August 21, 2008 C-SPAN
Shyam-Sunder, Sivaraj Director, National Institute of Standards and Technology, Building and Fire Research Laboratory
The National Institute of Standards and Technology released the findings and recommendations from its building and fire safety investigation of the collapse of World Trade Center Building 7 (WTC 7). WTC 7 was a 47-story building that fell nearly seven hours after the World Trade Center towers collapsed following the terrorist attacks of September 11, 2001. The report presents the probable collapse sequence for the building and provides recommendations for improving building and fire safety in other buildings similar to WTC 7. Mr. Sivaraj Shyam-Sunder, the lead investigator for the federal building and fire safety investigation of the World Trade Center disaster, presented the report and responded to questions from the reporters in the audience.
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I went to wtc.nist.gov to look closer at their study. I got to the Q&A section and laughed out loud when I read this:
Q:In videos, it appears that WTC 7 is descending in free fall, something that would not occur in the structural collapse that you describe. How can you ignore basic laws of physics?
A: WTC 7 did not enter free fall. According to NIST analysis of WTC 7 video, the building collapsed 18 stories in 5.3 seconds. If the building exhibited free fall, this process would have taken just 3.9 seconds. The actual collapse time exceeded the free fall time by 40 percent.
See? It wasn’t a free fall. It took a whole 1.4 seconds longer than a free fall. That 1.4 seconds clearly was all it needed for structural beams weighing 1,000 lbs per foot to buckle and rip free from steel reinforced concrete, reducing 18 floors of modern fire-coded architecture to dust. Case closed.