for determining if acceptable entry conditions are present, authorizing entry, overseeing the operation, and cancelling the permit when required. Can also serve as attendant or entrant if trained for those roles, but not while performing supervisor duties that would conflict.

Attendant

Stationed outside the permit space for the entire duration of the entry. The attendant monitors the entrants, maintains a count of who is inside, communicates with entrants, watches for hazards, and orders evacuation when conditions warrant. The attendant must never enter the space to attempt a rescue.

Authorized Entrant

The worker who actually enters the permit space. Must know the hazards, recognize signs of exposure, understand how to use the equipment, and communicate with the attendant. If the entrant detects a prohibited condition or the attendant orders evacuation, the entrant must exit immediately.

Rescue Team

Either an on-site team or an arranged outside rescue service. Rescue team members must be trained in basic first aid and CPR. If the team will enter the space for rescue, they must be trained as authorized entrants and practice making rescues from spaces similar in size, configuration, and hazards at least once every 12 months.

Ventilation and personal protective equipment work together to keep entrants safe. Neither one alone is sufficient for most permit space entries.

Forced air ventilation

Forced air ventilation is the primary method for controlling atmospheric hazards. Under 1910.146(c)(5)(ii), if an employer can demonstrate that forced air ventilation alone can maintain safe atmospheric conditions, the space may qualify for alternate entry procedures without a full permit. The ventilation must:

• Eliminate any hazardous atmosphere before entry
• Direct fresh air toward the work area
• Run continuously throughout the entry
• Supply air from a clean source (not near exhaust, chemical storage, or traffic)

Continuous atmospheric monitoring

Even with ventilation running, continuous monitoring is required during the entry. If the monitor alarms, everyone exits. The most common setup is a personal 4-gas monitor clipped to the entrant's collar or chest level, supplemented by a sample draw from the lowest point in the space.

Respiratory protection

When atmospheric hazards cannot be fully eliminated by ventilation, respiratory protection is required per OSHA 1910.134. This means a written respiratory protection program, fit testing, medical evaluations, and NIOSH-approved respirators appropriate for the identified contaminants.

Additional PPE

• Full-body harness with retrieval line (required for vertical entries)
• Hard hat where overhead hazards exist
• Chemical-resistant gloves and clothing when contaminants are present
• Communication equipment (two-way radio, visual signal) if voice contact is not reliable

1910.146(d)(9) and (k) lay out the rescue requirements. The employer must designate a rescue service before any entry begins. You have two options: an on-site rescue team or an outside rescue service.

On-site rescue team

• Members must be trained as authorized entrants for the spaces they may need to enter
• Must practice making permit space rescues at least once every 12 months
• At least one member must hold current first aid and CPR certification
• Must have the same PPE and rescue equipment as entrants, plus retrieval equipment

Outside rescue service

If you rely on a local fire department or private rescue service, you must evaluate their ability to respond in a timely manner and their capability to perform rescues from your specific types of confined spaces. OSHA expects you to verify this, not just assume the local fire department can handle it.

Non-entry rescue (retrieval systems)

Whenever feasible, employers should use non-entry rescue methods. This means a mechanical retrieval system (tripod, davit arm, or winch) attached to the entrant's full-body harness. The retrieval line allows the attendant to pull the entrant out without anyone else entering the space. For vertical entries over 5 feet deep, a mechanical retrieval device is required unless it would increase the overall risk.

Confined spaces exist in nearly every industry. Here are the most common types you will encounter on the job.

Confined space violations are among the most heavily penalized OSHA standards because of the high fatality rate associated with non-compliance.

Penalty amounts are adjusted annually for inflation. Actual penalties depend on employer size, good faith, violation history, and gravity of the hazard. When a fatality occurs, penalties are typically assessed at or near the maximum.

Energy isolation violations during confined space work may also trigger citations under OSHA 1910.147 (Lockout/Tagout), compounding the total penalty amount.

• 29 CFR 1910.146 Full Regulation Text
• OSHA Confined Spaces Safety Topic Page
• OSHA Publication 3138: Permit-Required Confined Spaces

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