In its progress report, NIST released a video and still-photo analysis of 7 World Trade Center before its collapse that appears to indicate a greater degree of structural damage from falling debris than originally assumed by FEMA. Specifically, NIST's interim report on 7 World Trade Center displays photographs of the southwest facade of the building that show it to have significant damage. The report also highlights a 10-story gash in the center of the south facade, toward the bottom, extending approximately a quarter of the way into the interior. A unique aspect of the design of 7 World Trade Center was that each outer structural column was responsible for supporting 2,000 sq ft (186 m²) of floor space, suggesting that the simultaneous removal of a number of columns severely compromised the structure's integrity. Consistent with this theory, news footage shows cracking and bowing of the building's east wall immediately before the collapse, which began at the penthouse floors. In video of the collapse, taken from the north by CBS News and other news media, the first visible sign of collapse is movement in the east penthouse 8.2 seconds before the north wall began to collapse, which took at least another 7 seconds.
The working hypothesis, released in the June 2004 progress report and reiterated in a June 2007 status update, was that an initial failure in a critical column occurred below the 13th floor, caused by damage from fire and/or debris from the collapse of the two main towers. The collapse progressed vertically up to the east mechanical penthouse. The interior structure was unable to handle the redistributed load, resulting in horizontal progression of the failure across lower floors, particularly the 5th to 7th floors. This resulted in "a disproportionate collapse of the entire structure."
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