A manhole just exploded in downtown Manhattan — here’s why that happens

Emergency responders at the scene of a manhole cover explosion in downtown Manhattan on March 22, 2018

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Emergency responders at the scene of a manhole cover explosion in downtown Manhattan on March 22, 2018
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Daniel Brown/Business Insider

  • An explosion rocked lower Manhattan on Thursday afternoon. The loud boom was heard for blocks around Wall Street.
  • The NYPD said the sound came from the pop of a manhole cover.
  • Manhole covers explode all the time in New York. Here’s why.

A loud boom heard throughout downtown Manhattan on Thursday afternoon was due to a manhole cover explosion, the NYPD reported.

The NYPD quickly confirmed that a manhole cover blew open in front of 53 Nassau Street, and minutes later said there was a second manhole explosion, just down the block. Police said there were no serious injuries, though one victim was seen standing at the scene.

Manhole explosions happen frequently in New York: on average, the city sees six such events per day. In the first week of February in 2015, Consolidated Edison, the local utility, counted a whopping 600 instances of smoke, fire, and explosions in manholes.

Old manholes throughout the city cover a maze of vulnerable, old wires and cables laid under the streets. When roads and sidewalks get coated with salt to keep ice from accumulating during snowy weather, the erosive material can seep into manholes and hit the wires. The salt wears away insulation that coats underground electrical wires. The city’s rats don’t help the problem: they’re also scurrying around down under the streets, nibbling and fraying the wires. If they get really frayed, the system can act like a combustible powder keg: the insulation heats and starts to spark and smoke. That triggers a build up of pressure that can lead to a loud boom and send the heavy metal cover flying into the air. In extreme cases, electrical fires can start.

Such was the case in Manhattan today, after a snowy nor’easter storm blew through the city on Wednesday. The salty snow-melt created a perfect recipe for manhole cover explosions.

Although a reporter from WCBS said on Twitter that a transformer blew underground near the Federal Reserve, Business Insider has not independently confirmed that information.

New York’s electrical system is the oldest in the country, and some of the underground wires here are near 100 years old. Con Edison has been working to replace old manhole covers with better vented ones in New York City since 2005. But with 246,000 manhole covers around the city’s five boroughs, there’s a lot of ground to cover.