3. How could the WTC towers have collapsed without a controlled demolition since no steel-frame, high-rise buildings have ever before or since been brought down due to fires? Temperatures due to fire don't get hot enough for buildings to collapse.

The collapse of the WTC towers was not caused either by a conventional building fire or even solely by the concurrent multi-floor fires that day. Instead, NIST concluded that the WTC towers collapsed because: (1) the impact of the planes severed and damaged support columns, dislodged fireproofing insulation coating the steel floor trusses and steel columns, and widely dispersed jet fuel over multiple floors; and (2) the subsequent unusually large, jet-fuel ignited multi-floor fires weakened the now susceptible structural steel. No building in the United States has ever been subjected to the massive structural damage and concurrent multi-floor fires that the towers experienced on Sept. 11, 2001.