I don't think there are any oxygen lines except in the cockpit. Oxygen generators are used in the cabin. They start to operate when the masks are pulled down. They do generate a bit of heat, but I don't think they would start a fire since they are used ocaissionally. They did bring down that Air Trans (not sure of the name) A/C a few years back, but that was because they were in a box in the bag pit and hadn't been discharged like they should have been. I believe they caught a tire on fire and it escalated from there.