FEW buildings could have withstood the blast that shook the World Trade Center.
"It hit the Achilles' heel of the building," says architect Randy Croxton of the Croxton Collaborative.
The Achilles' heel in this instance was the power and communications center of the building.
The blast ruptured water pipes that would normally have brought water to cool emergency generators. Firefighters drew off other available water to attack a very hot fire in the basement of the building.
Without power, emergency lights in the stairwells and the ventilation fans both failed. The only internal communications in the building was by a walkie-talkie. As a result, individuals walking down the fire stairwells were in total darkness, in sooty smoke, and without any idea what had happened. As these workers exited the building, they complained to television crews about the lack of lighting and information.
At the same time, high-rises, such as the World Trade Center, with a core in the middle and elevator shafts, creates a "stack effect." This stack effect pulled the smoke through the building. Croxton says architects are constantly trying to find ways to isolate the life systems in a building, through pressurization or floors that break up the stack effect.
Most fire safety systems are not designed to cope with a bomb going off - which is suspected in this blast - says Tom Klem, director of fire investigations at the National Fire Protection Association. NFPA writes the standards for fire protection. He notes that the center had circuits for the first 35 floors in the basement level. All of these circuits were knocked out by the blast or by flooding when pipes burst. Mr. Klem says the center may have to move its circuits, emergency generators, and water sou rces up to the 35th floor. The circuits from the 35th floor to the top worked, providing emergency lighting.
NFPA will begin an investigation to see whether changes need to be made, Klem says.
At a press conference on Saturday, Stanley Brezenoff, executive director of the Port Authority of New York and New Jersey, which runs the center, indicated it might need a third backup system, perhaps using batteries. He concluded that the evacuation of the building went "reasonably well" without panic, considering the circumstances.