SLIPPERY ROCK — A fire that caused an estimated $500,000 damage to a dental office Tuesday afternoon is being investigated by a state police deputy fire marshal.

An officer with the Slippery Rock Volunteer Fire Company suggested the cause could be electrical.

"It looks like it started on the side of the building around the electric meter," Assistant Chief Ron Steele said this morning. "It seems to be an accidental fire."

Office staff reported no recent electrical problems at the building, he said.

One of the dentists and two employees were at the building this morning, but they declined to comment.

The fire was discovered about 5 p.m. at the one-story building that houses the Allied Dental Center. Authorities said the fire broke out just 30 minutes after the last employee left for the day.

Trooper Brian Crouch, a state police deputy fire marshal, sifted through the rubble this morning in search of clues as to what started the fire at the brick building at 234 S. Main St., where five dentists practice.

"The good thing is that nobody got hurt," he said.

The blaze is not considered suspicious, but the fire marshal's office was called to investigate because of the extent of the damage, Steele said.

Slippery Rock firefighters did not return to their station until 7:45 p.m.