Nova Why the Towers Fell (1974– ) Online

This BBC documentary uses footage of the erection of the World Trade Center, the 1993 bombing, Sept 11 and Ground Zero, graphics of the towers and the planes hitting them, and testimony from survivors, engineers, firemen, and the builder Leslie Robertson.

The WTC was built to overcome what was previously seen as drawbacks to older buildings like The Empire State Building, with a new approach to provide more usable floorspace. This was to make a steel outer skeleton which would bend in the force of the wind, a steel inner core of girders, and steel floor trusses that braced the skeleton to the core. However, the heat-resistant foam that coated the trusses and the drywall plasterboard are what ultimately weakened the towers to the attack, since they both were practically blown away by the jet fuel fire, which weakened the steel.

What is interesting is that while both towers eventually suffered "progressive collapse", as the floors pancaked, each tower fell for a specific different reason. The south tower (which fell first) fell because the outer skeleton snapped, but the north tower fell because the inner core collapsed. The differences were also due to the angles of the planes and the height of the floors that were impacted, and the comparative time that each tower endured their fires. Although experts disagree as to whether different truss connections in the design might have helped the towers withstand the impact, they agree that the length of time the towers stood is remarkable.

Whilst this treatment is primarily concerned with the engineering approach, there are also emotional touches - footage of the doomed inhabitants of the floors above the impact (though no one is seen to jump), the guilt of Robertson, whose office has a view of Ground Zero, and of the firemen who abandoned the south tower after the north fell. We are told that they had only reached floor 26 (they were headed for 93) when the call came to go back, however it seems careless to comment that even if they had reached their destination, there is little they could have done. We hear the story of two men who were trapped in a stalled elevator and who fought through the drywall to escape, and the ghoulish announcement made for workers to return to the south tower before the second plane hit, as some people had evacuated upon hearing of the first plane's impact.

Although the engineering agenda makes the mercenary footage of the burning towers acceptable, draining the color at times seems unnecessary and exploitative.

Fascinating and eerie. Essentially , a prime example of all that can go wrong at once. All the elevators and sprinklers were in the center of each floor. A weak and unstable distribution of the weight of each floor by a precarious cantilever design using far too small girders, joints, and bolt-connectors. No cinder block to speak of or not used at all. Wallboard was used instead. About all that didn't happen is that electrical wiring didn't catch fire, like in "Inferno". I suspect that, in reality, a similar pancaking effect might have happened in the fictitious story of "The Towering Inferno". Again, the "specs" were not tough enough for a 100-story building, while it did meet building codes designed for much smaller buildings. The architect of the building looks totally "spooked" and guilty about the whole thing . All in the name of more "retail floor space" than the solidly built Empire State Building. Beautifully produced by the BBC and not at all dry or boring (to me). Tastefully produced with a minimum of explicit scenes. When you find out why the "Twin Towers" were selected as targets, you will be very surprised!

One of the worst productions in NOVA's history. The source of the animation used to depict how the buildings collapsed is far too close to the Bush administration and completely one-sided. There are no alternative theories, and the science and engineering conclusions make no sense in the real world. Nova has simply followed the dictates of what the National Science Foundation and the government have approved and sanctioned. There were many glaring omissions from the program; first, why did the buildings collapse at free-fall speed, that is, less time than it takes an unimpeded object to fall the height of the building? The smoke of the fire was a tell tale sign that the fires were not hot enough to melt the massive beams of steel used to construct the building. Nothing is mentioned about the heat generated nor the massive amounts of asbestos and cement dust that eventually caused so many emergency workers to lose their health. And, nothing at all is mentioned about Building 7, the building that supposedly housed the mayor's emergency headquarters, SEC records, and many other important government offices. Even though the building was only hit by spurious pieces from the nearby collapse of the twin towers, many hours later it too collapsed at free-fall speed, just like a planned demolition. This was one of Nova's worst moments.