The Twin Towers Collapse

New York City's World Trade Center was destroyed during the terrorist attacks of September 11, 2001 after being struck by two hijacked commercial airliners. The North Tower was hit at 8:46 am and collapsed at 10:28 am. The South Tower was hit at 9:03 am and collapsed at 9:59 am. The resulting debris severely damaged or destroyed more than a dozen other adjacent and nearby structures, ultimately leading to the collapse of Seven World Trade Center at 5:21 pm.

September 11 attacks

As a result of the attacks to the towers, a total of 2,763 people died including 2,192 civilians, 343 firefighters, and 71 law enforcement officers as well as all the passengers and crew on the airplanes, including 147 civilians and the 10 hijackers.

The scale of the destruction initially puzzled engineers, who had expected the buildings to survive airplane impacts. In September 2005, the National Institute of Standards and Technology published the results of its investigation into the collapse. The investigators did not find anything substandard in the design of the twin towers, noting that the severity of the attacks was beyond anything experienced in buildings in the past. They determined the fires to be the main cause of the collapses, finding that sagging floors pulled inward on the perimeter columns, causing them to bow and then to buckle. Once the upper section of the building began to move downwards, a total progressive collapse was unavoidable.

The cleanup of the World Trade Center site involved round-the-clock operations, many contractors and subcontractors, and cost hundreds of millions of dollars. The demolition of the surrounding damaged buildings continued even as new construction proceeded on the Twin Towers' replacement, One World Trade Center, which was opened in November 2014. As of July 2019, five new buildings had been erected on the site; the last one, Two World Trade Center, is scheduled for completion in 2022.