Are you shocked this led to a fire? Welding on the wall of a boxcar that is full of paper goods.
This is the exact set up OSHA warns us of…
1910.252(a)(2)(x) Noncombustible walls.
If welding is to be done on a metal wall, partition, ceiling, or roof, precautions shall be taken to prevent ignition of combustibles on the other side, due to conduction or radiation, preferably by relocating combustibles. Where combustibles are not relocated, a fire watch on the opposite side from the work shall be provided.