what would worry me about a house fire is when theres a semi-auto with a round in the chamber. when the round cooks off, it's going to shoot wherever the barrel is pointed, AND cycle the action to load another round.
This will continue until either A) the mag runs empty, or B) a round in the mag explodes before it gets chambered and takes out the magazine, and possibly the entire frame.
of course, there's also the possibility that the heat would kill the heat temper of the spring steel, and the weapon would never cycle back closed on a new round, and the rest will go off as if they were sitting on the shelf.
All I know for sure, is that I don't want to find out!! (with any of my own firearms anyway...