05-08-2003, 01:03 AM #1
NIST Report on fireproofing at WTC
NEW YORK (AP) - Fireproofing on the steel floor supports in the
World Trade Center was not tested and may have been too thin to
hold up under fire for the building code standard of two hours,
federal investigators said Wednesday.
The north tower, hit first, fell about an hour and 45 minutes
after terrorists struck with the first hijacked jetliner. The south
tower collapsed about an hour after the second plane attack. Nearly
2,800 people were killed.
According to a progress report by the National Institute of
Standards and Technology, which is conducting a two-year trade
center probe, documents show that builders in 1969 directed
contractors to coat the floor supports with a 1/2-inch-thick layer
of fireproofing. But investigators are stumped as to how the
owners, the Port Authority of New York and New Jersey, decided on
"We do not know if it was insufficient, but we are not sure
that it was sufficient," lead investigator Shyam Sunder said at a
Port Authority spokesman Greg Trevor said his agency has
provided "all of the documents that we have been able to locate,"
adding that the people who made the fireproofing decisions in the
1960s no longer work for the agency.
Arden Bement, NIST director, said the interim report released
Wednesday does not draw conclusions or make recommendations.
"That's for later, when we have a much more complete picture," he
In 1999, NIST found, the Port Authority issued guidelines to
upgrade the fireproof thickness to 1 1/2 inches. As recently as
2000, officials were still redoing the fireproofing, noting in one
property assessment that some areas could only withstand one hour
under fire, but that sprinklers also had been installed in the
By Sept. 11, 2001, the NIST report found, fireproofing had been
upgraded on 29 floors in the areas of the towers where the planes
struck. That included 19 floors in the north tower and 10 in the
Sally Regenhard, whose son was among the 343 firefighters
killed, said Wednesday she was "horrified to know we could build
such a fragile building with a minimum amount of fire protection."
When the trade center was built, the Port Authority - as an
interstate agency - was not bound to New York City building codes,
or any other for that matter. In May 1963, the agency instructed
engineers and architects to comply with the local building code,
but it wasn't until 30 years later that an agreement was
established to allow fire and other inspections.
In the 1960s, the architects of the complex chose to build
according to fire resistance standards that required floors to last
for two hours and columns to hold for three, NIST found.
A higher level, which required three hours for floors and four
hours for columns, was not chosen because there was "no economic
advantage in using Class 1A construction," stated a 1987
memorandum by a chief structural engineer for the World Trade
The code does not dictate how to meet the fire protection
standards; architects are left to develop specific measures.
In the case of the trade center, an innovative new floor system
using "bar joists" was used. The fireproofing manufacturer at the
time said a 1/2 inch layer would protect beams and girders for four
hours, but investigators have not found any evidence that the
elements used in the new floor system were tested with
Glenn Corbett, a fire science expert who has testified before
Congress about evacuation and other safety issues in the trade
center, said the system should have been tested.
"I don't think you could make a good decision without having
some kind of test to go back to," said Corbett, who also serves on
a team of experts advising the agency. "I don't know how you could
make an assumption about a new material."
But even the fast-moving fires that raged in the towers on Sept.
11, 2001, may have dwarfed the typical conditions assumed in the
one-size-fits-all fire resistance test, Corbett said.
In addition to the fireproofing, investigators are looking
closely at a photograph taken of the south tower's east face, about
12 minutes before the building crumbled. In the photograph, part of
the 83rd floor is seen sagging at an angle of about 45 degrees.
Sunder acknowledged the new evidence may put more focus on the
hypothesis that the buildings fell because the floors sagged first,
pulling the towers' side columns inward. Another theory envisions
that the columns failed and alone brought down the buildings.
"We have not yet taken a position on which of the two is the
most probable mechanism, but we are going to be looking at each of
these mechanisms in great detail," he said.
The photograph is part of a database of more than 3,100 pictures
and 3,400 video clips gathered by the agency.
The NIST investigation was launched last year to investigate the
collapse and evacuation of the trade center in an effort to make
buildings safer and improve emergency response procedures.
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(Copyright 2003 by The Associated Press. All Rights Reserved.)
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