Hazard Identification in Confined Spaces

OSHA calls it a confined space when it's big enough to enter and work in, has limited entry or exit, and isn't designed for people to stay in. On site that means manholes, tanks, boilers, pits, sewers, storm drains, crawl spaces, silos, and vaults.

It becomes a permit-required space when it adds a serious hazard: a hazardous atmosphere, material that could engulf you (loose grain, sand, liquid), a shape that could trap you (converging walls, a floor sloping to a narrow opening), or any other recognized danger like unguarded machinery or live wires. Construction permit spaces fall under OSHA 29 CFR 1926 Subpart AA.

Bad air is the number-one killer in confined spaces, and you can't see or smell most of it. Test the air from outside with a calibrated meter before entry — always in this order:

• Oxygen first
• Then flammable gases and vapors
• Then toxic contaminants

Safe ranges to check against:

• Oxygen — 19.5% to 23.5%. Below 19.5% drops you with no warning; above 23.5% everything burns violently.
• Flammable gas or vapor — below 10% of the LEL (Lower Explosive Limit).
• Toxic gases — below their permissible exposure limits.

Two common killers: hydrogen sulfide (H2S) smells like rotten eggs at first but kills your sense of smell as it rises, and carbon monoxide (CO) is odorless and often blows in from an engine, generator, or welding near the opening.

The space itself can hurt you. Watch for:

• Engulfment — loose sand, grain, or sludge that can bury a worker in seconds.
• Entrapment — converging walls or a funnel-shaped floor that pins you in.
• Machinery — augers, mixers, or blades that weren't locked out.
• Live wiring, heat buildup, standing water, poor footing, and falling objects.
• Low light or loud noise that hides hazards and makes it hard to communicate.

Hazards also come from the work. Welding adds fumes and burns up oxygen, solvents give off vapors, and a running engine outside can push exhaust in. A space that tested clean an hour ago can turn deadly once work starts — so monitor continuously, not just once.

Treat every confined space as dangerous until testing proves otherwise. Before entry:

• Identify and label the space, and check what it held or was used for.
• Lock out any energy, mechanical, or product lines feeding into it.
• Test the air from outside, and keep monitoring throughout.
• Set up ventilation if it's needed.

Then ask about this exact space:

• What's the only way in and out — and could a rescuer reach an injured worker through it?
• What could change while the crew is inside?
• Who's the attendant staying outside, and how do they keep in contact?

If a control is missing, damaged, or unclear — or conditions change — stop until it's fixed. Never enter to rescue someone without proper equipment and training; many confined space deaths are rescuers who rushed in unprotected.