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Impacts of Passive Ventilation on Manholes

November 5, 2018

In a 2016 video, Con Edison distribution manager Adrianne Ortizo explained how the company was implementing a program to replace solid manhole covers with slotted manhole covers:

“We’re doing this because the vented cover actually allows combustible gases to escape into the atmosphere. Salting streets makes it safer for vehicles and pedestrians, but it can cause issues to an underground electrical system. Salt and melted snow filter in through the manholes, and it coats all of the underground electrical equipment and wiring. The plan is to replace approximately 55,000 solid covers with vented covers over the next four years. So water will make sure to get into the structure regardless if the cover is solid or vented. What the vented cover does for us is it reduces the risk of a manhole explosion. It also lessens the impact of the event to the surrounding area and serves as an early warning system for us.”

The implementation of passive ventilation in manhole covers was used to replace existing solid manhole covers, and data was gathered on the effectiveness of this approach. This implementation reduced explosions by about 4.5X over a four year period, as seen in the graph below. However, the conventional vented cover increased the total number of fires substantially.

manhole explosion frequency
Anthony Cedrone (ConEd), “Manhole Explosion Roadmap,” ICC C34D, Oct. 2010.

In acknowledgement of these two potential solutions and their shortcomings, Plenovo examines the use of active ventilation. Join us for a webinar, “Manhole Explosions Part 2: How to Stop Them” to learn more about how active ventilation can improve manhole safety.