NEW YORK — Fireproofing, sprinkler systems and the water supply for hoses were all disabled in the twin towers 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.
Deseret News graphic
World Trade Center Collapse
Requires Adobe Acrobat.
The fire, combined with these failures, brought down the towers even after they had shown surprising and lifesaving resiliency to massive structural damage caused by the impact of two hijacked airliners, the report says.
The report's findings detail for the first time the horrific 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 both remarkable strength and critical weaknesses. As was obvious to television viewers worldwide, the towers sustained the initial impact of the planes. But the buildings were able to redistribute loads away from damaged columns so well that they could probably have remained standing indefinitely if not for the fires, an earthquake or a windstorm, the report said. Team members are still debating the delicate question of 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 concludes.
BORDER="0">
BORDER="1"> FACE="Verdana,Helvetica,Arial"
SIZE="2">Related stories:
FACE="Verdana,Helvetica,Arial" SIZE="2">
March 8, 2002: 9/11 film to honor fire crews
Feb. 19, 2002: Stark realities of WTC attacks shown on tape
Jan. 14, 2002: Building near towers will be rebuilt
Nov. 5, 2001: Secret CIA office destroyed in WTC attack, official says
Oct. 24, 2001: Huge gap left in N.Y. skyline and hearts
Sept. 20, 2001: Landmarks targeted throughout all history
Sept. 17, 2001: Cleanup of unparalleled size at World Trade Center site
Sept. 15, 2001: Experts to begin study to make buildings resilient
Sept. 11, 2001: Twin Towers' steel and concrete construction couldn't have sustained the hit
The report, a copy of which was obtained by The New York Times, is not due to be released officially until late April or early May. It provides documentary evidence that simultaneously supports and rejects many of the theories about what happened to the towers on Sept. 11.
What is already clear is that the jet fuel played a role somewhat different, though still critical, than some experts had speculated. After the planes slammed into the towers, the fireballs that burst over Lower Manhattan consumed perhaps a third of the 10,000 gallons of fuel on board each plane, for example, but did little structural damage themselves, 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.
Under normal circumstances, fire suppression systems are designed to allow a high-rise blaze to burn itself out before the building collapses. But the report concludes that there were across-the-board failures in the towers' fire suppression systems, raising disturbing questions about the safety and integrity of other tall buildings in out-of-control fires. But the ultimate significance of those failures is extremely difficult to gauge, the report says, because of the extraordinary circumstances of the attack.
In fact, besides just setting the fires, the impact of the jets may have jarred loose the light, fluffy 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, building codes and engineering practices should be studied extensively to consider changes, a step the federal government is already planning, with a $16 million two-year inquiry by the National Institute of Standards and Technology now getting under way. The final version of the FEMA report may recommend specific changes in building codes and standards.
The report is also significant for what it does not include. With the exception of a few contorted steel beams from 5 World Trade Center, a nine-story office building that also burned and had localized collapses because the beams failed where they were bolted together, little evidence collected from the piles of debris contributed in a meaningful way to the report's conclusions.
That absence could intensify criticism of an early decision by the city to recycle steel from the trade center rather than make it immediately available for collection and analysis by the research team. About 60 pieces of trade center steel are being sent to the technology institute for the investigation, so future analysis could provide additional answers.
Stripped of its fireproofing, a steel column heats up much more quickly in a fire. The hotter the steel, the less it is able to support loads, as it eventually becomes as soft as licorice.
Most of the tenants in the floors below impact, to the credit of the building and the emergency lighting in the stairwells, escaped. More than 400 firefighters, police officers and other rescue personnel and dozens of tenants who stayed behind during the evacuation were killed when the buildings finally collapsed.