It's very rare to get a gas tank to explode (as others have pointed out). You need to have very little fuel (or better, none at all) in the tank before a spark will cause explosions.

Take a 2l plastic soda bottle, fill it 90% full with petrol and (with tongs from a distance) drop in a lit cigarette. I've tried to get the bottle to go bang multiple times and it never happens - the ciggarette is extinguished every single time.

Then empty that bottle until there is less than 5ml of petrol in it, close the bottle and shake it up to get a rich mixture, and then repeat the experiment (I've gotten fairly big bangs every single time, this way).

The TLDR of it all is that there is danger of explosion when the tank is emptied, not when it is full, because the fumes cause explosions, not the liquid state of the fuel (which just catches fire).