A small methane gas fire that was not doused because of broken equipment sparked a massive coal dust explosion last April that killed 29 miners at Massey Energy Co. Upper Big Branch mine, the U.S. Mine Safety and Health Administration (MSHA) said January 19. Massey records and evidence found deep inside the West Virginia mine points to poor maintenance in the deadliest U.S. coal mine explosion since 1970, MSHA officials told reporters during a conference call. The agency expects to finish its probe in a few months, but said it wanted to issue preliminary findings. Those findings include worn and broken equipment investigators believe contributed to the initial fire and made it impossible to put out, and poor housekeeping that allowed excessive amounts of explosive coal dust to coat much of the mine just before the blast. Investigators believe the explosion started when badly worn teeth on a 1000-foot-wide mining machine created a spark that ignited as little as 13 cubic feet of methane. Tests that Massey resisted showed some of the machine 48 water sprayers for controlling dust and dousing sparks were not working at the time. When the flames ignited coal dust, it unleashed a blast that killed everyone, including co-workers more than 1 mile away. Investigators are still trying to determine whether the mine ventilation system was working properly at the time.