No one was injured in a fire at Weyerhaeuser’s medium density fiberboard plant in Columbia Falls Wednesday night, though the plant saw some water and other damage.

The initial call came out as an explosion and fire, though Tom Ray, vice president of Northwest resources and manufacturing said there was no explosion and the fire was small.

Ray said it was not an explosion, and what residents heard were the duct gates opening quickly to prevent an explosion as part of the plant’s mechanical fire-suppression system.

“It is very loud, but not an explosion,” Ray said.

Four Weyerhaeuser employees were transported to a local hospital and treated for smoke inhalation, and have since been released, Ray said.

The fire happened on production line two about 8 p.m., said Columbia Falls fire chief Rick Hagen. He said the initial fire was knocked down by the automatic deluge fire suppression system on the line and Weyerhauser employees.

Firefighters from Columbia Falls, Bad Rock, Whitefish and medical crews from Three Rivers Ambulance all responded. It took them most of the night to go through the line, battling the smoke to find any hot spots and to water down wood material to make sure the fire was dead out, Hagen said. Firefighters were working on the third floor of the massive building.

They didn’t get off the scene until about 1 a.m. he said. He said the fire suppression systems in the plant appeared to have worked properly.

The exact cause of the fire remains under investigation.

Fires over the years have not been uncommon at the plant, but since an explosion and fire a few years ago, the company bolstered its fire suppression system.

All told, 22 firefighters from Columbia Falls responded, 11 from Bad Rock and three from Whitefish. Three Rivers provided rehabilitation for firefighters who were in the plant for extended periods of time. Some employees were also checked out for smoke inhalation.

This story has been updated from its original version to reflect that the company believes there was no explosion.