As one who has had a fair amount of experience with steel and structures, I can also verify the obvious, well known from the dawn of the iron age. The secret of steel is that it is as hard and tough as almost any common material WHEN IT IS COLD, when it is hot say even 1500 degrees F. it is butter and well below ideal strength at even 1000 deg.F, even though melting might be 3000-3500deg. F. If there is sufficient oxygen, the steel itself will burn well below melting temps. The point about the aluminum is also well made, in an open field aluminum would not burn easily, but in a confined space that heat could not escape would be a very different matter. Then the hot aluminum would yank the oxygen even from CO2 and burn most vigorously. This supprising trait was a hard lesson learned in the Falklands War, when a missile hit an aluminum ship, and such fires were started. In short the insistance on demilition charges being placed on the floors the planes hit, and assuming the pilots would even hit the correct floor, shows great illogic and ignorance, and does much damage to the persuit of much more fruitful avenues of inquiry.