6 December 2006
Including change 1, 7 December 2006
try and find cable hot spots (if possible). If possible, look for damaged cable with
mirrors on a live line tool to try and locate the faulty cable. If the faulty cable is located,
deenergize this cable. If the faulty cable cannot be located, all the cables in the
manhole must be deenergized until the faulty cable is repaired or remains deenergized.
Pumping a Manhole. If manhole contains water and needs to be pumped,
water must not be allowed to enter storm drains, canals or waterways unless approved
by local, state, and federal laws. Water is permitted to be pumped into containers and
transported to an approved dumping area. If local policy permits, water may be placed
back into the manhole. After a manhole has been pumped, the removal of the water
may permit gas to flow into the manhole. Make the test at any open ducts. If a test
indicates that gas in entering, ventilate the manhole.
Removal of Duct Plugs. Immediately upon the removal of the duct plugs,
make a test at the opened duct. If gas is entering, ventilate the manhole.
Emergency Entrance. Use an approved positive pressure respirator or self-
contained breathing apparatus, and a safety harness attached to a retrieval device
attended by another worker stationed at the opening if it becomes necessary, to enter a
manhole or vault where a hazardous atmosphere is present.
Ventilation of Underground Structures. There are three methods that can
be used to ventilate a structure. These are the forced air, sail, and natural methods.
11-6.8.1 Forced Air. The forced air method consists of a power blower, blowing air
into the manhole. The blower hose is placed into the manhole, forcing fresh air to
circulate and oxygen-deficient air to be forced out. This is the best method of ventilating
11-6.8.2 Sail Method. The sail method (refer to Figure 11-1) ventilates the manhole
by using the wind. A piece of plywood or some other material is placed over the
manhole. The edge of the plywood facing the wind is lifted up until the plywood forms
about a 45-degree angle with the manhole opening. The wind enters the manhole,
forcing possible contaminated air out of the manhole.