BUFFALO, N.Y. — Authorities on Thursday identified the Buffalo firefighter who died in an explosive fire at a downtown building as Jason Arno, a 37-year-old married father.

“This is a heartbreaking time for our city," Mayor Byron Brown said in a statement. “Jason Arno showed his bravery and commitment to fire service by putting on his uniform and carrying out his sworn duty to protect and serve the residents of this city. Tragically, he lost his life protecting others.”

Arno's body was recovered from the brick commercial building several hours after he was reported missing following an emergency evacuation order early on in the four-alarm fire, Fire Commissioner William Renaldo told reporters Wednesday. He said Arno was 30 to 40 feet (nine to 12 meters) inside when there was a partial collapse.

“We don’t know exactly how he passed. We do know he was in that immediate collapse zone,” Renaldo said. “There was a mayday called and the rest of our firefighters, the rescue personnel that were on scene, had to evacuate the building immediately. And unfortunately, they weren’t able to retrieve him at the time.”

The fire may have been smoldering for some time before anyone noticed, Renaldo said, and is believed to have sparked an explosive backdraft that knocked firefighters who were outside the building off their feet. Video shows flames shooting from the ground floor of the building and a sudden explosion that sent debris flying and enveloped fire crews in a cloud of ash.

“If a fire is smoldering for a certain amount of time and oxygen is introduced abruptly, it’s basically sucked into the building and blown back,” Renaldo said.

The cause remains under investigation, but Renaldo said workers were using blowtorches on the building’s exterior before the fire and that heat may have transferred through brick or mortar and ignited paper or other combustibles inside. The building, which housed a theatrical costumes shop, was unoccupied when the fire started, Renaldo said.

Arno had been a firefighter for three years.

“A father, a husband, a son, a brother and a friend. Our deepest condolences to his family and those that loved him and those that knew him,” the Buffalo firefighters' union said in a post on social media. “We, the proud firefighters of the city of Buffalo will honor our fallen.”

Brown requested that city landmarks be lit in red in Arno's honor beginning Thursday. City flags were flying at half-staff.