World Trade Center 7, bygningen som ikke ble rammet av fly 9/11, men som likevel kollapset, falt ikke sammen pga indre detonasjoner, men fordi brannene fikk viktige bæresystemer til å svikte, viser en ny studie.
WTC 7 er den første skyskraper i historien som har kollapset pga brann.
At en bygning som lå 120 meter bortenfor de to tvillingtårnene også kollapset, har vært det ultimate bevis på ugler i mosen for tilhengere av konspirasjonsteoriene. En av sju amerikanere tror at ikke hele sannheten om 9/11 har kommet frem.
Men det var ikke noe mystisk med kollapsen. Den skyldes fysiske årsaker, konkluderer rapporten.
The long-delayed report by engineers at the National Institute of Standards and Technology in suburban Washington is intended to solve one of the lingering questions about the 2001 attacks: Why did the building at 7 World Trade Center fall, if it was not hit by an airplane?
«Heating of floor beams and girders caused a critical support column to fail,» said Shyam Sunder, the lead investigator. «Video and photographic evidence, combined with detailed computer simulations, show that neither explosives nor fuel oils played a role.»
The investigators determined that debris from the falling twin towers ignited fires on at least 10 floors at 7 World Trade Center, which was about 400 feet, or 120 meters, north of where the two tallest buildings in the city once stood. The blazes burned out of control for six hours. The city fire department, devastated by the collapse of the twin towers, abandoned its efforts to extinguish the fire and the sprinkler system was incapacitated.
The heat from these fires, the investigators said, caused the beams on the lower floors of the east side of the tower to expand, ultimately causing a girder on the 13th floor to disconnect from a critical interior column that supported the building’s long floor spans. Once the 13th floor gave way, a cascade of floor failures led to the overall collapse of the tower.
9/11 building brought down by fire, not explosives, report says