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Newsday

Report: WTC Towers May Have Been Weaker

By MICHAEL WEISSENSTEIN
Associated Press Writer

June 19, 2004, 12:16 AM EDT

NEW YORK -- The World Trade Center's designers may have severely underestimated the forces that wind exerted on the twin towers, leading them to design skyscrapers less able to handle the Sept. 11 attacks, a federal report says.

Wind tunnel tests conducted as part of litigation over the buildings' collapse found wind loads 20 to 60 percent higher than those found in tests performed during the towers' design in the 1960s, according to the report released Friday by a federal institute examining the collapse.

The buildings would have been stronger and might have performed better during the 2001 attacks by terrorists in hijacked jetliners if the higher wind load numbers had been used, said Shyam Sunder, the lead investigator for the National Institute of Standards and Technology.

"It is relevant to evaluating the buildings' capacity to withstand an unanticipated event," he said.

A spokesman for the Port Authority of New York and New Jersey, which owns the site, said he could not comment on the NIST findings. He repeated earlier statements that the towers were built according to building standards.

The report also provided the first official estimate of the number of people in the twin towers on the morning the planes struck.

The agency estimated that between 16,200 and 18,600 people were in the mammoth buildings, based on interviews with more than 1,000 of the occupants and with first responders.

The estimate does not vary greatly from newspaper estimates and statements by officials such as former Mayor Rudolph Giuliani, who had said rescuers saved 25,000 people that day. The NIST number does not include people who may have escaped surrounding buildings.

About 2,800 people were killed in the attack.

The institute's investigation began two years ago as an effort to determine why the buildings collapsed and apply the lessons to possible improvements in building codes and other standards. Its final report is due in December.

Investigators have found that north tower structural components that had been coated with thicker fireproofing during a 1990s upgrade had more than three times the ability to withstand fire than original components in the south tower.

The institute is examining whether fireproofing was a factor in the north tower's ability to stand twice as long as the south tower after it was hit.

The report also details the collapse of 7 World Trade Center, a 47-story building that was not hit by a plane but burned for hours before collapsing that afternoon.

The city's emergency operations center was located in the building, which housed diesel fuel to power the center and generators for other tenants. The NIST found that the collapse most likely originated around the fifth floor, near a distribution system for the fuel.

No one was killed in the collapse of 7 World Trade Center, but the Giuliani administration has been criticized for locating the city's emergency center in a building containing thousands of gallons of diesel fuel.
 

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New York Times
June 19, 2004

Towers' Wind-Force Design Questioned

By ERIC LIPTON

Engineers who designed the World Trade Center may have significantly underestimated the force of the winds that the twin towers needed to withstand in the worst of possible storms, federal investigators said yesterday, an oversight that could have led to weaker-than-needed exterior steel columns.

That design decision, although inconsequential for three decades, perhaps shortened the time that tenants and rescue workers had to evacuate the towers before they collapsed on Sept. 11, 2001.

The finding, which the engineers dispute and that investigators acknowledge needs more study and may turn out to be unfounded, was among dozens of interim conclusions released yesterday as a two-year study on the collapse of the twin towers neared a conclusion.

The report, released yesterday by the National Institute of Standards and Technology in Boulder, Colo., includes detailed photographs that identify, for the first time, the exact spots where the exterior steel columns gave way. These critical zones were around the 81st floor in the south tower, near the offices of Fuji Bank, and near the 96th floor of the north tower, where Marsh & McLennan was based.

For 7 to 10 minutes before the towers fell, the photographs show exterior columns bowing inward, almost like pieces of cooked spaghetti, a sign that they are about to give way.

Even so, the institute investigators have not pinpointed why the two towers collapsed after they were able to withstand the initial impacts by the Boeing 767 planes. But two primary theories have been identified.

As the fires ignited by the planes burned out of control, the exterior steel columns in the towers, designed primarily to resist wind, might have given way. Alternatively, the innovative lightweight floors that connected the exterior of the towers to their cores might have sagged, pulling the exterior columns inward and starting the collapse, the interim report says, adding that it might have been a combination of both factors.

The investigators also released yesterday, for the first time, an estimate that put the number of people in the towers at the time of the attack at about 17,000, about a third of their capacity given the early-morning hour. For that reason, the report said, at least in part, almost all the tenants below the floors of impact were able to flee before the towers fell. Those who died - 1,560 in the north tower and 599 in the south tower - were with few exceptions at or above the impact zone, or they were among the 433 firefighters, police and security guards involved in the rescue effort.

If the towers had been fully occupied, with 50,000 tenants and visitors, the evacuation would have taken about four hours, the report says. The unstated implication is obvious: many thousands more would have died, given that the south tower fell in 56 minutes and the north tower in 102 minutes.

A crucial remaining question, investigators said, is whether the design of the towers - their structure, their emergency stairwells and countless other safety features - might have contributed to the number of deaths.

When the inquiry is completed at the end of the year, the investigators expect to recommend changes in building and fire codes nationwide that would better protect tall buildings against fires or other calamities, although not necessarily an airplane crash.

"It is going to move forward the state of the art and improve the safety of buildings in the future," said Dr. S. Shyam Sunder, the acting deputy director of the Building Fire and Research Laboratory at the National Institute of Standards and Technology, and the leader of the investigation.

Something as simple as fireproof wall partitions, which were not required in the twin towers, might have limited the spread of the fires, Dr. Sunder said yesterday.

Corporate tenants typically prefer open floor plans - they were a major selling point for the twin towers - but the partitions might have slowed the spread of fires that were ignited by jet fuel, he said, perhaps allowing the fires to burn themselves out.

The questions about the wind tests conducted in the early 1960's as the twin towers were being designed surfaced after institute investigators examined data collected in 2002, when two laboratories conducted separate wind tests, as part of an insurance lawsuit. The tests both came up with different results. But they predicted a wind load on the towers during an extreme storm that was 20 to 60 percent greater than an engineer for the Port Authority of New York and New Jersey had reported using during the original design calculations. The structures are designed to handle a storm that might happen once every 500 years.

On the day of the attack, the winds were light, and the pressure on the exterior columns was so modest that they were using about 16 percent of their capacity, studies have shown.

When the planes hit, the towers swayed as much as 20 inches at their tops. Even though a large swath of outer columns in both buildings' facades had been blown out, the stress on the remaining columns rose to about 50 percent of their capacity in zones at the top of the towers, and to more than 90 percent in spots next to the impact holes, one study done for the insurance lawsuit has shown.

At this point, the towers were strong enough to remain standing, investigators said, but fire took its toll, weakening the steel columns and consuming any available reserve. Institute investigators are now trying to determine whether the original wind tests were accurate, or whether different results would have led to stronger columns, thus increasing their reserve capacity, and possibly preventing or delaying a collapse. Jack E. Cermak, a wind engineer in Fort Collins, Colo., who did the tests in the early 1960's, said that he remained confident that the original tests accurately predicted how much force an extreme storm would have applied to the towers. In fact, during the wind tunnel test - which used scale models of the towers - the vortex conditions created by the high winds were so extreme that the twin towers had to be redesigned to make them stronger. The twin towers were the first super tall buildings for which wind tunnels were used to estimate wind loads.

"The initial studies in 1964 were conducted using the most sophisticated modeling," Mr. Cermak said, "and it's an approach that is still being used at wind tunnels today."

Leslie E. Robertson, a primary structural engineer on the project, said yesterday that he had not read the interim report, but said it was unlikely that he and others underestimated the potential wind forces.

"That is nonsense," Mr. Robertson said. "It is a totally implausible position to take."

Among the reasons for the differences, Dr. Cermak said, is that data predicting how strong the worst possible winds might be in Lower Manhattan might have changed in 40 years.

Dr. Sunder said the matter was still being investigated, in part by trying to determine what kind of wind loads the towers, as built, could have sustained, instead of relying on a published statement from a Port Authority engineer at the time.

Regardless, he said, the findings suggest that there is a need for national standards governing wind tunnel testing to ensure that engineers are accurately estimating how strong skyscrapers and other buildings need to be in order to withstand monster storms, or other cataclysmic events.

"We want different laboratories to come up with the same results," Dr. Sunder said. "These results dictate the design of these tall buildings."

Copyright 2004 The New York Times Company
 

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These reports don't bode well. The Authorities will probably use them as an excuse not to bring new Twin Towers back (or to add extra floors to the 'Freedom Tower' and add a second one).

It's a given that many tougher structural standards will follow these reports.
 

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Long live the Twins!
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i don't think the death count would change that much if the towers stay up longer. i once read in a magazine saying that almost all the office workers that were in floors 1-77 of the south tower managed to leave the building within the 56 minute period (i remember that only 5 didn't make it out on time). the number of office workers that were in floors 1-91 of the north tower that didn't make it out were higher (there were a lot more ppl in the north tower than the south tower on that morning), but the numbers were still very low if compared to the total number of office workers on those floors just before the blast.

therefore almost all the ppl that were below the fireline (floor 92 for 1 wtc and floor 78 for 2 wtc) were the unlucky police officers, firefighters, and other rescue workers whose cheap communication radios totally got screwed up and they couldn't have known that the towers and their lives were in danger.

as for the outdated fireproofing on the south tower issue, i think the huge explosive blast that happened when the planes slammed into the building would have knocked out the walls and fireproofing out of the impacted floors of the towers (you need to construct something equal to a bomb shelter in order to keep that from happening) so the fireproofing wouldn't have done anything good, except to stop the fire from spreading to areas unaffected by the blast. but the amount of steel exposed to the fire was already enough to doom the towers. i don't think the freedom tower would perform any better.

why are ppl continuing to blast the twins for being structually unsafe? they performed so well and allowed almost every office workers not killed or trapped by the impact to escape with their lives. if you slam planes traveling at 600mph into other skyscrapers in the world, almost every one of them would have either have immediately collapsed or have their top totally knocked off. besides, how could anyone (except those islamic lunatic militants) imagine such a horrible and bizarre event happen to any building?
 

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7 World Trade said:
i don't think the death count would change that much if the towers stay up longer.
Maybe not, though one of the great tragedies that day was, after the first plane hit, workers in the south tower were told to stay in their offices. Many did because 1) the assumption was that the south tower was not in danger, 2) not everyone knew a plane had hit the north tower, and 3) some people who evacuated after the 1993 bombing didn't want to go through the hassle again if not necessary. As a result, a lot of people were trapped in the south tower who would have otherwise been evacuated.
 

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BigMac said:
Maybe not, though one of the great tragedies that day was, after the first plane hit, workers in the south tower were told to stay in their offices. Many did because 1) the assumption was that the south tower was not in danger, 2) not everyone knew a plane had hit the north tower, and 3) some people who evacuated after the 1993 bombing didn't want to go through the hassle again if not necessary. As a result, a lot of people were trapped in the south tower who would have otherwise been evacuated.
i agree with you...that was the biggest tragedy of the day. if only the workers were notified that it could be a potential terrorist attack and that the smoke could be dangerous, the south tower (the upper half at least) would've been empty by the time the 2nd plane hit. and few ppl would've died in the building.

or if only the trapped office workers in the south tower realized that one of the emergency stairwells survived the explosion from the impact, then many, if not all, would've made it out within the 1-hour timeframe. if only that happened, then the terrorists wouldn't have snatched 600 extra souls from the attack.
 
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7 World Trade said:
i agree with you...that was the biggest tragedy of the day. if only the workers were notified that it could be a potential terrorist attack and that the smoke could be dangerous, the south tower (the upper half at least) would've been empty by the time the 2nd plane hit. and few ppl would've died in the building.

or if only the trapped office workers in the south tower realized that one of the emergency stairwells survived the explosion from the impact, then many, if not all, would've made it out within the 1-hour timeframe. if only that happened, then the terrorists wouldn't have snatched 600 extra souls from the attack.
Agreed. When can people understand that it's better to be safe that sorry? Tiring your legs a bit after some extra stairs is worth it if there's even a 0.001% chance that you're going to die.

That being said, pretty much anything can be improved with "if I had known..." - including the structural strength of the WTC.
 

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Discussion Starter · #9 ·
NY1

Study Into Why Twin Towers Fell Finds They Exceeded Structural Standards

Sept 18

The National Institute of Standards and Technology says the Twin Towers' ability to stand up to wind was above and beyond the standards in place when they were attacked in 2001.

NIST is trying to determine, from an engineering standpoint, what led to the collapse of the towers.

Investigators reviewed the original wind tunnel data from the 1960s building plans.

A report due in December will offer suggestions to make buildings safer in the future.
 

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What'u smokin' Willis?
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Here's my conclusion based on all the reports, books and TV Specials:

The Twin Towers performed as or better than what should have been expected. Neither had a fundemental design flaw. Both took a 767-200 flying at high mach and still stood long enough to evacuate over 15,000 people.

Like all major engineering failures, alot have things had to go wrong for a failure to happen. Simple economic decisions, if made differently, could have dramtically changed things. Having said that, the following could have been done to increrase the length of time they stood, or in combination, prevented the collapse all together. It should be noted that hindsight is 20/20 and no one should be blamed for making what turned out be fatal mistakes 35 years ago.

1 Improved fireproofing. The use of modern, durable, fireproofing materials would have considerably improved the performance of the towers. Ironically, a fireproofing upgrade was planned for sometime this decade.

2 Use of I-beams as floor support instead of trusses. Better floor support to wall joints. These two parts kind of go together, the use of trusses is always an economic choice. They are strong, but are very prone to failure in fires. Even more imortant was the joints connecting the trusses to the core/outer loadbearing wall, as these were the elements first to fail. Simply using thicker bolts could have prevented or delayed collapse.

3 Use of concrete in central core instead of drywall. I'm sure we all heard the story of the firmen who survived the collapse in the stairwell of Tower 1. They survived probably because that portion of the core had used concrete instead, because of some heavy service machinery on that floor. Concrete that has been setting for 27 years is a extremely durable material that could have prevented total collapse.
 

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STR said:
3 Use of concrete in central core instead of drywall. I'm sure we all heard the story of the firmen who survived the collapse in the stairwell of Tower 1. They survived probably because that portion of the core had used concrete instead, because of some heavy service machinery on that floor. Concrete that has been setting for 27 years is a extremely durable material that could have prevented total collapse.
that's true. i never thought of that. yeah, indeed, the twins might have stayed up a bit longer if their cores are made of concrete, which can support the sagging trusses on the burning floors for at least a period of time, and thus allow a slower collapse that allows those on the ground in harm's way to have time to flee from the raining debris. and yeah, concrete cores can serve well as a shelter for those unable to leave the building on time.

the fact that the twins didn't just buckle after sustaining 500mph plane impacts is already miraculous enough. in fact, if the plane that slammed into the south tower flew any faster, the south tower could've just collapsed, but it still managed to stand for an hour with 1 corner of it structually disabled before it fell. it was a miracle...
 

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7 World Trade said:
that's true. i never thought of that. yeah, indeed, the twins might have stayed up a bit longer if their cores are made of concrete, which can support the sagging trusses on the burning floors for at least a period of time, and thus allow a slower collapse that allows those on the ground in harm's way to have time to flee from the raining debris. and yeah, concrete cores can serve well as a shelter for those unable to leave the building on time.
Like I said, a lot of things have to go wrong for a building to collapse. I'd bet if any two of those improvements were made, the towers would still be there, and I wouldn't know who the hell Daniel Libeskind is.

But as I had to (and still have to) remember, there is nothing more futile than arguing about how the past could have been different. Only the future matters, and we should do all we can to shape it for the better.
 

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Discussion Starter · #14 ·
NY1

WTC Probe To Conclude Better Fireproofing May Have Prevented Collapse

OCTOBER 19TH, 2004

Fireproofing could have prevented the collapse of the World Trade Center had it not been dislodged by the impact of the hijacked airliners on September 11, 2001, according to federal investigators.

The National Institute for Standards and Technology, which is nearing the end of a two-year probe of the structural causes of the destruction of the twin towers, released more preliminary findings Tuesday. The agency had already concluded that the raging fires weakened the structural steel and ultimately brought the skyscrapers down – not the force of the planes crashing into them.

According to the latest report, the buildings’ fireproofing may have prevented the steel from heating up, but much of it was knocked loose. The report also says a majority of the steel recovered at the site was stronger than the minimum required by building standards.

The institute also released results from interviews with survivors about evacuation procedures. The report says occupants were unprepared for the physical challenges of a full building evacuation. They reported inadequate and confusing communications, and rescue workers reported traffic problems in the hallways.

Other troubles reported by first-responders include an overall lack of information and perspective of the situation. A number of rescuers who went to the site without being dispatched there caused further confusion and congestion.

The institute’s final report on the twin towers’ collapse, which will also include recommendations to improving building codes and other safety measures for skyscrapers, is due in December.
 

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I agree hindsite is 20/20, who in the 1960's would have believed that a jetliner would be purposely crashed into a skyscraper? i think the towers performance was the best it could be, (if not better) given the time when they were built! i remember when they went up (i was 13 in 1973) hell we where amazed that it was being built. let alone two of them!!! it was,for the time a great achievment. one thing that i did not see mentioned in the reports was the fact that plastic and paper contributed to the fires burning and smoldering for so long, as high octaine jet fuel burns off rather quickly!
 

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New York Times
October 20, 2004

Study Suggests Design Flaws Didn't Doom Towers

By ERIC LIPTON

Video: Eric Lipton on the Study

After the most sophisticated building analysis in United States history, federal investigators have arrived at the clearest picture yet of the sequence of events that led to the collapse of the World Trade Center towers, largely ruling out a design flaw in the buildings as a central factor in the catastrophe.

Since the twin towers fell, questions have reverberated among families of victims and some fire-safety experts about whether insufficient fireproofing or an unusual weakness in the innovative, lightweight floors played a critical role in the collapse.

Instead, the investigators tentatively conclude in nearly 500 pages of documents released Tuesday, the twin towers failed because the structural columns at the buildings' core, damaged by the impact of the airliners, buckled and shortened as the fires burned, gradually shifting more load to the tower's trademark exterior pinstripe columns. The exterior columns ultimately suffered such extraordinary stress and heat that they gave way.

The investigation - based on an analysis of thousands of photographs and videos, an examination of nearly every element used to construct the towers and meticulous computer-enhanced modeling of the plane impacts and spreading fires - is not yet complete. A final report by the National Institute of Standards and Technology is not scheduled to be issued until December or perhaps January.

In interviews Tuesday, the lead investigator, as well as other engineers who have studied the collapse, said the evidence increasingly suggested that the giant structures - given the extreme conditions, including temperatures that reached more than 1,000 degrees - performed relatively well on Sept. 11, 2001.

"We always said we had no preconceived notions, and that we would look at the failure information dispassionately," said S. Shyam Sunder, the lead investigator at the institute, a division of the Department of Commerce, which has conducted the two-year, $16 million inquiry at the request of Congress. "The buildings performed as they should have in the airplane impact and extreme fires to which they were subjected. There is nothing there that stands out as abnormal."

Elements of the design and construction of the towers, investigators said, certainly played a part in how long the buildings stood. Buildings designed differently - with more robustly protected and spread-out emergency stairwells, for example - engineers said yesterday, might still have resulted in fewer deaths.

But the most severe shortcomings identified at the World Trade Center in the institute's comprehensive review do not pertain to how the buildings were conceived or built. Instead, the failings on Sept. 11 were chiefly found in the response by the New York City Fire and Police Departments, which was hampered by inadequate command, unreliable communications equipment and an overwhelmed dispatching system.

For Leslie E. Robertson, the structural engineer who helped design the twin towers as a young man back in the early 1960's, the latest findings buttress his longstanding assertion that the towers were fundamentally sound. His wife, Saw-Teen See, who is a managing partner at Mr. Robertson's New York design firm, said the report "validates the way we thought the structure would have performed."

The findings by the institute, however, still do not exonerate Mr. Robertson or the building's owner, the Port Authority of New York and New Jersey, which, in defending the trade center project from critics in the 1960s, boasted that the design was so robust that the towers could be hit by a jet traveling at 600 miles per hour without collapsing or endangering the lives of occupants beyond the impact zone. In retrospect, such a claim was unjustified because the engineers had failed to consider the added stresses caused by the resulting fires.

Sally Regenhard, who founded a group called the Skyscraper Safety Campaign in honor of her son, Christian Regenhard, a probationary firefighter who was one of 2,749 victims, said she was not ready to concede that the towers' design were not fundamentally at fault.

"It is far, far too premature to come to any conclusions that it wasn't the fault of the building, or nothing was wrong with the building," she said after listening to a daylong presentation in Gaithersburg, Md., about the latest findings.

The investigators have examined just about every possible factor that could have contributed to the collapse, including the steel used in the columns. Computer models were used to calculate, as accurately as possible, where different airplane parts traveled, and what kind of damage they did. Then, intricate models were built, essentially recreating the resulting fires.

Through all this, particular attention has been focused on the innovative floors that were central to the design of the twin towers. The floors were particularly critical in the trade center because in office buildings built before the 1960's, structural columns and beams were generally spread throughout - holding up the enormous weight and allowing the tower to resist the force from wind.

In the trade center, only the building's exterior and core had structural columns, and in between them were wide-open floors - relatively lightweight, decklike structures. Some engineers have wondered if insufficient fireproofing on the floor trusses led them to fail, undermining the structural integrity of the towers.

The federal investigators found, after conducting a test with a reconstructed section of the floor, that the original fireproofing on the floors, as built, was sufficient to ensure that they met the New York City building code under standard testing parameters.

Instead, the report released yesterday say, the Boeing 767 planes ripped through a swath of exterior steel columns, resulting in an immediate redistribution of the load to adjacent perimeter columns and, to a lesser extent, to the core columns.

As the planes penetrated the towers, they destroyed sections of the floors, knocked off spray-on fireproofing and severed three to 10 of the core columns in each tower.

The report found that the towers were able to stand, despite the initial assault, as "loads on the damaged columns were redistributed to other intact core and perimeter columns mostly via the floor systems and to a lesser extent, via the hat truss," a steel structure at the top of the towers that was connected to the core and perimeter columns.

The infernos that erupted in the two towers are to blame for the ultimate collapse, the report found. As temperatures rose in the buildings, the remaining core columns softened and buckled, shifting much of the burden to the building's exterior. The floors, which largely remained intact outside the impact zone, reacted by pulling the exterior columns inward, adding to the extreme stress on the exterior columns.

In the north tower, as fires consumed office furniture and other debris, softening the steel in the exterior columns, they gradually started to bow inward and then buckle. Ultimately, the entire upper section of the building above the impact zone tilted to the south, sealing the fate of the tower and anyone who remained inside.

"The buckled columns exceeded the strain energy that could be absorbed by the structure,'' the report says. "Global collapse then ensued."

The floors played a more significant role in the collapse sequence in the south tower, the investigators said. Fires there caused them to sag by as much as two feet, adding to the inward pulling that already had started because of the buckling of the core columns.

But the investigators say that without the plane impact - which weakened the structure and knocked fireproofing off the floor trusses and columns - if a typical office fire had occurred, "it is likely that burnout would have occurred without collapse."

The tentative conclusions by the federal investigators conflict with an earlier report by a team of structural engineers organized by the Federal Emergency Management Agency, who had asserted that the collapse of the north tower started in the core, not in the outer columns. But W. Gene Corley, a structural engineer from Skokie, Ill., who led that inquiry, said Tuesday that the new hypothesis was feasible, given that the federal team had the money to more closely dissect what happened.

But James G. Quintiere, a professor of fire protection engineering at University of Maryland, said he questioned the tentative conclusions, as his analysis showed that in the fires created by the impact, the lightweight floors rose to a temperature high enough to make them separate from the exterior columns. "They have not presented enough evidence," he said.





Copyright 2004 The New York Times Company
 

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Discussion Starter · #18 ·
NY1

Study Finds Flaws In Evacuation Plan For Twin Towers

A federal engineering study of the collapse of the World Trade Center, released Tuesday, highlights flaws in assumptions about evacuating skyscrapers and responding to emergencies.

The National Institute of Standards and Technology has been studying the structural reasons for the collapse of the twin towers in order to recommend changes to building codes and safety procedures.

According to the report, the airplanes caused significant internal and external damage to the buildings on impact, knocking off vital fire proofing materials in the process. Fires spurred on by debris in the buildings quickly engulfed those floors, weakening the external columns of the buildings.

"Sagging floors that pulled the external columns inward, that contributed eventually with weakened external columns to bring the buildings down," said NIST lead investigator Dr. Shyam Sunder.

Sunder says whether or not it was thick enough, more importantly, the fire-proofing materials didn't stick to the steel. He says modern fire-proofing can be applied like a paint.

"It's possible that you can have normal fire-proofing withstand higher degrees of impact, but as you know, buildings are not designed to withstand airplane impacts," said Dr. Sunder.

It took less than an hour from impact for the South Tower to collapse and just over 100 minutes for the North Tower to fall. The investigation says revised thinking on how to evacuate people could have saved lives.

NIST found current predictions on how long it takes to get people out of buildings don't include people's initial indecision about leaving, resting while in the stairwells, and bottlenecking.

"What ends up happening is those models predict much faster evacuation times than is usually the case in emergency situations," said Dr. Sunder.

The NIST report found some people lingered in their offices before going to stairwells after the attacks of September 11, 2001 – an issue that hadn't been taken into account in previous estimates of how long it would take people to evacuate skyscrapers.

In Tower 1 it took people about 48 seconds a flight to descend, far slower than in current fire safety handbooks. Bottlenecking further immobilized rescue workers who were struggling to climb 40 to 50 stories with heavy equipment and had virtually no communication with the outside. The engineers also emphasize the limited ability of rescue personnel to reach higher floors.

According to the preliminary report, first responders overloaded the radio receivers, with just under 1,000 of them trying to communicate on eight frequencies. Human and technical error were pervasive.

"The preponderance of the evidence that we have suggests that lack of the communication sharing and the inadequacy of the communication capabilities likely contributed to additional loss of first responders' lives," said Dr. Sunder.

Some firefighters said in interviews with the agency they would have had more useful information that day by watching TV than trying to communicate with each other on the ground.

"That is clearly something that needs to be corrected and fixed, because going forward I want to be sure that if there's an emergency these people will be able to talk to each other, talk to the other first responders and talk to me if I'm in a high rise building," said Monica Gabrielle, who lost her husband on 9/11.

The report is already leading to debate about stairwell and elevator design.

The report also says the attacks reduced city and state tax revenue by $6 billion through the fiscal year 2003.

According to the New York Times, the report says the city could lose an additional $550 million in taxes for the fiscal years 2004 and 2005. Those numbers are based on estimates from the city's Office of Management and Budget.

The National Institute of Standards and Technology report says one of the biggest financial impacts was the loss of about 1,700 securities jobs.

Earlier estimates of the financial impact were higher. That's because they didn't take into account the recession that was hitting New York before the attacks, the report says.

Investigators will incorporate the 10,000 pages of data into their safety and design recommendations for future high rise buildings due out in June.
 
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