WASHINGTON The government is taking the unusual step of responding to conspiracy theories about the destruction of the World Trade Center.
The National Institute of Standards and Technology (NIST, Gaithersberg, Md.), which investigated the causes of the collapse of the twin towers, said Wednesday (Aug. 30) that it has posted a "fact sheet" addressing alternatve theories about the fires and collapse. Several academics have put forth a "controlled demolition" and missile attack hypotheses for the destruction of the towers.
NIST concluded after a three-year building and fire safety investigation that the towers collapsed after being hit by separate, fuel-laden aircraft flown by terrorists. The impacts severed and damaged support columns, dislodging fireproofing insulation and dispersing jet fuel over multiple floors of each tower.
The resulting fire, which reached temperatures as high as 1,000 degrees C, weakened floors and columns, causing upper floors to collapse after sagging and pulling inward on perimeter columns. "This led to the inward bowing of the perimeter columns and failure of the south face of WTC 1 and the east face of WTC 2, initiating the collapse of each of the towers," NIST concluded.
NIST's probe rejected claims that upper floors "pancaked" on top of lower floors, causing the collapses. Other investigations pointed to huge amounts of office supplies, especially paper, as a source of fuel that significantly raised the temperature of tower fires beyond those that jet fuel would normally burn outside of an aircraft engine combustion chamber.
"Both photographic and video evidenceas well as accounts from the New York Police Department aviation unit during a half-hour period prior to collapsesupport this sequence for each tower." NIST concluded.
Far more controversial are theories about explosions inside the towers. Conspiracy theorists postulate that puffs of smoke seen at the time of each collapse are evidence of a controlled demolition. Critics of the official probe also cited seismic data they claim showed evidence of explosions just before each tower collapsed. Other theories alleged missiles were fired at the doomed towers.
While both NIST and the 9/11 Commission have dismissed these theories, U.S. officials have been compelled to address allegations widely disseminated on the Internet.
"NIST respects the opinions of others who do not agree with the findings in its report on the [World Trade Center] collapses," the agency said in a statement. "However, the WTC Investigation Team stands solidly behind the collapse mechanisms for each tower and the sequences of events (from aircraft
impact to collapse) as described in the report."