>>4682244 (lb)
Aluminum stores a lot of energy. Takes a lot to melt, but within estimated temp range of the theory "it wasn't hot enough to melt steel beams".
Molten Aluminum + Water = more than enough.
You may be able to see molten aluminum pouring out of the building; possibly on it's way down the stairwell. If that happens, it'd have reached the sprinklers. It's game on from there.
Admittedly, I'm as intrigued by any one theory there as I am the rest. I just like to add pieces when I can.
How about the No Floors theory? Is that a mind fuck or what?