The NIST World Trade Center Disaster Investigation was a report that the

National Institute of Standards and Technology The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical s ...

(NIST) conducted to establish the likely technical causes of the three building failures that occurred at the

World Trade Center World Trade Centers are sites recognized by the World Trade Centers Association. World Trade Center may refer to: Buildings * List of World Trade Centers * World Trade Center (2001–present), a building complex that includes five skyscrapers, a ...

following the

September 11, 2001 terrorist attacks The September 11 attacks, commonly known as 9/11, were four coordinated suicide terrorist attacks carried out by al-Qaeda against the United States on Tuesday, September 11, 2001. That morning, nineteen terrorists hijacked four commer ...

. The report was mandated as part of the

National Construction Safety Team Act The National Construction Safety Team Act (H.R. 4687), signed into law October 1, 2002, authorizes the National Institute of Standards and Technology (NIST) to establish investigative teams to assess building performance and emergency response and e ...

(NCST Act), which was signed into law on October 1, 2002 by President George W. Bush. NIST issued its final report on the collapse of the World Trade Center's twin towers in September 2005, and the agency issued its final report on 7 World Trade Center in November 2008. NIST concluded that the collapse of each tower resulted from the combined effects of

airplane An airplane or aeroplane (informally plane) is a fixed-wing aircraft that is propelled forward by thrust from a jet engine, Propeller (aircraft), propeller, or rocket engine. Airplanes come in a variety of sizes, shapes, and wing configurat ...

impact damage, widespread

fireproofing Fireproofing is rendering something (structures, materials, etc.) resistant to fire, or incombustible; or material for use in making anything fire-proof. It is a passive fire protection measure. "Fireproof" or "fireproofing" can be used as a ...

dislodgment, and the fires that ensued. The sequence of failures that NIST concluded initiated the collapse of both towers involved the heat-induced sagging of floor trusses pulling some of the exterior columns on one side of each tower inward until they buckled, after which instability rapidly spread and the upper sections then fell onto the floors below. 7 World Trade Center, which was never directly hit by an airplane, collapsed as a result of thermal expansion of steel beams and girders that were heated by uncontrolled fires caused by the collapse of the North Tower and failure of the fire-resistive material.

Context

Collapse of the World Trade Center

During the

September 11 attacks The September 11 attacks, commonly known as 9/11, were four coordinated suicide terrorist attacks carried out by al-Qaeda against the United States on Tuesday, September 11, 2001. That morning, nineteen terrorists hijacked four commer ...

, two

jet airliner A jet airliner or jetliner is an airliner powered by jet engines (passenger jet aircraft). Airliners usually have two or four jet engines; three-engined designs were popular in the 1970s but are less common today. Airliners are commonly clas ...

s struck the Twin Towers of the

(WTC), one to each tower. As a result, the two 110 stories-tall skyscrapers collapsed, causing complete destruction to the entire WTC complex and killing 2,763 people. The South Tower collapsed at 9:59 a.m. (EDT) after burning for approximately 56 minutes. 29 minutes later, the North Tower collapsed having burned for 102 minutes. When the North Tower collapsed, debris fell on the nearby 7 World Trade Center, damaging it and starting fires that burned for almost seven hours, compromising the building's structural integrity. Seven World Trade Center collapsed at 5:21 p.m. (EDT). The collapse of the World Trade Center buildings on September 11, 2001 was unprecedented; never before had a steel-framed multi-story building suffered a complete collapse as a result of

fire Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. At a certain point in the combustion reaction, called the ignition point, flames a ...

. In the immediate aftermath, knowledgeable structural engineers began providing a range of explanations in an attempt to help the public understand these tragic events. However, a coordinated effort would need to be organized to investigate and analyze the complex series of events that led to each collapse.

FEMA World Trade Center Building Performance Study

In the aftermath of the World Trade Center complex, researchers responded immediately by traveling to

ground zero In relation to nuclear explosions and other large bombs, ground zero (also called surface zero) is the point on the Earth's surface closest to a detonation. In the case of an explosion above the ground, ''ground zero'' is the point on the groun ...

where they began collecting data. Among the first was the

Federal Emergency Management Agency The Federal Emergency Management Agency (FEMA) is an agency of the United States Department of Homeland Security (DHS), initially created under President Jimmy Carter by Presidential Reorganization Plan No. 3 of 1978 and implemented by two Ex ...

(FEMA) and

American Society of Civil Engineers American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

(ASCE), who together formed a Building Performance Study Team to understand how the building structures failed and why. The team produced the first official government report attempting to explain the destruction of the World Trade Center complex. They were able to make many observations and findings, including preliminary analysis of the damaged structures, analysis of the buildings' fire suppression systems, and recommendations to building codes and fire standards for including airplane impact into building design. FEMA's final report, issued in May 2002, also provided a substantial amount of data about the event not documented elsewhere. Their findings suggested that fires, in conjunction with damage to the structural members and fire suppression systems inflicted by the jet airliners, played a key role in the collapse of the buildings. However, the team's investigation was hampered by a number of issues. The lack of authority of investigators to impound pieces of steel for examination before they were recycled led to the loss of important pieces of evidence that were destroyed early during the search and rescue effort, and much of the steel had already been recycled in the one month that had lapsed between the attack and the deployment of the team. The team was further impeded by ongoing criminal investigations by the

FBI The Federal Bureau of Investigation (FBI) is the domestic intelligence and security service of the United States and its principal federal law enforcement agency. Operating under the jurisdiction of the United States Department of Justice, t ...

and

NTSB The National Transportation Safety Board (NTSB) is an independent U.S. government investigative agency responsible for civil transportation accident investigation. In this role, the NTSB investigates and reports on aviation accidents and inci ...

. In a hearing to the U.S. House of Representatives' Committee on Science on March 6, 2002, a panel of witnesses and experts described the obstacles as: * No clear authority and the absence of an effective protocol for how the building performance investigators should conduct and coordinate their investigation with the concurrent search and rescue efforts, as well as any criminal investigation * Difficulty obtaining documents essential to the investigation, including blueprints, design drawings, and maintenance records * Uncertainty as a result of the confidential nature of the BPAT study * Uncertainty as to the strategy for completing the investigation and applying the lessons learned Because of these inadequacies, the Building Performance Study team could not "definitively determine the sequence of events leading to the collapse of each tower." The report was remarkably blunt in pointing out shortcomings and missteps in the investigation and its recommendation for another, more thorough and authoritative investigation.

National Construction Safety Team act

As a result of the inconclusive FEMA Building Performance Study team's findings and concerns over missteps in its investigation, the

U.S. House of Representatives The United States House of Representatives, often referred to as the House of Representatives, the U.S. House, or simply the House, is the lower chamber of the United States Congress, with the Senate being the upper chamber. Together they ...

drafted legislation that would give wide powers, including the right to issue subpoenas, to teams investigating building failures. The bill also mandates that the teams would be centered at the

(NIST) whose building and fire research laboratory in Maryland has conducted extensive investigations of building failures in the past. The bill, cited as the National Construction Safety Team (NCST) act, passed the House and the Senate and was signed into law on Oct. 1, 2002 by President George W. Bush. The NCST act gives NIST a clear mandate to: # establish the likely technical cause of building failures; # evaluate the technical aspects of procedures used for evacuation and emergency response; # recommend specific changes to building codes, standards, and practices; # recommend any research or other appropriate actions needed to improve the structural safety of buildings; and/or changes in emergency response and evacuation procedures; and, # make final recommendations within 90 days of completing an investigation.

Investigation

NIST began its investigation on 21 August 2002. Prior to this date, volunteers from NIST, FEMA, ASCE and others collected steel members important to the investigation from the four steel recycling facilities during the recovery effort. They collected and cataloged 236 steel artifacts, including exterior columns, core columns, floor trusses and other similar structural members. They were able to observe the

metallurgical Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys. Metallurgy encompasses both the sc ...

chemistry and structure and perform experiments on the recovered elements to measure their attributes such as mechanical properties under high temperatures. NIST's Building and Fire Research Laboratory created a complex

computer model Computer simulation is the process of mathematical modelling, performed on a computer, which is designed to predict the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be deter ...

to understand the collapse of the towers. Specifically, they wanted to know if the collapse of a core column could cause the

progressive collapse Progressive collapse is the process where a primary structural element fails, resulting in the failure of adjoining structural elements, which in turn causes further structural failure. Progressive collapses may be accidental, as the result of d ...

of the whole building. They also modeled the dispersion of the jet fuel and damage to the interior of the building that was not visible from photographic evidence and eyewitnesses. The model was used to understand the

hypothesis A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obse ...

of the collapse.

Findings

Twin Towers

The investigation team integrated their metallurgy analysis,

experiment An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into Causality, cause-and-effect by demonstrating what outcome oc ...

al results and computer simulation with video and photographs of the destruction and eyewitness accounts to form their understanding for how the buildings collapsed. They came to two conclusions: # A conventional fire should not have caused the collapse of the 110-story skyscrapers in the absence of structural and fire-proofing insulation damage. # The towers would likely not have collapsed if not for the impact and damage that the aircraft caused to the fire-proofing insulation. The most probable collapse sequence was similar between the South Tower and North Tower, but they were not identical. However, they both involved all major structural systems of the building design: the core columns, the exterior columns and the building floors. # First, the floors that lost fire-proofing insulation due to debris impact began to sag as a result of the high temperature of the fire. # The sagging floors pulled inward on the walls # The exterior walls began to bow inward under the combined forces of the sagging floors, the fire, and the severed core columns from aircraft impact damage. # Finally, the exterior walls buckled/caved in and the buildings collapsed. The stories below provided little resistance to relatively tremendous energy of the falling building, allowing them to fall very quickly. The NIST investigation's conclusions do not support the "pancake theory" of collapse initiation, in which the collapse is begun by a progressive failure of the floor system. However, "pancaking" was accepted as the mode of collapse progression.

7 World Trade Center

NIST released the final report of their investigation into the collapse of the 47-story World Trade Center 7 building on 20 August 2008. Their conclusion is that WTC7 collapsed primarily as a result of the fire that was started when the WTC1 collapsed. The collapse of the North Tower also damaged the south exterior wall of WTC7 but it was not a contributing factor. Because

FDNY The New York City Fire Department, officially the Fire Department of the City of New York (FDNY), is an American department of the government of New York City that provides fire protection services, technical rescue/special operations services, ...

could not attempt to extinguish the fires that were burning on six floors of the building, the fire-proofing insulation began to fail. After several hours of uncontrolled fire, the steel columns, girders and trusses absorbed heat and rapidly lost their strength. As they began to sag, deform and buckle, the interior structure below the east

penthouse Penthouse most often refers to: *Penthouse apartment, a special apartment on the top floor of a building *Penthouse (magazine), ''Penthouse'' (magazine), a British-founded men's magazine *Mechanical penthouse, a floor, typically located directly u ...

was brought down. The failed core columns' load was distributed to the remaining columns which all failed. This led to the progressive collapse of the building.

Reforms

The National Construction Safety Team Act of 2002, which mandated NIST to perform its investigation, specifically states that NIST, which is not a regulatory agency, is not authorized to require the adoption of building codes, standards or practices. However, NIST's final reports on the collapse of the WTC buildings provides the technical basis for new and improved standards, codes and practices on designing buildings to resist progressive collapse. Many NIST researchers are also key members of professional, standards-developing organizations, and NIST actively works with these organizations to ensure that lessons learned from investigations are put to use.

Fire Protection of Structural Members

The National Fire Protection Association has adopted many of NIST's recommended improvements to the building code. NIST's recommendation for improving a building's structural frame and support system under severe loading conditions, such as during a fire event, resulted in the adoption of a new approach to high-rise building design. Much more scrutiny is to be given to the primary and secondary structural members as well as the connections that tie them together. The steel columns of the WTC buildings significantly lost strength when they were subjected to the heat of the fire. Concrete heated to the same temperature, however, loses no strength at all. As a result, new high-rise buildings, including

One World Trade Center One World Trade Center (also known as One World Trade, One WTC, and formerly Freedom Tower) is the main building of the rebuilt World Trade Center complex in Lower Manhattan, New York City. Designed by David Childs of Skidmore, Owings & Mer ...

, are being constructed with reinforced, high-strength concrete.

Emergency Communication Systems

Due to the fact that

New York City New York, often called New York City or NYC, is the most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the most densely populated major city in the Un ...

's Office of Emergency Management was located in World Trade Center 7 on the day of the attacks and vital communications equipment was located in the North Tower, their response was significantly impeded. They have since moved their offices to

Brooklyn Brooklyn () is a borough of New York City, coextensive with Kings County, in the U.S. state of New York. Kings County is the most populous county in the State of New York, and the second-most densely populated county in the United States, be ...

, and disaster and emergency management teams around the country are also moving away from possible targets of

terrorist attacks The following is a list of terrorist incidents that have not been carried out by a state or its forces (see state terrorism and state-sponsored terrorism). Assassinations are listed at List of assassinated people. Definitions of terrori ...

, natural disasters and other emergency scenarios.

Criticism

9/11 conspiracy theorists 9/11 conspiracy theory, conspiracy theories attribute the preparation and execution of the September 11 attacks against the United States to parties other than, or in addition to, al-Qaeda. These include the theory that high-level government ...

argue that NIST had reached a predetermined conclusion by ignoring, dismissing, and denying the evidence. Critics of these conspiracy theories say they are a form of

conspiracism A conspiracy theory is an explanation for an event or situation that invokes a conspiracy by sinister and powerful groups, often political in motivation, when other explanations are more probable.Additional sources: * * * * The term has a nega ...

common throughout history after a traumatic event in which

conspiracy theories A conspiracy theory is an explanation for an event or situation that invokes a conspiracy by sinister and powerful groups, often political in motivation, when other explanations are more probable.Additional sources: * * * * The term has a nega ...

emerge as a mythic form of explanation. A related criticism addresses the form of research on which the theories are based. Thomas W. Eagar, an engineering professor at

MIT The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the m ...

, suggested they "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."

List of reports released

References

External links

Final Reports from the NIST World Trade Center Disaster Investigation

NIST Releases Final WTC 7 Investigation Report
{{September 11 Aftermath of the September 11 attacks Construction law National Institute of Standards and Technology World Trade Center