NIST addresses ‘alternative theories’ on WTC collapse

The National Institute of Standards and Technology has published an FAQ supplementing its report on the collapse of the World Trade Center twin towers on Sept. 11, 2001, addressing persistent theories that the buildings were brought down by something other than the impact of two jetliners.

“We believe we have the sequence of events on the towers,” said Michael Newman, spokesman for the NIST WTC investigation. “We never saw any evidence of additional factors that could contribute to the collapse.”

Nevertheless, in the months after the October 2005 release of the comprehensive 43-volume study, NIST received frequent calls and e-mails about alternative theories that questioned whether the observed effects on the twin towers could be accounted for solely by the impact of jetliners, and offered alternatives such as missiles or controlled demolition.

“While we had not concentrated on these claims originally because we felt confident of our findings after 3.5 years of the most intense study, we thought that with the fifth anniversary coming up it would be a good opportunity to put up a fact sheet to address 14 of the most commonly asked questions,” Newman said.

The full study is based on interviews with more than 1,000 people, the examination of 7,000 pieces of video and 7,000 photos, analysis of 236 pieces of steel from the wreckage, and the use of laboratory tests and computer simulations. Analysts concluded that the collapse was the result of a unique combination of factors:
  • Structural damage done by the impact of the planes
  • Fires ignited by jet fuel that were more widespread and intense than building standards anticipated
  • Dislocation of fireproofing from the impact, exposing structural steel to the heat of this fire.

These factors resulted in the central collapse of the damaged floors, pulling columns inward until the upper floors collapsed on the floors beneath.

“We see that in the visual evidence,” Newman said. “The video of the collapse shows this bowing very clearly.”

The FAQ addresses questions of a controlled demolition (the towers collapsed from above, not from below as in a demolition, and it would be impractical to hide the thousands of pounds of explosives required in an occupied building); how jet fuel could melt steel (the steel wasn’t melted, but it was heated enough to weaken); and why sprinkler systems did not extinguish the fires (they were damaged by the crashes and were not designed for massive conflagrations).

Newman said the FAQ is not intended to persuade hard-core devotees of alternative theories, but to provide a balanced response for the general public.

The WTC report produced 30 recommendations for improving building codes, which the NIST team now is shepherding through the standards-making process. The International Code Council has proposed 19 changes to model building codes that are expected to be voted on soon, Newman said. There are no national building codes, and ICC models provide a template often used for state and local codes.

The NIST team also is finalizing its study of the collapse of the building at 7 World Trade Center, the 47-story edifice that collapsed hours after the twin towers. That report is expected early in 2007.

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