Why the World Trade Center Towers Fell

W. Gene Corley, left, of the American Society of Civil Engineers, and Jonathan Barnett present the findings of the World Trade Center building performance study to the House Committee on Science on May 1.

Highlights of the building performance study:

It was the simultaneous fires, on multiple floors, rather than burning jet fuel (much of which was consumed in the initial fireballs), that weakened the structural steel elements enough to precipitate the collapse.
Robust and redundant steel framing, adequate and well-lighted stairways, and emergency training contributed to the towers' resilience and the safe egress of occupants.
Lightweight fireproofing, probably blown off of the structural steel, sprinkler supply pipes severed by flying debris, gypsum wallboard around the stairwells, which collapsed and blocked access, and the grouping of stairwells in the buildings' core, which increased their vulnerability to a single impact, may have contributed to the collapse or hindered the escape of occupants above the impact zones.

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Last modified: Sep 02, 2004, 14:13 EDT