Pillar guide · OSHA 29 CFR 1910.146
Confined space entry permits: the complete OSHA 1910.146 guide
A confined space permit is required whenever a confined space contains — or could contain — a hazardous atmosphere, engulfment material, an entrapment geometry, or any other recognised serious hazard (§1910.146(b)). This guide walks through the four OSHA triggers, the 14 fields the permit must contain, the atmospheric testing sequence, the roles that must be assigned, how to issue and cancel the permit, and where digital permits reduce the paperwork errors that show up most often in OSHA citations.
Last reviewed 2 July 2026 · SafeGuard EHS Editorial
OSHA 1910.146 trigger checklist
When is a confined space permit required?
A confined space permit is required when the space meets OSHA's confined-space definition in §1910.146(b) and at least one of the four trigger conditions below is present — or could become present during the work. If any single trigger applies, no one may cross the plane of the opening without a written, signed entry permit.
- Hazardous atmosphere. Oxygen outside 19.5%–23.5%, flammables at or above 10% LEL, any toxic contaminant above its OSHA PEL, or any airborne concentration immediately dangerous to life or health (IDLH).
- Engulfment potential. Loose material — grain, sand, sludge, sawdust, water — that could surround and capture an entrant, causing death by strangulation, constriction, crushing, or drowning.
- Entrapment geometry. Internally converging walls or a floor sloping downward and tapering to a smaller cross-section that could trap or asphyxiate an entrant.
- Any other recognised serious hazard. Unguarded machinery, exposed live parts, extreme heat or cold, corrosive chemicals, falls of more than 4 ft — anything a competent person would judge capable of causing serious injury or death.
One trigger is enough. The four are independent — you do not need multiple hazards, and a hazard that is only potentially present (a tank that could off-gas, a silo that could refill) still makes the space permit-required. Reclassification to non-permit is only allowed after every trigger has been eliminated and the basis documented (§1910.146(c)(7)).
Related: confined space entry equipment: selection, calibration & maintenance · permit vs non-permit confined spaces
Definitions
What is a confined space?
OSHA §1910.146(b) defines a confined space by three characteristics: it is large enough for an employee to enter and perform work, has limited or restricted means of entry or exit, and is not designed for continuous occupancy. Tanks, vessels, silos, storage bins, hoppers, vaults, pits, manholes, tunnels, equipment housings, and ductwork commonly qualify.
A permit-required confined space is a confined space that additionally contains, or has the potential to contain, one or more of: a hazardous atmosphere; engulfment material; internally converging walls or a downward-sloping floor that could trap or asphyxiate an entrant; or any other recognised serious safety or health hazard.
The permit-required label is not optional — if a space meets the criteria, a written entry programme and an entry permit are legally required before work begins. See how OSHA defines a confined space for a longer walk-through of edge cases.
Classification
Permit-required vs non-permit confined spaces
Not every confined space needs a permit. A non-permit confined space is one where the employer can demonstrate that the only hazard is posed by an atmospheric condition, and continuous forced-air ventilation alone will keep that atmosphere safe for entry. Everything else — anything with engulfment potential, entrapment geometry, or a serious mechanical, electrical, thermal, or chemical hazard — falls back into the permit-required category.
Reclassification is possible: if you eliminate all the hazards that made a space permit-required (for example, by isolating a chemical feed and demonstrating a clean atmosphere), you may reclassify it as non-permit for the duration of that condition. Document the basis of the reclassification and cancel it the moment conditions change. Read the full difference between permit and non-permit spaces.
Employer duties
OSHA 1910.146: what the employer must do
Under §1910.146(c) an employer with permit-required confined spaces on site must: evaluate the workplace for permit spaces; inform employees by posting danger signs; prevent unauthorised entry; and either develop a written permit-space programme or, if no employee will enter, take measures to prevent entry.
The written programme must specify how the employer identifies spaces, tests and monitors conditions, provides equipment, designates rescue services, coordinates with contractors, and reviews the programme at least annually using cancelled permits from the past 12 months. For a deeper reading of each subsection, see the full OSHA 1910.146 employer duties article.
§1910.146(f)
What a confined space entry permit must contain
The 14 fields OSHA requires on every entry permit. Miss any and the permit is defective on its face.
- 1The permit space to be entered
- 2The purpose of the entry
- 3The date and authorised duration of the permit
- 4The authorised entrants (by name or roster)
- 5The personnel serving as attendants
- 6The entry supervisor, with a space for the supervisor's signature
- 7The hazards of the permit space
- 8The measures used to isolate the space and eliminate or control hazards
- 9Acceptable entry conditions
- 10Results of initial and periodic atmospheric tests (with tester's initials and time)
- 11Rescue and emergency services and the means to summon them
- 12Communication procedures between attendants and entrants
- 13Equipment (PPE, testing, communications, alarm systems, rescue)
- 14Any other information necessary to ensure safe entry (e.g. permits from other work)
Roles
Who does what during a confined space entry
Entry supervisor
Authorises entry by signing the permit, verifies acceptable entry conditions, terminates entry when the task ends or conditions change, and cancels the permit.
Attendant
Stays outside the space throughout entry, maintains continuous communication with entrants, monitors conditions, orders evacuation, and summons rescue — but does not enter to attempt rescue unless relieved by another attendant.
Authorised entrant
Uses the specified PPE and equipment, communicates with the attendant, alerts to hazards, and self-evacuates on any warning sign, alarm, or attendant order.
Rescue service
Evaluated by the employer for capability and response time. Practises a mock rescue at least once every 12 months in each representative permit-space type.
Everyone in these roles needs documented training before their first entry — see the confined space training requirements article for the full syllabus and refresher cadence.
§1910.146(d)(5)
Atmospheric testing sequence (O₂ → flammable → toxic)
The legally required test order — and the physics behind it.
- 1
Oxygen (O₂)
Test oxygen first. Acceptable range is 19.5%–23.5%. Below 19.5% is oxygen-deficient; above 23.5% is oxygen-enriched and dramatically raises flammability risk.
- 2
Flammable gases and vapours
Test for combustibles second, expressed as a percentage of the Lower Explosive Limit (LEL). Entry is prohibited at or above 10% LEL.
- 3
Toxic contaminants
Test for toxics last — CO, H₂S, and any known process-specific contaminants must be below their OSHA Permissible Exposure Limits (PELs).
Testing continues throughout entry — not just as a pre-entry check. Record initial and periodic readings on the permit with the tester's initials and time. See the full atmospheric testing sequence (O₂ → flammable → toxic) for gas-detector calibration, bump-test cadence, and how to log continuous monitoring against the permit. For monitor selection, bump-test cadence, retrieval-system pre-checks and the wider equipment set, see the confined space entry equipment: selection, calibration & maintenance.
Acceptable entry conditions
Continuous monitoring during entry
Acceptable entry conditions are documented on the permit and must be maintained for its duration. If any monitored parameter drifts outside the acceptable range — oxygen deviation, flammables rising toward 10% LEL, toxics approaching PEL, unexpected temperature change — the attendant orders immediate evacuation and the entry supervisor cancels the permit.
Continuous forced-air ventilation is required in most entries. Never substitute oxygen from a compressed-gas cylinder for ventilation — oxygen enrichment above 23.5% dramatically expands the flammability range of any combustibles present.
Lifecycle
Issuing, cancelling, and retaining the permit
The entry supervisor signs the permit only after verifying that all required tests are complete, all documented isolation is in place, equipment and rescue services are available, and entry conditions match the acceptable ranges written on the permit. The permit is posted at the entry point for the duration of the task.
Cancel the permit the moment the task is done, an entry condition is breached, or a new hazard emerges. Cancelled permits are retained for at least one year (§1910.146(e)(6)) and reviewed annually to identify programme deficiencies. See who signs a confined space entry permit for authority-delegation rules across shifts.
§1910.146(g)
Training and certification requirements
Every employee whose duties fall under the programme must be trained to acquire the understanding, knowledge, and skills for safe performance — before first assignment, before duties change, whenever a new hazard is introduced, and whenever the employer has reason to believe a deficiency exists.
Certification records must include each trained employee's name, the trainer's signature or initials, and the dates of training. OSHA does not set a fixed expiry — most employers refresh every 12–36 months.
§1910.146(k)
Rescue and emergency services
The employer evaluates prospective rescue services against the expected response time and the hazards of the permit space, then selects a service demonstrably capable of that rescue. Rescue teams practise a mock rescue at least once every 12 months in each representative permit-space type from which rescue may be needed.
Non-entry rescue equipment — full-body harness with retrieval line attached at the centre of the wearer's back — is required for vertical entries deeper than 5 feet unless it would increase the overall risk or would not contribute to the rescue. Walk through the full §1910.146(k) evaluation and site-specific plan in the confined space rescue plan guide, or grab the rescue plan template to document your response chain end-to-end.
Common mistakes
Where confined space programmes go wrong
- Testing atmosphere in the wrong order — combustibles read before oxygen means unreliable LEL values.
- Attendants entering the space to attempt rescue without being relieved — the leading cause of confined-space fatality clusters.
- No documented rescue-service evaluation on file; a phone number for the local fire department is not an evaluation.
- Reclassifying a permit space to non-permit without documenting the basis or re-inspecting when conditions change.
- Cancelling the permit at end of shift but leaving the space open — the next shift enters under an expired authorisation.
- No annual programme review — the review is required, and cancelled permits from the past 12 months are the mandatory input.
Digital vs paper
Where a digital permit changes the math
A paper permit works — until you count the audit tail. The most common OSHA citations under 1910.146 are procedural: missing signatures, illegible atmospheric readings, no evidence of periodic testing, cancelled permits that never made it into the annual review. A digital permit fixes those failure modes by making the fields mandatory, timestamping every reading, tying the permit to the trained roster, and preserving the record for the full one-year retention window without a filing cabinet.
SafeGuard EHS's Permit-to-Work module ships confined space entry templates with the 14 required fields pre-populated, live gas-detector log integration, an attendant check-in cadence, and one-click cancellation that files the permit into the annual review queue.
Download the confined space entry permit template
The fillable template with all 14 §1910.146(f) fields, atmospheric testing log, roles, and rescue-service block — ready for your next entry.
FAQ
Confined space entry permits — common questions
Keep reading
Related resources
Eight supporting deep-dives extend this pillar. The three highlighted below are the highest-intent reads for anyone issuing a confined space entry permit today.
Most relevant for "confined space entry permit"
- Who signs a confined space entry permit?
The entry supervisor's signature under §1910.146 — plus the attendant and entrant acknowledgements the permit still needs.
- OSHA 1910.146 explained: employer duties
Subsection-by-subsection walkthrough of the confined-space standard behind every entry permit.
- Permit-required vs non-permit confined spaces
The classification test that decides whether an entry permit is legally required at all.
Start here
Related reading
Non-permit confined space reclassification — OSHA 1910.146(c)(7)
When a PRCS can be reclassified as a non-permit space — the elimination-vs-control test, the written certification, and the automatic reversion trigger.
Manual handling risk assessment guide — safe lifting & TILE
Entry teams routinely move tools, gas monitors and casualties in awkward postures. Pair permit control with a TILE(O) manual handling assessment and the HSE filter-weight triggers.