Worker in protective gear entering confined space tunnel.

OSHA Definition of a Confined Space (29 CFR 1910.146)

A confined space is any space that meets all three of the following OSHA criteria:

• Large enough to enter and perform work

• Limited or restricted means for entry or exit (e.g., manholes, hatches, ladders)

• Not designed for continuous occupancy (no ongoing ventilation/lighting for people)

If a space meets these three criteria, it is a confined space. The next question is whether it is permit-required.

Permit-Required vs. Non-Permit Confined Spaces

A Permit-Required Confined Space (PRCS) has one or more of these hazards:

Hazardous atmosphere (oxygen deficiency/enrichment, flammable or toxic gases/vapors)
Engulfment hazard (loose grains, liquids, flowable solids)
Inwardly converging walls or sloping floors that could trap/asphyxiate
Any other recognized serious safety or health hazard (energized parts, heat stress, mechanical hazards)

If none of the above apply—and hazards are eliminated—the space may be managed as a non-permit confined space. Reassess if conditions change.

Common Examples

Tanks, silos, bins, boilers, vaults, pits, sewers, pipelines, utility tunnels, reaction vessels, hoppers, crawl spaces, ship holds.

How to Identify Confined Spaces at Your Site (Fast Checklist)

Map spaces that match the 3-part definition
Sample for oxygen, flammables (%LEL), toxics before entry
Document engulfment or configuration hazards
Decide permit vs. non-permit based on hazards present
Post signage (“DANGER—PERMIT-REQUIRED CONFINED SPACE. DO NOT ENTER.”)
Create/maintain your written PRCS program

Employer Responsibilities (OSHA 1910.146 Highlights)

Evaluate the workplace to identify confined spaces
Develop a written PRCS program where required
Post signage and control unauthorized entry
Test the atmosphere before and during entry
Ventilate, isolate, lockout/tagout and control energy sources
Provide PPE, communications, lighting, and retrieval equipment
Train entrants, attendants, and entry supervisors
Plan rescue (in-house or third-party) and practice annually
Keep permits and records per policy

The Permit System—What Must Be on the Permit?

Space identification and purpose of entry
Date/time, work duration, and authorized entrants
Atmospheric test results (O₂, flammables, toxics) with tester’s initials
Isolation/LOTO steps completed
Required PPE and communication methods
Rescue service and how to summon it
Attendant and Entry Supervisor names/signatures
Termination conditions (when/how to cancel the permit)

Entry Roles (Who Does What)

Authorized Entrant – Performs the work; follows permit; uses PPE; maintains communication; exits when ordered or upon hazard signs.
Attendant – Remains outside; monitors space/entrants; prevents unauthorized entry; calls rescue; never leaves post.
Entry Supervisor – Verifies conditions, authorizes permit, ensures measures remain effective, cancels permit when complete.

Atmospheric Testing Sequence (Always in This Order)

First – Oxygen (safe range typically 19.5%–23.5%)

Second – Flammables (%LEL)

Third – Toxics (e.g., H₂S, CO)

Use a calibrated, pumped multi-gas meter to sample from top, middle, bottom—then continuously monitor during entry.

Air monitoring in confined spaces explained.

Controls That Reduce Risk

Ventilation (supply/exhaust; avoid dead zones)
Isolation (blanking, blinding, double-block-and-bleed)
LOTO (electrical, mechanical, pneumatic, hydraulic, thermal)
Retrieval (tripod/winch, full-body harness; consider obstructions)
Hot work permits if cutting/welding in the space
PPE (respirators, head/eye/hand/foot protection; chemical-specific)

Training That Sticks

Confined space entry poses significant risks to workers, necessitating stringent safety protocols. These environments, characterized by limited openings and poor ventilation, can harbor hazardous conditions such as toxic gases, low oxygen levels, and potential engulfment. Proper training and adherence to regulatory guidelines are essential to ensure safe practices during entry and work within these spaces. Employers must prioritize the health and safety of their personnel by implementing comprehensive risk assessments and emergency response plans.

All personnel must receive role-specific training before assignment, when hazards or procedures change, and as needed to maintain proficiency. Reinforce learning with hands-on drills—especially for air monitoring, ventilation setup, retrieval, and rescue activation.