I used to work in a foundry during university holidays, and when I first turned up one of the large sheds over a furnace was being repaired to replace an absent roof. The explanation I was given was the old iron scrap castings were being melted down, and some had been left outside in a pile in the rain. They were supposed to be checked for water pockets, but weren’t, and the roof was taken off in a ejection (and then shower) of molten iron.
But it paid for a student’s beer, so it was worth it.
