The cause of a Monday fire that damaged a two-story house in Butler remains under investigation by the state police fire marshal's unit.

But the blaze at 441 Mercer St. was not believed to be suspicious, Trooper Sean Christofferson, a deputy fire marshal, said Tuesday.

No one had recently been living at the house and no one was injured, authorities said. Electrical service still was connected to the home, Christofferson noted.

He said it appeared that the fire started on the outside of the house near the front.

Neighbor Elizabeth Jimenez, who lives across the street, told the Butler Eagle Monday that she was home when she heard a loud noise that she thought was thunder, just before the fire.

“I was cooking when I saw the flames (through the window),” she said.

The Butler Fire Department was called to the house at 1:55 p.m. Crews were there in five minutes, Butler Fire Chief Chris Switala said Tuesday.

“Fire was showing from the front of the house on the first floor,” he said, when firefighters arrived.

Hose lines were deployed for an initial exterior attack. A short time later, an attack crew went in through the front door.

“It was knocked down within 10 minutes,” Switala said.

The fire, he said, extended to the second floor, but the basement was not involved. Christofferson said the worst of the fire was confined to the first floor front area.

A damage estimate was not available, and it was not immediately known if the home was insured.

Christofferson inspected the damage and met with the owner Monday. He declined to release the owner's name. Switala said he did not have the name of the owner.

According to the Butler County Assessment Office, records listed Brian and Sandra Burnside as the owners. They bought the house in 1997. They could not be reached for comment.

It was not immediately known how long the house had been vacant, Christofferson said. He noted that there still was some furniture in it, and the owner told investigators that he regularly checked on the house.

Christofferson said he also spoke to neighbors, who reported hearing or seeing nothing suspicious around the time of the fire.