NIST WTC 7 FAQ alterations revealed

Initial discovery

On NIST’s current WTC 7 FAQ page, the headline reads: (emphasis mine)

Questions and Answers about the NIST WTC 7 Investigation (Updated 09/17/2010) [1]

In order to preempt further alterations, I cached this version.[2] When I noticed the date of the update, I first tried to look for previous versions of the FAQ in the Wayback Machine.[3]

I was in for a disappointment: previous versions of the page had curiously vanished from the archive. Normally this means game over: there are no cached versions. To my knowledge, there is no alternative for the Wayback Machine. I tried to look for alternatives nonetheless.

Thankfully, I found one: Jim Hoffman had apparently cached an older version of NIST’s FAQ on his website.[4] Apparently this version dates August 21, 2008. At the top, it shows the original source link of the cached version.[5]

The wildcard search in the Wayback Machine should have matched this page, but it didn’t. Either it was never stored, there was an error in the database or somebody made a request to for removal. It’s fortunate Jim Hoffman does so much caching: a good many of his cached sources are now unavailable anywhere else.

Having been involved in software development, I know how to compare two text files to each other, showing the alterations between the two. This is part and parcel of VCS, or Version Control Systems. This post on 911blogger is an abridged version of the document I wrote on how I did it, including a list of all NIST's changes with criticisms. To read this full version, download the attached PDF. I recommend it.

NIST's alterations revealed

So, shortly after September 11th 2010, NIST, for whatever reasons, decided it should make some alterations to its FAQ. I was now ready to reveal them.

To grease the process a little bit, I decided to use the graphical diff utility “P4Merge” from the free utility “Perforce”.[6]

Here's how it looks. To the left is the old WTC 7 FAQ, to the right the new version.

Screenshot of P4Merge in action, comparing NIST FAQs

So… what changed?

Since there is a considerable time gap between Jim’s cached version from 2008 and NIST’s current version I can’t know with certainty if the changes I report here were actually made on September 17 2010 or earlier. Nevertheless, at least one of the changes must have been.

To confuse matters further, the last line claims the page was “Last updated: October 5, 2010”, conflicting with the date in the headline, and moreover was created “April 21, 2009”. The latter is unremarkable: the new extension of the new FAQ page (cfm) probably indicates some kind of web server update or migration.

Keeping all this in mind, I summarize all alterations below.

First modification

In between the questions:

Why did WTC 7 collapse, while no other known building in history has collapsed due to fires alone?


Some people have said that a failure at one column should not have produced a symmetrical fall like this one. What's your answer to those assertions?

A new segment was added:

What are the major differences between "typical" major high rise building fires that have occurred in the United States and the fire in the WTC 7 building on September 11, 2001?

There are more similarities than differences between the uncontrolled fires that burned in WTC 7 and those that occurred in the following buildings: First Interstate Bank Building (1988), One Meridian Plaza Building (1981), One New York Plaza (1970), and WTC 5[1] (2001).

The following factors describe the fire events that occurred in both WTC 7 and the referenced buildings: 1) the fuel for the fires was ordinary office combustibles at ordinary combustible load levels; 2) there was no use of accelerants; 3) the spread of fire from combustible to combustible was governed by ordinary fire physics; 4) fire-induced window breakage provided ventilation for continued fire spread and growth; 5) there were simultaneous fires on multiple floors; 6) the fires on each floor occupied a substantial portion of the floor; 7) the fires on each floor had passed the point of flashover and the structure was subjected to typical post-flashover temperatures; 8) the sprinklers were inoperative or ineffective; and 9) the fires burned for sufficient time to cause significant distortion and/or failure to the building structure.

There were some differences between the fires in WTC 7 and those in the referenced buildings, but these differences were secondary to the fire factors that led to the collapse of WTC 7: 1) Fires in high rise buildings typically have a single point of origin on a single floor, whereas the fires in WTC 7 likely had a single point of origin on multiple (10) floors; 2); fires in other high rise buildings were due to isolated events, whereas the fires in WTC 7 followed the collapse of WTC 1; 3) water was available to fight fires in the other high rise buildings, but the water supply to fight fires in WTC 7 was impaired; and 4) while the fires in the other buildings were actively fought by fire fighters to the extent possible, in WTC 7, no efforts were made to fight the fires.

The differences in the fires were not meaningful for the following reasons. By the time that WTC 7 collapsed, the fires in WTC 7 had advanced well beyond the likely points of origin on multiple floors (i.e., south and west faces) and originating points of fire origin had no bearing on the fire conditions when the building collapsed (i.e., in the northeast quadrant). Additionally, in each of the other referenced buildings, the fires burned out several floors, even with available water and fire fighting activities (except for WTC 5). Thus, whether the fire fighters fought the WTC 7 fires or not is not a meaningful point of dissimilarity from the other cited fires.

[1] WTC 5 was a nine-story building with uncontrolled fires that had complete burnout on a number of floors and partial collapse on four floors.

The last line appears to be a footnote, although it probably doesn’t appear in the format NIST had in mind. I have identified and altered the number in the citation location to superscript in brackets, and the number in the footnote itself to include brackets as well.

Second modification

NIST has changed its explanation for freefall from: (emphasis mine)

In videos, it appears that WTC 7 is descending in free fall, something that would not occur in the structural collapse that you describe. How can you ignore basic laws of physics?

WTC 7 did not enter free fall. According to NIST analysis of WTC 7 video, the building collapsed 18 stories in 5.3 seconds. If the building exhibited free fall, this process would have taken just 3.9 seconds. The actual collapse time exceeded the free fall time by 40 percent.


In a video, it appears that WTC 7 is descending in free fall, something that would not occur in the structural collapse that you describe. How can you ignore basic laws of physics?

In the draft WTC 7 report (released Aug. 21, 2008; available at, NIST stated that the north face of the building descended 18 stories (the portion of the collapse visible in the video) in 5.4 seconds, based on video analysis of the building collapse. This time period is 40 percent longer than the 3.9 seconds this process would have taken if the north face of the building had descended solely under free fall conditions. During the public comment period on the draft report, NIST was asked to confirm this time difference and define the reasons for it in greater detail.

To further clarify the descent of the north face, NIST recorded the downward displacement of a point near the center of the roofline from first movement until the north face was no longer visible in the video. Numerical analyses were conducted to calculate the velocity and acceleration of the roofline point from the time-dependent displacement data. The instant at which vertical motion of the roofline first occurred was determined by tracking the numerical value of the brightness of a pixel (a single element in the video image) at the roofline. This pixel became brighter as the roofline began to descend because the color of the pixel started to change from that of the building façade to the lighter color of the sky.

The approach taken by NIST is summarized in Section 3.6 of the final summary report, NCSTAR 1A (released Nov. 20, 2008; available at and detailed in Section 12.5.3 of NIST NCSTAR 1-9 (available at

The analyses of the video (both the estimation of the instant the roofline began to descend and the calculated velocity and acceleration of a point on the roofline) revealed three distinct stages characterizing the 5.4 seconds of collapse:

  • Stage 1 (0 to 1.75 seconds): acceleration less than that of gravity (i.e., slower than free fall).
  • Stage 2 (1.75 to 4.0 seconds): gravitational acceleration (free fall)
  • Stage 3 (4.0 to 5.4 seconds): decreased acceleration, again less than that of gravity

This analysis showed that the 40 percent longer descent time—compared to the 3.9 second free fall time—was due primarily to Stage 1, which corresponded to the buckling of the exterior columns in the lower stories of the north face. During Stage 2, the north face descended essentially in free fall, indicating negligible support from the structure below. This is consistent with the structural analysis model which showed the exterior columns buckling and losing their capacity to support the loads from the structure above. In Stage 3, the acceleration decreased as the upper portion of the north face encountered increased resistance from the collapsed structure and the debris pile below.

Third modification

In between the questions:

An emergency responder caught in the building between the 6th and 8th floors says he heard two loud booms. Isn't that evidence that there was an explosion?


Did fuel oil systems in WTC 7 contribute to its collapse?

A new segment was added:

In June 2009, NIST began releasing documents in response to a Freedom of Information Act (FOIA) request from the International Center for 9/11 Studies for "all of the photographs and videos collected, reviewed, cited or in any other way used by NIST during its investigation of the World Trade Center building collapses." One of the items released, a video obtained from NBC News , shows World Trade Center Building 7 (WTC 7) in the moments before it collapsed, then cuts to the collapse already in progress, with the building's east penthouse "disappearing" from the scene (as it had already fallen in the intervening time). Other videos of the WTC 7 collapse show the penthouse falling first, followed by the rest of the building. Did NIST edit the NBC News video to remove the collapse of the penthouse?

The video footage released under the FOIA request was copied from the original video exactly as it was received from NBC News, with video documentation of the WTC 7 east penthouse collapse missing. The footage was not edited in any way by NIST.

Fourth modification

In between the questions:

Did fuel oil systems in WTC 7 contribute to its collapse?


Why did the investigation take so long to complete?

A new segment was added:

Why did NIST model the sprayed fire resistive material (SFRM, also referred to as fireproofing) on the WTC 7 beams and columns as a “perfect” installation (i.e., without any gaps or damage in the SFRM coating), when realistically most buildings have some gaps or damage in the SFRM coating, either due to improper installation or deterioration over time?

NIST carefully considered the condition of the SFRM installation in WTC 7, including the applied thickness and evidence of gaps or damage in the SFRM. The SFRM in WTC 7 was modeled as undamaged except in the southwest region of the building where there was debris impact damage[2]. A uniform thickness equal to the specified SFRM thickness was used for the finite element thermal analyses of WTC 7 because 1) the variability in the SFRM thickness was small, 2) no evidence of significant damage to the SFRM was found, and 3) small areas of SFRM damage would not have affected the thermal or structural response of the structural framing system.

A number of factors were considered when determining the condition of the SFRM application to the WTC 7 beams and columns:

  • Available measurements of SFRM thickness from inspections made during the SFRM application showed that the SFRM as applied was consistent with the required thickness and that the variability in the applied SFRM thickness was small. (NIST NCSTAR 1-9, Table 2-2)
  • Review of photographs of WTC 7 beams and columns taken during renovations showed that the SFRM appeared uniform, and there was no evidence of spalling or gaps. (NIST NCSTAR 1-9, Figures 2-27 to 2-29.)
  • Inspection of the building at 130 Liberty Street (formerly Bankers Trust or Deutsche Bank building) found no damage to the SFRM after impact by debris from the collapse of WTC 2, except in the immediate vicinity of the debris impact. (NIST NCSTAR1-9, Section 2.5.3)
  • An analysis of the SFRM thickness for trusses in the WTC towers showed that the average measured thickness exceeded the specified thickness and that use of the specified uniform thickness in the thermal analyses accounted for the effect of variability in the SFRM thickness. (NIST NCSTAR 1-6A, Chapter 5)
  • A thermal analysis of a steel plate (e.g., modeling a beam flange) with gaps in the SFRM showed that occasional gaps in the SFRM did not significantly alter the thermal response of the structural member. (NIST NCSTAR 1-6, Chapter 2)

[2] A different set of analyses for WTC 1 and WTC 2 led to a similar approach for modeling the SFRM, i.e., the SFRM was modeled as undamaged, except for areas subjected to direct debris damage from the aircraft impact.)

Again, the last line appears to be a footnote, and I have again identified and altered the place of citation to superscript in brackets, and the number in the footnote itself to include brackets as well.

Fifth modification

NIST changed the line:

Why is NIST studying the collapse of WTC 7?


Why did NIST study the collapse of WTC 7?

Then, the following section was removed:

How can I provide comments on the report?

NIST welcomes comments on the draft report and recommendations-available online at Comments must be received by noon Eastern Daylight Time on Sept.15, 2008. Comments may be submitted via:

  • e-mail to;
  • fax to (301) 869-6275; or
  • surface mail to WTC Technical Information Repository, Attn: Stephen Cauffman, NIST, 100 Bureau Dr., Stop 8611, Gaithersburg, Md. 20899-8610.

Instructions for submitting comments are available at

And it was replaced with:

How does the final report on WTC 7 issued on Nov. 23, 2008, differ from the draft report that was released for public comment on Aug. 21, 2008?

The final report is strengthened by clarifications and supplemental text suggested by organizations and individuals worldwide in response to the draft WTC 7 report, but the revisions did not alter the investigation team’s major findings and recommendations, which include identification of fire as the primary cause for the building’s failure.

The extensive three-year scientific and technical building and fire safety investigation found that the fires on multiple floors in WTC 7, which were uncontrolled but otherwise similar to fires experienced in other tall buildings, caused an extraordinary event. Heating of floor beams and girders caused a critical support column to fail, initiating a fire-induced progressive collapse that brought the building down.

In response to comments from the building community, NIST conducted an additional computer analysis. The goal was to see if the loss of WTC 7’s Column 79—the structural component identified as the one whose failure on 9/11 started the progressive collapse—would still have led to a complete loss of the building if fire or damage from the falling debris of the nearby WTC 1 tower were not factors. The investigation team concluded that the column’s failure under any circumstance would have initiated the destructive sequence of events.

Other revisions to the final WTC 7 report included:

  • Expanding the discussion of firestopping, the material placed between floors to prevent floor-to-floor fire spread;
  • Clarifying the description of thermal expansion as it related to WTC 7’s shear studs and floor beams; and
  • Explaining in greater detail the computer modeling approach used to define where and when the fire in WTC 7 started and the extent of window breakage as a result of fire.

Sixth modification

Finally, the last line of the FAQ was altered from:

Date created: 8/21/08 | Last updated: 8/21/08 | Contact:


The National Institute of Standards and Technology (NIST) is an agency of the U.S. Commerce Department.

Privacy policy / security notice / accessibility statement / Disclaimer / Freedom of Information Act (FOIA) / No Fear Act Policy / (performance of federal programs) / NIST Information Quality Standards

Date created: April 21, 2009 | Last updated: October 5, 2010 Contact: Webmaster


Besides reactive, NIST’s communication department is increasingly proactive and preemptive. The subtle change of the plural ‘videos’ to ‘video’, in reference to footage said to demonstrate freefall acceleration may indicate that NIST is keeping tabs on ongoing technical 9/11 research.

The choice of topics altered or added reveals priorities: IC911Studies, accusations of FOIA obstruction and evidence tampering, comparative high rise fires before and on 9/11 that did not result in full collapse, fireproofing, and, of course, the freefall conundrum.

I haven’t been able to pinpoint exactly what change(s) to the FAQ were applied on September 17, but it stands to reason that NIST expects increased website hits around 9/11 each year, and that some kind of publicity for 9/11 Truth triggered a response.

[1] NIST – “Questions and Answers about the NIST WTC 7 Investigation (Updated 09/17/2010)” –
[2] WebCite – “Questions and Answers about the NIST WTC 7 Investigation (Updated 09/17/2010)” –
[3] The query used was:*/*
[4] Jim Hoffman’s mirror of the older NIST FAQ –
[5] (defunct)
[6] Perforce Downloads: The Essentials –

p4merge_screenshot_nist.png113.73 KB
NIST WTC 7 FAQ alterations revealed.pdf648.18 KB

Good work, SnowCrash --

regarding NIST's attempt to back-peddle on the observed free-fall acceleration, can you tell me whether their graph showing acceleration at g=9.8 m/s**2 for 2.25 seconds (over 100 feet of free-fall) appears in their latest report?

I don't see how they can back away from that published graph -- which is so telling regarding what really happened to WTC 7.

They aren't back-peddling there

That's just when they changed it from "WTC 7 did not enter free fall" back in '08 to "Stage 2 (1.75 to 4.0 seconds): gravitational acceleration (free fall)", shortly after Chandler called them on it. Having reviewed the FAQ recently, I'm fairly sure the other modifications are new.

Thanks Prof. Jones

Yes it's still in there.. but graphing WTC 7's movements is still ongoing:

- WTC 7 appears to fall faster than g in the beginning: possibly due to a catapult effect of the core pulling down the perimeter
- There appear to be anomalies in the building movement well before NIST acknowledges them
- The east wing of the building appears to be rotating towards CAM #3, causing perspective distortion
- Mini-jolts have been detected in the 2.25 freefall period

The research about this @ the 9/11 Forum is ongoing, and I have a feeling NIST might be watching.

This research contradicts the NIST report, but it also contradicts our own research. To what extent, is yet unclear. In some graphs I miss the expected effect of the explosion heard in the new CAM #3 video... one would think this event (which implies a causal relationship with the collapse of the Penthouse) would turn up in graphs of the building's horizontal/vertical movement.

P.S. you may want to have a look at this, too...although you might be aware of it already.

Just curious...

NIST states that WTC 7 was in free-fall for 2.25 seconds, roughly 100 feet or 8 stories. However, when I do the calculation I get 24 meters or 81 feet for a 2.25 second free fall descent. Of course, a 2.5 second drop would put it right at 100 feet and that is only one quarter of a second difference. Maybe someone here can correct me....

"This free fall drop continued for approximately 8 stories or 32.0 m (105 ft)..."


" To my knowledge, there is no alternative for the Wayback Machine."

I bet that NIST still has the older versions and that they would give then to you in a few weeks with a simple FOIA request.


point taken, but obviously I don't trust NIST... and they have earned this mistrust. (Moreover, I'm not a US citizen, I don't have any money and no legal expertise)

File a FOIA Request

"(Moreover, I'm not a US citizen, I don't have any money and no legal expertise)"

This has nothing to do with trusting NIST per se and none of these things are required.

Filing FOIA requests in the US is usually free, very simple and they are very rarely denied if the information exists (which in this case it almost certainly does):

In addition to requesting the complete history html file history of the FAQ page, you should also request "any and all" documents, papers and files specifically including email that proposes or discusses any change to the FAQ page.

Sounds reasonable

Thanks for this tip, bofors

Great work!


Well done Snowcrash!

Good work.

If we plot a graph of alterations to the WTC7 official story over time will it too have a period of freefall, I wonder !?

Blood out of Stone

Getting information out of NIST is like trying to get blood out of stone. I was perturbed that NIST had replaced their originally FAQ with the updated one. When they updated it, their original FAQ seemed to completely disappear. One would think that they would have archived it somewhere. But it is difficult to find anywhere on the Internet. Fortunately, I did save the original FAQ to a wordpad document. I posted it at my blog for my own sake in case my computer ever crashed. The most important line from their original FAQ was, "WTC 7 did not enter free fall." Shyam Sunder stated this at the briefing upon the release of their final draft report,

"The analysis showed there is a difference in time between a free fall time-a free fall time would be an object that has no structural components below it. And if you look at the analysis of the video, it shows that the time it takes for the 17-for the roof line of the video to collapse down the 17 floors that you can actually see in the video, below which you can't see anything in the video, is about 3.9 seconds. What the analysis shows...and...uh...the structural analysis shows, the collapse analysis shows that same time that it took for the structural model to come down from the roof line all the way for those 17 floors to disappear 5.4 seconds. It's...uh..., about one point...uh...five seconds or roughly 40% more time for that free fall to happen. And that is not at all unusual because 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."

This video and transcript were also removed from NIST's website. Their computer model does not show the 2.25 seconds of free fall acceleration and at no point are there no structural components beneath the roofline. Their original FAQ might have been somewhat consistent with their model(though not with reality) but their updated FAQ is not even consistent with their model. It's not surprising that they want to make this information difficult to come by.

Anyone seen This Vid?

Pre-9/11 ?
In my opinion the camera person appears to be looking for surveillance cameras, among other things.

Was wondering what others notice ?

I can make

some observations, the camera man seems to film street names and signs, and then panning up and down the same building.

If this sort of video was found in the hands of a terrorist, well.. you know. It would look like a terrorist surveillance video.

I have no idea why this video was taken or why it was included in NIST's FOIA database, but it may have helped NIST with scene orientation?

That still doesn't settle the issue 'why' though.

As for this article, I emphatically encourage people to download and read through the PDF document, specifically the section "Discussion". I gave several logical problems about WTC 7 some extensive thought, and I will be following up on those at some point. I also attempt to analyze the intentions of the NIST researchers, why they make certain comments, why they include or exclude certain things from the FAQ, et cetera. For those relatively unfamiliar with NIST's report on WTC 7, it could be considered a small primer. I owe inspiration and gratitude to the folks at The 9/11 Forum (where debunkers and truthers meet, civilly) for their scientific research and insights.