The Ongoing Investigation by NIST

(written in late 2004 - for a more recent critique see Building a Better Mirage by Jim Hoffman)

Comments

The Promise:

NIST-SP 1000-5

June 2004
Progress Report on the Federal Building and Fire Safety Investigation of the World Trade Center
Chapter 1-Interim Findings and Accomplishment

1.2 COLLAPSE OF THE WTC TOWERS
Working Hypothesis
NIST is investigating possible collapse scenarios to establish the sequence of events that led to the
collapse of the WTC towers following the initial impact of the aircraft. The objectives of the NIST
analysis are to determine the most probable sequence of events from the moment of aircraft impact until
the initiation of global building collapse and to identify the factors that have the strongest influence on the most probable sequence.

NIST has developed a working hypothesis to explain the collapse initiation of the WTC towers. The
working hypothesis (summarized below and in Appendix Q) identifies the chronological sequence of
major events as the WTC tower structures redistributed loads from structural element to structural
element to accommodate the aircraft impact and subsequent fire damage until no further load
redistribution was possible to maintain overall stability, thus, leading to collapse. The hypothesis:

●  Is based on analysis of the available evidence and data, consideration of a range of
hypotheses (including those postulated publicly by experts), and a newly enhanced
understanding of structural and fire behavior.
●  Is consistent with all evidence currently held by NIST, including photos and videos,
eyewitness accounts, and emergency communication records.
●  Allows for multiple load redistribution paths and damage scenarios for each building,
currently under analysis.
●  Will be further refined based on the results of NIST's continuing analyses to identify specific
load redistribution paths and damage scenarios that are possible for each building, from
which the most probable collapse sequence will be identified.

The Reality: "...the collapses then ensued."
(Could it be any less specific?)

Finding 1a.1: The following chronological sequence of major events led to the eventual collapse of the towers; specific load redistribution paths and damage scenarios for each building continue to be refined:

● Aircraft impact damage to perimeter columns, resulting in redistribution of column loads to adjacent perimeter columns and to the core columns via the hat truss;

● After breaching the building's exterior, the aircraft continued to penetrate into the buildings, damaging core columns with redistribution of column loads to other intact core and perimeter columns via the hat truss and floor systems;

● The subsequent fires, influenced by the post-impact condition of the fireproofing, weakened columns and floor systems (including those that had been damaged by aircraft impact), triggering additional local failures that ultimately led to column instability; and

● Initiation and horizontal progression of column instability resulted when redistributing loads could not be accommodated any further. The collapses then ensued.

An interesting claim about the North Tower collapse:

Column Instability and Collapse Initiation  (Appendix Q.5)



"The perimeter columns were designed as part of a framed-tube system to carry both gravity and wind

forces. Instability of perimeter columns resulted from a combination of (1) redistributed loads from the

core columns via the floor system and possibly the hat truss, (2) inward bowing due to thermally

weakened and sagging floors, (3) increased unsupported length due to failed floors, and (4) thermal

effects directly on the perimeter columns.



"The instability of a few perimeter columns spread instability across the entire face and around the corners

just before or during collapse initiation. The initiation or spread of perimeter column instability also may

have been facilitated by the hoop stress demand on the framed-tube system exceeding the capacity of the

spandrels (horizontal steel plates) that tied the perimeter columns together (e.g., at the northeast corner of WTC-2)



"The initiation of global collapse for both towers was first observed by the tilting of the sections above the

impact regions of both WTC towers. The top section of WTC 1 rotated to the south (observed via

antenna tilting in a video recording) and the top of WTC 2 rotated to the east and south and twisted in a

counterclockwise motion. The primary direction of tilt of each tower was around the weaker axis of the

core (north-south for WTC 1 and east-west for WTC 2). The rigid body rotation associated with the

tilting and the propagation of column instability are synchronous processes that initiated global collapse.

The rigid body rotation may have caused forces such as shear and torsion to spread the column instability laterally."

Anyone who has looked at the videos of the WTC-1 collapse cannot help but find this description
at odds with the obvious facts.  What is remarkable about the North Tower collapse is that it does 
indeed begin at the very top of the building, and that it proceeds almost exactly vertically, with only 
a transient leaning of the antenna near the start.  Though the description better suits the South Tower,
there is quite clearly no "rigid body rotation" taking place synchronous with the initiation of the collapse
in this instance.

Fire Modeling

Despite the central role played by the fires and the importance of knowing the actual temperatures reached in various parts of the buildings, fire modeling is still very preliminary three years after the attacks.   The experimental chamber below subjects structural components such as the truss shown to a fire created by spraying hydrocarbon liquid (heptanes and toluene) into a 3'x6' metal pan through spray nozzles.  No attempt was made to simulate fire conditions in a real office in terms of amount of fuel available or other actual fire conditions - the specimen was simply heated to a predetermined surface temperature to study heat flows:
"In each test, the baseline signals from all the measurement devices were established; then the burner was ignited and continued burning at a steady rate until the temperature at any steel surface approached approximately 600 °C. (Above this temperature, there was concern that loss of strength might lead to collapse and accordant damage to the test facility.)"

Notice that all the worthy goals spelled out below remain only that, and only some of the preliminary experimental work intended to lead to the required computer fire modeling has been done.  Three years later, and hobbled by the "near absence of Physical evidence", NIST remains facing a monumental task that it has barely started, and that may prove near-impossibly with the very limited evidence left to work from.

Instrumented room for fire testing of structural elements, from Appendix-J

From the June 2004 NIST update:

• Which structural features of the buildings were affected, and thus what location, magnitude,
and duration of fire brought about the collapse, and

• Whether the nature of the fires is typical of what might be expected in common occupancies,
or whether there were special features that made these fires especially severe.

Due to the near absence of physical evidence, the recreation of the fires depends on computer modeling.
NIST is redefining the state-of-the-art in fire and thermostructural modeling, since this type of
reconstruction has never been done before. Fire experiments are being used to guide adaptation of
existing models and develop new algorithms for them; additional experiments form the basis for
validating the models.

H.6.1 WTC 1



It has already been mentioned that substantial fireballs formed on the north, east, and south faces

immediately following the plane strike. A brief period of intense burning from openings on these faces

was observed after the fireballs dissipated, but in a short period (on the order of 60 seconds) the fires

seemed to “damp down” and very little flame and only light smoke was evident from the outside. This

period of light burning lasted several minutes before fires began to reappear.



Rapid early fire growth was observed on the east side of the north face on floor 96 and floor 97, the center

of the east face on floor 94 and floor 97, and the western side of the south face on floor 96. Even though

relatively little initial damage was sustained by the west face, heavy smoke followed shortly by flame

appeared around window 97-437 at 8:55 a.m. After this time, a very rapid fire spread was observed

across the west face on this floor. Within a couple of minutes, over half of the windows were emitting

smoke, and flames were visible in many. Even though floor 92 was not directly struck by the airplane,

fire appeared on the east side of the tower on this floor shortly after 9:00 a.m.



Following the initial development of large fires, fire spread continued until WTC 1 collapsed around

10:28 a.m. At times the fires displayed the systematic, relatively slow spread expected for fire growth in

a typical building. For instance, after the initial rapid growth phase, fires on floors 92, 94, 96, and 97 on

the east face began to move deliberately toward the south. As they spread, the fires would burn intensely

at a given location for a while before dying down. As a result, these fires developed the appearance of a

wave moving slowly across the building.



There were also certain times and locations during which fire appeared to spread quite rapidly. Some of

these episodes were clearly connected with rapid fire growth and likely flashover in rooms. During the

first half hour, significant fires were observed toward the centers of floors 92, 94, 96, and 97 on the east

face that were spreading towards the north. Each of these fires eventually reached a certain point where

further fire spread was inhibited for many minutes. A review of building plans showed that walls of

offices or meeting rooms were presented at the locations where fire spread was inhibited.



Apparently, these walls served as effective fire breaks that protected against further fire spread. However,

for each of these floors fire and smoke eventually appeared at one of the windows beyond the walls, and

after one of these windows was broken fire growth was extremely rapid and robust across the remaining

windows. These observations are consistent with the occurrence of flashover within an enclosed space.

At other times, unusually rapid fire growth apparently occurred in areas that are believed to have been

relatively open and not constrained by walls. One of these episodes occurred around 9:54 a.m. on the

north face. Fire suddenly appeared on floor 96, a location to the west of the damage inflicted by the

airplane. Within a very short period of time, fire could be seen in roughly 10 windows covering a

distance of more than 30 ft.



Another example of very rapid fire growth appeared to take place on floor 98. In the early period of the

fire, this floor did not appear to be heavily involved, and this remained true for quite a while. However,

after 9:30 a.m., fire began to appear on this floor and by 10:00 a.m., fires were observed over significant

lengths on all four faces of the tower.

One of the more unusual fire spread episodes in WTC 1 occurred just after the collapse of WTC 2 around

9:59 a.m. Within a couple of minutes, a large intense fire suddenly appeared on the south side of the west

face on floor 104 in an area well above any other apparent fire. This unusual jump in fire location is

difficult to explain, but is likely associated with vertical shafts located in the core of the tower.



For most of the time following the plane strike, no fire was observed on any of the floors on the south

face over lengths extending from the eastern edge of the tower to near the center of the face. Fires were

not observed in this region of the building until around 10:00 a.m. By the time this tower collapsed

roughly 25 minutes later, intense fires extending over significant lengths of the originally uninvolved area

were burning on floor 94 to floor 98 in this area.



A final example of rapid fire spread and growth in WTC 1 was described previously in the May 2003

Progress Report for the Investigation (NIST 2003). In this case, a line of smoke appeared suddenly over

a significant length of floor 92 on the north face of WTC 1 at 10:18:48 a.m., or roughly 9 minutes before

the collapse of the tower. Puffs of smoke were observed simultaneously on the north face from floors 94,

95, and 97. More isolated puffs were seen at the same time from floor 92 and floor 95 on the west face

and from floor 92 on the south face. Very shortly (seconds) after the appearance of the smoke, a localized

fire on floor 95 to the west of the plane strike location grew very rapidly and flames erupted from

windows. Following the smoke release, a large fire began to spread rapidly across the western side of

floor 92 on the north face. Previous to the appearance of the smoke, only small fires were evident on this

floor. By the time the tower collapsed, this fire had spread across most of the floor and had reached the

western wall. This fire was responsible for the large burst of flame from the north face observed when

this tower collapsed.

H.6.2 WTC 2



The fire behavior observed in WTC 2 was qualitatively different than occurred in WTC 1. Intense

fireballs were created by the released jet fuel on the south, east, and north faces immediately after the

airplane struck the building. As observed for WTC 1, the fireballs were followed by a brief period (on the

order of a minute) of intense flaming from windows over a large area of the building. Most of these

flames then “damped down” as observed in WTC 1, but two regions of intense burning remained. One of

these areas was located on floor 81 and floor 82 at the northeast corner of the tower. Flames were evident

from windows on either side of the corner as well as the corner itself, which had become exposed by

removal of the corner facing during the plane strike. This area is in the vicinity of large piles of debris

formed during the plane strike. The second fire was located primarily on floor 79 just to the left of the

center (roughly from windows 79-231 to 79-238) of the north face. This is in the area of the second

debris pile described earlier. Both of these fires died slowly with time when compared to fires at other

locations in WTC 1 and WTC 2. Both were still burning lightly when the tower fell 56 minutes after the

plane strike.

A curious aspect of the fire behavior is the existence of an area of the building façade between these two

fire locations on the north face where very little fire and/or smoke was observed before the tower

collapsed. This area is roughly rectangular in shape, covering floor 80 to floor 82 and extending across

windows 249 to 239. Infrared images recorded shortly following the plane strike showed that this region

was quite cool relative to other sections close to the fires. This area will be referred to as the “cold spot.”

Spreading fires seemed to move around this cold spot.

In general, the fires in WTC 2 appeared to be less active than those observed in WTC 1. The fires

covered a smaller area of the façade and did not spread as quickly. This is true even when the shorter

time between the plane strike and collapse for WTC 2 (1 hour 42 minutes for WTC 1 and 56 minutes for

WTC 2) is taken into account. Nevertheless, there was significant fire spread, and instances of rapid fire

growth similar to those seen in WTC 1 did take place.



Around 9:29 a.m., large flames and heavy smoke erupted from an area on the north face just to the right

of the cold spot (around window 83-236) on floor 83. Four minutes and forty-one seconds later, flames

suddenly appeared at a separate location on the same floor further to the right near window 83-226.

Another area of fire formed just to the right of the cold spot on floor 82 around 9:54 a.m. or 5 minutes

before the collapse. The fires on floor 79 of the north face also spread towards the west, approaching the

western edge of the tower just prior to the collapse.



Initial fire growth on the east face was on floor 82. Around 9:12 a.m., flames could be seen in nearly half

of the windows on this floor, and heavy smoke was pouring from additional windows. Only limited fire

was evident on lower floors at this time. The fires on floor 82 grew smaller after this time, and most were

no longer visible when the tower collapsed. Around 9:35 a.m., heavy flames and smoke appeared over

large areas of floor 79 and floor 80. These fires abruptly died down 45 seconds later, before growing

back slowly during the remainder of the time before the tower collapsed.



In the early period following the plane strike, fire growth on the south face was seen primarily on floor 81

with active fires present on both sides of the airplane strike location. Smaller isolated fires were present

on other floors around the area damaged by the airplane. These fires were relatively quiet and stationary

until just prior to the collapse. At 9:56 a.m., there was a sudden release of smoke along much of floor 80

extending from the area of the plane strike to near the western edge. During the next 2 minutes, an

intense fire developed covering approximately windows 81-441 to 81-454.



No smoke or fire was observed near the floors struck by the airplane on the west face of WTC 2. Some

smoke was apparent at windows higher on the face. This was most likely coming from windows broken

by occupants located on these floors.

Disclaimer:

Comments

From: Stefan Grossmann

A wonderful summary of the vagueness. My comments would be, not only vagueness, but plain false! Such as:
- jumpers were not scalded
- hundreds of emergency callers in the towers survived right till collapse
- thousands of people managed to flee from the towers through no fires
- computer hard drives were restored (Convar, only up to ambient 600 degrees Fahrenheit)
- dark smoke color evidences mere smolder
- kerosene (and/or jet/rocket fuel of higher temperature) used up after 10 minutes
- firemen in above 70th floor in WTC2 saw only two local fire pockets and called for water
- no highrise has before or after collapsed due to fires
- fire burned for very short time only
- a thermogram shows the outside of south tower 15 minutes after impact was 220 degree Fahrenheit,
- clear massive evidence for alternate cause: internal explosions (many details)
etc.

The "fire did it" theory is yet another government fraud, like: JFK, Vietnam, October Surprize, Iraqgate, government dope pushing, election frauds, WTC first attack, Waco, OK City, TWA800 etc.

Stefan

From: Jeff Strahl

watch America itself fail at an amazing, "free-fall" rate

You mean it's not already?  Yee-hah, better snug up my seatbelt...

"Steel tends to soften or weaken and become more like Playdough when you
> heat it up," says Sunder.
>
Another classic line.  I guess physical reality itself "becomes more like Playdough"
(or is it Al-Play-Duh?) if you heat it up enough.  And burning the civil institutions and political heritage of
a quarter-trillion people sure generates a lot of heat, if remarkably little light so far.

Pup


Actually, "the heat" was from the highly offending portions of the BCCI and
Enron transcripts, often thought to reach temperatures well in excess of
Fahrenheit 911!

Like I said; crash a jumbo into the Sears Tower (before the election) and
you can watch America itself fail at an amazing, "free-fall" rate.

Tom

> From: jeff strahl 
> Subject: Latest official line on  collapses
>
> Why The WTC Towers Collapsed
>
> GAITHERSBURG, Md., June 17, 2004
>
>
> Members of the NIST have taken tiny samples of the steel and shot them
> through an air cannon to precisely calculate the damage done by the hijacked
> jets.
>
>
> (CBS) Thick black smoke churns in poisonous clouds as the World Trade Center
> is swallowed by flames.
>
> As CBS News Correspondent Bob Orr reports, the fire, an elaborate
> re-creation of the exact spot the north tower was hit, is at the heart of a
> two-year investigation into why the twin towers fell.
>
> While the fire burns inside the lab, outside lie the skeletal remains of the
> fallen skyscrapers. Investigators, picked through tons of wreckage, matched
> scarred serial numbers and incredibly identified the exact columns struck by
> the planes.
>
> "This particular piece was struck by the upper part of the fuselage," says
> Frank Gayle, a metallurgist at the National Institute of Standards and
> Technology. "We see how the bolts performed, everything along that line."
>
> They've taken tiny samples of the steel and shot them through an air cannon
> to precisely calculate the damage done by the hijacked jets.
>
> The tests strongly suggest the airplane strikes did not bring the towers
> down. And it wasn't the thousands of gallons of jet fuel the planes carried.
>
> "The fuel itself got consumed in a matter of minutes," says Shyam Sunder,
> NIST's lead investigator in the WTC probe.
>
> So the popular belief that all of this fuel made the building collapse
> inevitable, is not true, says Sunder.
>
> To find out what why the buildings actually collapsed, scientists at the
> NIST re-created the 96th floor, complete with computers, carpets, furniture
> and paper. Then they set it on fire. Now, investigators are close to proving
> that it was this everyday office material burning in a fire fed by oxygen
> from continually breaking windows that ultimately caused the steel to give.
>
> "Steel tends to soften or weaken and become more like Playdough when you
> heat it up," says Sunder.
>
> Investigators will lay out their final report this fall. They'll issue
> sweeping recommendations aimed at making buildings better able to withstand
> catastrophic events and will call for improving evacuations with an eye
> toward surviving the unthinkable.
>
> © MMIV, CBS Broadcasting Inc. All Rights Reserved.

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