Permit-Required vs. Non-Permit Confined Spaces: How to Classify a Space

Once you know a space is a confined space, the next question decides almost everything about how it's entered: is it permit-required?

The four permit-space characteristics

A permit-required confined space (permit space) is a confined space that has one or more of the following:

1. Contains or has the potential to contain a hazardous atmosphere.
2. Contains a material that has the potential for engulfing an entrant, such as grain, sand, sludge or water.
3. Has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls or by a floor that slopes downward and tapers to a smaller cross-section, like the bottom of a hopper.
4. Contains any other recognized serious safety or health hazard, such as unguarded machinery, exposed live electrical parts, extreme heat, or a fall hazard.

Non-permit confined spaces

A non-permit confined space is a confined space that doesn't contain, or with respect to atmospheric hazards have the potential to contain, any hazard capable of causing death or serious physical harm. An empty, clean, dry electrical vault with no energized parts exposed and no atmospheric potential might qualify.

Non-permit status isn't permanent. When the use or configuration of a non-permit space changes in a way that could increase hazards, the employer must reevaluate it and reclassify it as a permit space if needed (1910.146(c)(6)).

What employers must do first

Under 1910.146(c), employers must:

• Evaluate the workplace to determine whether any spaces are permit-required confined spaces.
• Inform exposed employees by posting danger signs or by another equally effective means. A sign reading "DANGER: PERMIT-REQUIRED CONFINED SPACE, DO NOT ENTER" or similar satisfies the requirement. See our confined space signs guide.
• If employees will not enter permit spaces, take effective measures to prevent entry, such as locks, bolted covers or barriers.
• If employees will enter, develop and implement a written permit space program that meets 1910.146(d).

Two special routes: alternate procedures and reclassification

OSHA allows two ways to enter some permit spaces without the full permit system. Both have strict conditions and written documentation.

Alternate procedures: 1910.146(c)(5)

Entry under alternate procedures is allowed when:

• The only hazard is an actual or potential hazardous atmosphere, and
• Continuous forced-air ventilation alone is enough to keep the space safe for entry, and
• Monitoring and inspection data support those findings, and the determinations and data are documented.

The space stays a permit space, but entry follows simplified procedures: eliminate unsafe conditions before removing the cover, guard the opening, test the air (oxygen, then flammables, then toxics) before entry, ventilate continuously from a clean air source, retest periodically, and get everyone out immediately if a hazardous atmosphere is detected. The employer must certify in writing, with date, location and signature, that the space is safe and pre-entry measures were taken.

Reclassification to non-permit: 1910.146(c)(7)

A permit space may be reclassified as non-permit if:

• It poses no actual or potential atmospheric hazards, and
• All hazards within the space are eliminated without entry, for example by locking out and blanking lines.

The reclassification lasts only as long as the non-atmospheric hazards stay eliminated. If entry is needed to eliminate the hazards, that entry is done under the full permit program. The employer documents the basis in a certificate with the date, location and signature, and makes it available to entrants. If hazards come back, everyone exits and the space is reevaluated.

Try the permit-space decision tool to walk through these questions for a space at your site.

Key takeaways

• A permit space has at least one of four characteristics: hazardous atmosphere (actual or potential), engulfment material, trapping configuration, or any other serious hazard.
• Non-permit spaces have no hazard capable of causing death or serious harm, and must be reevaluated when conditions change.
• Employers must evaluate spaces, post danger signs or equivalent, and either prevent entry or run a written permit program.
• Alternate procedures: atmospheric hazard only, controlled by continuous forced-air ventilation alone.
• Reclassification: no atmospheric hazard, and all hazards eliminated without entry.

Last reviewed: October 25, 2026 · Free general education based on OSHA 29 CFR 1910.146 and 29 CFR 1926 Subpart AA. It does not replace the site-specific training, written program and hands-on evaluation your employer must provide, and it does not issue a certificate. Nothing you enter on this page is saved or sent.