On this page
In this lesson
What you'll learn
- State the three conditions that make a space a confined space
- Recognize confined spaces in your workplace from common examples
- Explain exactly when "entry" happens under OSHA's rules
- Describe why confined spaces are so dangerous for workers and rescuers
Ask a room of workers what a confined space is and you will hear "a small space," "a tight space," or "somewhere underground." All three miss the point. Size is only part of OSHA's definition, and plenty of confined spaces are large enough to drive a truck into. This lesson gives you the exact definition and the reasons it matters.
OSHA's definition: three conditions
Under both the general industry standard (29 CFR 1910.146) and the construction standard (29 CFR 1926 Subpart AA), a confined space is a space that meets all three of these conditions:
- It is large enough and so configured 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.
1. Large enough to bodily enter
If a worker can get their whole body inside to do work, the first condition is met. Reaching an arm into an opening isn't bodily entry, but climbing into a tank, pit or crawl space is.
2. Limited or restricted entry or exit
Think about how hard it would be to get out quickly, or for someone to get you out. Manholes, hatches, small doorways, ladders, long crawls and openings at the top of a tank all limit entry and exit. OSHA's examples include tanks, vessels, silos, storage bins, hoppers, vaults and pits.
3. Not designed for continuous occupancy
The space was built to hold product, equipment or flow, not people. Workers go in occasionally for inspection, cleaning, maintenance or repair, then leave.
Common confined spaces
| Setting | Examples |
|---|---|
| Utilities and municipal | Manholes, sewers, storm drains, vaults, lift stations, wet wells, valve pits |
| Industrial and manufacturing | Tanks, vessels, boilers, silos, hoppers, bins, ducts, pits, mixers, degreasers |
| Construction | Crawl spaces, attics, pits, pier holes, precast vaults, enclosed beams, HVAC ducts |
| Agriculture and food | Grain bins, silos, manure pits, fermenters |
| Transportation | Tank trailers and rail cars, ship tanks and voids |
See many more in our guide to confined space examples.
What "entry" means
OSHA defines entry as the action by which a person passes through an opening into a permit-required confined space. Entry is considered to have occurred as soon as any part of the entrant's body breaks the plane of an opening into the space.
That means leaning your head and shoulders into a manhole to look around is entry. So is reaching in to the elbow, if any part of you crosses the plane of the opening.
Why confined spaces kill
Confined spaces concentrate hazards and make escape and rescue hard:
- The air can be deadly with no warning. Oxygen can be displaced by other gases, consumed by rust or decay, or toxic gases such as hydrogen sulfide and carbon monoxide can build up.
- Escape is slow. Narrow openings and ladders mean a worker who feels dizzy may not get out in time.
- Rescue is dangerous. NIOSH investigations have long found that co-workers who rush in to help often become victims themselves.
- Hazards change. A space that tested safe at 7 a.m. can become deadly when a valve leaks, a cleaning chemical reacts or a pump engine runs nearby.
Confined space vs. permit-required confined space
Being a confined space doesn't automatically mean a permit is needed. A confined space becomes a permit-required confined space when it contains, or could contain, a serious hazard such as a hazardous atmosphere, engulfment material, a trapping configuration, or another serious safety or health hazard. That's the subject of lesson 2.
Key takeaways
- A confined space meets all three conditions: bodily entry possible, limited or restricted entry or exit, not designed for continuous occupancy.
- Examples include tanks, vessels, silos, bins, hoppers, vaults, pits, manholes, sewers and crawl spaces.
- Entry happens the moment any part of your body breaks the plane of the opening.
- The danger comes from the air, the difficulty of escape and changing conditions, and it extends to would-be rescuers.
Knowledge check
Lesson 1 quiz: 8 questions
Choose one answer for each question, then select Check my answers. Score 80%% or higher to pass. Your answers stay in your browser and are never saved.
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.