From LE:
But how does a tank overheat? Wouldn’t it have to be exposed to a very hot fire for some period of time?
The most common way for a tank to overheat is by normal atmospheric exposure, but certainly, exposure to fire will increase the temperature of a propane tank.
Propane facts:
Propane boils (converts from liquid to vapor) at – 44 F (-42.2 C)
A gallon of propane converts to 270 gallons of vapor.
The ignition temperature of propane is between 920 F and 1120 F.
Propane requires an air mixture of between 2.15 and 9.60 percent propane for ignition.
Standard DOT 20# propane tanks have a pressure relief valve rated at 250 PSI. The actual pressure at which the valve will release is dependant on many factors including age of the tank/valve, how much propane is in the tank and conditions outside the tank itself.
The following are vapor pressures of propane at various temperatures:
70 F = 96 PSI
100 F = 127 PSI
110 F = 230 PSI
