>There was something fishy about a third WTC building collapsing much
>as the twin towers had done, but without being hit by a jet plane or
NY Times, March 2, 2002, Saturday
A NATION CHALLENGED: GROUND ZERO; Burning Diesel Is Cited in Fall Of 3rd Tower
By JAMES GLANZ and ERIC LIPTON
Massive structural beams that functioned as a sort of bridge to hold up the
47-story skyscraper known as 7 World Trade Center were compromised in a
disastrous blaze fed by diesel fuel, leading to the building's collapse on
Sept. 11, investigators have concluded in a preliminary report.
The tower was set on fire by debris from the twin towers and burned for
about seven hours before collapsing in the late afternoon under previously
unexplained circumstances. The analysis of its collapse is one of the first
detailed findings by a team of engineers organized by the Federal Emergency
Management Agency and the American Society of Civil Engineers to understand
the fate of all the buildings around the site.
As much as 42,000 gallons of diesel fuel was stored near ground level in
the tower and ran in pipes up to smaller tanks and emergency generators for
Mayor Rudolph W. Giuliani's command center, the Secret Service's office and
Investigators have determined that the burning fuel apparently undermined
what is known as a transfer truss. The trusses, a series of steel beams
that allowed the skyscraper to be built atop multistory electricity
transformers, were critical to the structural integrity of the building and
ran near the smaller diesel tanks.
A failure of the same type of structural bridge contributed to the collapse
of the Alfred P. Murrah Federal Building in Oklahoma City when it was
bombed in 1995. Federal guidelines for public buildings, created in 1996,
warned of the dangers of such trusses in terrorist attacks.
''It's certainly right in the vicinity where the columns go into this
transfer system,'' said a person knowledgeable about the investigators'
draft report on the World Trade Center. ''The rest of the building is built
on top of the bridge.''
While 7 World Trade Center, which stood across Vesey Street just to the
north of the twin towers, was not formally a federal building, it did house
crucial government offices that included the city's nerve center for
The investigators said that their conclusions, combined with other findings
about the failure and collapse of 5 World Trade Center, could prompt
serious changes in the codes used in building construction.
The findings are in a draft report that has already been circulated among
government agencies, and are based on videos made on Sept. 11, witnesses'
reports, interviews with firefighters, evidence from the debris pile and
structural analysis. Team members, who described many of the findings,
cautioned that the conclusions on the collapse of 7 World Trade Center
could still be modified as reviews proceed.
But Irwin Cantor, one of the building's original structural engineers, who
is now a consulting engineer and member of the City Planning Commission,
said the diesel-related failure of transfer trusses was a reasonable
explanation for the collapse.
He said he believed that diesel tanks were not envisioned in the original
design of the building. ''It ended up with tenants who had diesels,'' Mr.
Cantor said. ''I know none of that was planned at the beginning.''
According to floor plans submitted to the Port Authority of New York and
New Jersey, which owns the land on which 7 World Trade sat, the building
complied with city fire codes, said Frank Lombardi, the authority's chief
engineer. Those codes permit no more than one fuel tank with a capacity of
275 gallons or less on above-ground floors, he said.
Jerome M. Hauer, who was the director of Mayor Giuliani's Office of
Emergency Management at the time the command center was opened at 7 World
Trade, said several teams of engineers reviewed plans to open the office
there. But no one ever mentioned any hazard associated with placing fuel
tanks above ground, near a transfer truss, he said.
''There were a host of people who looked at this,'' said Mr. Hauer, who is
now a managing director of the crisis and consequence group at Kroll
Worldwide, a security consulting company based in New York. ''We relied on
Fire officials did at one point question the storage of large amounts of
fuel well above the ground level, saying that one large tank for the
mayor's command center, if ever compromised, might fuel a fire that would
threaten the building.
The Sept. 11 draft report also has photographs and a description of debris
collected from a previously undisclosed, multistory collapse within 5 World
Trade Center, a nine-story office building that also burned on Sept. 11 but
largely remained standing. The team has found that one specific type of
bolted connection, called a column tree connection, that joined
floor-support beams, failed in the heat of the fires, causing the
four-story collapse in the part of 5 World Trade at the corner of Vesey and
Although no one died as a result of the collapses in 5 and 7 World Trade
Centers, since both stood long enough to be evacuated, the team's findings
are likely to lead to recommended changes in the way public and government
buildings are constructed, much the way similar studies did after the
Northridge earthquake near Los Angeles in 1994 and the Oklahoma City bombing.
The team is still deliberating on how tightly it can pin down the precise
train of events that led to the collapse of the twin towers themselves. But
until now, the collapse of 7 World Trade has stood as one of the
outstanding mysteries of the Sept. 11 attack, since before then, no modern,
steel-reinforced high-rise in the United States had ever collapsed in a fire.
High-rise buildings are designed to be able to survive a fire, even if the
fire has to burn itself out. The strategy is to ensure that the steel
support structures are strong enough or protected well enough from fire
that they do not give way in the time it takes for everything inside an
office building, like furniture, to burn.
In major high-rise fires elsewhere in the country, such as the 1 Meridian
Plaza fire in Philadelphia in 1991 and the First Interstate Bank fire in
Los Angeles in 1988, this approach has worked. The 1 Meridian fire burned
for 19 hours, leaping from floor to floor and burning out as combustible
materials were used up. But the fires at 7 World Trade Center raged mainly
on lower floors and never burned out, and in the chaos of Sept. 11, the
Fire Department eventually decided to stop fighting the blazes.
''What the hell would burn so fiercely for seven hours that the Fire
Department would be afraid to fight it?'' said one member of the
According to the Port Authority floor plans, 275-gallon diesel tanks sat on
the fifth, seventh and eighth floors and were fed through pipes from the
larger tanks near ground level. The team member said that while the diesel
fuel remains the most likely candidate for feeding the fires, it was still
unknown whether there could have been other sources of fuel in the
building, kept there by tenants like the Secret Service that have disclosed
little of what their spaces contained.
The huge steel transfer trusses ran mostly through the fifth, sixth and
seventh floors where the fires burned. The purpose of the trusses, which
included zigzagging and horizontal members and were concentrated around the
building's core, was to allow 7 World Trade to be built over two
Consolidated Edison substations that already existed on that spot when the
building went up in the late 1980's. Together the stations held 10
transformers, each about 35 feet high and 40 feet wide.
Using the trusses to avoid having vertical structural columns pierce the
transformers, the building was constructed around them like a hen sitting
on a giant egg.
''We had to do design tricks to accommodate the existing Con Ed facility,''
said Mr. Cantor, the structural engineer. ''This building had an awful lot
Transfer trusses are a well-tested technique and are used in countless
high-rise buildings, as well as in bridges around the world. Engineers say
that transfer trusses, for most buildings, present no extraordinary hazard.
But if there is an explosion, earthquake or long-burning fire, they can
present a problem.
In Oklahoma City, during the 1995 bombing of the Federal Building, a large
transfer girder on the building's third floor gave way, helping to
precipitate a progressive collapse that later analysis showed was
responsible for most of the 168 deaths. After this attack, federal
guidelines for buildings that would hold government agencies were changed,
recommending that buildings be designed so that single-point failures did
not cause a catastrophic collapse.
Videos of the 5:28 p.m. collapse of 7 World Trade lend vivid support to the
truss-failure theory. Roughly 30 seconds before the building goes down, a
rooftop mechanical room starts to disappear, falling into the building's
core. Then a second larger rooftop room sinks. The building then quickly
Both rooms were above sections of the building held up by the trusses.
Other video evidence shows fire concentrated in the floors containing the
trusses and the fuel tanks.
Dr. John D. Osteraas, director of civil engineering practice, Exponent
Failure Analysis Associates, in Menlo Park, Calif., reviewed videos of the
collapse, discussed it with other engineers and came to a similar
conclusion; the fuel, the trusses and the fire brought 7 World Trade down.
''The pieces have come together,'' he said. ''Without the fuel, I think the
building would have done fine.''