Purdue Researchers
Simulate 9/11 Attacks

STEVE HERMAN / AP 21jun2007

A Purdue University computer simulation of the 2001 World Trade Center attacks shows in 3-D animation how the hijacked airplanes plowed through the towers, stripping fireproofing material from steel columns and causing the weakened skyscrapers to collapse.

The two-year Purdue study, funded in part by the National Science Foundation, supports a federal agency's findings that the towers could have remained standing if the fireproofing had not been stripped away, researchers said.

"One thing it does point out . . . is the absolute essential nature of fireproofing steel structures," Christoph Hoffmann, a professor of computer science and one of the lead researchers, said. "This is something that wasn't done originally in the World Trade Center when it was built. It wasn't code at that time."

The animation, intended in part to help engineers design safer buildings, shows a plane slicing through several stories of the World Trade Center's north tower and follows the disintegrating plane through the interior and out the opposite side.

The report concludes that the weight of the aircraft's fuel, when ignited, produced "a flash flood of flaming liquid" that knocked out a number of structural columns within the building and removed the fireproofing insulation from other support structures, Hoffmann said.

The simulation also found that the airplane's metal skin peeled away shortly after impact and shows how the titanium jet engine shafts flew through the building like bullets.