After nearly 7 years of investigation, the NIST (National Institute of Standards and Technology), charged with producing reports explaining how the World Trade Center buildings were destroyed, held a press conference today announcing the publication of a final report on WTC7 (pdf) -- the third building in the New York City complex that inexplicably collapsed in 7 seconds late in the afternoon of 9/11/2001.
From today's press release (emphasis mine):
The fall of the 47-story World Trade Center building 7 (WTC 7) in New York City late in the afternoon of Sept. 11, 2001, was primarily due to fires, the Commerce Department’s National Institute of Standards and Technology (NIST) announced today following an extensive, three-year scientific and technical building and fire safety investigation. This was the first known instance of fire causing the total collapse of a tall building, the agency stated as it released for public comment its WTC investigation report and 13 recommendations for improving building and fire safety.Reasons for WTC7's collapse have been touted, over the years, by Popular Mechanics, FEMA, and NIST itself. A favorite debunking theory was that debris from the exploding towers caused excessive, critical damage to WTC7. Here's what Popular Mechanics said to debunk "conspiracy theorists." Note that PM quotes Shyam Sunder, the same fellow who gave the press briefing today:
The most important thing we found was that there was, in fact, physical damage to the south face of building 7," NIST's Sunder tells PM. "On about a third of the face to the center and to the bottom — approximately 10 stories — about 25 percent of the depth of the building was scooped out." NIST also discovered previously undocumented damage to WTC 7's upper stories and its southwest corner.Well, in today's announcement, we hear:
Finally, the report notes that "while debris impact from the collapse of WTC 1 initiated fires in WTC 7, the resulting structural damage had little effect in causing the collapse of WTC 7."How conveeeenient! Now the photographs of this excessive south side damage that Popular Mechanics claimed they alone were privileged to see no longer have to be produced...!
In it's initial report, FEMA postulated that "a fire fed by fuel oil caused the collapse" and suggested that the cantilevered construction over the power station was a contributing factor in WTC7's demise. At least FEMA acknowledged that more study needed to take place (emphasis mine):
The loss of the east penthouse on the videotape suggests that the collapse event was initiated by the loss of structural integrity in one of the transfer systems. Loss of structural integrity was likely a result of weakening caused by fires on the 5th to 7th floors. The specifics of the fires in WTC 7 and how they caused the building to collapse remain unknown at this time. Although the total diesel fuel on the premises contained massive potential energy, the best hypothesis has only a low probability of occurrence. Further research, investigation, and analyses are needed to resolve this issue.Yet today, NIST tosses this notion into oblivion:
“Video and photographic evidence combined with detailed computer simulations show that neither explosives nor fuel oil fires played a role in the collapse of WTC 7,” Sunder said. The NIST investigation team also determined that other elements of the building’s construction—namely trusses, girders and cantilever overhangs that were used to transfer loads from the building superstructure to the columns of the electric substation (over which WTC 7 was constructed) and foundation below—did not play a significant role in the collapse.Instead, we are told that ordinary office fires "burned out of control" (see picture above) and created enough heat to expand steel beams which eventually caused Floor 13 (unlucky floor, eh what?) to lose its connection, and then in domino-like fashion, all the other columns and beams simultaneously failed resulting in a total collapse. In 6.5 seconds. In a neat pile. Totally symmetric. Read it and weep:
Determining the probable collapse sequence for WTC 7, NIST found that the impact of debris from the collapse of WTC 1 ignited fires on at least 10 floors of WTC 7, and the fires burned out of control on six lower floors. The heat from these uncontrolled fires caused thermal expansion of the steel beams on the lower floors of the east side of WTC 7, damaging the floor framing on multiple floors. Eventually, a girder on Floor 13 lost its connection to a critical interior column that provided support for the long floor spans on the east side of the building. The displaced girder and other local fire-induced damage caused Floor 13 to collapse, beginning a cascade of floor failures down to the fifth floor. Many of these floors had already been at least partially weakened by the fires in the vicinity of the critical column. This collapse of floors left the critical column unsupported over nine stories.I wonder if there is any other possible explanation for a rapid onset for the failures of 81 core and perimeter columns? (Like some helper mechanism to dismember the structural support?) We have to recognize that there are certain paths NIST would not walk. And since the physical evidence has been destroyed, there can be no conclusive finding from any outside investigation.
“When this critical column buckled due to lack of floor supports, it was the first domino in the chain,” Sunder explained. “What followed in rapid succession was a progression of structural failures. Failure first occurred all the way to the roof line—involving all three interior columns on the most eastern side of the building. Then, progressing from east to west across WTC 7, all of the columns in the core of the building failed. Finally, the entire façade collapsed.”