Collapse of the World Trade Center

On September 11, 2001, the two main towers of the World Trade Center complex were each hit by aircraft as part of the September 11, 2001 attacks. The south tower (2 WTC) collapsed at 9:59 am, less than an hour after being hit, and the north tower (1 WTC) followed at 10:28 am, causing massive damage to the rest of the complex and nearby buildings. In all, 2,595 people inside and near the towers were killed, along with the 157 passengers and crew aboard the two airplanes. The Federal Emergency Management Agency (FEMA) issued a performance study of the buildings in May 2002, declaring the WTC design sound and attributing the collapses wholly to extraordinary factors beyond the control of the builders. In its September 2005 report, the National Institute of Standards and Technology (NIST) concurred with this view, noting that the severity of the attacks and the magnitude of the destruction was beyond anything experienced in U.S. cities in the past. It did add, however, that the towers' stairwell design lacked adequate reinforcement. The collapse of 7 World Trade Center occurred at 5:20 pm with no casualties, and was the result of structural damage sustained during the collapse of Towers 1 and 2, combined with widespread fires in the building.