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{{Short description|9/11 conspiracy theories}}
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]
{{Use mdy dates|date=October 2013}}
{{See also|9/11 conspiracy theories}}
] can be seen left of WTC 7's ruins.]]
The '''World Trade Center controlled demolition conspiracy theory''' is the hypothesis that the ] was not caused by the plane crash damage that occurred as part of the ], nor by resulting fire damage, but by explosives 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> The ] was first suggested in late 2001. Though central to 9/11 conspiracy theorists,<ref name="Feuer">{{cite news|journal=New York Times|last=Feuer|first=Alan|date=June 5, 2006|title=500 Conspiracy Buffs Meet to Seek the Truth of 9/11|accessdate=May 5, 2009|url=http://www.nytimes.com/2006/06/05/us/05conspiracy.html}}</ref> it is rejected by the mainstream media and the mainstream engineering community.


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 ].
Demolition theory proponents, such as physicist ], architect ], software engineer ], and theologian ], argue that the aircraft impacts and resulting fires could not have weakened the buildings sufficiently to initiate a catastrophic collapse, and that the buildings would not have collapsed completely, nor at the speeds that they did, without additional energy involved to weaken their structures. Jones has presented the hypothesis that ] or ] was used to demolish the buildings.<ref name="NYTCountersTheories">{{cite news|journal=New York Times|author=Jim Dwyer|title=2 U.S. Reports Seek to Counter Conspiracy Theories About 9/11|date=September 2, 2006|url=http://www.nytimes.com/2006/09/02/nyregion/02conspiracy.html|accessdate=April 30, 2009}}</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|accessdate=May 7, 2009}}</ref><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|accessdate=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|accessdate=May 28, 2009|title=Great Day Talks To Architect Richard Gage About 9/11|publisher=KMPH Fox 26}}</ref>


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>
Many mainstream scientists refuse to debate conspiracy theorists to avoid giving them unwarranted credibility.<ref>{{cite web |url=http://209.85.135.132/search?q=cache:U8bhYz1aoksJ:www.cbsnews.com/stories/2006/08/06/ap/national/mainD8JB6LTG0.shtml+%229/11+Conspiracy+Theorists+Thriving%22+site:cbsnews.com&cd=1&hl=en&ct=clnk |title=9/11 Conspiracy Theorists Thriving| work = CBS News | date=2006-08-06 |accessdate=July 12, 2009}}</ref> The ] (NIST) has rejected the theory. Specialists in structural mechanics and structural engineering generally 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|

last=Bažant|
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.
first=Zdeněk P.|

coauthors=Mathieu Verdure|
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
authorlink=Zdeněk Bažant|
title=Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions| |title=Active Thermitic Material Discovered in Dust from the 9/11 World Trade Center Catastrophe
|journal=The Open Chemical Physics Journal
year=2007|
|date=April 3, 2009
month=March|
|first1=Niels H.
journal=J Engrg Mech|
|last1=Harrit
volume=133|
|author2=Jeffrey Farrer
issue=3|
|author3=Steven E. Jones
pages=308–319|
|author4=Kevin R. Ryan
doi=10.1061/(ASCE)0733-9399(2007)133:3(308)|
|author5=Frank M. Legge
url=http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/466.pdf|
|author6=Daniel Farnsworth
accessdate=2007-08-22|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 }}</ref><ref name="Chronicle" /><ref>{{cite journal|last=Asquith|first=Christina|date=2006-09-07|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|pages=12|url=http://findarticles.com/p/articles/mi_m0WMX/is_15_23/ai_n27000635/pg_1?tag=artBody;col1|accessdate=2008-10-09}}</ref>
|author7=Gregg Roberts
|author8=James R. Gourley
|author9=Bradley R. Larsen
|name-list-style=amp
|volume=2
|issue=1
|pages=7–31
|doi=10.2174/1874412500902010007
|bibcode=2009OCPJ....2....7H
|doi-access=free
}}</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" />


==History== ==History==
Controlled demolition conspiracy theories were first suggested in October 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 two most prominent advocates of the theory.<ref name="Clarke"/> Griffin's book<ref>{{cite news|last=Reid|first=Sue|title=An explosion of disbelief — fresh doubts over 9/11|journal=Daily Mail|date=February 9, 2007|url=http://www.dailymail.co.uk/news/article-435265/An-explosion-disbelief--fresh-doubts-9-11.html|accessdate=May 14, 2009}}</ref> '']'', published in 2004,<ref name="Powell">{{cite news|last=Powell|first=Michael|journal=The Washington Post|date=September 8, 2006|title=The Disbelievers|url=http://www.washingtonpost.com/wp-dyn/content/article/2006/09/07/AR2006090701669_pf.html|accessdate=May 30, 2009|quote=The loose agglomeration known as the ‘9/11 Truth Movement’|accessdate=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|accessdate=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 ] amount to a cover-up by government officials and says that the Bush administration was complicit in the 9/11 attacks.<ref>{{cite web|publisher=Book TV on C-SPAN2. Top Nonfiction Authors Every Weekend|title=The 9/11 Commission Report: Omissions and Distortions|date=July 3, 2005|url=http://www.booktv.org/program.aspx?ProgramId=5677&SectionName=|accessdate=May 15, 2009}}</ref> 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>


Steven E. Jones has become the leading academic voice of the proponents of the theories.<ref>{{cite web|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|accessdate=May 23, 2009}}</ref> In 2006, he published the paper "Why Indeed Did the WTC Buildings Completely Collapse?".<ref name="NYTCountersTheories"/> ] responded to Jones's "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<!--Just in case anyone thinks of reintroducing the word "resigned" here: This would be a factually incorrect description of the ongoing relationship of BYU and Prof. Jones, see Jones's website at BYU.--> from the university.<ref>{{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|accessdate=2009-01-04}} {{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=September 11, 2006|accessdate=April 26, 2009}} {{cite web|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|accessdate=May 15, 2009}} {{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|title=BYU professor in dispute over 9/11 will retire|accessdate=May 15, 2009}} {{cite web|title=Steven E. Jones. Retired Professor|publisher=Brigham Young University |url=http://www.physics.byu.edu/research/energy/|accessdate=May 6, 2009}}</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>{{cite news|url=http://newsnet.byu.edu/story.cfm/57724|title=Censor rumors quelled|last=McIlvain|first=Ryan|date=2005-12-05|publisher=BYU NewsNet|accessdate=2009-08-25}}</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 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>
David Ray Griffin has questioned the "pancake collapse" theory suggested in the ] produced by the ] (FEMA).<ref>{{cite news|last=Griffin|first=David Ray|date=September 10, 2006|journal=CBC News|url=http://www.cbc.ca/sunday/2006/09/091006_15.html|title=David Ray Griffin interview|accessdate=May 4, 2009}}</ref> NIST's ] rejected the theory in favor of the column failure theory.<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> 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 September 11, 2001"<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 | title = Consideration of Public Comments | work = NIST Response to the World Trade Center Disaster | publisher = National Institute of Standards and Technology | accessdate =}}</ref> and posted a ] about related issues to its website in August 2006.<ref name="nistfaq" /> The major elements of the theory have been rebutted in mainstream engineering scholarship,<ref name="bazant07a">{{cite paper |last=Bažant |first=Zdeněk P. |authorlink=Zdeněk Bažant |coauthor=Jia-Liang Le, Frank R. Greening, David B. Benson |title=Collapse of World Trade Center Towers: What Did and Did Not Cause It? |version=2007-06-22 |publisher=Department of Civil and Environmental Engineering, Northwestern University, Evanston, Illinois 60208, USA |date=2007-05-27 |url=http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/00%20WTC%20Collapse%20-%20What%20Did%20&%20Did%20Not%20Cause%20It.pdf |id=Structural Engineering Report No. 07-05/C605c |accessdate=2007-09-17}}</ref> where its proponents are considered "outsiders".<ref name="bazant07"/> The journal '']'' challenged the theories in the special report "Debunking the 9/11 Myths".<ref name="Potocki">{{cite news|last=Potocki|first=P. Joseph|journal=Bohemian|title=Down the 9-11 Rabbit Hole|date=August 27, 2008|url=http://www.bohemian.com/bohemian/08.27.08/cover-911.truth-0835.html|accessdate=May 25, 2009}}</ref>


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}}
The internet and homemade videos have contributed to the growth of the movement associated with the conspiracy theory that explosives had been planted in the three buildings of the World Trade Center, and the theory is often associated with allegation that the U.S. government had planned the destruction of the WTC in order to justify the invasion of Iraq and Afghanistan.<ref name="NYT-Lipton-2008">{{cite news|author=Eric Lipton|journal=New York Times|date=August 22, 2008|title=Fire, Not Explosives, Felled 3rd Tower on 9/11, Report Says|url=http://www.nytimes.com/2008/08/22/nyregion/22wtccnd.html}}</ref> The theory features prominently in the movies '']''<ref>{{cite news|last=Pilkington|first=Ed|journal=The Guardian|date=January 26, 2007|title='They're all forced to listen to us'|url=http://www.guardian.co.uk/media/2007/jan/26/digitalmedia|accessdate=May 6, 2009}}</ref>. The two-hour movie ''9/11: Blueprint for Truth'', which is popular in the 9/11 Truth movement, is based on a presentation 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=http://www.boston.com/news/local/articles/2007/11/29/airing_of_911_film_ignites_debate|accessdate=May 23, 2009}}</ref> a leading proponent of the theories.{{Citation needed|date=August 2009}}
</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 }}
</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."
</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."
</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 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 | year = 2006 | month = March | accessdate = | url = http://nymag.com/news/features/16464/index6.html}}</ref> The theory has been cited by popular actors, musicians and politicians, including ],<ref>{{cite web|url=http://transcripts.cnn.com/TRANSCRIPTS/0603/22/sbt.01.html |title=CNN.com - Transcripts |publisher=Transcripts.cnn.com |date= |accessdate=2008-10-30}}</ref><ref>{{Cite news | title = Charlie Sheen doesn't buy 9/11 spin | work = The Boston Herald | accessdate = 2009-04-25 | date = 2006-03-23 }}</ref> ],<ref></ref> former Governor of Minnesota, ],<ref>. Retrieved on April 8, 2008.</ref> and talkshow host ].<ref>{{cite news|last=Dwyer|first=Jim|title=A Notion From 9/11 Is Kept Alive|date=May 30, 2007|journal=New York Times|url=http://select.nytimes.com/2007/05/30/nyregion/30about.html|accessdate=May 17, 2009}}</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>
A 2006 poll found that 6 percent of Americans considered it "very likely" that "the collapse of the twin towers in New York was aided by explosives secretly planted in the two buildings", another 10% found it "somewhat likely", and 77% found the demolition theory "unlikely".<ref>{{cite web|publisher=Scripps Survey Research Center|date=July 6, 2006|title=Question VAR 29|url=http://web.archive.org/web/20080108130106/www.newspolls.org/question.php?question_id=718|accessdate=May 16, 2009}}</ref><ref>{{cite journal|
last=Hargrove|
first=Thomas|
coauthors=Guido H. Stempel III|
title=Anti-government anger spurs 9/11 conspiracy belief|date=2006-08-02|
journal=Scripps Howard News Service|
url=http://www.newspolls.org/story.php?story_id=55|
accessdate=2007-03-09}}</ref><ref>{{cite news|last=Aaronovitch|first=David|journal=The Times|title=9/11 conspiracy theories: The truth is out there...just not on the internet|date=April 29, 2009|url=http://women.timesonline.co.uk/tol/life_and_style/women/the_way_we_live/article6187493.ece}}</ref>


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 ].
==Main towers==


==Propositions and hypotheses==
]
{{See also|List of buildings damaged or destroyed in the September 11 attacks}}
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 minutes after the impact, and the North Tower collapsed 102 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|accessdate=2009-04-28}}</ref> 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 ] 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|accessdate=2009-05-03}}</ref>


===Main towers===
Steven Jones has claimed that anecdotal evidence<ref name="bazant07a" /> of molten steel found in the rubble of the collapse<ref name="NYTCountersTheories" /><ref>{{cite web|url=http://www.bentham-open.org/pages/gen.php?file=7TOCPJ.pdf|title=Active Thermitic Material Discovered in Dust|month=August | year=2008|work=Active Thermitic Material Discovered in Dust from the 9/11 World Trade Center Catastrophe|publisher=The Open Chemical Physics Journal|accessdate=2009-08-25}}</ref> and a stream of molten metal that poured out of the South Tower before it collapsed<ref name="Chronicle" /> are evidence of temperatures beyond those produced by the fire (which was not expected to be hot enough to melt steel). Jones has argued that the molten metal may have been ], a product of a thermite reaction. 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" /> A test performed by the ] showed that conventional thermite was unable to melt a column much smaller than those used in the World Trade Center.<ref>{{cite web|url=http://channel.nationalgeographic.com/episode/9-11-science-and-conspiracy-4067/conspiracy-vs-science|title=9/11: Science and Conspiracy|publisher=]|accessdate=2009-09-16}}</ref>
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>
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 "progressive collapse" 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 at least ten times greater than that which the lower section could support.<ref name="bazant07"/>


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>
Engineers who have investigated the collapses generally disagree that controlled demolition is 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=http://www.pbs.org/wgbh/nova/wtc/collapse.html |title=NOVA &#124; Building on Ground Zero &#124; PBS |publisher=Pbs.org |date= |accessdate=2008-10-30}}</ref> Controlled demolition of a building 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>{{cite web|url=http://www.civil.usyd.edu.au/wtc.shtml|title=World Trade Center - Some Engineering Aspects|last=Wilkinson|first=Tim|date=2006-01-14|publisher=University of Sydney School of Civil Engineering|accessdate=2008-09-07}}</ref> Controlled demolition is done from the bottom of buildings, not the top. 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" />


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"/>
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=http://www.telegraph.co.uk/news/newstopics/howaboutthat/3483477/The-30-greatest-conspiracy-theories-part-1.html|accessdate=May 30, 2009|quote=Many witnesses - including firemen, policemen and people who were inside the towers at the time - claim to have heard explosions below the aircraft impacts (including in basement levels) and before both the collapses and the attacks themselves.}}</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=http://www.guardian.co.uk/education/2006/sep/05/internationaleducationnews.highereducation|accessdate=May 6, 2009}}</ref> There are many causes 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|accessdate=2008-09-28}}</ref> and ] records of the collapse do not show evidence of explosions.<ref>{{cite web|url=http://www.popularmechanics.com/technology/military_law/1227842.html?page=5|title=Seismic Spikes|month=March | year=2005|work=Debunking the 9/11 Myths: Special Report|publisher=Popular Mechanics|accessdate=2008-09-28}}</ref> Puffs of dust and debris which were ejected from the towers as they collapsed have been taken as evidence that explosives were used.<ref name="Grossman">{{cite news|last=Grossman|first=Lev|journal=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}}<br>• the 9/11 Truth Movement, as many conspiracy believers refer to their passion</ref><ref>{{cite journal|url=http://www.popularmechanics.com/technology/military_law/1227842.html?page=4#puffs|date=March 2005|title=Debunking the 9/11 Myths: Special Report - Puffs Of Dust|publisher=Popular Mechanics}}</ref> NIST attributes these puffs to pressure exerted by the falling mass of the building.<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 |last=Gross|first=John L.|coauthors=McAllister, Therese P.|date=September 2005|publisher=NIST|pages=320|accessdate=2009-03-21}}</ref>


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" />
== 7 World Trade Center ==


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>
]
]
] was a 47-story skyscraper that stood across Vesey Street north of the main part of the ]. Though not hit by a plane, it was hit by debris from the WTC towers and damaged by fires which burned for seven hours, until it collapsed about 5:20 p.m. on the evening of September 11. Several videos of the event exist in the public domain thus enabling comparative analysis from different angles of perspective.


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>
Some proponents of World Trade Center controlled demolition conspiracy theories suggest that 7 WTC was demolished because it served as an operational center for the alleged conspiracy, while others believe the government also wanted to destroy key files held there about corporate fraud. According to a statement reported by the ], ] thinks the building was suspicious because it had some unusual tenants such as a CIA field office and several government agencies. 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" />


===7 World Trade Center===
No ] high rise had ever before collapsed because of a fire.<ref>FEMA. ''World Trade Center Building Performance Study'', p. 4.</ref> BBC News reported the collapse of 7&nbsp;WTC twenty minutes before it actually fell. 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. .</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>
]
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>
Steven Jones says the debris contained ]ic compounds, suggesting that ], a mixture of thermitic materials and sulfur, might have been used to destroy the building.<ref>{{Cite web | url = http://www.cbsnews.com/stories/2006/08/06/ap/national/mainD8JB6LTG0.shtml | last = Pope | first = Justin | title = 9/11 Conspiracy Theorists Thriving | work = Associated Press Online | accessdate = 2009-04-25 | date = 2006-08-07 }}</ref><ref>{{Cite web | url=http://www.deseretnews.com/article/1,5143,645200098,00.html | last = Walch | first = Tad | title = Controversy dogs Y.'s Jones | work = Deseret Morning News (Salt Lake City) | accessdate = 2009-04-25 | date = 2006-09-09 }}</ref> He asserts that videos show a yellow molten substance, which he identifies as iron, splashing off the side of the South Tower about 50 minutes after the airplane's impact. According to Jones, pictures also show white ash of aluminium-oxide, another product of the thermite reaction.<ref name="Deseret-Dean-2006" /> Professor Richard Sisson of ] thinks the sulfur came from ] in the wallboards.<ref name="BBCFAQ">{{cite web|title=Q&amp;A: The Collapse of Tower 7|publisher=BBC|url=http://news.bbc.co.uk/1/hi/programmes/conspiracy_files/7434230.stm|accessdate=2008-07-05}}</ref> The NIST's question and answer page for the 7 WTC investigation also mentions the presence of sulphur in the gypsum wallboard, and states that an analysis of the steel for thermite or thermate would therefore not necessarily be conclusive.<ref name="7FAQ"/>


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>
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.<ref name="BBCFAQ" /><ref>{{cite web |url=http://web.archive.org/web/20080214143807/http://usinfo.state.gov/media/Archive/2005/Sep/16-241966.html|title=Identifying Misinformation: 9/11 Revealed? |accessdate=2009-04-30|date=2005-09-16 |publisher=usinfo.state.gov (as recorded by www.archive.org)}}</ref><ref name="FTpt3" />


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>
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"/> 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 notes that 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 notes another 80 boxes of documents related to 7&nbsp;WTC were found and had to be analyzed. These delays fueled suspicion 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=2008-06-07|publisher=Financial Times|pages=14|accessdate=2008-08-22}}</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>
Following a three year investigation NIST released its final report on the collapse 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|accessdate=2009-04-25}}</ref> Investigators used videos, photographs and building design documents to come to their conclusions. The report concluded that the building collapsed 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.


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" />
NIST considered the possibility that 7&nbsp;WTC was brought down with explosives. It concluded that a blast event did not occur and that the "use of thermite to sever columns in 7&nbsp;WTC on 9/11/01 was unlikely".<ref>{{cite web|url = http://www.nist.gov/public_affairs/factsheet/wtc_qa_082108.html|publisher=NIST|title=Questions and Answers about the NIST 7&nbsp;WTC Investigation (Updated 04/21/2009)|accessdate=2009-04-29}}</ref> The investigation noted that no blast was audible on recordings of the collapse and that no blast was reported by witnesses, even though it would have been audible at a level of at least 130-140 decibels at a distance of half a mile. NIST also concluded that it is unlikely that the quantities of thermite needed could have been carried into the building undetected. The theory that fires from the large amount of diesel fuel stored in the building caused the collapse was also investigated and ruled out.<ref name="7FAQ">{{cite web|url=http://www.nist.gov/public_affairs/factsheet/wtc_qa_082108.html|title=Questions and Answers about the NIST 7&nbsp;WTC Investigation|date=2008-08-21|publisher=NIST|accessdate=2008-08-21}}</ref>


====NIST report====
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." Richard Gage, leader of the group '']'' said, "How much longer do we have to endure the coverup of how Building 7 was destroyed?".<ref name="NYT-Lipton-2008"/> 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." Quintiere said NIST wasted time employing outside experts to consider it.<ref>{{cite web | url=http://www.guardian.co.uk/world/2008/aug/22/september11.usa | title=World Trade Centre building seven not destroyed by explosives, says US study |accessdate=2009-04-24}}</ref>
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>


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.
==Reaction of the engineering community==


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}}
The controlled demolition theory has been dismissed in the structural engineering literature.<ref name="bazant07"/><ref>]</ref>{{page needed}} ] 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>http://chronicle.com/free/v52/i42/42a01001.htm</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"/>


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" />
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| work = |publisher = The Chronicle of Higher Education | accessdate =2007-01-24 |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|accessdate = 2006-09-09}}</ref>


==External links== ====UAF study====
] (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}}
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==Criticism==
;United States government sources
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>
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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"/>
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;Engineering publications
] 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"/>
*{{cite web

| author =Banovic, S.W., ''et al''
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>
| title =The Role of Metallurgy in the NIST Investigation of the World Trade Center Towers Collapse

| work =
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>
| url =http://www.tms.org/pubs/journals/JOM/0711/banovic-0711.html

}}
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>
*{{cite web

| last =Eagar
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"/>
| first =Thomas
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>
| title =Why Did the World Trade Center Collapse? Science, Engineering, and Speculation
| work =
| url =http://www.tms.org/pubs/journals/JOM/0112/Eagar/Eagar-0112.html
}}
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;Proponents of controlled demolition conspiracy theories
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;Debunkers of controlled demolition conspiracy theories
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==References== ==References==
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==External links==
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Latest revision as of 21:58, 27 November 2024

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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