The three-condition test
Under 29 CFR §1910.146(b), a confined space is any space that meets all three of the following: it is large enough and so configured that an employee can bodily enter and perform assigned work; it has limited or restricted means of entry or exit; and it is not designed for continuous employee occupancy. Miss any one condition and it's not a confined space in OSHA's sense.
This is the definition every confined space entry permit hangs off — see our pillar guide to [confined space entry permits](/resources/confined-space-entry-permits) for the full lifecycle. Getting this classification right up front is what determines whether a written entry programme, a permit, an attendant, and a rescue plan are all legally required for a given task.
What counts as 'limited means of entry or exit'?
OSHA does not fix a dimension. The test is functional: could a worker be delayed in self-rescue by the geometry of the opening, the interior obstructions, or the vertical distance to safety? A 24-inch manhole on top of a wet-well is limited access. A tank you crawl into on hands and knees is limited access. A room with a standard doorway is not.
Ladders, harnesses, and awkward body positions all count against ease of exit. If the fastest way out involves rope rescue or a tripod winch, treat it as limited access even when the opening itself is generous.
Common examples across industries
Storage tanks, process vessels, silos, hoppers, and bins are the archetypal confined spaces. So are vaults, manholes, pits, sumps, tunnels, sewers, boilers, furnaces, degreasers, digesters, pipelines, ductwork, crawl spaces, ship holds, and rail tank cars.
Confined space isn't only a heavy-industry problem. Wastewater manholes, HVAC plenums, elevator pits, agricultural silos, and even the interior of large printing presses have all been the site of permit-space fatalities in recent OSHA investigations.
When it becomes permit-required
A confined space is a permit-required confined space when it also contains — or has the potential to contain — a hazardous atmosphere; engulfment material like grain, sand or liquid; internally converging walls or a downward-sloping floor that could trap or asphyxiate an entrant; or any other recognised serious safety or health hazard.
'Potential to contain' matters. A silo that is empty today but is periodically filled with grain still has engulfment potential and is permit-required for every entry, not only when filled.
What to do after you identify one
Post a danger sign at each entry point, inform affected employees, and prevent unauthorised entry. If any employee will enter, develop the written permit-space programme required by §1910.146(c)(4) and issue an entry permit before every entry.
Ready to build the programme? Start with our [confined space entry permits](/resources/confined-space-entry-permits) pillar, then [book a SafeGuard EHS demo](/book-demo) to see the digital permit and rescue-plan workflow end-to-end.