Boston fire briefly shut down Congress Street around 4:30 a.m. Tuesday after smoke came billowing out of a manhole cover at the corner of Quaker Lane.
Firefighters said they found arcing underground and elevated carbon monoxide levels inside 15 Congress St. They used fans to help ventilate the building.
No one was injured, and the road was reopened around 6:30 a.m.
Eversource crews spent several hours on scene before ultimately determining the cause was an underground equipment issue.
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"We worked with local first responders to make the area safe and immediately began investigating what caused this equipment issue," the company said. "The manhole was equipped with a new energy release cover, which worked as designed."
Heavy fire department activity could be seen on Congress Street between Water and State streets. The closure was located next to the Old State House and a block from City Hall. It’s unclear whether there was any work being done in the area at the time of the fire.
No one was injured, Boston police said.
First responders took the scare seriously after four manhole cover explosions and fires over the past two months in Boston.
In June, a woman was injured when two manhole covers blew off on High Street as a result of an over-pressurization underground. And back in May, fire burst from two other manholes on Boylston Street, causing smaller explosions but no injuries.
Eversource said there was no property damage or power outages as a result of Tuesday's incident. They have not said yet whether they were able to determine what caused the equipment issue.