Aerial view of the debris field of the North Tower, 6 WTC, and 7 WTC (upper right)

The World Trade Center controlled demolition conspiracy theory is a conspiracy theory which contends that the collapse of the World Trade Center was not caused by the airliner crash damage that occurred as part of the September 11, 2001 attacks, and the resulting fire damage, but by explosives installed in the buildings in advance.^[1] Early advocates such as physicist Steven E. Jones, architect Richard Gage, software engineer Jim Hoffman, and theologian David Ray Griffin, argued that the aircraft impacts and resulting fires could not have weakened the buildings sufficiently to initiate a catastrophic collapse,^{[citation needed]} and that the buildings would not have collapsed completely, nor at the speeds that 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.^[2][3][4] NIST did not test for explosive compound residue in steel samples, stating the potential for inconclusive results, and noting that similar compounds would have been present during construction of the towers.^[5]

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.^[6][7][8][9] Niels H. Harrit and others, 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.^{[citation needed]} In April 2009, Jones 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'. ^[10] NIST then said 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.^[11]

History[link]

Questions related to the technical details of the collapse of the buildings of the World Trade Center have been debated for years, including rebuttals and ridicule.^[12] Controlled demolition conspiracy theories were first suggested in October 2001.^[1] 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.^[1] David Ray Griffin and Steven E. Jones are the two most prominent advocates of the theory.^[1] Griffin's book^[13] The New Pearl Harbor, published in 2004,^[14] has become a reference work for the 9/11 Truth movement.^[15] 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.^[16] Griffin theorized in a June 2010 article that those in the alleged false flag operation wanted the buildings to fall straight down. If they had toppled over, they would have destroyed dozens of other buildings and killed tens of thousands of people.^[17]

Steven E. Jones has been a leading academic voice of the proponents of demolition theories.^[18] In 2006, he published the paper "Why Indeed Did the WTC Buildings Completely Collapse?".^[6] 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.^[19] The structural engineering faculty at the university issued a statement which said that they "do not support the hypotheses of Professor Jones".^[3][20]

David Ray Griffin has questioned the "pancake collapse" theory suggested in the Building Performance Study produced by the Federal Emergency Management Agency (FEMA).^[21] NIST's report on the collapse of the WTC towers rejected the theory in favor of the column failure theory.^[22] 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"^[23] and posted a FAQ about related issues on its website in August 2006.^[22] The major elements of the theory have been rebutted by mainstream engineering scholarship,^[24] where its proponents are considered "outsiders".^[2] The magazine Popular Mechanics challenged the theories in the special report "Debunking the 9/11 Myths".^[25]

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.^[26] 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.^[27] Later that same year, in October 2008, a comment by James R. Gourley, describing what he considers fundamental errors in a Bažant and Verdure paper, was published in the Journal of Engineering Mechanics.^[28] And 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.^[10][29]

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 1,500 architects and engineers.^[30] 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.^[31] The theory features prominently in popular entertainment type movies, such as Loose Change,^[32] as well as more documentary type films, such as 9/11: Blueprint for Truth, by San Francisco-area architect Richard Gage, which are based mainly on presentations of scientific and engineering evidence for the controlled demolition theory.^[33]

While mainstream press has a significant history of derogatory labels, descriptions and interpretations of demolition theory advocates (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."^[34]), the theory has been supported by a number of popular actors, musicians and politicians, including Charlie Sheen,^[35][36] Willie Nelson,^[37] former Governor of Minnesota Jesse Ventura,^[38] talkshow host Rosie O'Donnell,^[39] and actors Ed Asner and Daniel Sunjata.

Propositions and hypotheses[link]

Main towers[link]

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.^[40] 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.^[22] 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".^[41]

Physicist Steven E. Jones, among others, points to many descriptions by individuals working on the WTC rubble pile suggesting the presence of molten steel in the pile^[6][10] and a stream of molten metal that poured out of the South Tower before it collapsed^[3] 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.^[10] 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.^[11]

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.^[22] A test performed by the Energetic Materials Research and Testing Center showed that conventional thermite was unable to melt a column much smaller than those used in the World Trade Center.^[42] 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 which 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.^[43]

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.^[2]

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.^[2][44] 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.^[6][45] 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.^[6]

Members of the group Scholars for 9/11 Truth have collected eyewitness accounts^[46] of flashes and loud explosions immediately before the fall.^[14][47] 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.^[48] There are many types of loud sharp noises that are not caused by explosives,^[49] and seismographic records of the collapse do not show evidence of explosions.^[50] Physicist Steven E. 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.^[51][52][53] NIST attributes these puffs to air pressure, created by the decreasing volume of the falling building above, traveling down elevator shafts and exiting some open elevator shaft doors on lower levels).^[54]

In September 2011 Iranian President 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.^[55] Al-Qaida sharply criticised Ahmadinejad in their English-language publication, Inspire, calling his assertions "a ridiculous belief that stands in the face of all logic and evidence".^[56]

7 World Trade Center[link]

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 totally 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.^[57] 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.^[58]

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."^[59] 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 [7 World Trade Center] came down by itself. I was gratified to see Geraldo Rivera investigating it."^[60] FOX News was heavily criticized for airing programs questioning the basis for the collapse of 7 World Trade Center by the internet media groups Media Matters and Newsbusters.^[61]

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.^[62] 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.^[62] 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.^[63]

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.^[64] BBC News reported the collapse of 7 WTC twenty minutes before it actually fell.^[65] The BBC has stated that many news sources were reporting the imminent collapse of 7 WTC on the day of the attacks.^[66] 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.^[67]

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.^[63][68][69]

Evidence[link]

In 2009 a paper by nine scientists described their discovery and chemical and physical analysis of small "red/gray chips in all the samples we have studied of the dust produced by the destruction of the World Trade Center," which were collected at four separate sites. Such chips "have apparently not been discussed in previously published reports. It is worth emphasizing that one sample was collected about ten minutes after the collapse of the second Tower, so it cannot possibly have been contaminated by clean-up operations." "[W]e conclude that the red layer of the red/gray chips we have discovered in the WTC dust is active, unreacted thermitic material, incorporating nanotechnology, and is a highly energetic pyrotechnic or explosive material."^[10][70][71] Others have analyzed 9/11 dust samples and reached similar but more extensive conclusions.^[72]

Earlier, in 2006, Professor Steven E. Jones, of BYU, said debris from 7 WTC contained sulfuric compounds, suggesting that thermate, a mixture of thermitic materials and sulfur, was present.^[73][74] Presence of sulfur is of interest because when used in a thermite compound it reduces the melting point of steel.^[70][71][72] Professor Richard Sisson of Worcester Polytechnic Institute said that he believed the sulfur came from gypsum in the wallboards.^[63] The NIST's question and answer page for the 7 WTC investigation also mentions the presence of sulfur in the gypsum wallboard, and states that an analysis of the steel for thermite or thermate would therefore not necessarily be conclusive.^[75] However, NIST simply never checked for the presence of thermite or thermate (the thermite with sulfur added).^[71][76] Also, extremely high temperatures are necessary to disassociate the sulfur and the calcium that are contained in gypsum board. "[A]nd if you've got those temperatures you've got the temperatures to melt the steel. ... this is impossible to achieve in a normal office fire, even a jet fuel-fed office fire. This is one of the reasons they use wallboard; it's not going to disassociate in normal office fires and attack steel members that are part of steel structures." ^[70]

NIST Report[link]

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.^[75] 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.^[75] The agency also says another 80 boxes of documents related to 7 WTC were found and had to be analyzed. These delays fueled suspicion the agency was struggling to come up with a plausible conclusion.^[69]

NIST released its final report on the collapse of 7 World Trade Center on November 20, 2008.^[77] 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.^[75][78] 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".^[75] 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.^[48]

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 nano-thermite, far more powerful than thermite, was used. Finally, the theory that fires from the large amount of diesel fuel stored in the building caused the collapse was also investigated and ruled out.^[75]

Reactions[link]

The structural engineering community rejects the controlled-demolition conspiracy theory. Its consensus is that the collapse of the World Trade Center buildings was a fire-induced, gravity-driven collapse, an explanation that does not involve the use of explosives.^{[2][79][page needed]}

The American Society of Civil Engineers Structural Engineering Institute issued a statement calling for further discussion of NIST's recommendations,^[80] 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.^[81]

Following the publication of Jones' paper "Why Indeed Did the WTC Buildings Completely Collapse?"^[6] 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.^[19] The structural engineering faculty at the university issued a statement which said that they "do not support the hypotheses of Professor Jones".^[3][20] 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.^[20]

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.^[82] 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).^[2]

Thomas Eagar, a professor of materials science and engineering at the Massachusetts Institute of Technology, also dismissed the controlled-demolition conspiracy theory.^[3] 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."^[83]

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 concluded to be proof that explosives brought down the buildings,^{[10][6][7][84]} Brent Blanchard, author of "A History of Explosive Demolition in America",^[85] 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.^[86] 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.^[87]

Preparing a building for a controlled demolition takes considerable time and effort.^[88] The tower walls would have had to be opened on dozens of floors.^[6] Thousands of pounds of explosives, fuses and ignition mechanisms would need to be sneaked past security and placed in the towers^[6][89] without the tens of thousands of people working in the World Trade Center noticing.^{[1][45][88][89][90][91]} 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?"^[92]

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.”^[31] 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.^[93]

See also[link]

• 9/11 conspiracy theories

References[link]

External links[link]

World Trade Center[1]
The original World Trade Center in March 2001. The reddish-brown building (back left) is the original 7 World Trade Center. The North Tower (left), with antenna spire, is 1 WTC. The South Tower (right) is 2 WTC. All 7 buildings are partially visible (see map below). Background shows the East River.
Record height
Tallest in the world from 1971 to 1973[I]
Preceded by	Empire State Building
Surpassed by	Willis Tower
General information
Location	New York City
Coordinates	40°42′42″N 74°00′45″W / 40.71167°N 74.0125°W / 40.71167; -74.0125Coordinates: 40°42′42″N 74°00′45″W / 40.71167°N 74.0125°W / 40.71167; -74.0125
Groundbreaking	August 25, 1966
Construction started	1 WTC: August 1968 2 WTC: January 1969 3 WTC: December 1979 4, 5, & 6 WTC: 1970 7 WTC: 1983
Completed	1 WTC: December 23, 1970 2 WTC: July 19, 1971 3 WTC: February 1981 4, 5, & 6 WTC: 1975 7 WTC: 1987
Opening	April 4, 1973
Destroyed	September 11, 2001
Height
Antenna spire	1 WTC: 1,727 ft (526.3 m)
Roof	1 WTC: 1,368 ft (417.0 m) 2 WTC: 1,362 ft (415.0 m) 3 WTC: 242 ft (74.0 m) 4 & 5 WTC: 118 ft (36.0 m) 6 WTC: 105 ft (32.0 m) 7 WTC: 610 ft (186.0 m)
Top floor	1 WTC: 1,347 ft (411.0 m) 2 WTC: 1,341 ft (409.0 m)
Technical details
Floor count	1 & 2 WTC: 110 floors 3 WTC: 22 floors 4 & 5 WTC: 9 floors 6 WTC: 8 floors 7 WTC: 47 floors
Floor area	1 & 2 WTC:[clarification needed] 4,300,000 sq ft (400,000 m2) 4, 5, & 6 WTC: 500,000 sq ft (50,000 m2) 7 WTC: 1,868,000 sq ft (170,000 m2)
Elevators	Both had 99 elevators
Design and construction
Owner	Port Authority of New York and New Jersey
Architect	Minoru Yamasaki Emery Roth & Sons
Engineer	Leslie E. Robertson Associates

The original World Trade Center was a complex with seven buildings featuring landmark twin towers in Lower Manhattan, New York City, United States. The complex opened on April 4, 1973, and was destroyed in 2001 in the September 11 attacks. The site is being rebuilt with five new skyscrapers and a memorial to the casualties of the attacks. As of November 2011^[update], only one skyscraper has been completed; the other four are expected to be completed before 2020. One World Trade Center will be the lead building for the new complex, reaching more than 100 stories at its completion.^[2] It became the tallest building in New York City on April 30, 2012, and is expected to be finished by 2013. A sixth tower is awaiting confirmation.

At the time of their completion, the original 1 World Trade Center (the North Tower) and 2 World Trade Center (the South Tower), known collectively as the Twin Towers, were the tallest buildings in the world. The other buildings included 3 WTC (the Marriott World Trade Center), 4 WTC, 5 WTC, 6 WTC (which housed United States Customs), and 7 WTC. All of these buildings were built between 1975 and 1985.

The complex was designed in the early 1960s by Minoru Yamasaki and Associates of Troy, Michigan, and Emery Roth and Sons of New York.^[3] The twin 110-story towers used a tube-frame structural design. To gain approval for the project, the Port Authority of New York and New Jersey agreed to take over the Hudson & Manhattan Railroad, which became the Port Authority Trans-Hudson (PATH). Groundbreaking for the World Trade Center took place on August 5, 1966. The North Tower was completed in December 1972 and the South Tower was finished in July 1973. The construction project involved excavating a large amount of material, which was later used as landfill to build Battery Park City on the west side of Lower Manhattan. The cost for the construction was $400 million ($2,300,000,000 in 2012 dollars).^[4] The complex was located in the heart of New York City's downtown financial district and contained 13.4 million square feet (1.24 million m²) of office space.^[5][6]

The Windows on the World restaurant was located on the 106th and 107th floors of 1 World Trade Center (the North Tower) while the Top of the World observation deck was located on the 107th floor of 2 World Trade Center (the South Tower). The second King Kong film was filmed in 1976 with some scenes mentioning and showing the World Trade Center.

The World Trade Center experienced a fire on February 13, 1975, and a bombing on February 26, 1993. In 1998, the Port Authority decided to privatize the World Trade Center, leasing the buildings to a private company to manage, and awarded the lease to Silverstein Properties in July 2001.

On the morning of September 11, 2001, Al-Qaeda-affiliated hijackers flew two Boeing 767 jets into the complex, one into each tower, in a coordinated terrorist attack. After burning for 56 minutes, the South Tower (2) collapsed, followed a half-hour later by the North Tower (1), with the attacks on the World Trade Center resulting in 2,753 deaths.^[7] 7 World Trade Center collapsed later in the day and the other buildings, although they did not collapse, had to be demolished because they were damaged beyond repair. The process of cleanup and recovery at the World Trade Center site took eight months. The first new building at the site was 7 World Trade Center, which opened in May 2006. The Lower Manhattan Development Corporation (LMDC), established in November 2001 to oversee the rebuilding process, organized competitions to select a site plan and memorial design. Memory Foundations, designed by Daniel Libeskind, was selected as the master plan, but this went through substantial changes in design. The new World Trade Center complex will include One World Trade Center, three other high-rise office towers, and the National September 11 Memorial & Museum.

Planning and construction[link]

The idea of establishing a World Trade Center in New York City was first proposed in 1943. The New York State Legislature passed a bill authorizing New York Governor Thomas E. Dewey to begin developing plans for the project^[8] but the plans were put on hold in 1949.^[9] During the late 1940s and 1950s, economic growth in New York City was concentrated in Midtown Manhattan, while Lower Manhattan was left out. To help stimulate urban renewal, David Rockefeller suggested that the Port Authority build a World Trade Center in Lower Manhattan.^[10]

Initial plans, made public in 1961, identified a site along the East River for the World Trade Center.^[11] As a bi-state agency, the Port Authority required approval for new projects from the governors of both New York and New Jersey. New Jersey Governor Robert B. Meyner objected to New York getting a $335 million project.^[12] Toward the end of 1961, negotiations with outgoing New Jersey Governor Meyner reached a stalemate.^[13]

At the time, ridership on New Jersey's Hudson and Manhattan Railroad (H&M) had declined substantially from a high of 113 million riders in 1927 to 26 million in 1958 after new automobile tunnels and bridges had opened across the Hudson River.^[14] In a December 1961 meeting between Port Authority director Austin J. Tobin and newly elected New Jersey Governor Richard J. Hughes, the Port Authority offered to take over the Hudson & Manhattan Railroad to have it become the Port Authority Trans-Hudson (PATH). The Port Authority also decided to move the World Trade Center project to the Hudson Terminal building site on the west side of Lower Manhattan, a more convenient location for New Jersey commuters arriving via PATH.^[13] With the new location and Port Authority acquisition of the H&M Railroad, New Jersey, agreed to support the World Trade Center project.^[15]

Approval was also needed from New York City Mayor John Lindsay and the New York City Council. Disagreements with the city centered on tax issues. On August 3, 1966, an agreement was reached that the Port Authority would make annual payments to the City in lieu of taxes for the portion of the World Trade Center leased to private tenants.^[16] In subsequent years, the payments would rise as the real estate tax rate increased.^[17]

Architectural design[link]

On September 20, 1962, the Port Authority announced the selection of Minoru Yamasaki as lead architect and Emery Roth & Sons as associate architects.^[18] Yamasaki devised the plan to incorporate twin towers; Yamasaki's original plan called for the towers to be 80 stories tall.^[19] To meet the Port Authority's requirement for 10,000,000 square feet (930,000 m²)) of office space, the buildings would each have to be 110 stories tall.^[20]

A typical floor layout and elevator arrangement of the WTC towers.

A major limiting factor in building height is the issue of elevators; the taller the building, the more elevators are needed to service the building, requiring more space-consuming elevator banks.^[20] Yamasaki and the engineers decided to use a new system with two "sky lobbies"—floors where people could switch from a large-capacity express elevator to a local elevator that goes to each floor in a section. This allowed the design to stack local elevators within the same elevator shaft. Located on the 44th and 78th floors of each tower, the sky lobbies enabled the elevators to be used efficiently, increasing the amount of usable space on each floor from 62 to 75 percent by reducing the number of elevator shafts.^[21][22] Altogether, the World Trade Center had 95 express and local elevators.^[23] This system was inspired by the New York City Subway system whose lines include express stations where both express and local trains stop and local stations where only local trains stop.^[24]

Yamasaki's design for the World Trade Center, unveiled to the public on January 18, 1964, called for a square plan approximately 208 feet (63 m) in dimension on each side.^[19][25] The buildings were designed with narrow office windows 18 inches (46 cm) wide, which reflected Yamasaki's fear of heights as well as his desire to make building occupants feel secure.^[26] Yamasaki's design included building facades sheathed in aluminum-alloy.^[27] The World Trade Center was one of the most-striking American implementations of the architectural ethic of Le Corbusier, and it was the seminal expression of Yamasaki's gothic modernist tendencies.^[28]

In addition to the twin towers, the plan for the World Trade Center complex included four other low-rise buildings, which were built in the early 1970s. The 47-story 7 World Trade Center building was added in the 1980s, to the north of the main complex. Altogether, the main World Trade Center complex occupied a 16-acre (65,000 m²) superblock.^[29]

Structural design[link]

The World Financial Center and Battery Park City were built on reclaimed land.

The structural engineering firm Worthington, Skilling, Helle & Jackson worked to implement Yamasaki's design, developing the tube-frame structural system used in the twin towers. The Port Authority's Engineering Department served as foundation engineers, Joseph R. Loring & Associates as electrical engineers, and Jaros, Baum & Bolles as mechanical engineers. Tishman Realty & Construction Company was the general contractor on the World Trade Center project. Guy F. Tozzoli, director of the World Trade Department at the Port Authority, and Rino M. Monti, the Port Authority's Chief Engineer, oversaw the project.^[30] As an interstate agency, the Port Authority was not subject to local laws and regulations of the City of New York including building codes. Nonetheless, the structural engineers of the World Trade Center ended up following draft versions of the new 1968 building codes.^[31] The tube-frame design, earlier introduced by Fazlur Khan, was a new approach that allowed more open floor plans than the traditional design that distributed columns throughout the interior to support building loads. The World Trade Center towers used high-strength, load-bearing perimeter steel columns called Vierendeel trusses that were spaced closely together to form a strong, rigid wall structure, supporting virtually all lateral loads such as wind loads, and sharing the gravity load with the core columns. The perimeter structure containing 59 columns per side was constructed with extensive use of prefabricated modular pieces each consisting of three columns, three stories tall, connected by spandrel plates.^[31] The spandrel plates were welded to the columns to create the modular pieces off-site at the fabrication shop.^[32] Adjacent modules were bolted together with the splices occurring at mid-span of the columns and spandrels. The spandrel plates were located at each floor, transmitting shear stress between columns, allowing them to work together in resisting lateral loads. The joints between modules were staggered vertically so the column splices between adjacent modules were not at the same floor.^[31]

The core of the towers housed the elevator and utility shafts, restrooms, three stairwells, and other support spaces. The core of each tower was a rectangular area 87 by 135 feet (27 by 41 m) and contained 47 steel columns running from the bedrock to the top of the tower. The large, column-free space between the perimeter and core was bridged by prefabricated floor trusses. The floors supported their own weight as well as live loads, providing lateral stability to the exterior walls and distributing wind loads among the exterior walls.^[33] The floors consisted of 4 inches (10 cm) thick lightweight concrete slabs laid on a fluted steel deck. A grid of lightweight bridging trusses and main trusses supported the floors.^[34] The trusses connected to the perimeter at alternate columns and were on 6 foot 8 inch (2.03 m) centers. The top chords of the trusses were bolted to seats welded to the spandrels on the exterior side and a channel welded to the core columns on the interior side. The floors were connected to the perimeter spandrel plates with viscoelastic dampers that helped reduce the amount of sway felt by building occupants.

Hat trusses (or "outrigger truss") located from the 107th floor to the top of the buildings were designed to support a tall communication antenna on top of each building.^[34] Only 1 WTC (north tower) actually had an antenna fitted; it was added in 1978.^[35] The truss system consisted of six trusses along the long axis of the core and four along the short axis. This truss system allowed some load redistribution between the perimeter and core columns and supported the transmission tower.^[34]

The tube frame design using steel core and perimeter columns protected with sprayed-on fire resistant material created a relatively lightweight structure that would sway more in response to the wind compared to traditional structures such as the Empire State Building that have thick, heavy masonry for fireproofing of steel structural elements.^[36] During the design process, wind tunnel tests were done to establish design wind pressures that the World Trade Center towers could be subjected to and structural response to those forces.^[37] Experiments also were done to evaluate how much sway occupants could comfortably tolerate, however, many subjects experienced dizziness and other ill effects.^[38] One of the chief engineers Leslie Robertson worked with Canadian engineer Alan G. Davenport to develop viscoelastic dampers to absorb some of the sway. These viscoelastic dampers, used throughout the structures at the joints between floor trusses and perimeter columns along with some other structural modifications, reduced the building sway to an acceptable level.^[39]

Construction[link]

This portion of Cortlandt Street (shown in 1936) was acquired and demolished.

In March 1965, the Port Authority began acquiring property at the World Trade Center site.^[40] Demolition work began on March 21, 1966, to clear thirteen square blocks of low rise buildings in Radio Row for construction of the World Trade Center.^[41] Groundbreaking for the construction of the World Trade Center took place on August 5, 1966.^[42]

The site of the World Trade Center was located on landfill with the bedrock located 65 feet (20 m) below.^[43] To construct the World Trade Center, it was necessary to build a "bathtub" with a slurry wall around the West Street side of the site, to keep water from the Hudson River out.^[44] The slurry method selected by Port Authority's chief engineer, John M. Kyle, Jr., involved digging a trench, and as excavation proceeded, filling the space with a "slurry" mixture composed of bentonite and water, which plugged holes and kept groundwater out. When the trench was dug out, a steel cage was inserted and concrete was poured in, forcing the "slurry" out. It took fourteen months for the slurry wall to be completed; it was necessary before excavation of material from the interior of the site could begin.^[45] The 1.2 million cubic yards (917,000 m³) of material excavated were used (along with other fill and dredge material) to expand the Manhattan shoreline across West Street to form Battery Park City.^[46][47]

World Trade Center under construction in 1971

The World Trade Center from the then newly completed West Side Highway in July 2001.

In January 1967, the Port Authority awarded $74 million in contracts to various steel suppliers, and Karl Koch was hired to erect the steel.^[48] Tishman Realty & Construction was hired in February 1967 to oversee construction of the project.^[49] Construction work began on the North Tower in August 1968; construction on the South Tower was underway by January 1969.^[50] The original Hudson Tubes, carrying PATH trains into Hudson Terminal, remained in service as elevated tunnels during the construction process until 1971 when a new PATH station opened.^[51]

The topping out ceremony of 1 WTC (North Tower) took place on December 23, 1970, while 2 WTC's ceremony (South Tower) occurred later on July 19, 1971.^[50] The first tenants moved into the North Tower in December 1970; the South Tower accepted tenants in January 1972.^[52] When the World Trade Center twin towers were completed, the total costs to the Port Authority had reached $900 million.^[53] The ribbon cutting ceremony was on April 4, 1973.^[54]

Criticism[link]

Plans to build the World Trade Center were controversial. The site for the World Trade Center was the location of Radio Row, home to hundreds of commercial and industrial tenants, property owners, small businesses, and approximately 100 residents, many of whom fiercely resisted forced relocation.^[55] A group of small businesses affected filed an injunction challenging the Port Authority's power of eminent domain.^[56] The case made its way through the court system to the United States Supreme Court; the Court refused to accept the case.^[57]

Private real estate developers and members of the Real Estate Board of New York, led by Empire State Building owner Lawrence A. Wien, expressed concerns about this much "subsidized" office space going on the open market, competing with the private sector when there was already a glut of vacancies.^[58][59] Others questioned whether the Port Authority really ought to take on a project described by some as a "mistaken social priority".^[60]

The World Trade Center design brought criticism of its aesthetics from the American Institute of Architects and other groups.^[27][61] Lewis Mumford, author of The City in History and other works on urban planning, criticized the project and described it and other new skyscrapers as "just glass-and-metal filing cabinets".^[62] The twin towers' narrow office windows, only 18 inches (46 cm) wide, were disliked by many for impairing the view from the buildings.^[26]

The trade center's "superblock", replacing a more traditional, dense neighborhood, was regarded by some critics as an inhospitable environment that disrupted the complicated traffic network typical of Manhattan. For example, in his book The Pentagon of Power, Lewis Mumford denounced the center as an "example of the purposeless giantism and technological exhibitionism that are now eviscerating the living tissue of every great city".^[63]

For many years, the immense Austin J. Tobin Plaza was often beset by brisk winds at ground level.^[64] In 1999, the outdoor plaza reopened after undergoing $12 million renovations, which involved replacing marble pavers with gray and pink granite stones, adding new benches, planters, new restaurants, food kiosks and outdoor dining areas.^[65]

Complex[link]

North and South towers[link]

The WTC site building arrangement

With the construction of 7 World Trade Center in the 1980s, the World Trade Center had a total of seven buildings, but the most notable were the main two towers. Each stood over 1,350 feet (410 m) high, and occupied about one acre (43,560 square feet) of the total 16 acres (65,000 m²) of the site's land. During a press conference in 1973, Yamasaki was asked, "Why two 110-story buildings? Why not one 220-story building?" His response was: "I didn't want to lose the human scale."^[66]

When completed in 1972, 1 World Trade Center (the North Tower) became the tallest building in the world for two years, surpassing the Empire State Building after a 40-year reign. The North Tower stood 1,368 feet (417 m) tall and featured a telecommunications antenna or mast that was added at the top of the roof in 1978 and stood 360 feet (110 m) tall. With the 360-foot (110 m)-tall antenna/mast, the highest point of the North Tower reached 1,728 ft (527 m). 2 World Trade Center (the South Tower) became the second tallest building in the world when completed in 1973. The South Tower's rooftop observation deck was 1,362 ft (415 m) high and its indoor observation deck was 1,310 ft (400 m) high.^[67] The World Trade Center towers held the height record only briefly: Chicago's Sears Tower, finished in May 1973, reached 1,450 feet (440 m) at the rooftop.^[68] Throughout their existence, however, the WTC towers had more floors (at 110) than any other building. This number was not surpassed until the advent of the Burj Khalifa, which opened in 2010.

Of the 110 stories, eight were set aside for technical services in mechanical floors Level B5/B6 (floors 7/8, 41/42, 75/76, and 108/109), which are four two-floor areas that evenly spaced up the building. All the remaining floors were free for open-plan offices. Each floor of the towers had 40,000 square feet (3,700 m²) of space for occupancy.^[23] Each tower had 3,800,000 square feet (350,000 m²) of office space. Altogether the entire complex of seven buildings had 11,200,000 square feet (1,040,000 m²) of space.

Lobby of Tower 1, looking south along the east side of the building

Initially conceived as a complex dedicated to companies and organizations directly taking part in "world trade", they at first failed to attract the expected clientele. During the early years, various governmental organizations became key tenants of the World Trade Center including the State of New York. It was not until the 1980s that the city's perilous financial state eased, after which an increasing number of private companies—mostly financial firms tied to Wall Street—became tenants. During the 1990s, approximately 500 companies had offices in the complex including many financial companies such as Morgan Stanley, Aon Corporation, Salomon Brothers and the Port Authority itself. The basement concourse of the World Trade Center included The Mall at the World Trade Center along with a PATH station.^{[citation needed]} The North Tower became the home of the corporate headquarters of Cantor Fitzgerald,^[69] and it also became the headquarters of the Port Authority of New York and New Jersey.^[70]

Electrical service to the towers was supplied by Consolidated Edison (ConEd) at 13,800 volts. This service passed through the World Trade Center Primary Distribution Center (PDC) and sent up through the core of the building to electrical substations located on the mechanical floors. The substations "stepped" the 13,800 primary voltage down to 480/277 volt secondary power and further to 120/208 volt general power and lighting service. The complex also was served by emergency generators located in the sublevels of the towers and on the roof of 5 WTC.^[71][72]

The 110th floor of 1 World Trade Center (the North Tower) housed radio and television transmission equipment. The roof of 1 WTC contained a vast array of transmission antennas including the 360 ft (approx 110 m) center antenna mast, rebuilt in 1999 by Dielectric Inc. to accommodate DTV. The center mast contained the television signals for almost all NYC television broadcasters: WCBS-TV 2, WNBC-TV 4, WNYW 5, WABC-TV 7, WWOR-TV 9 Secaucus, WPIX 11, WNET 13 Newark, WPXN-TV 31 and WNJU 47 Linden. It also had four NYC FM broadcasters: WPAT-FM 93.1, WNYC 93.9, WKCR 89.9, and WKTU 103.5. Access to the roof was controlled from the WTC Operations Control Center (OCC) located in the B1 level of 2 WTC.

Top of the World observation deck[link]

Two World Trade Center's observation deck received an estimated 80,000 visitors a day.

Although most of the space in the World Trade Center complex was off-limits to the public, the South Tower featured an indoor and outdoor public observation area called Top of the World Trade Center Observatories on its 107th and 110th floors. Visitors would pass through security checks added after the 1993 World Trade Center bombing,^[73] then were whisked to the 107th floor indoor observatory at a height of 1,310 feet (400 m). The columns on each face of the building were narrowed on this level to allow 28 inches of glass between them. The Port Authority renovated the observatory in 1995, then leased it to Ogden Entertainment to operate. Attractions added to the observation deck included a simulated helicopter ride around the city. The 107th floor food court was designed with a subway car theme and featured Sbarro and Nathan's Famous Hot Dogs.^[74][75] Weather permitting, visitors could take two short escalator rides up from the 107th floor viewing area to an outdoor viewing platform on the 110th floor at a height of 1,377 ft (420 m).^[76] On a clear day, visitors could see up to 50 miles (80 km).^[74] An anti-suicide fence was placed on the roof itself, with the viewing platform set back and elevated above it, requiring only an ordinary railing and leaving the view unobstructed, unlike the observation deck of the Empire State Building.^[75]

Windows on the World restaurant[link]

The North Tower had a restaurant on its 106th and 107th floors called Windows on the World, which opened in April 1976. The restaurant was developed by Joe Baum at a cost of more than $17 million.^[77] Aside from the main restaurant, two offshoots were located at the top of the North Tower: "Hors d'Oeuvrerie" (offered a Danish smorgasbord during the day and sushi in the evening) and "Cellar in the Sky" (a small wine bar).^[78] Windows on the World also had a wine school program run by Kevin Zraly. Windows on the World was closed following the 1993 World Trade Center bombing.^[77] Upon reopening in 1996, Hors d'Oeuvrerie and Cellar in the Sky were replaced with the "Greatest Bar on Earth" and "Wild Blue".^[78] In 2000, its last full year of operation, Windows on the World reported revenues of $37 million, making it the highest-grossing restaurant in the United States.^[79] The Skydive Restaurant, opened in 1976 on the 44th floor of the North Tower, was also operated by Windows on the World restaurant, but served only lunch.

Other buildings[link]

Five smaller buildings stood around the 16 acres (65,000 m²) block. One was the 22-floor hotel, which opened in 1981 as the Vista Hotel, and in 1995 became the Marriott World Trade Center (3 WTC) at the southwest corner of the site. Three low-rise buildings (4 WTC, 5 WTC, and 6 WTC) in the same hollow tube design as the towers also stood around the plaza. 6 World Trade Center, at the northwest corner, housed the United States Customs Service and the U.S. Commodities Exchange. 5 World Trade Center was located at the northeast corner above the PATH station and 4 World Trade Center was at the southeast corner. In 1987, a 47-floor office building called 7 World Trade Center was built north of the block. Beneath the World Trade Center complex was an underground shopping mall, which in turn had connections to various mass transit facilities including the New York City Subway system and the Port Authority's own PATH trains connecting Manhattan to Jersey City, Hoboken, and Newark.

One of the world's largest gold depositories was stored underneath the World Trade Center, owned by a group of commercial banks. The 1993 bomb detonated close by the vault held. Seven weeks after the September 11 attacks, $230 million in precious metals was removed from basement vaults of 4 WTC, which included 3,800 100-Troy-ounce registered gold bars and 30,000 1,000-ounce silver bars.^[80]

Life and events[link]

On a typical weekday 50,000 people worked in the towers^[81] with another 200,000 passing through as visitors.^[82] The complex was so large that it had its own zip code: 10048.^[83] The towers offered expansive views from the observation deck atop the South Tower and the Windows on the World restaurant on top of the North Tower. The Twin Towers became known worldwide, appearing in numerous movies and television shows as well as on postcards and other merchandise, and became seen as a New York icon, in the same league as the Empire State Building, Chrysler Building and the Statue of Liberty.^[84]

French high wire acrobatic performer Philippe Petit walked between the towers on a tightrope in 1974, as shown in the documentary film Man on Wire.^[85]

Brooklyn toymaker George Willig scaled the exterior of the south tower in 1977.^[86] In 1983, on Memorial Day, high-rise firefighting and rescue advocate Dan Goodwin successfully climbed the outside of the WTC's North Tower. His stunt was meant to call attention to the inability to rescue people potentially trapped in the upper floors of skyscrapers.^[87][88]

The 1995 PCA world chess championship was played on the 107th floor of the South Tower.^[89]

In January 1998, Mafia member Ralph Guarino, who had gained maintenance access to the World Trade Center, arranged a three-man crew for a heist that netted over $2 million from a Brinks delivery to the eleventh floor of the World Trade Center.^[90]

February 13, 1975 fire[link]

On February 13, 1975, a three-alarm fire broke out on the 11th floor of the North Tower. Fire spread through the core to the 9th and 14th floors by igniting the insulation of telephone cables in a utility shaft that ran vertically between floors. Areas at the furthest extent of the fire were extinguished almost immediately and the original fire was put out in a few hours. Most of the damage was concentrated on the 11th floor, fueled by cabinets filled with paper, alcohol-based fluid for office machines, and other office equipment. Fireproofing protected the steel and there was no structural damage to the tower. Other than the damage caused by the fire, a few floors below suffered water damage from the extinguishing of the fires above. At that time, the World Trade Center had no fire sprinkler systems.^[91][92]

February 26, 1993 bombing[link]

Underground bombing.

On February 26, 1993, at 12:17 p.m., a Ryder truck filled with 1,500 pounds (680 kg) of explosives, planted by Ramzi Yousef, detonated in the underground garage of the North Tower.^[93] The blast opened a 100 foot (30 m) hole through five sublevels with the greatest damage occurring on levels B1 and B2 and significant structural damage on level B3.^[94] Six people were killed and 50,000 other workers and visitors were left gasping for air within the 110 story towers. Many people inside the North Tower were forced to walk down darkened stairwells that contained no emergency lighting, some taking two hours or more to reach safety.^[95][96]

Yousef fled to Pakistan after the bombing but was arrested in Islamabad in February 1995, and was extradited back to the United States to face trial.^[97] Sheikh Omar Abdel Rahman was convicted in 1996 for involvement in the bombing and other plots.^[98] Yousef and Eyad Ismoil were convicted in November 1997 for their carrying out the bombing.^[99] Four others had been convicted in May 1994 for their involvement in the 1993 bombing.^[100] According to a presiding judge, the conspirators' chief aim at the time of the attack was to destabilize the north tower and send it crashing into the south tower, toppling both landmarks.^[101]

Following the bombing, floors that were blown out needed to be repaired to restore the structural support they provided to columns.^[102] The slurry wall was in peril following the bombing and loss of the floor slabs that provided lateral support against pressure from Hudson River water on the other side. The refrigeration plant on sublevel B5, which provided air conditioning to the entire World Trade Center complex, was heavily damaged.^[103] Subsequent to the bombing, the Port Authority installed photoluminescent markings in the stairwells.^[104] The fire alarm system for the entire complex needed to be replaced because critical wiring and signaling in the original system was destroyed.^[105] As a memorial to the victims of the bombing of the tower, a reflecting pool was installed with the names of those who had been killed in the blast.^[106] However, the memorial was destroyed following the September 11 attacks. Names of the victims of the 1993 bombing are included in the National September 11 Memorial & Museum.

Lease[link]

In 1998, the Port Authority approved plans to privatize the World Trade Center.^[107] In 2001, the Port Authority sought to lease the World Trade Center to a private entity. Bids for the lease came from Vornado Realty Trust, a joint bid between Brookfield Properties Corporation and Boston Properties,^[108] and a joint bid by Silverstein Properties and The Westfield Group.^[109] By privatizing the World Trade Center, it would be added to the city's tax rolls^[109] and provide funds for other Port Authority projects.^[110] On February 15, 2001, the Port Authority announced that Vornado Realty Trust had won the lease for the World Trade Center, paying $3.25 billion for the 99-year lease.^[111] Vornado outbid Silverstein by $600 million though Silverstein upped his offer to $3.22 billion. However, Vornado insisted on last minute changes to the deal, including a shorter 39-year lease, which the Port Authority considered nonnegotiable.^[112] Vornado later withdrew and Silverstein's bid for the lease to the World Trade Center was accepted on April 26, 2001,^[113] and closed on July 24, 2001.^[114]

Destruction[link]

United Airlines Flight 175 hits the south tower

On September 11, 2001, terrorists hijacked American Airlines Flight 11 and crashed it into the northern façade of the north tower at 8:46 a.m., the aircraft striking between the 93rd and 99th floors. Seventeen minutes later, at 9:03 a.m., a second team of terrorists crashed the similarly hijacked United Airlines Flight 175 into the south tower, striking it between the 77th and 85th floors.^[115] The damage caused to the north tower by Flight 11 destroyed any means of escape from above the impact zone, trapping 1,344 people.^[116] Flight 175 had a much more off-centered impact compared to Flight 11, and a single stairwell was left intact; however, only a few people managed to pass through it successfully before the tower collapsed. Although the south tower was struck lower than the north tower, thus affecting more floors, a smaller number, fewer than 700, were killed instantly or trapped.^[117]

At 9:59 a.m., the South Tower collapsed after burning for approximately 56 minutes. The fire caused steel structural elements, already weakened from the plane impact, to fail. The north tower collapsed at 10:28 a.m., after burning for approximately 102 minutes.^[118] At 5:20 p.m.^[119] on September 11, 2001, 7 World Trade Center started to collapse with the crumble of the east penthouse, and it collapsed completely at 5:21 p.m.^[119] owing to uncontrolled fires causing structural failure.^[120] This account of the collapse's cause was disputed by proponents of World Trade Center controlled demolition conspiracy theories.

The 3 World Trade Center, a Marriott hotel, was destroyed during the collapse of the two towers. The three remaining buildings in the WTC plaza sustained heavy damage from debris and were ultimately demolished.^[121] The Deutsche Bank Building across Liberty Street from the World Trade Center complex was later condemned owing to the uninhabitable toxic conditions inside; it was deconstructed, with work completed in early 2011.^[122][123] The Borough of Manhattan Community College's Fiterman Hall at 30 West Broadway was also condemned owing to extensive damage in the attacks and is slated for deconstruction.^[124]

The World Trade Center on fire with the Statue of Liberty in the foreground

In the immediate aftermath of the attacks, media reports suggested that tens of thousands might have been killed in the attacks, as on any given day over 50,000 people could be inside the towers. Ultimately, 2,753 death certificates (excluding those for hijackers) were filed relating to the 9/11 attacks, including one filed for Felicia Dunn-Jones, who was added to the official death toll in May 2007; Dunn-Jones died five months later from a lung condition linked to exposure to dust during the collapse of the World Trade Center.^[125] Three other victims were then added to the official death toll by the city medical examiner's office: Dr. Sneha Anne Philip, who was last seen the day before the attacks; Leon Heyward, a man who developed lymphoma and subsequently died in 2008 as a result of dust ingestion during the events following the attacks to the Twin Towers;^[126][127] and Jerry Borg, who died in December 2010 of pulmonary sarcoidosis determined in June 2011 to be the result of dust from the attacks.^[7] Cantor Fitzgerald L.P., an investment bank on the 101st–105th floors of One World Trade Center, lost 658 employees, considerably more than any other employer,^[128] while Marsh & McLennan Companies, located immediately below Cantor Fitzgerald on floors 93–101 (the location of Flight 11's impact), lost 295 employees, and 175 employees of Aon Corporation were killed.^[129] In addition, 343 of the dead were New York City firefighters, 84 were Port Authority employees, of whom 37 were members of the Port Authority Police Department, and another 23 were New York City Police Department officers.^{[130][131][132]} Ten years after the attacks, only 1,629 victims have been positively identified.^[133] Of all the people who were still in the towers when they collapsed, only 20 were pulled out alive. PAPD Officers William Jimeno and Sgt. John McLoughlin were survivors 18 and 19.^[134]

Rebuilding[link]

After years of delay and controversy, reconstruction at the World Trade Center site is now well underway. The new complex will include One World Trade Center (formerly known as the Freedom Tower), 7 World Trade Center, three other high-rise office buildings, a museum and memorial, and a transportation hub similar in size to Grand Central Terminal. Both One and Four World Trade Center are on track for completion and occupancy by 2013.^[135][136] The 9/11 memorial is complete, with the museum set to open in 2012.^[137] Two and Three World Trade Center, as well as the Transportation Hub, are also making progress, set to be finished by around 2015.

History[link]

The process of cleanup and recovery continued 24 hours a day over a period of eight months. Debris was transported from the World Trade Center site to Fresh Kills on Staten Island, where it was further sifted. On May 30, 2002, a ceremony was held to officially mark the end of the cleanup efforts.^[138] In 2002, ground was broken on construction of a new 7WTC building located just to the north of the main World Trade Center site. Since it was not part of the site master plan, Larry Silverstein was able to proceed without delay on the rebuilding of 7 World Trade Center, which was completed and officially opened in May 2006; this had been considered a priority since restoring the Consolidated Edison Cos. electrical substation in the building's lower floors was necessary to meet power demands of Lower Manhattan.^{[139][140][141]} While 7 World Trade Center was not part of the master plan for the Twin Towers site, Silverstein and Con Edison recognized that the rebuilding of 7 World Trade Center would have to be consistent with the master plan which was expected to re-open the street grid which had been blocked by the original World Trade Center super-block. As a result, the design for the new 7 World Trade Center allowed for the re-opening of Greenwich Street, which had been blocked by the original 7 World Trade Center.^[142] A temporary PATH station at the World Trade Center opened in November 2003; it will be replaced by a permanent station designed by Santiago Calatrava.^[143]

With the main World Trade Center site, numerous stakeholders were involved including Silverstein and the Port Authority, which in turn meant the Governor of New York State, George Pataki, had some authority. In addition, the victims' families, people in the surrounding neighborhoods, Mayor Michael Bloomberg, and others wanted input. Governor Pataki established the Lower Manhattan Development Corporation (LMDC) in November 2001 as an official commission to oversee the rebuilding process.^[144] The LMDC held a competition to solicit possible designs for the site. The Memory Foundations design by Daniel Libeskind was chosen as the master plan for the World Trade Center site.^[145] The plan included the 1,776 feet (541 m) Freedom Tower (now known as One World Trade Center) as well as a memorial and a number of other office towers. Out of the World Trade Center Site Memorial Competition, a design by Michael Arad and Peter Walker titled Reflecting Absence was selected in January 2004.^[146]

On March 13, 2006, workers arrived at the World Trade Center site to remove remaining debris and start surveying work. This marked the official start of construction of the National September 11 Memorial & Museum, though not without controversy and concerns from some family members.^[147] In April 2006, the Port Authority and Larry Silverstein reached an agreement in which Silverstein ceded rights to develop the Freedom Tower and Tower Five in exchange for financing with Liberty Bonds for Towers Two, Three, and Four.^[148][149] On April 27, 2006, a ground-breaking ceremony was held for the Freedom Tower.^[150]

In May 2006, architects Richard Rogers and Fumihiko Maki were announced as the architects for Towers Three and Four, respectively.^[151] The final designs for Towers Two, Three and Four were unveiled on September 7, 2006. Tower Two, or 200 Greenwich Street, will have a roof height of 1,254 feet (382 m) and a 96 feet (29 m) tripod spire for a total of 1,350 feet (410 m). Tower Three, or 175 Greenwich Street will have a roof height of 1,155 feet (352 m) and an antenna height reaching 1,255 feet (383 m). Tower Four, or 150 Greenwich Street, will have an overall height of 946 feet (288 m).^[152] On June 22, 2007, the Port Authority of New York and New Jersey announced that JP Morgan Chase will build Tower 5, a 42-story building on Site 5 occupied by the Deutsche Bank Building,^[153] and Kohn Pedersen Fox was selected as the architect for the building.^[154] Four renowned architects, including Spanish architect Santiago Calatrava, who designed the transit hub, One WTC designer David Childs of Skidmore, Owings and Merrill, and the famed British architect Norman Foster of Foster and Partners designed Tower Two and masterminded the iconic diamond design, will greatly enhance the street-level atmosphere of the rebuilt site. The projects will be complete between early 2013 to mid 2014.^[155]

As of August 2011, One World Trade Center is at 80 stories with glass up to the 54th floor, Tower Four is up around 38 stories with glass up to the 15th floor, and the former Deutsche Bank Building has been completely dismantled and the Port Authority is working on their Vehicle Security Center.^[156] The World Trade Center Transportation Hub's PATH hall is nearly complete. The memorial officially opened to relatives of the deceased on September 11, 2011, and to the general public on September 12. World Trade Center Tower Three's foundations are becoming visible, and will be completed in mid 2014 if Silverstein Properties can meet requirements set by the Port Authority, as they very likely will.^[157][158] Tower Two will also be completed on schedule according to the construction company. In the December of 2011, Tower Two's foundations are finished and is starting to assemble the frame. ^[159] Because numerous American and Chinese companies are "very interested" in leasing space at the WTC, Two World Trade Center is likely to be finished earlier than expected.^[160] Publishing Giant Conde Nast has agreed to move its headquarters to One World Trade Center, and with this shift, many more are expected to follow.^[161]