(5:20 p.m.) September 11, 2001: WTC Building 7 Collapses; Cause Remains Unclear

World Trade Center Building 7 collapses down into its footprint. [Source: unknown] (click image to enlarge)Building 7 of the WTC complex, a 47-story tower, collapses. No one is killed. [CNN, 9/12/2001; Washington Post, 9/12/2001; MSNBC, 9/22/2001; Associated Press, 8/21/2002] It collapses in 6.6 seconds, which is just 0.6 of a second longer than it would have taken a free-falling object dropped from its roof to hit the ground. [Deseret Morning News, 11/10/2005] Many questions will arise over the cause of this collapse in the coming weeks and months. Building 7, which was not hit by an airplane, is the first modern, steel-reinforced high-rise to collapse because of fire. [Chicago Tribune, 11/29/2001; Stanford Report, 12/5/2001; New York Times, 3/2/2002] Some later suggest that the diesel fuel stored in several tanks on the premises may have contributed to the building’s collapse. The building contained a 6,000-gallon tank between its first and second floors and another four tanks, holding as much as 36,000 gallons, below ground level. There were also three smaller tanks on higher floors. [Chicago Tribune, 11/29/2001; New York Times, 3/2/2002; New York Observer, 3/25/2002; Federal Emergency Management Agency, 5/1/2002, pp. 1-17] However, the cause of the collapse is uncertain. A 2002 government report concludes: “The specifics of the fires in WTC 7 and how they caused the building to collapse remain unknown at this time. Although the total diesel fuel on the premises contained massive potential energy, the best hypothesis has only a low probability of occurrence.” [Federal Emergency Management Agency, 5/1/2002, pp. 1-17] Some reports indicate that the building may have been deliberately destroyed. Shortly after the collapse, CBS News anchor Dan Rather comments that the collapse is “reminiscent of… when a building was deliberately destroyed by well-placed dynamite to knock it down.” [CBS News, 9/11/2001]