I heard a mention that Mythbusters tried to see what would happen if an LP tank were in a fire. I assume this was a BBQ-sized, gas grill type of tank. I heard they claim the relief valve will prevent the tank from exploding. But, can someone describe how they tested this, such as:
Was the gas flowing, or not?
Was the tank full? Perhaps they expressed this as a percentage full…
What was the heat source?
How was the tank exposed to the heat source?
How much of the tank was exposed?
and, for how long was the exposure sustained?
I have done work in this field, and I am sorry I missed this one.
Going from memory: They started with a full, modern tank with the safety valve in place. They built a model garage filled with firewood, put the tank in the middle, doused the lot with gasoline and lit the whole mess. Result was the relief valve opening and adding burning propane to the mix.
They then disabled the relief valve on another tank to simulate an older tank. Details were edited out to prevent us yahoos from blowing ourselves up.
Rather than the structure fire they moved to a large LP ring, fueled by a remote tank. The tank swelled and eventually burst, but did not ignite, the LP blew out the gas ring.
Finally, they rigged a 9mm pistol to shoot the bottom of the tank to create a rocket effect. (which was the basis of the myth, that the tank would launch like a rocket) Again, they heated the tank nearly to bursting before firing the pistol. The tank took off on the stream of LP, which again did not ignite, purely launching on the pressure of the gas.
That’s about it - they had an extremely hard time getting a BBQ tank to misbehave.
A standard tank in a small structure fire resulted in the relief opening and producing a small jet of fire. No explosion.
BBQ tank with the safeties disabled and placed on a fire did eventually fail from overpressure. The cylinder was expanded to nearly a sphere before it failed. It went “boom” but there was no BLEVE and no fireball. The sudden release of propane actually smothered the fire and extinguished it.
The net conclusion is that BBQ tanks are safer than we give them credit for. Yes, you have to respect the stuff, but it’s not likely to explode in residential conditions. They were trying quite hard to make a tank explode and really didn’t have much luck at it.
Also, in the James Bond special, they attempted to make the large 400lb tanks explode by shooting them, with equal lack of success. I think they had to use detcord to finally get a fireball.
At work I have a propane forklift,which uses 60 lb tanks. Like a barbacue tank, but skinnier and about 3x as tall. One day one of my employees tried to change the tank without checking that the valve on the new tank was was closed. It wasn’t. As soon as he partially tightened the fitting, the tank started to vent. As LP is cryogenic, there’s no reaching in to turn off the valve. We had to wait about 10 mins for it to fully vent, keeping everyone at a safe distance. Fortunately, there were no ignition sources nearby and no one was hurt. Scary, though.
There were two other tests (these guys really love to blow things up). They create a weakpoint in the bottom of the tank (the argument was they were simulating a rust spot) and they heated up a tank that was about three quarters empty (based on theory that the gas inside would vaporize and make a better fireball).
Yes, I think this was an example of them nit-picking over the definition of plausibility. They set a standard that the myth was something like 150 feet up in the air and then declared it wasn’t proven because their tank was only launched 100 feet up in the air.
I feel they had a better point over the issue of it being launched at all. They demonstrated that a propane tank would not launch itself even one foot under any reasonable conditions - so at that point the myth was busted. Rigging up a tank so it could be launched by heat and then quibbling over the height it reached was a poor justification for a plausible verdict.
