Reply #21: there was fire and huge chunks of debris

[never cry wolf]

the building was gutted by an uncontrolled fire caused by burning debris which also did structural damage. there is speculation the the 6,000 gallons of deisel fuel on the second floor and the 36,000 gallons below the first floor in the loading dock contributed to the uncontrolled fires if their containment systems were comprimised by the devastation across the street.

here is a very nice link with many other engineering type links: http://www.wpi.edu/Academics/Depts/Fire/News/wtc.html