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A federal technical building and fire safety investigation of the collapses of the Twin Towers and 7 WTC has been conducted
by the United States Department of Commerce's National Institute of Standards and Technology (NIST). The goals of this investigation,
completed on April 6, 2005, were to investigate the building construction, the materials used, and the technical conditions
that contributed to the outcome of the WTC disaster. The investigation was to serve as the basis for:
* Improvements in the way in which buildings are designed, constructed, maintained, and used
* Improved tools and guidance for industry and safety officials
* Revisions to building and fire codes, standards, and practices
* Improved public safety
The report concludes that the fireproofing on the Twin Towers' steel infrastructures was blown off by the initial impact
of the planes and that, if this had not occurred, the towers would likely have remained standing. The fires weakened the trusses
supporting the floors, making the floors sag. The sagging floors pulled on the exterior steel columns to the point where exterior
columns bowed inward. With the damage to the core columns, the buckling exterior columns could no longer support the buildings,
causing them to collapse. In addition, the report asserts that the towers' stairwells were not adequately reinforced to provide
emergency escape for people above the impact zones. NIST stated that the final report on the collapse of 7 WTC will appear
in a separate report.This was confirmed by an independent study by Purdue University.
Although potential improvements were found, Gene Corley, the director of the original investigation, commented that the
original towers did quite well overall.
"Our report points out that the towers really did amazingly well," Corley said. "The terrorist aircraft
didn’t bring the buildings down; it was the fire which followed. It was proven that you could take out two thirds
of the columns in a tower and the building would still stand."
Nonetheless, additional fireproofing and improvements to stairwells will certainly be priorities for the reconstruction
of the towers.
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