Controlled demolition hypothesis for the collapse of the World Trade Center

The controlled demolition hypothesis is a 9/11 conspiracy theory that claims the complete structural failure of the World Trade Center towers was not caused by the plane crash damage that occurred as part of the September 11, 2001 attacks, nor by the fire damage that followed, but by explosives or other devices planted in the buildings in advance.Clarke, Steve. "Conspiracy Theories and the Internet: Controlled Demolition and Arrested Development". "Episteme", Volume 4, Issue 2, 2007, pp. 167-180.] It was first suggested in late 2001 and has since become increasingly important to the 9/11 Truth Movement, but is rejected by the mainstream media and engineering community.

The most detailed statements of the hypothesis have come from physicist Steven Jones, architect Richard Gage, software engineer Jim Hoffman, theologian David Ray Griffin, and author Webster Griffin Tarpley. Proponents argue that the aircraft impacts and resulting fires could not have weakened the buildings sufficiently to initiate collapse and that the buildings would in any case not have collapsed as completely, and quickly as they did without an additional source of destructive energy to undermine their structure. Various sources of this energy have been proposed; the use of thermite, explosives, or some combination thereof is the most common suggestion being made today.cite journal
last=Jones|first=Steven E.|authorlink=Steven E. Jones|date=2006-09
title=Why Indeed Did the World Trade Center Buildings Completely Collapse
journal=Journal of 9/11 Studies
volume=3
url=http://www.journalof911studies.com/volume/200609/Why_Indeed_Did_the_WTC_Buildings_Completely_Collapse_Jones_Thermite_World_Trade_Center.pdf
accessdate=2008-04-11|format=PDF] [cite news|url=http://www.cbsnews.com/stories/2006/08/06/ap/national/mainD8JB6LTG0.shtml |title=9/11 Conspiracy Theorists Thriving| work = CBS News | date=2006-08-06 |accessdate=2008-03-09] cite journal
author=Kevin R. Ryan, James R. Gourley, Steven E. Jones|date=2008-08
title=Environmental anomalies at the World Trade Center: evidence for energetic materials
journal= [http://www.springer.com/environment/nature+conservation+-+biodiversity/journal/10669 The Environmentalist]
volume= [http://www.springerlink.com/content/100165/?Content+Status=Accepted Online First]
url=http://www.springerlink.com/content/f67q6272583h86n4/
accessdate=2008-08-08] The National Institute of Standards and Technology (NIST), an agency of the United States Department of Commerce, has rejected the hypothesis that collapse due to fire would be impossible, as has the engineering community.cite journal
last=Bažant
first=Zdeněk P.
coauthors=Mathieu Verdure
authorlink=Zdeněk Bažant
title=Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions
year=2007
month=March
journal=J Engrg Mech
volume=133
issue=3
pages=pp. 308–319
doi=10.1061/(ASCE)0733-9399(2007)133:3(308)
url=http://www.civil.northwestern.edu/people/bazant/PDFs/Papers/466.pdf
accessdate=2007-08-22
format=PDF] [cite news|url=http://chronicle.com/free/v52/i42/42a01001.htm|title=Professors of Paranoia?|last=Gravois|first=John|date=2006-06-23|publisher=The Chronicle of Higher Education|accessdate=2008-10-09] [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] Members of the 9/11 Truth movement have filed Requests for Correction to the NIST report, [ cite web |url=http://stj911.org/actions/NIST_DQA_Petition.pdf |title=Scholars and Family Members Submit Request for Correction to 9/11 NIST Report |accessdate=2007-04-14 |author= [http://stj911.org/press_releases/NIST.html Scholars for 9/11 Truth and Justice] |date=2007-04-10|format=pdf] . Only one of their requests resulted in a changehttp://wtc.nist.gov/ErratumNCSTAR1-2.pdf] [cite web|url=http://www.journalof911studies.com/volume/2007/NISTresponseToRequestForCorrectionGourleyEtal2.pdf|title=NIST response to request for correction|publisher=Journal of 9/11 Studies|accessdate=2008-08-17|format=PDF] to correct an inconsistency between two parts of the NIST report. This resulted with another appeal from the 9/11 Truth movement.cite web |url=http://journalof911studies.com/volume/2007/AppealLetterToNISTGourleyEtAl.pdf |title=Appeal Filed with NIST, Pursuant to Earlier Request for Correction to 9/11 NIST Report |accessdate=2008-08-20 |author= James Gourley, Bob McIlvaine, Bill Doyle, Steven Jones, Kevin Ryan, Richard Gage, Scholars for 9/11 Truth and Justice|date=2007-11-10|format=pdf]

History

Controlled demolition hypothesis proponents cite mainstream news reports on the day of the attacks that suggested explosions and secondary devices. [ [http://911research.wtc7.net/disinfo/retractions/index.html 9-11 Research: Notable Retractions] Journalists and experts commenting on the events as they happened speculated that the World Trade Center collapses were caused by intentionally planted explosives. ABC News anchor Peter Jennings said "Anybody who ever watched a building being demolished on purpose knows that if you're going to do this you have to get at the under infrastructure of a building and bring it down" [ [http://www.archive.org/details/abc200109110954-1036 Internet Archive: Details: ABC Sept. 11, 2001 9:54 am - 10:36 am ] ] While watching footage of the collapse of WTC 7, CBS News anchor Dan Rather said "For the third time today, it's reminiscent of those pictures we've all seen too much on television before when a building was deliberately destroyed by well-placed dynamite to knock it down." [http://www.youtube.com/watch?v=Nvx904dAw0o YouTube - 9/11: DAN RATHER SAYS WTC COLLAPSES LOOK LIKE DEMOLITIONS ] ] Some of these suggestions would later be retracted or revised. In a notable example, the "Albuquerque Journal" quoted Dr. Van D. Romero, an engineer who said that the collapses looked "too methodical" and that "some explosive devices inside ... caused the towers to collapse", speculating that the collision of the planes into the towers was a diversionary attack intended to attract emergency personnel to the scene, followed by the detonation of "a relatively small amount of explosives placed in strategic points" of the towers as the primary attack. [cite news |first= Olivier |last= Uyttebrouck |title=Use Of Explosives Believed |url=http://www.abqjournal.com/terror/anniversary/pmvan09-21-01.htm |work=Extra |publisher=Albuquerque Journal |page=A2 |date=2001-09-11 |accessdate=2007-11-01] He soon withdrew this assessment [cite news |first=John |last=Fleck|title=Expert Now Thinks No Explosives in Towers |url=http://www.abqjournal.com/terror/anniversary/pmvan09-21-01.htm|publisher=Albuquerque Journal |page=A5 |date=2001-09-22 |accessdate=2007-11-01 ] and later said he had been misquoted: "I only said that that's what it "looked" like."cite journal
author=The Editors
title=Debunking The 9/11 Myths
year=2005|month=March
journal=Popular Mechanics
volume=182
issue=3
pages=pp. 70–81
url=http://www.popularmechanics.com/technology/military_law/1227842.html
accessdate=2007-08-22]

Engineers were in fact initially surprised by the collapses [cite web | last = Oliver | first = Anthony | date= 2005-06-30 | url = http://cruachan.televisual.co.uk/asset/GetArticle.exe?DB=e2&DATABASE=e2&LABEL=emap2&RECORD=191265&SEARCH=1| title = Lasting lessons of WTC | work = | publisher = New Civil Engineer | accessdate =] [cite journal
title=Why Did the World Trade Center Collapse?—Simple Analysis
last=Bažant
first=Zdeněk P.
coauthors=Yong Zhou
authorlink=Zdeněk Bažant
journal=J Engrg Mech
location=New York
year=2002
volume=128
issue=1
pages=pp. 2–6
publisher=ASCE American Society of Civil Engineers
issn=0733-9399
doi=10.1061/(ASCE)0733-9399(2002)128:1(2)] 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 |format=PDF] and at least one considered explosives as a possible explanation. [Kevin Ryan has drawn attention to the initial impressions of Ronald Hamburger, who participated in the FEMA and NIST investigations. See his Power Point presentation “A New Standard of Deception”, [http://www.911truth.org/downloads/slideshows/A_New_Standard.ppt#334 here] . See also Joseph T. Hallinan, Thomas M. Burton and Jonathan Eig. “Top Structural Engineers To Do Autopsy On Twin Towers To Assess Why They Fell.” Wall Street Journal, September 19, 2001 (PDF [http://www.absconsulting.com/news/wsjsept11.pdf here] ).] The broad outlines of an explanation that did not involve such explosives quickly emerged, however, and took its current shape in the 2005 NIST report.cite web
last=Gross
first=John L.
coauthors =Therese P. McAllister|date=2005-09
url=http://wtc.nist.gov/oct05NCSTAR1-6index.htm
accessdate=2007-01-13
title=NIST NCSTAR 1-6: Structural Fire Response and Probable Collapse Sequence of the World Trade Center Towers
work=Federal Building and Fire Safety Investigation of the World Trade Center Disaster
publisher=National Institute of Standards and Technology] 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] It has come to be known as "the official account" among proponents of controlled demolition.

The hypothesis was first suggested in October 2001. An early book-length treatment of the hypothesis [cite book | first = Eric | last = Hufschmid | title = Painful Questions: An Analysis of the September 11th Attack | isbn = 1-931947-05-8 | publisher = Endpoint Software | year = 2002 | month = September] inspired both David Ray Griffin's critical inquirycite book | first = David Ray | last = Griffin |authorlink=David Ray Griffin| title = | isbn = 1-56656-552-9 | publisher = Olive Branch Press | year = 2004 | location = Northampton, MA] as well as the Popular Mechanics investigation of 9/11 conspiracy theories. In late 2005, Brigham Young University Professor of Physics Steven Jones made his own pursuit of the hypothesis public. Even before publication of the article in 2006,cite book | first = David Ray | last = Griffin |authorlink=David Ray Griffin| title =9/11 and the American Empire: Intellectuals Speak Out | coauthors= Peter Dale Scott | publisher=Olive Branch Press |date=2006-09-30 |isbn=1566566592] his interest in the hypothesis brought a measure of media exposure to the theory. BYU responded to Jones' "increasingly speculative and accusatory" statements by placing him on paid leave in September, 2006.Walch, Tad. "BYU places '9/11 truth' professor on paid leave", Deseret Morning News, September 8, 2006.] 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 =] Shortly thereafter, Jones accepted BYU's offer of early retirement.

Proponents of the controlled demolition have questioned the "pancake collapse" hypothesis originally suggested by FEMAcite web|url=http://www.bentham-open.org/pages/content.php?TOCIEJ/2008/00000002/00000001/35TOCIEJ.SGM|title=Fourteen Points of Agreement with Official Government Reports on the World Trade Center Destruction|accessdate=2008-05-29] which the NIST also rejected and finally replaced with the current column failure theory.

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"cite web | last = Sunder | first = Shyam | year = 2005 | url = http://www.nist.gov/public_affairs/ncst/sept2005_meeting/SunderNCSTAC(2)091205%20final.pdf | format = pdf | title = Consideration of Public Comments | work = NIST Response to the World Trade Center Disaster | publisher = National Institute of Standards and Technology | accessdate =] and posted a FAQ about related issues to its website in August of 2006. The major elements of the hypothesis have been rebutted in mainstream engineering scholarship, where its proponents are considered "outsiders".

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", while another 10% found it "somewhat likely". 77% found the demolition hypothesis "unlikely".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] A 2007 poll found that 67% of Americans fault the 9/11 Commission for not investigating the collapse of World Trade Center 7. [cite web |url=http://www.zogby.com/news/ReadNews.dbm?ID=1354 | title=Zogby Poll: 51% of Americans Want Congress to Probe Bush/Cheney Regarding 9/11 Attacks; Over 30% Seek Immediate Impeachment |date=2007-09-06 |accessdate=2007-09-15] An August 2007 Zogby poll found that 4.8% of Americans believe that "certain US government elements actively planned or assisted some aspects of the attacks". [ [http://www.911truth.org/images/ZogbyPoll2007.pdf X-911T.spo ] ]

In June 2008, Arizona State Senator Karen Johnson delivered a letter to the office of U.S. Senator John McCain asking him to meet with a group of professionals to discuss the events of 9/11. [ [http://www.tucsoncitizen.com/ss/elections_other/87165.php AZ legislator wants McCain to hear Sept. 11 suspicions] Tucson Citizen June 3, 2008] She also gave a speech on the floor of the Arizona Senate [ [http://www.azcapitoltimes.com/story.cfm?id=8833 WTC destroyed by bombs, not planes, senator says] Arizona Capitol Times June 10, 2008] that included her support for the demolition theory, its proponents, and its relevance to current foreign policy in the US. Johnson said in her speech:

"You don’t have to embrace every theory about 9/11. Indeed, there are some that should be soundly rejected. But if you believe, as these scientists, architects and engineers do, that the buildings were brought down by explosive demolition, then you must also agree that we need a new investigation. I have no preconceived notions about who did it and I am not pointing the finger of blame at anyone. But I do think that the worst attack on U.S. soil in American history deserves the best investigation possible."

World Trade Center Seven

7 World Trade Center was a 47-story steel-framed skyscraper that stood across Vesey Street north of the main WTC complex. Its tenants included Salomon Smith Barney (which leased 44% of the available office space), ITT Hartford Insurance Group (8%), the Securities and Exchange Commission (8%), the Secret Service (5%), and the Internal Revenue Service (IRS) Regional Council (3%). [http://www.fema.gov/pdf/library/fema403_ch5.pdf] Smaller tenants included the Central Intelligence Agency (CIA) and the Department of Defense, though these shared a single floor with the IRS. Altogether, U.S. local, state, and federal government agencies occupied 11 of the overall 47 floors, or about 28% of the available 39 floors of office space. [http://www.fema.gov/pdf/library/fema403_ch5.pdf] Though damaged by fires which burned for seven hours, it was not hit by a plane, and collapsed at about 5:20 p.m. EDT on the evening of September 11, 2001.

Some journalists commenting on the nature of the collapse of WTC 7 said that it resembled a controlled demolition, [ [http://www.cooperativeresearch.org/entity.jsp?entity=dan_rather Dan Rather ] ] although the explanation that fires in the building, started by falling debris from the collapse of WTC 1, had caused the structure to fail, quickly emerged. No steel-frame high rise had ever before collapsed because of a fire. [FEMA. "World Trade Center Building Performance Study", p. 4.] BBC News reported the collapse of WTC 7 twenty minutes before it actually fell. The BBC has stated that many news sources were reporting the imminent collapse of WTC 7 on the day of the attacks. [Porter, Richard. "Part of the conspiracy? (2)" March 2, 2007. [http://www.bbc.co.uk/blogs/theeditors/2007/03/part_of_the_conspiracy_2.html The Editors, BBC] .] . Jane Staley, 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. [ [http://www.independent.co.uk/arts-entertainment/film-and-tv/tv-radio-reviews/the-weekends-tv-the-conspiracy-files-911-ndash-the-third-tower-sun-bbc2br-george-gently-sun-bbc2-861141.html The Weekend's TV: The Conspiracy Files: 9/11 – The Third Tower The Independent July 6, 2008] ]

Proponents of controlled demolition often emphasize the collapse of WTC 7 because its collapse looked like a bottom-to-top "conventional" controlled demolition, as opposed to the more explosive top-to-bottom collapses of the two main towers. Support for this theory comes from features argued to have been visually observed in the collapse--the speed of the collapse, the way it fell down vertically and symmetrically, the rapid onset, and the way the center of the roof fell first.Fact|date=June 2008 Steven Jones claims that the presence of sulphur is evidence that indicates the use of explosives such as thermate, along with reports of molten metal and extremely high temperatures in the rubble. However, metallurgist Prof. Richard Sisson asserts that the sulfur came from gypsum in the wallboards, [cite web|title=Q&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] an opinion which was also given in the NIST report.

In the PBS documentary "America Rebuilds," which aired in September 2002, Larry Silverstein, the owner of WTC 7 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." Some proponents of the controlled demolition hypothesis have taken the remark as a confession that he ordered the building to be demolished. Silverstein issued a statement that rejects this interpretation, asserting that it was the firefighting team, not the building, that was to be pulled. [cite web |url=http://usinfo.state.gov/media/Archive/2005/Sep/16-241966.html |title=Identifying Misinformation: 9/11 Revealed? |accessdate=2007-01-06 |date=2005-09-16 |publisher=usinfo.state.gov]

Hugo Bachmann and Jörg Schneider, professors emeritus of structural engineering at the Swiss Federal Institute of Technology, believe that WTC 7 was intentionally demolished based on video footage. [cite news
url = http://www.911truthhumboldt.org/docs/Research/bitterdebate.htm
title = The embittered controversy over September 11
accessdate=2006-09-20
last = Ganser|first = Daniele|date=2006-09-09
work=Tages Anzeiger] The 9/11 Family Steering Committee also asked what happened to WTC 7 in their 'Questions Regarding the 9/11 Commission Interview of Mayor Rudy Giuliani,' asking, "On 9/11, no aircraft hit WTC 7. Why did the building fall at 5:20 PM that evening?" [cite web
url = http://www.911independentcommission.org/giuliani31804.html
title = Statement and Questions Regarding the 9/11 Commission Interview of Mayor Rudy Giuliani and Members of his Administration
accessdate=2007-11-07
date=2004-05-11|]

In 2002 the National Institute of Standards and Technology began a general investigation into the collapse of the World Trade Center but soon made a decision to focus on the collapse of the Twin Towers first. A draft version of its final report on the collapse of building 7 was released in August 2008. The agency has blamed the slowness of this investigation on the complexity of the computer model it is using, which simulates the collapse from the moment it begins all the way to the ground, and notes that the time taken on the investigation into building 7 is comparable to the time taken to investigate an aircraft crash. The agency also notes another 80 boxes of documents related to WTC7 were also found and had to be analyzed. These delays fueled suspicion that the agency was struggling to come up with a plausible conclusion.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=p.14|accessdate=2008-08-22]

Preliminary investigations did not include the mechanics of the actual collapse, concentrating instead on the events leading up to it. However, the final draft report on the collapse of WTC7 by NIST provides a detailed investigation into the collapse timeline, starting with the failure of a critical column, Column 79 (initial failure event). 6 seconds later, the collapse of the East Penthouse on the roof was visible. The collapse of the core columns progressed from east to west for another 6.9 seconds (12.9 seconds total since the initial failure event). At this point, the report says, "all the interior columns had buckled" and "the remaining exterior structure above began to fall vertically as a single unit." To calculate the timeline of the collapse of the rest of the building, NIST focused on the time between the initial collapse of the roofline and the last position that the complete roofline could be observed before portions of it started to become obscured by dust, at the top of Floor 29. NIST calculated the timeline for this observable descent as 5.4 seconds and calculated the theoretical free-fall time for the same portion of the building as 3.9 seconds, and concluded that, "The actual collapse time of the upper 18 floors of the north face of WTC7 (the floors clearly visible in the video evidence) was 40 percent greater than the computed free fall time. This was consistent with physical principles." [http://wtc.nist.gov/media/NIST_NCSTAR_1-9_vol2_for_public_comment.pdf]

Following a three year investigation NIST released a draft version of its final report on the collapse on August 21, 2008. 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.

NIST considered the possibility that the towers were brought down with explosives and concluded that a blast event did not occur. 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 investigated the possibility that the collapse was caused by thermite and concluded that it is unlikely that the quantities 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.cite web|url=http://www.nist.gov/public_affairs/factsheet/wtc_qa_082108.html|title=Questions and Answers about the NIST WTC 7 Investigation|date=2008-08-21|publisher=NIST|accessdate=2008-08-21]

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 Architects and Engineers for 9/11 Truth said, "How much longer do we have to endure the coverup of how Building 7 was destroyed?". James Quintiere, professor of fire protection engineering at the University of Maryland, College Park, 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." [ [http://ap.google.com/article/ALeqM5isReaHAE4U2HLBEPKqetS6J8_BvgD92MU19G0 Feds: Fire took down building next to twin towers Associated Press August 21, 2008] ] [ [http://www.nytimes.com/2008/08/22/nyregion/22wtccnd.html?bl&ex=1219464000&en=920506ca2f959545&ei=5087%0A Fire, Not Explosives, Felled 3rd Tower on 9/11, Report Says NMew York Time August 21, 2008 ] ] [ [http://www.newsday.com/news/local/newyork/ny-nywtc225811348aug22,0,1646551.story Report: Fire destroyed 7 World Trade Center Newsday August 22, 2008] ] Following the NIST final draft on Building 7 in August of 2008, a group of demolition proponents submitted a response challenging several points of the draft. [cite web|url=http://stj911.org/blog/?p=42|title=Scientists, Scholars, Architects & Engineers respond to NIST|date=2008-09-15|accessdate=2008-09-17]

Main towers

The controlled demolition hypothesis is also offered to explain dramatic collapses of the two main towers of the World Trade Center complex on September 11, 2001. It emphasizes the speed, symmetry and totality of the collapses, which, it suggests, could not have been caused by the airplane crashes alone. The effects of the fires and the progress of the collapses after they began have been the main areas of contention.

The hypothesis suggests that the fires could not have been hot enough to weaken the steel structure of the two towers to the point of collapse. However, those who pursue the hypothesis emphasize evidence of temperatures well beyond those that, by general consensus, can be attributed to the fires. Molten metal streamed out of the south tower shortly before it collapsed. There are first-hand reports of claims that molten metal was discovered in the piles of rubble in the weeks following the collapses. [ A list of 9/11 molten metal reports from [http://911research.wtc7.net/wtc/evidence/moltensteel.html 911 research] : [http://www.zuckerman.com/script.php?page=html&printid=NewsID&NewsID=46&shownews=1&showevents= Fire Power: It Took Three Lawyers to Stop the Destruction of CDI Inc.,The Daily Record] , [http://www.wasteage.com/mag/waste_dday_ny_sanitation/ Day: NY Sanitation Workers' Challenge of a Lifetime] , [http://www.gcn.com/21_27a/news/19930-1.html Handheld app eased recovery tasks] , [http://www.messenger-inquirer.com/news/attacks/4522011.htm Recovery worker reflects on months spent at Ground Zero] , [http://www.recordonline.com/adayinseptember/trimpe.htm The Chaplain's Tale] , [http://www.jhsph.edu/Publications/Special/Welch.htm Mobilizing Public Health, Johns Hopkins Public Health Magazine] , [http://www.neha.org/9-11%20report/index-The.html The scene at Ground Zero] , [http://www.seau.org/SEAUNews-2001-10.pdf WTC a Structural Success] , [http://www.findarticles.com/p/articles/mi_qa3731/is_200112/ai_n9015802#continue Ground Zero] ] Steven Jones has argued that the molten metal may have been iron, a byproduct of a thermite reaction. Thermite reactions can reach temperatures of up to 4500°F (2500°C), well beyond the temperature (approximately 1500°C (2732°F) required to melt structural steel.

In response, NIST has 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. NIST concluded that some of the observed molten metal may have been molten aluminum from the fuselage of the plane. Aluminum melts at significantly lower temperatures than steel.

The controlled demolition hypothesis is also offered to explain a belief that the towers collapsed close to free fall speed. Most estimates agree that the structures offered little resistance to the progress of the collapses and that they took about 50% longer than a free falling object dropped from the tops of the towers. Without explosives to destroy the internal support structure of the WTC towers, argue proponents of controlled demolition, the fall of the towers would violate the principle of conservation of momentum. [ [http://911research.wtc7.net/wtc/analysis/proofs/speed.html 9-11 Research: Speed of Fall ] ] Others say that these claims are only supported by intuition without any quantitative analysis. They point to their own analyses posted on a website suggesting that the fall may be explained without violating the principle of conservation of momentum and without requiring any explosives. [http://www.911myths.com/WTCREPORT.pdf] [ [http://www.debunking911.com/freefall.htm Debunking 9/11 Conspiracy Theories and Controlled Demolition - Free Fall ] ]

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. Supporters of the controlled demolition hypothesis often emphasize that NIST did not simulate the structural response of the lower parts of the buildings, which they find of primary interest, but do not analyze either. A paper by Zdeněk Bažant 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.

Engineers who have investigated the collapses generally deny 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. [ [http://www.pbs.org/wgbh/nova/wtc/collapse.html NOVA | Building on Ground Zero | PBS ] ] 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. [cite news|url=http://query.nytimes.com/gst/fullpage.html?res=9803E5DC1F3EF931A3575AC0A9609C8B63&sec=&spon=&pagewanted=1|title=U.S. Counters 9/11 Theories Of Conspiracy |last=Dwyer|first=Jim|date=2006-09-02|publisher=The New York Times|accessdate=2008-09-07] [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]

Several other common points underlie the Controlled Demolition hypothesis. First, proponents underscore similarities in video footage of the collapses of the WTC towers with footage of known controlled demolitions. One of the most commonly cited similarities are the tightly focused horizontal plumes of smoke and debris being ejected from the twin towers just before and during the collapse. While these plumes are attributed by demolition theory opponents to material ejected due to the compression of air as the floors collapsed, proponents claim that they may be evidence for exploding demolition charges ("squibs").cite web | last = Griffin|first=David Ray | authorlink=David Ray Griffin|title = The Destruction of the World Trade Center: Why the Official Account Cannot Be True | url = http://911review.com/articles/griffin/nyc1.html |accessdate=2007-10-31]

Proponents claim that eyewitness accounts made by firefighters and emergency medical responders of explosions just prior to the start of the collapse of the towers are suggestive of controlled demolition. [cite web|last=Griffin|first=David Ray|authorlink=David Ray Griffin|url=http://www.911truth.org/article.php?story=20060118104223192|title= Explosive Testimony: Revelations about the Twin Towers in the 9/11 Oral Histories|accessdate=2007-10-31 Griffin analyzes "The Firefighters’ Testimony to Explosions in the Twin Towers", released by FDNY in August 2005 under order from the New York Court of Appeals.] However there are many causes of loud sharp noises that are not caused by explosives, [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|format=PDF] and seismographic records of the collapse do not show evidence of explosions. [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]

Additionally, the production and expansion of the enormous dust clouds that covered Manhattan after the collapses has also been taken as an indication of an additional source of energy, such as explosives. Some proponents suggest that the energy required for this expansion alone (ignoring the energy needed to slice the steel and pulverize the concrete and other materials) exceeded the gravitational energy available by 9.7 × 10¹² J to 4.2 × 10¹³ J. [Griffin cites the work of Jim Hoffman. Cf. Hoffman, Jim, 2003. “The North Tower's Dust Cloud: Analysis of Energy Requirements for the Expansion of the Dust Cloud Following the Collapse of 1 World Trade Center” [http://911research.wtc7.net/papers/dustvolume/volume.html] .] This corresponds to extra energy of about 2000 to 10000 tons of TNT, or 40 to 200 times the yield of the most powerful conventional bomb. NIST attributes these clouds to the ejection of air from compressed parts of the building.

Debris removal

Some of the steel from the Twin Towers was removed and sent to scrap yards before engineers were allowed access to the site on October 6, 2001. Proponents of controlled demolition often see this as part of a cover up. Webster Griffin Tarpley, an author, has criticized the official response to the crime scene, saying that the cleanup process resulted in the destruction of most of the evidence, identifying the New York City Mayor's office as a key player in this regard.cite book|first=Webster Griffin|last=Tarpley|authorlink=Webster Griffin Tarpley|title=9/11 Synthetic Terror|edition=4th edition|publisher=Progressive Press|date=2007-05-07|isbn= 0930852370|location=Joshua Tree, CA|chapter=Chapter VI: The Collapse of World Trade Center 1, 2, and 7.]

The debris removal process began shortly after the attacks, and concluded in May 2002. [ [http://www.foxnews.com/story/0,2933,54002,00.html FOXNews.com - Silent Tribute Marks End of Ground Zero Search - U.S. & World ] ] Some members of the 9/11 Truth Movement allege that engineers were not granted access to Ground Zero until most of the debris had been removed, while others allege that engineers were not granted access to Ground Zero or even the salvage yards at all. [ [http://911research.wtc7.net/wtc/groundzero/cleanup.html 9-11 Research: WTC Steel Removal ] ] However, Robert F. Shea of FEMA testified to the House of Representatives that, "Because of the importance of the rescue effort at the World Trade Center complex, it was clear that information would have to be gathered without interfering with response and rescue activities. Based on this fact, the FEMA-ASCE team first visited the site on October 6, [2001] but gathered information from others who had been on-site before this date." [http://commdocs.house.gov/committees/science/hsy77747.000/hsy77747_0f.htm Learning From 9/11-Understanding the Collapse of the World Trade Center ] ] Regarding access to the scrap yards, appendix D of the FEMA report states that, "As of March 15, 2002, a total of 131 engineer visits had been made to these yards on 57 separate days." [ [http://911research.wtc7.net/mirrors/guardian2/wtc/WTC_apndxD.htm Appendix D - The WTC Report ] ]

A call to action by Bill Manning, the chief editor of the trade journal "Fire Engineering", is often quoted in this connection. Manning called the early ASCE investigation (which would later turn into the FEMA building performance study) a "half-baked farce" and said that "the destruction and removal of evidence must stop immediately." He said that the cleanup of the WTC site differed in many respects from that of other engineering disasters. [Manning, Bill. ""Burning Questions...Need Answers": FE's Bill Manning Calls for Comprehensive Investigation of WTC Collapse." Editorial in "Fire Engineering". January 4, 2002. [http://fe.pennnet.com/Articles/Article_Display.cfmSection=OnlineArticles&SubSection=Display&PUBLICATION_ID=25 &ARTICLE_ID=131225] ] In defense of the decision to dispose of the steel, Mayor Bloomberg said: "If you want to take a look at the construction methods and the design, that's in this day and age what computers do." [http://www.china.org.cn/english/2002/Jan/25776.htm Baosteel Will Recycle World Trade Center Debris] [http://english.eastday.com EastDay.com] "via" [http://www.china.org.cn/english/ China.org.cn] , January 24, 2002] David Ray Griffin notes that this is exactly what Manning had worried about when he warned that "the investigation into the World Trade Center fire and collapse will amount to paper-and computer-generated hypotheticals."

However, allegations against a "speedy removal" of the steel hampering the engineering investigations appear to be unfounded, according to Dr. Gene Corley, head of the BPAT team and one of the lead engineers for the investigation by the National Institute of Standards and Technology (NIST), which began in September 2002. He testified to the House of Representatives in March 2002 that, "There has been some concern expressed by others that the work of the team has been hampered because debris was removed from the site and has subsequently been processed for recycling. This is not the case. The team has had full access to the scrap yards and to the site and has been able to obtain numerous samples. At this point there is no indication that having access to each piece of steel from the World Trade Center would make a significant difference to understanding the performance of the structures".

Notable proponents

The most notable statements of the controlled demolition hypothesis have been made by Steven Jones, David Ray Griffin, Webster Griffin Tarpley and Kevin Ryan. Jones has published his paper "Why Indeed Did the World Trade Center Buildings Collapse?" in a book called "9/11 and the American Empire: Intellectuals Speak Out", edited by Peter Dale Scott and David Ray Griffin. Griffin, a retired professor of theology, published his own version of the hypothesis in "The Hidden History of 9-11-2001", [cite book | first = Paul (ed.) | last = Zarembka | title =The Hidden History of 9-11-2001 | publisher=JAI Press, an imprint of Elsevier |date=2006-07-14 | isbn= 0762313056 |series=Research in Political Economy, Volume 23 ] a book of critical essays on 9/11 edited by Paul Zarembka. Webster Griffin Tarpley has devoted a chapter of his book "9/11 Synthetic Terror" to the hypothesis. Kevin Ryan, who was fired from his job at Underwriters Laboratories for voicing his criticism of the official investigation, has also contributed a chapter to the Griffin and Scott volume. While his work remains largely self-published, Jim Hoffman's detailed web site, [http://911research.wtc7.net/index.html 9-11 Research] , is often cited by proponents of the controlled demolition hypothesis as an inspiration.

Criticism of the NIST Report

Criticism of the NIST Report plays a prominent role in presentations of the hypothesis. Critics point out that the report does not provide an account of the structural behaviour of the towers after the collapses began. [NIST Report, p80] This is important because "much of the external evidence for controlled demolition typically comes after collapse initiation". [Steven Jones, "Why Indeed Did the World Trade Center Buildings Collapse?", p27] It is argued that not modelling the totality of the collapses allowed NIST to ignore evidence of demolition, such as the complete, rapid and symmetrical nature of the collapses, the observed explosive "squibs", the early drop of the North Tower antenna, and the pools of molten metal found in the rubble. [Steven Jones, "Why Indeed Did the World Trade Center Buildings Collapse?", p38] Kevin Ryan's criticism of the NIST investigation and subsequent report is often mentioned in this regard. [Steven Jones, "Why Indeed Did the World Trade Center Buildings Collapse?"] Jones also criticises NIST for "tweaking" the computer simulations of the pre-collapse sequence "until [it got] the desired result.” [Steven Jones, "Why Indeed Did the World Trade Center Buildings Collapse?", p37] Jones goes on to quote the NIST report itself as proof for this claim, "The Investigation Team then defined three cases for each building by combining the middle, less severe, and more severe values of the influential variables. Upon a preliminary examination of the middle cases,it became clear that the towers would likely remain standing...The more severe case was used for the global analysis of each tower..To the extent that the simulations deviated from the photographic evidence or eyewitness reports" [NIST, 2005, p. 142]

On February 28, 2007, NIST's conclusion 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" was challenged in a request for correction (per Section 515 of Public Law 106-554). The request was based on NIST's acknowledgement that it did not investigate controlled demolition nor look for evidence. [ [http://ocio.os.doc.gov/ITPolicyandPrograms/Information_Quality/PROD01_002622 Fire Investigation Report on World Trade Center Bldg 7] United States Department of Commerce Office of the CIO March 1, 2007]

Reaction of the engineering community

The controlled demolition hypothesis has been dismissed in the structural engineering literature. [9/11 Commission Report] Northwestern University Professor of Civil Engineering Zdeněk Bažant, who was the first to offer a published peer reviewed hypothesis of the collapses, mentions the controlled demolition hypothesis in passing in a 2007 paper, co-authored with Mathieu Verdure. Affirming the view as presented in the NIST report, they note "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 hypothesis assumes).

Thomas Eagar, a professor of materials science and engineering at the Massachusetts Institute of Technology, also dismissed the controlled demolition hypothesis.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.] 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." [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] Finally, Leslie Robertson, who helped design the Twin Towers, debated the issue with Steven Jones on a radio program in December 2006. [cite interview|first=Steven|last=Jones|first2=Leslie|last2=Robertson|callsign=KGNU|date=2006-10-26|url=http://www.911podcasts.com/files/audio/StevenJones_LeslieRobertson_20061026.mp3|accessdate=2007-02-27] [cite web|last=Roberts|first=Gregg|year=2007|url=http://journalof911studies.com/volume/200704/Roberts_AnnotatedJones-RobertsonTranscript.pdf |title=Jones v. Robertson, A Physicist and a Structural Engineer Debate the Controlled Demolition of the World Trade Center|accessdate=2007-12-02|format=PDF]

In April 2008, a letter by advocates of the demolition hypothesis was published as a paper in an online civil engineering journal.. In July 2008, an article was published in an environmental journal.]

In popular culture

The demolition hypothesis first entered mainstream media by way of negative press coverage of "9/11 conspiracy theories" or "9/11 myths". Critical articles in "Popular Mechanics", which were later expanded into a book, and the popular magazine "Skeptic" [Molé, Phil. "9/11 Conspiracy Theories: The 9/11 Truth Movement Perspective" and "What Demolition Experts Say About 9/11" in "Skeptic", v. 12, n. 4. 2006] presented rebuttals to the hypothesis for a mainstream audience. In 2006, a "New York Magazine" reported that, "A new generation of conspiracy theorists is at work on a secret history of New York’s most terrible day."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] The hypothesis has been cited by numerous popular actors, musicians and politicians, including Charlie Sheen [ [http://transcripts.cnn.com/TRANSCRIPTS/0603/22/sbt.01.html CNN.com - Transcripts ] ] , Martin Sheen, Willie Nelson, Mos Def, and former Governor of Minnesota, Jesse Ventura. The hypothesis also features prominently in the controversial online documentary "Zeitgeist, the Movie".

References