Trade Center puzzle lingers
March, 2002, 10:25 GMT
Investigations began as the wreckage was cleared
Better construction could have saved hundreds of
lives in the World Trade Center (WTC), but
investigators are still puzzling over the
The WTC towers "did very well" to stand
as long as they did, the head of the official
inquiry into their collapse said in a BBC Horizon
programme broadcast in the UK on Thursday.
But other structural engineers say use of more
robust materials would have definitely allowed
some people trapped on the upper floors of the
centre to escape and may have prevented their
The issue is of vital interest because the WTC's
design was revolutionary and its construction
methods influenced skyscrapers across the world.
Designed for impact
Leslie Robertson designed the structural elements
of the WTC towers to withstand the impact of the
largest airliner then in service, the Boeing 707.
Would they ultimately have collapsed? Maybe not
"With the 707 however, to the best of my
knowledge, the fuel load was not considered in the
design," he told Horizon.
But as the programme explained, it was the fuel
aboard the hijacked Boeing 767s that led to the
Each tower had a strong central column and a
strong external steel skeleton.
Bound to fall
But neither could ever be strong enough to stand
by itself, so the key to stability was the steel
floor trusses which linked the two.
Investigators believe that foam fireproofing
surrounding these trusses blew away when the
planes hit the towers, leaving the steel to buckle
in the heat of the fires that followed.
Once the crucial trusses began to fail, the towers
were bound to fall.
In the minutes that they remained standing, most
of the people below the levels where the planes
hit were able to escape.
But those above were trapped as fire blocked the
central columns and their stairways.
Only four people from either tower managed to
escape from the levels above the impacts.
Some investigators believe that better
fireproofing of the central columns would have
saved hundreds of them, even if the towers had
still collapsed in the end.
The drywall fireproofing surrounding the central
columns was highly fire-resistant but not very
Researchers believe much of it was dislodged on
And it was weak enough for a man trapped between
floors in a lift to hack his way through it with
the squeegee he used for cleaning windows.
Gene Corley, head of the official inquiry into the
towers' collapse, says that the towers did well
not to fall down immediately.
I cannot escape the people who died there
WTC structural engineer
"The fact that one of them lasted 55 minutes
and the other about an hour and 40 minutes says
they did very well," he told the programme.
Mr Corley is due to publish his interim findings
But other engineers appearing in the programme
speculate that a better tower design could have
"Had the floor system been a more robust
floor system with much stronger connections
between the exterior and the inside, I think the
buildings... would have lasted longer," said
"Would they ultimately have collapsed? Maybe
Mr Robertson is plagued by the wisdom of hindsight
and deeply distressed by the memory of what
happened to those inside his buildings.
"I cannot escape the people who died there...
that still to me somehow up there in the air are
"I cannot make that go away," he said.
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