Last night on Mythbusters they tested whether a faulty water heater could actually explode and destroy a home. They disconected the electrical safety shutoffs and disabled the relief valves to mimick a faulty heater. They tested a 30 gallon in the open by it self, it shot up like a rocket almost 500 feet in the air and totally destroyed the housing around the tank . Then they put a 52 gallon in a small one room house that they built and specified that the roof was built to California building codes. When the pressure built up this tank took of like a rockect again straight through the roof like it was paper and blew every wall out to pieces. They said it was one of the best explosions they have ever created and that the tank would have easily shot through multiple floors of a building with the force it exploded with. Hope those TPR valves are functional.
I saw that one a few weeks ago–boy was that a fantastic explosion. 
Here is a link to video from that segment of the show where they blow up a water heater … 
http://www.youtube.com/watch?v=JmJoyuUJj2Q
And here is another one with a water heater explosion …
That’s awesome. Thanks for the link Robert. I think I’m going to check my valves this weekend!
That was awesome Dominic, unless it is one of our houses. Yikes!
Seriously. Anyone know if that’s ever happened to a real house?
I saw it a couple of weeks ago.