The OSHA confined space definition is shorter than most people expect. Under 29 CFR 1910.146, a space qualifies if it meets three conditions at once: it is large enough for a worker to bodily enter and perform assigned work, it has limited or restricted means of entry or exit, and it is not designed for continuous occupancy.
All three must apply. A crawl space with a wide opening is not confined. A cabinet too small to enter is not confined. A tank with a manway on top meets all three, which is why tanks, vessels, pits, sewers and silos account for most of the spaces that fall under the rule.
Confined is not the same as permit required
The definition above establishes that a space is confined. It does not yet establish what the employer has to do about it.
A confined space becomes a permit required confined space when it also contains, or has the potential to contain, a serious hazard. A hazardous atmosphere is the most common trigger. Others include a material capable of engulfing an entrant, an internal configuration that could trap or asphyxiate, and any other recognized serious safety or health hazard.
For atmospheres, OSHA is specific about what counts as hazardous. Oxygen below 19.5 percent or above 23.5 percent qualifies. So does any substance present above its published permissible exposure limit, and any condition immediately dangerous to life or health.
That is the point where the definition stops being paperwork and starts requiring an instrument.
The testing sequence is not a suggestion
Before an employee enters, the internal atmosphere must be tested with a calibrated direct reading instrument, in a fixed order: oxygen first, then flammable gases and vapors, then potential toxic air contaminants.
OSHA explains the reasoning in Appendix B to the standard. Oxygen goes first because most combustible gas meters are oxygen dependent and will not read reliably in an oxygen deficient atmosphere. Combustible gases come next because fire and explosion are the more immediate threat. Toxics are tested last.
Two operational consequences follow. The instrument needs a pump and probe, because the test happens from outside the space before anyone enters. And the space is stratified, so a reading taken at the opening says nothing about what has settled at the bottom.
Inteccon’s solution: the G460 from GfG monitors up to six gases in one unit, combining toxic sensors, a catalytic sensor for combustible gases, a PID lamp for volatile organic compounds and an NDIR sensor for carbon dioxide, available with an extractable pump for remote sampling. Our portable gas detection range covers the configurations confined space programs actually need.
The word most programs overlook
The standard does not say tested with a direct reading instrument. It says calibrated. An instrument that has drifted since its last bump test produces readings that satisfy nobody during an inspection, and protect nobody during an entry.
Pre entry testing and calibration records belong to the same obligation. One is worthless without the other.
Conclusion
The OSHA confined space definition is three simple tests, and passing them puts a space inside a rule that governs everything from permits to instrumentation. The definition is where compliance begins, not where it ends.
Have you classified every space in your facility, or only the ones that look the part?