Learn more and compare subscriptions content expands above. Full Terms and Conditions apply to all Subscriptions. Or, if you are already a subscriber Sign in. Other options. Close drawer menu Financial Times International Edition. Search the FT Search. All input data, results data, and simulations that were used or generated during this study can be downloaded as a ZIP file:.
Therefore, downloading the ZIP file and unzipping it will require approximately GB of storage space. This is a study of the collapse of World Trade Center Building 7 WTC 7 — a story building that suffered a total collapse at PM on September 11, , following the horrible events of that morning.
Yes, this possibility was investigated carefully. NIST concluded that blast events inside the building did not occur and found no evidence supporting the existence of a blast event. In addition, no blast sounds were heard on the audio tracks of video recordings during the collapse of WTC 7 or reported by witnesses. According to calculations by the investigation team, the smallest blast capable of failing the building's critical column would have resulted in a sound level of decibels dB to dB at a distance of at least half a mile, if unobstructed by surrounding buildings.
This sound level is consistent with a gunshot blast, standing next to a jet plane engine, and more than 10 times louder than being in front of the speakers at a rock concert. Preparing a column includes steps such as cutting sections with torches, which produces noxious and odorous fumes. Intentional demolition usually requires applying explosive charges to most, if not all, interior columns, not just one or a limited set of columns in a building.
Thermite is a combination of aluminum powder and a metal oxide that releases a tremendous amount of heat when ignited. It is typically used to weld railroad rails together by melting a small quantity of steel and pouring the melted steel into a form between the two rails.
To apply thermite to a large steel column, approximately 0. For a steel column that weighs approximately 1, lbs.
This is for one column. It is unlikely that lbs. Given the fires that were observed that day, and the demonstrated structural response to the fires, NIST does not believe that thermite was used to fail any columns in WTC 7. The metal compounds also would have been present in the construction materials making up the WTC buildings, and sulfur is present in the gypsum wallboard used for interior partitions. The sound levels reported by all witnesses do not match the sound level of an explosion that would have been required to cause the collapse of the building.
If the two loud booms were due to explosions that were responsible for the collapse of WTC 7, the emergency responder-located somewhere between the 6th and 8th floors in WTC 7-would not have been able to survive the near immediate collapse and provide this witness account.
The footage was not edited in any way by NIST. The building had three separate emergency power systems, all of which ran on diesel fuel. As background information, the three systems contained two 12, gallon fuel tanks, and two 6, gallon tanks beneath the building's loading docks, and a single 6, gallon tank on the 1st floor. In addition one system used a gallon tank on the 5th floor, a gallon tank on the 8th floor, and a 50 gallon tank on the 9th floor. Another system used a gallon day tank on the 7th floor.
Several months after the WTC 7 collapse, a contractor recovered an estimated 23, gallons of fuel from these tanks. The fate of the fuel in the day tanks was unknown, so NIST assumed the worst-case scenario, namely that they were full on Sept.
The fate of the fuel of two 6, gallon tanks was also unknown. Therefore, NIST also assumed the worst-case scenario for these tanks, namely that all of the fuel would have been available to feed fires either at ground level or on the 5th floor.
A uniform thickness equal to the specified SFRM thickness was used for the finite element thermal analyses of WTC 7 because 1 the variability in the SFRM thickness was small, 2 no evidence of significant damage to the SFRM was found, and 3 small areas of SFRM damage would not have affected the thermal or structural response of the structural framing system.
The time between the technical conference on the WTC towers report and the issuance of this draft WTC 7 report is approximately three years, comparable to the length of a typical investigation of an aircraft crash. The WTC 7 investigation was an extensive, state-of-the-art reconstruction of the events that affected WTC 7 and eventually led to its collapse. Numerous facts and data were obtained, then combined with validated computer modeling that is believed to be close to what actually occurred.
A single computer simulation of the structural response to fires took about eight months to complete on powerful computing workstations and clusters. The debris caused structural damage to the southwest region of the building-severing seven exterior columns-but this structural damage did not initiate the collapse.
The fires initiated by the debris, rather than the structural damage that resulted from the impacts, initiated the building's collapse after the fires grew and spread to the northeast region after several hours. The debris impact caused no damage to the spray-applied fire resistive material that was applied to the steel columns, girders, and beams except in the immediate vicinity of the severed columns.
A separate analysis showed that even without the structural damage due to debris impact, WTC 7 would have collapsed in fires similar to those that occurred on Sept. None of the large pieces of debris from WTC 2 the south tower hit WTC 7 because of the large distance between the two buildings.
Even without the structural damage, WTC 7 would have collapsed from the fires that the debris initiated. The growth and spread of the lower-floor fires due to the loss of water supply to the sprinklers from the city mains was enough to initiate the collapse of the entire building due to buckling of a critical column in the northeast region of the building. The sprinkler systems did not fail. The water main served as both the primary and backup source of water for the sprinkler system in the lower 20 floors.
Therefore, the sprinkler system could not function. In contrast, the sprinklers and standpipes on the building's middle levels 21st floor through 39th floor and upper levels 40th floor through 47th floor received water from two large overhead storage tanks on the 46th floor, and used the city's water mains as a backup.
Conspiracy theorists have long pointed to the collapse of the story structure as key evidence that the U. No planes struck the building, and the commonly available views of the exterior didn't show significant damage. Since WTC 7 housed Secret Service and CIA offices, conspiracy theorists claimed that the building was destroyed in a controlled demolition in order to obliterate evidence of the U.
It is physically impossible," she said. Today's report confirms that a fire was, indeed, the cause. The final report describes how debris from the collapse of WTC 1 ignited fires on at least 10 floors of WTC 7 at the western half of the south face. Fires on Floors 7 through 9 and 11 through 13 burned out of control, because the water supply to the automatic sprinkler system had failed. The primary and backup water supply to the sprinkler systems for the lower floors relied on the city's water supply.
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