In our previous article, “Built to Last or Built to Fail?” (FSJA, March 2025), we covered some of the details of the National Institute of Standards and Technology (NIST) claims of the fire-induced collapse of World Trade Center building 7 (WTC7), on September 11, 2001.
That article covered the importance of firefighting confidence in highrise operational procedures, touching upon the investigations of the WTC7 incident by both FEMA and NIST, the building’s fire protection ratings and exposure to fire, what we know and accept about the performance of steel under thermal stress in relation to normal office load fires, and the documented history of modern highrise fires.
It’s important to note that the FEMA and the NIST reports (both from two governmental agencies) did not agree with one another as to the cause of the collapse.
One of the responsibilities of NIST is to set structural design codes for buildings.
The NIST Report, was published in November 2008. Understandably, most firefighters won’t be aware of this report and even less will have read it.
It’s an investigation based on computer modeling to arrive at its conclusions.
To this day, its data has been withheld from peer review and public scrutiny, in the interests of “public safety.” The computer modelling was used to reassemble a “virtual” WTC 7 building, and relied on the data it was provided to draw its conclusions.
The lead investigator, Dr. Sivaraj Shyam-Sunder stated: “We drew conclusions and validated them against video and photographic records.”
Dr. Sunder is also quoted as saying: “This extraordinary event, the collapse of WTC 7 was primarily due to fire…This is a new phenomenon, a new kind of progressive collapse that we have discovered here: the fire-induced progressive collapse due to thermal expansion.
“In fact, we have shown for the first time that fire can produce a progressive collapse… This is the first time that we are aware of, that a building taller than 15 stories has collapsed primarily due to fire. A rare event.”
These are profound statements.
So, why isn’t the American fire service studying what should be the most important case study in the history of highrise firefighting? The current 2021 edition of NFPA 1700, Guide for Structural Firefighting makes no mention of this newly discovered phenomenon, “fire-induced progressive collapse due to thermal expansion”.
The first notable problem centers around the fact that NIST’s investigation did not use any physical evidence, only theories.
In clear contravention of federal laws and the most basic national standards set by the National Fire Protection Association, particularly – ‘NFPA 921-Spoliation of Evidence’ and ‘NFPA 921-Preservation of the Fire Scene and Physical Evidence’, almost all of the physical evidence was removed and disposed of.
NIST declared: “The collapse of World Trade Center 7 is the first known instance of a total global collapse of a tall building primarily due to fire.
“The collapse could not have been prevented without first controlling the fires before most of the combustible building contents were consumed.”
Yet, WTC 7 only had normal office combustible load levels ranging from 20-32 kg/m2, which was only enough material to burn for approximately 20 to 30 minutes in any given area, according to NIST.
These approximate burn times are consistent with the evidence shown in the video recordings and photographs of the day.
It has to be said that the fire volume and flame intensity at any given time in WTC 7 was insignificant compared to historical case studies like the First Interstate fire, One Meridian Plaza fire, or the Grenfell Tower fire in West London.
Other international highrise fire case studies are more spectacular and burned longer than the fires burning in WTC 7, but none of these buildings collapsed.
NIST released a video animation based on its computer model which is problematic as it differs considerably from videos of the actual collapse in several significant ways.
It fails to replicate the observed sudden onset of the symmetrical freefall collapse.
It shows a gradual initiation instead of a sudden release, and an asymmetrical descent with large bulges and deformations in the exterior walls that are not observed in the videos.
The modeled building twists and tips to the east, but the video ends prematurely after 2-seconds and doesn’t illustrate the rest of the collapse to its conclusion.
These inconsistencies suggest that NIST’s explanation does not adequately reflect the actual video coverage of the event; and as both the scientific method and common-sense dictate, if your hypothesis fails to match the observed reality, its wrong.
In the years following NIST’s 2008 report, it became apparent that essential structural details had been over-looked in the investigation.
In 2011, a Freedom of Information Act (FOIA) request for the shop fabrication and erection drawings of WTC7, revealed that NIST had omitted crucial data from its computer simulation model regarding the correct girder seat width, girder web stiffeners, lateral support beams and shear studs; all of which serve to seriously undermine, if not entirely refute NIST’s theory of the cause of collapse initiation in WTC7.
In amongst all the finer details and complexity, there exists a very telling data set.
A measurement which is crucial to the true understanding of the entire situation.
A measurement which identifies and accurately quantifies the building’s descent at freefall acceleration.
NIST initially denied WTC 7 underwent a freefall collapse.
Dr. Sunder parried: “A freefall time would be an object that has no structural components below it.”
But in the case of WTC 7, he claimed that their collapse analysis showed (according to their computer modeling) that the downward acceleration was 40% slower than freefall: “There was structural resistance that was provided in this particular case, and you had a sequence of structural failures that had to take place, and everything was not instantaneous.”
However, when challenged by members of the physics, science, and structural engineering community prior to release of its final report, NIST was forced to yield, and reversed its position.
It reluctantly confirmed that the building did in fact collapse at freefall (9.82m/s2) for the first 2.5 seconds (108 feet) of its seven-second descent.
The significance of this data set has huge and obvious implications.
Specifically, for this symmetrical freefall to occur, the vertical support from all eighty-two structural columns, over eight lower stories, would have to have been completely removed, instantly.
The sudden transition to freefall rules out a progressive collapse from normal travelling fires, or any other known natural mechanism.
Firefighters usually don’t get into the science of fire dynamics, but you don’t need to have a Ph.D. in physics to understand the basic science of gravity and physical resistance.
Nevertheless, we can present you with a Ph.D. expert in forensic structural engineering who investigated this very subject.
The University of Alaska, Fairbanks (UAF) report, A Structural Reevaluation of the Collapse of World Trade Center 7, was a four-year study, published in March 2020 by a team of Ph.D. structural engineers.
In an attempt to verify or nullify NIST’s conclusions, the objective of the study was threefold:
Using similar computer modeling technology programs to create their own virtual WTC 7, the UAF research team first simulated the local structural response to fire loading that may have occurred below Floor 13, where most of the fires in WTC 7 are reported to have occurred.
They then supplemented their own simulation by examining the collapse initiation hypothesis developed by NIST.
Finally, they simulated a number of scenarios within the overall structural system in order to determine what types of local failures and their locations may have caused the total collapse to occur as observed.
Additionally, WTC7 utilized composite flooring assemblies employing shear bolts, or more commonly shear studs, and concrete.
These are vital connectors that transfer shear forces between the steel beam and the concrete slab, ensuring they act as a single, stronger composite unit.
A composite flooring assembly has significantly higher resistance to thermal expansion than steel alone.
Yet, NIST argued that shear bolts were not part of WTC7’s design and construction, but as previously detailed, a 2011 FOIA revealed that this was simply not true. The shear bolts were used.
The structural significance of the distinct planar trapezoidal shape of WTC7 must also be considered.
The building’s footprint, a trapezoid, led to the discovery of numerous geometric structural issues related to its shape.
NIST claimed that fire-induced expansion of flooring assemblies initiated this building’s collapse.
Their theory proposed that the building’s exterior was extremely stiff, resulting in an inward pushing expansion of the floor structural framing.
This is said to have caused issues with a single column (#79), as well as other issues within the floor framing.
However, it must be pointed out that the greatest strength and stiffness of the trapezoid building was at its center core, meaning that the building exterior was NOT stiff relative to the internal framing, and therefore, it was expanding away from the thermal centroid (center) which was at the elevators.
In other words, the thermal expansion would push out, towards the path of least resistance – the exterior walls of WTC7, the opposite of NIST’s claims of inward expansion towards the center.
The center plane of the building (the centroid),which ran through the framing of the elevator shafts, adds stiffness to the core.
It would take more load to bend around this major center core axis than another possible axis.
This means that during a wind or seismic event, the structure would bend around the centroid axis, but due to its shape, during a pure gravitational collapse, WTC7 would be expected to fail asymmetrically toward the short base of the trapezoid on the south side, tipping over toward WTC 1.
The short base is the weakest side of the trapezoid.
Yet, rather than tipping, WTC7 came straight down symmetrically in freefall as a total system into its own footprint. These facts rule out NIST’s claim of progressive failure.
The principal conclusions of the UAF study is that “ fire did not cause the collapse of WTC 7,” Supported by the results of its various analyses, fires could not have caused the weakening or displacement of structural members capable of initiating any of the hypothetical local failures alleged to have triggered the total collapse of the building.
Class A office fuels are not going to burn long enough to produce and sustain the elevated temperatures required to weaken and collapse the steel.
Nor could any local failures, even if they had occurred, have triggered a sequence of failures that would have resulted in the observed complete total freefall collapse.
Based upon their findings, the only way WTC7 could have globally and symmetrically collapsed in freefall the way it did, and fall within its own footprint would have been from the simultaneous removal of all 82 columns on eight consecutive floors in the lower part of the building.
The synchronized failure of all core columns over eight stories, followed by the concurrent failure of all exterior columns over eight stories, 1.3 seconds later, alone could produce the behavior observed in the videos of the collapse, whereas no other sequence of simulated failures produced the observed behavior.
We know that this is not a pattern of failure which can be attributed through the normal progression of office fires.
The UAF report also stated, “We cannot completely rule out the possibility that an alternative scenario may have caused the observed collapse; however, the near simultaneous failure of every column is the only scenario we identified that was capable of producing the observed behavior.”
They’re being nice…and professional, but in other words, they were saying NIST’s theoretical positions are untenable, they’re wrong, and in fact, impossible.
Professor Hulsey’s team could not replicate NIST’s computer modeling conclusions, but instead, ended up invalidating them – entirely.
Think about it. There are 81 columns on each floor across this football field-length trapezoid building. There are 8 floors of freefall (2.25 seconds).
That makes 648 columns that provided absolutely no resistance.
What else can accomplish the simultaneous removal of core and exterior columns on a building-wide horizontal plane?
From our perspective, only the intentional building destruction process known as explosive controlled demolition.
And that, in turn, could have only happened with strategically pre-placed explosives. But they can’t say that.
However, I can. We all know what we’re looking at on the videos. If it looks like a duck, walks like a duck, and quacks like a duck, it’s a duck!
This article uses common sense to follow the science and physics without emotion.
It has been said that physics can be cruel, and this issue is not going away because there is too much information and evidence to ignore.
If we really want to honor and remember the 343, and the thousands of other lives that were lost on that day, I would beseech every firefighter to objectively consider watching the YouTube documentary, Calling Out Bravo 7, 2020 edition.
Then, carefully read the findings of the UAF report on the collapse of WTC Building 7 and compare their computer modeling against the computer modeling in the NIST Report in order to make a determination of true cause.
Everything needs to match up with the video observations of the freefall collapse.
The video is the key and the only convincing evidence of the reality that took place that day.
These are two equally qualified, academically credentialed scientific bodies that have diametrically opposing conclusions regarding the cause of the collapse of WTC 7.
It is the reliability of our textbooks that address and instruct the fire service on how to do our dangerous job correctly.
Civilian and firefighter lives depend on us to get it right.
Their conclusions either change or confirm our accepted fire service highrise strategy and tactics in Type I fire resistive buildings, but they can’t both be right.
If there is controversy, it means that not everyone is satisfied with the answers.
In order to clear up the implications and confusion, we must formally review and compare both reports as a collective body of firefighters, fire prevention inspectors, and building and fire code officials.
We must then choose which conclusion is more logical, and acknowledge the implications, wherever they may lead.
The NIST report doesn’t match the video, and it does not stand up to the principles of science, nor the scrutiny conducted by the forensic structural engineers at the UAF.
We cannot simply rely upon the official narrative issued by NIST, just because they’re NIST.
“The Great Oz has spoken!… Pay no attention to the man behind the curtain.” –The Wizard of Oz
Captain Raul Angulo is a 38-year veteran of the Seattle (WA) Fire Department, and author of the new NFPA textbook Engine Company Fireground Operations 4th Edition, published by Jones and Bartlett Learning. He is an international instructor on fireground strategy and tactics, and a member of the Editorial Advisory Board for Fire Apparatus and Emergency Equipment magazine. He has been an FDIC International instructor since 1996.
Professor Emeritus J. Leroy Hulsey, Ph.D. P.E. S.E. earned his B.S. degree in Civil Engineering at the Missouri School of Mines and Metallurgy, his M.S. degree in Civil Engineering at University of Missouri at Rolla, his postgraduate work at the University of Illinois, and his Ph.D. in Structural Engineering from the University of Missouri‑Rolla. He was the program chair of the University of Alaska Fairbanks, School of Engineering. He has expert experience as a draftsman, a surveyor, computer modeling, instrumentation, and in the designs of buildings, bridges, special structures, special excavations, foundations, and stress analysis in buildings.
An expert forensic structural engineer, Dr. Hulsey has been responsible for structural failure investigations throughout the U.S. including installing instrumentation and testing structures in given conditions, explaining the behavior of existing structures, and determining the effects of temperature extremes on structural systems and precision-controlled demolition.
He has authored more than 75 publications, 40 journal articles, 26 referred conference papers, numerous short courses, published lectures, over 25 published reports, and one textbook. He was the lead forensic investigator in the UAF A Structural Reevaluation of the Collapse of World Trade Center 7.
Firefighter Paul Kayley is a 25-year veteran of the North Yorkshire Fire Service (UK). Also a filmmaker, he produced the WTC 7 documentary, Calling Out Bravo 7.
Engine Company Fireground Operations, 4th Edition, Raul Angulo, Jones and Bartlett Learning 2021
Sudden Building Collapse, An Evaluation of a New Risk in Operational Fire Fighting, Paul S. Kayley BA (Honors) July 2016
Calling Out Bravo 7 2020 Edition, Paul S. Kayley, Video documentary
NIST Final Report on the Collapse of World Trade Center Building 7/Federal Building and Fire Safety Investigation of the World Trade Center Disaster (NIST NCSTAR 1A)
A Structural Reevaluation of the Collapse of World Trade Center 7, Final Report,
J. Leroy Hulsey Ph.D., P.E., S.E., Zhili Quan, Ph.D., Feng Xiano Ph.D., University of Alaska, Fairbanks 2020
NFPA 1700 Guide for Structural Firefighting 2021
Brannigan’s Building Construction for the Fire Service 6th Edition, Glenn P. Corbett, Francis Brannigan, Jones and Bartlett Learning 2021
The Mysterious Collapse of World Trade Center 7, David Ray Griffin, Olive Branch Press 2010
Waiting for Seven: WTC 7 Collapse Warnings in the FDNY Oral Histories,
Graeme MacQueen, January 11, 2008
Fire-How it affects Structural Steel Framing, Blake Mayberry PE, CFEI, February 22, 2018
This article was originally published in the May 2025 Edition of Fire and Safety Journal Americas Magazine. To read your FREE copy, click here.
