 In the aftermath of the collapse, the questions came quickly and urgently: was it inevitable that such a severely damaged structure would completely collapse? Or was there something about the building s design or construction that made it especially susceptible to failure? What exactly caused that failure-fire, heat, internal damage? Was the evacuation plan adequate enough to save the maximum number of lives? And are other tall buildings just as vulnerable to collapse when the blast is great and the fire uncontrolled? In the gray wasteland of smoke and dust and mangled steel that was once the third tallest building in the world, forensic engineers began sifting the wreckage for clues and answers to these and other structural truths. This blue-ribbon team of engineers is nearing the end of its task, and NOVA has been there from the beginning, following its investigation of the causes of the calamity. Why the Towers Fell presents the engineers  conclusions in the most definitive explanation yet of how and why the towers collapsed. But the Twin Towers weren t the only buildings that collapsed. Standing well over a city block from Trade Center Tower #1, a forty-eight-story glass and steel structure known simply as Building #7 did not seem to suffer structural damage from the collapsing towers but nonetheless crashed to the ground after several hours of severe and uncontrolled fire. Since Building #7 is a typical glass and steel building and seems to have collapsed from fire alone, does this mean that office workers the world over are far more vulnerable than anyone ever imagined? Featuring many of this country s best structural engineers including Gene Corley, the lead investigator on the Oklahoma City bombing; Charles Thornton, the builder of the Petronas Towers (the world s tallest building); and Mark Loiseaux, the leading expert on the "purposeful" demolition of big buildings, the program takes viewers through the process by which these professionals came to understand the how s and why s of one of modern America s greatest tragedies. Also presented are several of the buildings  survivors, who tell compelling real-life stories of their harrowing journeys to safety, including three firemen who miraculously escaped death as Tower #2 collapsed around them. With rare, video-enhanced footage showing details of the buildings  structural damage never before seen on TV, and detailed animation sequences that let viewers "see through" the buildings to the damage that had occurred inside, this NOVA is one of its most harrowing and memorable hours.