How to Reduce Manhole Explosions in the Utility Industry
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Manhole explosions are a relatively common occurrence in the utility industry. In fact, while many are unreported, an estimated 3,000-5,000 manhole events (includes explosions as well as smoking manholes and burning manholes) occur in the U.S. every year. As such, they should be proactively managed and included in utility emergency plans.
Tips for Mitigating the Impact of Manhole Explosions
Manhole explosions can contain the same amount of destructive force as 20 sticks of TNT. According to a 60-page guidance document published by the Institute of Electronics and Electrical Engineers (IEEE) in Aug. 2022, although many root causes exist, the primary issue relates to “aged or damaged cable and components.”
Manhole explosions can occur due to an arc flash situation, combustible gases ignited by a cable defect, and similar events. Approximately 75% are caused by some form of combustion. It’s up to the utilities to take the steps necessary to keep the public safe from these events.
The most obvious prevention method is to ensure that all cables are in good shape prior to installation, and to inspect them after the installation to make sure no damage occurred during the process. The latter often happens due to dragging cables across debris and other obstructions. Another safety tactic is to latch each manhole cover to its opening so they don’t get thrown into the air from an explosion.
Other options are more proactive. One is to monitor for combustible gases. This is something that Con Edison has been implementing, by installing thousands of gas-detecting sensors across its service area. Another is to utilize mobile survey equipment to locate faults by identifying contact voltages produced by cable deterioration. In either case, early detection will allow crews to fix the issue before it turns into a disaster.
In the final analysis, manholes present numerous safety challenges, not the least of which is manhole explosions. Performing the proactive steps above, as well as accounting for manhole explosions in emergency preparedness plans, goes a long way toward maximizing manhole safety.
