Img: WTC 7 on fire following the 9/11 attacks. Credit: Prints and Photographs Division. Library of Congress.
A long-standing conspiracy theory concerning the destruction of the 47-story World Trade Centre building 7, located to the north of the Twin Towers, has been debunked.
Federal investigators with the National Institute of Standards and Technology (NIST) handed down the findings of a three-year investigation which said fire from falling debris caused the collapse of the building making it the first time a fire had caused the total failure of a modern skyscraper.
"The reason for the collapse of World Trade Center 7 is no longer a mystery," said Dr. Shyam Sunder, the lead investigator on the NIST team. "It did not collapse from explosives or fuel oil fires."
Skeptics have long believed that fire and debris alone should not have caused the collapse of such a strong building and have hinted at a timed explosion as being the cause of the collapse. The building was not hit at any stage by the hijacked aircraft.
However the report dismissed this suggestion saying other factors brought the building down.
"Heating of floor beams and girders caused a critical support column to fail," said Sunder. "Video and photographic evidence combined with detailed computer simulations show that neither explosives nor fuel oils played a role in the collapse that brought the building down."
However, the report is unlikely to satisfy conspiracy theorists, with the New York Times quoting a survey claiming 1-in-7 Americans believes the attack on the World Trade Centre was an inside job.
"Seven World Trade Centre is one of the key points of evidence, one of the smoking guns," said Richard Gage, a California architect and leader of a group called Architects and Engineers for 9/11 Truth, to the newspaper. "There have been much hotter, longer lasting and larger fires in skyscrapers that have not fallen down."
For a demonstration video of why the building fell, see the NIST Web site by clicking here.