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New York Times, November 29, 2001
THE SITE
Engineers Suspect Diesel Fuel in Collapse of 7 World Trade Center
By JAMES GLANZ
Almost
lost in the chaos of the collapse of the World Trade Center is a
mystery that under normal circumstances would probably have captured
the attention of the city and the world. That mystery is the collapse
of a nearby 47-story, two-million-square-foot building seven hours
after flaming debris from the towers rained down on it, igniting what
became an out-of-control fire.
Engineers and other experts, who
quickly came to understand how hurtling airplanes and burning jet fuel
had helped bring down the main towers, were for weeks still stunned by
what had happened to 7 World Trade Center. That building had housed,
among other things, the mayor's emergency command bunker. It tumbled to
its knees shortly after 5:20 on the ugly evening of Sept. 11.
The
building had suffered mightily from the fire that raged in it, and it
had been wounded by the flying beams falling off the towers. But
experts said no building like it, a modern, steel-reinforced high-rise,
had ever collapsed because of an uncontrolled fire, and engineers have
been trying to figure out exactly what happened and whether they should
be worried about other buildings like it around the country.
As
engineers and scientists struggle to explain the collapse of 7 World
Trade Center, they have begun considering whether a type of fuel that
was inside the building all along created intensely hot fires like
those in the towers: diesel fuel, thousands of gallons of it, intended
to run electricity generators in a power failure.
One tank
holding 6,000 gallons of fuel was in the building to provide power to
the command bunker on the 23rd floor. Another set of four tanks holding
as much as 36,000 gallons were just below ground on the building's
southwest side for generators that served some of the other tenants.
Engineers
and other experts have already uncovered evidence at the collapse site
suggesting that some type of fuel played a significant role in the
building's demise, but they expect to spend months piecing together the
picture of what remains a disturbing puzzle.
"Even though
Building 7 didn't get much attention in the media immediately, within
the structural engineering community, it's considered to be much more
important to understand," said William F. Baker, a partner in charge of
structural engineering at the architectural firm Skidmore, Owings &
Merrill. "They say, `We know what happened at 1 and 2, but why did 7
come down?' "
Engineers said that here and across the country,
diesel-powered generators are used in buildings like hospitals and
trading houses, where avoiding power outages is crucial. Partly for
that reason, Jonathan Barnett said, a definitive answer to the question
of what happened in 7 World Trade Center is perhaps the most important
question facing investigators.
"It's just like when you
investigate a plane crash," said Dr. Barnett, a professor of fire
protection engineering at the Worcester Polytechnic Institute. "If we
find a weakness in the building or a deficiency in the building that
causes that collapse, we then want to find that weakness in other
buildings and fix it."
In many ways, 7 World Trade Center, built
and owned by Silverstein Properties, was structurally similar to its
towering cousins across Vesey Street to the south. The weight of the
building was supported by a relatively tight cluster of steel columns
around the center of each floor and a palisade of columns around the
outside, in the building's facade.
Sprayed on the steel, almost
like imitation snow in holiday decorations, was a layer of fireproofing
material, generally less than an inch thick. Although the fireproofing
was intended to withstand ordinary fires for at least two hours,
experts said buildings the size of 7 World Trade Center that are
treated with such coatings have never collapsed in a fire of any
duration.
Most of three other buildings in the complex, 4, 5 and
6 World Trade, stood despite suffering damage of all kinds, including
fire.
Still, experts concede, in a hellish day, 7 World Trade
might have sustained structural injuries never envisioned in fire
codes. That day began with flaming pieces of steel and aluminum and,
horribly, human bodies raining around the building.
With the
collapse of both towers by 10:30 a.m., larger pieces of the twin towers
had smashed parts of 7 World Trade and set whole clusters of floors
ablaze. An hour later, the Fire Department was forced to abandon its
last efforts to save the building as it burned like a giant torch. It
fell in the late afternoon, hampering rescue efforts and hurling its
beams into the ground like red-hot spears.
Within the building,
the diesel tanks were surrounded by fireproofed enclosures. But some
experts said that like the jet fuel in the twin towers, the diesel fuel
could have played a role in the collapse of 7 World Trade.
"If the enclosures were damaged, then yes, this would be enough fuel to explain why the building collapsed," Dr. Barnett said.
Dr.
Barnett and Mr. Baker are part of an assessment team organized by the
American Society of Civil Engineers and the Federal Emergency
Management Agency to examine the performance of several buildings
during the attacks. If further studies of the debris confirm the
findings of extremely high temperature, Dr. Barnett said, "the smoking
gun would be the fuel."
Others experts agreed that the diesel
fuel could have speeded the collapse, but said the building might have
met the same fate simply because of how long it burned.
"The
fuel absolutely could be a factor," said Silvian Marcus, executive vice
president for the Cantor Seinuk Group and a structural engineer
involved in the original design of the building, which was completed in
1987. But he added, "The tanks may have accelerated the collapse, but
did not cause the collapse."
Because of those doubts, engineers
hold open the possibility that the collapse had other explanations,
like damage caused by falling debris or another source of heat.
The
fuel tanks were not the only highly flammable materials in the
building. But while some engineers have speculated that a high-pressure
gas main ruptured and caught fire, there was none in the area, said
David Davidowitz, vice president of gas engineering at Consolidated
Edison. The building was served only by a four-inch, low-pressure line
for the building's cafeteria, Mr. Davidowitz said.
The mayor's
command bunker, built in 1998, included electrical generators on the
seventh floor, where there was a small fuel tank, said Jerome M. Hauer,
director of the mayor's Office of Emergency Management from 1996 to
2000. That tank was fed by a tank containing thousands of gallons of
diesel fuel on a lower floor, he said.
Francis E. McCarton, a
spokesman for the emergency management office, confirmed that
assessment. "We did have a diesel tank in the facility," he said. "Yes,
it was used for our generating system."
The manager of the
building when it collapsed, Walter Weems, said the larger tank sat on a
steel-and-concrete pedestal on the second floor and held 6,000 gallons
of diesel fuel. He said an even larger cache, four tanks containing a
total of 36,000 gallons of diesel fuel, sat just below ground level in
the loading dock near the southwest corner of the building.
"I'm
sure that with enough heat it would have burned," Mr. Hauer said of the
diesel. "The question is whether the collapse caused the tank to
rupture, or whether the material hitting the building caused the tank
to rupture and enhance the fire."
Falling debris also caused
major structural damage to the building, which soon began burning on
multiple floors, said Francis X. Gribbon, a spokesman for the Fire
Department. By 11:30 a.m., the fire commander in charge of that area,
Assistant Chief Frank Fellini, ordered firefighters away from it for
safety reasons.
A combination of an uncontrolled fire and the
structural damage might have been able to bring the building down, some
engineers said. But that would not explain steel members in the debris
pile that appear to have been partly evaporated in extraordinarily high
temperatures, Dr. Barnett said.
"Any structure anywhere in the
world, if you put it in these conditions, it will not stand," Mr.
Marcus said. "The buildings are not designed to be a torch."
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