Study: Fire caused WTC collapse
Following a three-year investigation, a government agency concludes that fire caused to the collapse of the 47-story Building 7 in the World Trade Center complex.
The Commerce Department’s National Institute of Standards and Technology (NIST) has concluded that the 47-story World Trade Center (WTC) Building 7 collapsed on Sept. 11, 2001, primarily due to fire--the first known instance of fire leading to the complete collapse of a tall building.
“Heating of floor beams and girders caused a critical support column to fail, initiating a fire-induced progressive collapse that brought the building down,” said NIST WTC lead investigator Shyam Sunder. “Video and photographic evidence, combined with detailed computer simulations, show that neither explosives nor fuel oil fires played a role in the collapse of WTC 7.”
The report pointed to one key factor leading to the collapse: thermal expansion of long-span floor systems at temperatures “hundreds of degrees below those typically considered in current practice for fire resistance ratings.” Also, the report recommended stronger building codes and standards that ensure even in the face of severe fire and failure of fire-fighting systems, buildings remain standing.