After three manhole covers exploded last month, causing minor injuries to two children and one adult as they walked through the crosswalk at Warren and Church, I’ve wanted to learn why — as have many of you, so it is a collective Nosy Neighbor. (I am still haunted by the story from more than 20 years ago, when a woman walking her dogs in the East Village was electrocuted on a manhole cover.)

ConEd said that these sort of events are caused by melting snow mixing with road salt and seeping into the underground electric equipment, causing damage. “Our crews work around the clock to make the necessary repairs to restore service as quickly and safely as possible,” the press office said.

In the case of the February 26 event on Church, the FDNY called it an explosion, though the manhole cover did not lift into the air but just tilted, releasing soot-filled steam and a black residue that shot several feet into the air. M. heard the sound from her apartment nearby — it was so loud that she rushed outside to see what had happened — and sent the picture above within minutes of the explosion.

In fact three manhole covers were blown on the site, and from what I understand by asking around to electricians I know, when the city puts down salt and it mixes with snowmelt, it erodes the insulation around the electrical cables in the manholes. Some of the cracks in the insulation are tiny fissures not even visible to the eye, but they still allow moisture to reach the copper cables.

When the salty water connects with the copper, it can cause fire, smoke or built-up steam, as was the case of this explosion.

Some manhole covers have slits in them to release heat and steam, but that is a mixed bag since it also allows more detritus to get into the manhole.