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1. A building undergoing progressive collapse would come down in a sequential manner. Sections would be expected to fail as they lost support. However, from measurements of the collapse time, it could not have been progressive or sequential:
   • From the time of the collapse of the East Penthouse to the onset of global collapse, the building appeared, from all external signs, to retain its overall integrity. The transition from total support to freefall was sudden. [8] The building fell with a horizontal roofline, implying that catastrophic failure across the entire width of the building (100 meters east to west) occurred virtually simultaneously within a fraction of a second.
   • The building buckled horizontally near the middle about 1.5 seconds prior to the onset of freefall, but this was not accompanied by downward motion. The building retained its full height until the onset of global collapse. The initial downward motion, measured at the northwest corner of the building, was a sudden transition to freefall.
2. In addition to the fact that the collapse of a steel-framed building entering into freefall in the absence of explosives to remove the steel supports is inherently implausible, the graphical output from NIST’s computer simulations does not match the actual observations at all. The two cases presented in NIST’s Final Report represent two, very different, scenarios:
   • In one of these, damage caused by debris from the North Tower collapse was a contributing factor.
   • In the other one, there is no mention of debris-caused damage.

   The scenario that included debris-caused damage to the south face of WTC 7 somewhat resembled the observed fall, but NIST concluded that debris-caused damage was not a significant factor in the collapse.

   It is quite apparent, from even casual inspection, that the simulation does not account for observations:

   • The simulated building shows marked deformations that would be easily detectable from exterior views. [9] These were not observed.
   • The actual building did not even undergo window breakage during the interval leading up to the freefall collapse, whereas window breakage was quite conspicuous during the much smaller local collapse under the East Penthouse. If, as NIST reported, the interior collapse of the majority of the building had been actually occurring, one would expect window breakage to be at least as evident as what was observed in the smaller collapse event.
   • When the simulated building starts to collapse, it does not enter freefall, whereas freefall is the most notable aspect of the actual collapse and the feature most in need of explanation.
   • The animation depicting the collapse of the simulated building is cut short. It does not cover the entire period of observed freefall.

   Therefore, NIST cannot justify its claim that freefall was consistent with its sequential collapse model. In fact, freefall is not consistent with any collapse model that does not involve the sudden removal of all supports across the entire width of the building.

3. In statements following the release of NIST’s Final Report, project director Shyam Sunder still struggled to come to terms with the reality of the observed period of freefall. His claim, presumably speaking for NIST, was that we are not seeing the actual collapse, but only the north facade of the building. According to this explanation, the interior collapsed first (in progressive collapse, as described by their model), leaving the facade to fall at freefall as a separate event.This explanation does not pass scrutiny, however, for four reasons:
   • There is video footage showing both the north and west faces of the building. Both of these faces, along with the corners connecting to the south and east faces of the building, appear to remain stable and intact until the sudden onset of free fall.
   • The West Penthouse, and therefore the interior structure that supported it, did not fail until about a second before the onset of freefall. Therefore the interior of the building got no more than about half a story head start. [10]
   • Even though the smaller collapse of the East Penthouse brought about a brief period of window breakage, no further windows were broken until the onset of freefall, so it is not believable that total internal collapse was occurring.
   • The roiling clouds of debris that raced down the street, often likened to pyroclastic flow, did not occur until the visible collapse of the building. If the interior of the building had collapsed earlier, we would expect the flow of debris to have started earlier.

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