Every permit-required confined space is a confined space; most confined spaces are not permit-required. The confined space test has three parts and all three must be true. The permit-required test has four characteristics and only one has to be true. Get those two counts the right way round and the rest of 29 CFR 1910.146 falls into place.
Step one: is it a confined space at all?
1910.146(b) defines a confined space as a space that meets all three of the following. The word "and" between them is doing real work:
| Test | Regulatory wording | What trips people up |
|---|---|---|
| Bodily entry | "Is large enough and so configured that an employee can bodily enter and perform assigned work" | Reaching an arm into a hopper is not bodily entry; a space nobody can get into is not a confined space |
| Restricted access | "Has limited or restricted means for entry or exit" | "Or exit" - a space you can walk into but must climb out of qualifies |
| Not for occupancy | "Is not designed for continuous employee occupancy" | Designed, not used. A dusty basement people work in daily was designed for occupancy; a valve pit was not |
The standard supplies its own examples in the definition - "tanks, vessels, silos, storage bins, hoppers, vaults, and pits are spaces that may have limited means of entry." The construction standard's scope note in 1926.1201 goes much further and is the better checklist for a jobsite walk: bins, boilers, elevator and pump pits, sewer and storm drain manholes, tanks, incinerators, scrubbers, concrete pier columns, transformer vaults, HVAC ducts, water mains, precast manhole units, drilled shafts, enclosed beams, digesters, lift stations, cesspools, silos, air receivers, sludge gates, air preheaters, step-up transformers, turbines, chillers, bag houses and mixers.
Step two: any one of four things makes it permit-required
A permit-required confined space, per 1910.146(b), is a confined space with one or more of these characteristics:
- Contains or has a potential to contain a hazardous atmosphere. "Potential" is the operative word - an empty, clean tank that once held solvent still has the potential.
- Contains a material that has the potential for engulfing an entrant. Grain, sand, sludge, pellets, water.
- Has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls, or by a floor that slopes downward and tapers to a smaller cross-section. Hoppers and cyclones, by shape alone.
- Contains any other recognized serious safety or health hazard. The catch-all: unguarded agitators, live conductors, steam lines, extreme heat, a 15-foot drop inside the vessel.
What "hazardous atmosphere" actually means
The first characteristic points at a defined term, and the definition is five-pronged - an atmosphere that may expose employees to death, incapacitation, impairment of the ability to self-rescue, injury or acute illness from any of:
| Cause | Threshold |
|---|---|
| Flammable gas, vapor or mist | Above 10% of its lower flammable limit |
| Airborne combustible dust | At or above its LFL - the standard's note approximates this as dust obscuring vision at 5 feet or less |
| Oxygen | Below 19.5% or above 23.5% by volume |
| Any substance with a Subpart G or Subpart Z limit | A concentration that could result in exposure above its dose or permissible exposure limit |
| Anything else IDLH | Any other atmospheric condition immediately dangerous to life or health |
The non-permit confined space
A non-permit confined space is not "not a confined space." It passes the three-part test and simply has no permit trigger. The two standards word it differently, and the difference matters if you work under both:
- General industry, 1910.146(b): "a confined space that does not contain or, with respect to atmospheric hazards, have the potential to contain any hazard capable of causing death or serious physical harm."
- Construction, 1926.1202: "a confined space that meets the definition of a confined space but does not meet the requirements for a permit-required confined space, as defined in this subpart."
Two duties survive even in a non-permit space. 1910.146(c)(6) requires reevaluation and, if necessary, reclassification as a permit space "when there are changes in the use or configuration of a non-permit confined space that might increase the hazards to entrants." And nothing in Subpart J switches off the rest of the standards - lockout/tagout, fall protection, hot work, electrical - inside that space.
Alternate procedures: ventilation-only entry, not a downgrade
1910.146(c)(5) is a genuine relief route, and it is routinely misdescribed as "ventilating it down to a non-permit space." It is not that. The space stays a permit space; the employer is excused from paragraphs (d) through (f) and (h) through (k) - the program, the permit and the attendant, entrant, supervisor and rescue duties - but only on a stack of conditions:
- The only hazard is an actual or potential hazardous atmosphere.
- Continuous forced air ventilation alone is sufficient to keep it safe, demonstrated with monitoring and inspection data.
- If entry is needed to gather that data, that entry is a full permit entry.
- The determinations and data are documented and made available to each entering employee or their representative.
And the entry itself keeps real controls: eliminate unsafe conditions before removing the cover, guard the opening once it is off, test in the prescribed order with a calibrated direct-reading instrument, allow entrants to observe the testing, no hazardous atmosphere inside while anyone is in there, ventilation from a clean source directed at the work area and continuing until everyone is out, periodic testing, and if a hazardous atmosphere is detected - everyone leaves immediately, the space is evaluated to find out how it developed, and measures are put in place before the next entry. 1910.146(c)(5)(ii)(H) then requires a written pre-entry verification with the date, the location of the space and a signature.
Reclassification: elimination, not control
1910.146(c)(7) is the only route that genuinely turns a permit space into a non-permit space, and it hinges on one distinction:
"Control of atmospheric hazards through forced air ventilation does not constitute elimination of the hazards."
Note to 29 CFR 1910.146(c)(7)
So the conditions are strict. The space must pose no actual or potential atmospheric hazards, and all hazards within it must be eliminated - ideally without entry. Blanked and bled lines, a de-energized and locked-out agitator, a drained and cleaned vessel: those are eliminations. A running fan is not. If entry is necessary to eliminate the hazards, that entry runs under paragraphs (d) through (k) - full permit conditions - and reclassification can only follow if testing and inspection during it show the hazards are gone. The employer documents the basis with date, location and signature, and if hazards arise later, every employee exits and the space is reevaluated.
| Full permit entry | Alternate procedures (c)(5) | Reclassified (c)(7) | |
|---|---|---|---|
| Hazards | Any | Atmospheric only | All eliminated, none atmospheric |
| Entry permit | Required, 15 elements | Not required | Not required |
| Attendant | Required | Not required | Not required |
| Rescue service arranged | Required | Not required | Not required |
| Atmospheric testing | Initial and periodic | Pre-entry and periodic, in order | Not applicable - no atmospheric hazard |
| Ventilation | As needed | Continuous, mandatory | Cannot be the basis |
| Paperwork | Signed permit | Written verification: date, location, signature | Written determination: date, location, signature |
On a construction site: Subpart AA, not 1910.146
1910.146(a) says plainly that the section "does not apply to agriculture, to construction, or to shipyard employment." Construction lives in 29 CFR 1926 Subpart AA, published in 2015. It uses the same four permit-space characteristics and the same atmospheric thresholds, and then differs in ways that change how a jobsite runs:
- A competent person identifies the spaces. 1926.1203(a): before work begins, each employer must ensure a competent person identifies all confined spaces its employees may work in, and identifies each one that is a permit space, "through consideration and evaluation of the elements of that space, including testing as necessary."
- Three named roles. 1926.1202 defines the host employer (owns or manages the property), the controlling contractor (overall responsibility for construction at the site) and the entry employer. 1926.1203(h) then requires an information exchange: the host tells the controlling contractor the location of each known permit space, its hazards and the reason it is a permit space, and the controlling contractor becomes the hub for that information.
- Continuous monitoring is the default. Under 1926.1203(e)(2)(vi), the atmosphere "must be continuously monitored unless the entry employer can demonstrate that equipment for continuous monitoring is not commercially available or periodic monitoring is sufficient" - and a continuous monitor needs an alarm, or somebody checking it often enough for entrants to escape.
- PPE is not a control. The construction definition of "control" is engineering methods - ventilation and the like - and states outright: "Personal protective equipment is not a control." Subpart AA also defines "physical hazard" explicitly, listing explosives, mechanical, electrical, hydraulic and pneumatic energy, radiation, temperature extremes, engulfment, noise and inwardly converging surfaces.
- Three carve-outs. 1926.1201(b) excludes work regulated by Subpart P (excavations), Subpart S (underground construction, caissons, cofferdams, compressed air) and Subpart Y (diving). Where Subpart AA does apply and another standard also addresses a confined space hazard, 1926.1201(c) requires compliance with both.
One wording difference is worth knowing if you write procedures for both worlds: the construction definition of confined space drops "and perform assigned work" and reads "large enough and so configured that an employee can bodily enter it," with restricted means "for entry and exit." Its reclassification route, 1926.1203(g), also allows hazards to be eliminated or isolated - and requires a competent person to make the determination.
Bottom line
- Confined space: three tests, all must be true. Permit-required: four characteristics, one is enough.
- "Potential to contain" a hazardous atmosphere is a trigger. A clean, empty tank that used to hold something is still a permit space.
- Ventilation controls; it does not eliminate. That one sentence separates (c)(5) alternate procedures from (c)(7) reclassification.
- Both relief routes still produce paper: date, location, signature, before entry.
- Construction is Subpart AA - competent person, host and controlling contractor information exchange, continuous monitoring by default, and no coverage for trenches.
- When the classification is genuinely arguable, run it as a permit space. Nobody has ever been cited for the permit they did write.