Three firefighters were injured, one seriously, after a natural gas explosion led to a fire Monday at a commercial building on Amherst Street in Nashua.
Officials said none of the injuries were considered to be life-threatening.
One firefighter was released from the hospital, while the other two will remain hospitalized overnight.
>> Raw aerial video: Firefighters respond to flames, explosion in Nashua
The fire happened at the Greater Nashua Mental Health building at 440 Amherst St.
About 40 people were working inside when a ruptured natural gas line was reported around 2:15 p.m., according to fire officials.
Nashua fire Chief Steve Buxton said workers evacuated after smelling gas and hearing a hissing sound.
Investigators believe no one was inside when the building caught fire.
Fire Marshal Sean Toomey said there was no active fire when crews arrived to investigate the reported gas leak. Some firefighters became trapped for a short time after a small explosion, but were able to get out.
Flames quickly spread, and the building was eventually destroyed.
Buxton said four people were initially unaccounted for, but Mayor Jim Donchess later told News 9 he believed everyone had been contacted.
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Authorities later confirmed all staff and patients were accounted for.
An emergency alert was sent to cellphones across southern New Hampshire at 2:39 p.m., warning of a potential gas leak.
The alert urged people in the area to extinguish burners or other flames, avoid the area and prepare to evacuate.
All firefighters were ordered out of the building as conditions worsened, and crews continued battling the fire from outside. Heavy smoke could be seen pouring from the roof.
Buxton said firefighters had difficulty accessing water because some hydrants had apparently frozen. He said the gas issue was limited to the single building.
Amherst Street was closed between Somerset Parkway and Thornton Road.
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Liberty Utilities said its crews were on scene working with fire officials.
“The safety of our customers and communities is our highest priority,” the company said in a statement. “Residents should continue to follow safety precautions as directed by Nashua fire department and other public officials.”
People nearby reported hearing a loud boom.
Eversource said power was cut to about 10 customers in the area and would be restored when it’s safe to do so.
Officials at Nashua Airport said the fire had minimal impact on airport operations.
The fire was determined to be under control by 6 p.m. There is no ongoing threat to public safety at this time.
While the cause of the fire remains under investigation, investigators are now looking into whether falling ice may have damaged the gas line.
Earlier, News 9 spoke with Bob Duval, an expert in fire investigations, who said determining the cause will be a complex process.
“They’ll take in the scene as it is now and begin to formulate a plan on how to get to the points where they need to investigate that building, with the compromised status of the building, after the collapse and the explosion,” Duval said. “They’re going to have to do it layer by layer with heavy equipment and possibly use drones and/or maybe robots, little tanks or tracked vehicles to get in and get pictures in areas where they can’t safely put people to see what they need to see.”
Toomey said the fire is a good reminder to leave immediately and call 911 if you smell gas.
“I think the biggest thing today, a safety message, is if you smell gas, call 911 and get out,” Toomey said. “That’s the biggest message out of all of this. We hopefully will have more answers, hopefully tomorrow, but I’m not confident of that quite yet.”
Fire crews will be back on Tuesday to continue investigating.