Underground work requires a means of safe entrance and exit from the workspace. Employees should follow the guidance given in the following subsections to ensure safety in entering and leaving such work spaces.

7.10.1 WORKING IN MANHOLES, UTILITY TUNNELS, AND VAULTS

Manholes, utility tunnels, and vaults may be considered confined spaces and shall comply with 29 CFR 1910.146,1910.269(e) and (t), and 1926.956. The following may apply to employees working in manholes, utility tunnels, and vaults:

1. Employees who enter manholes shall be trained in the hazards of the confined spaces, confined space entry procedures, and confined space emergency and rescue procedures.

2. When opening a manhole, employees shall completely remove the manhole cover from the opening. Manhole covers should be removed before the cable is rodded or installed and removed.

3. Open manholes shall be barricaded and protected by flags or guards as required. All open manholes shall be protected as required by 29 CFR 1910.269(e).

4. Before the pit is entered, it shall be tested for oxygen content and the flammable-gas explosive limit. Workers shall not smoke or use an open flame while tests for an explosive mixture of gas are being made.

5. If the oxygen level is less than 19.510 or greater than 2110, the pit shall be ventilated and retested before any work begins.

6. If the flammable-gas content is more than 1010 of the lower explosive limit, the pit shall be ventilated and retested before any work begins. When testing indicates that a manhole contains either a mixture of explosive gas and air richer than safe working limits or flammable liquids, corrective measures shall be taken before work in the manhole is allowed to proceed.

7. When nitrogen is used in manholes or confined areas, approved atmosphere testing devices shall be placed in operation where they can be observed by people in the manhole. When the testing devices show a deficiency of oxygen, all personnel shall leave the manhole until the proper atmosphere is restored.

8. The manhole shall be ventilated continuously when occupied.

9. An attendant is required topside with the means to summon help without leaving his or her station. The attendant shall be capable of instituting a rescue without entering the manhole. The attendant on the surface is responsible for the safety of the persons in the manhole.

10. The topside attendant can perform other duties outside of the enclosed space if these duties do not distract the attendant from monitoring employees within the space. All manholes over 4 ft. deep should be entered with the use of a ladder as required by 29 CFR 1910.269 (t)(1).

11. Workers should open all entrance bars or chains on the topside of manhole guards before entering or leaving a manhole. All chains or bars should be closed at all other times, except when raising or lowering tools or materials.

12. Operations involving chemical cleaning agents, solvents, volatile chemicals, cutting and welding equipment, and other hazardous agents or tools require additional consideration. Consultation with and concurrence of appropriate industrial safety and industrial hygiene personnel are required.

13. The employee shall enter or leave a manhole by means of a ladder. The employer shall not use a cable, cable hanger, or manhole rack as a support for climbing. A manhole ladder should neverbe removed while a worker is in the manhole unless absolutely necessary. In the instance of a ladder being removed to make it easier to rescue a worker, the topside attendant shall fully devote his or her attention and efforts to instituting a rescue using the worker's body harness and lifeline if necessary. The ladder shall be replaced as soon as practical.

Note: The other worker's) in the hole should be warned that the ladder is to be removed in time to allow him or her to exit the hole if necessary.

14. Materials, tools, and equipment should be kept at a sufficient distance from the entrance to the manhole to avoid any hazard to the occupant from falling objects or from hot metal or spilled compounds.

15. Blowtorches and furnaces should be ignited before being lowered into manholes unless this creates additional hazards.

16. Rags, tape, refuse, and combustible and flammable materials should not be allowed to accumulate in a manhole.

17. Instrumentation shall be calibrated per manufacturer's instructions. [See 29 CFR 1910.269(e)(8)]. A record of calibration should be maintained.

18. Ground-fault circuit interrupters (GFCIs) shall be used for 120-V ac power unless such power is supplied by a portable or vehicle-mounted two-wire, single-phase generator rated not more than 5 kW, where the circuit conductors of the generator are insulated from the generator frame and all other grounded surfaces. (See Section 6.4).

19. All cables and insulated wires that do not have grounded conducting sheaths or shielding should be treated as bare conductors. They shall be considered energized unless approved methods have been used to determine that they are deenergized. Barricade or cover these conductors with protective equipment or devices that will be within reach of a worker's position.

20. Where multiple cables are present the cable to be worked on shall be identified by electrical means unless its identity is obvious. [See 29 CFR 1910.269(t)(5)]. Where cable has one or more abnormalities that could be an indication of an impending fault, the defective cable shall be deenergized, except when service load conditions and a lack of feasible alternatives require that the cable remain energized. In that case, employees may enter the manhole if they are protected by the affects of the failure by flash blankets or other devices capable of containing the adverse effects of the fault. [See 29 CFR1910.269(t)(7)].

7.10.2 WORKING ON ENERGIZED UNDERGROUND CABLES

In general, work should not be performed on energized underground cables. However, strictly external work, not requiring an appreciable change in location of the cable, may be performed under direct supervision. Energized cables that are to be moved shall be inspected for defects. [See 29 CFR 1910.269(t)(6)].

7.10.3 TERMINALS OF UNDERGROUND CABLES (POTHEADS)

Before work is started, the overhead line connections to a cable terminal upon which work is to be performed should be either:

1. Deenergized and grounded or

2. Disconnected and covered with protective equipment.