The most dangerous spaces are the ones that look harmless.

The standard's logic begins with inventory: identify every confined space (enterable, limited egress, not designed for continuous occupancy), then determine which are permit-required because of actual or potential hazardous atmospheres, engulfment hazards, inwardly converging walls or floors, or any other recognized serious hazard. Non-permit spaces can become permit spaces the moment work introduces a hazard — welding in a pit, solvents in a tank — and the standard's reclassification and alternate-entry provisions (§1910.146(c)(5) and (c)(7)) are precise about when reduced procedures are allowed.

Employers who don't enter permit spaces still have duties: evaluate, post danger signs or otherwise inform employees, and prevent unauthorized entry. Host employers coordinating contractor entries carry information-sharing obligations both directions.

Every permit entry runs on a documented system: an entry permit signed by the entry supervisor listing hazards, control measures, test results, and duration; atmospheric testing in the mandated order — oxygen first, then flammables, then toxics — with continuous monitoring as conditions require; an attendant stationed outside who tracks entrants and never abandons the post; and rescue and emergency services evaluated and available before anyone crosses the plane of the opening. Non-entry retrieval systems are the default unless they'd increase risk.

The rescue provision is where programs fail catastrophically: "call 911" is not compliant unless the employer has evaluated that the service can respond with confined-space rescue capability in a timely manner. The fatality statistics that haunt this standard — most victims are rescuers — are the reason inspectors read this section of the permit first.

Construction work has its own confined space standard, 1926 Subpart AA, with a similar architecture and important differences in competent-person duties and coordination. RegLogic keeps both a search away, with the reclassification and alternate-procedure LOIs attached where the judgment calls happen. Pin your site's space inventory to §1910.146(c)(1) as team notes, and every entry supervisor works from the same map.