Why Confined Space Safety Matters
Confined space incidents kill approximately 90 workers per year in the United States, with many additional fatalities among would-be rescuers who enter without proper equipment. In construction, confined space hazards are present in manholes, trenches, tanks, vaults, tunnels, and excavations.
OSHA's construction confined space standard (29 CFR 1926 Subpart AA) was specifically created because construction work presents unique hazards not addressed by the general industry standard (1910.146) — including multi-employer worksites, continuously changing conditions, and temporary entry points.
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Permit-Required vs. Non-Permit Confined Spaces
What Is a Confined Space?
A space is a confined space if it meets ALL three criteria:
1. Large enough to enter and perform work
2. Limited or restricted means of entry/exit
3. Not designed for continuous human occupancy
When Does It Become Permit-Required?
A confined space becomes a Permit-Required Confined Space (PRCS) if it has one or more of these hazards:
| Hazard Category | Examples |
|----------------|----------|
| Hazardous atmosphere | Oxygen deficiency/enrichment, flammable gases, toxic vapors (H2S, CO) |
| Engulfment hazard | Grain, sand, water, loose material that could bury an entrant |
| Configuration hazard | Inwardly converging walls, floors that slope to a smaller cross-section |
| Other serious hazards | Moving mechanical parts, energized electrical, extreme temperatures |
Reclassification
A PRCS may be reclassified as a non-permit confined space only if:
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Atmospheric Testing: The Critical Step
Atmospheric testing must be performed before any entry and continuously during occupancy. The testing order matters:
Testing Sequence
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