Dad- the standard pressure relief valve setting is 250 psi. In a fire, pressure goes up, valve opens, released propane burns but does not explode.
However, a pool fire under a tank, or a jet fire impinging ON the tank does 2 things. It raises pressure- AND- at the top of the level of liquid in the tank, a stress line is developed. Metal below liquid level transfers heat to liquid. Metal ABOVE liquid cannot transfer heat to vapor. Uneven heating results, causing deformation of metal. At around 121% above the PRV setting, under THOSE conditions, wall can tear, and BLEVE.
Changing temp of propane makes major change in pressure inside tank.
70 F = 96 PSI
100 F = 127 PSI
110 F = 230 PSI
Under MOST circumstances, the PRV does it's job, and no explosion. However, heat it rapidly enough, pressure increase is SO rapid, the PRV cannot keep up. And propane tanks are built to a VERY different spec than ordinary compressed gas cylinders. Oxygen tanks are at 2080 psi, and have a rupture pressure far higher.
Yeah, I am just a veritable fount of obscure and useless info.