OSHA Safety and Health Regulations for Construction (29 CFR Part 1926) 1926.953: 1926.953 Enclosed spaces

Governs routine entries into enclosed spaces such as manholes and vaults, except vented vaults whose ventilation the employer has confirmed, before entry, is working to protect employees. If, after the precautions of this section and 1926.965, remaining hazards could endanger an entrant's life or hinder escape, entry must follow the Subpart AA permit-space rules; otherwise this section applies instead of 1926.1204 to 1926.1211. Entries made under Subpart AA permit rules count as compliance. The employer ensures safe work practices for entry, work and rescue; trains each entrant and attendant in enclosed-space hazards, entry procedures and rescue procedures; and provides equipment for prompt, safe rescue. Before removing any entrance cover, the employer checks for atmospheric pressure or temperature differences and evaluates whether a hazardous atmosphere might be present, eliminating unsafe conditions first. An opened entrance must promptly be protected by a railing, a temporary cover or some other barrier, so nobody falls through and objects cannot drop onto those inside. Nobody enters while a hazardous atmosphere exists unless the entry meets Subpart AA. Where traffic patterns near the entry opening create a hazard, an attendant with first-aid training must be immediately available outside while work goes on; the attendant may do other outside tasks only if they do not distract from monitoring entrants and keeping entry and exit safe. Atmospheric test instruments must be kept calibrated with accuracy of at least plus or minus 10 percent. Before entry, a direct-reading instrument checks the atmosphere for low oxygen, unless continuous forced-air ventilation is provided under procedures that ensure no oxygen-deficiency exposure; then, once oxygen is shown sufficient, it is tested for flammable gases and vapors. If either hazard is found, forced-air ventilation keeps oxygen safe and prevents flammable build-up, though continuous monitoring may replace ventilation where flammables are first detected at safe levels. Forced-air ventilation must start before entry, run long enough to demonstrate a safe atmosphere, be aimed at the area where employees are, continue until all have left, and draw from a clean source that adds no hazard. Where open flames are used, flammable-gas testing is done immediately before use and at least once per hour during use, or more often if conditions warrant.