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Context of 'August 21, 2002: Commencement of NIST Investigation Announced'

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The hole caused by the Flight 11 crash.The hole caused by the Flight 11 crash. [Source: Reuters]Flight 11 slams into the WTC North Tower (Building 1). Hijackers Mohamed Atta Waleed Alshehri, Wail Alshehri, Abdulaziz Alomari, and Satam Al Suqami presumably are killed instantly, and many more in the tower will die over the next few hours. Seismic records pinpoint the crash at 26 seconds after 8:46 a.m. [CNN, 9/12/2001; New York Times, 9/12/2001; North American Aerospace Defense Command, 9/18/2001; USA Today, 12/20/2001; Federal Emergency Management Agency, 5/1/2002, pp. 1-10; New York Times, 5/26/2002; USA Today, 8/12/2002; Associated Press, 8/21/2002; Newsday, 9/10/2002] The NIST report states the crash time to be 8:46:30. [National Institute of Standards and Technology, 9/2005, pp. 19] The 9/11 Commission Report states the crash time to be 8:46:40. [9/11 Commission, 7/24/2004, pp. 7] Investigators believe the plane still has about 10,000 gallons of fuel (see 8:57 a.m. September 11, 2001). [New York Times, 5/26/2002] The plane strikes the 93rd through 99th floors in the 110-story building. No one above the crash line survives; approximately 1,360 people die. Below the crash line, approximately 72 die and more than 4,000 survive. Both towers are slightly less than half full at the time of the attack, with between 5,000 to 7,000 people in each tower. This number is lower than expected. Many office workers have not yet shown up to work, and tourists to the observation deck opening at 9:30 A.M. have yet to arrive. [USA Today, 12/20/2001; National Institute of Standards and Technology, 9/2005, pp. 20-22] The impact severs some columns on the north side of the North Tower. Each tower is designed as a “tube-in-tube” structure and the steel columns which support its weight are arranged around the perimeter and in the core. The plane, which weighs 283,600 lb and is traveling at an estimated speed of around 430 mph (see October 2002-October 2005), severs 35 of the building’s 236 perimeter columns and damages another two. The damage to the South Tower’s perimeter will be similar (see 9:03 a.m. September 11, 2001). [National Institute of Standards and Technology, 9/2005, pp. 5-9, 20, 22] The perimeter columns bear about half of the tower’s weight, so this damage reduces its ability to bear gravity loads by about 7.5 percent. [National Institute of Standards and Technology, 9/2005, pp. 6] The actual damage to the 47 core columns is not known, as there are no photographs or videos of it, but there will be much speculation about this after 9/11. It will be suggested that some parts of the aircraft may have damaged the core even after crashing through the exterior wall. According to the National Institute of Standards and Technology (NIST): “Moving at 500 mph, an engine broke any exterior column it hit. If the engine missed the floor slab, the majority of the engine core remained intact and had enough residual momentum to sever a core column upon direct impact.” [National Institute of Standards and Technology, 9/2005, pp. 107] According to NIST’s base case computer model, three of the core columns are severed and another ten suffer some damage. [National Institute of Standards & Technology, 9/2005, pp. 189 pdf file] If this is accurate, it means that the impact damage to the core reduces the Tower’s strength by another approximately 7.5 percent, meaning that the building loses about 15 percent of its strength in total. This damage will be cited after 9/11 by NIST and others researchers as an event contributing to the building’s collapse (see October 23, 2002 and October 19, 2004). In addition, some of the fireproofing on the steel columns and trusses may be dislodged. The original fireproofing on the fire floors was mostly Blazeshield DC/F, but some of the fireproofing on the flooring has recently been upgraded to Blazeshield II, which is about 20 percent denser and 20 percent more adhesive. [National Institute of Standards & Technology, 9/2005, pp. xxxvi, 83 pdf file] Photographs and videos of the towers will not show the state of fireproofing inside the buildings, but NIST will estimate the damage to it using a computer model. Its severe case model (see (October 2002-October 2005)) will predict that 43 of the 47 core columns are stripped of their fireproofing on one or more floors and that fireproofing is stripped from trusses covering 60,000 ft2 of floor area, the equivalent of about one and a half floors. NIST will say that the loss of fireproofing is a major cause of the collapse (see April 5, 2005), but only performs 15 tests on fireproofing samples (see October 26, 2005). [National Institute of Standards and Technology, 9/2005, pp. 23] According to NIST, more fireproofing is stripped from the South Tower (see 9:03 a.m. September 11, 2001).

Entity Tags: Mohamed Atta, National Institute of Standards and Technology, Satam Al Suqami, Waleed Alshehri, Abdulaziz Alomari, World Trade Center, Wail Alshehri

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

Flight 175 hits the WTC South Tower. The picture was taken from a traffic helicopter.Flight 175 hits the WTC South Tower. The picture was taken from a traffic helicopter. [Source: WABC 7/ Salient Stills]Flight 175 hits the South Tower of the World Trade Center (Tower Two). Seismic records pinpoint the time at six seconds before 9:03 a.m. (rounded to 9:03 a.m.). Hijackers Marwan Alshehhi, Fayez Ahmed Banihammad, Mohand Alshehri, Hamza Alghamdi, and Ahmed Alghamdi presumably are killed instantly, and many more in the tower will die over the next few hours. [New York Times, 9/12/2001; CNN, 9/12/2001; CNN, 9/17/2001; North American Aerospace Defense Command, 9/18/2001; USA Today, 12/20/2001; Federal Emergency Management Agency, 5/1/2002, pp. 1-10; New York Times, 5/26/2002; Associated Press, 8/21/2002; USA Today, 9/2/2002] According to the NIST report, the crash time is 9:02:59. [National Institute of Standards and Technology, 9/2005, pp. 38] According to the 9/11 Commission Report, the crash time is 9:03:11. [9/11 Commission, 7/24/2004, pp. 8] Millions watch the crash live on television. The plane strikes the 77th through 85th floors in the 110-story building. Approximately 100 people are killed or injured in the initial impact; 600 people in the tower eventually die. The death toll is far lower than in the North Tower because about two-thirds of the South Tower’s occupants have evacuated the building in the 17 minutes since the first tower was struck. [USA Today, 12/20/2001; National Institute of Standards and Technology, 9/2005, pp. 5-9, 41] The combined death toll from the two towers is estimated at 2,819, not including the hijackers. [Associated Press, 8/21/2002] The impact severs some columns on the south side of the South Tower. Each of the Twin Towers is designed as a “tube-in-tube” structure and the steel columns which support its weight are arranged around the perimeter and in the core. The plane, which is traveling at an estimated speed of around 500 mph (see October 2002-October 2005), severs 33 of the building’s 236 perimeter columns and damages another one. [National Institute of Standards and Technology, 9/2005, pp. 39] The perimeter columns bear about half of the tower’s weight, so the damage to them reduces the tower’s ability to bear gravity loads by about 7.1 percent. [National Institute of Standards and Technology, 9/2005, pp. 6] The actual damage to the 47 core columns is not known, as there are no photographs or videos of it, but there will be much speculation about this after 9/11. It will be suggested that some parts of the aircraft may be able to damage the core even after crashing through the exterior wall (see 8:46 a.m. September 11, 2001). [National Institute of Standards and Technology, 9/2005, pp. 107] According to NIST’s base case model, five of the core columns are severed and another five suffer some damage. [National Institute of Standards & Technology, 9/2005, pp. 235 pdf file] This may reduce the tower’s ability to bear loads by a further approximately 8 percent, meaning that the aircraft impact accounted for a loss of about 15 percent of the building’s strength. This damage will be cited as an event contributing to the building’s collapse after 9/11 (see October 23, 2002 and October 19, 2004). NIST’s base case estimate of damage to the North Tower’s core will be similar, even though the aircraft impact there was dissimilar (see 8:46 a.m. September 11, 2001). Flight 11 hit the North Tower’s core head on, whereas Flight 175 only hits the corner of the South Tower’s core. [National Institute of Standards and Technology, 9/2005, pp. 20-23, 38-41] In addition, some of the fireproofing on the steel columns and trusses may be dislodged (see 8:46 a.m. September 11, 2001). [National Institute of Standards & Technology, 9/2005, pp. xxxvi, 83 pdf file] Photographs and videos of the towers will not show the state of fireproofing inside the buildings, but the National Institute of Standards and Technology (NIST) will try to estimate the damage to fireproofing using a series of computer models. Its severe case model (see (October 2002-October 2005)) will predict that 39 of the 47 core columns are stripped of their fireproofing on one or more floors and that fireproofing is stripped from trusses covering 80,000 ft2 of floor area, the equivalent of about two floors. NIST will say that the loss of fireproofing is a major cause of the collapse (see April 5, 2005), but only performs 15 tests on fireproofing samples (see October 26, 2005). [National Institute of Standards and Technology, 9/2005, pp. 41] According to NIST, less fireproofing is stripped from the North Tower (see 8:46 a.m. September 11, 2001).

Entity Tags: World Trade Center, Marwan Alshehhi, Fayez Ahmed Banihammad, Hamza Alghamdi, National Institute of Standards and Technology, Ahmed Alghamdi, Mohand Alshehri

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

The South Tower of the World Trade Center collapses.The South Tower of the World Trade Center collapses. [Source: Associated Press]The South Tower of the World Trade Center tilts to the southeast and then collapses. It was hit by Flight 175 at 9:03 a.m., 56 minutes earlier (see 9:03 a.m. September 11, 2001). [Washington Post, 9/12/2001; New York Times, 9/12/2001; MSNBC, 9/22/2001; USA Today, 12/20/2001; Associated Press, 8/21/2002; ABC News, 9/11/2002; National Institute of Standards and Technology, 9/2005, pp. 44] The first sign of the collapse is visible on floor 82. [National Institute of Standards and Technology, 9/2005, pp. 87] The angle of the tilt will be disputed after 9/11 (see September-November 2005), as will the time it takes the towers to fall to the ground (see September 12, 2001-September 2005). [Scientific American, 10/9/2001; Eagar and Musso, 12/2001; PBS Nova, 5/2002; National Institute of Standards and Technology, 8/30/2006]

Entity Tags: World Trade Center

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

Damage to the southwest corner of WTC 7.Damage to the southwest corner of WTC 7. [Source: Arquelio Galarza]World Trade Center Building 7 (WTC 7) suffers some damage, caused by debris from the collapse of the north WTC tower, according to later official reports. [Federal Emergency Management Agency, 5/1/2002, pp. 5-16; National Institute of Standards and Technology, 11/2008, pp. 16]
WTC 7 Undamaged by South Tower Collapse - WTC 7 is a 47-story office building located 370 feet north of the North Tower (WTC 1). In the final report of its investigation into WTC 7’s collapse, published in November 2008 (see November 20, 2008), the National Institute of Standards and Technology (NIST) will state that although a few windows on the lower floors of WTC 7’s south face were broken when the South Tower (WTC 2) collapsed at 9:59 a.m. (see 9:59 a.m. September 11, 2001), “None of the large pieces of debris from WTC 2 hit WTC 7, because of the large distance between the two buildings,” and there is “no evidence of structural damage to WTC 7” as a result of the South Tower’s collapse.
Debris Reportedly Damages Exterior Columns - However, when the North Tower collapses (see 10:28 a.m. September 11, 2001), some fragments of debris are “forcibly ejected” from it, and travel “distances up to hundreds of meters.” According to NIST, pieces of this debris “hit WTC 7, severing six columns on floors 7 through 17 on the south face and one column on the west face near the southwest corner.” NIST will add that the debris also causes “structural damage between floor 44 and the roof,” and breaks a large number of windows on WTC 7’s south face.
Building Core Undamaged - However, NIST will state, based on “photographic evidence, witness accounts, and engineering judgment, it is likely that the structural damage (steel and floor slabs) did not penetrate beyond the perimeter of the building core. At the southwest corner, the structural damage extended only about one-third of the distance from the exterior wall to the building core.” NIST will comment, “Compared to the airplane impact damage to the WTC towers, there was relatively little damage to the interior of WTC 7.” There is also “no superficial or structural damage” to WTC 7’s north and east faces. And the sprayed fire resistive material that has been applied to the building’s steel columns, girders, and beams is only damaged in the “immediate vicinity of the WTC 1 debris impact.” NIST will admit, however, that there are “uncertainties” in its accounting of the events leading up to the collapse of WTC 7, because “the remains of all the WTC buildings were disposed of before Congressional action and funding was available for [its] investigation [of the WTC collapses] to begin” (see Shortly After September 11, 2001 and September 12-October 2001). [National Institute of Standards and Technology, 8/21/2008; National Institute of Standards and Technology, 11/2008, pp. 15-16]
FEMA Describes WTC 7 Damage - According to an earlier report on the collapse of WTC 7, published by the Federal Emergency Management Agency (FEMA) in May 2002 (see May 1, 2002), at that time, the “extent and severity of the resulting damage to WTC 7” when the North Tower collapses “are currently unknown.” But based on “photographic evidence and eyewitness accounts,” it is “assumed that the south side of the building was damaged to some degree.” FEMA’s report will state: “It does not appear that the collapse of WTC 1 affected the roof, or the east, west, and north elevations of WTC 7 in any significant way. However, there was damage to the southwest corner of WTC 7 at approximately floors 8 to 20, 24, 25, and 39 to 46.” The report will add: “According to firefighters’ eyewitness accounts from outside of the building, approximately floors 8-18 were damaged to some degree. Other eyewitness accounts relate that there was additional damage to the south elevation.” [Federal Emergency Management Agency, 5/1/2002, pp. 5-16, 5-20]
Structural Damage Not Responsible for Collapse - WTC 7 will collapse at 5:20 p.m. this afternoon (see (5:20 p.m.) September 11, 2001). [National Institute of Standards and Technology, 8/21/2008] However, NIST will conclude that the structural damage the building suffers plays no role in causing it to come down. NIST will state, “Other than initiating the fires in WTC 7, the damage from the debris from WTC 1 had little effect on initiating the collapse of WTC 7.” [National Institute of Standards and Technology, 11/2008, pp. xxxvii] WTC 7 suffers fires on some floors, which are reportedly initiated by debris from the collapse of the North Tower (see (10:28 a.m.-5:20 p.m.) September 11, 2001). According to NIST, it is these fires, “rather than the structural damage that resulted from the impacts” of debris, which “initiated the building’s collapse.” [National Institute of Standards and Technology, 8/21/2008]

Entity Tags: World Trade Center, National Institute of Standards and Technology, Federal Emergency Management Agency

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

A four-image progression of photos showing World Trade Center Building 7 collapsing down into its footprint.A four-image progression of photos showing World Trade Center Building 7 collapsing down into its footprint. [Source: unknown] (click image to enlarge)Building 7 of the World Trade Center complex, a 47-story tower, collapses. No one is killed. [CNN, 9/12/2001; Washington Post, 9/12/2001; MSNBC, 9/22/2001; Associated Press, 8/21/2002] It collapses in 6.6 seconds, which is just 0.6 of a second longer than it would have taken a free-falling object dropped from its roof to hit the ground. [Deseret Morning News, 11/10/2005] Many questions will arise over the cause of its collapse in the coming months and years. Building 7, which was not hit by an airplane, is the first modern, steel-reinforced high-rise to collapse because of fire. [Chicago Tribune, 11/29/2001; Stanford Report, 12/5/2001; New York Times, 3/2/2002] Some will later suggest that the diesel fuel stored in several tanks on the premises may have contributed to the building’s collapse. The building contained a 6,000-gallon tank between its first and second floors and another four tanks, holding as much as 36,000 gallons, below ground level. There were also three smaller tanks on higher floors. [Chicago Tribune, 11/29/2001; New York Times, 3/2/2002; New York Observer, 3/25/2002; Federal Emergency Management Agency, 5/1/2002, pp. 1-17] However, the cause of the collapse is uncertain. A 2002 government report will conclude: “The specifics of the fires in WTC 7 and how they caused the building to collapse remain unknown at this time. Although the total diesel fuel on the premises contained massive potential energy, the best hypothesis has only a low probability of occurrence.” [Federal Emergency Management Agency, 5/1/2002, pp. 1-17] Some reports indicate that the building may have been deliberately destroyed. Shortly after the collapse, CBS News anchor Dan Rather comments that the collapse is “reminiscent of… when a building was deliberately destroyed by well-placed dynamite to knock it down.” [CBS News, 9/11/2001] And moments after the collapse, MSNBC’s Brian Williams joins David Restuccio, an FDNY lieutenant, by phone to ask him about the collapse. “You guys knew this was coming all day?” asks Williams. Restuccio replies: “We had heard reports that the building was unstable, and that it would eventually need to come down on its own, or it would be taken down. I would imagine it came down on its own.” Restuccio does not explain what he means by “it would be taken down.” [MSNBC, 9/11/2001]

Entity Tags: Dan Rather, World Trade Center, David Restuccio

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

Steel beams from the WTC were already being removed and recycled on September 20, 2001.Steel beams from the WTC were already being removed and recycled on September 20, 2001. [Source: Associated Press]In the month following 9/11, a significant amount of the steel debris from the WTC collapses is removed from the rubble pile, cut into smaller sections, and either melted at a recycling plant or shipped out of the US. [US Congress, 3/6/2002] Each of the Twin Towers contained 78,000 tons of recyclable steel. Much of this is shipped to India, China, and other Asian countries, where it will be melted down and reprocessed into new steel products. Asian companies are able to purchase the steel for just $120 per ton, compared, for example, to a usual average price of $150 per ton in China. Industry officials estimate that selling off the steel and other metals from the WTC for recycling could net a few tens of million dollars. [New York Times, 10/9/2001; Reuters, 1/21/2002; Reuters, 1/22/2002; Eastday, 1/24/2002; CorpWatch, 2/6/2002] 9/11 victims’ families and some engineers are angered at the decision to quickly discard the steel, believing it should be examined to help determine how the towers collapsed. A respected fire fighting trade magazine comments, “We are literally treating the steel removed from the site like garbage, not like crucial fire scene evidence.” [Fire Engineering, 1/2002] Rep. Joseph Crowley (D-NY) will later call the loss of this evidence “borderline criminal.” By March 2002, 150 pieces of steel from the WTC debris will have been identified by engineers for use in future investigations (see March 6, 2002). [Federal Emergency Management Agency, 5/1/2002, pp. D-13] A study by the National Institute of Standards and Technology (NIST), which commences in August 2002 [National Institute of Standards and Technology, 8/21/2002; Associated Press, 8/21/2002] , will have 236 pieces of recovered steel available to it. Of these, 229 pieces are from WTC 1 and 2, representing “roughly 0.25 percent to 0.5 percent of the 200,000 tons of structural steel used in the construction of the two towers.” [National Institute of Standards and Technology, 9/2005, pp. 85 pdf file] New York Mayor Mike Bloomberg defends the decision to quickly get rid of the WTC steel, saying, “If you want to take a look at the construction methods and the design, that’s in this day and age what computers do. Just looking at a piece of metal generally doesn’t tell you anything.” Officials in the mayor’s office decline to reply to requests by the New York Times regarding who decided to have the steel recycled. [New York Times, 12/25/2001; Eastday, 1/24/2002]

Entity Tags: Joseph Crowley, World Trade Center, Michael R. Bloomberg

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

The New York Police and FBI are investigating the theft of over 250 tons of steel from the remains of the collapsed WTC towers. Apparently, the steel was hauled away by trucks involved in the official clear-up operation (see September 12-October 2001), but instead of being taken to Fresh Kills—the FBI-controlled dump on Staten Island where it was intended to go—the steel was driven to three independently-owned scrapyards, two in New Jersey and one on Long Island. The London Telegraph says the scrap metal value of the stolen steel would have been roughly $17,500. Investigators believe the theft was organized by one of New York’s Mafia families. [Daily Telegraph, 9/29/2001] Consequently, on November 26, 2001, the city initiates use of an in-vehicle Global Positioning System (GPS), to monitor the locations of nearly 200 trucks removing steel from the WTC collapse site, at a cost of $1,000 per unit. This system sends out alerts if any truck travels off course or arrives late at its destination. One driver involved with the clear-up operation is subsequently dismissed simply for taking an extended lunch break. [Access Control and Security Systems, 7/2002]

Entity Tags: World Trade Center, New York City Police Department, Federal Bureau of Investigation

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

A sample of WTC steel eroded and corroded due to eutectic formations.A sample of WTC steel eroded and corroded due to eutectic formations. [Source: FEMA]The Journal of the Minerals, Metals and Materials Society (JOM) reports that the examination of a beam from the remains of WTC Building 7—which collapsed late in the afternoon of 9/11 (see (5:20 p.m.) September 11, 2001)—has revealed “unexpected erosion” of the steel. The article states: “The formation of the eutectic mixture of iron oxide and iron sulfide lowers the temperature at which liquid can form in this steel. This strongly suggests that the temperatures in this region of the steel beam approached around 1,000°C, forming the eutectic liquid by a process similar to making a ‘blacksmith’s weld’ in a hand forge.” [Barnett, Biederman, and Sisson, 12/2001] The New York Times will call this “perhaps the deepest mystery uncovered in the investigation.” [New York Times, 2/2/2002] FEMA’s World Trade Center Building Performance Study, released in May 2002 (see May 1, 2002), will add that the same “unusual erosion patterns” have been observed in a sample of the remaining structural steel from one of the Twin Towers. It will state, “This sulfur-rich liquid penetrated preferentially down grain boundaries of the steel, severely weakening the beam and making it susceptible to erosion.” FEMA is unable to explain this phenomenon, saying, “The severe corrosion and subsequent erosion… are a very unusual event. No clear explanation for the source of the sulfur has been identified.… It is possible that this is the result of long-term heating in the ground following the collapse of the buildings. It is also possible that the phenomenon started prior to collapse and accelerated the weakening of the steel structure.” [Federal Emergency Management Agency, 5/1/2002, pp. C-1 - C-13] Despite FEMA’s call for further research, the National Institute of Standards and Technology (NIST) will make no mention of the eutectic formations in its final report into the WTC collapses, released in late 2005, following its three-year investigation. [National Institute of Standards and Technology, 9/2005, pp. 13]

Entity Tags: National Institute of Standards and Technology, World Trade Center, Federal Emergency Management Agency

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

The House Committee on Science holds a hearing on the investigation into the collapse of the World Trade Center on 9/11. Witnesses from industry, academia, and government testify on the collapses and the subsequent efforts to find out how and why they occurred. The hearings charter points out several problems that have severely hampered investigations. It says, “Early confusion over who was in charge of the [WTC collapse] site and the lack of authority of investigators to impound pieces of steel for examination before they were recycled led to the loss of important pieces of evidence that were destroyed early during the search and rescue effort.… Some of the critical pieces of steel—including the suspension trusses from the top of the towers and the internal support columns—were gone before the first BPAT [Building Performance Assessment Team] team member ever reached the site” (see September 12-October 2001). Furthermore, “The building owners, designers and insurers, prevented independent researchers from gaining access—and delayed the BPAT team in gaining access—to pertinent building documents largely because of liability concerns.” Regarding the decision to rapidly recycle the WTC steel, US Representative Joseph Crowley (D-NY) says, “I do believe that conspiracy theorists are going to have a field day with this,” and says this loss of important physical evidence “is not only unfortunate, it is borderline criminal.” In his statement before the committee, Glenn Corbett, a science professor at John Jay College, claims that the “lack of significant amounts of steel for examination will make it difficult, if not impossible, to make a definitive statement as to the cause and chronology of the collapse.” He also complains, “[W]e are staffing the BPAT with part-time engineers and scientists on a shoestring budget.” [US Congress, 3/6/2002; Associated Press, 3/7/2002]

Entity Tags: World Trade Center, Glenn Corbett, House Committee on Science, Joseph Crowley

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

FEMA’s World Trade Center Building Performance Study.FEMA’s World Trade Center Building Performance Study. [Source: FEMA]FEMA releases its report of the WTC collapses. It concludes, “[W]ith the information and time available, the sequence of events leading to the collapse of each tower could not be definitively determined.” On Building 7: “The specifics of the fires in WTC 7 and how they caused the building to collapse remain unknown at this time.” [Federal Emergency Management Agency, 5/1/2002]

Entity Tags: World Trade Center, Federal Emergency Management Agency

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

A brief ceremony marks the official ending of the cleanup and recovery effort at Ground Zero, eight months and 19 days after 9/11. As part of the ceremony, attended by thousands of people, a flatbed truck carries the last steel beam from the World Trade Center away from the site. The cleanup has been completed three months sooner than predicted and at a cost of $750 million. More than 108,000 truckloads of debris, comprising 1.8 million tons of steel and concrete, have been removed from the site. The debris was taken to the Fresh Kills landfill on Staten Island. Controversially, much of the steel was melted down or shipped out of the US for recycling (see September 12-October 2001). A small number of workers will remain at the site for a few more weeks, due to a delay by Deutsche Bank in letting firefighters search its high-rise at 130 Liberty Street. The final truckload of debris will be removed on June 24 and control of the site will be turned over to the New York Port Authority, which owns the land. Forensic investigators will continue sifting through debris at Fresh Kills, in the hope of finding and identifying more victims, until mid-July. [CBS News, 5/16/2002; CBS News, 5/30/2002; CNN, 5/30/2002; PBS, 5/30/2002; BBC, 7/15/2002; Glanz and Lipton, 2004, pp. 316-318; Stout, Vitchers, and Gray, 2006, pp. 219 and 226-227]

Entity Tags: World Trade Center

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

The National Institute of Standards and Technology (NIST)—an agency of the US Commerce Department’s Technology Administration—announces details of its forthcoming investigation into the collapses of the World Trade Center Twin Towers and Building 7 on 9/11. The NIST investigation aims “to investigate the building construction, the materials used, and the technical conditions that contributed to the outcome of the World Trade Center (WTC) disaster.” It also aims to examine the activities of building occupants and emergency responders on 9/11, studying such issues as emergency communications within the WTC, the movement of people during the evacuations, and issues around persons with disabilities. Leading technical experts from industry, academia, and other laboratories, alongside NIST’s own expert staff, will participate in the investigation. Expert professionals from the private sector will also be involved. Glenn Corbett, a fire science professor at John Jay College, says, “This is going to be the most extensive building disaster investigation ever performed.” [Associated Press, 8/21/2002; National Institute of Standards and Technology, 8/21/2002; National Institute of Standards and Technology, 8/3/2005] The investigation is formally authorized in October 2002, when the National Construction Safety Team Act is signed into law. The act, which gives NIST authorization to investigate major building failures in the US, is written largely as a result of the World Trade Center collapses. [National Institute of Standards and Technology, 10/2/2002; New York Times, 5/8/2003] NIST’s investigation is originally proposed to last two years, with a budget of $16 million. [National Institute of Standards and Technology, 8/21/2002] However, it eventually will last three years, with its final report into the collapses of the Twin Towers being released in October 2005 (see October 26, 2005). A previous analysis of the WTC collapses conducted by FEMA and the American Society of Civil Engineers (ASCE) was completed earlier in 2002 (see May 1, 2002), but this had a budget of just $1.1 million. By the time NIST starts its investigation, much of the crucial steel debris from the WTC collapses has already been destroyed (see September 12-October 2001). They later refer to there being a “scarcity of physical evidence that is typically available in place for reconstruction of a disaster.” [National Institute of Standards and Technology, 9/2005, pp. xxxvi]

Entity Tags: World Trade Center, National Institute of Standards and Technology, Glenn Corbett

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

One of the key variables in the computer simulations used by the National Institute of Standards and Technology (NIST) (see (October 2002-October 2005)) to explain the WTC collapses is the speed of the aircraft that hit the towers. However, there is no consensus on how fast the planes were traveling. The first estimate was contained in an initial research paper by engineers Zdenek Bazant and Yong Zhou, who stated that the planes were traveling at 342 miles per hour. [Bazant and Zhou, 1/2002 pdf file] However, the Federal Emergency Management Agency (FEMA) and American Society of Civil Engineers (ASCE) report said that the plane that hit the North Tower was traveling at 470 miles per hour, whereas the plane that hit the South Tower was traveling at 590 miles per hour (see May 1, 2002). [Federal Emergency Management Agency, 5/1/2002, pp. 31] NIST initially estimates speeds of 435 miles per hour for the plane that hit the North Tower and 497 miles per hour for the plane that hit the South Tower. These estimates closely match figures produced by the Massachusetts Institute of Technology, which finds speeds of 429 miles per hour and 503 miles per hour for the two planes. However, NIST is dissatisfied with these results and does a second study, which finds speeds of 466 and 545 miles per hour. It then uses speeds of 472 and 570 miles per hour in its severe case model, on which its final report is based. In this model, the simulation of the planes traveling faster means greater damage to the towers’ structure, making them more unstable. [Kausel, 5/2002 pdf file; National Institute of Standards & Technology, 9/2005, pp. 152-165 pdf file; National Institute of Standards and Technology, 9/2005, pp. 109]

Entity Tags: Zdenek Bazant, National Institute of Standards and Technology, World Trade Center, Yong Zhou, Massachusetts Institute of Technology, American Society of Civil Engineers, Federal Emergency Management Agency

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

Matthys Levy.Matthys Levy. [Source: PBS]A report is made publicly available, which the Engineering News-Record calls the “most comprehensive study yet on the destruction of the World Trade Center.” The study was commissioned by WTC leaseholder Silverstein Properties Inc. to support a $7 billion insurance claim, and conducted by a team of engineers from several leading firms, including Weidlinger Associates, LZA Technology/Thornton-Tomasetti, and ARUPFire. It is intended to build on a previous study sponsored by FEMA (see May 1, 2002). The report’s findings are based on an analysis of original structural drawings, thousands of photos, and dozens of videos. Investigators used fire evaluation techniques and powerful computer software to simulate the condition of each tower at critical times between the planes’ impacts and the towers’ collapses. The earlier FEMA investigators had no access to such computer modeling. Matthys Levy, the chairman of Weidlinger Associates and one of the engineers on the study team, says, “The buildings had tremendous reserve capacity and that was reflected in all of the elements we analyzed. In fact, because there were so much excess capacity, the columns even in the impact floors did not buckle immediately, but failed as the result of the fire.” The report states that failure of the WTC’s steel floor supports (“trusses”) did not contribute to the collapses. Instead, the collapses were caused by the failure of steel structural columns that were either destroyed when the planes hit or lost fireproofing, leaving them vulnerable to the weakening effects of the ensuing fires. It says that debris and dust distributed by the plane crashes inhibited the fires, such that the average air temperatures on the impact floors were between 400 and 700°C (750-1,300°F): significantly lower than those associated with typical “fully developed” office fires. However, says Matthys Levy, “By the time the temperature inside the buildings reached 400 degrees, the steel would have lost approximately 50% of its strength. Eventually, gravity took over and the towers began to fall.” Then, according to the analysis led by researchers from LZA Technology/Thornton-Tomasetti, “Once collapse initiated in each tower, essentially all of the interior structure of the tower fell straight down with floors pancaking on top of one another. The network of perimeter steel columns and spandrels acted like a chute to funnel the interior contents into the tower footprint.” According to the computer simulations, the damage to the South Tower’s steel core columns was so severe that the tower should have collapsed immediately after the plane hit. Civil engineer John Osteraas says this incorrect result casts doubt upon some of the study’s predictions. The report concludes that the collapse of the South Tower did not cause or contribute to the subsequent collapse of the North Tower, thus supporting Silverstein Properties’ claim that the terrorist attack represented two occurrences, entitling it to two $3.5 billion insurance policy limits. A separate study commissioned by the insurers contradicts this (see October 23, 2002). The Silverstein report apparently does not examine the collapse of WTC Building 7, a 47-story skyscraper that also collapsed on 9/11 (see (5:20 p.m.) September 11, 2001). It has been passed on to the National Institute of Standards and Technology (NIST), which is undertaking its own investigation of the WTC collapses (see August 21, 2002). [New York Times, 9/30/2002; Business Insurance, 10/23/2002; Silverstein Properties, Inc., 10/23/2002 pdf file; Engineering News-Record, 10/25/2002; New York Times, 10/29/2002; Engineering News-Record, 11/4/2002; Real Estate Weekly, 4/30/2003]

Entity Tags: World Trade Center, Silverstein Properties, Thornton-Tomasetti Engineers, Weidlinger Associates, Matthys Levy

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

Insulated trusses in the World Trade Center.
Insulated trusses in the World Trade Center. [Source: Gilsanz Murray Steficek]At a press briefing in New York City, the National Institute of Standards and Technology (NIST) releases a 122-page progress report on its investigation into the WTC collapses. NIST began its study in August 2002 (see August 21, 2002). Investigators say they believe that the Port Authority of New York and New Jersey, who built the Twin Towers, failed to carry out vital tests to establish how the buildings would cope with a major fire. They have been unable to find evidence that tests were conducted on the fireproofing material used in the buildings. Their report also states that in 1969, builders directed contractors to coat the WTC floor supports with half an inch of spray-on fireproofing. In 1999, the Port Authority issued guidelines to triple the thickness of the fireproofing, and by 9/11, about 30 floors in the upper areas of the two towers had been upgraded. Almost all the floors in the impact zone of the North Tower had their fireproofing upgraded, while in the South Tower just the 78th floor—the lowest in its impact zone—had been upgraded. As the New York Times states, though, “investigators took great care… to say they were nowhere close to definitively determining how and why the towers collapsed after they were struck by hijacked airliners.” [National Institute of Standards and Technology, 5/2003, pp. 81; National Institute of Standards and Technology, 5/7/2003; Guardian, 5/8/2003; New York Times, 5/8/2003]

Entity Tags: National Institute of Standards and Technology, Port Authority of New York and New Jersey, World Trade Center

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

The National Institute of Standards and Technology (NIST) issues a progress report on its investigation into the World Trade Center collapses. Since 2002, NIST has been investigating the collapses of the Twin Towers and WTC Building 7 (see August 21, 2002). The progress report includes its “working hypothesis” for the collapse of WTC 7. This was a 47-story building, located about 350 feet from the north side of WTC 1, which collapsed completely at around 5:20 in the afternoon of 9/11. The report claims that “fire appears to have played a key role” in the collapse, though it points out, “No fire was observed or reported in the afternoon on floors 1-5, 10, or above Floor 13.” It also says, “there may have been some physical damage on the south side of the building.” NIST summarizes its working hypothesis of the WTC 7 collapse as follows:
bullet “An initial local failure at the lower floors (below Floor 13) of the building due to fire and/or debris induced structural damage of a critical column (the initiating event), which supported a large span floor bay with an area of about 2,000 square feet.”
bullet “Vertical progression of the initial local failure up to the east penthouse, as large floor bays were unable to redistribute the loads, bringing down the interior structure below the east penthouse.”
bullet “Horizontal progression of the failure across the lower floors… triggered by damage due to the vertical failure, resulting in the disproportionate collapse of the entire structure.”
NIST claims this hypothesis “is consistent with all evidence currently held by NIST, including photographs and videos, eyewitness accounts and emergency communication records,” but says it “will be revised and updated as results of ongoing, more comprehensive analyses become available.” [National Institute of Standards and Technology, 6/2004, pp. L1, L3, L17, L34, L38, L51-L52; National Institute of Standards and Technology, 6/18/2004] NIST will release its final reports on the collapses of the Twin Towers in October 2005 (see October 26, 2005). As of mid-2007, it has yet to release a final report on the collapse of WTC 7. In early 2006, Dr. S. Shyam Sunder, who is the lead investigator for NIST’s WTC investigation, will admit, “truthfully, I don’t really know” what caused WTC 7 to collapse. He will add, “We’ve had trouble getting a handle on building no. 7” (see March 20, 2006). [New York Magazine, 3/20/2006] An earlier report on the WTC collapses, released by the Federal Emergency Management Agency (FEMA) in May 2002, had been inconclusive on what caused WTC 7 to collapse, and stated that “Further research, investigation, and analyses” were necessary (see May 1, 2002). [Federal Emergency Management Agency, 5/1/2002, pp. 5-31]

Entity Tags: World Trade Center, National Institute of Standards and Technology

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

Shyam Sunder.Shyam Sunder. [Source: NIST]The National Institute of Standards and Technology (NIST) releases nearly 500 pages of documents, detailing the latest findings of its investigation of the WTC collapses on 9/11. These include its hypotheses for the collapse sequences of each of the Twin Towers; details of their analysis of interviews with nearly 1,200 building occupants, emergency responders, and victims’ relatives; and information from their analysis of the emergency response and evacuation procedures. Their investigation into the collapses is based upon an analysis of thousands of photos and videos, examination of many of the elements used to construct the towers, and computer-enhanced modeling of the plane impacts and the spreading of the fires. Their hypothesis is that the towers collapsed ultimately due to the fires they suffered: As the fires burned, the buildings’ steel core columns buckled and shortened. This shifted more load to the buildings’ perimeter columns, which were already affected by the heat of the fires, and caused them to give way under the increased stress. Investigators have conducted a test with a reconstructed section of the WTC floor, and found that the original fireproofing was sufficient to meet the New York City building code. They say that had a typical office fire occurred in the towers, without the structural damage and the loss of some fireproofing caused by the plane impacts, it is likely the buildings would have remained standing. Lead investigator Dr. Shyam Sunder says, “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.” NIST’s theories of why the WTC buildings collapsed conflict with an earlier investigation by FEMA, which claimed the collapse of the North Tower had begun in its core, rather than its perimeter columns (see May 1, 2002). [National Institute of Standards and Technology, 10/19/2004; New York Times, 10/20/2004]

Entity Tags: Shyam Sunder, National Institute of Standards and Technology, World Trade Center

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

Based upon its three-year investigation of the WTC collapses, the National Institute of Standards and Technology (NIST) calls for changes in the planning, construction, and operation of skyscrapers. NIST releases 43 draft reports, totaling about 10,000 pages, for public comments. These include 25 pages of recommendations, intended to learn from 9/11 and make building occupants and emergency responders safer in any future disasters. NIST’s inquiry has been conducted by more than 200 technical experts and contractors, and had two main parts: to look at the causes of the collapses and to identify weaknesses in building codes. Their recommendations include specific improvements to building standards, codes and practices; changes to evacuation and emergency response procedures; and research to help prevent future building failures. NIST does not have the authority to change building codes, but hopes to influence the policies of local authorities. The cost of implementing their recommended changes would add an estimated extra 2 to 5 percent to the development costs of buildings. Some are critical of their recommendations. Structural engineer Jon Magnusson, whose firm is the descendant of the company that designed the Twin Towers, says, “They are leading the public down the wrong path. They are saying we are going to fix the codes in order to deal with Sept. 11th. The physics say that you can’t do that.” [New York Times, 6/22/2005; National Institute of Standards and Technology, 6/23/2005; Associated Press, 6/24/2005] The New York Times points out that between 1989 and 1999, only five civilians had been killed in some 6,900 reported high-rise office building fires within the US. [New York Times, 6/24/2005] NIST will release its final report on the Twin Towers collapses four months later (see October 26, 2005).

Entity Tags: National Institute of Standards and Technology, World Trade Center, Jon Magnusson

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

Both towers of the World Trade Center tilted to one side before beginning to fall on 9/11 (see 9:59 a.m. September 11, 2001 and 10:28 a.m. September 11, 2001). The National Institute of Standards and Technology, which investigated the collapses (see August 21, 2002), states that the South Tower, which was hit on its south side, tilted about 7-8 degrees to the east and 3-4 degrees to the south, and the North Tower, which was hit on its north side, tilted about 8 degrees to the south, before starting to fall. [National Institute of Standards and Technology, 9/2005, pp. 300, 308 pdf file] However, these findings are criticized by Canadian scientist Frank Greening. After examining photo and video evidence, Greening says that the South Tower tilted by no more than two degrees and the North Tower by no more than three degrees before collapse initiation. Greening also says that the tilt angles NIST gives cannot correspond to the downward movement of the towers’ walls NIST claims before they started to fall, and points out that the tilt angles NIST uses are inconsistent throughout its reports. Though Greening agrees with NIST that the towers were destroyed by the plane impacts and fire damage, he concludes that its computer model is “highly inaccurate and therefore of no value in explaining the demise of the Twin Towers.” [Greening, 11/2005 pdf file] Greening is a leading figure in the post-9/11 dispute over why the WTC collapsed and publishes a series of papers dealing with various aspects of the Twin Towers’ collapse. For example, a CBC documentary uses Greening for analysis of the WTC’s fall. [Canadian Broadcasting Corporation, 8/25/2005]

Entity Tags: World Trade Center, Frank Greening, National Institute of Standards and Technology

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

The 43 NIST reports ran to over 10,000 pages.The 43 NIST reports ran to over 10,000 pages. [Source: NIST]The National Institute of Standards and Technology (NIST) issues the final report of its three-year, $16 million study into the WTC collapses on 9/11. NIST has produced over 10,000 pages of findings, and its report includes 30 recommendations for improving building safety, such as having wider stairwells and structurally hardened elevators for use in emergencies. The recommendations are mostly the same as those outlined in an earlier draft of the report (see June 23, 2005). [Engineering News-Record, 10/27/2005; New York Times, 10/27/2005] NIST has made some amendments and clarifications, though, based upon nearly 500 comments received during a six-week public review period. [National Institute of Standards and Technology, 10/26/2005] NIST’s theory about what caused the Twin Towers to collapse remains the same as that described in its previously released findings (see October 19, 2004). However, the NIST’s account only examines events up to the initiation of each collapse; the investigation “does not actually include the structural behavior of the tower after the conditions for collapse initiation were reached and collapse became inevitable.” [National Institute of Standards and Technology, 9/2005, pp. 82] NIST makes no mention of molten metal found at the collapse site in the weeks and months after 9/11, which has been described in numerous reports (see September 12, 2001-February 2002). The “NIST found no corroborating evidence for alternative hypotheses suggesting that the WTC towers were brought down by controlled demolition using explosives planted prior to September 11, 2001.” [National Institute of Standards and Technology, 9/2005, pp. 146] Members of Congress are critical of NIST’s recommendations, saying they are not detailed enough, or adequately documented, to be rapidly incorporated into standard building code publications. [New York Times, 10/27/2005] According to Glenn Corbett, a technical adviser to NIST and fire science professor at John Jay College, NIST is not aggressive enough to carry out major forensic investigations. He says, “Instead of a gumshoe inquiry that left no stone unturned, I believe the investigations were treated more like research projects in which they waited for information to flow to them.” [Associated Press, 10/26/2005; US Congress, 10/26/2005 pdf file] NIST will release its final report on the collapse of Building 7 of the WTC separately, at a later date. [National Institute of Standards and Technology, 9/2005, pp. xiii]

Entity Tags: World Trade Center, Glenn Corbett, National Institute of Standards and Technology

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

Dr. S. Shyam Sunder, head of the National Institute of Standards and Technology government investigation into the collapse of the World Trade Center building, is asked about the collapse of WTC Building 7. Sunder says that he hopes to release something about that by the end of 2006. He adds, NIST did have some “preliminary hypotheses… We are studying the horizontal movement east to west, internal to the structure, on the fifth to seventh floors.… But truthfully, I don’t really know. We’ve had trouble getting a handle on building No. 7.” [New York Magazine, 3/20/2006]

Entity Tags: Shyam Sunder, National Institute of Standards and Technology

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

In a reply to criticisms of its World Trade Center investigation, the National Institute of Standards and Technology (NIST) admits that it is unable to fully explain the total collapse of the Twin Towers on 9/11. NIST’s letter is a response to a “request for correction” letter sent to it five months earlier by Bob McIlvaine and Bill Doyle, who both lost family members on 9/11, along with scientists Kevin Ryan and Steven E. Jones, architect Richard Gage, and the group Scholars for 9/11 Truth and Justice. This letter made several assertions about NIST’s final reports of its WTC investigation, and suggested they had violated the Data Quality Act and NIST’s information quality standards. NIST’s reply denies the requests for corrections. However, it also mentions, “[W]e are unable to provide a full explanation of the total collapse” of the World Trade Center. [National Institute of Standards and Technology, 9/27/2007 pdf file] In its final report on the Twin Towers collapses, released in October 2005, NIST admitted that its investigation did “not actually include the structural behavior of the tower after the conditions for collapse initiation were reached and collapse became inevitable” (see October 26, 2005). [National Institute of Standards and Technology, 9/2005, pp. 82]

Entity Tags: National Institute of Standards and Technology, World Trade Center

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

The National Institute of Standards and Technology (NIST) publishes a fact sheet responding to 14 “frequently asked questions” about its investigation into the collapse of the Twin Towers on September 11. Some of the key questions and answers are as follows:
bullet Regarding the question, “Why was the collapse of WTC 1 and 2 not arrested by the intact structure below the floors where columns first began to buckle?” NIST replies, “The vertical capacity of the connections supporting an intact floor below the level of collapse was adequate to carry the load of 11 additional floors if the load was applied gradually and 6 additional floors if the load was applied suddenly (as was the case).” As the number of floors above the points where the collapses initiated exceeded six (12 in the case of the North Tower, 29 for the South), NIST says, “[T]he floors below the level of collapse initiation were unable to resist the suddenly applied gravitational load from the upper floors of the buildings.”
bullet In answer to the question of “Why was physical evidence not collected immediately following the collapse of the WTC towers,” NIST says, “In the initial days and weeks following the WTC disaster, the emphasis was on rescue and later on recovery, necessitating the removal of steel and disturbing the collapse site.” It adds, “NIST did not receive the legal authority to collect and preserve physical evidence from a disaster/failure site until the National Construction Safety Team Act became law in October 2002.” The decision to rapidly scrap the remaining steel from the WTC was made shortly after 9/11 (see Shortly After September 11, 2001), but the destruction of this steel was strongly protested by some within the engineering and firefighting communities (see December 25, 2001 and January 4, 2002).
bullet In response to a question about why it did not use its subpoena authority during its investigation, NIST states that its “experience during the investigation was that it was able to obtain all essential documentary and visual evidence without the need to invoke subpoena authority.”
bullet In answer to the question, “Why didn’t NIST fully model the collapse initiation and propagation of WTC towers?” NIST says, “Once the collapse had begun, the propagation of the collapse was readily explained without the same complexity of modeling” as was used to determine the sequence of events leading up to the collapse initiation.
bullet During its investigation, NIST had selected several variables for its computer simulations, and then experimented with different possible values (see (October 2002-October 2005)). But it has been asked: “Why didn’t NIST consider the ‘base’ and ‘less severe’ cases throughout its analysis of the WTC towers? What was the technical basis for selecting only the ‘more severe’ case for its analyses?” Its answer is that, “Of the three [possible values], the more severe case resulted in the closest agreement with the visual and physical evidence.” [National Institute of Standards and Technology, 12/14/2007]
NIST published its final report on the Twin Towers collapse in October 2005 (see October 26, 2005). It released an earlier fact sheet answering previous “frequently asked questions” in August 2006 (see August 30, 2006). [National Institute of Standards and Technology, 8/30/2006]

Entity Tags: National Institute of Standards and Technology

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

NIST lead investigator Shyam Sunder answering questions about NIST’s three-year study of the collapse of WTC 7.NIST lead investigator Shyam Sunder answering questions about NIST’s three-year study of the collapse of WTC 7. [Source: Don Berkemeyer / National Institute of Standards and Technology]The National Institute of Standards and Technology (NIST) announces the findings of its study of the collapse of World Trade Center Building 7, and says the 47-story tower fell late in the afternoon of 9/11 primarily due to fires. [National Institute of Standards and Technology, 8/21/2008; National Institute of Standards and Technology, 8/21/2008] NIST releases its findings as part of a 915-page report, which is the result of three years’ work by over 50 federal investigators and a dozen contractors (see August 21, 2008). [New York Times, 8/21/2008]
Collapse Is 'No Longer a Mystery' - In a news conference at NIST’s headquarters in Gaithersburg, Maryland, lead investigator Shyam Sunder admits: “[W]e knew from the beginning of our study that understanding what happened to Building 7 on 9/11 would be difficult. It did not fit any textbook description that you could readily point to and say, yes, that’s why the building failed.” But, he says, “[T]he reason for the collapse of World Trade Center 7 is no longer a mystery.” [National Institute of Standards and Technology, 8/21/2008; New York Times, 8/21/2008]
'New Phenomenon' Caused Collapse - Sunder says the “critical factor” that initiated the collapse was “thermal expansion of long-span floor systems located in the east side of the building,” and adds that NIST’s study “has identified thermal expansion as a new phenomenon that can cause structural collapse. For the first time we have shown that fire can induce a progressive collapse.”
Collapse Sequence - Sunder describes the sequence of events NIST believes led to the collapse of WTC 7. He says debris from the collapse of the north WTC tower “started fires on at least 10 floors of the building. The fires burned out of control on six of these 10 floors for about seven hours. The city water main had been cut by the collapse of the two WTC towers, so the sprinklers in Building 7 did not function for much of the bottom half of the building.” He continues: “Fires on floors 7 through 9 and 11 through 13 were particularly severe.… Eventually, a girder on floor 13 lost its connection to a critical interior column.” Floor 13 collapsed, beginning a cascade of floor failures down to the fifth floor. “With the support of these floors gone, column 79 buckled, which initiated the fire-induced progressive collapse of the building.… This in turn caused the failure of nearby columns 80 and 81 and floor failures up to the roof line.… As the roof line begins to fall adjacent columns buckle as well. In quick succession, the remaining interior columns failed from east to west across WTC 7, until the entire core began moving downward. Finally, the remaining outer shell or fa├žade of the building fell.”
NIST Created 'Virtual WTC 7' Model - Sunder says that NIST reached its conclusions about the collapse “by reconstructing the entire building, beam by beam, column by column, connection by connection into a computer model, a virtual WTC 7 building. We then filled that virtual building with as much detail as possible about exactly what types of furnishings were on each floor. Then we set fire to those virtual offices on the floors where video and other visual evidence told us the fires burned.” The investigators “used a well-validated computer program developed at NIST, for studying the growth and spread of fires, to calculate temperatures throughout the building.… And we used well-established data on the properties of structural steel, the sprayed fire resistive material or fireproofing, and other building materials to determine how those temperatures affected the structure.”
Explosives Not Used - Sunder says that the investigators “did not find any evidence that explosives were used to bring the building down” (see August 21, 2008), nor was the collapse “due to fires from the substantial amount of diesel fuel stored in the building” (see August 21, 2008). NIST commenced its investigation of the WTC collapses in 2002 (see August 21, 2002) and issued its findings on the collapses of the Twin Towers in October 2005 (see October 26, 2005). Since then it has been focused on WTC 7. [Government Computer News, 8/21/2008; National Institute of Standards and Technology, 8/21/2008]
Final Report to Be Released - After suggestions are made by members of the public in response to its current report, NIST will release a finished version of the same report in November 2008, thereby completing its WTC investigation (see November 20, 2008). [National Institute of Standards and Technology, 11/20/2008]

Entity Tags: World Trade Center, National Institute of Standards and Technology, Shyam Sunder

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

NIST’s ‘Final Report on the Collapse of World Trade Center Building 7.’NIST’s ‘Final Report on the Collapse of World Trade Center Building 7.’ [Source: National Institute of Standards and Technology.]The National Institute of Standards and Technology (NIST) releases the final report of its three-year investigation of the collapse of World Trade Center Building 7, the 47-story skyscraper which collapsed late in the afternoon of 9/11 (see (5:20 p.m.) September 11, 2001). This is the completed version of the report, and comes three months after a draft version was released for public comment (see August 21, 2008). NIST states that the new report “is strengthened by clarifications and supplemental text suggested by organizations and individuals worldwide in response to the draft WTC 7 report.” NIST conducted an additional computer analysis in response to comments from the building community, and made several minor amendments to the report. But, it says, “the revisions did not alter the investigation team’s major findings and recommendations, which include identification of fire as the primary cause for the building’s failure.” With the release of this report, NIST has completed its six-year investigation of the World Trade Center collapses, which it commenced in August 2002 (see August 21, 2002). The final report of its investigation of the Twin Towers’ collapses was published in October 2005 (see October 26, 2005). [National Institute of Standards and Technology, 11/20/2008; Occupational Health and Safety, 11/25/2008]

Entity Tags: World Trade Center, National Institute of Standards and Technology

Timeline Tags: Complete 911 Timeline, 9/11 Timeline

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