A confined space is an area large enough for a worker to bodily enter and perform assigned work, with limited or restricted means of entry or exit, and not designed for continuous employee occupancy. Tanks, silos, vaults, pits, manholes and pipelines are common examples. When a confined space also contains serious hazards, OSHA classifies it as a permit-required confined space.
OSHA regulates confined space entry in general industry under 29 CFR 1910.146 and in construction under 29 CFR 1926 Subpart AA. Classifying each space correctly is the first decision in any safe entry plan.
What Is a Confined Space?
Under 29 CFR 1910.146(b), 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.
A permit-required confined space (often called a permit space) is a confined space that has one or more of the following characteristics:
- It contains or has the potential to contain a hazardous atmosphere.
- It contains a material that has the potential to engulf an entrant.
- It has an internal configuration that could trap or asphyxiate an entrant, such as inwardly converging walls or a floor that slopes downward and tapers to a smaller cross-section.
- It contains any other recognized serious safety or health hazard.
The standard defines a hazardous atmosphere in specific terms. It includes flammable gas, vapor or mist above 10 percent of its lower flammable limit (LFL), airborne combustible dust at or above its LFL, atmospheric oxygen below 19.5 percent or above 23.5 percent, and any substance above its permissible exposure limit or other applicable dose limit. A confined space with none of the permit space hazards is a non-permit confined space.
Why Confined Spaces Are So Dangerous
Confined spaces concentrate hazards and make escape and rescue difficult. A worker who becomes dizzy or unconscious inside a tank cannot simply walk out, and the narrow opening also slows anyone trying to help.
Atmospheric hazards
Oxygen can be displaced by inert gases such as nitrogen or consumed by rusting metal and decomposing material. Hydrogen sulfide, carbon monoxide and flammable vapors can build up from process residue, coatings or nearby engines. Many of these hazards are colorless and odorless, so only testing reveals them.
Physical and rescue hazards
Grain, sand, sludge and liquids can engulf a worker in seconds, and agitators or augers can start unexpectedly if energy is not isolated. Coworkers who enter to help a collapsed entrant without training or respiratory protection can be overcome by the same hazard, which is why OSHA requires rescue to be planned before entry.
Examples of Confined Spaces
Confined spaces appear in nearly every industry. Common examples include:
- Storage tanks, process vessels, reactors and boilers
- Silos, hoppers and grain bins
- Utility vaults, manholes, sewers, pits and sumps
- Crawl spaces and attics in construction
- Ductwork, pipelines, rail tank cars and tanker trailers
A space is not a confined space just because it is small. A room with standard doors designed for people to work in, such as a control room, typically does not meet the definition.
Key OSHA Requirements for Permit-Required Confined Spaces
Evaluate the workplace
Employers must evaluate the workplace to determine whether any spaces are permit-required confined spaces. If they are, the employer must inform exposed employees, for example with danger signs, of their existence, location and hazards. In construction, 29 CFR 1926.1203 requires a competent person to identify all confined spaces and determine which are permit spaces before work begins.
Written permit space program
If employees will enter permit spaces, the employer needs a written program covering unauthorized entry prevention, entry procedures, equipment, testing, roles, rescue and permits. The program must be reviewed using canceled permits within 1 year after each entry, and a single annual review covering all entries in the previous 12 months is acceptable.
Entry permits
The entry permit is the written authorization for a specific entry. It lists the space, purpose, duration, personnel, hazards, control measures, acceptable entry conditions, test results and rescue services. The permit cannot last longer than the time needed to complete the task, and canceled permits must be retained for at least 1 year. A permit to work system is the broader framework many sites use to manage this process alongside other high-risk tasks.
Isolation and atmospheric testing
Before entry, hazardous energy must be isolated, often through lockout/tagout, and lines must be blanked, blinded or disconnected where needed. Atmospheric testing must follow a set order: oxygen first, then combustible gases and vapors, then toxic gases and vapors. Conditions must be tested or monitored during entry to confirm they stay acceptable.
Roles and training
The standard defines three entry roles:
- Authorized entrant: knows the hazards, uses required equipment, communicates with the attendant and exits when ordered or when warning signs appear.
- Attendant: stays outside the space, keeps an accurate count of entrants, monitors conditions inside and outside, orders evacuation when needed and summons rescue. The attendant must not perform duties that interfere with monitoring.
- Entry supervisor: verifies tests and equipment are in place before signing the permit, confirms rescue services are available, removes unauthorized individuals and terminates entry and cancels the permit when required.
Each person must be trained before first assignment and again when duties, hazards or procedures change.
Rescue and emergency services
Employers must evaluate and select rescue services that can respond in a timely way to the hazards of the space. Rescuers must be trained, equipped and practice permit space rescue at least once every 12 months. Retrieval systems must be used for entries unless they would increase the overall risk or not contribute to rescue, and a mechanical device must be available to retrieve entrants from vertical permit spaces more than 5 feet deep.
How to Plan a Permit-Required Confined Space Entry
- Identify and classify the space. Confirm it meets the confined space definition and decide whether it is a permit space using a documented risk assessment.
- Define the work. Describe the task, tools and materials, including any hot work or chemicals that could create new hazards.
- Isolate hazards. Lock out energy, blank or disconnect lines, drain and clean the space, and ventilate it.
- Test the atmosphere. Use a calibrated multi-gas meter in the required order and at several levels, then record the results.
- Brief the team. Confirm entrants, attendants and the entry supervisor are trained and know the communication method.
- Confirm rescue. Verify the rescue team is available, set up retrieval equipment and confirm how to summon help.
- Issue the permit. The entry supervisor signs only when all acceptable entry conditions are met, and the permit is posted at the entry point.
- Monitor, close out and review. Monitor conditions during work, cancel the permit when the job ends or conditions change, and file it for the annual program review.
Confined Space vs. Permit-Required Confined Space
Every permit space is a confined space, but not every confined space needs a permit. A non-permit confined space has no actual or potential hazard capable of causing death or serious physical harm, so the full permit process does not apply.
The general industry standard also offers two middle paths. Under 1910.146(c)(5), employers may use alternate procedures for spaces where the only hazard is an actual or potential hazardous atmosphere that continuous forced air ventilation alone can control, supported by monitoring and inspection data. Under 1910.146(c)(7), a permit space may be reclassified as a non-permit space if its hazards are eliminated, and that reclassification must be documented and certified. If hazards arise again, the space must be reevaluated.
Common Mistakes to Avoid
- Assuming a space is safe because it was safe last time or has no odor.
- Testing only at the opening instead of at the top, middle and bottom of the space.
- Relying on 911 without confirming responders can perform permit space rescue in time.
- Issuing permits that cover a whole week instead of the specific task.
- Skipping the annual review of canceled permits.
How SMS360 Helps
The SMS360 Work Permits module helps teams manage confined space entry permits digitally. Supervisors can create permits, record atmospheric test results, assign entrants and attendants, and route permits for approval from a mobile device. Canceled permits are stored as searchable records, which supports the 1-year retention requirement and the annual program review. Dashboards show open permits across sites, so managers can see where entry work is underway.
Frequently Asked Questions
What are the three criteria for a confined space?
Under OSHA 29 CFR 1910.146, a confined space is large enough and configured so an employee can bodily enter and perform assigned work, has limited or restricted means for entry or exit, and is not designed for continuous employee occupancy. All three conditions must be met. If the space also has a hazardous atmosphere, engulfment potential, a trapping configuration or another serious hazard, it is a permit-required confined space.
How often must confined space rescue be practiced?
OSHA requires each member of a rescue service to practice permit space rescue at least once every 12 months. Practice uses simulated rescues from the actual permit spaces or from representative spaces with similar openings, size and configuration. Employers using an outside rescue service must confirm the service can respond in time and has the right equipment.
How long must confined space entry permits be kept?
Canceled entry permits must be retained for at least 1 year under 1910.146(e)(6). Employers use these permits during the required review of the permit space program, which must take place within 1 year after each entry. Any problems noted on a permit during the entry should be reviewed and used to revise the program where needed.
Can a confined space attendant enter the space?
An attendant may not enter a permit space to attempt a rescue unless they have been trained and equipped for rescue and have been relieved by another attendant. The attendant's job is to remain outside, track entrants, monitor conditions and summon rescue. Entering without relief leaves the remaining entrants unmonitored and puts the attendant at risk of becoming a second victim.
