In order to do their collapse timing calculations, the NIST relied on video of the visible 18 stories of the WTC 7 north face collapse.
It is important to note that in spite of a large staff, abundant resources, and seven long years to do the calculations and analysis, the NIST in their August 2008, Final WTC 7 Report for public comment, pointedly did not include any confirmation of a period of free fall during the WTC 7 global collapse.
It could not have been through oversight or missed calculation.
Before everyone says "so what?", consideration should be given to what free fall entails.
A 47-story building dropping for a period of free fall, while maintaining a relatively level roofline, requires the near instantaneous removal of all its gravity-resisting vertical support over the distance travelled at free fall speed.
The NIST did not want this problematic information to come out at their August 2008 press conference.
The NIST presented a theory based on the idea that column 79 in the northeast corner of WTC 7 buckled over a number of floors, ultimately resulting in the collapse of the east penthouse, followed by an east-to-west progressive failure of interior columns and floor systems.
By not acknowledging the existence of free fall, the NIST theory for the collapse allowed for a fast, but still gradual failure, throughout the whole structure.
The theory did not adequately account for the possibility of significant free fall as exhibited by a relatively level descending roofline.
For the NIST explanation to hold true, the east, north and west faces, shown in videos to be solidly joined during global collapse, could not be free falling in unison.
With no free fall, the observed unison collapse of those building-faces could roughly fit into the NIST gradual collapse scenario.
What is particularly amazing, is the NIST acceptance of the idea that WTC 7, following the internal collapse of its interior columns and floor systems, was effectively reduced to a shell prior to the observed global collapse.
Figure 2–2. Eastward buckling of Column 79, viewed from the southeast.
During this theorized several seconds of internal devastation, the internal structure, solidly joined to perimeter walls, was supposedly being pulled downward, yet
the only outward display was a few broken windows appearing on the upper east side of the north face.
Unfortunately for the NIST, in the brief period they alloted for public comment, a high school science teacher named David Chandler, using the same video data as the NIST, submitted his finding that WTC 7 underwent a period of free fall.
Shortly thereafter, the video he created to illustrate his proof went viral on YouTube.
The NIST found themselves in a position where they could no longer ignore the existence of free fall during the WTC 7 global collapse.
So what did the NIST do?
In their NIST WTC7 FINAL - 1A Report, under TIMING OF COLLAPSE INITIATION AND PROGRESSION, the NIST now presented
"A more detailed examination of the same video led to a better understanding of the vertical motion of the building in the first several seconds of descent..."
The global collapse which they had previously described as a single event, was now broken down into three stages.
"- In Stage 1, the descent was slow and the acceleration was less than that of gravity. This stage corresponds to the initial buckling of the exterior columns in the lower stories of the north face.
By 1.75 s, the north face had descended approximately 2.2 m (7 ft).
- In Stage 2, the north face descended at gravitational acceleration, as the buckled columns provided negligible support to the upper portion of the north face. This free fall drop continued for approximately 8 stories or 32.0 m (105 ft), the distance traveled between times t = 1.75 s and t = 4.0 s.
- In Stage 3, the acceleration decreased somewhat as the upper portion of the north face encountered increased resistance from the collapsed structure and the debris pile below. Between 4.0 s and 5.4 s, the north face corner fell an additional 39.6 m (130 ft)."
bolding is mine
Note that the NIST, making their calculations from the descending north face roofline, somewhat disingenuously refer only to the
"north face", when making their reference to a descent at gravitational acceleration.
Official Conspiracy Theory supporters often like to seize on this as an indication that the NIST was arguing the north face only. In doing so, they ignore the unbroken connectivity between the east, north and west building faces during the visible descent that the NIST used to base their free fall finding.
So there you have it.
The NIST were forced to concede that 1.75 seconds into global collapse, for 105 feet, 8 stories, the east, north and west faces of WTC 7 were known to be falling in unison at free fall speed. The kinked roofline remained relatively level through this descent, indicating vertical support was removed virtually instantaneously on the east, north and west sides of WTC 7.
The NIST did not update their detailed collapse scenarios to include any reference to this known free fall, so it is unknown how they feel their theory satisfactorily explains how all three sides could agree to fail at the same time.
MM
