Fireproofing, sprinkler systems and the water supply for hoses were all disabled in the World Trade Center's twin towers on Sept. 11 in the face of a blaze so intense that it drove temperatures as high as 2,000fWhat is already clear is that the jet plane fuel played a somewhat different though still critical role from some experts had speculated.
For example, after the planes slammed into the towers, the fireballs that burst over Lower Man-hattan consumed perhaps a third of the 38,000 liters of jet fuel on board each plane, 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 several floors and igniting the catastrophic inferno that brought down the towers.
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 fire suppression systems inside the towers, 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 the extraordinary circumstances of attacks.
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, the possibility of changes to building codes and engineering practices should receive extensive further study, a step the federal government is already planning, with a US$16 million, two-year inquiry by the National Institute of Standards and Technology now getting underway. The report's final version 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 torn, contorted steel beams from 5 World Trade Center, a nine-story office building on the site that also burned and suffered localized collapses because the beams failed where they were bolted together, not a single piece of evidence collected from the piles of debris contributed in a meaningful way to the report's conclusions.
That gap 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 team. Some 60 pieces of trade center steel are being sent to the National Institute of Standards and Technology for the continuing investigation, so it is possible that future analysis of the steel remnants could provide additional answers.
The draft report also does not contain any discussion of what could, potentially at least, become an explosive new issue in attempts to explain why the south trade tower, though struck after the north tower, fell first. That issue involves a program, started after the 1993 bombing of the towers, to increase the the thickness of the fireproofing on the lightweight steel joists that held up the floors in the trade center.