I came across this interesting account of a locomotive boiler explosion in Smithville, TX from March 28, 1911. The engine had just been overhauled, and someone had screwed the pop valve down all the way. The force of the explosion must have been incredible:
http://www.texasescapes.com/TexasRailroads/Locomotive-Boiler-Explosion.htm
Yeah, Ray, I have read other accounts of boiler explosions. Scary stuff. And yet, in the making of one of those films about the building of the first transcontiental railroad or something, when they had two trains colliding, they had to use a ton of explosives, which caused only superficial damage to the two locos. Go figure.
Yep, a real boiler explosion would have been caused by excess pressure in the boiler, not by external damage from a wreck. Otherwise locos would have been blowing up all the time in wrecks. But of course even back then film makers always go for the big kaboom regardless of reality.
Boiler explosions have sent many a warship to the bottom.