What Is a Confined Space?
OSHA defines a confined space as an area that:
- Is large enough for a worker to enter and perform work
- Has limited or restricted entry or exit
- Is not designed for continuous human occupancy
Examples include:
- Trenches and hydro-excavated pits
- Utility vaults or manholes
- Crawl spaces or pipelines
- Storage tanks and silos
Important note: These spaces can be hazardous but aren't automatically classified as PRCS unless additional risks exist.
What Is a Permit-Required Confined Space (PRCS)?
A PRCS is a confined space containing additional hazards requiring a formal permit system and OSHA-compliant entry procedures.
A confined space becomes a PRCS if it has one or more of these conditions:
- Hazardous Atmosphere (toxic gases, low oxygen, flammable vapors)
- Engulfment Hazards (soil, water, or loose material that could trap workers)
- Entrapment Risks (tapered walls, sloping floors, or converging surfaces)
- Other Recognized Hazards (electrical, mechanical, thermal, or live utilities)
PRCS examples:
- Sewer manholes with toxic gas buildup
- Excavation pits deeper than 4 feet with collapse or engulfment risks
- Tanks or vessels with chemical residue
- Underground utility vaults with live power lines
Key Differences
| Feature | Confined Space | PRCS |
|---|---|---|
| Definition | Space with limited entry/exit, not meant for continuous occupancy | Confined space with additional serious hazards |
| Examples | Trenches, crawl spaces, empty tanks | Sewer vaults, excavations with toxic gas, tanks with chemical residue |
| Hazard Level | Potentially hazardous | Known hazardous |
| Permit System Required | No | Yes, written permit required before entry |
| Atmospheric Testing | Not required unless hazards suspected | Mandatory continuous monitoring |
| Attendant Requirement | Not required | Required: attendant must stay outside and monitor |
| Rescue Procedures | Not formally required | Formal non-entry or entry rescue plan required |
| OSHA Standard | General duty to ensure safety | 29 CFR 1910.146 |
Why the Distinction Matters
Many job sites misclassify confined spaces, exposing workers to serious risks. The differences impact:
- Safety Procedures – Whether permits, attendants, and rescue systems are required
- OSHA Compliance – Misclassification can result in fines and liability
- Worker Safety – PRCS conditions account for many severe workplace incidents
Best Practices for Confined Space and PRCS Safety
- Evaluate every space for hazards before entry
- Use atmospheric testing, especially in excavations, manholes, or vaults
- Implement permit systems for any PRCS entry with trained supervisors
- Have an attendant and rescue plan; non-entry retrieval systems are preferred
- Train all workers to understand the difference between confined space and PRCS
Frequently Asked Questions
Q: What is the main difference between a confined space and a PRCS? A PRCS has additional hazards and requires a permit system.
Q: Who decides if a space is a PRCS? The employer is responsible for hazard evaluation and classification.
Q: Do all trenches count as PRCS? No. Trenches deeper than 4 feet may be confined spaces, but they become PRCS only if additional hazards exist.
Q: Is atmospheric testing required for confined spaces? Not always, but it is mandatory for PRCS entry.
Q: What OSHA standard applies to PRCS? 29 CFR 1910.146 — Permit-Required Confined Spaces Standard.
