September 11, 2001 attacks, a variety of conspiracy theories have emerged about the attacks which contradict the mainstream account of events that day. The theories typically include suggestions that individuals in the government of the United States knew of the impending attacks and refused to act on that knowledge, or that they played a role in the attacks. Conspiracy theorists have claimed that the collapse of the World Trade Center was the result of a controlled demolition. Some also contend that a commercial airliner did not crash into the Pentagon, and that United Airlines Flight 93 was shot down. The scientific community does not support the controlled demolition hypothesis and U.S. officials, mainstream journalists, and researchers have concluded that only al-Qaeda was involved in the attacks.

The collapse of the World Trade Center was a surprise to the engineering community. While no skyscraper had ever before completely collapsed due to fire or other local damage, three skyscrapers collapsed on September 11, 2001. The challenge for engineers was then to explain how the local damage caused by the airplanes (or, in the case of WTC 7, falling debris) was able to occasion a global progressive collapse. After an intensive three-year investigation, the National Institute of Standards and Technology published an account that has been largely accepted in the engineering community. The official collapse mechanism refers only to the aircraft impacts and the subsequent fires, which are taken to have caused sufficient structural damage to occasion the collapses. Conspiracy theorists emphasize that the only precedents for global collapse before 9/11 are controlled demolitions, and demand a more thorough investigation of this possibility.

The controlled demolition hypothesis plays a central, albeit not essential, role in the 9/11 conspiracy theories.[40] Jeff King and Jim Hoffman were early defenders of the controlled demolition hypothesis and published their observations online. David Ray Griffin included the theory in his book The New Pearl Harbor. It received its most notable proponent to date in early 2006, when Steven E. Jones, a physicist at Brigham Young University, argued that a “gravity driven collapse” without demolition charges would defy the laws of physics. There is a range of opinion about the most likely sort and amount of explosives, the way they were distributed, and how they were successfully brought into the building. Proponents of the hypothesis sometimes cite reports of what they believe are unusual power outages, maintenance work and emergency drills in the weeks leading up to September 11, 2001. Some conspiracy theorists propose a regular controlled demolition, in which the role of the demolition charges would have been to remove the main structural supports in order to let gravity and the weight of the building do the rest. Steven Jones believes that thermite (thermate), perhaps in combination with other devices, was likely involved.

NIST has explicitly rejected this hypothesis. Among the several reasons was that “…”a very large quantity of thermite (a mixture of powdered or granular aluminum metal and powdered iron oxide that burns at extremely high temperatures when ignited) or another incendiary compound would have had to be placed on at least the number of columns damaged by the aircraft impact and weakened by the subsequent fires to bring down a tower. Thermite burns slowly relative to explosive materials and can require several minutes in contact with a massive steel section to heat it to a temperature that would result in substantial weakening. Separate from the WTC towers investigation, NIST researchers estimated that at least 0.13 pounds of thermite would be required to heat each pound of a steel section to approximately 700 degrees Celsius (the temperature at which steel weakens substantially). Therefore, while a thermite reaction can cut through large steel columns, many thousands of pounds of thermite would need to have been placed inconspicuously ahead of time, remotely ignited, and somehow held in direct contact with the surface of hundreds of massive structural components to weaken the building. This makes it an unlikely substance for achieving a controlled demolition.”

There is widespread agreement, however, about the significance of the controlled demolition hypothesis, even among those who don’t endorse it specifically or conspiracy theories in general. The necessary devices could only have been planted well in advance of the September 11 attacks and would have required extraordinary access to three highly secured buildings.


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