God Emperor Akhenaton
Octane is a chemical and a fire is a chemical reaction. Now if you want to say that the jet fuel didn't cause the collapse, then that's your opinion.
The article above is proposing that the burning jet fuel melted the aluminum aircraft bodies and caused them to flow down through the buildings, eventually coming into contact with the water used in the fire suppression systems. This water-molten aluminum mixing would have caused violent explosions.
I thought the explanation was interesting because not only is it not far from the official story (only in the specific mechanism) but it also explains the reports of explosions after the initial impacts and possibly the "controlled demolition" look of the collapses. I know there are a lot of people here that don't buy the official story so I'm curious to see how they feel about this relatively mundane (but still alternate) explanation.