See: 1910.269(e) on Enclosed Spaces

Underground enclosed spaces refer to manholes and vaults that contain operating transmission and distribution equipment. If personnel entering such spaces are 269-qualified employees performing routine work covered by the 269 standard, and if the only potential hazards in the manholes and vaults are electrical, then the requirements of 1910.269(e) and (t) apply. If the personnel are not 269-qualified, or if the work is not routine or covered by the 269 standard, or if actual or other potential hazards continue to exist even after complying with the requirements in 1910.269(e) and (t), then the requirements in 1910.146, Permit Required Confined Spaces, must be followed.

Aboveground Attendant
When work is being done in an enclosed space, including underground electrical installations, an attendant trained in first aid, CPR, and rescue procedures is required to be above the hole and maintain communication with the worker(s) in the hole. If a potential hazard exists inside the space or outside (for example, heavy traffic), the attendant must remain above the hole to ensure that the hazard does not expose the worker(s) to injury. If no potential hazard exists, then the attendant may periodically enter the hole to assist for brief periods. [See 1910.269(e)(7) and (t)(3)].

Workers Working Alone
A lone worker can enter a manhole briefly to inspect, perform housekeeping, and take readings as long as the worker is protected from any electrical hazard. However, attendants covered by the enclosed space requirements (1910.269(e)(7)) or permit-required confined space provisions (1910.146) are not permitted to enter a manhole. [See 1910.269(e)(7) and (t)(3)].

See: 1910.269(t) on Underground Electrical Installations, including additional manhole requirements

Cover Removal, Entry and Exit
Before removing a cover, the enclosed space must be checked for indications of potential problems (for example, heat or pressure from a faulted cable), and a guardrail or barrier must be set up around the opening to prevent objects from falling or being dropped into the space. Rescue equipment (or a rescue service) must also be available and ready for the prompt rescue of an injured worker if needed. [See 1910.269(e)(3), (4),and (5)].

When a cover is removed for entry, the atmosphere in the enclosed space must be tested first for oxygen and then for flammable gases or vapors using calibrated instruments. Workers may not enter any enclosed space while the space contains a hazardous atmosphere. If testing instruments are not available, forced air ventilation can be applied long enough to ensure that the space contains enough oxygen. If flammable gases/vapors or oxygen deficiency is found, forced air ventilation must be used to maintain oxygen at a safe level and prevent a hazardous concentration of gases and vapors from accumulating. Alternatively, a continuous monitoring program may be followed in lieu of ventilation if flammable gases or vapors are detected at safe levels. [See 1910.269(e)(6)]. Workers must enter or exit holes greater than 4 feet in depth using a ladder (or similar device). Cables or cable supports may not be stepped on while climbing into or out of a manhole. [See 1910.269(t)(1)].

Cables
A cable to be worked on must be identified by electrical means unless its identify is obvious, and any energized cable that needs to be moved must be inspected for defects. If a potentially defective cable (for example, leaking compound, swollen joint, sheath breaks) is found, that cable must be deenergized except when service load conditions and a lack of feasible alternatives require that the cable remain energized. If work needs to be done and the cable cannot be deenergized, the cable needs to be protected by wrapping or shielding to avoid an injury if the cable faults. Sheath continuity for cables must be maintained or the cable sheath must be treated as energized. [See 1910.269(t)(5), (6), (7), and (8)].

Flame Use and Lowering Equipment
Attendants must be sure that workers in an enclosed space or manhole are clear of the opening before lowering any equipment into the space. If a flame (torch) is to be used in an enclosed space, an additional test for flammables must be conducted before the flame is used and at least once an hour thereafter while the flame is in use. [See 1910.269(e)(14) and (t)(2)].

Medical Services and First Aid
Pole Top and Manhole Requirements