COLUMBIA FALLS, Montana — The Columbia Falls Weyerhaeuser MDF plant was rocked by an explosion and fire Wednesday. The explosion may have been caused by an electrical arc in the power distribution center, which runs both lines of the plant, Columbia Falls Fire Chief Karl Weeks said. No one was injured in the blast, which blew walls out of the building and garage doors off their hinges. The electrical surge at the time was so great that Flathead Electric Co-op noticed the power draw on the grid, Weeks said. …The production lines were not damaged. The plant has two lines and is capable of producing 265 million square feet of 3/4-inch MDF annually. The plant has about 200 employees. …Weyerhaeuser spokesman Matt Peterson said, “We will resume normal operations when it is safe to do so.”