What actually caused the initial fires at the World Trade Center buildings to start on September 11, 2001?
DON PAUL: So far as I know, collisions by airliners started the first fires in the Twin Towers on 9/11. Regarding WTC-7, the origin of its intern fires appears more mysterious. FEMA’s Study says that fires burned in WTC 7 for 7 hours before its collapse. That puts their start in the same hour as the North Tower, WTC 1, which fell at 10:29. There’s no evidence I know, however, that debris from 1 ignited anything inside 7. Video and photographs show that 7 remains wholly upright and scarcely marred at mid-afternoon of 9/11, only small fires visible on the 7th and 12th floors. Its upper floors begin to fall straight-down from its base at 5:25. Before 9/11, no buildings of structural steel had ever collapsed due to fire. In February of 1991 a fire burned for 19 hours in the 38-story building at One Meridian Plaza in Philadelphia, spreading to 8 floors and causing the death of three firefighters. But this building stood. WTC 7 contained offices of the FBI and CIA and then-Mayor Rudolph Giul