twin towers falling

The Twin Towers of the World Trade Center, located in Lower Manhattan, New York City, collapsed on September 11, 2001, after being struck by two hijacked commercial airliners. The North Tower (WTC 1) was hit first at 8:46 a.m. by American Airlines Flight 11 and collapsed at 10:28 a.m. after burning for 1 hour and 42 minutes. The South Tower (WTC 2) was struck at 9:03 a.m. by United Airlines Flight 175 and collapsed at 9:59 a.m. after burning for 56 minutes. The collapses were caused by the impacts of the planes and the ensuing fires which severely weakened the steel structural components. In both towers, the section damaged by the airplanes failed first, and the structural steel lost fireproofing, causing it to heat rapidly and weaken. This led to progressive collapse as the floors above the impact zones fell onto the floors below, creating a domino effect that brought the entire towers down symmetrically and mostly straight down. The collapse caused massive destruction of adjacent buildings and large clouds of dust and debris enveloped lower Manhattan. Almost all deaths in the towers occurred at or above the impact zones, with a total death toll of about 2,606 persons at the site, including rescue personnel and civilians. The destruction of the Twin Towers is one of the deadliest and costliest building collapses in history and remains a defining event of the September 11 terrorist attacks.