PORTLAND, Maine (AP) — Firefighters who responded to a fire at a Maine lumber mill used tactics that inadvertently contributed to a massive explosion that killed three people, according to a report from federal investigators. The fire companies tried to extinguish the May 15 fire inside a silo at the Robbins Lumber mill in rural Searsmont, Maine, by injecting it with water — unaware of warnings from the manufacturer that doing so would be dangerous. The report recommends that fire departments make sure firefighters choose appropriate tactics for silo fires and never direct water or foam into oxygen-limiting silos.