SUNBURY - A state police fire marshal isn't sure how Saturday's fire started inside the kitchen of Northumberland County Prison, but he is sure it was an accident.

Trooper Kirk Renn said Tuesday he narrowed the cause either to electrical or spontaneous combustion of rags on a prep table in the kitchen.

"I can't rule out two separate causes," he said.

"There was no one in the kitchen for 1 1/2 hours prior to the fire," Renn said.

Total damage is estimated at $25,000.

The fire caused heavy smoke in and around the kitchen, which is in the basement. It was reported to Northumberland County 911 at 8:35 p.m. and extinguished with a fire extinguisher.

Exhaust fans were used to ventilate the area. Firefighters were on scene about 90 minutes. City police officers were also on scene.

Inmates on the south side of the prison were moved to the north side, Russ Wertz, second assistant chief of the Sunbury Fire Department, said at the scene. Rick Shoch, Northumberland County commissioner, who also was on scene, had said female inmates were moved to the prison's law library, and he believed some inmates were in the yard.

All inmates were returned to where they belonged inside the prison shortly after 10 p.m., Shoch said.