The Unforgettable Fire
Editor's note: The following report is gleaned from a special panel constituted of some of the leading fire-protection engineers in the community assembled to discuss the tragic fire that consumed the World Trade Center Sept. 11, 2001 and the impact the event may have on the design and maintenance of high-rise buildings from a life safety aspect.
Many questions have arisen in the wake of the horrific destruction of the World Trade Center Sept. 11, 2001, namely, could anything have been done to stop or contain the fire that ultimately caused the buildings to implode? Despite many advances in fire-protection technology since the towers were designed some 30 years ago, the answer is no, according to a number of top fire-protection engineers.
"Even if it was a brand new building that opened the day before the attack, it wouldn't have made a difference," says Les Strull, with the RJA Group's Chicago office.
Technology alone, not enough
Rob Sedlak, P.E., a senior vice president, with New York's Flack+Kurtz, the designers of Petronas Towers in Malaysia—currently the world's tallest building—concurs. "The technology we used in Petronas was similiar because the codes were similar. Most of the advances [in fire-protection engineering] have been in labor savings, with the exception of quick-response sprinkler heads."
Even then, Strull, who also sits on the Chicago City Council on High-Rise Buildings, explains the 767s that crashed into the buildings ruptured sprinkler lines and plumbing risers so that even more sophisticated devices like quick-response sprinkler heads wouldn't have operated.
"What people really have to remember is that this was basically a bomb," says Thomas Jaeger, P.E., president of Gage Babcock & Associates, Fairfax, Va.
Buildings, he says, are simply not designed to handle—let alone contain—fire that occurs on multiple floors and that burn as hot as jet fuel, in the vicinity of 2,000°F.
In fact, it was the intensity of heat that literally melted the remainder of the building's steel skin structure, already weakened by the damage the aircraft did upon impact.
The World Trade Center did have an unusual structural frame—a columnless design based on the principle of a tube—but Gerald Schultz, P.E., a principal with Woodridge, Ill.-based Fire Protection International, says the fact that nearly 25,000 people were able to successfully evacuate the buildings following the planes' impact, testifies to its structural strength. "What I think is remarkable is that the building stood for as long as it did with a fire sprinkler system that was likely taken out immediately by the crash, while also being subject to jet fuel fire, a much more severe fire than any fireproofing was designed to withstand."
Would more conventional designs have made any difference? The answer, again, no. "I'm not sure it would have mattered," says Sedlak. "When we evaluate buildings as to whether they should be steel or concrete, it's still a 2-hour-rated building, so a concrete-framed building would have failed as well."
As to the proposition of reinforcing steel with concrete for both structural and fire resistance purposes, Jaeger says it becomes a question of practicality.
"How much concrete are you talking about? Enough to make a plane bounce off a building?" he asks.
Strull agrees. "I don't think anything can be done, unless you design it like a WW II concrete bunker. And of course, it's too expensive to do that—You have to balance between making a building functional, usable and affordable," says Strull.
Still, Schultz believes the incident will impact future design. "I think we'll have to start looking at minimum egress and stairwell width. Especially if you're trying to move firemen up 43-inch stairwells," says the engineer. "But the real question is how do you fight fires in a building like this? Do we really expect firemen to climb 100 stories?"
This begs the question as to whether high-rises should be built beyond a reasonable height. "It's going to be purely driven by the economy," says Sedlak. "If companies need space, they're going to build buildings. But they may not build landmark buildings that you'll know on the other side of the ocean."
The public will also have a large say, according to Schultz. "If the public starts complaining about high-rises, and businesses start looking for new rental space, the market will dictate the situation, not what we say," says Schultz.
Engineers must lead
Strull agrees, but adds it's the engineer's and other leader's job to reassure the public that they are not in imminent danger by being in a high-rise. "You're not going to have an incident like this happening day after day or even year after year. Things are being put in place to prevent this from happening," says Strull.
Enhanced fire protection will be a part of that, believes Sedlak, even from the stark perspective that developers will simply need a marketing tool to reassure the public about the safety of their buildings. The question, however, becomes the degree of life safety measures.
"I think you have to look at the cost," says Jaeger.
For example, he points to the wake of the terrorist bombing of the Murrah Building in Oklahoma. "The government certainly has upgraded its blast-resistance capabilities at a huge cost. But I'm not sure private industry is prepared to do that. The same for the average building tenant.