WHITE SWAN -- A fire in the ventilation system at the Yakama Forest Products mill in White Swan caused $25,000 damage early Friday, firefighters say.

The fire was reported shortly after midnight at the mill on Medicine Valley Road. Mill employees were already wetting down the outside parts of the air handler system when the first fire crews arrived, according to a news release from Yakima County Fire District 5.

It took about four hours to access the duct work in order to extinguish the fire, which was confined to the air system.

An unknown mechanical problem was apparently responsible for starting the fire.