cargosales
There have been at least 2 accidents attributed to smoking in toilets starting a fire that led to loss of ALL on board. Search the air disaster sites for details. One was a DC10, and I can't remember the other type, EgyptAir? Hundreds lost. In the more famous of the 2, the aircraft made it onto to the ground, but everyone onboard was dead from the fumes (the pilots passed out during landing roll). That's how they could determine the cause.
Makes you wonder how many more unexplained hull-losses were caused this way. There's a lot of plastic in planes.