BERRYVILLE -- An explosion at Berryville Graphics on Saturday heavily damaged a portion of the plant but caused no serious injuries, fire officials said.

Firefighters were dispatched to the plant on Jack Enders Boulevard about 7:30 p.m. Saturday in what became a marathon effort for nearly a dozen fire companies to extinguish the blaze.

The fire reportedly began in one of the printing company's baler rooms, said Jason Porter, chief of the John H. Enders Fire Company.

The facility was evacuated.

Porter said although the cause of the fire is still under investigation, it is suspected a buildup of dust and other paper particles in one of the baler's ducts contributed to the explosion.

At least two company employees were in the large baler room at the time, he said, but no one was seriously injured. Two firefighters were treated for minor injuries at Winchester Medical Center and released, he said. He declined to identify the men.

Berryville Graphics officials could not be reached for comment at the plant Sunday, where a cleanup effort was under way. There was no visible damage to the building's exterior.

The investigation will be turned over to Clarke County building inspector Gary Pope. No foul play is suspected, Porter said.

Fire and rescue companies from Clarke, Frederick and Loudoun counties, as well as Winchester units and personnel from the Mount Weather Emergency Operations Center were dispatched to the plant in a "tremendous response," Porter said. Crews cleared the scene after 3 a.m. Sunday.

Firefighters made several cuts into the roof to better access duct work, he said, while others battled flames inside.

"We were constantly rotating crews," he said. "With the heat and the humidity, it really wears down on people."

Firefighters were called again to the plant about 9 a.m. Sunday after power was turned back on to the plant, Porter said.

"We had some embers and dust get inside of a wall," he said.

Frederick County companies, along with Jefferson County, W.Va., units, assisted Clarke County companies Sunday morning.

Berryville Graphics, owned by Providence, R.I.-based Bertelsmann Arvato AG, is Clarke County's largest employer.