Actually nothing in a luquid state can burn it's the complete opposite. A liquid state removes the one portion of the fire triangle needed for fire which is oxygen. The other two parts are heat and fuel. Vapors or rather a concentration of vapors make the fuel. A lot of persons who fix leaks in gas tanks actually fill the tank with either gasoline or water but never will you find anyone willing to wield an empty gas tank. But as for 800 I think a stinger brought it down. It was hushed for reasons we now see the damage control to the stock market.
You are taking my comment out of context. I was responding to another comment regarding the inability of scientists to ignite vapors in the lab. Yellow Rose of Texas said "If jet fuel does not explode then were the WTC buildings on fire from candles?", and I responded that jet fuel is not explosive like gasoline, it burns more smoothly.
I realize that oxygen is needed and I was not saying that it wasn't. If a flammable liquid is enclosed in a container with no air, combustion is not possible, like you say. However, liquids can burn if oxygen is present in the vapors above the fuel. Pour alcohol into a saucepan and light it. It burns. Technically it is the vapor immediately on the surface that is burning, not the liquid itself. The situation in the fuel tank is not like this, however. The fuel tank has some gas above the liquid inside, but there is very little oxygen present. It would be either a vacuum or carbon dioxide (depending on how the fuel system handles the evacuation of fuel). This is what the scientists did in the lab. They had re-created the environment inside the fuel tank and could not get the vapor to explode, because there was not enough oxygen. This is why I do not believe that a fuel tank explosion was the cause. If they had done the same experiment with gasoline, I'm sure it would have exploded because gasoline is much more volatile.
The point I was making to YROT was that jet fuel DOES burn, it doesn't explode like gasoline. It is a fuel which is not as volatile as others, which is why the vapors would not ignite.