A bearing failure led to explosions and fire Tuesday at the Plum Creek Medium Density Fiberboard plant in Columbia Falls.

Plum Creek spokeswoman Kate Tate said Friday that a catastrophic failure of a bearing on a raw material feed line triggered a series of events.

“The failure ignited both wood fiber and the belt, and heat from that fire caused the insulation on the duct pipe above it carrying wood fiber to catch fire, and then the fire on the outside of the pipe had enough heat to cause the fiber on the inside to catch fire,” Tate said.

The burning wood fiber then caused a series of explosions in the ductwork at the sprawling seven-acre plant.

“Knowing this, we can design fire protection for this area of the plant to prevent future bearing failure issues,” Tate said.

Since the fire, MDF plant employees have been working their normal hours, but instead of their regular jobs they are helping with cleanup and repairs.

Company officials previously estimated the plant could be back up and running within 30 days.

The explosions and resulting fire drew 10 fire departments, an ambulance service, two law enforcement agencies and the county’s emergency services department.

Columbia Falls Fire Chief Rick Hagen said nearly 70 firefighters battled the fire in rotating teams split into three zones.

Although the majority of the fire was put out within six hours, an undiscovered fire in a second location flared up Wednesday morning.

No damage estimates have been compiled yet, but Tate said equipment damage was minimal thanks to  the work of firefighters.