A brief overview of the two opposing hypotheses.

According to the National Institute of Standards and Technology (NIST), videos of the collapse of the 47-story World Trade Center 7 on September 11, 2001 show the building succumbing to a fire-induced progressive collapse. Many independent researchers and scientists, however, including over 1,400 professional architects and engineers who have signed a petition calling for a new investigation, disagree, pointing to evidence that it was deliberately brought down in a controlled demolition.

Despite the dramatically different conclusions drawn, there does exist widespread agreement on both sides on a number of important questions. Proponents of both hypotheses agree that the damage to WTC 7 sustained from the impact of debris from the collapse of the north tower (WTC 1) was not an initiating or determinative factor in the collapse. Both sides also agree that the system of transfer trusses and girders in the building that allowed it to be constructed above the Consolidated Edison New York electric power substation played no role in the collapse, that hypothetical fuel oil fires from tanks stored in the building for emergency generators was not a causal factor, and that the office fires did not result in any significant loss of strength of the building’s load-bearing steel columns.

While NIST initially denied that the building achieved gravitational acceleration during its collapse in its draft report for public comment, it was forced to acknowledge that this was indeed the case in its final report after high school physics teacher David Chandler submitted his own analysis showing that the building collapsed at free-fall for approximately 2.5 seconds, and that there was a sudden onset of free-fall. According to NIST, the period of free-fall was 2.25 seconds.

To illustrate, what this means is that for 8 stories, or more than 100 feet, the building fell at the same rate as would a bowling ball dropped from the same height and falling through the air.

Proponents of the controlled demolition hypothesis argue that elementary laws of physics rule out the fire-induced collapse hypothesis. They point out, for example, that the law of conservation of energy dictates that free-fall means all of the building’s potential energy was converted to kinetic energy, which means there was no energy remaining to do the work of buckling the columns, as is required by NIST’s hypothesis. The corollary is that there must have been some external source of energy acting on the columns for this free-fall to have occurred.

NIST argues in its final report that the rate of collapse was consistent with its computer models. However, language that the collapse was consistent with physical principles that existed in the draft report, in which NIST denied free-fall, was removed from the final report, in which free-fall is acknowledged.

Active Thermitic Material in the WTC Dust

Photographs of the red/gray chips found in the WTC dust from a study conducted by a team of international scientists and published in a peer-reviewed journal.

Independent researchers point to other evidence that NIST failed to account for in its hypothesis, such as the presence of active thermitic material in the dust from the collapses of the World Trade Center buildings, consistent with nano-thermite. This material was found in four separate samples of the dust collected from four separate locations following the collapses. An international team of scientists issued a paper of their study of these red/gray chips found in the dust in the peer-reviewed Open Chemical Physics Journal in 2009, though to date, there remains a blackout on the topic in the mainstream U.S. media.

The material found in the dust is not a naturally occurring substance, but a manufactured material of highly advanced technology. The Lawrence Livermore National Laboratory, working under the auspices of the U.S. Department of Energy, has released a paper noting that by controlling the composition of energetic materials at the nanometer scale, a more efficient chemical reaction can be produced, with applications for making explosives. The thermite reaction is specifically cited as an example. A publication of the U.S. Department of Defense has similarly pointed out that energetic materials produced on the nanoscale, such nanothermite, has applications for “high-power, high-energy composite explosives”.

The ability of thermite to cut through steel has long been known. It involves a chemical reaction between aluminum and iron oxide, which produces aluminum oxide and molten iron. When sulfur is added to the thermite mixture, it is known as thermate. Conventional thermite, however, is an incendiary, while nano-thermite, or super thermite, results in a much more efficient chemical reaction, with much more explosive results, as noted by the Departments of Energy and Defense.

Also a “signature” of the WTC dust is the presence of iron-rich microspheres, which shows that the iron must have been molten prior to or during the destruction of the World Trade Center buildings, with the surface tension of the liquid forming a sphere before cooling and solidifying in that shape. Yet NIST itself points out that fires did not burn at anywhere near the temperature required to melt iron or steel. Such spheres are a known byproduct, however, of the thermite reaction.

Eutectic Steel

A photograph of a steel sample recovered from WTC 7 from Appendix C of the FEMA report.

And while NIST claims that no steel was recovered from WTC 7, it could not have been unaware of a sample that was recovered and studied by a team from the Worcester Polytechnic Institute. The steel had been severely corroded, showing signs of intergranular melting and sulfidation, with a “swiss cheese”-like appearance. The New York Times referred to this piece of steel as “Perhaps the deepest mystery uncovered in the investigation”, and the team’s findings and recommendations for further study were published as Appendix C of the report of the Federal Emergency Management Agency (FEMA). Although NIST was tasked with carrying out the recommendations of the FEMA report, it ignored Appendix C altogether and implicitly denied the very existence of this steel.

Dr. Abolhassan Astaneh-Asl, a professor at the Department of Civil and Environmental Engineering at the University of California, Berkeley, who headed up a separate effort with funding from the National Science Foundation to investigate the steel and recover important evidence, also recovered a piece of steel from WTC 7. He described steel flanges that “had been reduced from an inch thick to paper thin” to the New York Times. “Parts of the flat top of the I [of the “I-beam”], once five-eighths of an inch thick, had vaporized,” he observed.

The reason so little steel was recovered from WTC 7 is that it was quickly destroyed after having been removed from the site during the search and rescue operations. Engineers across the country were outraged by the destruction, prompting Bill Manning, editor-in-chief of Fire Engineering magazine, to write an editorial lambasting the official investigation under FEMA as “a half-baked farce”.

In stark contrast, in testimony at the Hearing Before the Committee on Science in the U.S. House of Representatives, the head of the FEMA investigation, Dr. Gene Corley, expressed little concern about the destruction of evidence and denied that it hampered the investigation.

Corley’s insouciance about the destruction was further contrasted by Manning’s prescient conclusion that “if they continue in such fashion, the investigation into the World Trade Center fire and collapse will amount to paper- and computer-generated hypotheticals.” Indeed, the NIST report itself observes that its WTC 7 investigation was conducted with no physical evidence, and its hypothesis relied entirely upon computer models.

While the removal of debris from the site of the World Trade Center disaster, or Ground Zero, was normal and necessary, the destruction of evidence from a crime scene is a felony offense under U.S. law. Yet no government or law enforcement agency has sought to hold anyone accountable for the destruction of the steel and other evidence from the WTC.

Another unsolved mystery about the collapse is the prolonged fires that burned under the rubble for months afterward, despite a number of rainfalls and the round-the-clock efforts of firefighters to extinguish them. Many credible witnesses, including scientists and engineers, reported seeing molten iron or steel at the site.

Molten metal at the WTC

Red hot metal being lifted from the WTC debris (Photo: Frank Silecchia).

When asked about this phenomenon, NIST investigator Dr. John Gross responded by denying not only that there was molten iron or steel, but that he had even heard any such reports. Yet one witness who described seeing “hot spots of molten metal” at Ground Zero was Mark Loizeaux, president of Controlled Demolitions, Inc., who was contracted to remove debris from the site and was also a consultant for the NIST report. Dr. Astaneh-Asl was also among those testified to having seen “melting of girders”.

While the official response to this and other testimonial evidence is to dismiss it, proponents of the alternative hypothesis have suggested the possibility that ongoing chemical reactions from the use of thermitic materials might help to explain why the fires could have burned for so long, despite several rainfalls and firefighters’ best efforts, and how such temperatures could have occurred in the oxygen-starved environment under the rubble.

There are other holes in NIST’s hypothesis apart from its failure to account for the physical and testimonial evidence. It requires, for example, that fires were raging in the northeast area on the 12th floor, and it input data assuming this scenario into its simulations. Yet the NIST report itself states that fires only burned in any given area for 20-30 minutes before moving on, and NIST extensively documents the fires from photographic and video evidence, showing that the fire had burned through this area and already moved on, burning towards the west end of the floor at the time of the collapse at 5:20 pm.

Apart from the unscientific approach of inputting data according to an assumption contradicted by their own evidence, NIST also assumed its own worst-case scenario for maximum fire temperature and duration, and carried only that scenario forward into its final computer analyses. NIST has also refused to release its computer data for others to verify and reproduce their results — a remarkable rejection of the scientific method for an agency claiming to have used science to prove the fire-induced collapse hypothesis.

Ph.D. chemist F. R. Greening, who does not accept the controlled demolition hypothesis and has debated it with its proponents, stated in comments on the NIST draft report, “The main problem with the NIST fire simulation appears to be the calculated duration of the fire on the 12th and 13th floors of WTC 7…. In view of the fact that NIST appears to have overestimated the intensity and duration of the fires in WTC 7, particularly on floors 12 and 13, it follows that the heating of the structural steel is also overestimated in the WTC 7 Draft Report. This is fatal to the overall validity of NIST’s collapse initiation hypothesis….”

The NIST hypothesis is that fires on the 12th floor caused thermal expansion of 13th floor beams in the northeast of the building. As a result of this thermal expansion, shear studs, which make the beams composite with the metal decking and concrete floor slab above, failed. The expanding beams then pushed a girder spanning between the core and perimeter columns, causing its welds and connections to fail and the girder to rock off its seat where it was attached to the northeastern-most core column, number 79. This failure resulted in the local collapse of the 13th floor. The floors below, where beams were also weakened due to heat from the fires, could not sustain the impact, and so a cascading series of floor failures resulted. Column 79, unsupported laterally over nine stories, buckled. Column failure then progressed through the core, from east to west, and, as load was transferred to the perimeter columns, the entire building began to move downward as a single unit.

This is what one may witness in videos of the collapse of WTC 7, according to NIST. The FEMA report noted that the building “imploded”, and NIST lead investigator Dr. Shyam Sunder stated that because the core failed first, due to fire, followed by the perimeter columns, “you get the impression it was like a controlled demolition”.

Many architects, engineers, scientists, firefighters, scholars, and other groups of independent researchers calling for a new investigation argue that the alternative hypothesis better explains all the available evidence. They offer a perhaps simpler explanation for what one witnesses in videos of the collapse: it appears to be a controlled demolition because it was.