Associated Press National Writer
NEW YORK (AP) -- Inadequate fireproofing may have contributed to the collapse of the World Trade Center on Sept. 11, engineers studying the destruction of the buildings said Wednesday.
Inspections performed during the 1990s indicate that at least some of the steel rods supporting the floors of the twin towers were not covered with enough fireproofing insulation, fire safety expert Frederick W. Mowrer told his colleagues during a meeting on the buildings' collapse. Those floor joists are thought to have been the first parts of the buildings to fail as intense fires heated and weakened them.
``This is something that is going to have to be factored into the analysis,'' said Mowrer, a professor of fire protection engineering at the University of Maryland in College Park.
Building codes required that each of the 7/8-inch-thick steel rods making up the floor joists at the World Trade Center be coated with 2 inches of fire protection. But some photographs taken during the inspections show only a spattering of spray-on fireproofing.
``Do we have vulnerabilities that are beginning to emerge?'' Cornell University structural engineer Thomas O'Rourke wondered after seeing the photographs.
But Hyman Brown, an engineer who supervised the construction of the World Trade Center, said the fireproofing met the highest standards and was not a factor in the collapse.
``It lasted the amount of time it was supposed to last and 95 percent of the people got out,'' said Brown, who is now a professor at the University of Colorado in Boulder. ``To say that it wasn't adequate when it did its job, I don't understand.''
Mowrer, a professor of fire protection engineering at the University of Maryland, said it is too early to say definitively whether the inadequate fireproofing played a part in the buildings' collapse. But he said his research so far indicates it should be seriously considered.
``I think that's one of the tracks. One of the good, solid tracks,'' agreed Abolhassan Astaneh-asl, an engineering professor at the University of California in Berkeley.
Astaneh-asl has examined twisted and broken steel beams from the twin towers in the New Jersey scrap yard where they are being recycled.
His observations indicate the airplanes damaged or completely severed 40 percent of the columns holding up the buildings. They even penetrated into the ring of columns at the structures' cores, as evidenced by a steel beam Astaneh-asl found that had been pierced by a jet engine.
``It's like a bullet hole,'' he said.
The buildings simply redistributed their loads onto the intact columns when the airplanes hit. But as the fires burned, the floor joists were the first elements of the buildings' structures to fail. Their failure pulled the buildings' exterior columns inward, initiating complete collapse of the structures.
``If you didn't have the fires you would be fine,'' Astaneh-asl said.
Mowrer's calculations indicate the planes' fuel, initially assumed to have made the World Trade Center fires much more intense than a conventional building fire, may not have played such a significant role. His calculations show that much of the fuel was burned up in the fireballs that could be seen outside the buildings just after the planes hit. What was left inside the buildings would have been consumed within about 10 minutes.
Other high-rise buildings have survived intense multi-floor fires. In 1988 five floors of the 62-story First Interstate Bank Building in Los Angeles burned for 3 1/2 hours without causing the building to collapse. Three years later, the upper nine floors of Philadelphia's One Meridian Plaza burned until sprinklers eventually extinguished the flames.
``We need to look at the difference between the World Trade Center and these other fires,'' Mowrer said. ``We need to do the analysis and not just assume that just because it was hit by jet planes that (collapse) was inevitable.''