New York Times
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
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.
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
"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
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,
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
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.
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
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."
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
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."