Mythbusters Water Heater Rocket
Anyone seen it yet? AWESOME! Best explosion I've ever seen on MythBusters and there was no chemicals, flammables or explosives involved. http://www.spikedhumor.com/articles/132341/Mythbusters_Water_Heater_Rocket.html

I watched this the other night. They just keep topping themselves in explosions. I've always wanted to submit a couple of myths but just never have.

They have cool jobs.

Wow, methinks I'll build a HD steel crate around my hot water heater ;) Scary stuff. Every old hot water heater I've seen fail ends up just leaking water from the bottom of the tank and a slow leak at that.

Well this is an extreme case. The reason your average water heater leaks eventually is because it gets rusty and the pressure eventually cracks the tank. Nothing dramatic because under normal circumstances there's not THAT much pressure in there. Mythbusters defeated the two primary safety devices: the thermostat (actually plural - most heaters have two of them) that would normally cut off the heating elements at a certain temperature AND the pressure relief valve which is there just in case of the highly unlikely event of a failure of the thermostat that keeps the heater turned on. The problem is, as they pointed out in the show, the first sign that you have a faulty thermostat is when water starts dripping out of the drain for the emergency pressure release valve. Your average idiot says to himself "Look, I have a leak. I'll just stop up that pipe.". Well now there's no safety mechanism and the thermostat is failing and the pressure builds. As impressive as that explosion was, can you imagine what it must be like when a boiler fails catastrophically? Same concept but higher pressures and instead of flimsy sheet metal a boiler is made of cast iron making the shrapnel a LOT more dangerous.

That was incredible!

Yeah but most boilers are monitored by humans or complicated electrical systems. When something goes wrong they cut the heat and dump the steam. Alltho, if it were to suddenly blow a weld there is no warning for that. Most steam engines ran between 125 and 300 PSI. that heater blew at 350. but it was only rated 150. boilers are rated higher then that. but yea boiler explosins are a horrific sight. Anybody remember the SS Norway?

Lots of steam locomotives had boiler explosions in the 1800's. I've seen photos - they were horrible things to see.