Start with the confined-space definition
Both categories are confined spaces first — meaning both satisfy the three-condition test in §1910.146(b): worker can enter and work, limited entry/exit, not designed for continuous occupancy. The split happens on top of that. See our [confined space entry permits](/resources/confined-space-entry-permits) pillar for the full permit lifecycle.
What makes a space permit-required
A permit-required confined space contains, or has the potential to contain, at least one of four categories of hazard: (1) a hazardous atmosphere; (2) a material that could engulf an entrant; (3) internally converging walls or a downward-sloping floor that could trap or asphyxiate; or (4) any other recognised serious safety or health hazard — heat, mechanical, electrical, chemical, or noise.
'Potential to contain' is doing a lot of work in that sentence. An empty grain bin has engulfment potential the moment it's next filled. A pipe that normally carries inert nitrogen has atmospheric potential every time it's opened. Assess the worst-case operating state, not the state at the moment of assessment.
What qualifies a space as non-permit
A non-permit confined space is one where the employer can demonstrate that the only hazard is atmospheric AND that continuous forced-air ventilation alone will maintain a safe atmosphere for entry. If ventilation would have to be paired with any other control — respirators, isolation, hot-work suspension — the space stays permit-required.
In practice, non-permit spaces are rare in industrial settings. Most manholes, tanks, and vessels have engulfment, chemical, or mechanical hazards that push them into permit-required territory regardless of atmosphere.
Reclassification: temporary and revocable
Section §1910.146(c)(7) allows a permit-required space to be reclassified as non-permit when all the hazards that made it permit-required have been eliminated. Document this on a certificate signed by the person making the determination, kept at the entry point, and available to entrants.
Reclassification is not the same as controlling hazards with a permit. Isolating a chemical feed at a valve is control; removing the chemical feed line entirely may be elimination. If a hazard could return without human intervention — a valve leaks, a process cycle refills the vessel — the reclassification cannot stand.
A three-question decision checklist
1. Does the space meet all three confined-space conditions? If no → not a confined space. 2. Could the space contain, at any point in its normal operating cycle, a hazardous atmosphere, engulfment material, entrapment geometry, or another serious hazard? If yes → permit-required. 3. Is the only hazard atmospheric, and can continuous forced-air ventilation alone keep it safe? If yes → non-permit; document it and post it.
Anything else defaults to permit-required. When in doubt, err toward permit — the downside of over-classifying is paperwork; the downside of under-classifying is fatalities. Ready to lock this into policy? See our [confined space entry permits](/resources/confined-space-entry-permits) guide and [book a demo](/book-demo).