What is a Confined Space? Definition, Examples and Requirements

Confined spaces are one of the deadliest workplace hazards. According to OSHA, confined space incidents kill roughly 90 workers every year in the United States - and many of those fatalities involve rescuers who enter without proper preparation. Understanding what qualifies as a confined space is the first step toward preventing these tragedies.

This guide covers the OSHA definition, the difference between permit-required and non-permit spaces, real-world examples across industries and the entry requirements that keep workers alive.

OSHA's Official Confined Space Definition

Under OSHA 29 CFR 1910.146, a confined space is any space that meets all three of the following criteria:

1. Large enough for an employee to bodily enter and perform work
2. Has limited or restricted means of entry or exit - meaning you cannot simply walk in and out freely (hatches, ladders, narrow openings)
3. Is not designed for continuous occupancy - the space was not built for people to work in all day

All three criteria must be met simultaneously. A small closet might feel confined, but if it has a standard door and is designed as a workspace, it does not meet the OSHA definition.

Permit-Required vs Non-Permit Confined Spaces

Not all confined spaces require entry permits. OSHA distinguishes between two categories:

Non-Permit Confined Space

A confined space that does not contain or have the potential to contain any hazard capable of causing death or serious physical harm. Examples include a clean, well-ventilated attic access point or an empty, dry water tank with no chemical residue.

Permit-Required Confined Space (PRCS)

A confined space that has one or more of the following characteristics:

• Hazardous atmosphere - oxygen-deficient, oxygen-enriched or containing toxic/flammable gases
• Engulfment hazard - material that could bury or drown an entrant (grain, sand, water)
• Converging walls or floors - configuration that could trap or asphyxiate an entrant
• Any other recognized serious safety or health hazard - energized equipment, extreme temperatures, biological hazards

Most confined spaces encountered in industrial settings are permit-required. When in doubt, treat the space as permit-required until a competent person evaluates it.

15+ Confined Space Examples by Industry

Construction

• Manholes and underground vaults
• Excavations and trenches deeper than 4 feet
• Crawl spaces under buildings
• Pipe runs and utility tunnels

Manufacturing

• Storage tanks and process vessels
• Silos and hoppers
• Mixers and blenders (when de-energized for maintenance)
• Ductwork and large ventilation systems

Oil and Gas

• Separators and treaters
• Produced water tanks
• Wellhead cellars
• Pipeline segments during maintenance

Maritime and Marine Terminals

• Ship holds and ballast tanks
• Double bottoms and void spaces
• Chain lockers

Utilities and Municipal

• Sewer lines and lift stations
• Water treatment basins (when drained)
• Electrical vaults
• Boiler fireboxes

Atmospheric Hazards: The Invisible Killer

The majority of confined space fatalities involve atmospheric hazards. Before anyone enters a permit-required confined space, atmospheric testing must confirm:

Condition	Acceptable Range	Action Required
Oxygen level	19.5% - 23.5%	Ventilate if outside range; do not enter below 19.5%
Flammable gases (LEL)	Below 10% of LEL	Ventilate; do not enter above 10% LEL
Carbon monoxide	Below 25 ppm	Ventilate; investigate source
Hydrogen sulfide	Below 10 ppm	Ventilate; H2S rescue plan required

Atmospheric testing must be conducted in the following order: oxygen first, then combustible gases, then toxic gases. Testing must be continuous during the entire entry.

Confined Space Entry Requirements

For permit-required confined spaces, OSHA mandates a comprehensive entry program that includes:

1. Written permit system - documenting the space, hazards, precautions and authorized personnel
2. Entry supervisor - a qualified person who authorizes and oversees the entry
3. Attendant - stationed outside the space at all times, maintaining communication with entrants
4. Atmospheric testing - before and during entry using calibrated direct-reading instruments
5. Ventilation - continuous forced-air ventilation when feasible
6. Rescue plan - either on-site rescue team or arrangement with local emergency services
7. Communication system - reliable method for entrants to communicate with the attendant
8. Entry/exit procedures - including retrieval systems (tripod and winch) for vertical entries

Track and document confined space entries digitally with Make Safety Easy's incident and entry tracking module. Every permit, atmospheric reading and personnel log is stored and retrievable for audits.

Rescue Planning: The Most Critical Element

OSHA data shows that roughly 60% of confined space fatalities are would-be rescuers. This makes rescue planning the single most important element of any confined space program.

Self-Rescue

The entrant exits on their own when conditions deteriorate. This is only viable if the entrant can physically exit without assistance.

Non-Entry Rescue

The attendant retrieves the entrant using mechanical retrieval equipment (tripod, winch, body harness) without entering the space. OSHA requires non-entry rescue capability for all vertical entries.

Entry Rescue

Trained rescuers physically enter the space to retrieve the entrant. Entry rescue teams must have the same atmospheric monitoring, PPE and training as the original entrants - plus medical first-responder training.

Training Requirements

All employees involved in confined space operations must receive training before their first assignment and whenever conditions change. Training must cover:

• How to recognize confined spaces and their hazards
• Entry permit procedures and atmospheric monitoring
• Proper use of PPE and retrieval equipment
• Emergency and rescue procedures
• Duties specific to their role (entrant, attendant or supervisor)

Learn more about confined space terminology in our confined space glossary entry.

Confined Space Signage and Marking

OSHA 1910.146(c)(2) requires employers to inform exposed employees of the existence, location and danger of permit-required confined spaces by posting danger signs or by any other equally effective means. Proper signage includes:

• DANGER signs at every entry point to a permit-required confined space
• Signs must read "DANGER - PERMIT-REQUIRED CONFINED SPACE, DO NOT ENTER" or equivalent language
• Signs must be durable, weather-resistant and visible from all approach directions
• If a confined space has been reclassified as non-permit, documentation must be maintained and accessible

Multi-Employer Worksite Considerations

On construction sites and other multi-employer worksites, confined space coordination becomes critical. OSHA 1926.1203 (construction confined spaces standard) requires:

• Host employer duties - the controlling employer must identify all confined spaces on the site, inform all contractors of their locations and hazards and coordinate entry operations
• Entry employer duties - the contractor performing the confined space work must develop their own entry program, ensure their workers are trained and obtain permits
• Information exchange - before entry operations begin, the host and entry employers must exchange information about hazards, entry procedures and rescue capabilities
• Coordination meeting - when multiple employers will enter the same space or adjacent spaces, a coordination meeting is required to prevent hazards created by one contractor from affecting another

This coordination requirement is one reason digital permit systems are gaining traction. With Make Safety Easy, permits and hazard information can be shared instantly between all parties on a worksite.

Common Confined Space Hazards by Type

Different types of confined spaces present different primary hazards. Understanding the likely hazards for each space type helps you prepare the right controls:

Space Type	Primary Hazards	Key Controls
Tanks/vessels	Toxic atmospheres, oxygen deficiency, residual chemicals	Atmospheric testing, ventilation, lockout/tagout
Silos/hoppers	Engulfment, bridging material, dust explosion	Lockout of filling systems, top-entry only, retrieval system
Sewers/manholes	H2S, methane, oxygen displacement, flooding	Continuous gas monitoring, forced ventilation, flood watch
Excavations (>4 ft)	Cave-in, atmospheric hazards, water accumulation	Shoring/sloping, atmospheric monitoring, dewatering
Boilers/fireboxes	Heat, residual combustion gases, confined geometry	Cool-down period, ventilation, lockout of fuel supply

Confined Space Program Requirements

OSHA 1910.146 requires employers who have permit-required confined spaces to establish a comprehensive written program. The program must include:

• Space inventory - identification of all confined spaces in the workplace
• Hazard evaluation - assessment of each space to determine if it is permit-required
• Written entry procedures - step-by-step protocols for safe entry
• Permit system - standardized permits that document hazards, precautions and personnel
• Attendant procedures - duties, communication methods and emergency actions for attendants
• Rescue and emergency services - on-site rescue team or documented arrangement with external services
• Training program - initial and refresher training for all involved personnel
• Annual program review - evaluation of the program using canceled permits from the past year

The annual review is critical and often overlooked. OSHA requires employers to review entry permits within one year of cancellation to identify problems, trends and areas where the program needs revision.

Preventing the "Rescuer Fatality" Problem

The most tragic aspect of confined space incidents is that the majority of fatalities are would-be rescuers who rush in without preparation. OSHA data consistently shows that 50-60% of confined space deaths are rescuers. Preventing rescuer fatalities requires:

• Never allow impulsive rescue - train all employees that entering a confined space to rescue someone without proper equipment and procedures will likely result in additional deaths
• Pre-positioned retrieval equipment - tripods, winches and full-body harnesses must be set up before entry, not after an emergency occurs
• Continuous communication - the attendant must maintain constant contact with entrants; any loss of communication triggers the emergency response
• Practice rescue drills - at least annually, rescue teams must practice actual confined space rescue scenarios

Track all confined space entries, permits and incidents with Make Safety Easy's incident reporting and permit tracking to ensure every entry follows your program requirements.

Frequently Asked Questions

Is a crawl space under a house a confined space?

Yes, in most cases. A residential crawl space typically meets all three criteria: it is large enough for a person to enter, has limited entry/exit points and is not designed for continuous occupancy. Whether it is permit-required depends on the presence of hazards such as gas lines, sewage pipes or poor ventilation.

Is a manhole a confined space?

Almost always, yes. Manholes meet all three OSHA criteria and are usually permit-required due to potential atmospheric hazards from sewer gases, oxygen displacement and engulfment risks from water or debris.

Who needs confined space training?

Anyone who enters, attends or supervises a confined space entry needs role-specific training. This includes the entrant, the attendant stationed outside and the entry supervisor who authorizes the permit. Rescue team members need additional rescue-specific training.

Can I reclassify a permit-required space as non-permit?

Yes, under OSHA 1910.146(c)(7). If you can demonstrate that all hazards have been eliminated (not just controlled) without entry, you can reclassify the space. This must be documented, and the space must be re-evaluated any time conditions change.

What is the difference between a confined space and an enclosed space?

An enclosed space is a broader term that includes any space with limited ventilation. A confined space specifically meets OSHA's three-part definition. Not all enclosed spaces are confined spaces, but all confined spaces are enclosed spaces. The distinction matters because OSHA's permit-required entry procedures apply only to confined spaces as defined in 1910.146.