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{{Short description|9/11 conspiracy theories}}
]
{{pp-move-indef}}
{{main|Collapse of the World Trade Center|9/11 conspiracy theories}}
{{Use mdy dates|date=October 2013}}
The '''controlled demolition hypothesis''' is the disputed proposition that the ] was not destroyed by the planes that crashed into it as part of the ], nor by the fires that followed, but by explosives or other devices planted in the buildings in advance. Though the findings of the ] (NIST) do not suggest that ] was involved, the hypothesis has become central to the ]. The most detailed statements of the hypothesis have come from ], Kevin Ryan, ], ] and ]. In making their case, they often emphasize the collapse of ], which was not hit by a plane.
] can be seen left of WTC 7's ruins.]]


Some ] contend that the ] was caused not solely by the airliner crash damage that occurred as part of the ] and the resulting fire damage but also by ]s installed in the buildings in advance.<ref name="Clarke">Clarke, Steve. "Conspiracy Theories and the Internet: Controlled Demolition and Arrested Development". ''Episteme'', Volume 4, Issue 2, 2007, pp. 167-180.</ref> Controlled demolition theories make up a major component of ].
While it is has won significant popular support, the idea of controlled demolition is normally presented as a ] still to be tested, not a proven claim. Mainstream engineers, official investigators, and industry experts generally dismiss the idea and are not currently carrying out such tests.


Early advocates such as physicist ], architect ], software engineer ], and ] ] proposed that the aircraft impacts and resulting fires themselves alone could not have weakened the buildings sufficiently to initiate the ] and that the buildings would have neither collapsed completely nor at the speeds they did without additional energy involved to weaken their structures.<ref>{{Cite web|title=The 9/11 enigmas...|url=https://www.worldarchitecturenews.com/article/1503665/9-11-enigmas|access-date=2021-09-14|website=www.worldarchitecturenews.com}}</ref>
==Overview==
While engineers were initially very surprised by the ],<ref>{{cite web | last = Oliver | first = Anthony | year = 2001 | url = http://cruachan.televisual.co.uk/asset/GetArticle.exe?DB=e2&DATABASE=e2&LABEL=emap2&RECORD=191265&SEARCH=1| title = Lasting lessons of WTC | work = | publisher = New Civil Engineer | accessdate = 2006-07-28}}</ref> the broad outlines of a collapse theory quickly emerged in the days that followed the attacks of ]. The details have been significantly revised as investigations proceeded, but engineers have consistently attributed the collapse of the main towers to the combination of structural damage from the impact and weakening of the steel frame due to the fires.<ref name="ncstar1-6">{{cite web|
last=Gross|
first=John L.|
coauthors=and Therese P. McAllister|
date=2005-09|
url=http://wtc.nist.gov/oct05NCSTAR1-6index.htm|
accessdate=2007-01-13|
title=NIST NCSTAR 1-6: Structural Fire Response and Probable Collapse Sequence of the World Trade Center Towers|
work=Federal Building and Fire Safety Investigation of the World Trade Center Disaster|
publisher=National Institute of Standards and Technology}}</ref>
Although the investigation into the collapse of WTC 7 has not yet been completed, the working hypothesis also suggests a combination of structural damage and weakening by fire.<ref name="nistfaq">{{cite web|
author=NIST|
date=2006-08|
title=Answers to Frequently Asked Questions|
work=Federal Building and Fire Safety Investigation of the World Trade Center Disaster|
url=http://wtc.nist.gov/pubs/factsheets/faqs_8_2006.htm|
accessdate=2006-01-12}}</ref>


The ] (NIST) and the magazine '']'' examined and rejected these theories. Specialists in ] and ] accept the model of a fire-induced, gravity-driven collapse of the World Trade Center buildings, an explanation that does not involve the use of explosives.<ref name="bazant07">{{Cite journal |last1=Bažant |first1=Zdeněk P. |author2=Mathieu Verdure |author-link=Zdeněk Bažant |title=Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions |date=March 2007 |journal=Journal of Engineering Mechanics |volume=133 |issue=3 |pages=308–319 |doi=10.1061/(ASCE)0733-9399(2007)133:3(308) |url=http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/466.pdf | access-date=August 22, 2007 |quote=As generally accepted by the community of specialists in structural mechanics and structural engineering (though not by a few outsiders claiming a conspiracy with planted explosives), the failure scenario was as follows | archive-url =https://web.archive.org/web/20070809030224/http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/466.pdf |archive-date =August 9, 2007|citeseerx=10.1.1.121.4166 }}</ref><ref name="Chronicle" /><ref>{{Cite journal |last=Asquith |first=Christina |date=September 7, 2006 |title=Conspiracies continue to abound surrounding 9/11: on the eve of the fifth anniversary, a group of professors say the attacks were an "inside job."|journal=Diverse Issues in Higher Education |page=12 |url=http://findarticles.com/p/articles/mi_m0WMX/is_15_23/ai_n27000635/pg_1?tag=artBody;col1 |access-date=October 9, 2008}}</ref> NIST "found no corroborating evidence for alternative hypotheses suggesting that the WTC towers were brought down by controlled demolition using explosives planted prior to Sept. 11, 2001."<ref name="nistfaq">{{cite web|url=http://wtc.nist.gov/pubs/factsheets/faqs_8_2006.htm |title=NIST's Investigation of the Sept. 11 World Trade Center Disaster |publisher=NIST |date=August 2006 |archive-url=https://web.archive.org/web/20100527151823/http://wtc.nist.gov/pubs/factsheets/faqs_8_2006.htm |archive-date=May 27, 2010 |url-status=dead |access-date=May 29, 2014 }}</ref> Professors Zdeněk Bažant of ],<ref name=":0" /> Thomas Eagar, of the ]<ref name="Chronicle" /> and James Quintiere of the ],<ref name=":1" /> have also dismissed the controlled-demolition conspiracy theory.
Proponents of the controlled demolition hypothesis are critical of this consensus. Specifically, they do not accept that fire could weaken the buildings sufficiently to initiate collapse (even given the structural damage). They also do not accept that, after the collapses began, the buildings would collapse completely, straight down, and at near free-fall speed without an additional source of destructive energy.
It is argued, therefore, that the additional energy needed to undermine the structure must have come from secondary devices planted in the building before ], ]. This is normally presented as a plausible hypothesis in need of independent testing.<ref name="JonesWhyCollapse">{{cite journal|
last=Jones|first=Steven E.|
date=2006-09|
title=Why Indeed Did the World Trade Center Buildings Completely Collapse|
journal=Journal of 9/11 Studies|
volume=3|
url=http://worldtradecentertruth.com/volume/200609/WhyIndeedDidtheWorldTradeCenterBuildingsCompletelyCollapse.pdf|
accessdate=2006-01-13}}</ref>


In 2006, Jones suggested that ] or ] may have been used by government insiders with access to such materials and to the buildings themselves to demolish the buildings.<ref name="NYTCountersTheories">{{Cite news |first=Jim |last=Dwyer |title=2 U.S. Reports Seek to Counter Conspiracy Theories About 9/11 |date=September 2, 2006 |url=https://www.nytimes.com/2006/09/02/nyregion/02conspiracy.html|access-date=April 30, 2009 |work=The New York Times| archive-url=https://web.archive.org/web/20110512221337/http://www.nytimes.com/2006/09/02/nyregion/02conspiracy.html | archive-date=May 12, 2011<!--DASHBot-->| url-status=live}}</ref><ref name="Deseret-Dean-2006">{{Cite news |last=Dean |first=Suzanne |journal=Deseret Morning News |title=Physicist says heat substance felled WTC |date=April 10, 2006 |url=http://www.deseretnews.com/article/1,5143,635198488,00.html |access-date=May 7, 2009 |archive-url=https://web.archive.org/web/20090510002116/http://www.deseretnews.com/article/1%2C5143%2C635198488%2C00.html |archive-date=May 10, 2009 |url-status=dead }}</ref><ref name="Barber">{{Cite news|last=Barber|first=Peter|date=June 7, 2008|journal=Financial Times|title=The truth is out there|url=http://www.ft.com/cms/s/2/8d66e778-3128-11dd-ab22-000077b07658.html|access-date=May 23, 2009}}</ref><ref name="kmphGage">{{cite web|url=http://www.kmph.com/global/video/flash/popupplayer.asp?ClipID1=3804709&h1=Great%20Day%20Talks%20To%20Architect%20Richard%20Gage%20About%209/11&vt1=v&at1=Promotion%201&d1=449534&LaunchPageAdTag=Search%20Results&activePane=info&rnd=89888300|access-date=May 28, 2009|title=Great Day Talks To Architect Richard Gage About 9/11|publisher=KMPH Fox 26}}{{Dead link|date=March 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> In April 2009, Jones, Dane Niels H. Harrit and seven other authors published a paper in ], causing the editor, Prof. ], to resign as she accused the publisher of printing it without her knowledge;<ref name="Chefredaktor">{{cite journal |last=Hoffmann |first=Thomas |title=Chefredaktør skrider efter kontroversiel artikel om 9/11|journal=Videnskab|date=April 28, 2009|url=http://videnskab.dk/teknologi/chefredaktor-skrider-efter-kontroversiel-artikel-om-911 |access-date=November 4, 2013|quote=Mailen får hende til med det samme at smække med døren til tidsskriftet.}}</ref><ref name="Oder">{{cite web|url=http://lj.libraryjournal.com/2009/06/academic-libraries/hoax-article-accepted-by-peer-reviewed-oa-bentham-journal/|title=Hoax Article Accepted by "Peer-Reviewed" OA Bentham Journal|last=Oder|first=Norman|access-date=November 4, 2013|archive-date=August 10, 2017|archive-url=https://web.archive.org/web/20170810011520/http://lj.libraryjournal.com/2009/06/academic-libraries/hoax-article-accepted-by-peer-reviewed-oa-bentham-journal/|url-status=dead}}<!-- or if link goes bad, use https://www.webcitation.org/5vPwiJDw7?url=http://www.libraryjournal.com/article/CA6664637.html --></ref> this article was titled 'Active Thermitic Material Discovered in Dust from the 9/11 World Trade Center Catastrophe', and stated that they had found evidence of ] in samples of the dust that was produced during the collapse of the World Trade Center towers.<ref name="ActiveThermitic">{{Cite journal
In addition to this basic disagreement with the official explanation, proponents of the controlled demolition hypothesis point to a variety of features of the actual collapses that, they argue, is more consistent with demolition than progressive collapse. These features appear mainly in stages of the collapses that the official investigation did not deem relevant to understanding how they happened.<ref name="nistfaq"/>
|title=Active Thermitic Material Discovered in Dust from the 9/11 World Trade Center Catastrophe

|journal=The Open Chemical Physics Journal
In its final report, NIST stated that it "found no corroborating evidence for alternative hypotheses suggesting that the WTC towers were brought down by controlled demolition using explosives planted prior to ], ]"<ref name="Sunder"/> and posted an FAQ about related issues to its website in August of 2006.<ref name="nistfaq"/> The hypothesis has also never been suggested in mainstream engineering scholarship and its proponents are considered "outsiders".<ref name="bazant2006">{{cite journal|
|date=April 3, 2009
last=Bažant|first=Zdenĕk P.|coauthors=and Mathieu Verdure|
|first1=Niels H.
date=to appear 2007-03|
|last1=Harrit
title=Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions|
|author2=Jeffrey Farrer
journal=Journal of Engineering Mechanics|
|author3=Steven E. Jones
publisher=ACSE|
|author4=Kevin R. Ryan
url=http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/ProgressiveCollapseWTC-6-23-2006.pdf|
|author5=Frank M. Legge
accessdate=2007-01-13}}</ref> Explicit criticism of the controlled demolition hypothesis normally involves a combination of a defense of the official account of the collapses<ref> New York Times ]</ref> and an emphasis on the insurmountable difficulties of arranging the demolition of such large buildings covertly. By association with other 9/11 conspiracy theories, the controlled demolition hypothesis is also often accused of being disrespectful of the victims of 9/11 and their families.
|author6=Daniel Farnsworth

|author7=Gregg Roberts
==World Trade Center Seven==
|author8=James R. Gourley
]
|author9=Bradley R. Larsen
Videos that show the fall of ] have become a mainstay of presentations of the controlled demolition hypothesis.<ref>One collection is available at www.wtc7.net.</ref> This was a 47-story steel-framed skyscraper that stood across Vesey Street north of the main WTC complex. Though not hit by a plane, it collapsed at about 5:20 p.m. EDT on the evening of ], ]. No modern, steel-reinforced high-rise, had ever before collapsed because of an uncontrolled fire.<ref>{{cite web | last = Glanz | first = James | year = 2001 | url = http://web.archive.org/web/20020214182921/http:/www.chicagotribune.com/news/local/chi-0111290236nov29.story | title = Diesel suspected in 7 WTC collapse | work = Across the nation | publisher = Chicago Tribune | accessdate = 2006-07-06}}</ref> NIST has postponed publication of its report several times, attributing the delays to reassignment of investigators to other tasks.
|name-list-style=amp

|volume=2
In addition to its being officially unexplained, proponents of controlled demolition often emphasize the collapse of WTC7 for two reasons. First, because it was not hit by a plane and, second, because its collapse looked even more like a bottom-to-top standard controlled demolition than the more explosive top-to-bottom collapses of the two main towers. Support for this theory comes from visually observed features of the collapse--the swift and symmetrical fall, the pulverization of concrete, the lateral ejection of debris from high up for large distances. They also cite an early report of molten and partly evaporated steel found in the debris.
|issue=1

|pages=7–31
In the PBS documentary ''America Rebuilds,'' which aired in September 2002, ], the owner of Building Seven and leaseholder and insurance policy holder for the remainder of the WTC Complex, recalled a conversation with the Fire Department commander in which it was decided that "the smartest thing to do is just pull it", after which they "watched the building collapse." While Silverstein has issued a statement that rejects this interpretation,<ref>{{cite web |url=http://usinfo.state.gov/media/Archive/2005/Sep/16-241966.html |title=Identifying Misinformation: 9/11 Revealed? |accessdate=2007-01-06 |date=16 September 2005 |publisher=usinfo.state.gov}}</ref> proponents of controlled demolition have taken the remark as a confession that the building was intentionally demolished.<ref>Griffin, David Ray in ''The Hidden History'' (will fix ref).</ref><ref name="blanchard"/>
|doi=10.2174/1874412500902010007

|bibcode=2009OCPJ....2....7H
In a ''New York Magazine'' interview in March 2006, Dr S. Shyam Sunder, NIST's lead WTC disaster investigator, said "We are studying the horizontal movement east to west, internal to the structure, on the fifth to seventh floors," and then added, "but truthfully, I don’t really know. We’ve had trouble getting a handle on Building No. 7."<ref name='nymag2006-03'>{{cite web | publisher = New York Magazine | title = The Ground Zero Grassy Knoll | author = Mark Jacobson | year = 2006 | month = March | accessdate = 2006-11-26 | url = http://nymag.com/news/features/16464/index6.html}}</ref> Hugo Bachmann and Jörg Schneider, both of the ], believe that building 7 was intentionally demolished based on video footage.<ref>{{cite news|
|doi-access=free
url = http://www.911truthhumboldt.org/docs/Research/bitterdebate.htm|
}}</ref> NIST responded that there was no "]" to prove that the four samples of dust came from the WTC site. Jones invited NIST to conduct its own studies using its own known "chain of custody" dust, but NIST did not investigate.<ref name="SBIndependent" />
title = The embittered controversy over September 11|
accessdate=2006-09-20|
last = Ganser|first = Daniele|
date=2006-09-09|
work=Tages Anzeiger}}</ref>

Proponents have timed the collapse at just under seven seconds.<ref name="JonesWhyCollapse"/> Preliminary official investigations do not include the mechanics of the actual collapse, concentrating instead on the events leading up to it. The FEMA report begins its "timed collapse sequence" with a seismic event recorded at 5:22:33 pm. FEMA marks this as the time the building "begins to collapse." At this time, the report says, the east and west mechanical penthouses--the structures at the very top of the building--are still intact. Approximately thirty seconds later, FEMA says, video evidence shows the east mechanical penthouse begin to disappear into the building. Five seconds later the west penthouse also disappears, and at 5:22:10
"WTC 7 collapses completely."<ref>, page 5-23.</ref> This is roughly the point at which Jones begins timing the collapse, noting that his results correspond with the free, unimpeded fall of the roofline. This observed "near freefall" collapse time is a recurrent theme of the controlled demolition hypothesis.


==History== ==History==
The ] ] were first suggested in September 2001.<ref name="Clarke"/> Eric Hufschmid's book, ''Painful Questions: An Analysis of the September 11th Attack'', in which the controlled demolition theory is explicitly advocated, was published in September 2002.<ref name="Clarke"/> ] and ] are the best known advocates of the theory.<ref name="Clarke"/> Griffin's book '']'', published in 2004,<ref name="Powell">{{Cite news|last=Powell|first=Michael|newspaper=The Washington Post|date=September 8, 2006|title=The Disbelievers|url=https://www.washingtonpost.com/wp-dyn/content/article/2006/09/07/AR2006090701669_pf.html|quote=The loose agglomeration known as the '9/11 Truth Movement'|access-date=June 1, 2009}}</ref> has become a reference work for the ].<ref>{{Cite news|last=Barber|first=Peter|date=June 7, 2008|title=The truth is out there|url=http://www.ft.com/cms/s/2/8d66e778-3128-11dd-ab22-000077b07658.html|work=Financial Times|access-date=May 23, 2009}}</ref> In the same year, Griffin published the book ''The 9/11 Commission Report: Omissions and Distortions'', in which he argues that flaws in the commission's ] amounts to a cover-up by government officials and says that the ] was complicit in the 9/11 attacks.<ref>{{cite web|publisher=]|title=The 9/11 Commission Report: Omissions and Distortions|date=April 18, 2005|url=http://www.c-span.org/video/?186335-1/book-discussion-911-commission-report-omissions-distortions|access-date=April 4, 2015}}</ref>
On the day of the attacks, there were reports suggesting explosions<!-- links to videos of doubtful copyright are beng commented out <ref>{{cite web | url = http://youtube.com/watch?v=UbYwPQ9pTzk | title = BBC reporter Stephen Evans talking about a big explosion at the lower floors of WTC. | author = BBC | date = 11/9/2001 | format = flash | publisher = YouTube | quote = Then, an hour later, we had that big explosion, from much much lower. I don't know what on earth caused that}}</ref><ref>{{cite web | url = http://youtube.com/watch?v=xToXTufCL5Q | title = MSNBC's Ann Thompson - second explosion | author = MSNBC | date = 11/9/2001 | format = flash | publisher = YouTube }}</ref>--> and secondary devices. Several journalists reporting on the events speculated that the World Trade Center collapses were caused by intentionally planted explosives<!-- references to videos of doubtful copyright are being commented out <ref>{{cite web | url = http://youtube.com/watch?v=x5LIwtLh5OA | title = Reporter on 9/11- Bombs in the World Trade Center| author = NBC | date = 11/9/2001 | format = flash | publisher = YouTube | quote = there were actually devices that were planted within the building.}}</ref><ref>{{cite web | url = http://youtube.com/watch?v=xhDOq305oh0 | title = NBC anchor: WTC collapse planned| author = CNBC | date = 11/9/2001 | format = flash | publisher = YouTube | quote = This was clearly -- the way the structure is collapsing -- this was the result of something that was planned.}}</ref>--> and some experts made similar suggestions in the days following the attacks. As an official explanation that did not involve explosives emerged, however, these speculations ceased, and some were retracted.<ref>Webster Tarpley. ''9/11 Synthetic Terror'', Chapter 6, quotes Danish military explosives expert Bent Lund from Danish press sources. Kevin Ryan, who supports the controlled-demolition hypothesis, has said that Ronald Hamburger, who worked on the official explanation from an early stage, originally suspected explosives. His initial reaction was published as part of the announcement that he would work on the ASCE study. (PDF here)</ref>


Steven E. Jones has been another voice of the proponents of demolition theories.<ref>{{Cite news|last=Rudin|first=Mike|publisher=BBC|title=The evolution of a conspiracy theory|date=July 4, 2008|url=http://news.bbc.co.uk/2/low/uk_news/magazine/7488159.stm|access-date=May 23, 2009}}</ref> In 2006, he published the paper "Why Indeed Did the WTC Buildings Completely Collapse?".<ref name="NYTCountersTheories"/> On September 7, 2006, ] placed Jones on ] citing the "increasingly speculative and accusatory nature" of his statements, pending an official review of his actions. Six weeks later, Jones retired from the university.<ref name="Walch 1">{{Cite news|last=Walch|first=Tad|date=September 8, 2006|journal=Deseret Morning News|url=http://www.deseretnews.com/article/1,5143,645199800,00.html|title=BYU places '9/11 truth' professor on paid leave|access-date=January 4, 2009|archive-url=https://web.archive.org/web/20090108144212/http://deseretnews.com/article/1%2C5143%2C645199800%2C00.html|archive-date=January 8, 2009|url-status=dead}}</ref><ref name="Sullivan usnews">{{Cite news|first=Will |last=Sullivan |title=BYU takes on a 9/11 conspiracy professor |url=https://www.usnews.com/usnews/news/articles/060911/11conspiracy.htm |work=U.S. News & World Report |publisher=www.usnews.com |date=September 11, 2006 |access-date=April 26, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20090430003625/http://www.usnews.com/usnews/news/articles/060911/11conspiracy.htm |archive-date=April 30, 2009 }}</ref><ref name="foxnews retirement">{{Cite news|url=http://www.foxnews.com/story/0,2933,223318,00.html|title=BYU Professor Who Believes WTC Brought Down by Explosives Resigns|publisher=Fox News|date=October 21, 2006|access-date=May 15, 2009}}</ref><ref name="Walch 2">{{Cite news|last=Walch |first=Tad |date=October 22, 2006 |journal=Deseret Morning News |url=http://deseretnews.com/dn/view/0,1249,650200587,00.html|archive-url=https://archive.today/20121208174134/http://deseretnews.com/dn/view/0,1249,650200587,00.html|url-status=dead|archive-date=December 8, 2012|title=BYU professor in dispute over 9/11 will retire|access-date=May 15, 2009}}</ref><ref name="BYU re Jones">{{cite web|title=Steven E. Jones. Retired Professor |publisher=Brigham Young University |url=http://www.physics.byu.edu/research/energy/ |access-date=May 6, 2009 |archive-url=https://web.archive.org/web/20100610062849/http://www.physics.byu.edu/research/energy/ |archive-date=June 10, 2010 |url-status=live }}</ref> The structural engineering faculty at the university issued a statement which said that they "do not support the hypotheses of Professor Jones".<ref name="Chronicle" /><ref name="McIlvain">{{cite news |last1=McIlvain |first1=Ryan |title=Censor rumors quelled |url=http://newsnet.byu.edu/pdf/du20051205.pdf |access-date=22 July 2020 |work=] |agency=NewsNet |publisher=] |date=5 December 2005 |archive-url=https://web.archive.org/web/20200722025246/http://newsnet.byu.edu/pdf/du20051205.pdf |archive-date=22 July 2020 |pages=1; 3 |language=en}}</ref>
In a notable example, the ''Albuquerque Journal'' quoted Van Romero, Vice President for Research at New Mexico Institute of Mining and Technology, who said that the collapses looked "too methodical" and that his opinion, based on the videotapes, was that there were some explosive devices inside that caused the towers to collapse. He further said "detonation of bombs within the towers is consistent with a common terrorist strategy."<ref>{{cite web | last = Uyttebrouck| first = Oliver| year = | url = http://www.911readingroom.org/bib/whole_document.php?article_id=257 | format = | title = Explosives Planted In Towers, N.M. Tech Expert Says | work = | publisher = Albuquerque Journal | accessdate = 2006-07-28}}</ref> After speaking with structural engineers, however, he revised his opinion and said "certainly the fire is what caused the building to fail".<ref>{{cite web | last = Fleck | first = John | year = | url = http://www.maebrussell.com/Articles%20and%20Notes/WTC%20Explosives.html | format = | title = Fire, Not Extra Explosives, Doomed Buildings, Expert Says | work = | publisher = Albuquerque Journal | accessdate = 2006-07-28}}</ref> He further said he had been misquoted and had "only said that that's what it ''looked'' like."


In its final report, NIST stated that it "found no corroborating evidence for alternative hypotheses suggesting that the WTC towers were brought down by controlled demolition using explosives planted prior to Sept. 11, 2001. NIST also did not find any evidence that missiles were fired at or hit the towers. Instead, photographs and videos from several angles clearly show that the collapse initiated at the fire and impact floors and that the collapse progressed from the initiating floors downward until the dust clouds obscured the view"<ref name="Sunder">{{citation | last = Shyam-Sunder | first = S. |year = 2005 | title = Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Final Report of the National Construction Safety Team on the Collapses of the World Trade Center Towers |id=NIST NCSTAR 1 | journal= NIST | page = xxxviii | url = https://www.nist.gov/manuscript-publication-search.cfm?pub_id=909017| doi = 10.6028/NIST.ncstar.1 }}</ref> and posted a ] about related issues on its website in August 2006.<ref name="nistfaq" /> Allegations of controlled demolition have been found to be devoid of scientific merit by mainstream engineering scholarship.<ref name="bazant07"/><ref name="bazant2008a">{{Cite journal | last1 = Bažant | first1 = Z. K. P. | author-link1 = Zdeněk Bažant| last2 = Le | first2 = J. L. | last3 = Greening | first3 = F. R. | last4 = Benson | first4 = D. B. | title = What Did and Did Not Cause Collapse of World Trade Center Twin Towers in New York? | doi = 10.1061/(ASCE)0733-9399(2008)134:10(892) | journal = Journal of Engineering Mechanics | volume = 134 | issue = 10 | pages = 892 | year = 2008 | url = http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/00%20WTC%20Collapse%20-%20What%20Did%20%26%20Did%20Not%20Cause%20It.pdf}}</ref> The magazine '']'' also found the theories lacked scientific support in its special report "Debunking the 9/11 Myths".<ref name="pmDebunking">{{Cite news |author=<!-- The Editors --> |newspaper=Popular Mechanics |title=Debunking the 9/11 Myths: Special report| date=March 2005 |url=http://www.popularmechanics.com/technology/military/news/1227842 |archive-url=https://web.archive.org/web/20100317153323/http://www.popularmechanics.com/technology/military_law/1227842.html |archive-date=March 17, 2010}}</ref>
An early version of the controlled-demolition hypothesis, explictly stated in opposition to the official explanation, was formulated by J. McMichael. His ironic essay "Muslims Suspend the Laws of Physics" recalled Romero's initial remarks and introduced some of the lasting elements of the hypothesis: that the fires could not have sufficiently weakened the steel to initiate the collapses, and that the undamaged structure underneath the impact zones would have resisted a total progressive collapse.<ref>McMichael, J. "Muslims Suspend the Laws of Physics." ''Public Action News Service'', October 21, 2001 (revised November 25, 2001). </ref> These ideas were then developed in greater detail by Jeff King and ] on their websites, with little attention from the mainstream media.


Articles, letters and comments by controlled demolition advocates have been published in scientific and engineering journals. In April 2008, a letter titled "Fourteen Points of Agreement with Official Government Reports on the World Trade Center Destruction," was published by ], Frank Legge, Kevin Ryan, Anthony Szamboti and James Gourley in ''The Open Civil Engineering Journal''.<ref>{{cite web |url=http://www.benthamscience.com/open/tociej/articles/V002/35TOCIEJ.htm |title=Fourteen Points of Agreement with Official Government Reports on the World Trade Center Destruction |author1=Steven E. Jones |author2=Frank M. Legge |author3=Kevin R. Ryan |author4=Anthony F. Szamboti |author5=James R. Gourley |year=2008 |publisher=Bentham Science Publishers |access-date=September 25, 2011 |archive-url=https://web.archive.org/web/20120926001225/http://www.benthamscience.com/open/tociej/articles/V002/35TOCIEJ.htm |archive-date=September 26, 2012 |url-status=dead }}</ref> A few months later, in July 2008, an article titled "Environmental anomalies at the World Trade Center: evidence for energetic materials," was published by Ryan, Gourley and Jones in ''the Environmentalist.''<ref>{{cite journal |title=Environmental anomalies at the World Trade Center: evidence for energetic materials |journal=The Environmentalist |volume=29 |pages=56–63 |author1=Kevin R. Ryan |author2=James R. Gourley |author3=Steven E. Jones |year=2008 |doi=10.1007/s10669-008-9182-4 |doi-access=free }}</ref> Later that same year, in October 2008, the ''Journal of Engineering Mechanics'' published a comment<ref name="Gourley2008">{{Cite journal | last1 = Gourley | first1 = J. R. | title = Discussion of "Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions" by Zdenĕk P. Bažant and Mathieu Verdure | doi = 10.1061/(ASCE)0733-9399(2008)134:10(915) | journal = Journal of Engineering Mechanics | volume = 134 | issue = 10 | pages = 915–916| year = 2008 | url = http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/D25.pdf}}
Eric Hufschmid's ''Painful Questions'' was the first book-length treatment of the hypothesis, and included questions about Building Seven.<ref>Hufschmid, Eric. ''Painful Questions''. Endpoint Software. 2002.</ref> In 2004 this book was singled out by proponents and debunkers alike. ''Popular Mechanics'' started its investigation into this and other 9/11 conspiracy theories when ''Painful Questions'' was advertised in the ''New York Times''<ref name="popmechanics">{{cite journal|
</ref> by chemical engineer and attorney James R. Gourley, in which he describes what he considered fundamental errors in a 2007 paper on the mechanics of progressive collapse by Bažant and Verdure.<ref name="Bazant2007">{{Cite journal | last1 = Bažant | first1 = Z. K. P. | author-link1 = Zdeněk Bažant | last2 = Verdure | first2 = M. | doi = 10.1061/(ASCE)0733-9399(2007)133:3(308) | title = Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions | journal = Journal of Engineering Mechanics | volume = 133 | issue = 3 | pages = 308–319| year = 2007 | url = http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/466.pdf| citeseerx = 10.1.1.121.4166 }}
last=Dunbar|
</ref> In the same issue, Bažant and Le rebutted Gourley's arguments, finding his criticisms scientifically incorrect.<ref>{{Cite journal | last1 = Bažant | first1 = Z. K. P. | author-link1 = Zdeněk Bažant| last2 = Le | first2 = J. L. | doi = 10.1061/(ASCE)0733-9399(2008)134:10(917) | title = Closure to "Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions" by Zdenĕk P. Bažant and Mathieu Verdure | journal = Journal of Engineering Mechanics | volume = 134 | issue = 10 | pages = 917–921| year = 2008 | url = http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/D25.pdf}} "The interdisciplinary interests of Gourley, a chemical engineer with a doctorate in jurisprudence, are appreciated. Although none of the discusser's criticisms is scientifically correct, his discussion provides a welcome opportunity to dispel doubts recently voiced by some in the community outside structural mechanics and engineering."
first=Brad|
</ref> They suggested future critics should "become acquainted with the relevant material from an appropriate textbook on structural mechanics" or risk "misleading and wrongly influencing the public with incorrect information."<ref>{{Cite journal | last1 = Bažant | first1 = Z. K. P. | author-link1 = Zdeněk Bažant| last2 = Le | first2 = J. L. | doi = 10.1061/(ASCE)0733-9399(2008)134:10(917) | title = Closure to "Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions" by Zdenĕk P. Bažant and Mathieu Verdure | journal = Journal of Engineering Mechanics | volume = 134 | issue = 10 | pages = 917–921| year = 2008 | url = http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/D25.pdf}} "Although everyone is certainly entitled to express his or her opinion on any issue of concern, interested critics should realize that, to help discern the truth about an engineering problem such as the WTC collapse, it is necessary to become acquainted with the relevant material from an appropriate textbook on structural mechanics. Otherwise critics run the risk of misleading and wrongly influencing the public with incorrect information."
coauthors=and David Regan|
</ref>
title=Debunking The 9/11 Myths|
date=2005-03|
journal=Popular Mechanics|
url=http://www.popularmechanics.com/technology/military_law/1227842.html?page=4|
accessdate=2007-01-12}}</ref>
and theologian ] listed Hufschmid's questions among the reasons to re-investigate the events of 9/11 in his influential book ''The New Pearl Harbor''<ref name="NPH">{{cite book | first = David Ray | last = Griffin | title =The New Pearl Harbor | id = ISBN 1-56656-552-9 }}</ref>.


In April 2009, Danish chemist Niels H. Harrit, of the University of Copenhagen, and eight other authors published a paper in ''The Open Chemical Physics Journal'', titled, "Active Thermitic Material Discovered in Dust from the 9/11 World Trade Center Catastrophe." The paper concludes that chips consisting of unreacted and partially reacted ], or nano-thermite, appear to be present in samples of the dust.<ref name="ActiveThermitic"/><ref>]: , ]: {{Webarchive|url=https://web.archive.org/web/20120604222738/http://jp.dk/nyviden/article1654301.ece |date=June 4, 2012 }}, ]: , Kristeligt Dagblad: , Videnskab: . The journal Videnskab is sponsored by the Danish Ministry for Science and Technology. {{webarchive|url=https://web.archive.org/web/20100315023754/http://www.videnskab.dk/content/dk/teknologi/dansk_forsker_eksplosivt_nanomateriale_fundet_i_stovet_fra_world_trade_center |date=March 15, 2010 }}</ref> The editor in chief of the publication subsequently resigned.<ref name=NYTCountersTheories/><ref name="Deseret-Dean-2006"/><ref name="ActiveThermitic"/><ref>{{Cite news|last=Barber|first=Peter|date=June 7, 2008|journal=Financial Times|title=The truth is out there|url=http://www.ft.com/cms/s/2/8d66e778-3128-11dd-ab22-000077b07658.html|access-date=May 23, 2009| archive-url= https://web.archive.org/web/20090603164130/http://www.ft.com/cms/s/2/8d66e778-3128-11dd-ab22-000077b07658.html| archive-date=June 3, 2009 <!--DASHBot-->| url-status=live}}</ref>
In late 2005, Steven E. Jones, a physicist at Brigham Young University, made his own pursuit of the hypothesis public.<ref name="JonesWhyCollapse"/> Even before peer review and publication of the article in the 2006 book "9/11 and the American Empire: Intellectuals speak out," his interest in the hypothesis brought a measure of scientific credibility and increased media exposure to the theory. In consequence, however, Jones was placed on paid leave by his university in September 2006 for his "increasingly speculative and accusatory" statements.<ref name=DMorning_pleave>Walch, Tad. "BYU places '9/11 truth' professor on paid leave", Deseret Morning News, September 8, 2006.</ref><ref name=USNW_BYUtakes>{{cite news |first = Will |last = Sullivan|title = BYU takes on a 9/11 conspiracy professor|url = http://www.usnews.com/usnews/news/articles/060911/11conspiracy.htm|work = U.S.News & World Report |publisher = www.usnews.com|date = 2006-09-11}}</ref>


Internet websites and videos have contributed to the growth of the movement of individuals supporting the theory that planted explosives destroyed the World Trade Center. The website of ] cites the membership of over 2,400 architects and engineers.<ref>{{cite web|title=Architects and Engineers for 9/11 Truth|url=http://ae911truth.org | access-date=July 30, 2011}}</ref> The controlled demolition theory often includes allegations that U.S. government insiders planned and / or participated in the destruction of the WTC in order to justify the ].<ref name="NYT-Lipton-2008">{{Cite news|author=Eric Lipton|date=August 22, 2008|title=Fire, Not Explosives, Felled 3rd Tower on 9/11, Report Says|url=https://www.nytimes.com/2008/08/22/nyregion/22wtccnd.html | journal=The New York Times}}</ref> The theory features prominently in popular entertainment type movies, such as '']'',<ref>{{Cite news|last=Pilkington|first=Ed|journal=The Guardian|date=January 26, 2007|title='They're all forced to listen to us'|url=https://www.theguardian.com/media/2007/jan/26/digitalmedia|access-date=May 6, 2009 | location=London}}</ref> as well as ] such as ''9/11: Blueprint for Truth'', by San Francisco-area architect ].<ref>{{Cite news|last=Moskowitz|first=Eric|journal=The Boston Globe|title=Airing of 9/11 film ignites debate|date=November 29, 2007|url=https://www.boston.com/news/local/articles/2007/11/29/airing_of_911_film_ignites_debate|access-date=May 23, 2009}}</ref>
The controlled demolition hypothesis and the official explanations of the collapse developed alongside each other.<ref name="Sunder">{{cite web | last = Sunder | first = Shyam | year = 2005 | url = http://www.nist.gov/public_affairs/ncst/sept2005_meeting/SunderNCSTAC(2)091205%20final.pdf | format = pdf | title = Consideration of Public Comments | work = NIST Response to the World Trade Center Disaster | publisher = National Institute of Standards and Technology | accessdate = 2006-07-28}}. See also NCSTAR1, p. 146.</ref> Proponents of the controlled demolition hypothesis, for example, were among the first to question the "pancake collapse" hypothesis, in which floors progressively detached from the columns due to the force of higher floors falling on them. This theory, which constituted the official consensus until the middle of 2005, was ultimately rejected by NIST.<ref name="popmechanics"/> In its effort to understand the collapse of Building Seven, moreover, NIST claims to be currently developing "hypothetical blast scenarios" that will be of interest to proponents of controlled demolition. Likewise, Zdenek P. Bazant, who co-authored the first published analysis of the collapses of the two towers, has proposed examining data from controlled demolitions in order to better model the progressive-collapse of the towers.<ref name="bazant2006"/> The controlled demolition hypothesis has been pursued mainly by experts in fields other than structural engineering and by a network of amateur investigators.


While mainstream press has a significant history of dismissing conspiracy theories (i.e., in 2006, the magazine ] reported that a "new generation of conspiracy theorists is at work on a secret history of New York's most terrible day."<ref name="nymag2006-03">{{cite web| publisher = New York Magazine | title = The Ground Zero Grassy Knoll | author = Mark Jacobson |date=March 2006 |url = https://nymag.com/news/features/16464/index6.html}}</ref>), the theory has been supported by a number of popular actors, musicians and politicians, including ],<ref>{{Cite news|url=http://transcripts.cnn.com/TRANSCRIPTS/0603/22/sbt.01.html |title=CNN.com - Transcripts |publisher=Transcripts.cnn.com |access-date=October 30, 2008}}</ref><ref>{{Cite news| title = Charlie Sheen doesn't buy 9/11 spin | work = The Boston Herald | date =March 23, 2006}}</ref> ],<ref>{{Cite web|url=https://www.foxnews.com/story/world-trade-center-truth-or-fiction|title='World Trade Center': Truth or Fiction?|first=Catherine|last=Donaldson-Evans|date=March 25, 2015|website=Fox News}}</ref> former Governor of Minnesota ],<ref> {{Webarchive|url=https://web.archive.org/web/20080405211026/http://wcco.com/watercooler/jesse.ventura.911.2.691525.html |date=April 5, 2008 }}. Retrieved on April 8, 2008.</ref> talkshow host ],<ref>{{Cite news|last=Dwyer|first=Jim|title=A Notion From 9/11 Is Kept Alive|date=May 30, 2007|url=https://www.nytimes.com/2007/05/30/nyregion/30about.html|access-date=May 17, 2009 | journal=The New York Times}}</ref> and actors ] and ].
An August 2006 poll concluded that 16 percent of Americans considered it at least somewhat likely that "the collapse of the twin towers in New York was aided by explosives secretly planted in the two buildings."<ref>{{cite news|
last=Hargrove|
first=Thomas|
coauthors=and Guido H. Stempel III|
date=2006-08-02|
title=Anti-government anger spurs 9/11 conspiracy belief|
publisher=Scripps Howard News Service|
url=http://newspolls.org/story.php?story_id=55|
accessdate=2006-01-12}}</ref>


==Propositions and hypotheses==
==Notable proponents==
{{See also|List of buildings damaged or destroyed in the September 11 attacks}}
The most notable statements of the controlled demolition hypothesis have been made by Steven Jones, David Ray Griffin, Webster Griffin Tarpley and Kevin Ryan. Jones has published his paper "Why Indeed Did the World Trade Center Buildings Collapse?"<ref name="JonesWhyCollapse"/> in a book called ''9/11 and the American Empire: Intellectuals Speak Out'', edited by ] and ].<ref>{{cite book | first = David Ray | last = Griffin | title =9/11 and the American Empire: Intellectuals Speak Out | coauthors= Scott, Peter Dale | publisher=Olive Branch Press |date=2006-09-30 | id = ISBN 1-56656-659-2 }}</ref> Griffin, a retired professor of theology, published his own version of the hypothesis in ''The Hidden History of 9-11-2001'',<ref>{{cite book | first = Paul | last = Zarembka | title =The Hidden History of 9-11-2001 | publisher=JAI Press |date=2006-05-10 | id = ISBN 0762313056)) }}</ref> a book of critical essays on 9/11 edited by Paul Zarembka. ] has devoted a chapter of his book ''9/11 Synthetic Terror''<ref>{{cite book | first = Webster Griffin | last = Tarpley | title =9/11 Synthetic Terror | publisher=Tree of Life Publications |date=2005-12-01 | id = ISBN 0-930852-31-1 }}</ref> to the hypothesis. Kevin Ryan, who was fired from his job at Underwriters Laboratories for voicing his criticism of the official investigation, has also contributed chapter to the Griffin and Scott volume.<ref>{{cite book | first = David Ray | last = Griffin | title =9/11 and the American Empire: Intellectuals Speak Out | coauthors= Scott, Peter Dale | publisher=Olive Branch Press |date=2006-09-30 | id = ISBN 1-56656-659-2 }}</ref>


===Main towers===
All these authors refer to the controlled demolition of the World Trade Center as a hypothesis in need of further investigation before it can be accepted as true. Their accounts of the hypothesis overlap in many ways, but they each offer a distinct perspective. Jones concentrates on the physical plausibility of the official explanation and possible similarities to controlled demolition. While Griffin also summarizes suggestive physical features of the collapses, he adds a reading of the oral histories that were released by the New York Fire Department in August 2005 and published by the ''New York Times''. These constitute a substantial body of eyewitness testimony of the collapses and the events that led to them. Tarpley takes a more historical view, emphasizing expert opinions proposing controlled demolition shortly after the attacks; the behavior of government agencies (especially the New York Mayor's Office) in the handling of the WTC site; and public criticism of the official investigation into the collapses. This criticism of both the motives and the methods of official investigations is central to the defense of the controlled demolition hypothesis and here Ryan's contribution has become influential.
On September 11, the North Tower (1&nbsp;WTC) was hit by ] and the South Tower (2&nbsp;WTC) was hit by ], both ] aircraft. The South Tower collapsed 56&nbsp;minutes after the impact, and the North Tower collapsed 102&nbsp;minutes after.<ref>{{cite web|url=http://wtc.nist.gov/NCSTAR1/NCSTAR1-6index.htm|title=NIST NCSTAR 1-6: Structural Fire Response and Probable Collapse Sequence of the World Trade Center Towers|date=September 2005|publisher=NIST|pages=liv|access-date=April 28, 2009}}</ref> An investigation by ] concluded that the collapse was caused by a combination of damage to support columns and fire insulation from the aircraft impacts and the weakening of columns and floors by ] ignited fires.<ref name="nistfaq"/> NIST also 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".<ref>{{cite web|url=http://wtc.nist.gov/NCSTAR1/NCSTAR1index.htm|title=NIST NCSTAR 1: Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Final Report of the National Construction Safety Team on the Collapses of the World Trade Center Tower|date=September 2005|publisher=NIST|pages=xxxviii|access-date=May 3, 2009}}</ref>


Jones, among others, points to many descriptions by individuals working on the WTC rubble pile suggesting the presence of molten steel in the pile<ref name="NYTCountersTheories" /><ref name="ActiveThermitic"/> and a stream of molten metal that poured out of the South Tower before it collapsed<ref name="Chronicle" /> as evidence of temperatures beyond those produced by the fire. Jones has argued that the molten metal may have been ], a product of a thermite reaction. Jones and other researchers analyzed samples of dust from the World Trade Center buildings and reported their findings for evidence of ] in the dust.<ref name="ActiveThermitic" /> Jones informed NIST of his findings and NIST responded that there was no "clear chain of custody" proving that the dust indeed came from the WTC site. Jones invited NIST to conduct its own studies with dust under custody of NIST itself, but NIST has not done so.<ref name="SBIndependent">{{Cite news|last1=Levin|first1=Jay|last2=McKenzie|first2=Tom|title=The Elements of a Great Scientific and Technical Dispute|journal=Santa Barbara Independent|date=September 17, 2009|url=http://www.independent.com/news/2009/sep/17/elements-great-scientific-and-technical-dispute/|access-date=September 19, 2009}}</ref>
==Main towers==
Like WTC 7, both of the main towers collapsed at essentially the rate of free fall. While fires were still burning, the top sank into the damage area. A cloud developed around the failure as it progressed downward, and large pieces of debris fell away from the sides of the building. As the cloud reached the level of other buildings, it expanded through the streets of surrounding blocks. Along with WTC 7, the Twin Towers are the only buildings of their kind to have suffered global collapse as a result of local damage. This lack of precendent is often emphasized by proponents of the controlled demolition hypothesis.<ref>http://911research.wtc7.net/wtc/analysis/compare/fires.html</ref>


NIST found that the condition of the steel in the wreckage of the towers does not provide conclusive information on the condition of the building before the collapse and concluded that the material coming from the South Tower was molten ] from the plane, which would have melted at lower temperatures than steel. NIST also pointed out that cutting through the vertical columns would require planting an enormous amount of explosives inconspicuously in highly secured buildings, then igniting it remotely while keeping it in contact with the columns.<ref name="nistfaq" /> The ] performed a test with conventional thermite and was unable to cut a vertical column, despite the column being much smaller than those used in the World Trade Center.<ref>{{cite web|url=http://channel.nationalgeographic.com/channel/videos/911-science-and-conspiracy/|archive-url=https://web.archive.org/web/20120915034830/http://channel.nationalgeographic.com/channel/videos/911-science-and-conspiracy/|url-status=dead|archive-date=September 15, 2012|title=9/11: Science and Conspiracy|publisher=]|access-date=September 16, 2009}}</ref> Jones and others have responded that they do not believe that thermite was used, but rather a form of thermite called ], a nanoenergetic material developed for military use, propellants, explosives, or pyrotechnics. Historically, explosive applications for traditional thermites have been limited by their relatively slow energy release rates. But because nano-thermites are created from reactant particles with proximities approaching the atomic scale, energy release rates are far improved.<ref>{{cite web|url=http://www.informaworld.com/index/780214180.pdf |title=Effect of Al particle size on the thermal degradation of Al/teflon mixtures |publisher=Informaworld.com |date=August 8, 2007 |access-date=March 3, 2010}}</ref>
Because a detailed official explanation of these collapses is available, proponents present controlled demolition as an alternative hypothesis that better explains the data, i.e., the observable aspects of the collapses. They often emphasize the symmetry, completeness and near free-fall speed of the collapses; the reported sounds of explosions; the shooting out of debris and smoke (so-called "squibs"); and reports of molten metal. Counter-arguments by official investigators and mainstream engineers rarely deny these aspects of the collapses, but offer explanations for them that do not depend on preplanted explosives or other devices in the buildings.


The NIST report provides an analysis of the structural response of the building only up to the point where collapse begins, and asserts that the enormous ] transferred by the falling part of the building makes ] inevitable once an initial collapse occurs. A paper by ] indicates that once collapse began, the kinetic energy imparted by a falling upper section onto the floor below was an order of magnitude greater than that which the lower section could support.<ref name="bazant07"/>
===Basic argument===
Proponents often encourage their audiences to compare the video footage of the collapses of the WTC towers with footage of known controlled demolitions.<ref>The websites of Controlled Demolition, Inc. and ImplosionWorld are often suggested. The Landmark Towers demolition has become a common reference.</ref> They count the following features of the WTC collapses among telltale signs of controlled demolition:<ref name=JonesWhyCollapse/><ref name=GriffinCannotBe>{{cite paper | author = Griffin, D.R. | title = The Destruction of the World Trade Center: Why the Official Account Cannot Be True | publisher = Progressive Democrats–East Bay, http://www.pdeastbay.org | date = October, 2005 | url = http://www.pdeastbay.org/911MythReality/DestructionofWTC.pdf | format = pdf }}</ref>
*'''Direction of descent:''' The towers collapsed around their bases rather than tipping over in one direction. Debris fell to all sides.
*'''Speed of descent:''' The towers came down just slightly slower than the rate of free fall in a vacuum.
*'''Demolition waves:''' Proponents claim that small, apparently timed explosions occurred around the perimeter of each tower.
*'''Demolition squibs:''' As the towers collapsed they exhibited what appeared to be high-velocity gas ejections well below the descending rubble.
*'''Pulverization:''' The towers' non-metallic components, such as their concrete floors, were pulverized into fine dust.
*'''Totality:''' The towers were destroyed totally, their steel skeletons allegedly shredded into pieces less than 30 feet long.


Engineers who have investigated the collapses generally agree that controlled demolition is not required to understand the structural response of the buildings. While the top of one of the towers did tilt significantly, it could not ultimately have fallen into the street, they argue, because any such tilting would place sufficient stress on the lower story (acting as a pivot) that it would collapse long before the top had sufficiently shifted its center of gravity. Indeed, they argue, there is very little difference between progressive collapse with or without explosives in terms of the resistance that the structures could provide after collapse began.<ref name="bazant07"/><ref>{{cite web|url=https://www.pbs.org/wgbh/nova/wtc/collapse.html |title=NOVA &#124; Building on Ground Zero &#124; PBS |publisher=Pbs.org |access-date=October 30, 2008|archive-url = https://web.archive.org/web/20060717211559/http://www.pbs.org/wgbh/nova/wtc/collapse.html |archive-date=July 17, 2006 |url-status=dead}}</ref> Controlled demolition of a building to ] requires weeks of preparation, including laying large quantities of explosive and cutting through beams, which would have rendered the building highly dangerous and which would have to be done without attracting the attention of the thousands of people who worked in the building.<ref name="NYTCountersTheories" /><ref name="Wilkinson">{{cite web|url=http://www.civil.usyd.edu.au/wtc.shtml|title=World Trade Center - Some Engineering Aspects|last=Wilkinson|first=Tim|date=January 14, 2006|publisher=University of Sydney School of Civil Engineering|access-date=September 7, 2008|archive-date=March 6, 2012|archive-url=https://web.archive.org/web/20120306020131/http://sydney.edu.au/engineering/civil/wtc.shtml|url-status=dead}}</ref> Controlled demolition is traditionally done from the bottom of buildings rather than the top, although there are exceptions depending on structural design. There is little dispute that the collapse started high up at the point where the aircraft struck. Furthermore, any explosives would have to withstand the impact of the airliners.<ref name="NYTCountersTheories" />
Steven Jones has argued that without explosives to destroy the internal support structure of the WTC towers, the fall of the towers would violate the principle of ]. He says that the collapse of the towers at near free-fall speed indicates that the central core below the impact zone had lost its structural integrity and thus provided almost no resistance to the falling upper stories. Controlled demolition, he says, is the best way to explain this lack of structural resistance.


Members of the group ''Scholars for 9/11 Truth'' have collected eyewitness accounts<ref name="Hunt">{{Cite news|last=Hunt|first=H.E.|journal=The Daily Telegraph|date=November 19, 2008|title=The 30 greatest conspiracy theories - part 1|url=https://www.telegraph.co.uk/news/newstopics/howaboutthat/3483477/The-30-greatest-conspiracy-theories-part-1.html|access-date=May 30, 2009|quote=Many witnesses - including firemen, policemen and people who were inside the towers at the time - say they heard explosions below the aircraft impacts (including in basement levels) and before both the collapses and the attacks themselves. | location=London}}</ref> of flashes and loud explosions immediately before the fall.<ref name="Powell"/><ref name="Guardian-Asquith-2006">{{Cite news|last=Asquith|first=Christina|journal=The Guardian|title=Who really blew up the twin towers?|date=September 5, 2006|url=https://www.theguardian.com/education/2006/sep/05/internationaleducationnews.highereducation|access-date=May 6, 2009 | location=London}}</ref> Eyewitnesses have repeatedly reported of explosions happening before the collapse of the WTC towers, and the organization "International Center for 9/11 Studies" has published videos obtained from NIST, together with indications about when such explosions could be heard.<ref name="Bild Videos">{{cite news|journal=] |title=Neue Videos vom 11. September aufgetaucht |date=September 10, 2010 |url=http://www.bild.de/BILD/news/2010/09/10/neue-videos-911-aufgetaucht/terror-anschlaege-world-trade-center.html |access-date=September 18, 2010 |quote=Mehr als ein Dutzend der neuen Videos ist auf der Youtube-Seite des Zentrums zu finden. Unter den Videos stehen zum Teil Hinweise, wo solche Explosionen zu sehen oder hören sind. Augenzeugen hatten immer wieder von Explosionen berichtet, bevor die beiden Türme zusammenbrachen. |archive-url=https://web.archive.org/web/20100912211248/http://www.bild.de/BILD/news/2010/09/10/neue-videos-911-aufgetaucht/terror-anschlaege-world-trade-center.html |archive-date=September 12, 2010 |url-status=live }}</ref>{{Obsolete source|date=June 2021}} There are many types of loud sharp noises that are not caused by explosives,<ref>{{cite web|url=http://www.implosionworld.com/Article-WTC%20STUDY%208-06%20w%20clarif%20as%20of%209-8-06%20.pdf|title=A Critical Analysis of the Collapse of WTC Towers 1, 2 & 7 from an Explosives and Conventional Demolition Industry Viewpoint|last=Blanchard|first=Brent|year=2006|publisher=implosionworld.com|access-date=September 28, 2008|archive-date=July 18, 2021|archive-url=https://web.archive.org/web/20210718231858/http://www.implosionworld.com/Article-WTC%20STUDY%208-06%20w%20clarif%20as%20of%209-8-06%20.pdf|url-status=dead}}</ref> and ] records of the collapse do not show evidence of explosions.<ref>{{Cite news |author=<!-- The Editors --> |newspaper=Popular Mechanics |title=Debunking the 9/11 Myths: Special report – Seismic Spikes| date=March 2005 |url=http://www.popularmechanics.com/technology/military_law/1227842.html?page=5 |archive-url=https://web.archive.org/web/20100317153323/http://www.popularmechanics.com/technology/military_law/1227842.html?page=5 |archive-date=March 17, 2010}}</ref> Jones and others have argued that horizontal puffs of smoke seen during the collapse of the towers would indicate that the towers had been brought down by controlled explosions.<ref name="Grossman">{{Cite news|last=Grossman|first=Lev|magazine=Time|date=September 3, 2006|title=Why the 9/11 Conspiracy Theories Won't Go Away|url=http://www.time.com/time/magazine/article/0,9171,1531304,00.html|archive-url=https://web.archive.org/web/20061110053438/http://www.time.com/time/magazine/article/0%2C9171%2C1531304%2C00.html|url-status=dead|archive-date=November 10, 2006}}<br />• the 9/11 Truth Movement, as many conspiracy believers refer to their passion</ref><ref>{{Cite news |author=<!-- The Editors --> |newspaper=Popular Mechanics |title=Debunking the 9/11 Myths: Special report – Puffs Of Dust| date=March 2005 |url=http://www.popularmechanics.com/technology/military_law/1227842.html?page=4#puffs |archive-url=https://web.archive.org/web/20100317153323/http://www.popularmechanics.com/technology/military_law/1227842.html?page=4#puffs |archive-date=March 17, 2010}}</ref> NIST attributes these puffs to air pressure, created by the decreasing volume of the falling building above, traveling down elevator shafts and exiting from the open elevator shaft doors on lower levels.<ref>{{cite web|url=http://wtc.nist.gov/NCSTAR1/NCSTAR1-6index.htm|title=NIST NCSTAR 1-6: Structural Fire Response and Probable Collapse Sequence of the World Trade Center Towers |last1=Gross|first1=John L.|author2=McAllister, Therese P.|date=September 2005|publisher=NIST|page=320|access-date=March 21, 2009}}</ref>
Photographs and videos show tightly focused horizontal plumes of smoke and debris being ejected from the twin towers during the collapse. The plumes appear approximately 10 stories below the area of main destruction and are ejected only from the centers of the towers.<ref>http://911research.wtc7.net/wtc/analysis/collapses/squibs.html Squibs</ref> These plumes appear in both towers, at regular intervals, and from multiple camera angles. They are identified by proponents of controlled demolition as evidence for "squibs", i.e., explosing shaped charges intentionally destroying the structure of the buildings.


In September 2011, Iranian president ], who holds a PhD in Transportation Engineering and Planning, said that it would have been impossible for two jetliners to bring down the towers simply by hitting them and that some kind of planned explosion must have taken place.<ref>{{Cite web|url=https://www.newsday.com/news/new-york/diplomats-depart-as-ahmadinejad-speaks-g13642|title=Diplomats depart as Ahmadinejad speaks|website=Newsday|date=September 23, 2011 }}</ref> Al-Qaida sharply criticized Ahmadinejad in their English-language publication, '']'', calling his assertions "a ridiculous belief that stands in the face of all logic and evidence".<ref>{{Cite web|url=http://www.theguardian.com/world/2011/sep/28/al-qaida-ahmadinejad-911-conspiracy|title=Al-Qaida calls on Ahmadinejad to end 9/11 conspiracy theories|date=September 28, 2011|website=the Guardian}}</ref>
The official theory says the plumes consisted merely of material ejected due to the evacuation of air as the floors collapsed.
]
Engineers who have investigated the collapses also deny that their appearance was suspicious or suggests a controlled demolition. Thomas Eagar, professor of materials engineering and engineering systems at MIT, said that the towers could not have fallen by tipping over. He notes that the top would have to be displaced by 100 feet to move the center of gravity outside the base, and that the steel columns would have buckled well in advance of this.<ref>http://www.pbs.org/wgbh/nova/wtc/collapse.html</ref> Bažant and colleagues have commented that, although the top of the south tower initially tilted significantly, this tilting did not continue because the horizontal reaction to the rate of angular momentum{{clarifyme}} would have have exceeded the shear resistance of the lower story{{clarifyme}} by a factor of at least 10.3.<ref name="bazant2006"/>


===7 World Trade Center===
The total collapses of WTC 1 and 2 have not been modeled with the intention of either refuting or confirming the controlled-demolition hypothesis.<ref name="bazant2006"/> The NIST report provided a finite element analysis of the structural response of the building up to the point where, NIST says, collapse was inevitable due to the enormous weight of the buildings above the damaged floors. NIST did not, however, simulate the structural response of the lower floors, which are of primary interest to supporters of the demolition theory.<ref name=JonesWhyCollapse/> Bažant and Zhou, in the days after the attacks, provided some rough estimates that would support NIST's approach. They concluded that the weight was at least an "order of magnitude" over that required to occasion total collapse. Bažant and Verdure later reaffirmed this in 2006.
]
Proponents of World Trade Center controlled demolition theories allege that ]—a 47-story skyscraper that stood across Vesey Street north of the main part of the ]—was intentionally destroyed with explosives. Unlike the Twin Towers, 7 World Trade Center was not hit by a plane, although it was hit by debris from the Twin Towers and was damaged by fires which burned for seven hours, until it collapsed completely at about 5:20&nbsp;p.m. on the evening of September 11 (a new building has been erected on the site of the old and opened in May 2006). Several videos of the collapse event exist in the public domain, thus enabling comparative analysis from different angles of perspective.<ref>{{cite web |url=http://www.wtc7.net/videos.html |title=Videos Show Building 7's Vertical Collapse |work=wtc7.net |access-date=July 30, 2011}}</ref> Proponents typically say the collapse of 7 World Trade Center was not mentioned in the ] and that the federal body charged with investigating the event, ], required seven years to conduct its investigation and issue a report.<ref>{{cite web |url=http://rememberbuilding7.org/7-facts-about-building-7/ |title=7 Facts about Building 7 |work=rememberbuilding7.org |access-date=July 25, 2011 |archive-url=https://web.archive.org/web/20110730060516/http://rememberbuilding7.org/7-facts-about-building-7/ |archive-date=July 30, 2011 |url-status=dead |df=mdy-all}}</ref>


In November 2010, ] reporter ] hosted members of a television ad campaign called "BuildingWhat?", a series of commercials in which 9/11 family members ask questions about 7 World Trade Center and call for an investigation into its collapse. Rivera called the television ads "not so easy to dismiss as those demonstrators were," and stated that, "If explosives were involved, that would mean the most obnoxious protesters in recent years ... were right."<ref>{{cite news |last=Webster |first=Stephen C. |url=http://www.rawstory.com/rs/2010/11/14/geraldo-much-open-minded-911-campaign/ |title=Geraldo 'much more open minded' about 9/11 thanks to NYC television ads |access-date=July 27, 2011 |journal=The Raw Story |date=November 14, 2010 |archive-date=August 18, 2014 |archive-url=https://web.archive.org/web/20140818000309/http://www.rawstory.com/rs/2010/11/14/geraldo-much-open-minded-911-campaign/ |url-status=dead }}</ref> Days later, Rivera appeared on the program '']'' with legal analyst Judge ] on the ] to discuss the BuildingWhat? TV ad campaign. Napolitano stated, "It's hard for me to believe that came down by itself. I was gratified to see Geraldo Rivera investigating it."<ref name=foxtakesheat>{{cite news|author=CNN Political Unit|url=http://politicalticker.blogs.cnn.com/2010/12/01/fox-takes-heat-from-left-and-right-over-analyst/|title=Fox takes heat from left and right over analysts|access-date=July 27, 2011|work=politicalticker.blogs.cnn.com|date=December 1, 2010|archive-date=December 18, 2021|archive-url=https://web.archive.org/web/20211218025754/https://politicalticker.blogs.cnn.com/2010/12/01/fox-takes-heat-from-left-and-right-over-analyst/|url-status=dead}}</ref>
NIST has noted, as its primary reasons for rejecting the controlled demolition hypothesis, that the failure began specifically in the damage area and progressed downward.<ref name="nistfaq"/> Implosive demolitions initially sever supports at the bottom of the building to start the whole structure moving downward. Explosive charges higher in the building serve only to fragment the debris.<ref name="blanchard">{{cite web|
last=Blanchard|
first=Brent|
date=2006-08|
title=A Critical Analysis of the Collapse of WTC Towers 1, 2 & 7 from an Explosives and Conventional Demolition Industry Point of View|
publisher=ImplosionWorld.com|
url=http://www.implosionworld.com/Article-WTC%20STUDY%208-06%20w%20clarif%20as%20of%209-8-06%20.pdf|
accessdate=2006-01-12}}</ref><ref name="staceyloizeaux">{{cite web|
title=Interview with Stacey Loizeaux|
work=NOVA Online/Kaboom!|
url=http://www.pbs.org/wgbh/nova/kaboom/loizeaux.html|
accessdate=2006-01-12}}</ref>


Some proponents of World Trade Center controlled demolition theories suggest that 7 WTC was demolished because it may have served as an operational center for the demolition of the Twin Towers, while others suggest that government insiders may have wanted to destroy key files held in the building pertaining to corporate fraud. The WTC buildings housed dozens of federal, state and local government agencies.<ref name="SALAZAR">{{cite news |first=Cristian |last=Salazar |url=https://news.yahoo.com/mystery-surrounds-loss-records-art-9-11-164719650.html |title=Mystery surrounds loss of records, art on 9/11 |agency=Associated Press |date=July 30, 2011 |url-status=live |archive-url=https://web.archive.org/web/20111128134918/http://news.yahoo.com/mystery-surrounds-loss-records-art-9-11-164719650.html |archive-date=November 28, 2011 |access-date=May 29, 2014}}</ref> According to a statement reported by the ], '']'' film producer ] thinks the destruction of the building was suspicious because it housed some unusual tenants, including a clandestine CIA office on the 25th floor, an outpost of the U.S. Secret Service, the Securities and Exchange Commission, and New York City's emergency command center.<ref name="SALAZAR"/> The former chief counter-terrorism adviser to the President, ], does not think that 7 WTC is mysterious, and said that anyone could have rented floor space in the building.<ref name="BBCFAQ">{{cite news |title=Q&A: The Collapse of Tower 7 |publisher=BBC |url=http://news.bbc.co.uk/1/hi/programmes/conspiracy_files/7434230.stm |access-date=July 5, 2008 |date=July 4, 2008}}</ref>
Demolishing buildings by implosion typically requires weeks of active preparation. This preparation includes removing non-supporting walls, cutting non-essential structural elements, and drilling into the steel supports to place explosive charges. Most charges are placed in the bottom floors of the building, although charges may be placed higher to reduce the size of the debris.<ref name="staceyloizeaux"/><ref name="blanchard"/> NIST raised logistical objections to Jones's thermite hypothesis, saying that cutting through the vertical columns would require placing "many thousands of pounds of thermite" inconspicuously before the collapse, igniting it remotely, and holding it in contact with the columns.<ref name="nistfaq"/> At least one documentary on the controlled demolition hypothesis has addressed the question of logistics.<ref name="911mysteries">''9/11 Mysteries''</ref>


At the time, no ] high rise had ever before collapsed because of a fire, although there had been previous cases of collapses or partial collapses of smaller steel buildings due to fire.<ref>FEMA. ''World Trade Center Building Performance Study'', p. 4.</ref> However, the ability of such a building to be completely destroyed by fire would be demonstrated by the collapse of the ] in ]<ref name="bbc">{{cite web | url = https://www.bbc.com/news/world-middle-east-38675628 | title = Tehran fire: Many feared dead as high-rise collapses | date = 19 January 2017 | access-date = 19 January 2017 | work = ] }}</ref><ref name="latimes">{{cite web | url = https://www.latimes.com/world/la-fg-iran-high-rise-20170119-story.html | title = 50 firefighters killed in Iran as burning high-rise collapses | first1 = Shashank | last1= Bengali | first2= Ramin | last2= Mostaghim | date = 19 January 2017 | access-date = 19 January 2017 | work = ] }}</ref> in 2017 and the ] in ], ], the following year.<ref>{{cite web|title=Blazing building collapses in Sao Paulo|url=https://www.reuters.com/news/picture/blazing-building-collapses-in-sao-paulo-idUSRTS1PEAM|website=]|access-date=1 May 2018|archive-date=May 13, 2018|archive-url=https://web.archive.org/web/20180513014307/https://www.reuters.com/news/picture/blazing-building-collapses-in-sao-paulo-idUSRTS1PEAM|url-status=dead}}</ref><ref name="Brazil fire: São Paulo building collapses in huge blaze">{{cite news|title=Brazil fire: São Paulo building collapses in huge blaze|url=https://www.bbc.com/news/world-latin-america-43960778|access-date=1 May 2018|date=May 2018}}</ref><ref name="Building in Sao Paulo collapses in fire; at least 1 dead">{{cite web|last1=Prengaman|first1=Peter|last2=Penner|first2=Andre|title=Building in Sao Paulo collapses in fire; at least 1 dead|url=https://www.bostonglobe.com/news/world/2018/05/01/building-sao-paulo-collapses-fire-least-dead/WbrPzmIOXTfqpCIIidudKP/story.html|website=]|access-date=1 May 2018|archive-date=May 7, 2018|archive-url=https://web.archive.org/web/20180507202016/http://www.bostonglobe.com/news/world/2018/05/01/building-sao-paulo-collapses-fire-least-dead/WbrPzmIOXTfqpCIIidudKP/story.html|url-status=dead}}</ref><ref name="Blazing building collapses in Sao Paulo; one dead, three missing">{{cite web|last1=Bohone|first1=Flavia|title=Blazing building collapses in Sao Paulo; one dead, three missing|url=https://www.yahoo.com/news/blazing-building-collapses-sao-paulo-1-dead-3-094024949.html|website=]|date=May 2018 |access-date=1 May 2018}}</ref><ref name="‘Occupied’ Sao Paulo high rise collapses amid fire, 1 dead">{{cite news|last1=Dilorenzo|first1=Sarah|last2=Prengaman|first2=Peter|title='Occupied' Sao Paulo high rise collapses amid fire, 1 dead|url=https://www.washingtonpost.com/world/the_americas/building-in-sao-paulo-collapses-during-fire-victims-unknown/2018/05/01/0d7f5192-4d17-11e8-85c1-9326c4511033_story.html?noredirect=on|newspaper=]|access-date=1 May 2018}}{{dead link|date=June 2021|bot=medic}}{{cbignore|bot=medic}}</ref> In addition, NIST claims debris ejected during the collapse of 1 WTC caused significant structural damage in 7 WTC before the fire.<ref name="NIST-june2004">{{cite web |year=2004 |url=http://wtc.nist.gov/progress_report_june04/appendixl.pdf |title=Interim Report on WTC 7 |work=Appendix L |publisher=National Institute of Standards and Technology |access-date= October 24, 2015 |archive-url=https://web.archive.org/web/20070809030232/http://wtc.nist.gov/progress_report_june04/appendixl.pdf |archive-date=August 9, 2007 |url-status=dead |pages= L–17 – L–26}}</ref>
===Critique of fire theory===
Proponents of controlled demolition argue that the fires could not have been hot enough, nor burnt long enough, to significantly weaken the steel in the buildings to a point of collapse. Sometimes they refer also to examples such as NIST's 2004 fire test in which sample structures exposed to fire were shown to be "able to withstand standard fire conditions for between one and two hours" without failure.<ref>{{cite web |url=http://www.sciencedaily.com/releases/2004/08/040829130757.htm |title=NIST Tests Provide Fire Resistance Data On World Trade Center Floor Systems |accessdate=2007-01-05 |date= August 27, 2004 |publisher= Science Daily|quote= Note: This story has been adapted from a news release issued by National Institute Of Standards And Technology.}}</ref>


] reported the collapse of 7&nbsp;WTC twenty minutes before it actually fell.<ref>{{cite web |url=https://archive.org/details/bbc200109111654-1736 |title=BBC Sept. 11, 2001 4:54&nbsp;pm - 5:36&nbsp;pm (September 11, 2001) |work=Archive.org |access-date=November 9, 2010 |date=September 11, 2001}}</ref> The BBC has stated that many news sources were reporting the imminent collapse of 7&nbsp;WTC on the day of the attacks.<ref>Porter, Richard. "Part of the conspiracy? (2)" March 2, 2007. . {{webarchive |url=https://web.archive.org/web/20070304065001/http://www.bbc.co.uk/blogs/theeditors/2007/03/part_of_the_conspiracy_2.html |date=March 4, 2007}}</ref> Jane Standley, the reporter who announced the collapse prematurely, called it a "very small and very honest mistake" caused by her thinking on her feet after being confronted with a report she had no way of checking.<ref>.</ref>
Some have compared the heat of the fires in the twin towers and the fires' effect on steel to findings in actual fire tests carried out by steel manufacturer ] (formerly British Steel) on unprotected steel beams in open-sided car parks. The highest recorded steel temperatures in those parks when beams were exposed to hydrocarbon-fuelled fires was 360°C,<ref>
{{cite web |url=http://911research.wtc7.net/talks/towers/columnstemps.html |title=The Column Failure Theory is Inapplicable |accessdate=2007-01-05 |last=Hoffman |first= Jim |year=2003-2006 |publisher=911research.wtc7.net}}</ref> well below the estimated 800°C temperature of the steel supports in the twin towers at the time of the fires.<ref>{{cite web |url=http://news.bbc.co.uk/1/hi/world/americas/1540044.stm |title=How the World Trade Center fell |accessdate=2007-01-05 |last=Barter |first=Sheila |date=13 September, 2001 |publisher=BBC News}}</ref>


In the PBS documentary ''America Rebuilds,'' which aired in September 2002, ], the owner of 7&nbsp;WTC and leaseholder and insurance policy holder for the remainder of the WTC complex, recalled a discussion with the fire department in which doubts about containing the fires were expressed. Silverstein recalled saying, "We've had such terrible loss of life, maybe the smartest thing to do is pull it". "They made that decision to pull", he recalled, "and we watched the building collapse." Silverstein issued a statement that it was the firefighting team, not the building, that was to be pulled, contradicting theorists' allegation that "pull" was used in a demolition-related sense.<ref name="BBCFAQ" /><ref>{{cite web |url=http://usinfo.state.gov/media/Archive/2005/Sep/16-241966.html |title=Identifying Misinformation: 9/11 Revealed? |access-date=April 30, 2009|date=September 16, 2005 |archive-url=https://web.archive.org/web/20080214143807/http://usinfo.state.gov/media/Archive/2005/Sep/16-241966.html |archive-date=February 14, 2008}}</ref><ref name="FTpt3" />
Several studies made by NIST also showed that temperatures were relatively low. A paint study shows that neither perimeter nor core columns were exposed to temperatures exceeding 615°C for longer than 15 minutes and mostly temperatures were below 250°C.<ref name=NIST_P3Mechanical>{{cite web| last =| first =| year = 2004| url = http://wtc.nist.gov/media/P3MechanicalandMetAnalysisofSteel.pdf| title = Analysis of Structural Steel - presentation by Frank W. Gale, NIST| format = pdf| publisher = NIST}}</ref> Furthermore the simulation data in the NIST report indicates that the temperature of the steel was falling at the time of collapse.


===Oral history=== ====NIST report====
In 2002, the National Institute of Standards and Technology (NIST) began a general investigation into the collapse of the World Trade Center but soon made a decision to focus first on the collapse of the Twin Towers.<ref name="7FAQ">{{cite web|url=http://www.nist.gov/public_affairs/factsheet/wtc_qa_082108.cfm |title=Questions and Answers about the NIST 7&nbsp;WTC Investigation |date=August 21, 2008 |publisher=NIST |access-date=August 21, 2008 |archive-url=https://web.archive.org/web/20101124065139/http://www.nist.gov/public_affairs/factsheet/wtc_qa_082108.cfm |archive-date=November 24, 2010 |url-status=live }}</ref> A draft version of its final report on the collapse of 7&nbsp;WTC was released in August 2008. The agency has blamed the slowness of this investigation on the complexity of the computer model it used, which simulated the collapse from the moment it begins all the way to the ground; and NIST says the time taken on the investigation into 7&nbsp;WTC is comparable to the time taken to investigate an aircraft crash.<ref name="7FAQ"/> The agency also says another 80 boxes of documents related to 7&nbsp;WTC were found and had to be analyzed. These delays fueled suspicion among those already questioning the validity of the September 11 attacks that the agency was struggling to come up with a plausible conclusion.<ref name="FTpt3">{{cite news |url=http://www.ft.com/cms/s/0/8a580372-342b-11dd-869b-0000779fd2ac.html |title=The Truth Is Out There - Part III |last=Barber |first=Peter |date=June 7, 2008 |publisher=Financial Times |page=14 |access-date=August 22, 2008 |archive-date=May 7, 2015 |archive-url=https://archive.today/20150507003421/http://www.ft.com/cms/s/0/8a580372-342b-11dd-869b-0000779fd2ac.html%23axzz3ZPNgh3CX |url-status=dead }}</ref>
There were a number of eyewitness accounts of explosions just prior to the start of the collapse of the towers. These are cited as evidence for controlled demolition. Witness statements are numerous, redundant and detailed. "It seemed like it was going all the way around like a belt, all these explosions," one witness said. "You see three explosions and then the whole thing coming down," said another.<ref>http://911research.wtc7.net/wtc/evidence/oralhistories/explosions.html</ref> Many firefighters, in oral histories obtained by the ''NY Times'', also testified to what they perceived as explosions.<ref>"The Firefighters’ Testimony to Explosions in the Twin Towers," released by FDNY in August 2005 under order from the New York Court of Appeals. This material was reviewed by Griffin, David Ray in .</ref>


NIST released its final report on the collapse of 7 World Trade Center on November 20, 2008.<ref>{{cite web |url=http://wtc.nist.gov/NCSTAR1/NCSTAR1Aindex.htm |title=NIST NCSTAR 1A: Final Report on the Collapse of World Trade Center Building 7 |date=November 2008 |publisher=NIST |access-date=April 25, 2009}}</ref> Investigators used videos, photographs and building design documents to come to their conclusions. The investigation could not include physical evidence as the materials from the building lacked characteristics allowing them to be positively identified and were therefore disposed of prior to the initiation of the investigation.<ref name="7FAQ" /><ref>{{cite web |url=http://wtc.nist.gov/NCSTAR1/NCSTAR1Aindex.htm |title=NIST NCSTAR 1A: Final Report on the Collapse of World Trade Center Building 7 |date=November 2008 |publisher=NIST |access-date=April 26, 2010 |page=15}}</ref> The report concluded that the building's collapse was due to the effects of the fires which burned for almost seven hours. The fatal blow to the building came when the 13th floor collapsed, weakening a critical steel support column that led to catastrophic failure, and extreme heat caused some steel beams to lose strength, causing further failures throughout the buildings until the entire structure succumbed. Also cited as a factor was the collapse of the nearby towers, which broke the city water main, leaving the sprinkler system in the bottom half of the building without water.
A few witnesses describe what they believed to be 'basement bombs'. ], a WTC janitor in the North Tower at that time, reported that while he was in the basement of the north tower with about 20 others a large explosion took place on Sublevel B3 actually before the plane hit. He reports people running up the stairs with "skin hanging off of their bodies"<ref>{{cite web |title=Janitor tells 9/11 panel of brush with WTC thug |publisher=New York Daily News |date=June 2004 |url=http://www.nydailynews.com/front/story/203065p-175130c.html |accessdate=2006-12-08}}</ref> He said Mike Pecoraro, a mechanical engineer who had seen the bomb attack in 1993 and was working in the sixth sub-basement of the north tower on 9/11, also gave detailed observations of what he believed to be damage from bombs.<ref name="pecoraro">{{cite web |title=We Will Not Forget: A Day of Terror |publisher=The Chief Engineer |date=July 2002 |url=http://www.chiefengineer.org/article.cfm?seqnum1=1029 |accessdate=2006-10-04}}</ref> WTC construction worker Phillip Morelli described a basement explosion sound at the time of the plane impact that knocked him to the ground, although he later explained that it was most likely the freight elevators being cut loose above and hitting the ground.<ref>{{cite web |title=Honoring The Survivors |publisher=NY1 News |date=2002 |url=http://www.ny1.com/pages/RRR/911special_survivors.html |accessdate=2006-12-08}}</ref> Some researchers suggest other possible reasons for explosions in the basements, such as explosions of electrical equipment.<ref>{{cite web |title=Basement Bombs: Theories that Subterranean Bombs Destroyed the Twin Towers|url=http://911research.wtc7.net/wtc/analysis/theories/basementbomb.html|accessdate=2006-12-08}}</ref>Many other witnesses of explosions hold to their stories; many eyewitness accounts by firefighters recorded at that time were released in late 2006 and describe features of bombs detonating before and during the collapses.


NIST considered the possibility that 7&nbsp;WTC was brought down with explosives and concluded that a blast event did not occur, that the "use of thermite to sever columns in 7&nbsp;WTC on 9/11/01 was unlikely".<ref name="7FAQ" /> The investigation cited as evidence the claim that no blast was audible on recordings of the collapse and that no blast was reported by witnesses, stating that it would have been audible at a level of 130-140 decibels at a distance of half a mile. Demolition proponents say eyewitnesses repeatedly reported explosions happening before the collapse of the towers, and have published videos obtained from NIST, together with indications about when such explosions could be heard in support of the sounds of explosions before collapse.<ref name="Bild Videos"/>{{Obsolete source|date=June 2021}}
Some firefighters who had reported explosions later came to a different view of what they had perceived. For example, one said, "We realized later after talking and finding out" that the ten or so "explosions" he and others had heard coming from the south tower were actually "the floors collapsing to where the plane had hit."<ref>http://graphics8.nytimes.com/packages/pdf/nyregion/20050812_WTC_GRAPHIC/9110505.PDF</ref>


NIST also concluded that it is unlikely that the quantities of thermite needed could have been carried into the building undetected. Demolition advocates have responded that they do not claim that thermite was used, but rather that ], far more powerful than thermite, was used. Finally, the NIST investigated and ruled out the theory that fires from the large amount of diesel fuel stored in the building caused the collapse.<ref name="7FAQ" />
===Thermite hypothesis===
Proponents of controlled demolition argue there was evidence of temperatures well beyond those that, by general consensus, can be attributed to the fires. Steven Jones, specifically, believes observed molten material was actually molten iron, a byproduct of a thermite reaction.<ref>{{cite web|last = Toreki|first = Rob|year = 2006 |url = http://www.ilpi.com/genchem/demo/thermite/|title = The Thermite Reaction |work = The General Chemistry Demo Lab|publisher = Interactive Learning Paradigms Incorporated. |accessdate = 2006-07-04}}</ref> ] reactions can reach temperatures of up to 4500°F (2500°C), well beyond the temperature (approximately 1500°C) required to melt structural steel. He takes this to be an indication that thermite, a metallic agent used in incendiary munitions, might have provided the energy required to demolish the buildings.


====UAF study====
NIST proposed that some of the observed molten metal may have been molten aluminum from the fuselage of the plane. Aluminum melts at significantly lower temperatures than steel.
] (UAF) Professor of Civil Engineering J. Leroy Hulsey subsequently led a 4-year (2015–2019) investigation funded by ] titled "A Structural Reevaluation of the Collapse of World Trade Center 7", taking advantage of the improvement in computing resources since NIST's study. The UAF provides a 256 GB downloadable file that contains "All input data, results data, and simulations that were used or generated during this study."<ref name="hulsey1">{{Cite web|url=https://ine.uaf.edu/wtc7|title=World Trade Center 7 (WTC 7) University of Alaska Fairbanks|website=ine.uaf.edu|accessdate=2023-09-07}}</ref> Hulsey's group concluded in their final report:<ref name="hulsey2">{{cite web|url=https://files.wtc7report.org/file/public-download/A-Structural-Reevaluation-of-the-Collapse-of-World-Trade-Center-7-March2020.pdf |title=A Structural Reevaluation of the Collapse of World Trade Center 7 - Final Report |archiveurl=https://web.archive.org/web/20221004222034/https://files.wtc7report.org/file/public-download/A-Structural-Reevaluation-of-the-Collapse-of-World-Trade-Center-7-March2020.pdf |archivedate=2022-10-04 |url-status=dead}}</ref> {{Blockquote|text=The principal conclusion of our study is that fire did not cause the collapse of WTC 7 on 9/11, contrary to the conclusions of NIST and private engineering firms that studied the collapse. The secondary conclusion of our study is that the collapse of WTC 7 was a global failure involving the near-simultaneous failure of every column in the building.|author=Hulsey JL, Quan Z, Xiao F, University of Alaska Fairbanks}}


==Criticism==
In late ] Jones conducted molecular analyses to ascertain the presence of explosive residues on steel samples from Ground Zero and in the released dust<ref>{{cite web |first Steve E.| last Jones| title=Dr. Jones' Talk at ISU Physics Department Updated 9/11/06|publisher=http://journalof911studies.com| url=http://worldtradecentertruth.com/volume/200609/DrJonesTalksatISUPhysicsDepartment.pdf}}</ref> and says he found chemicals consistent with the presence of ] (a mixture of thermite and other oxidizing agents used in incendiary munitions). The initial FEMA investigation team also found sulfur within the structural steel from 7 WTC along with indications of extremely high temperatures.<ref>{{cite web|last = Barnett|first = Jonathan|coauthors = Ronald R. Biederman, R.D. Sisson, Jr.|year = 2002|url = http://www.fema.gov/pdf/library/fema403_apc.pdf |title = Limited Metallurgical Examination|format = pdf|work = FEMA 403 -- Appendix C.6, Suggestions for Future Research |publisher = Federal Emergency Management Agency |accessdate = 2006-07-04}} - "The severe corrosion and subsequent erosion of Samples 1 and 2 are a very unusual event. No clear explanation for the source of the sulfur has been identified. The rate of corrosion is also unknown. 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. A detailed study into the mechanisms of this phenomenon is needed to determine what risk, if any, is presented to existing steel structures exposed to severe and long-burning fires."</ref> Neither the FEMA study nor the NIST report identify a source for the sulfur, but NIST has since noted that sulfur is present in gypsum drywall and other construction materials used in the towers.<ref name="nistfaq"/>
The ] Structural Engineering Institute issued a statement calling for further discussion of NIST's recommendations,<ref>{{cite web | url = http://www.asce.org/uploadedFiles/Government_Relations_-_New/writtentestimony102605.pdf | title = Testimony of Dr.James Harris, PhD, P.E. | access-date = July 16, 2010 | date = October 26, 2005 | publisher = American Society of Civil Engineers | archive-url = https://web.archive.org/web/20120303130110/http://www.asce.org/uploadedFiles/Government_Relations_-_New/writtentestimony102605.pdf | archive-date = March 3, 2012 | url-status=dead | df = mdy-all }}</ref> and Britain's ] published a statement in May 2002 welcoming the FEMA report, noting that the report expressed similar views to those held by its group of professionals.<ref>{{cite web |url=http://www.istructe.org/thestructuralengineer/files/se/se102002.pdf |title=Welcome - The Institution of Structural Engineers |publisher=Istructe.org |access-date=December 2, 2012 |archive-url=https://web.archive.org/web/20110930170904/http://www.istructe.org/thestructuralengineer/files/se/se102002.pdf |archive-date=September 30, 2011 |url-status=dead |df=mdy-all }}</ref>


Following the publication of Jones' paper "Why Indeed Did the WTC Buildings Completely Collapse?"<ref name="NYTCountersTheories"/> ] responded to Jones' "increasingly speculative and accusatory" statements by placing him on paid leave, and thereby stripping him of two classes, in September 2006, pending a review of his statements and research. Six weeks later, Jones retired from the university.<ref name="Walch 2"/> The structural engineering faculty at the university issued a statement which said that they "do not support the hypotheses of Professor Jones".<ref name="Chronicle" /><ref name="McIlvain"/> On September 22, 2005, Jones gave a seminar on his hypotheses to a group of his colleagues from the Department of Physics and Astronomy at BYU. According to Jones, all but one of his colleagues agreed after the seminar that an investigation was in order and the lone dissenter came to agreement with Jones' suggestions the next day.<ref name="McIlvain"/>
===Dust clouds===
Some have argued that the production and expansion of the enormous dust clouds that covered Manhattan after the collapses are an indication of an additional source of energy, such as explosives. They say that the energy required for this expansion alone (ignoring the energy needed to slice the steel and pulverize the concrete and other materials) exceeded the gravitational energy available by at least 10 times.<ref>Hoffman (“The Twin Towers Demolition”) says that the clouds expanded to five times the diameter of the towers in the first ten seconds. The Demolition of the Kingdome can be viewed at the website of Controlled Demolition, Inc. (http://www.controlled-demolition.com/default.asp?reqLocId=7&reqItemId=20030317140323). The demolition of the Reading Grain Facility can be seen at ImplosionWorld.com (http://implosionworld.com/reading.html).</ref><ref>King, Jeff, 2003. “The WTC Collapse: What the Videos Show,” Indymedia Webcast News, November 12 (http://ontario.indymedia.org/display.php3?article_id=7342&group=webcast ).</ref> NIST attributes these clouds to the ejection of air from compressed parts of the building. They were once taken as an indication of the subsequently abandoned pancake collapse hypothesis.<ref name="popmechanics"/>


] Professor of ] Zdeněk Bažant, who was the first to offer a published peer-reviewed theory of the collapses, wrote "a few outsiders claiming a conspiracy with planted explosives" as an exception.<ref name=":0">{{Cite web|url=http://chronicle.com/free/v52/i42/42a01001.htm|title=Professors of Paranoia? - Faculty - The Chronicle of Higher Education}}</ref> Bažant and Verdure trace such "strange ideas" to a "mistaken impression" that safety margins in design would make the collapses impossible. One of the effects of a more detailed modeling of the progressive collapse, they say, could be to "dispel the myth of planted explosives". Indeed, Bažant and Verdure have proposed examining data from controlled demolitions in order to better model the progressive collapse of the towers, suggesting that progressive collapse and controlled demolition are not two separate modes of failure (as the controlled-demolition conspiracy theory assumes).<ref name="bazant07"/>
===Debris removal===
Webster Tarpley, in particular, has criticized the official response to the crime scene, saying the speedy cleanup resulted in the destruction of most of the evidence, identifying the New York City Mayor's office as a key player in this regard.<ref name="Tarpley 6">. ISBN 0930852311 </ref> Under Tarpley's theory, this would constitute ] tampering under New York state law.<ref name="215.40"> New York State Statutes</ref> <!-- The scenario described by Tarpley fits the law, and Tarpley has asserted that the destruction of the evidence is illegal. It is not OR to source the relevant law. Per ]: esearch that consists of collecting and organizing information from existing primary and/or secondary sources is, of course, strongly encouraged.-->


Thomas Eagar, a professor of materials science and engineering at the ], also dismissed the controlled-demolition conspiracy theory.<ref name="Chronicle">{{cite web|last = Gravois |first = John | date = June 23, 2006 | url = http://chronicle.com/free/v52/i42/42a01001.htm |title=Professors of Paranoia? Academics give a scholarly stamp to 9/11 conspiracy theories|publisher = The Chronicle of Higher Education | access-date=January 24, 2007|quote=Thomas W. Eagar is one scientist who has paid some attention to the demolition hypothesis — albeit grudgingly. A materials engineer at the Massachusetts Institute of Technology, Mr. Eagar wrote one of the early papers on the buildings' collapses, which later became the basis for a documentary on PBS. That marked him for scrutiny and attack from conspiracy theorists. For a time, he says, he was receiving one or two angry e-mail messages each week, many accusing him of being a government shill. When Mr. Jones's paper came out, the nasty messages increased to one or two per day.}}</ref> Eagar remarked, "These people (in the 9/11 truth movement) use the 'reverse ].' They determine what happened, throw out all the data that doesn't fit their conclusion, and then hail their findings as the only possible conclusion."<ref>{{cite web|last = Walch|first = Tad|year = 2006|url = http://deseretnews.com/dn/view/0,1249,645200098,00.html|title = Controversy dogs Y.'s Jones|work = Utah news|publisher = Deseret News Publishing Company|access-date = September 9, 2006|archive-date = March 2, 2007|archive-url = https://web.archive.org/web/20070302104135/http://deseretnews.com/dn/view/0,1249,645200098,00.html|url-status = dead}}</ref>
A call to action by Bill Manning, the chief editor of the trade journal ''Fire Engineering'', is often quoted in this connection. Manning called the early ASCE investigation (which would later turn into the FEMA building performance study) a "half-baked farce" and said that "the destruction and removal of evidence must stop immediately". He said that the cleanup of the WTC site differed in many respects from that of other engineering disasters.<ref>Manning, Bill. ""Burning Questions...Need Answers": FE's Bill Manning Calls for Comprehensive Investigation of WTC Collapse." Editorial in ''Fire Engineering''. January 4, 2002. </ref>
In defense of the decision to dispose of the steel, Mayor Bloomberg said: "If you want to take a look at the construction methods and the design, that's in this day and age what computers do."{{fact}} David Ray Griffin notes that this is exactly what Manning had worried about when he warned against letting "the investigation into the World Trade Center fire and collapse will amount to paper-and computer-generated hypotheticals." <ref>Griffin, David Ray. "The Destruction of the World Trade Center: why the official account cannot be true." (This is an updated version of his chapter in ''The Hidden History of 9-11''. </ref>


Regarding Jones' theory that ] was used to bring down the towers, and the assertion that ] and nanothermite composites were found in the dust and debris were found following the collapse of the three buildings, which was considered to be evidence that explosives brought down the buildings,<ref name=NYTCountersTheories/><ref name="Deseret-Dean-2006"/><ref name="Barber"/><ref name="ActiveThermitic"/> Brent Blanchard, author of "A History of Explosive Demolition in America",<ref name=HEDA>{{cite conference | author = Brent Blanchard | title = A History of Explosive Demolition in America | book-title = Proceedings of the Annual Conference on Explosives and Blasting Technique | pages = 27–44 |date=February 2002 | issn=0732-619X | publisher = International Society of Explosives Engineers}}</ref> states that questions about the viability of Jones' theories remain unanswered, such as the fact that no demolition personnel noticed any telltale signs of thermite during the eight months of debris removal following the towers' collapse. Blanchard also stated that a verifiable chain of possession needs to be established for the tested beams, which did not occur with the beams Jones tested, raising questions of whether the metal pieces tested could have been cut away from the debris pile with acetylene torches, shears, or other potentially contaminated equipment while on site, or exposed to trace amounts of thermite or other compounds while being handled, while in storage, or while being transferred from Ground Zero to memorial sites.<ref>Blanchard, Brent. {{Webarchive|url=https://web.archive.org/web/20210718231858/http://www.implosionworld.com/Article-WTC%20STUDY%208-06%20w%20clarif%20as%20of%209-8-06%20.pdf |date=July 18, 2021 }}. implosionworld.com. August 8, 2006</ref> Dave Thomas of '']'' magazine, noting that the residue in question was claimed to be thermitic because of its iron oxide and aluminum composition, pointed out that these substances are found in many items common to the towers. Thomas stated that in order to cut through a vertical steel beam, special high-temperature containment must be added to prevent the molten iron from dropping down, and that the thermite reaction is too slow for it to be practically used in building demolition. Thomas pointed out that when ] hired ] to conduct a demonstration showing nanothermite slicing through a large steel beam, the nanothermite produced copious flame and smoke but no damage to the beam, even though it was in a horizontal, and therefore optimal, position.<ref>Thomas, Dave. "The 9/11 Truth Movement: The Top Conspiracy Theory, a Decade Later". '']''. July/August 2011. Pages 34-40</ref>
In response to concerns about the destruction of evidence, W. Gene Corley, head of the Building Performance Assessment Team on the site, stated, that "The team has had full access to the scrap yards and to the site and has been able to obtain numerous samples."<ref>http://www.house.gov/science/hearings/full02/mar06/corley.htm</ref> NIST has numerous sections of steel from both Towers as well as 7 WTC.<ref></ref>


Preparing a building for a controlled demolition takes considerable time and effort.<ref name="skeptic.com">{{cite web|last=Mol |first=Phil |url=http://www.skeptic.com/eskeptic/06-09-11 |title=eSkeptic » Monday, September 11th, 2006 |publisher=Skeptic |access-date=September 19, 2009|date=2006-09-11 }}</ref> The tower walls would have had to be opened on dozens of floors.<ref name="NYTCountersTheories" /> Thousands of pounds of explosives, fuses and ignition mechanisms would need to be sneaked past security and placed in the towers<ref name="NYTCountersTheories" /><ref name="Knight">{{Cite journal |last=Knight |first=Peter |title=Outrageous Conspiracy Theories: Popular and Official Responses to 9/11 in Germany and the United States |journal=New German Critique |volume=35 |issue=1 (103) |pages=165–193 |year=2008 |doi=10.1215/0094033X-2007-024 }}</ref> without the tens of thousands of people working in the World Trade Center noticing.<ref name="Clarke"/><ref name="Wilkinson" /><ref name="skeptic.com" /><ref name="Knight" /> Referring to a conversation with ], a professor of psychology, an article in the ''Hartford Advocate'' asks, "How many hundreds of people would you need to acquire the explosives, plant them in the buildings, arrange for the airplanes to crash&nbsp; and, perhaps most implausibly of all, never breathe a single word of this conspiracy?"<ref name="Abel">{{Cite news|last=Abel|first=Jennifer|date=Jan 29, 2008|title=Theories of 9/11|journal=Hartford Advocate|url=http://www.hartfordadvocate.com/article.cfm?aid=5546 |access-date=November 5, 2010 |archive-url = https://web.archive.org/web/20080430203236/http://www.hartfordadvocate.com/article.cfm?aid=5546 |archive-date = April 30, 2008}}</ref>
==Popularizations==
The research of proponents like Hoffman, Griffin, Jones and Tarpley has entered popular culture by a variety of means, many involving ]. A Scripps/Howard poll found that people who are most likely to endorse this hypothesis get most of their information from the Internet.


World Trade Center developer Larry Silverstein said, "Hopefully this thorough report puts to rest the various 9/11 conspiracy theories, which dishonor the men and women who lost their lives on that terrible day." Upon presentation of the NIST's detailed report on the failure of Bldg. 7, Richard Gage, leader of the group ] said, "How much longer do we have to endure the coverup of how Building 7 was destroyed?" in which Dr. S. Shyam Sunder, the lead NIST investigator said he could not explain why the skepticism would not die. "I am really not a psychologist," he said. "Our job was to come up with the best science."<ref name="NYT-Lipton-2008"/>
Several documentaries have also defended the controlled demolition hypothesis, including ''9/11 Mysteries'',<!-- Videos of doubtful copyright are being commented out <ref>{{cite web |url=http://www.911weknow.com/index.php?option=com_content&task=view&id=34&Itemid=31 |title= 9/11 Mysteries - Part 1: Demolitions (full) |accessdate=2006-12-08 |year= 2006 |month=10 |publisher=http://www.911weknow.com/, Google Video |language=eng}}</ref>--> ''Improbable Collapse,''<ref> - the documentary website.</ref> and Dylan Avery's '']''. A number of lectures by Hoffman, Jones and Griffin have also been made available online.<ref>Links to lectures</ref>
James Quintiere, professor of ] at the ], who does not believe explosives brought down the towers, questioned how the agency came to its conclusions, remarking, "They don't have the expertise on explosives," though he adds that NIST wasted time employing outside experts to consider it.<ref name=":1">{{cite news |url=https://www.theguardian.com/world/2008/aug/22/september11.usa |title=World Trade Centre building seven not destroyed by explosives, says US study |access-date=April 24, 2009 |work=The Guardian |location=London |date=August 22, 2008 |first=McClatchy |last=Newspapers}}</ref>

The demolition hypothesis first entered mainstream media by way of negative press coverage of "9/11 conspiracy theories" or "9/11 myths". An article in ''Popular Mechanics'', which was later expanded into a book, also presented the hypothesis to a mainstream audience, as did the popular magazine ''Skeptic''.<ref>Molé, Phil. "9/11 Conspiracy Theories: The 9/11 Truth Movement Perspective" and "What Demolition Experts
Say About 9/11" in ''Skeptic'', v. 12, n. 4. 2006.</ref> Such coverage generally takes a very critical view of the hypothesis.

''New York Magazine'' published one of the first major articles that offered a partially sympathetic take on the hypothesis.<ref name='nymag2006-03' /> Finally, the hypothesis has also been cited by a number of celebrities, including ] and ], inviting much interest from the public.

==Reactions from engineers==
The controlled demolition hypothesis has been unambiguously rejected by official investigators and mainstream structural engineers.

Zdenek P. Bazant, who was among the first to offer an explanation of the collapses, mentioned the controlled demolition hypothesis in passing in a 2006 paper, co-authored with Mathieu Verdure. Affirming the mainstream consensus as presented in the NIST report, Bazant and Verdure note "a few outsiders claiming a conspiracy with planted explosives" as an exception. They trace "strange ideas" about, among other things, controlled demolition, to a "mistaken impression" that safety margins in design would make the collapses impossible. While strictly speaking superfluous, one of the effects of a more detailed modeling of the progressive collapse, they say, could be to "dispel the myth of planted explosives".<ref name="bazant2006"/>

Other engineers, such as Thomas Eagar, have also dismissed the controlled demolition hypothesis with reference to the consensus that has formed in the engineering community about the collapses.<ref name="Chronicle">{{cite web |last = Gravois |first = John | year = June 23, 2006 | url = http://chronicle.com/free/v52/i42/42a01001.htm |title = Professors of Paranoia? Academics give a scholarly stamp to 9/11 conspiracy theories| work = |publisher = The Chronicle of Higher Education | accessdate = 2006-07-27}}</ref>

Leslie Robertson, who helped design the Twin Towers, debated Steven Jones on a radio program.<ref>, Oct. 26, 2006.</ref>


==References== ==References==
{{Reflist|30em}}
<div class="references-small"><references/></div>


==External links== ==External links==
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* , Oct. 26, 2006.
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* - 44m30s in Dr Griffin speaks about collapses of WTC 1,2 & 7.
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* UC Berkeley Campus, November, 11 2006 - Jones speaks about WTC7, molten metal, about thermite and explosive
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* {{webarchive |url=https://web.archive.org/web/20090107042317/http://debunk911myths.org/ |date=January 7, 2009 |title=Debunk 9/11 Myths, a Guide to 9/11 Facts, Myths, and Theories}}
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9/11 conspiracy theories

Aerial view of the debris field of the North Tower, 6 WTC, and 7 WTC (upper right). The damaged Verizon Building can be seen left of WTC 7's ruins.

Some conspiracy theories contend that the collapse of the World Trade Center was caused not solely by the airliner crash damage that occurred as part of the September 11 attacks and the resulting fire damage but also by explosives installed in the buildings in advance. Controlled demolition theories make up a major component of 9/11 conspiracy theories.

Early advocates such as physicist Steven E. Jones, architect Richard Gage, software engineer Jim Hoffman, and theologian David Ray Griffin proposed that the aircraft impacts and resulting fires themselves alone could not have weakened the buildings sufficiently to initiate the catastrophic collapse and that the buildings would have neither collapsed completely nor at the speeds they did without additional energy involved to weaken their structures.

The National Institute of Standards and Technology (NIST) and the magazine Popular Mechanics examined and rejected these theories. Specialists in structural mechanics and structural engineering accept the model of a fire-induced, gravity-driven collapse of the World Trade Center buildings, an explanation that does not involve the use of explosives. NIST "found no corroborating evidence for alternative hypotheses suggesting that the WTC towers were brought down by controlled demolition using explosives planted prior to Sept. 11, 2001." Professors Zdeněk Bažant of Northwestern University, Thomas Eagar, of the Massachusetts Institute of Technology and James Quintiere of the University of Maryland, have also dismissed the controlled-demolition conspiracy theory.

In 2006, Jones suggested that thermite or super-thermite may have been used by government insiders with access to such materials and to the buildings themselves to demolish the buildings. In April 2009, Jones, Dane Niels H. Harrit and seven other authors published a paper in The Open Chemical Physics Journal, causing the editor, Prof. Marie-Paule Pileni, to resign as she accused the publisher of printing it without her knowledge; this article was titled 'Active Thermitic Material Discovered in Dust from the 9/11 World Trade Center Catastrophe', and stated that they had found evidence of nano-thermite in samples of the dust that was produced during the collapse of the World Trade Center towers. NIST responded that there was no "clear chain of custody" to prove that the four samples of dust came from the WTC site. Jones invited NIST to conduct its own studies using its own known "chain of custody" dust, but NIST did not investigate.

History

The controlled demolition conspiracy theories were first suggested in September 2001. Eric Hufschmid's book, Painful Questions: An Analysis of the September 11th Attack, in which the controlled demolition theory is explicitly advocated, was published in September 2002. David Ray Griffin and Steven E. Jones are the best known advocates of the theory. Griffin's book The New Pearl Harbor, published in 2004, has become a reference work for the 9/11 Truth movement. In the same year, Griffin published the book The 9/11 Commission Report: Omissions and Distortions, in which he argues that flaws in the commission's report amounts to a cover-up by government officials and says that the Bush administration was complicit in the 9/11 attacks.

Steven E. Jones has been another voice of the proponents of demolition theories. In 2006, he published the paper "Why Indeed Did the WTC Buildings Completely Collapse?". On September 7, 2006, Brigham Young University placed Jones on paid leave citing the "increasingly speculative and accusatory nature" of his statements, pending an official review of his actions. Six weeks later, Jones retired from the university. The structural engineering faculty at the university issued a statement which said that they "do not support the hypotheses of Professor Jones".

In its final report, NIST stated that it "found no corroborating evidence for alternative hypotheses suggesting that the WTC towers were brought down by controlled demolition using explosives planted prior to Sept. 11, 2001. NIST also did not find any evidence that missiles were fired at or hit the towers. Instead, photographs and videos from several angles clearly show that the collapse initiated at the fire and impact floors and that the collapse progressed from the initiating floors downward until the dust clouds obscured the view" and posted a FAQ about related issues on its website in August 2006. Allegations of controlled demolition have been found to be devoid of scientific merit by mainstream engineering scholarship. The magazine Popular Mechanics also found the theories lacked scientific support in its special report "Debunking the 9/11 Myths".

Articles, letters and comments by controlled demolition advocates have been published in scientific and engineering journals. In April 2008, a letter titled "Fourteen Points of Agreement with Official Government Reports on the World Trade Center Destruction," was published by Steven E. Jones, Frank Legge, Kevin Ryan, Anthony Szamboti and James Gourley in The Open Civil Engineering Journal. A few months later, in July 2008, an article titled "Environmental anomalies at the World Trade Center: evidence for energetic materials," was published by Ryan, Gourley and Jones in the Environmentalist. Later that same year, in October 2008, the Journal of Engineering Mechanics published a comment by chemical engineer and attorney James R. Gourley, in which he describes what he considered fundamental errors in a 2007 paper on the mechanics of progressive collapse by Bažant and Verdure. In the same issue, Bažant and Le rebutted Gourley's arguments, finding his criticisms scientifically incorrect. They suggested future critics should "become acquainted with the relevant material from an appropriate textbook on structural mechanics" or risk "misleading and wrongly influencing the public with incorrect information."

In April 2009, Danish chemist Niels H. Harrit, of the University of Copenhagen, and eight other authors published a paper in The Open Chemical Physics Journal, titled, "Active Thermitic Material Discovered in Dust from the 9/11 World Trade Center Catastrophe." The paper concludes that chips consisting of unreacted and partially reacted super-thermite, or nano-thermite, appear to be present in samples of the dust. The editor in chief of the publication subsequently resigned.

Internet websites and videos have contributed to the growth of the movement of individuals supporting the theory that planted explosives destroyed the World Trade Center. The website of Architects and Engineers for 9/11 Truth cites the membership of over 2,400 architects and engineers. The controlled demolition theory often includes allegations that U.S. government insiders planned and / or participated in the destruction of the WTC in order to justify the invasion of Iraq and Afghanistan. The theory features prominently in popular entertainment type movies, such as Loose Change, as well as documentaries such as 9/11: Blueprint for Truth, by San Francisco-area architect Richard Gage.

While mainstream press has a significant history of dismissing conspiracy theories (i.e., in 2006, the magazine New York reported that a "new generation of conspiracy theorists is at work on a secret history of New York's most terrible day."), the theory has been supported by a number of popular actors, musicians and politicians, including Charlie Sheen, Willie Nelson, former Governor of Minnesota Jesse Ventura, talkshow host Rosie O'Donnell, and actors Ed Asner and Daniel Sunjata.

Propositions and hypotheses

See also: List of buildings damaged or destroyed in the September 11 attacks

Main towers

On September 11, the North Tower (1 WTC) was hit by American Airlines Flight 11 and the South Tower (2 WTC) was hit by United Airlines Flight 175, both Boeing 767 aircraft. The South Tower collapsed 56 minutes after the impact, and the North Tower collapsed 102 minutes after. An investigation by NIST concluded that the collapse was caused by a combination of damage to support columns and fire insulation from the aircraft impacts and the weakening of columns and floors by jet fuel ignited fires. NIST also 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".

Jones, among others, points to many descriptions by individuals working on the WTC rubble pile suggesting the presence of molten steel in the pile and a stream of molten metal that poured out of the South Tower before it collapsed as evidence of temperatures beyond those produced by the fire. Jones has argued that the molten metal may have been elemental iron, a product of a thermite reaction. Jones and other researchers analyzed samples of dust from the World Trade Center buildings and reported their findings for evidence of nano-thermite in the dust. Jones informed NIST of his findings and NIST responded that there was no "clear chain of custody" proving that the dust indeed came from the WTC site. Jones invited NIST to conduct its own studies with dust under custody of NIST itself, but NIST has not done so.

NIST found that the condition of the steel in the wreckage of the towers does not provide conclusive information on the condition of the building before the collapse and concluded that the material coming from the South Tower was molten aluminum from the plane, which would have melted at lower temperatures than steel. NIST also pointed out that cutting through the vertical columns would require planting an enormous amount of explosives inconspicuously in highly secured buildings, then igniting it remotely while keeping it in contact with the columns. The Energetic Materials Research and Testing Center performed a test with conventional thermite and was unable to cut a vertical column, despite the column being much smaller than those used in the World Trade Center. Jones and others have responded that they do not believe that thermite was used, but rather a form of thermite called nano-thermite, a nanoenergetic material developed for military use, propellants, explosives, or pyrotechnics. Historically, explosive applications for traditional thermites have been limited by their relatively slow energy release rates. But because nano-thermites are created from reactant particles with proximities approaching the atomic scale, energy release rates are far improved.

The NIST report provides an analysis of the structural response of the building only up to the point where collapse begins, and asserts that the enormous kinetic energy transferred by the falling part of the building makes progressive collapse inevitable once an initial collapse occurs. A paper by Zdeněk Bažant indicates that once collapse began, the kinetic energy imparted by a falling upper section onto the floor below was an order of magnitude greater than that which the lower section could support.

Engineers who have investigated the collapses generally agree that controlled demolition is not required to understand the structural response of the buildings. While the top of one of the towers did tilt significantly, it could not ultimately have fallen into the street, they argue, because any such tilting would place sufficient stress on the lower story (acting as a pivot) that it would collapse long before the top had sufficiently shifted its center of gravity. Indeed, they argue, there is very little difference between progressive collapse with or without explosives in terms of the resistance that the structures could provide after collapse began. Controlled demolition of a building to code requires weeks of preparation, including laying large quantities of explosive and cutting through beams, which would have rendered the building highly dangerous and which would have to be done without attracting the attention of the thousands of people who worked in the building. Controlled demolition is traditionally done from the bottom of buildings rather than the top, although there are exceptions depending on structural design. There is little dispute that the collapse started high up at the point where the aircraft struck. Furthermore, any explosives would have to withstand the impact of the airliners.

Members of the group Scholars for 9/11 Truth have collected eyewitness accounts of flashes and loud explosions immediately before the fall. Eyewitnesses have repeatedly reported of explosions happening before the collapse of the WTC towers, and the organization "International Center for 9/11 Studies" has published videos obtained from NIST, together with indications about when such explosions could be heard. There are many types of loud sharp noises that are not caused by explosives, and seismographic records of the collapse do not show evidence of explosions. Jones and others have argued that horizontal puffs of smoke seen during the collapse of the towers would indicate that the towers had been brought down by controlled explosions. NIST attributes these puffs to air pressure, created by the decreasing volume of the falling building above, traveling down elevator shafts and exiting from the open elevator shaft doors on lower levels.

In September 2011, Iranian president Mahmoud Ahmadinejad, who holds a PhD in Transportation Engineering and Planning, said that it would have been impossible for two jetliners to bring down the towers simply by hitting them and that some kind of planned explosion must have taken place. Al-Qaida sharply criticized Ahmadinejad in their English-language publication, Inspire, calling his assertions "a ridiculous belief that stands in the face of all logic and evidence".

7 World Trade Center

The position of 7 WTC in relation to the other WTC buildings. WTC 1, 2 and 7 collapsed on September 11, 2001.

Proponents of World Trade Center controlled demolition theories allege that 7 World Trade Center—a 47-story skyscraper that stood across Vesey Street north of the main part of the World Trade Center site—was intentionally destroyed with explosives. Unlike the Twin Towers, 7 World Trade Center was not hit by a plane, although it was hit by debris from the Twin Towers and was damaged by fires which burned for seven hours, until it collapsed completely at about 5:20 p.m. on the evening of September 11 (a new building has been erected on the site of the old and opened in May 2006). Several videos of the collapse event exist in the public domain, thus enabling comparative analysis from different angles of perspective. Proponents typically say the collapse of 7 World Trade Center was not mentioned in the 9/11 Commission Report and that the federal body charged with investigating the event, NIST, required seven years to conduct its investigation and issue a report.

In November 2010, Fox News reporter Geraldo Rivera hosted members of a television ad campaign called "BuildingWhat?", a series of commercials in which 9/11 family members ask questions about 7 World Trade Center and call for an investigation into its collapse. Rivera called the television ads "not so easy to dismiss as those demonstrators were," and stated that, "If explosives were involved, that would mean the most obnoxious protesters in recent years ... were right." Days later, Rivera appeared on the program Freedom Watch with legal analyst Judge Andrew Napolitano on the Fox Business Network to discuss the BuildingWhat? TV ad campaign. Napolitano stated, "It's hard for me to believe that came down by itself. I was gratified to see Geraldo Rivera investigating it."

Some proponents of World Trade Center controlled demolition theories suggest that 7 WTC was demolished because it may have served as an operational center for the demolition of the Twin Towers, while others suggest that government insiders may have wanted to destroy key files held in the building pertaining to corporate fraud. The WTC buildings housed dozens of federal, state and local government agencies. According to a statement reported by the BBC, Loose Change film producer Dylan Avery thinks the destruction of the building was suspicious because it housed some unusual tenants, including a clandestine CIA office on the 25th floor, an outpost of the U.S. Secret Service, the Securities and Exchange Commission, and New York City's emergency command center. The former chief counter-terrorism adviser to the President, Richard Clarke, does not think that 7 WTC is mysterious, and said that anyone could have rented floor space in the building.

At the time, no steel frame high rise had ever before collapsed because of a fire, although there had been previous cases of collapses or partial collapses of smaller steel buildings due to fire. However, the ability of such a building to be completely destroyed by fire would be demonstrated by the collapse of the Plasco Building in Tehran in 2017 and the Wilton Paes de Almeida Building in São Paulo, Brazil, the following year. In addition, NIST claims debris ejected during the collapse of 1 WTC caused significant structural damage in 7 WTC before the fire.

BBC News reported the collapse of 7 WTC twenty minutes before it actually fell. The BBC has stated that many news sources were reporting the imminent collapse of 7 WTC on the day of the attacks. Jane Standley, the reporter who announced the collapse prematurely, called it a "very small and very honest mistake" caused by her thinking on her feet after being confronted with a report she had no way of checking.

In the PBS documentary America Rebuilds, which aired in September 2002, Larry Silverstein, the owner of 7 WTC and leaseholder and insurance policy holder for the remainder of the WTC complex, recalled a discussion with the fire department in which doubts about containing the fires were expressed. Silverstein recalled saying, "We've had such terrible loss of life, maybe the smartest thing to do is pull it". "They made that decision to pull", he recalled, "and we watched the building collapse." Silverstein issued a statement that it was the firefighting team, not the building, that was to be pulled, contradicting theorists' allegation that "pull" was used in a demolition-related sense.

NIST report

In 2002, the National Institute of Standards and Technology (NIST) began a general investigation into the collapse of the World Trade Center but soon made a decision to focus first on the collapse of the Twin Towers. A draft version of its final report on the collapse of 7 WTC was released in August 2008. The agency has blamed the slowness of this investigation on the complexity of the computer model it used, which simulated the collapse from the moment it begins all the way to the ground; and NIST says the time taken on the investigation into 7 WTC is comparable to the time taken to investigate an aircraft crash. The agency also says another 80 boxes of documents related to 7 WTC were found and had to be analyzed. These delays fueled suspicion among those already questioning the validity of the September 11 attacks that the agency was struggling to come up with a plausible conclusion.

NIST released its final report on the collapse of 7 World Trade Center on November 20, 2008. Investigators used videos, photographs and building design documents to come to their conclusions. The investigation could not include physical evidence as the materials from the building lacked characteristics allowing them to be positively identified and were therefore disposed of prior to the initiation of the investigation. The report concluded that the building's collapse was due to the effects of the fires which burned for almost seven hours. The fatal blow to the building came when the 13th floor collapsed, weakening a critical steel support column that led to catastrophic failure, and extreme heat caused some steel beams to lose strength, causing further failures throughout the buildings until the entire structure succumbed. Also cited as a factor was the collapse of the nearby towers, which broke the city water main, leaving the sprinkler system in the bottom half of the building without water.

NIST considered the possibility that 7 WTC was brought down with explosives and concluded that a blast event did not occur, that the "use of thermite to sever columns in 7 WTC on 9/11/01 was unlikely". The investigation cited as evidence the claim that no blast was audible on recordings of the collapse and that no blast was reported by witnesses, stating that it would have been audible at a level of 130-140 decibels at a distance of half a mile. Demolition proponents say eyewitnesses repeatedly reported explosions happening before the collapse of the towers, and have published videos obtained from NIST, together with indications about when such explosions could be heard in support of the sounds of explosions before collapse.

NIST also concluded that it is unlikely that the quantities of thermite needed could have been carried into the building undetected. Demolition advocates have responded that they do not claim that thermite was used, but rather that nano-thermite, far more powerful than thermite, was used. Finally, the NIST investigated and ruled out the theory that fires from the large amount of diesel fuel stored in the building caused the collapse.

UAF study

University of Alaska Fairbanks (UAF) Professor of Civil Engineering J. Leroy Hulsey subsequently led a 4-year (2015–2019) investigation funded by Architects and Engineers for 9/11 Truth titled "A Structural Reevaluation of the Collapse of World Trade Center 7", taking advantage of the improvement in computing resources since NIST's study. The UAF provides a 256 GB downloadable file that contains "All input data, results data, and simulations that were used or generated during this study." Hulsey's group concluded in their final report:

The principal conclusion of our study is that fire did not cause the collapse of WTC 7 on 9/11, contrary to the conclusions of NIST and private engineering firms that studied the collapse. The secondary conclusion of our study is that the collapse of WTC 7 was a global failure involving the near-simultaneous failure of every column in the building.

— Hulsey JL, Quan Z, Xiao F, University of Alaska Fairbanks

Criticism

The American Society of Civil Engineers Structural Engineering Institute issued a statement calling for further discussion of NIST's recommendations, and Britain's Institution of Structural Engineers published a statement in May 2002 welcoming the FEMA report, noting that the report expressed similar views to those held by its group of professionals.

Following the publication of Jones' paper "Why Indeed Did the WTC Buildings Completely Collapse?" Brigham Young University responded to Jones' "increasingly speculative and accusatory" statements by placing him on paid leave, and thereby stripping him of two classes, in September 2006, pending a review of his statements and research. Six weeks later, Jones retired from the university. The structural engineering faculty at the university issued a statement which said that they "do not support the hypotheses of Professor Jones". On September 22, 2005, Jones gave a seminar on his hypotheses to a group of his colleagues from the Department of Physics and Astronomy at BYU. According to Jones, all but one of his colleagues agreed after the seminar that an investigation was in order and the lone dissenter came to agreement with Jones' suggestions the next day.

Northwestern University Professor of Civil Engineering Zdeněk Bažant, who was the first to offer a published peer-reviewed theory of the collapses, wrote "a few outsiders claiming a conspiracy with planted explosives" as an exception. Bažant and Verdure trace such "strange ideas" to a "mistaken impression" that safety margins in design would make the collapses impossible. One of the effects of a more detailed modeling of the progressive collapse, they say, could be to "dispel the myth of planted explosives". Indeed, Bažant and Verdure have proposed examining data from controlled demolitions in order to better model the progressive collapse of the towers, suggesting that progressive collapse and controlled demolition are not two separate modes of failure (as the controlled-demolition conspiracy theory assumes).

Thomas Eagar, a professor of materials science and engineering at the Massachusetts Institute of Technology, also dismissed the controlled-demolition conspiracy theory. Eagar remarked, "These people (in the 9/11 truth movement) use the 'reverse scientific method.' They determine what happened, throw out all the data that doesn't fit their conclusion, and then hail their findings as the only possible conclusion."

Regarding Jones' theory that nanothermite was used to bring down the towers, and the assertion that thermite and nanothermite composites were found in the dust and debris were found following the collapse of the three buildings, which was considered to be evidence that explosives brought down the buildings, Brent Blanchard, author of "A History of Explosive Demolition in America", states that questions about the viability of Jones' theories remain unanswered, such as the fact that no demolition personnel noticed any telltale signs of thermite during the eight months of debris removal following the towers' collapse. Blanchard also stated that a verifiable chain of possession needs to be established for the tested beams, which did not occur with the beams Jones tested, raising questions of whether the metal pieces tested could have been cut away from the debris pile with acetylene torches, shears, or other potentially contaminated equipment while on site, or exposed to trace amounts of thermite or other compounds while being handled, while in storage, or while being transferred from Ground Zero to memorial sites. Dave Thomas of Skeptical Inquirer magazine, noting that the residue in question was claimed to be thermitic because of its iron oxide and aluminum composition, pointed out that these substances are found in many items common to the towers. Thomas stated that in order to cut through a vertical steel beam, special high-temperature containment must be added to prevent the molten iron from dropping down, and that the thermite reaction is too slow for it to be practically used in building demolition. Thomas pointed out that when Jesse Ventura hired New Mexico Tech to conduct a demonstration showing nanothermite slicing through a large steel beam, the nanothermite produced copious flame and smoke but no damage to the beam, even though it was in a horizontal, and therefore optimal, position.

Preparing a building for a controlled demolition takes considerable time and effort. The tower walls would have had to be opened on dozens of floors. Thousands of pounds of explosives, fuses and ignition mechanisms would need to be sneaked past security and placed in the towers without the tens of thousands of people working in the World Trade Center noticing. Referring to a conversation with Stuart Vyse, a professor of psychology, an article in the Hartford Advocate asks, "How many hundreds of people would you need to acquire the explosives, plant them in the buildings, arrange for the airplanes to crash  and, perhaps most implausibly of all, never breathe a single word of this conspiracy?"

World Trade Center developer Larry Silverstein said, "Hopefully this thorough report puts to rest the various 9/11 conspiracy theories, which dishonor the men and women who lost their lives on that terrible day." Upon presentation of the NIST's detailed report on the failure of Bldg. 7, Richard Gage, leader of the group Architects & Engineers for 9/11 Truth said, "How much longer do we have to endure the coverup of how Building 7 was destroyed?" in which Dr. S. Shyam Sunder, the lead NIST investigator said he could not explain why the skepticism would not die. "I am really not a psychologist," he said. "Our job was to come up with the best science." James Quintiere, professor of fire protection engineering at the University of Maryland, who does not believe explosives brought down the towers, questioned how the agency came to its conclusions, remarking, "They don't have the expertise on explosives," though he adds that NIST wasted time employing outside experts to consider it.

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