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A confined space, under the US OSHA standard at 29 CFR 1910.146, is a space large enough for a person to bodily enter and do assigned work, with limited or restricted means of entry or exit, that is not designed for continuous occupancy. It becomes a permit-required confined space when it also carries a specified hazard, such as a hazardous atmosphere, and entry then runs under a written entry permit.
This page goes one level further than the definition: it lays out the fifteen items an entry permit must identify, shows how the classification decision is built, and connects the framework to laboratory and clinic settings where low-lying gas is already a recognized hazard.
Short answer
Confined space means a space defined by three conditions together: people can enter and work in it, its entry and exit are limited, and it was not built to be occupied continuously. Confined space entry is, in the regulation’s wording, the action by which a person passes through an opening into a permit-required confined space. A confined space permit is the written or printed document the employer provides to allow and control that entry.
What counts as a confined space
OSHA’s definition in 29 CFR 1910.146 has three parts, and a space needs all of them:
- It is large enough, and configured so, that an employee can bodily enter and perform assigned work.
- It has limited or restricted means for entry or exit.
- It is not designed for continuous employee occupancy.
OSHA’s confined spaces page lists tanks, vessels, silos, storage bins, hoppers, vaults, pits, manholes, tunnels, equipment housings, ductwork and pipelines as examples. The list is illustrative; the three-part test decides, not the name of the structure. The definitions here are the US federal general industry rules, and other jurisdictions word their own.
Permit-required confined spaces versus other confined spaces
A confined space is not automatically a permit space. The permit-required category applies to a confined space with one or more of the listed characteristics. The standard names a hazardous atmosphere (actual or potential), and OSHA’s page adds material with the potential to engulf an entrant, walls or floors that could trap or suffocate, and any other recognized safety or health hazard such as unguarded machinery, exposed live wires or heat stress.
How the classification decision is built
- Does the space meet all three confined-space conditions? If not, the standard’s confined-space provisions do not classify it.
- If it does, does it contain or have the potential to contain a hazardous atmosphere, hold engulfment material, have trapping geometry, or carry another recognized serious hazard? Any one makes it a permit-required confined space.
- Who decides? Paragraph (c)(1) states that the employer shall evaluate the workplace to determine whether any spaces are permit-required confined spaces, and (c)(2) requires the employer to inform exposed employees, by danger signs or an equally effective means.
The standard defines a hazardous atmosphere as one that may expose employees to the risk of death, incapacitation, or impairment of ability to self-rescue, among other harms. The classification is therefore tied to what a space can do to a person who is inside it, and the duty to make that call sits with the employer.
What a confined space entry permit must identify
Paragraph (f) of the standard lists what the permit shall identify. Laid out as a checklist, the permit covers fifteen items:
| # | The permit identifies |
|---|---|
| 1 | The space |
| 2 | The purpose of entry |
| 3 | The date and the authorized duration of the entry permit |
| 4 | The authorized entrants |
| 5 | The attendants |
| 6 | The entry supervisor |
| 7 | The hazards of the permit space |
| 8 | The measures used to isolate the space and to eliminate or control hazards |
| 9 | The acceptable entry conditions |
| 10 | The results of initial and periodic tests, with the names or initials of the testers and when the tests were done |
| 11 | The rescue and emergency services available and how to summon them |
| 12 | The communication procedures entrants and attendants use to stay in contact |
| 13 | The equipment provided, including personal protective equipment, testing equipment and communications equipment |
| 14 | Any other information needed to make entry safe |
| 15 | Any additional permits, such as hot work permits, issued for work in the space |
Two points follow from the text. The permit is a control document, not a notice: it names people (entrants, attendants, the entry supervisor) and conditions (acceptable entry conditions, test results). And under paragraph (e)(5) the entry supervisor shall terminate entry and cancel the permit when operations are completed, or when a condition that is not allowed under the permit arises in or near the permit space.
Where it matters in labs and clinics
The confined space framework is usually pictured around industrial tanks, but its central concept, an atmosphere that can incapacitate someone before they can leave, shows up in research and healthcare facilities. CASRAI’s guide to liquid nitrogen and cryogen handling safety explains how boil-off gas pools in low, enclosed spaces such as cold rooms and freezer rooms and displaces oxygen, and it cites the 19.5% oxygen threshold that 29 CFR 1910.146 uses for an oxygen-deficient atmosphere. A related page on dry ice covers the hazards of that material.
Facilities that handle these materials keep a written safety framework; the OSHA chemical hygiene plan is the lab-specific example. For the protective equipment side, see lab PPE and the lab safety equipment checklist. Whether a particular room or vessel in your facility is a permit-required confined space is the employer’s evaluation under paragraph (c)(1), not something a general web page can settle.
Common misunderstandings
“Any confined space needs an entry permit”
No. The permit requirement attaches to permit-required confined spaces, those with one or more of the listed hazard characteristics.
“Entry means walking into any tight space”
In the standard, entry is defined as passing through an opening into a permit-required confined space. That definition is tied to the permit-space category, and the standard adds that entry includes the ensuing work activities in the space.
“The permit stays valid until its date runs out”
The permit states an authorized duration, but the entry supervisor must cancel it earlier when the operations are completed or when a condition not allowed under the permit arises in or near the space.
“A space is safe if it looks empty”
The standard’s concern is the potential for a hazardous atmosphere as well as an actual one, which is why the employer’s evaluation looks at what a space can contain.
FAQ
What is confined space entry?
Under 29 CFR 1910.146, entry is the action by which a person passes through an opening into a permit-required confined space.
What is a confined space permit?
It is the written or printed document the employer provides to allow and control entry into a permit space. Its required contents are the fifteen items in the table above.
Who decides whether a space is permit-required?
The employer. Paragraph (c)(1) requires the employer to evaluate the workplace and determine whether any spaces are permit-required confined spaces.
Sources
- OSHA, 29 CFR 1910.146, Permit-required confined spaces: osha.gov/laws-regs/regulations/standardnumber/1910/1910.146, checked 2026-10-29.
- OSHA, Confined Spaces: osha.gov/confined-spaces, checked 2026-10-29.
