PORTLAND, Maine – Federal investigators with the Bureau of Alcohol, Tobacco and Firearms were at the Robbins Lumber Company Mill in Searsmont Monday, assisting the State Fire Marshal’s Office in the investigation. At this point, the cause of the fire has yet to be determined. A select board member from Searsmont says sawdust may be behind the explosion. …Richard Meier is the principal expert at Meier Fire Investigations. He’s researched hundreds of fires all over the world, including in mills like Searsmont. “this has the hallmarks of possibly being a dust explosion, in which case the cleanliness and housekeeping at the mill may be a major contributor.” He stresses the investigation is still in the early stages and no conclusions have been drawn yet.