The fire at Masjid-e-Zakariya, 182 Sobieski St., was reported at about 4:30 p.m. and within minutes went to three alarms. Almost as quickly, investigators learned how it started.

A plumber was working with a welding torch in the rear of the mosque, officials said.

"He started a fire in the insulation in the wall," said Fire Commissioner Cornelius J. Keane. "He tried to put it out and it got away from him."

"We are investigating it further," Keane added.

The old, wooden building, which stretches from Sobieski Street to Sweet Avenue, was the former home of Holy Mother of the Rosary Cathedral. It was sold in 1993 by the Polish National Catholic Church to Darul Uloom Al Madania Inc., a nonprofit religious organization that uses it as a mosque and school.

Flames spread up the wall and through the ceiling in what was the apse, as the conical roof burned through to its timbers. The collapse of a horizontal timber caused onlookers on Sweet Avenue to jump back.

An estimated 80 firefighters were on the scene at the height of the blaze, battling poor water pressure in the neighborhood as well as the flames.

After the third alarm was sounded, three additional pumper trucks were summoned in order to get more water.

"We were in there initially and our firefighters were driven out in an emergency situation," Keane said. It took approximately 12 minutes to make sure all firefighters made it out safely, he noted.

The plumber was working alone in the building and safely escaped. No injuries were reported.

"It spread like a wildfire," said Dr. Khalid J. Qazi, president of the local American Muslim Council.

Renovations were under way inside and a new gallery had been inspected by city officials just last week, he said.

Investigators from the federal Bureau of Alcohol, Tobacco and Firearms and the FBI responded and conferred with members of Buffalo's Fire Investigation Unit.

The findings by the investigators were a "great relief" to Qazi.

"I think, for me personally, the biggest relief was it was an accident; it was not mischief or vandalism," Qazi said. "That was lucky nobody got hurt and nobody got trapped inside."

"We truly appreciate the promptness with which the Fire Department, police and federal agencies showed up on the scene - immediately," Qazi said. "That was another reassuring thing."

Even as firefighting efforts continued in the mosque, afternoon prayers were said in the school next door.

"It's a fair-sized mosque," Qazi said, where at least 50 people come to pray on an average day and at least 200 on Fridays.

Mosques, he explained, are open to all Muslims, regardless of affiliation or geography. And that solves one of two pressing issues the fire has raised.

"There are other mosques in the area" where Muslims can pray, he said.

The second issue is rebuilding.

"It's going to take a lot of resources to put it back in shape. I'm hoping the community will come through again," Qazi said.