If there's one thing that annoys me then it's the way Hollywood using exploding vehicles! They don't explode! If they exploded like Hollywood vehicles do then we wouldn't be able to drive them around safely!!
In order for an explosion to occur then all the right components must be present in as close as possible the right quantities throughout the mixture. Petrol requires air in it to burn and that is what petrol does - it burns! In a car engine the fuel and air is premixed in the correct quantities to cause the mixture to burn rapidly in the combustion chamber. Note the word 'combustion' NOT explosion. It burns so rapidly, turning a small amount of fuel and air into a very large volume of hot gas that people talk of an explosion - but it's combustion.
Now if you set fire to a petrol tank it will burn rapidly and will heat up the metal around it and could cause the tank to rupture spilling burning fuel everywhere - but it will not explode. If you do this to a larger vehicle or vessel the same thing will happen.
There is a seemingly contradictory element to this... If you weld an empty petrol tank it could very well explode! No, it may very well combust so rapidly and with so much force it will rip the tank to shreds and throw shrapnel around. As good as an explosion anyway. This is because the tank is NOT empty but an 'empty' tank enjoys about the correct mixture of petrol vapour and air. So if you find yourself wanting to weld a petrol tank then fill it with water first!.