Permit-Required Confined Spaces
29 CFR 1910.146 Compliance
Understanding confined space hazards, entry permits, atmospheric testing, and rescue requirements to prevent fatal entries
Critical Safety Issue
Confined space incidents kill an average of 92 workers per year in the United States. Over 60% of confined space fatalities are would-be rescuers who entered without proper equipment or training. Understanding the difference between a confined space and a permit-required confined space — and following entry procedures — saves lives.
Confined Space vs. Permit-Required Confined Space
A confined space has three defining characteristics 1910.146(b): (1) it is large enough for an employee to bodily enter and perform work, (2) it has limited or restricted means of entry or exit (e.g., tanks, manholes, silos, vaults, pits), and (3) it is not designed for continuous occupancy.
A confined space becomes permit-required when it contains or has the potential to contain one or more of these additional hazards:
Hazardous Atmosphere
Oxygen-deficient (<19.5%), oxygen-enriched (>23.5%), flammable gases/vapors (>10% LEL), or toxic contaminants above the PEL
Engulfment Hazard
Material such as grain, sand, or water that could surround and suffocate an entrant
Converging Configuration
Inwardly converging walls or a floor that slopes downward and tapers to a smaller cross-section, trapping an entrant
Any Other Serious Hazard
Unguarded machinery, energized electrical conductors, extreme heat, or other conditions that could cause death or serious injury
Common examples of permit-required confined spaces include storage tanks, process vessels, sewers, boilers, underground vaults, and silos. Even a seemingly harmless pit or crawl space can become permit-required if a hazardous atmosphere develops.
Atmospheric Testing
Atmospheric testing is one of the most critical elements of confined space entry. Tests must be performed before entry and continuously during occupancy 1910.146(c)(5). The testing sequence matters — test in this exact order:
Always test at multiple levels (top, middle, bottom) because gases stratify by density. Hydrogen sulfide (H₂S), for example, is heavier than air and accumulates at the bottom of a space, while methane rises to the top. Multi-gas monitors with remote sampling probes allow testing before any part of the body enters the space.
Entry Permit Requirements
The entry permit is a living document that authorizes and controls entry into a permit-required confined space. It must be completed before entry and posted at or near the entry point 1910.146(f). Required elements include:
- Space to be entered and purpose of entry.
- Date and authorized duration of entry.
- Names of authorized entrants, attendants, and entry supervisor.
- Hazards identified for the space.
- Measures to isolate the space and eliminate or control hazards (lockout/tagout, ventilation, barriers).
- Acceptable entry conditions (atmospheric test results with limits).
- Results of initial and periodic atmospheric tests, with tester name and calibration date.
- Rescue and emergency services — how to summon them and how they will reach the space.
- Communication procedures between entrants and attendants.
- Equipment provided (ventilation, PPE, lighting, communications, retrieval systems).
- Entry supervisor signature authorizing entry.
Permits must be cancelled when entry is complete or conditions change. Cancelled permits are retained for at least one year for the annual program review.
Key Personnel Roles
Authorized Entrant
Knows the hazards, uses equipment properly, communicates with the attendant, exits immediately when ordered or when they recognize a dangerous condition
Attendant
Remains outside the space at all times, monitors entrants and conditions, maintains an accurate count, orders evacuation if needed, summons rescue, prevents unauthorized entry
Entry Supervisor
Authorizes entry by signing the permit, verifies all precautions are in place, terminates entry and cancels the permit when conditions change or work is complete
Critical Rule: The attendant must never enter the confined space to perform a rescue. Over 60% of confined space fatalities are rescuers. The attendant's job is to summon trained rescue services and, if equipped, perform non-entry rescue using retrieval systems.
Rescue Planning
Every permit-required confined space program must address rescue 1910.146(d)(9). Employers have three options:
- Non-entry rescue — retrieval lines and mechanical devices (tripod/winch) pull the entrant out without anyone entering the space. This is the preferred method when space geometry allows it.
- In-house rescue team — employer-trained rescue personnel who practice space entry at least annually and are equipped with SCBA, retrieval systems, and first aid/CPR capability.
- Third-party rescue service — local fire department or private rescue company. The employer must verify that the service can respond in a timely manner, has the capability to rescue from the specific type of space, and has agreed to provide the service.
Entrants must wear a chest or full-body harness with a retrieval line attached to a mechanical device whenever entry is made into a permit space, unless the retrieval equipment would increase the overall risk of entry or would not contribute to rescue 1910.146(k)(3).
Reclassification to Non-Permit Space
A permit-required confined space may be reclassified as a non-permit confined space if the employer can demonstrate that all hazards have been permanently eliminated — not just controlled 1910.146(c)(7). For example, if a tank's only hazard was a toxic residue and the tank has been thoroughly cleaned, purged, and ventilated, it may qualify for reclassification. The employer must document the basis for the determination and certify that the space poses no actual or potential atmospheric hazard. If hazards cannot be permanently eliminated, the space remains permit-required even if hazards are temporarily controlled through ventilation or isolation.
Alternate Entry Procedures
When the only hazard is an actual or potential hazardous atmosphere that can be controlled with continuous forced-air ventilation alone, employers may use alternate entry procedures 1910.146(c)(5) instead of full permit entry. This allows entry without a complete permit system but still requires atmospheric monitoring, ventilation, and documentation. This is not the same as reclassification — the space is still permit-required, but simplified procedures apply.
References
1. OSHA 29 CFR 1910.146 — Permit-Required Confined Spaces (General Industry).
2. OSHA 29 CFR 1926 Subpart AA — Confined Spaces in Construction (2015).
3. NFPA 350: Guide for Safe Confined Space Entry and Work, 2022 Edition.
4. NIOSH: Confined Space — Worker Deaths in Confined Spaces.
Was this article helpful?
Rate this article to help us improve
Discussion (2)
The number one killer in confined spaces is not the original hazard — it is the would-be rescuer who jumps in without testing the atmosphere. NIOSH data shows that over 60% of confined space fatalities are rescuers. We drill it into every class: never enter a space to rescue someone unless you have SCBA or supplied air, a retrieval system, and a trained team. A dead rescuer does not save anyone.
This statistic is one of the most sobering in all of workplace safety. OSHA 1910.146(k) requires that employers either have an in-house rescue team that practices entry and rescue at least annually, or arrange for an outside rescue service and verify they can respond within an appropriate timeframe. The permit itself must identify the rescue method before entry begins — not after something goes wrong.
A detail that trips up a lot of facilities: atmospheric testing must be done in the correct order — oxygen first, then combustibles, then toxics. If you test for LEL before confirming oxygen is in the 19.5-23.5% range, your combustible gas reading is meaningless because the sensor needs oxygen to function. I have seen entry permits with all three readings checked off but done out of order with a single bump of the multi-gas meter.