Here is the detail so far from RR forums. Eastbound train of 5 engines and 73 oil cars parks in a siding 7 miles west of town. Engineer leaves about midnight, ties down train brakes and leaves one of 5 engines running so as to re-charge air brake system. That 5th engine an hour later catches fire, local FD responds. To stop fuel from pumping into the fire they turn off the engine, douse the fire. Shortly brake air bleeds off. Some minutes later a trackside resident sees the train going by, lights out, high speed, heading towards the town. Engine and maybe 12 cars make it through the town, train splits and other cars run into propane cars in a siding causing explosions.
FD says they left the engine in the care of railroad men, not sure what the MMA RR is saying at this time