[stansdds]

The liquid portion of gasoline does not burn, it is the vapor that burns. When a fuel tank registers empty, the tank is not really empty. Fuel tank pick ups require a small amount of space between the bottom of the pick up tube and the bottom of the tank. So a tank may be empty, but there may still be several gallons of fuel remaining and that means lots of vapor. The only way to prevent a empty or partially emptied tank from catching fire or exploding is to either line the tank with a collapsing bladder or pressurize the tank with an inert gas, usually CO2.