Blaze, failed fireproofing cited in towers' collapse

Heat hit 2,000 degrees, sprinkler systems broke, federal report concludes


NEW YORK - Fireproofing, sprinkler systems and the water supply for hoses all largely failed in the twin towers of the World Trade Center on Sept. 11 in the face of a blaze so intense that it drove temperatures as high as 2,000 degrees and generated heat equivalent to the energy output of a nuclear power plant, a federal report on how the towers fell has concluded.

The fire, combined with these failures, brought down the towers even after they had shown surprising and lifesaving resiliency to huge structural damage caused by the impact of two hijacked airliners, the report says.

The report's findings detail for the first time the series of events that led to the collapse of two of the world's tallest buildings. They are contained in a draft of a report commissioned by the Federal Emergency Management Agency and the American Society of Civil Engineers.

The draft describes a structure that showed remarkable strength and critical weaknesses. The towers sustained the initial impact of the planes and were able to redistribute loads away from damaged columns so well that they could probably have remained standing indefinitely if not for the fires, a major earthquake or an overwhelming windstorm, the report said. Team members are debating whether the tremendous fires could have brought the towers down on their own.

"The ability of the two towers to withstand aircraft impact without immediate collapse was a direct function of their design and construction characteristics, as was the vulnerability of the two towers to collapse as a result of the combined effects of the impacts and ensuing fires," the report says.

The report, a copy of which was obtained by The New York Times, is not scheduled to be officially released until late next month or early May. It provides documentary evidence that supports and rejects many of the theories about what happened to the towers.

What is clear is that the jet plane fuel played a different though still critical role than experts had speculated. For example, after the planes slammed into the towers, the fireballs that burst over Lower Manhattan consumed perhaps a third of the 10,000 gallons of jet fuel on board each plane but did little structural damage, the report says. Like a giant well of lighter fluid, though, the remaining fuel burned within minutes, setting ablaze furniture, computers, paper files and the planes' cargo over multiple floors and igniting the catastrophic inferno that brought the towers down.

Fire suppression systems are designed to allow a high-rise blaze to burn itself out before the building collapses. But the report concludes there were across-the-board failures. Besides just setting the fires, the impact of the jets may have jarred loose the light fireproofing that had been sprayed on steel columns, and flying debris almost certainly sliced through the vertical pipes that supplied water for the hoses and sprinklers.

Because of those uncertainties, the report says, the possibility of changes to building codes and engineering practices should receive extensive further study.

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