Decades after the September 11, 2001, attacks, experts are still working to debunk persistent conspiracy theories surrounding the collapse of the World Trade Center towers. Investigator David Dunbar, who co-authored a 2005 Popular Mechanics article that examined many of these claims, expressed frustration with the continued lack of interest in verifiable facts among some theorists.
"There seemed to be little interest on the part of the conspiracy theorists to do any fact-checking for themselves," Dunbar told the Daily Mail. "But if people don't want to be don't want to be convinced by verifiable facts, if they're so invested psychologically, emotionally, spiritually, in every way with this alternative worldview, then they're not going to be receptive to the findings of an expert who, for example, proves that steel doesn’t have to melt to lose its structural strength."
The roots of the 9/11 conspiracy theories are often traced back to right-wing broadcaster Alex Jones, who in the immediate aftermath of the attacks promoted the idea of a controlled demolition and accused the Bush administration of orchestrating the events.
Jet Fuel and Steel Strength
One of the most common conspiracy theories disputes the collapse of the Twin Towers, with skeptics claiming the planes' impacts were not sufficient to bring down the skyscrapers. They argue that the planes struck too high to cause the collapse, with impacts on the North Tower between the 94th and 98th floors and on the South Tower between the 78th and 84th floors.
However, National Institute of Standards and Technology (NIST) investigators, cited in the 2005 Popular Mechanics study, concluded that the collapses were initiated by the planes severing utility shafts in the towers' cores. This action distributed burning jet fuel, igniting the interiors for approximately 56 minutes before the structures began to fall within six minutes of each other.
A related and well-known claim is that "jet fuel doesn't melt steel beams." Skeptics point out that jet fuel burns at a maximum of 1500 degrees Fahrenheit, below the melting point of steel at 2750 degrees Fahrenheit. Dunbar explained that while the steel did not melt, it lost its structural integrity due to the heat. "The steel frames of the Twin Towers did not need to melt for them to collapse - they merely had to lose their structural strength, which caused the steel support beams to bend and buckle," he stated.
NIST found that combustible materials within the buildings, such as furniture and rugs, acted as kindling, raising temperatures to over 1800 degrees Fahrenheit. Forman Williams, a professor of engineering at the University of California, San Diego, and a structural engineer consulted for the Popular Mechanics research, clarified that the jet fuel served as the ignition source, but "the rest of the stuff burning afterward that was responsible for the heat transfer that eventually brought them down."
Controlled Demolition Claims
Another theory suggests that visible puffs of dust and debris ejected from the buildings during their collapse were evidence of explosives set to trigger a controlled demolition. Van Romero, an explosives expert initially quoted by the Albuquerque Journal as saying the collapse was caused by explosives, later clarified to Popular Mechanics that he was misquoted and never believed explosives brought down the building.
Researchers explain the "puffs" as a result of the floors "pancaking" onto each other with immense force, expelling air and debris. Shyam Sunder, NIST lead investigator, told Popular Mechanics that while the effect resembles small explosions, "it is the floor pancaking that leads to that perception."
Dunbar further elaborated that his team consulted a demolition company owner regarding the feasibility of a controlled demolition. The owner indicated that such an operation would be logistically impossible. The explosives would need to be thousands of pounds each, requiring forklifts to transport. A crew of 75 would need up to two months to covertly place and wire charges after stripping fireproofing from structural columns, all while thousands of workers were present in the buildings. Furthermore, demolition experts typically place charges on the ground floor or basement, allowing the building's weight to bring it down, not on upper floors. "So the idea that there would be somehow a team of demolition experts who go in the building after everybody's gone home for the day and start planting detonation devices... I mean, it was just absurd," Dunbar recounted the owner saying, highlighting the lack of research and understanding of demolition principles among conspiracy theorists.