Crews assessed neighboring structures for possible carbon monoxide seepage as a result of the fire.
Due to elevated levels found, 30 people from buildings at 31-01, 31-11 and 31-17 were evacuated, FDNY officials said.
A handful of buildings also lost power, but no injuries were reported.
Firefighters say thick black smoke just kept pouring out of the manhole that exploded which sent the carbon monoxide into the buildings.
Officials said the blast was caused by a volatile cocktail of road salt mixed with an aging, underground system.
"You got old wires, old infrastructure, whenever it snows, you got the salt mix with water, it eats away at insulation of wire, it arcs, causes a problem, it exploded," said FDNY Chief Brian Deery.