Most confined-space deaths are from the atmosphere — and most victims are would-be rescuers. Work this pre-entry checklist for a permit-required confined space (OSHA 1910.146). Test the air in order: oxygen first, then flammables, then toxics, before anyone enters.
Atmospheric testing & respiratory gear
Atmospheric acceptance limits
| Parameter | Acceptable range |
|---|---|
| Oxygen | 19.5% – 23.5% |
| Flammable gas/vapor | Below 10% of the LEL |
| Toxics (e.g. CO, H₂S) | Below the OSHA PEL |
FAQ
Why test oxygen first?
Many combustible-gas sensors need adequate oxygen to read correctly, and oxygen displacement is an immediate killer. Test O₂, then flammables, then toxics — and continuously monitor during entry.
Can I rescue a downed entrant myself?
Never enter without proper respiratory protection and a retrieval plan. Non-entry rescue (retrieval line) is the goal; most multiple-fatality events are untrained rescuers entering a bad atmosphere.
Educational pre-entry aid summarizing OSHA 29 CFR 1910.146. It does not replace a written permit program, a qualified entry supervisor, calibrated continuous monitoring, or a rescue plan.
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