World Trade Center Investigation "Exonerates" Twin Towers' Design in Sept. 11, 2001 Collapse 10/21/2004
Structural steel of the twin 110-story towers of the World Trade Center was stripped of its fireproofing by debris from the aircraft impact and weakened by the resulting fires, eventually causing the towers to collapse, according to an interim report by the National Institute of Standards & Technology. The report says the region of dislodged fireproofing was determined from the predicted path of the debris.
Had the fireproofing not been dislodged, the temperature rise of the structural components would likely have been insufficient to cause the global collapse of the towers, says NIST in the Oct. 19 release of another interim report of its $16-million study of the WTC destruction on Sept. 11, 2001, by terrorists. Fireproofing dislodged by debris left the components more sensitive to heat than any areas where there was missing or thin fireproofing before the aircraft impacts, says the report.