A minor explosion at a closed Boise Corp. plywood mill likely was caused when flames from a small fire were sucked into an air-compressor filter, fire investigators from Jackson County Fire District No. 3 concluded.

Neighbors of the plant at 1795 Antelope Road, White City, reported hearing an explosion and seeing smoke at about 9:30 a.m. Friday.

What firefighters described as a "low-order explosion" blew out a large metal vent and buckled metal siding in the compressor room.

A fire sprinkler system doused the flames before they could spread.

"We could see a black column of smoke from the station, but by the time we were part way here, the smoke was white, indicating that water was getting on it," said Don Hickman, a deputy fire marshal with the district, which has its headquarters just down Antelope Road.

Hickman said sparks from a fan motor likely started a small fire in a barrel of absorbent material used to soak up spilled oil.

Big fans that help cool the compressors sucked the flames into a compressor air filter, igniting it.

Hickman said only one compressor was running as crews winterized the closed plant. No one was injured.