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: 
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.” 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). 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.” 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. 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]
April 8, 2008: Engineering Journal Publishes Scientific Challenge to Government Account of WTC Destruction
For the first time, a scientific journal publishes a letter by scientists who think the World Trade Center buildings were destroyed by explosives, rather than impact damage and fire. The letter, cautiously entitled “Fourteen Points of Agreement with Official Government Reports on the World Trade Center Destruction,” is published in the Open Civil Engineering Journal. The lead author is Steven E. Jones, a physicist formerly at Brigham Young University. The abstract says: “Reports by FEMA and NIST lay out the official account of the destruction of the World Trade Center on 9/11/2001. In this Letter, we wish to set a foundation for productive discussion and understanding by focusing on those areas where we find common ground with FEMA and NIST, while at the same time countering several popular myths about the WTC collapses.” [Open Civil Engineering Journal, 4/8/2008; Deseret News, 5/3/2008] However, unlike the vast majority of journals, the Open Civil Engineering Journal charges authors to publish their articles or letters in it. [Open Civil Engineering Journal, 2007]
August 21, 2008: Critics Unconvinced by NIST’s Claim that Explosives Not Used to Bring Down WTC 7
After the National Institute of Standards and Technology (NIST) announces the results of its investigation into the collapse of World Trade Center Building 7, some critics dispute its explanation for the collapse and question its apparent debunking of claims that explosives were used to demolish the building. The 47-story tower collapsed late in the afternoon of 9/11, even though no plane hit it (see (5:20 p.m.) September 11, 2001). Some have argued that fire and the falling debris from the Twin Towers’ collapses should not have brought down such a large steel and concrete structure. [Associated Press, 8/21/2008]
NIST Lacks ‘the Expertise on Explosives’ – James Quintiere, a professor of fire protection engineering at the University of Maryland who previously worked as the chief of NIST’s fire science and engineering division, says that NIST does not “have the expertise on explosives, so I don’t know how they came to that conclusion,” that explosives did not cause the collapse. However, Quintiere says he never personally believed explosives were involved. [Los Angeles Times, 8/22/2008] Richard Gage, a California architect and leader of a group called Architects and Engineers for 9/11 Truth, complains, “How much longer do we have to endure the cover-up of how Building 7 was destroyed?” The New York Times points out that “the collapse of 7 World Trade Center—home at the time to branch offices of the Central Intelligence Agency, the Secret Service, and the Giuliani administration’s emergency operations center—is cited in hundreds of Web sites and books as perhaps the most compelling evidence that an insider secretly planted explosives, intentionally destroying the tower.” [New York Times, 8/21/2008]
NIST Presentation – At a presentation of its findings earlier in the day, NIST announced that, in its three-year study of the collapse, it found no evidence showing explosives were used to bring the building down. [National Institute of Standards and Technology, 8/21/2008; National Institute of Standards and Technology, 8/21/2008] During his summary of the findings of NIST’s WTC 7 investigation (see August 21, 2008), lead investigator Shyam Sunder said, “We did not find any evidence that explosives were used to bring the building down.” [National Institute of Standards and Technology, 8/21/2008]
‘No Witness Reports’ of Loud Explosions – In the draft version of its final report on the collapse, which is released on this day (see August 21, 2008), NIST explains: “Blast from the smallest charge capable of failing a critical column… would have resulted in a sound level of 130 dB to 140 dB at a distance of at least half a mile if unobstructed by surrounding buildings.… This sound level is consistent with standing next to a jet plane engine and more than ten times louder than being in front of the speakers at a rock concert. There were no witness reports of such a loud noise, nor was such a noise heard on the audio tracks of video recordings of the WTC 7 collapse.” [National Institute of Standards and Technology, 8/2008, pp. 44-45 
]
NIST Rules out Thermite – Skeptics have argued that an incendiary material called thermite was used to bring down WTC 7 (see August 4, 2008), and this would not necessarily have created such a loud explosive boom. [New York Times, 8/21/2008] But in a fact sheet published on this day, NIST responds: “To apply thermite to a large steel column, approximately 0.13 lb of thermite would be needed to heat and melt each pound of steel. For a steel column that weighs approximately 1,000 lbs. per foot, at least 100 lbs. of thermite would need to be placed around the column, ignited, and remain in contact with the vertical steel surface as the thermite reaction took place. This is for one column… presumably, more than one column would have been prepared with thermite, if this approach were to be used. It is unlikely that 100 lbs. of thermite, or more, could have been carried into WTC 7 and placed around columns without being detected, either prior to Sept. 11 or during that day.” [National Institute of Standards and Technology, 8/21/2008] Sunder says that investigators therefore decided not to use their computer model to evaluate whether a thermite-fueled fire might have brought down WTC 7. Pointing to the omission, one skeptic says, “It is very difficult to find what you are not looking for.” [New York Times, 8/21/2008] In a 2006 fact sheet, NIST in fact admitted it “did not test for the residue” of explosives or thermite in the remaining structural steel from the WTC collapses (see August 30, 2006). [National Institute of Standards and Technology, 8/30/2006] And, as the New York Times notes, “Adding to the suspicion is the fact that in the rush to clean up the site, almost all of the steel remains of the tower were disposed of, leaving investigators in later years with little forensic evidence” (see Shortly After September 11, 2001 and September 12-October 2001). [New York Times, 8/21/2008]
Extensive Preparations for Demolition – NIST’s new fact sheet also points out: “For [WTC 7] to have been prepared for intentional demolition, walls and/or column enclosures and fireproofing would have to be removed and replaced without being detected. Preparing a column includes steps such as cutting sections with torches, which produces noxious and odorous fumes. Intentional demolition usually requires applying explosive charges to most, if not all, interior columns, not just one or a limited set of columns in a building.” [National Institute of Standards and Technology, 8/21/2008]
August 21, 2008: NIST Rules out Diesel Tanks in Collapse of WTC 7
The National Institute of Standards and Technology (NIST) publicly rejects the theory that diesel fuel tanks installed in World Trade Center Building 7 played any role in the 47-story tower’s collapse, late in the afternoon of 9/11. This is clearly set out in a question-and-answer factsheet published on this day, together with an announcement of NIST’s draft report on the building’s collapse (see August 21, 2008 and August 21, 2008). The factsheet asks, “Did fuel oil systems in WTC 7 contribute to its collapse?” The answer is “No…. The worst-case scenarios associated with fires… could not have been sustained long enough, could not have generated sufficient heat to weaken critical interior columns, and/or would have produced large amounts of visible smoke from the lower floors, which were not observed.” [National Institute of Standards and Technology, 8/21/2008; New York Times, 8/21/2008] These findings are echoed in the draft version of its final report on the collapse. [National Institute of Standards and Technology, 8/2008, pp. xxxii ] WTC 7 had three emergency power systems, all of which ran on diesel fuel. The systems contained two 12,000 gallon fuel tanks and two 6,000 gallon tanks located beneath the building’s loading docks, and another 6,000 gallon tank on its first floor. There were also 275 gallon tanks on the fifth, seventh, and eighth floors, and a 50 gallon tank on the ninth floor. [National Institute of Standards and Technology, 8/21/2008] It has previously been suggested that diesel stored in these tanks might have contributed to fires that led to WTC 7’s collapse (see March 2, 2002). [New York Times, 3/2/2002] This possibility was proposed in the final report of the Federal Emergency Management Agency (FEMA) investigation of the WTC collapses, published in May 2002 (see May 1, 2002). [Federal Emergency Management Agency, 5/1/2002, pp. 5-28 – 5-29] But in his summary of the findings of NIST’s three-year study of WTC 7, lead investigator Shyam Sunder says the building’s collapse was “not due to fires from the substantial amount of diesel fuel stored in the building.” [National Institute of Standards and Technology, 8/21/2008]
August 21, 2008: NIST Announces Conclusions of WTC 7 Investigation, Presents New Theory for Collapse
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 façade 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]
August 21, 2008: NIST Releases Draft Final Report on WTC 7 Collapse
The National Institute of Standards and Technology (NIST) releases a draft version of the final report of its 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). [National Institute of Standards and Technology, 8/21/2008] The report describes NIST’s conclusions on how fires that followed the impact of debris from the north WTC tower’s collapse resulted in the eventual collapse of WTC 7. It evaluates the emergency response and building evacuation procedures, and provides 13 recommendations for construction of buildings in the future, and improved procedures and practices. [National Institute of Standards and Technology, 8/2008, pp. xiii ] Some of the report’s key findings are: NIST describes its theory of what caused WTC 7 to collapse: “The probable collapse sequence… was initiated by the buckling of a critical interior column.… This column had become unsupported over nine stories after initial local fire-induced damage led to a cascade of local floor failures. The buckling of this column led to a vertical progression of floor failures up to the roof and to the buckling of adjacent interior columns to the south of the critical column. An east-to-west horizontal progression of interior column buckling followed, due to loss of lateral support to adjacent columns, forces exerted by falling debris, and load redistribution from other buckled columns. The exterior columns then buckled as the failed building core moved downward, redistributing its loads to the exterior columns. Global collapse occurred as the entire building above the buckled region moved downward as a single unit.” [National Institute of Standards and Technology, 8/2008, pp. xxxii ] The collapse of WTC 7 “represents the first known instance of the total collapse of a tall building primarily due to fires. The collapse could not have been prevented without controlling the fires before most of the combustible building contents were consumed.” [National Institute of Standards and Technology, 8/2008, pp. 43 ] The fires in WTC 7 “were ignited as a result of the impact of debris from the collapse of WTC 1, which was approximately 370 ft to the south.… The fires were ignited on at least 10 floors; however, only the fires on floors 7 through 9 and 11 through 13 grew and lasted until the time of the building collapse.” [National Institute of Standards and Technology, 8/2008, pp. xxxi-xxxii ] “Even without the initial structural damage caused by debris impact from the collapse of WTC 1, WTC 7 would have collapsed from fires having the same characteristics as those experienced on September 11, 2001.” [National Institute of Standards and Technology, 8/2008, pp. 44 ] “Had a water supply for the automatic sprinkler system been available and had the sprinkler system operated as designed, it is likely that fires in WTC 7 would have been controlled and the collapse prevented.” [National Institute of Standards and Technology, 8/2008, pp. 43 ] Other skyscrapers had previously survived comparable fires. “The fires in WTC 7 were similar to those that have occurred previously in several tall buildings (One New York Plaza, 1970, First Interstate Bank, 1988, and One Meridian Plaza, 1991) where the automatic sprinklers did not function or were not present. However, because of differences between their structural designs and that of WTC 7, these three buildings did not collapse.” [National Institute of Standards and Technology, 8/2008, pp. 43 ] NIST found that “temperatures did not exceed 300°C in the core or perimeter columns in WTC 7,” including the three interior columns that NIST says were the first to buckle in the collapse. “None of these columns were significantly weakened by elevated temperatures.” [National Institute of Standards and Technology, 8/2008, pp. 49-50 ] NIST says it found “no evidence to suggest that WTC 7 was not designed in a manner generally consistent with applicable building codes and standards.” [National Institute of Standards and Technology, 8/2008, pp. 53 ] The report concludes that neither explosives nor fuel oil fires fed by diesel tanks in WTC 7 played any role in the collapse (see August 21, 2008 and August 21, 2008). [National Institute of Standards and Technology, 8/2008, pp. 44-45 ] However, the report points out that WTC 7 “and the records kept within it were destroyed, and the remains of all the WTC buildings were disposed of before congressional action and funding was available for this investigation to begin. As a result, there are some facts that could not be discerned, and thus there are uncertainties in this accounting. Nonetheless, NIST was able to gather sufficient evidence and documentation to conduct a full investigation upon which to reach firm findings and recommendations.” [National Institute of Standards and Technology, 8/2008, pp. xxxi ]
NIST released a progress report in June 2004, which had included its “working hypothesis” at that time for the collapse of WTC 7 (see June 18, 2004). [National Institute of Standards and Technology, 6/18/2004] After suggestions are made by members of the public in response to the current draft report, NIST will release the finished version of the report in November 2008, which includes the same major findings and recommendations as the draft version (see November 20, 2008). [National Institute of Standards and Technology, 11/20/2008]
November 20, 2008: NIST Releases Final Report on WTC 7 Collapse, Repeats Conclusions of Earlier Draft Report
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]
