Now we're getting somewhere! Propane is very dangerous stuff. Overfilled tanks can vent gas if subjected to heat and the gas is heavier than air. It collects and creates a teriffic explosion when it goes. But oxygen is scarier still. It feeds the flames and makes them burn with terrible intensity. It's not unimaginable that some people in an apartment complex might have oxygen tanks for medical purposes.
Accident or terrorism? I'm one of those wishy-washy people who prefers to base my opinions on facts. There are some cases like Flight 800 where I'm still very much an agnostic. We'll probably know soon enough what caused this one though.