There is a new(The above title should be, "new(?) 911 bad science) site that seeks to explain the fireball in the elevator shafts as a new type of thermobaric bomb.
This site describes this bomb.
You have to wade through a short woo-woo MIB are following me section first to get to it.
A few things struck me as idiocy such as a piezoelectric crystal becoming a capacitor(they spell piezoelectric wrong too).
Other things bother me though as well.(actually was pointed out to me)
I can find no reference to simple aluminum silicate being flammable let alone explosive and it seems that this 'bomb' is comprised of this material and oxidizers. There is no 'fuel'.
At best all I can envision is that with the release of a lot of oxidizing material that any combustibles in the area would ignite and possibly burn quite hot but I fail to see that this would result in any blast wave at all.
My chemistry ended in high school and we had to end class early sometimes to go fight the saber-toothed tigers roaming about, lol.