The National Institute of Standards and Technology (NIST) released its final report on the collapse of the World Trade Center 7 building on Thursday, 6 years after it began its investigation into the collapses of WTC buildings on September 11, 2001.
The symmetrical and rapid collapse of 47-story WTC 7 into its own footprint in what appeared to be an “implosion” like those initiated by demolitions experts to safely bring down buildings has for many years fueled conspiracy theories that the towers were intentionally destroyed, indicating that the attacks of 9/11 were an “inside job.”
Adding more intrigue to conspiracy theories, WTC 7 housed offices of the Internal Revenue Service (IRS), the Department of Defense (DOD), the Central Intelligence Agency (CIA), the Office of Emergency Management (OEM), the Securities and Exchange Commission (SEC), and the Secret Service.
The NIST report goes a long way toward explaining how WTC 7 might have collapsed due to fire, but in doing so, ironically, also confirms many of the arguments put forward by conspiracy theorists.
The Federal Emergency Management Agency released a report in 2002 that noted, “The performance of WTC 7 is of significant interest because it appears the collapse was due primarily to fire, rather than any impact damage from the collapsing towers. Prior to September 11, 2001, there was little, if any, record of fire-induced collapse of large fire-protected steel buildings.”
The NIST report likewise notes, “This was the first known instance of the total collapse of a tall building primarily due to fires.” It adds, “WTC 7 was unlike the WTC towers in many respects. It was a more typical tall building in the design of its structural system. It was not struck by an airplane. The fires in WTC 7 were quite different from those in the towers. Since WTC 7 was not doused with thousands of gallons of jet fuel, large areas of any floor were not ignited simultaneously. Instead the fires in WTC 7 were similar to those that have occurred in several tall buildings where the automatic sprinklers did not function or were not present. These other buildings did not collapse, while WTC 7 succumbed to its fires.”
NIST also notes that “the remains of all the WTC buildings were disposed of before congressional action and funding was available for this Investigation to begin”, a fact long pointed to as indicative of a cover-up by conspiracy theorists.
The FEMA report speculated as to the possible causes of the collapse, but noted that “confirmation will require additional study and analysis.” It stated that “the sequence of the WTC 7 collapse is consistent with an initial failure that occurred internally in the lower floors on the east side of the building.” Fires resulted in the building as a result of the impact damage of debris from the collapse of the twin towers. The building’s fire suppression system was not sufficient to control the resulting fires on multiple floors.
“In addition,” it stated, “the firefighters made the decision fairly early on not to attempt to fight the fires, due in part to the damage to WTC 7 from the collapsing towers.” The report reiterated, “It appears that the sprinklers may not have been effective due to the limited water on site, and that the development of the fires was not significantly impeded by the firefighters because manual firefighting efforts were stopped fairly early in the day.”
The NIST report similarly states that “The decision not to continue evaluating the building and not to fight the fires was made hours before the building collapsed, so no emergency responders were in or near the building when the collapse occurred.”
The FEMA report suggested fuel from tanks for emergency generators might have contributed to the fires in the building. Conspiracy theorists have argued that there is no evidence to support this widely propagated theory and that it is in any event an unlikely explanation for the collapse. FEMA itself acknowledged that this is a “hypothesis based on potential rather than demonstrated fact” and that “there is no physical evidence available” to support the theory.
Indeed, the NIST report states that “fuel oil fires did not play a role in the collapse of WTC 7,” confirming what conspiracy theorists have argued: that ruptured fuel lines could not have sustained fires long enough or generated enough heat “to raise the temperature of the critical interior column to the point of significant loss of strength or stiffness.” Nor was any smoke that would have resulted from such fires observed.
FEMA noted in its report that the steel structure was fireproofed to 2 inches, but speculated that “During the course of the day, fires may have exposed various structural elements to high temperatures for a sufficient period of time to reduce their strength to the point of causing collapse.” NIST contradicts FEMA, reporting thinner layers of fireproofing, and stating that “The installed thickness of the thermal insulation on the floor beams was below that required for unsprinklered or sprinklered buildings, but it is unlikely that the collapse of WTC 7 could have been prevented even if the thickness had been consistent with building code requirements.” In other words, WTC 7 was not up to code.
According to the FEMA report, it took 27 seconds from initiation to total collapse. There is no explanation for how they arrived at the starting time, but the report’s timeline also notes that from the time video footage shows the first apparent sign of the collapse, the disappearance of the penthouse, it took just seven seconds for the entire structure to fail and completely collapse to the ground. At 186 meters tall, that means WTC 7 collapsed at near free-fall speed.
Conspiracy theorists have long argued that such a rapid collapse demonstrates that demolition explosives must have been used to take out major load-bearing columns. A collapse initiating at one point, they argue, would have resulted in a less symmetrical collapse and remaining intact structure, even if ultimately stressed to the point of failure, would have provided substantial resistance to the collapse such that it would have been more progressive rather than so instantaneous, and taken longer; certainly not near free-fall speed.
The NIST report states that “The probable collapse sequence that caused the global collapse of WTC 7 was initiated by the buckling of a critical interior column in” the northeast of the building.
This column had become unsupported over nine stories after initial local fire-induced damage led to a cascade of local floor failures. The buckling of this column led to a vertical progression of floor failures up to the roof and to the vertical progression of floor failures up to the roof and to the buckling of adjacent interior columns to the south of the critical column. An east-to-west horizontal progression of interior column buckling followed, due to loss of lateral support to adjacent columns, forces exerted by falling debris, and load redistribution from other buckled columns. The exterior columns then buckled as the failed building core moved downward, redistributing its loads to the exterior columns. Global collapse occurred as the entire building above the buckled region moved downward as a single unit. This was a fire-induced progressive collapse, also known as disproportionate collapse, which is defined as the spread of local damage, from an initiating event, from element to element, eventually resulting in the collapse of an entire structure or a disproportionately large part of it.
The report claims that “within seconds” of the failure of “Column 76” due to the loss of lateral support from the thermal expansion of beams leading to the collapse of several floors, “the entire core was failing.” With the loss of the core columns, loads were redistributed to the exterior columns, which buckled under the extra weight. “The entire building above the buckled-column region then moved downward as a single unit, completing the global collapse sequence.”
In examining the speed of the collapse, “NIST was interested in estimating how closely the time for WTC 7 took to fall compared with the descent time if the building were falling freely under the force of gravity.” Using video footage of the collapse, NIST calculated the speed of the collapse based on how far the roofline of the north face could be observed falling before being obstructed by other buildings and how long it took for the building to collapse that far. The report concludes that “the actual time for the upper 18 stories to collapse, based on video evidence, was approximately 40 percent longer than the computed free fall time and was consistent with physical principles.”
NIST notes that “thermal expansion” contributing to failure occurred “at temperatures hundreds of degrees below those typically considered in design practice for establishing structural fire resistance ratings.” In other words, it should have required hotter fires to expand structural elements to the point where it risked failure. But the report also says the effect of thermal expansion was magnified due to the length of floor spans. Connections failed “that were designed to resist gravity loads, but not thermally induced lateral loads”.
It then adds the curious statement that WTC 7 had “a structural system that was not designed to prevent fire-induced progressive collapse.”
Conspiracy theorists have long argued that the damage to WTC 7 from the collapse of the twin towers was not sufficient to significantly affect the structure to lead to global collapse. NIST confirms this, noting:
Other than initiating the fires in WTC 7, the damage from the debris from WTC 1 had little effect on initiating the collapse of WTC 7. The building withstood debris impact damage that resulted in seven exterior columns being severed and subsequently withstood conventional fires on several floors for almost seven hours. The debris damaged the spray-applied fire resistive material that was applied to the steel columns, girders, and beams, only in the vicinity of the structural damage from the collapse of WTC 1. This was near the west side of the south face of the building and was far removed from the buckled column that initiated the collapse.
The FEMA report suggested the unique design of WTC 7, relying upon stress transfer elements to support the building over a substation below, might have contributed to the collapse. Conspiracy theorists have noted that FEMA fails to elaborate and explain just how such design elements might have resulted in such a collapse. And the NIST report states that “The transfer elements such as trusses, girders, and cantilever overhangs that were used to support the office building over the Con Edison substation did not play a significant role in the collapse of WTC 7.”
While thus confirming many of the arguments put forth by conspiracy theorists, NIST also discounts the use of explosives to bring down the building, stating that:
Hypothetical blast events did not play a role in the collapse of WTC 7. NIST concluded that blast events did not occur, and found no evidence whose explanation required invocation of a blast event. Blast from the smallest charge capable of failing the critical column would have resulted in a sound level of 130 dB to 140 dB at a distance of at least half a mile. There were no witness reports of such a loud noise, nor was such a noise heard on the audio tracks of video recordings of the WTC 7 collapse.
“Considerable effort was expended,” the report states, “to compile evidence and to determine whether intentionally set explosives might have caused the collapse of WTC 7,” using both scenarios in which explosives were prepared in advance of 9/11 or placed on the day of the attacks. “Attention focused on a single hypothetical blast scenario explosive location. This involved preliminary cutting of Column 79 and the use of 4 kg (9lb) of RDX explosives in linear shaped charges.” Neither the breakage of windows nor the blast sound that would have resulted are evidenced in the collapse, the report states.
This conclusion is unlikely to satisfy conspiracy theorists, who have long argued that thermite, not RDX explosives, was used to take out load-bearing columns.
In its recommendations, NIST suggests that its findings be taken with “urgency” since they are pertinent “to the collapse of a tall building that was based on a structural system design that is in widespread use.” In other words, there could be a great many other high-rise buildings at risk of total collapse due to fire, suggesting that existing building codes are insufficient and conventional wisdom on engineering and architectural standards outdated.