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 silo then blasted skyward like a rocket as flames and a shock wave from the explosion hurled workers and firefighters away. 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. Officials with the town of Searsmont said in a statement that a final investigation into the explosion is still ongoing. The mill is a part of the historic lumber and wood products industry in Maine.