9/11 evacuation slower than expected

When the planes hits the twin towers on Sept. 11, 2001, they dislodged the fireproofing protecting of the steel columns and trusses that held the buildings together. That proved to be the key factor, according to the National Institute of Standards and Technology. Stripped of protection, the steel sagged following prolonged exposure to temperatures of at least 1,000 degrees Fahrenheit, triggering the towers’ pan caking collapse. The attacks killed 2,749 people in the towers and on the two planes.

But lead investigator Shyam Sunder said the failure of the fireproofing was not as a result of improper installation when the towers were constructed more than 30 years before or lax maintenance that followed. “You would not expect fireproofing to be installed to withstand the impact of an airplane,” Sunder said, speaking at a press briefing at a Times Square hotel. “We are not suggesting here that people should design buildings to withstand airplanes.” New government reports showed conflicting information on how people evacuate skyscrapers.

The Two architects who worked on the new report said there are incorrect assumptions on how quickly people exit the buildings. One reason, they said, is that people linger before heading to a stairwell. The two-year study found the lack of protection from the damaged fireproofing allowed fires fed by jet fuel to spread through the buildings. Weakened floors sagged and pulled in fire-weakened exterior columns that led to the collapse.

The standards institute, which will issue recommendations in June, said stronger stairwells and elevators, clearer communications between rescuers and better preparedness among occupants of the buildings would have cut down the death toll of 2,749. The investigation included hundreds of interviews with people who escaped the fiery buildings and rescuers. Computer models of the hijacked airliners, the twin towers and their interiors were created to explore the effects of the crashes. Some 7,000 photographs and 150 hours of videotapes were also studied for evidence in the scientific reenactment.

“We simulated the aircraft impact, the fire dynamics, the response of the fire on the structure and the thermal insulation and the progression of failures in the structure that eventually led to the collapse,” Sunder said.