SCHENECTADY — The failure of a worn secondary power cable caused a manhole cover to pop open on State Street Friday morning, according to National Grid.
It was the third manhole cover to burst in that part of downtown since early 2016.
The block between Erie Boulevard and South Ferry Street remained closed to traffic Friday night.
Nate Stone, a spokesman for National Grid, said repair crews would work into Saturday morning replacing the cable underneath the pavement.
Stone said the cable that failed was between 70 and 80 years old. Once it failed, he said, pressure built up under the pavement and blew out the manhole cover.
"Those manhole covers are designed to release the pressure," Stone said. "It wasn't an explosion. If there's a discharge, there's going to be a release, that's what we want."
Stone said there are two cables running under State Street. "The primary was still good," he said. "As far as we know, nobody lost power."
Firefighters at the scene after 9 a.m. did not evacuate any businesses on the north side of State Street: Saratoga National Bank and Trust Co., The Photo Lab and Downtown Convenience are all nearby.
Construction workers on the Electric City apartment unit-retail space project on the south side of State Street also remained on the job as firefighters investigated the incident.
"We had multiple crews in all the buildings down here checking for explosive gases within the structure," said Deputy Fire Chief Donald Mareno, of the Schenectady Fire Department. "All the structures are safe; all the people within those structures are safe."
Firefighters said someone saw smoke coming from the manhole after the lid popped. The manhole is across from the bank, in the middle of the block.
The street was closed as a precaution.
"We don't want traffic going back and forth, and we don't want people walking here," Mareno said.
A 2017 manhole explosion on March 30, in front of Proctors, also resulted in closure of the street.
Pictured: A National Grid employee stands by a manhole that blew its cover on State Street between Erie Boulevard and South Ferry Street Friday morning. (Jeff Wilkin)
After the March explosion, National Grid officials said a stretch of underground cable began smoldering during the early morning hours. The explosion sent the manhole cover flying more than a story into the air; a city camera captured the event on video.
Police were forced to close State Street between Clinton and Broadway while crews looked for the cause and made repairs.
On Jan. 5, 2016, an early afternoon explosion on Barrett Street lifted a manhole cover five feet into the air. Firefighters blocked State Street from Clinton to Lafayette Street and Barrett from State to Franklin streets.
Several buildings were evacuated in that incident.
National Grid officials later said the blast was caused by an electrical cable that caught fire and caused a pressure build-up. Friday afternoon, Stone said cables in both the 2016 and 2017 breakdowns involved aged equipment.
He said the cable degradation partly comes from decades of winter season salt, mixed with water, that reaches equipment through street sewers. "The easy answer is yes, it comes down to wear and tear," Stone said.
Schenectady Mayor Gary McCarthy said the city will wait to hear National Grid's report on the equipment failure.
"We're always concerned with these types of incidents," he said, adding minor flooding occurred on Erie and South Ferry Street earlier this week when water from the ice-swollen Mohawk caused problems in the city's Stockade section.
"Was that a contributing factor? It may have been, it may not have been," McCarthy said. "We're waiting for the final evaluation-determination."
The mayor also said the city does not have an adversarial relationship with National Grid, which he said has upgraded gas lines in the city.
"They are generally very responsive when we put out requests," McCarthy said. "I want to know what the actual cause was, long-term maintenance, fluke. We'll go from there."
On Friday morning, people inside the nearby State Street buildings said they did not hear any explosion.
"No sound," said Basil Alsaraf, who manages Downtown Convenience, a narrow food store on State near the corner of Erie Boulevard.
Micheala Smith was inside the New Choices Recovery Center on State Street when firefighters came in to check the building.
"I was kind of nervous," Smith said. "I thought something had happened to our water."
Sales personnel inside The Photo Lab also heard nothing out of the ordinary.
Business owner John Eoff got into work around 9:30, joining a sales assistant already in the store, and saw red lights flashing on fire and police vehicles.
"I thought somebody had robbed the bank," he said.
Reach Gazette reporter Jeff Wilkin at 518-395-3124 or at [email protected]