According to the official explanation, the World TradeCenter Twin Towers (WTC 1 and WTC 2) collapseddue to damage from airplane impacts and ensuingfires, while World Trade Center Building 7 (WTC 7), a47-story skyscraper also in the World Trade Centercomplex, collapsed completely and symmetricallyinto its own footprint due to office fires ignited bydebris from the earlier collapse of WTC 1. Thoughfew people have studied it closely, a majority of thepublic, including most architects, engineers, andscientists, accept the official explanation.1Much of the public, however, including a consider-able number of architects, engineers, and scien-tists, do not accept the official explanation.2 3 Amongthose who reject it, the most common explanationis that WTC 1, WTC 2, and WTC 7 were destroyedin a procedure known as “controlled demolition,”whereby carefully placed explosives or other de-vices are detonated to bring down a structure in adesired manner. September 11, 2001, aside, everytotal collapse of a steel-framed high-rise buildingin history has been caused by controlled demolition.