Permit-Required Confined Spaces
A confined space is a space large enough for a worker to enter and perform work, has limited or restricted means of entry or exit, and is not designed for continuous occupancy. A permit-required confined space (PRCS) is a confined space that contains or has potential to contain a serious safety or health hazard — specifically: a hazardous atmosphere, a material that could engulf the entrant, an internal configuration that could trap or asphyxiate (converging walls, inwardly sloping floor), or any other recognized serious safety or health hazard. OSHA's PRCS standard is 29 CFR 1910.146, and it is among the most complex and hazard-dense standards in the general industry canon.
Before any entry into a PRCS, a written entry permit must be issued. The permit must include: the space to be entered and purpose of entry, date and duration authorized, names of authorized entrants, attendant(s), and entry supervisor, hazards identified and the means of isolating them (LOTO, blanking, blocking), acceptable entry conditions (atmospheric readings must be within parameters), atmospheric test results and equipment calibration data, rescue and emergency services available, communication procedures, and special equipment required. The entry supervisor signs and authorizes the permit, and must cancel it if conditions change.
Atmospheric testing is mandatory before entry and must be performed in the order: oxygen first (19.5–23.5% is acceptable range), then flammable gas/vapor (below 10% LEL), then toxic contaminants (CO, H2S, and other space-specific hazards). This testing sequence matters because low oxygen may mask a combustible gas reading (a meter that hasn't been zeroed in low-O2 atmosphere may underread LEL), and because oxygen enrichment dramatically lowers the ignition energy for flammable vapors. Continuous monitoring is required during entry whenever atmospheric conditions can change.
Three distinct roles are required for PRCS entry: the Authorized Entrant (worker entering the space) who must know the hazards, signs/symptoms of exposure, and how to use retrieval equipment; the Attendant (stationed outside) who monitors entrants and conditions, maintains personnel accountability, never enters the space, and initiates rescue immediately when required; and the Entry Supervisor who authorizes and oversees entry, verifies all preconditions are met, terminates entry when conditions change, and cancels the permit. Rescue must be addressed before entry — the preferred method is non-entry retrieval (tripod with winch, wristlets on entrant). OSHA statistics show that 60% of confined space deaths are would-be rescuers who entered without proper preparation.