(NIST NCSTAR throughout this document refers to one of the 43 volumes
comprise NIST's final report on the WTC Towers issued in October 2005.
sections of the report listed in this document are available at
If the World Trade Center (WTC) towers were designed to withstand
impacts by Boeing 707 aircraft, why did the impact of individual 767s
As stated in Section 5.3.2 of NIST NCSTAR 1, a document from the Port
of New York and New Jersey (PANYNJ) indicated that the impact of a
multiple] Boeing 707 aircraft was analyzed during the design stage of
towers. However, NIST investigators were unable to locate any
the criteria and method used in the impact analysis and, therefore,
to verify the assertion that "... such collision would result in only local damage which could not cause collapse or substantial damage to the building...."
The capability to conduct rigorous simulations of the aircraft impact, the
growth and spread of the ensuing fires, and the effects of fires on
the structure is a recent development. Since the approach to structural
modeling was developed for the NIST WTC investigation, the technical
capability available to the PANYNJ and its consultants and contractors
to perform such analyses in the 1960s would have been quite limited
in comparison to the capabilities brought to bear in the NIST investigation.
The damage from the impact of a Boeing 767 aircraft (which is about 20
bigger than a Boeing 707) into each tower is well documented in NCSTAR
massive damage was caused by the large mass of the aircraft, their high
and momentum, which severed the relatively light steel of the exterior
on the impact floors. The results of the NIST impact analyses matched
observations (from photos and videos and analysis of recovered WTC
exterior damage and of the amount and location of debris exiting from
buildings. This agreement supports the premise that the structural
damage to the
towers was due to the aircraft impact and not to any alternative
NOTE: This merely asserts that the impact of the planes did damage. It does
not establish that, from a structural point of view, the damage done
was other than negligible. Frank DeMartini's characterization--that
the intricate lattice design and 47 core columns and their sophisticated
load redistribution capability would have accommodated even multiple
impacts of Boeing 707s and that the effect would have been analogous
to "sticking a pencil through mosquito netting"--is conveniently omitted,
even though it was supported by at least three other engineers who
worked on the towers. Not being able to locate documentation is not
the same thing as establishing that DeMartini and others were mistaken.
Why did NIST not consider a "controlled demolition" hypothesis with
computer modeling and explanation as it did for the "pancake theory"
A key critique of NIST's work lies in the complete lack of analysis
"progressive collapse" after the point of collapse initiation and the
consideration given to a controlled demolition hypothesis.
NIST conducted an extremely thorough three-year investigation into what
the WTC towers to collapse, as explained in NIST's dedicated Web site,
http://wtc.nist.gov. This included consideration of a number of
the collapses of the towers.
Some 200 technical experts--including about 85 career NIST experts and
leading experts from the private sector and academia--reviewed tens of
of documents, interviewed more than 1,000 people, reviewed 7,000
video footage and 7,000 photographs, analyzed 236 pieces of steel from
wreckage, performed laboratory tests and sophisticated computer
the sequence of events that occurred from the moment the aircraft
towers until they began to collapse.
Based on this comprehensive investigation, NIST concluded that the WTC
collapsed because: (1) the impact of the planes severed and damaged
columns, dislodged fireproofing insulation coating the steel floor
steel columns, and widely dispersed jet fuel over multiple floors; and
subsequent unusually large jet-fuel ignited multi-floor fires (which
temperatures as high as 1,000 degrees Celsius) significantly weakened
and columns with dislodged fireproofing to the point where floors
pulled inward on the perimeter columns. This led to the inward bowing
perimeter columns and failure of the south face of WTC 1 and the east
WTC 2, initiating the collapse of each of the towers. Both photographic
video evidence--as well as accounts from the New York Police Department
unit during a half-hour period prior to collapse--support this sequence
NIST's findings do not support the "pancake theory" of collapse, which is premised
on a progressive failure of the floor systems in the WTC towers (the
composite floor system--that connected the core columns and the perimeter
columns--consisted of a grid of steel "trusses" integrated with a
concrete slab; see diagram below). Instead, the NIST investigation
showed conclusively that the failure of the inwardly bowed perimeter
columns initiated collapse and that the occurrence of this inward
bowing required the sagging floors to remain connected to the columns
and pull the columns inwards. Thus, the floors did not fail progressively
to cause a pancaking phenomenon.
Diagram of Composite WTC Floor System (OMITTED HERE)
NIST's findings also do not support the "controlled demolition" theory
there is conclusive evidence that:
- the collapse was initiated in the impact and fire floors of the WTC towers and nowhere else, and;
- the time it took for the collapse to initiate (56 minutes for
WTC 2 and 102 minutes for WTC 1) was dictated by (1) the extent of damage caused
by the aircraft impact, and (2) the time it took for the fires to reach
critical locations and weaken the structure to the point that the towers could
not resist the tremendous energy released by the downward movement of the massive
top section of the building at and above the fire and impact floors.
Video evidence also showed unambiguously that the collapse progressed
top to the bottom, and there was no evidence (collected by NIST, or by
York Police Department, the Port Authority Police Department or the
Department of New York) of any blast or explosions in the region below
impact and fire floors as the top building sections (including and
98th floor in WTC 1 and the 82nd floor in WTC 2) began their downward
upon collapse initiation.
In summary, NIST found no corroborating evidence for alternative
suggesting that the WTC towers were brought down by controlled
explosives planted prior to Sept. 11, 2001. NIST also did not find any
that missiles were fired at or hit the towers. Instead, photographs and
from several angles clearly show that the collapse initiated at the
impact floors and that the collapse progressed from the initiating
downward until the dust clouds obscured the view.
NOTE: How can the NIST completely ignore the 47 core columns, which
were the distinctive engineering feature of the Twin Towers and would
have made the kind of collapse they describe here impossible unless
all of the support columns on a floor had simultaneously failed? Otherwise,
even if the temperature of the fire had been as great as 1,000 degrees
C, which it was not, the collapse would have involved gradual and
asymmetrical sagging and buckling, not the complete, total and abrupt
destruction (from the top down) that was actually observed. This response
also ignores the seismic records of events prior to "collapse", which
is related to question 5. The order of the questions seems to be being
used to obfuscate the importance of evidence in relation to the time
sequence. To assert that NIST "found no corroborating evidence" for
alternative accounts, such as controlled demolition, would be significant
only if NIST had actually looked for evidence that might support alternative
accounts. In fact, it has found sulfur residue on remnants of the
steel, which provides "corroborating evidence" of the use of thermate
(thermite and sulfur) to cut the steel as a partial explanation of
how the buildings may have been destroyed as a result of controlled
demolitions, which means that what the NIST is saying here is false.
How could the WTC towers have collapsed without a controlled
no steel-frame, high-rise buildings have ever before or since been
due to fires? Temperatures due to fire don't get hot enough for
The collapse of the WTC towers was not caused either by a conventional
fire or even solely by the concurrent multi-floor fires that day.
concluded that the WTC towers collapsed because: (1) the impact of the
severed and damaged support columns, dislodged fireproofing insulation
the steel floor trusses and steel columns, and widely dispersed jet
multiple floors; and (2) the subsequent unusually large, jet-fuel
multi-floor fires weakened the now susceptible structural steel. No
the United States has ever been subjected to the massive structural
concurrent multi-floor fires that the towers experienced on Sept. 11,
NOTE: This simply ignores (a) most of the fuel was consumed in those
massive fireballs upon impact, (b) the fires were oxygen-starved,
as the billowing black clouds indicated, (c) they were burning far
below 1,000 degrees C, probably on the average closer to 250 degrees
C, which was (d) far too low to have caused the steel to weaken, much
less melt. Indeed, (e) even if the fires had been as hot as 1,000
degrees C, they did not last long enough to bring about effects of
that kind. Compare the 13 February 1975 fire on the 11th floor of
the North Tower, which burned hotter (around 1,000 degrees C) and
longer (more than three hours), enveloping the core and destroying
65% of the floor, yet none of the steel--in particular, the trusses--had
to be replaced. That is as close to a crucial experiment (confirming
controlled demolition while refuting the official account) as could
be arranged insofar as the buildings are no longer standing.
Weren't the puffs of smoke that were seen, as the collapse of each
starts, evidence of controlled demolition explosions?
No. As stated in Section 6.14.4 of NIST NCSTAR 1, the falling mass of
building compressed the air ahead of it--much like the action of a
smoke and debris out the windows as the stories below failed
These puffs were observed at many locations as the towers collapsed. In
cases, they had the appearance of jets of gas being pushed from the
through windows or between columns on the mechanical floors. Such jets
expected since the air inside the building is compressed as the tower
must flow somewhere as the pressure builds. It is significant that
"puffs" were observed numerous times on the fire floors in both towers
their collapses, perhaps due to falling walls or portions of a floor.
from WTC 1 were even observed when WTC 2 was struck by the aircraft.
observations confirm that even minor overpressures were transmitted
towers and forced smoke and debris from the building.
NOTE: This might have been true if the floors had actually collapsed as the
government maintains, but they were blown up from the top down. Judy
Wood, a mechanical engineer, has compared them to two gigantic trees
that are turning to sawdust from the top down. The massive energy
required to pulverize concrete flooring, turn office furniture into
tiny particles, and disintegrate living things has no source on the
official account. Steel beams are being blown outward and even upward
while this massive cloud of toxic dust envelopes the structures. Yet,
in some footage, such as seen in "9/11 Revisited", you can see some
of the floors being blown apart before the dust cloud obscures the
Why were two distinct spikes--one for each tower--seen in seismic
before the towers collapsed? Isn't this indicative of an explosion
The seismic spikes for the collapse of the WTC Towers are the result of
from the collapsing towers impacting the ground. The spikes began
10 seconds after the times for the start of each building's collapse
continued for approximately 15 seconds. There were no seismic signals
occurred prior to the initiation of the collapse of either tower. The
record contains no evidence that would indicate explosions occurring
the collapse of the towers.
NOTE: This is false. There were seismic recordings of .7 and .9 on
the Richter scale that, according to a new study that appears on www.911Scholars.org
("Seismic Proof: 9/11 was an Inside Job"), actually preceded the impact
of the aircraft by 14 and 17 seconds, which resulted from massive
explosions in the subbasements that were observed by custodians in
the buildings, including William Rodriquez, who was in the North Tower
and saw a fellow custodian with most of the skin blown off his body
as well as other effects of these explosions, which appear to have
had the purpose of dislodging the 47 core columns from the bedrock.
This would appear to be conclusive evidence that the structures were
not destroyed by the combined interaction of jet-plane-impact/jet-fuel-fires/and
How could the WTC towers collapse in only 11 seconds (WTC 1) and 9
(WTC 2)--speeds that approximate that of a ball dropped from similar
height in a
vacuum (with no air resistance)?
NIST estimated the elapsed times for the first exterior panels to
ground after the collapse initiated in each of the towers to be
seconds for WTC 1 and approximately 9 seconds for WTC 2. These elapsed
were based on: (1) precise timing of the initiation of collapse from
evidence, and (2) ground motion (seismic) signals recorded at
that also were precisely time-calibrated for wave transmission times
Manhattan (see NCSTAR 1-5A).
As documented in Section 6.14.4 of NIST NCSTAR 1, these collapse times
"... the structure below the level of collapse initiation offered minimal resistance to the falling building mass at and above the impact zone. The potential energy released by the downward movement of the large building mass far exceeded the capacity of the intact structure below to absorb that energy through energy of deformation."
"Since the stories below the level of collapse initiation provided little resistance to the tremendous energy released by the falling building mass, the building section above came down essentially in free fall, as seen in videos. As the stories below sequentially failed, the falling mass increased, further increasing the demand on the floors below, which were unable to arrest the moving mass."
In other words, the momentum (which equals mass times velocity) of the
12 to 28
stories (WTC 1 and WTC 2, respectively) falling on the supporting
below (which was designed to support only the static weight of the
and not any dynamic effects due to the downward momentum) so greatly
the strength capacity of the structure below that it (the structure
unable to stop or even to slow the falling mass. The downward momentum
each successive lower floor was even larger due to the increasing mass.
From video evidence, significant portions of the cores of both
(roughly 60 stories of WTC 1 and 40 stories of WTC 2) are known to have
to 25 seconds after collapse initiation before they, too, began to
Neither the duration of the seismic records nor video evidence (due to
obstruction of view caused by debris clouds) are reliable indicators of
total time it took for each building to collapse completely.
NOTE: The laws of physics cannot be violated by buildings or other
They were not falling in a vacuum. The rate of free fall for an object
from the top of a 110 story building encountering only air resistance
on the way
down would have been equal to or greater than 12 seconds. The
have "collapsed" at a speed faster than free fall in the air even if
no resistance at all provided by the 110 floors because explosives were
remove lower floors before higher floors impacted with them. The only
this effect to be attained if is the floors were being destroyed faster
building would have collapsed under the force of gravity alone. The
the buildings' "collapse" provides conclusive proof of controlled
7a. How could the steel have melted if the fires in the WTC towers
enough to do so?
7b. Since the melting point of steel is about 2,700 degrees
temperature of jet fuel fires does not exceed 1,800 degrees Fahrenheit
Underwriters Laboratories (UL) certified the steel in the WTC towers to
degrees Fahrenheit for six hours, how could fires have impacted the
to bring down the WTC towers?
In no instance did NIST report that steel in the WTC towers melted due
fires. The melting point of steel is about 1,500 degrees Celsius (2,800
Fahrenheit). Normal building fires and hydrocarbon (e.g., jet fuel)
generate temperatures up to about 1,100 degrees Celsius (2,000 degrees
Fahrenheit). NIST reported maximum upper layer air temperatures of
degrees Celsius (1,800 degrees Fahrenheit) in the WTC towers (for
NCSTAR 1, Figure 6-36).
However, when bare steel reaches temperatures of 1,000 degrees Celsius,
softens and its strength reduces to roughly 10 percent of its room
value. Steel that is unprotected (e.g., if the fireproofing is
reach the air temperature within the time period that the fires burned
the towers. Thus, yielding and buckling of the steel members (floor
beams, and both core and exterior columns) with missing fireproofing
expected under the fire intensity and duration determined by NIST for
UL did not certify any steel as suggested. In fact, in U.S. practice,
not certified at all; rather structural assemblies are tested for their
resistance rating in accordance with a standard procedure such as ASTM
(see NCSTAR 1-6B). That the steel was "certified ... to 2000 degrees Fahrenheit for six hours" is simply not true.
NOTE: This response trades upon an equivocation. If UL certified "assemblies"
whose principal components are steel, then the claim that UL had certified
the steel is justified. The temperatures only averaged about 500 degrees
F, far, far below those specified as required for the steel to even
weaken. Steel is an excellent thermal conductor, which means that
it would have required raising the temperature of major portions of
the whole structure to initiate any effects of the alleged heat. Moreover,
most of the jet fuel was consumed in the massive fireballs that occurred
upon impact. That means it was no longer available to sustain the
fires alleged. The UL had certified the steel in accordance with standards
that required it to be capable of sustaining temperatures up to 2,000
degrees F for three to four hours before it would even significantly
weaken. (I have in the past used the figure of six hours; Kevin Ryan
has corrected me.) Denying the NIST had alleged the steel had melted
becomes extremely interesting insofar as massive pools of molten metal
were discovered in the subbasements three, four, and five weeks after
9/11. That phenomenon is inexplicable on the government's account,
but would be an expectable effect of the use of powerful explosives.
This "answer" offers an example of linguistic deceit and deception.
We know that the sprinkler systems were activated because survivors
water in the stairwells. If the sprinklers were working, how could
there be a
'raging inferno' in the WTC towers?
Both the NIST calculations and interviews with survivors and
indicated that the aircraft impacts severed the water pipes that
water to the sprinkler systems. The sprinklers were not operating on
principal fire floors.
However, there were ample sources of the water in the stairwells. The
pipes ran vertically within the stairwells. Moreover, there would have
copious water from the broken restroom supply lines and from the water
that supplied the initial water for the sprinklers. Thus, it is not
that evacuating occupants encountered a lot of water.
Even if the automatic sprinklers had been operational, the sprinkler
systems--which were installed in accordance with the prevailing fire
code--were designed to suppress a fire that covered as much as 1,500
on a given floor. This amount of coverage is capable of controlling
fires that are likely to occur in an office building. On Sept. 11,
jet-fuel ignited fires quickly spread over most of the 40,000 square
several floors in each tower. This created infernos that could not have
suppressed even by an undamaged sprinkler system, much less one that
NOTE: The massive fire in the North Tower on 13 February 1975 had
led to the installation of more sophisticated sprinkler systems and
other measures that enhanced the buildings' capacity to withstand
fires. Not only were persons in the buildings looking out the impact
holes but the windows on the buildings remained intact. If the fires
had been as hot as NIST maintains, then those windows could not have
remained intact. The NIST account cannot be correct.
If thick black smoke is characteristic of an oxygen-starved, lower
temperature, less intense fire, why was thick black smoke exiting the
when the fires inside were supposed to be extremely hot?
Nearly all indoor large fires, including those of the principal
the WTC towers, produce large quantities of optically thick, dark
smoke. This is
because, at the locations where the actual burning is taking place, the
is severely depleted and the combustibles are not completely oxidized
colorless carbon dioxide and water.
The visible part of fire smoke consists of small soot particles whose
is favored by the incomplete combustion associated with oxygen-depleted
Once formed, the soot from the tower fires was rapidly pushed away from
fires into less hot regions of the building or directly to broken
breaks in the building exterior. At these lower temperatures, the soot
longer burn away. Thus, people saw the thick dark smoke characteristic
burning under oxygen-depleted conditions.
NOTE: This is a nice example of conceding a point while denying that
conceded it. The billowing black clouds of smoke were indicative of
deprived fires, which were burning at temperatures way below those that
attained under ideal conditions in the presence of pure oxygen. This
the whole NIST account, since if the fires were burning at temperatures
below those required to even weaken, much less melt, steel, then it
the case that the steel weakened, much less melted, as an effect of
This is another case of shifting the location of the question to
from the issues to which it is directly related, such as questions 7a
Why were people seen in the gaps left by the plane impacts if the
the fires behind them was so excessive?
NIST believes that the persons seen were away from any strong heat
most likely in an area that at the time was a point where the air for
was being drawn into the building to support the fires. Note that
observed only in the openings in WTC 1.
According to the International Standard ISO/TS 13571, people will be in
pain within seconds if they are near the radiant heat level generated
by a large
fire. Thus, it is not surprising that none of the photographs show a
standing in those gaps where there also was a sizable fire.
The fire behavior following the aircraft impacts is described in NIST
1-5A. In general, there was little sustained fire near the area where
aircraft hit the towers. Immediately upon impact of the aircraft,
fireballs from the atomized jet fuel consumed all the local oxygen.
itself would have made those locations rapidly unlivable.) The
quickly and were followed by fires that grew inside the tower where
there was a
combination of combustible material, air and an ignition source. Little
combustible material remained near the aircraft entry gashes since the
"bulldozed" much of it toward the interior of the building. Also, some
contents fell through the breaks in the floor to the stories below.
Therefore, the people observed in these openings must have survived the
impact and moved--once the fireballs had dissipated--to the openings
temperatures were cooler and the air was clearer than in the building
NOTE: The fires were not even hot enough to destroy the windows, much
weaken the steel to the point of initiating a "pancake collapse".
structural engineer, Charles N. Pegelow, has recently observed (during
interview on "Non-Random Thoughts", rbnlive.com (24 August 2006) that
not the kinds of buildings that are susceptible to "pancake collapse",
only way it could occur with a building of this kind is if all of the
columns on a floor had failed simultaneously. Since the fires were
temperature and brief in duration, there is no possible way for that to
- Why do some photographs show a yellow stream of molten metal
the side of WTC2 that NIST claims was aluminum from the crashed plane
aluminum burns with a white glow?
NIST reported (NCSTAR 1-5A) that just before 9:52 a.m., a bright spot
at the top of a window on the 80th floor of WTC 2, four windows removed
east edge on the north face, followed by the flow of a glowing liquid.
lasted approximately four seconds before subsiding. Many such liquid
observed from near this location in the seven minutes leading up to the
of this tower. There is no evidence of similar molten liquid pouring
another location in WTC 2 or from anywhere within WTC 1.
Photographs, and NIST simulations of the aircraft impact, show large
debris in the 80th and 81st floors of WTC 2 near the site where the
liquid eventually appeared. Much of this debris came from the aircraft
and from the office furnishings that the aircraft pushed forward as it
to this far end of the building. Large fires developed on these piles
after the aircraft impact and continued to burn in the area until the
NIST concluded that the source of the molten material was aluminum
the aircraft, since these are known to melt between 475 degrees Celsius
degrees Celsius (depending on the particular alloy), well below the
temperatures (about 1,000 degrees Celsius) in the vicinity of the
Aluminum is not expected to ignite at normal fire temperatures and
there is no
visual indication that the material flowing from the tower was burning.
Pure liquid aluminum would be expected to appear silvery. However, the
metal was very likely mixed with large amounts of hot, partially
organic materials (e.g., furniture, carpets, partitions and computers)
display an orange glow, much like logs burning in a fireplace. The
color also would have been affected by slag formation on the surface.
NOTE: NIST should consult with Professor Steven Jones of BYU, who has
conducting experiments with molten aluminum and molten iron relevant to
question and the adequacy of the NIST response, which I do not address
- Did the NIST investigation look for evidence of the WTC towers
down by controlled demolition? Was the steel tested for explosives or
residues? The combination of thermite and sulfur (called thermate)
"slices through steel like a hot knife through butter."
NIST did not test for the residue of these compounds in the steel.
The responses to questions number 2, 4, 5 and 11 demonstrate why NIST
that there were no explosives or controlled demolition involved in the
of the WTC towers.
Furthermore, a very large quantity of thermite (a mixture of powdered
granular aluminum metal and powdered iron oxide that burns at extremely
temperatures when ignited) or another incendiary compound would have
had to be
placed on at least the number of columns damaged by the aircraft impact
weakened by the subsequent fires to bring down a tower. Thermite burns
relative to explosive materials and can require several minutes in
a massive steel section to heat it to a temperature that would result
substantial weakening. Separate from the WTC towers investigation, NIST
researchers estimated that at least 0.13 pounds of thermite would be
heat each pound of a steel section to approximately 700 degrees Celsius
temperature at which steel weakens substantially). Therefore, while a
reaction can cut through large steel columns, many thousands of pounds
thermite would need to have been placed inconspicuously ahead of time,
ignited, and somehow held in direct contact with the surface of
massive structural components to weaken the building. This makes it an
substance for achieving a controlled demolition.
Analysis of the WTC steel for the elements in thermite/thermate would
necessarily have been conclusive. The metal compounds also would have
present in the construction materials making up the WTC towers, and
present in the gypsum wallboard that was prevalent in the interior
NOTE: NIST should be citing and discussing the work of Steven Jones of
who has conducted the most extensive research related to termite and
Professor Jones would be an appropriate expert to address this NIST
Why did the NIST investigation not consider reports of molten steel
from the WTC towers?
NIST investigators and experts from the American Society of Civil
(ASCE) and the Structural Engineers Association of New York (SEONY)--who
inspected the WTC steel at the WTC site and the salvage yards--found no
that would support the melting of steel in a jet-fuel ignited fire in
prior to collapse. The condition of the steel in the wreckage of the
(i.e., whether it was in a molten state or not) was irrelevant to the
investigation of the collapse since it does not provide any conclusive
information on the condition of the steel when the WTC towers were
NIST considered the damage to the steel structure and its fireproofing
the aircraft impact and the subsequent fires when the buildings were
standing since that damage was responsible for initiating the collapse
Under certain circumstances it is conceivable for some of the steel in
wreckage to have melted after the buildings collapsed. Any molten steel
wreckage was more likely due to the high temperature resulting from
exposure to combustion within the pile than to short exposure to fires
explosions while the buildings were standing.
NOTE: The presence of molten metal in the subbasements three, four, and five
weeks later cannot be "irrelevant" to the NIST explanation of the
"collapse", since it was an effect of that event. If the NIST cannot
explain it, then the NIST's account is incomplete and fails to satisfy
a fundamental requirement of scientific reasoning, known as the requirement
of total evidence, which states scientific reasoning must be base
upon all of the available relevant evidence. Evidence is relevant
when its presence or absence, truth or falsity, makes a difference
to (affects the support for) the truth or falsity of a conclusion.
NIST is evading the issue. It cannot account for important, relevant
Why is the NIST investigation of the collapse of WTC 7 (the
building that collapsed on Sept. 11, 2001, hours after the towers)
long to complete? Is a controlled demolition hypothesis being
explain the collapse?
When NIST initiated the WTC investigation, it made a decision not to
staff to support the investigation. After the June 2004 progress report
WTC investigation was issued, the NIST investigation team stopped
working on WTC
7 and was assigned full-time through the fall of 2005 to complete the
investigation of the WTC towers. With the release and dissemination of
report on the WTC towers in October 2005, the investigation of the WTC
collapse resumed. Considerable progress has been made since that time,
the review of nearly 80 boxes of new documents related to WTC 7, the
of detailed technical approaches for modeling and analyzing various
hypotheses, and the selection of a contractor to assist NIST staff in
out the analyses. It is anticipated that a draft report will be
The current NIST working collapse hypothesis for WTC 7 is described in
2004 Progress Report on the Federal Building and Fire Safety
the World Trade Center Disaster (Volume 1, page 17, as well as Appendix
- An initial local failure occurred at the lower floors (below
floor 13) of
the building due to fire and/or debris-induced structural damage of a
column (the initiating event) which supported a large-span floor bay
area of about 2,000 square feet;
- Vertical progression of the initial local failure occurred up to
penthouse, and as the large floor bays became unable to redistribute
it brought down the interior structure below the east penthouse; and
- Triggered by damage due to the vertical failure, horizontal
of the failure across the lower floors (in the region of floors 5 and 7
were much thicker and more heavily reinforced than the rest of the
resulted in a disproportionate collapse of the entire structure.
This hypothesis may be supported or modified, or new hypotheses may be
developed, through the course of the continuing investigation. NIST
considering whether hypothetical blast events could have played a role
initiating the collapse. While NIST has found no evidence of a blast or
controlled demolition event, NIST would like to determine the magnitude
hypothetical blast scenarios that could have led to the structural
one or more critical elements.
NOTE: WTC-7 came down in a classic controlled demolition at 5:20 PM/ET
after Larry Silverstein suggested the best thing to do might be to "pull it".
NIST would like to bury it because it displayed all the characteristics of
classic controlled demolitions, including complete, abrupt, and total collapse
into its own footprint, where the floors are all falling at the same time, at
about the speed of free fall (6.6 seconds compared to 6.0), an event so
embarrassing to the official account it is not even mentioned in THE 9/11 COMMISSION
REPORT. If NIST is doing more, that is because its original studies are clearly
inadequate as, indeed, has been demonstrated by the comments made here about its
For additional information, go to: WTC Contacts | Building and Fire
Research Laboratory | NIST
NIST is an agency of the U.S. Commerce Department's Technology
Last updated: October 5, 2006