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That's why one of the first decisions fire commanders made at the World Trade Center was to forgo any effort to fight the flames and instead concentrate on rescuing people. The fire that day was, of course, unusually large. But the decision to "defend in place" is standard FDNY procedure for high-rise blazes. "The building is supposed to be fire resistant," says retired FDNY deputy chief Vincent Dunn. "We just wait until all the fuel is consumed, and that usually takes one to two hours."
Neither of the twin towers lasted two hours, but that was hopefully a once-in-a-lifetime event. Skyscraper safety, however, is an everyday worry, and it's in the news once more after last week's unveiling of the revised design for the Freedom Tower.
On 9-11, the monumental collapse at ground zero was mainly because of the flames, not the planes. The steel towers withstood the impact of the jets, but not the warping effect of the inferno they ignited. A report by the National Institute of Standards and Technology released two weeks ago says the planes knocked the fireproofing material off the building's structures, exposing them to the intense heat. (A technical adviser to the Skyscraper Safety Campaign disputes that finding, saying it's possible there was not enough fireproofing to begin with.) The planes also severed pipes that fed the buildings' sprinklers.
That sort of damage wouldn't be seen in most high-rise fires. Deadly high-rise fires are rare in New York because many skyscrapers have their smoke alarms wired right to Fire Department dispatch, so firefighters are often on the scene before a blaze can swell. Heat-activated sprinklers also help. But in a building without sprinklers, or where sprinklers were being repaired or had been sabotaged, a healthy fire could get going fast. In the large, open-air office floors that are currently in favor, where everyone has cubicles instead of smaller rooms, a phenomenon called "flashover"in which all the combustible material goes up at about the same timecan occur.
"When you have flashover, it's extremely difficult to get enough water," says Russ Sanders, a former Louisville fire chief who now consults for the National Fire Protection Association. The problem is that the bigger the fire, the hotter it gets. And in high-rise blazes where firefighters must attack from inside the building, some fires are so large that no hose can spray enough water to extinguish the flames. Dunn says that a single hose can put out only about 2,500 square feet of fire. The World Trade Center's floors were 40,000 square feet.
Adding to the trouble, hoses connected to water pipes high up in buildings sometimes lack adequate pressure. And even getting firefighters to a high-rise fire can be difficult, since they might each carry 100 pounds of gear, the elevators might be unreliable, and stairways could be crowded with people fleeing down. That's why full-scale evacuations are discouraged in many high-rise fires.
If a standard house fire gets too hot to handle from the inside, firefighters can go into what Sanders calls "a defensive mode" and just spray water from outside. "The difference is you don't have another 60 floors of fuel above it," says Sanders. When a high-rise fire reaches flashover, he says, "it communicates. It starts lapping out the windows and it literally just climbs the floors." People trapped above the flames are then in peril. Ninety-five percent of the WTC tenants and visitors who died on 9-11 were caught above the floors where the planes hit.
Sent back to the drawing board after the NYPD raised worries about truck bombs, Freedom Tower architect David Childs presented a building set farther back from the street, mounted on a 200-foot, steel-reinforced concrete pedestal plated with shimmering steel. Developer Larry Silverstein said the Tower would be "the safest building ever constructed."
But the ground-level protections do little to protect people if fires break out above, as they did at the World Trade Center. The NIST report found that "stairwell capacity was adequate" at the WTC on 9-11, but only because the building was one-third occupied. "If the towers had been fully occupied . . . over 14,000 people might have perished," the report stated. One of the problems was that there were only three stairwells in each tower. Another was that in the north tower, all the staircases were bunched into the building core, and destroyed when the plane hit. In the south tower, one staircase was set apart from the others, and it remained passable, allowing at least 18 people who were located above the plane's impact to escape from tower two.
Childs tells the Voice that the Freedom Tower design "exceeded the code" with wider staircases, larger areas of refuge, and a staircase running the entire height of the building reserved for firefighters only. The building's staircases, sprinkler pipes, and emergency communications lines will all be encased in the building's core wall, which is, according to building plans, three feet thick in most places. It is not clear how far apart the staircases will be.