ures that NIST claims occurred are not apparent in the videos, which instead show the sudden fall and disintegration of the upper sections.
Constant Acceleration through the Path of Greatest Resistance According to NIST, once collapse initiated, WTC 1 and WTC 2 fell in approximately 11 seconds and 9 seconds, respectively,5 each coming down “essentially in free fall.”6 To many observers, the speed of collapse was the most striking feature of their destruction. Yet, NIST’s explanation for why WTC 1 and WTC 2 collapsed “essentially in free fall” was limited to a half-page section of its 10,000-page report titled “Events Following Collapse Initiation.” In this section, NIST attempted to explain the speed and completeness of the collapses simply by saying:
“
It was not stopped by the floors below. So there was no calculation that we did to demonstrate what is clear from the videos.”
— NIST Investigator John Gross
ARCHITECTS & ENGINEERS FOR 9/11 TRUTH
The story immediately below the stories in which the columns failed was not able to arrest this initial movement as evidenced by videos from several vantage points.
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The structure below the level of collapse initiation offered minimal resistance to the falling building mass at and above the impact zone. The potential energy released by the downward movement of the large building mass far exceeded the capacity of the intact structure below to absorb that through energy of deformation. Since the stories below the level of collapse initiation provided little resistance to the tremendous energy released by the falling building mass, the building section above came
down essentially in free fall, as seen in videos. However, NIST provided no calculations or modeling to support its claims. Instead it simply cited the videos as evidence. A Request for Correction to NIST’s report, filed under the Information Quality Act in 2007 by a group of scientists, an architect, and two 9/11 family members, argued that this was not scientifically valid: Here, NIST has not offered any explanation as to why (i.e. the technical cause of) the story below the collapse zone was not able to arrest the downward movement of the upper floors. The statement “as evidenced by the videos from several vantage points” is only an explanation of what occurred, but gives the reader absolutely no idea why it occurred. Basic principles of engineering (for example, the conservation of momentum principle) would dictate that the undamaged steel structure below the collapse zone would, at the very least, resist and slow the downward movement of the stories above. NIST’s use of the videos as evidence to explain why the lower structures failed to resist the fall of the upper sections was repeated by investigator John Gross in a talk he gave at the University of Texas in October 2006. In his talk, he actually refers to the video evidence as the reason why NIST did not need to perform analysis: “Once the collapse initiated, the video evidence is rather clear. It was not stopped by the floors below. So there was no calculation that we did to demonstrate what is clear from the videos.”7 But, as the Request for Correction pointed out, the inability of the lower structures to arrest the fall of the upper sections is what effectively claimed the lives of 421 first responders and 118 occupants at or below the impact zones,8 and thus it deserved thorough explanation: The families of the firefighters and WTC employees that were trapped in the stairwells when the entirety of the WTC Towers collapsed on top of them would surely appreciate an adequate explanation of why the lower structure failed to arrest or even resist the collapse of the upper floors. In its reply, NIST stated: NIST carried its analysis to the point where
