Underground

DOE-HDBK-1092-98

2. The opening of a time clock, a photoelectric relay, or remote control overcurrent control

equipment shall not be considered as isolation points that provide a safe work condition while

employees work on series lighting circuits.

3. The use of series lighting circuits is discouraged.

7.10 UNDERGROUND

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 19.5% or greater than 21%, the pit shall be ventilated and

retested before any work begins.

6. If the flammable-gas content is more than 10% 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.

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