OSHA requires employers to inform exposed employees of the existence, location and danger of permit-required confined spaces. The most common way to do that is a sign at every entrance.
What OSHA requires
Under 29 CFR 1910.146(c)(2) (general industry) and 1926.1203(b) (construction), if the workplace contains permit spaces, the employer must inform exposed employees by posting danger signs or by any other equally effective means. The standard gives the wording directly:
You can use similar language, such as "DANGER: Confined Space. Entry by Permit Only," as long as the message is the same: this is a permit space and unauthorized entry is prohibited.
Sign format and colors
OSHA's general sign rule, 29 CFR 1910.145, says danger signs are used where an immediate hazard exists, and specifies red, black and white as the colors for danger signs. Most employers buy signs that follow the ANSI Z535 format:
- A "DANGER" signal word panel in white letters on a red oval, on a black background.
- A white message panel with black lettering: "PERMIT-REQUIRED CONFINED SPACE, DO NOT ENTER."
- Optional pictogram showing a person entering a space with a prohibition symbol.
Where to post
- At every entrance to the permit space: each manhole, hatch, door or access panel.
- Where it's visible before someone opens or enters, such as on the cover or next to the hatch, not on the inside of a lid.
- On the equipment itself for tanks, vessels, bins and hoppers, in a spot that won't be painted over or covered by insulation.
Use durable signs or labels made for the environment: outdoor, washdown, chemical or high-temperature areas need materials that won't fade or peel.
Languages
The purpose is to inform exposed employees, so the sign has to be understood by them. Post signs in English and in the other languages your workers read, often English and Spanish, and add a pictogram for clarity. Training should reinforce what the signs mean.
Non-permit confined spaces
The DANGER sign requirement applies to permit-required confined spaces. Non-permit confined spaces don't need a DANGER sign, but many employers post a NOTICE or CAUTION sign stating that the space must be evaluated before entry, especially when conditions could change.
When a sign isn't enough
A sign informs. It doesn't physically prevent entry. If the employer decides employees will not enter a permit space, 1910.146(c)(3) also requires effective measures to prevent entry, such as:
- Locked or bolted covers and hatches.
- Barriers, fences or guards around open spaces.
- Lockout of access panels.
And if employees will enter, the sign is just the start: the employer needs a written permit space program, training and permits.
Sources and official references
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.