A Tank FULL of FUEL will never EXPLODE - Why??

You should have seen someone throwing match sticks inside the Petrol/Diesel tank of Vehicles or some huge tanks in many movies after which an EXPLOSION takes place. Will this action of just dropping a small match stick explode the whole tank??

                 

                 An  Interesting fact is, the chances of explosion is less when the tank is completely filled with fuel and there are MORE chances of a BLAST if the FUEL present in the tank is LESS.In brief, the chances for the tank to explode depends upon the quantity of fuel (COMBUSTIBLE MATERIAL) present and the SIZE of the TANK.   

       

                .An explosion occurs as a result of IGNITION ( a small fire). Fire is a CHEMICAL REACTION. There are THREE things necessary for a FIRE to take place.They are OXYGEN, HEAT and FUEL. The fuel must be in GASEOUS FORM to catch fire.

                  The figure above is called the FIRE TRIANGLE. The proportion of AIR present inside the TANK is also very important.The air-fuel mixture doesn't get ignited always. The air and fuel must be in certain proportion for the mixture to get ignited. The graph below shows the range of air-fuel ratio's which can get ignited 

               As you can see from the GRAPH above. There wont be any fire in the two cases if.                                                                         1. Fuel is more and volume of AIR is very less

2.AIR is more and quantity of FUEL is very less

               When the FUEL inside the tank is MORE the vacant space inside the tank will be very less, so only small amount of FUEL VAPOUR will be present in it.So, even if you drop a FIRE STICK inside the tank there wont be sufficient air for the FUEL to EXPLODE.The upper layer of the FUEL may catch fire but it will definitely not EXPLODE.That's why the chances of a BLAST is less if the tank is FULL of FUEL.

                 

                  If the TANK is half-filled with FUEL, there will be much free space in the tank and it will be filled with FUEL VAPOR. If someone introduces a small fire inside the tank the tank in this CONDITION surely the tank will EXPLODE.

                     Now I hope you have understood all the concepts and the reason WHY A TANK FULL OF FUEL WILL NOT BLAST. Thank you :)

                    

                  What go you think about this post? Please let me know through your comment.