Holy cow - what was going on with that exploding water heater? Was that just an example of one bursting, or what?
*EDIT* - wow. Definitely on the DO NOT DISABLE list!
http://kwc.org/mythbusters/2007/11/episode_89_exploding_water_hea.htmlExploding Water Heater
Myth: A water heater can explode like a rocket through the roof of your house and land 500 ft away
Water heaters have two protection mechanisms to prevent them from rocketing off:
Thermostat in an emergency cutoff switch
Temperature and pressure valve (T&P valve)
The T&P valve is a pipe sticking out near the bottom of the water heater. Adam hypothesized that a homeowner might see the T&P valve and think that it was an old pipe that was no longer being used. Seeing that it occasionally leaks water, this hypothetical homeowner might cap it off, thus disabling it.
6 gallon tank test 1
The MythBusters first tested how the tank responded to the failure of its safety mechanisms. They setup a six gallon water tank in a container outside their headquarters. They removed the thermostat in the emergency cutoff switch, rendering it useless. At 165 degrees, the T&P valve started to release, preventing explosion. They next disabled the T&P valve and rigged up their own emergency release valve. At 248 degrees, the tank started to rapidly lose pressure and they had to end the test.
So much steam was released from their own emergency valve that they decided to take their setup to Alameda for additional safety. The tank failed after 20 minutes at 370F/191 psi. Rather than launch like a rocket, the top split enough to allow steam vapor to spread across the concrete.
30 gallon tank
Satisfied that they could get a tank to rupture with the safety mechanisms disabled, they moved up to a larger tank. They filled a 30 gallon tank 80% full with 24 gallons of water to see if they could get a good mixture of steam and water. After 50 minutes (350 psi), the tank launched like a rocket -- it took several seconds for the tank to land and there was tank lining scattered everywhere.
52 gallon 'Home' test
Their final test was to confirm the conditions of the myth. They built a tiny home with roof to California code. The house included a door, a window, and simulaid dummy in a bathtub. At 350psi, the water heater shot rocketed through the roof as the rest of the house exploded into little bits. The tank went through two layers of 2x4 trusses in the roof while the steam and water ruptured the rest of the structure.
The MythBusters' researchers found two confirmed cases of this happening in real life. In 2001, a burrito shop's water heater launched 439 ft into the air. In Minnesota, a water heater went through all the floors and roof of the house and another 150 ft into the air. The house was knocked off its foundation, two were injured, and a dog was killed.
Adam's lesson to the viewers is:
When they see that pipe sticking out of their water heater that doesn't go anywhere that's dripping water, that they don't go, "oh, maybe I should cap that."
confirmed
