A completely full tank of gasoline will not explode like tnt, even if you tossed a match in it. A nearly empty tank, on the other hand, has a high volume of explosive vapor…big boom, a bit of shrapnel and then its done. There probably wouldn’t even be a fire in that case. In a car accident where the fuel tank is damaged, the real killer is from a spark igniting some spilled fuel which ignites the plastic, rubber and fabric in the car, which can then lead to an explosion as the tank empties and the fuel gets heated. It takes time and while it can lead to a big problem, if you are conscious and not trapped somehow, generally you have enough time to get out and to a safe distance before the car becomes a raging inferno and possibly explodes. Of course, we are building cars out of duct tape and scrap metal, so probably more likely to have issues.
On a side note, how about a chance to blow up a gas tank while removing it when your skill levels are low? It’ll be FUN!
This article that was at the top of my google search for “gas tank explosion” uses big words and science to explain what happens in a car crash:
http://jalopnik.com/why-cars-explode-into-fireballs-and-why-they-usually-do-560552028
