Your point about expertise is well taken Rock_Jock, BUT, regardless of how many degrees I have or don't have, I AM able to observe and to extrapolate my experiences without needing to ONLY follow the advice of the experts. I prefer to see what I see, NOT what others tell me to see.
Admitedly, as much as 40,000 gallons of fuel makes a very large molotov but also, even in a tower fire inferno like these I am unable to see how a fuel fire can take down that much steel and concrete so effectively TWICE.
The floors that I saw where about 2 1/2 feet thick cabled, pre-stressed concrete with riveted and welded steel beams the size of a car body.
I could more easily understand bomb like fuel vapor explosions and gallons of fuel flowing down the building in various ways resulting in bomb like series of explosions in floor after floor as the fuel and fire flowed down the building's innards.
Rock_Jock what sort of engineering are you involved in?