Discussion of the definition of unfought fires and are they considered in designing a stucture

Henkka

Member
If what you say above is true, that all skyscrapers were/are DESIGNED to survive complete burnout and not collapse, then why did they propose a code change to provide for burnout without collapse as stated below?
I'm just guessing, but I think it wouldn't make much sense to put down such a requirement in writing, since the only way to check if the building fulfils that requirement would be to set it on fire and see what happens. So instead you have requirements that can actually be checked, and an assumption that if all those requirements are fulfilled, the structure should be able to survive a complete burnout. This fire in Beijing comes to mind:

Source: https://www.youtube.com/watch?v=6hSPFL2Zlpg

Not only did this building not collapse, it didn't have to be demolished afterwards. Its opening was merely delayed by a few years. The Wiki page states:
The initial images of the blaze suggested that the tower might be nearly destroyed. However Rem Koolhaas said that "they are simply rebuilding it as it was, because there was no structural damage."
However, it also states:
The engineering firm for the building was Arup, East Asia, who designed and built the TVCC after an extensive internal study of the World Trade Center building collapses on 11 September 2001.
https://en.wikipedia.org/wiki/Beijing_Television_Cultural_Center_fire
 

Oystein

Senior Member
That's kind of worrisome. It raises the question, what lesson should the firefighting industry take from the collapses of WTC 7 and the Plasco tower? It seems like overwhelmingly, steel buildings can be relied to stand in fires. But in these two cases, you got a rather sudden, total collapse of the structure. So is the next burning steel building going to collapse or not? How long will it take? Should you risk the lives of firefighters, or just evacuate the area and let it burn?
It has been consistent experience of fire fighters for many decades that steel frames can and do collaps from fires, and that, when they fail, they collapse suddenly and quickly. I have been told this by close friends: one a structural engineer, while we were beholding the knewly done (and fire-proofed) steel structure of our local tall church spire, the other being the municipal head of building administration, discussing the effects of a fire in a cookie factory, the steel-framed roof of which had caved in.

Fire fighters therefore know what subtle signals of looming doom to watch for, in order to "pull it" in time.
Incidentally, this is what happened at WTC7: the building signalled structural instability, and fire fighters retreated. So it seems your worries have already been dealt with.
There is, potentially, increaser pressure to stay despite the risk when many lives of occupants are still in need of rescue, hence the loss of fire fighters at the Twins and Plasco.
 

Henkka

Member
There is, potentially, increaser pressure to stay despite the risk when many lives of occupants are still in need of rescue, hence the loss of fire fighters at the Twins and Plasco.
The Plasco had been evacuated, the only casualties in the fire and collapse were firefighters afaik. It apparently exhibited no "subtle signals", or the firefighters did not pick up on them.
 

Gamolon

Active Member
(b) Understanding that in the scope of these discussions of WTC collapses an "unfought fire" is simply what it says, A fire that was not fought by application of "active fire fighting" processes. However, those are defined in the relevant jurisdiction and fire agency SOPs.
So what could be considered "active fire fighting" processes? Are these considered "active" only when firefighters are physically performing them? Is a sprinkler system that was activated by a fire considered an "active fire fighting" process?
 

econ41

Senior Member
So what could be considered "active fire fighting" processes? Are these considered "active" only when firefighters are physically performing them? Is a sprinkler system that was activated by a fire considered an "active fire fighting" process?
Please read what I said and what you quoted. The topic is "...in the scope of these discussions of WTC collapses". Specifically the WTC7 collapse. Where the deliberate decision was taken to not engage in "active fire fighting" by bringing external resources into play.

I am not familiar with either the SOPs or the range of equipment available to US firefighters in New York. BUT the second critical resource I would identify after getting personnel at the firefront would be the need to get firefighting water available at that same high level. The Twin Towers were certainly too high for conventional single-stage pumping to push water to the upper levels. That is also probably true of WTC7.

This is why I stated - referring to active fire fighting operations: "However, those are defined in the relevant jurisdiction and fire agency SOPs."
In the context of this discussion, it matters not what is included in "active fire fighting response" because that response was deliberately not made.

The two critical factors for WTC7 collapse were (a) no active fire fighting (whatever that includes) and (b) no effective sprinklers ( even if you do want to "spin" them into being "active".)
 
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Oystein

Senior Member
The Plasco had been evacuated, the only casualties in the fire and collapse were firefighters afaik. It apparently exhibited no "subtle signals", or the firefighters did not pick up on them.
You're right:
https://en.wikipedia.org/wiki/Plasco_Building#Fire_and_collapse
The combined brigades had been trying to stop the fire for hours—while assuring that the building had been evacuated—when the building's north wall collapsed without warning, leading to the collapse of the rest of the building a few moments later.
...

Twenty firefighters have been reported to be killed.
Which illustrates perfectly what I said: When steel frame structures fail in fires, they do so suddenly and quickly. Since the building was evacuated, it seems indeed that the commanders of the Tehran fire department made a poor decision to keep their men in harm's way.
 

Henkka

Member
Which illustrates perfectly what I said: When steel frame structures fail in fires, they do so suddenly and quickly. Since the building was evacuated, it seems indeed that the commanders of the Tehran fire department made a poor decision to keep their men in harm's way.
How would they have known the firefighters were in harm's way though?
 

Thomas B

Active Member
When steel frame structures fail in fires, they do so suddenly and quickly. Since the building was evacuated, it seems indeed that the commanders of the Tehran fire department made a poor decision to keep their men in harm's way.
One way of defending the decision would be to say that the total collapse of a building in a city is a very dangerous thing to let happen. Even if it is now the recieved view among firefighters that steel-framed buildings can collapse completely due to fire, I doubt it is also the received view that when they collapse it happens in a safe and orderly fashion. That is, I doubt the received view is that steel framed structures may collapse suddenly and quickly and straight down without causing any trouble outside its footprint. The risk of such trouble may be considered a good reason to risk lives putting the fire out.
 

Jeffrey Orling

Senior Member
One way of defending the decision would be to say that the total collapse of a building in a city is a very dangerous thing to let happen. Even if it is now the recieved view among firefighters that steel-framed buildings can collapse completely due to fire, I doubt it is also the received view that when they collapse it happens in a safe and orderly fashion. That is, I doubt the received view is that steel framed structures may collapse suddenly and quickly and straight down without causing any trouble outside its footprint. The risk of such trouble may be considered a good reason to risk lives putting the fire out
The debris "field" depends on the size / mass if of the tower. it's unlikely that it stays inside the footprint.
 

econ41

Senior Member
How would they have known the firefighters were in harm's way though?
The incident commanders were professional firefighters.
It was a steel-framed building.
Affected by serious uncontrolled fires.

Of course, they were in harm's way. And should have been aware of that reality.

Unless they were all 9/11 "truthers" who deny the vulnerability of steel frames to fire.
 

Henkka

Member
The incident commanders were professional firefighters.
It was a steel-framed building.
Affected by serious uncontrolled fires.

Of course, they were in harm's way. And should have been aware of that reality.

Unless they were all 9/11 "truthers" who deny the vulnerability of steel frames to fire.
Um, are we going to just ignore the vast majority of steel-framed buildings that didn’t collapse in a fire? WTC 7 and the Plasco are the only ones I’m aware of.

So again, how would they have known the Plasco would behave like WTC 7, and not the vast majority that didn’t collapse?
 

econ41

Senior Member
Um, are we going to just ignore the vast majority of steel-framed buildings that didn’t collapse in a fire?
No. They are not the topic of the current discussion. You are the one doing the ignoring. Of what I have already said.

You asked:
How would they have known the firefighters were in harm's way though?
I responded clearly identifying the key relevant points:
The incident commanders were professional firefighters.
It was a steel-framed building.
Affected by serious uncontrolled fires.

Of course, they were in harm's way. And should have been aware of that reality.
As I said - they were professional firefighters who should have been aware of the risks associated with steel framed buildings. Given that Plasco was Jan 2017 - more than 16 years post 9/11 - suggests even less excuse for firefighters not being aware of the risks.

WTC 7 and the Plasco are the only ones I’m aware of.

So again, how would they have known the Plasco would behave like WTC 7, and not the vast majority that didn’t collapse?
Read what I said. They should have known the risks. The emergency managers at WTC on 9/11 certainly did recognise and act on the risks. Whether or not the Plasco Incident Managers were less competent is a separate topic.
 
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Henkka

Member
As I said - they were professional firefighters who should have been aware of the risks associated with steel framed buildings. Given that Plasco was Jan 2017 - more than 16 years post 9/11 - suggests even less excuse for firefighters not being aware of the risks.
I just don't think this makes much sense, especially considering you yourself have argued that WTC 7 collapsed largely due to the fires being unfought. The fires in the Plasco were being fought, so I don't understand how any incident commander in Tehran could have rationally deduced that the building was in imminent danger of collapse. So it appears that even when the fires are fought, steel-framed buildings can suddenly and totally collapse without warning, although this is extremely rare.

Is it your position that whenever there's "serious uncontrolled fires" in a steel-framed building, the area should just be evacuated and wait for the building to come down?
 

econ41

Senior Member
I just don't think this makes much sense,...
The assertion is: "...professional firefighters ...should have been aware of the risks associated with steel framed buildings."

Why do you disagree with that assertion? Given that it is common knowledge that firefighters are trained to fight fires in buildings constructed of different materials? (And fueled by different forms of incendiaries. And taught the types of hazards both of toxicity and incendiary types) How much basic fire fighting expertise do you want to deny?
especially considering you yourself have argued that WTC 7 collapsed largely due to the fires being unfought. The fires in the Plasco were being fought, so I don't understand how any incident commander in Tehran could have rationally deduced that the building was in imminent danger of collapse.
How do you expect any incident commander fighting a fire in 2017 to be influenced by any argument I make in 2022??
So it appears that even when the fires are fought, steel-framed buildings can suddenly and totally collapse without warning, although this is extremely rare.
Yes. That should have been an agreed starting premise.
Is it your position that whenever there's "serious uncontrolled fires" in a steel-framed building, the area should just be evacuated and wait for the building to come down?
Please stop attempting to "verbal me" AKA "put words in my mouth". My comments have been explicitly clear and focused. IF you don't understand anything I write just ask for clarification of what I wrote without meandering off into other issues.
 

econ41

Senior Member
How is

not asking for a clarification? (I ask because I have the same question.)
Please desist from tag team trolling. My comment was quite explicit and clear "ask for clarification of what I wrote". The quote mining and similar trolling tricks do become tiresome.

Remember the OP topic is: "Discussion of the definition of unfought fires and are they considered in designing a structure". And I have responded to both of those questions multiple times. In several threads despite the efforts of members to avoid the serious discussion by fragmenting the topic into multiple threads.
 

Thomas B

Active Member
I have responded to both of those questions multiple times.
But @Henkka's question was a good, clarifying yes/no question that would make it easier to understand what you're saying:
Is it your position that whenever there's "serious uncontrolled fires" in a steel-framed building, the area should just be evacuated and wait for the building to come down?
It relates directly to this question of designing for unfought fires. Can this sort of decision (fight or flight) be made on a building-to-building basis? Or is the only relevant fact that the building is steel-framed and therefore "associated" (as you put it) with a risk of collapse? How great is that risk? What actions does it imply for the firefighters?
 
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Jeffrey Orling

Senior Member
Designing for unfought fires involves knowing the "fuel load" in a building... My hunch is that the typical fuel load is not sufficient for the frame to be fatally compromised by a fire if the sprinklers stop/fail. But I suppose a floor full of file cabinets would be a source for fueling a large fire.
 

FatPhil

Senior Member.
How is

not asking for a clarification? (I ask because I have the same question.)

If your true intent was to clarify someone's position you should quote, with sufficient context, the person's expression of their position that has left you unclear. Isolate within those quotes the parts that you are unclear about, and preferably why.

It might be that no strongly held or simply definable opinion has been expressed about a particular matter in that quoted material, but if the quoted material is self-contained and coherent, then that means that there was no attempt to address that particular issue - you're not asking for clarification, you're asking a different question from whatever was being addressed by the paragraph. And in that case, it's best not to word your questions in such an adversarial way. Expand into the new topic gently, don't just throw the other person into the middle of it to see which way he orients.

In simpler terms, if you suspect a response to your question about someone's position could possibly be "what makes you think that?", then you're probably asking the wrong question.
 

Thomas B

Active Member
If your true intent was to clarify someone's position you should quote, with sufficient context, the person's expression of their position that has left you unclear. Isolate within those quotes the parts that you are unclear about, and preferably why.

It might be that no strongly held or simply definable opinion has been expressed about a particular matter in that quoted material, but if the quoted material is self-contained and coherent, then that means that there was no attempt to address that particular issue - you're not asking for clarification, you're asking a different question from whatever was being addressed by the paragraph. And in that case, it's best not to word your questions in such an adversarial way. Expand into the new topic gently, don't just throw the other person into the middle of it to see which way he orients.

In simpler terms, if you suspect a response to your question about someone's position could possibly be "what makes you think that?", then you're probably asking the wrong question.
Is this a reflection on my post (#57) or on @Henkka's (#55), which @econ41 refused to answer (#54) ... twice (#58)?
 
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deirdre

Senior Member.
Is it your position that whenever there's "serious uncontrolled fires" in a steel-framed building, the area should just be evacuated and wait for the building to come down?
if SERIOUS uncontrolled fire, then ...yes. no building is worth human life. that is what insurance is for.

(although i primarily blame the building code and building inspectors for not alerting fire departments to unsafe conditions pre fire.)
edit add: ^^this pertains to Plasco. the building was a fire nightmare before the fire even started.
 
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benthamitemetric

Senior Member
Just a suggestion: instead of bickering and speculating about the state of the art of something as widely studied and practiced as fire fighting, how about just buy a reputable textbook and see what fire fighters are being taught? I did that a few years ago and picked up Collapse of Burning Buildings, 2nd Edition: A Guide to Fireground Safety by Vincent Dunn, a respected author of many firefighting-related training books.

It should surprise no one that Mr. Dunn cites the NIST WTC7 report extensively in describing the need for fire fighters to be aware that steel buildings can collapse:

1656355458775.png

Equally unsurprisingly, however, given how rare an occurrence WTC7's collapse was, he ultimately concluded the ultimate fire fighting response should be left up to fire chiefs in each situation:
1656355592230.png


1656355646360.png

So fire fighters should know of the risk of collapse, but the scene commander will still need to make a call in each case as to whether fire fighting operations should continue. In the case of Plasco, the wrong call was made in retrospect, but that doesn't mean it was the wrong call was made ex ante. In most cases, the correct answer is going to likely be to try to fight such fires in the hopes that doing so can save lives and prevent further damage. WTC7 was a special case in that regard because it was largely evacuated before the towers collapsed, so the fires there were not likely to have been endangering anyone. That was not the case with the Plasco building.

Back to the actual topic of the thread, there is an extensive discussion in the NIST report about the fire protection systems in WTC7 and how they stemmed from the various applicable regulations. If there is anything left to actually be discussed on this topic (and I doubt it), surely all of that information alone should be sufficient for anyone to figure out the assumptions underlying the building's fire performance design. At this point I'm pretty bored with posting such low hanging fruit that has been in the public domain for around 15 years, so I'll leave it to others if they think there is actually a point to this thread.
 
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Henkka

Member
Just a suggestion: instead of bickering and speculating about the state of the art of something as widely studied and practiced as fire fighting, how about just buy a reputable textbook and see what fire fighters are being taught? I did that a few years ago and picked up Collapse of Burning Buildings, 2nd Edition: A Guide to Fireground Safety by Vincent Dunn, a respected author of many firefighting-related training books.
Thanks, that was interesting. Although, I do think it should be pointed out that the author pretty explicitly does not answer the question we've been talking about:

This information poses the question to fire chiefs, How long should firefighters remain inside a burning high rise building that may collapse? This question will be answered by tomorrow's fire chiefs.

Kinda leaves you on a cliffhanger... But I get that it's a hard question to answer. Before 9/11, something like One Meridian Plaza surely stood as an example of the worst case scenario. Absolutely devastating fire, lasting up to 19 hours, yet the building did not collapse. So based on that experience, you would think firefighters could remain as long as needed, unless there was a fire somehow far more severe than One Meridian. Then WTC 7 comes along and throws everything into uncertainty. And presumably WTC 7 could have collapsed even earlier, if the fires had gotten to the area around column 79 faster.
 

econ41

Senior Member
My thanks, @FatPhil, for your clear explanation of the current problems that @Henka and @Thomas B are exacerbating.
If your true intent was to clarify someone's position you should quote, with sufficient context, the person's expression of their position that has left you unclear. Isolate within those quotes the parts that you are unclear about, and preferably why.
EXACTLY. I made an explicit clear statement: "ask for clarification of what I wrote". @Thomas B "quote mined" by omitting the "what I wrote" in his attempt to support @Henkka's personally directed "loaded" and "off topic" question.
In simpler terms, if you suspect a response to your question about someone's position could possibly be "what makes you think that?", then you're probably asking the wrong question.
Yes.

Meanwhile, this thread raises two specific and clearly identified issues viz:

ISSUE #1: "Discussion of the definition of unfought fires..." which has been responded to. Put simply, in the context of the discussion of WTC 9/11 fires the term "unfought" should need no explanation. Building fires are resisted by protective measures built into the building. So called "passive measures". Those are augmented by external "active" fire fighting by resources brought to the site in the event of a fire. "Unfought" in that context means reliance placed on "passive" measures with no assistance from active fire fighting.

ISSUE #2: "...and are they considered in designing a structure." Which has been partially discussed - it opens a can of worms. Whilst the topic should not be excessively complex for most members discussion has not progressed. Members seem reluctant to address the overall issue hence the several threads attempting to narrow the focus to specific sub-issues. This thread a prime and the latest example.

Put as simply as I can the question of "unfought fires" has not been adequately addressed in either design or fire response. The topic of "burnout" seems to have been a presumption of wishful thinking. That a building on fire should remain standing - not collapse - until all the fuel has burned. That is not the status in the real world. Discussion has started in other threads.
 
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Thomas B

Active Member
There seem to me to be two related questions and some of you think second is off-topic while some of us don't.

1. Did/do engineers consider the possibility of unfought fires in the design of steel-framed buildings?
2. Did/do firefighters consider the design of a steel-framed building when deciding whether to fight fires in them?

("Did/do" markes the before/after of the knowledge gained from 9/11.)

Here "fighting" can be understood as putting firefighters in the way of harm as opposed to "pulling" them from the building -- as with WTC7 and, to an extent, One Meridian. And "design" can be understood in terms of specific concepts like light-weight trusses, large floor spans, transfer systems, etc. I.e., features of a building beyond the fact that it is "steel-framed".

As usual, @benthamitemetric has provided an informative source to look at, so thanks for that, but I agree with @Henkka that it doesn't actually answer our questions. It states them more clearly, perhaps.

A way of putting this question, for me, which is suggested by Dunn's question for "tomorrow's fire chiefs" is whether the possibility of total progressive collapse by a few hours of fire can be read off the design (plans) of the building quickly enough to inform the fight/pull decision.

(I don't know enough about how prepared urban fire departments are for major fires in specific buidings. Maybe they need to look at their plans for buildings that are most similar to WTC7 and rethink them?)
 

Mendel

Senior Member.
all skyscrapers are designed to survive the complete burnout of their contents. [...] The science has not evolved to the point of designing to meet the performance objective of burnout without collapse
Do you see the contradiction?

If it is impossible to design for burnout without collapse because nobody knows how, then no skyscraper can be designed to achieve this.
There is no certain way to tell from the design if that goal has been met.

There seem to me to be two related questions and some of you think second is off-topic while some of us don't.

1. Did/do engineers consider the possibility of unfought fires in the design of steel-framed buildings?
2. Did/do firefighters consider the design of a steel-framed building when deciding whether to fight fires in them?
The stated topic is "Discussion of the definition of unfought fires and are they considered in designing a stucture", and the OP talks about buildings, not about fire fighters. Your #2 is raising a different issue.

As usual, @benthamitemetric has provided an informative source to look at, so thanks for that, but I agree with @Henkka that it doesn't actually answer our questions.
It does answer your question #2. With respect to the 1991 Meridian Plaza fire, @benthamitemetric quotes Vincent Dunn:
SmartSelect_20220628-100644_Samsung Internet.jpg
The structural engineer certainly considered "the design" of the building, so that did influence the decision to stop fighting the fire. #2 is answered in the affirmative.

Dunn's textbook also teaches the fire fighters who read it to consider that a burning steel-framed building may collapse, because (see the first part of this post) they can't be guaranteed not to:
SmartSelect_20220628-101654_Samsung Internet.jpg
This ensures that fire fighters will continue to consider the design of steel-framed buildings (via experts, if need be) when making the decision to send fire crews into them.
 
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Thomas B

Active Member
Do you see the contradiction?

If it is impossible to design for burnout without collapse because nobody knows how, then no skyscraper can be designed to achieve this.
There is no certain way to tell from the design if that goal has been met.
I've said this before and I'm not sure why we keep misunderstanding each other on this. Surely, the Tacoma Narrow's bridge was "designed for" a 40 mph wind? It collapsed (under that load) because its designers didn't know enough about the effect of wind on the structure. That's not a contradiction.

Likewise, it's clear from the reading that I've done (and cited here) that engineers were confident that buildings like WTC7 would burn out in the worst-case, i.e., entirely "unfought", fire scenario but remain standing.

I don't know what the worst-case wind scenario in Puget Sound is considered to be, but there's this:
Puget Sound is sheltered compared to the Washington Coast, but it can still receive sustained winds of 60-70 mph and gusts up to 90mph.573 Local terrain has a strong effect on wind speeds. Winds speed up as they move over hills and ridges.
Content from External Source
https://www.seattle.gov/emergency-management/hazards/windstorms

I'm not sure how I can make it clearer what I mean by "designed for". Maybe we need to invoke good old Donald Rumsfeld. The possibility of a total progressive collapse due to fire -- before burnout -- was an "unknown unknown" until 9/11.
 

Henkka

Member
I'm not sure how I can make it clearer what I mean by "designed for". Maybe we need to invoke good old Donald Rumsfeld. The possibility of a total progressive collapse due to fire -- before burnout -- was an "unknown unknown" until 9/11.
That seems like a good way of putting it. About the collapse concerns regarding One Meridian, I think the concern there was that some concrete floors might collapse due to the expansion and contraction of the steel frame. It's discussed at around 3:30 in this video:

Source: https://www.youtube.com/watch?v=SiwW7rnIB5A

Reporter: At one point commissioner Ulshafer had pulled most of his men out of the building, fearing that floors number 28 and down might collapse all the way down to the 18th floor. There are still hotspots in there. Normally, they would be hosing them down, but they're holding off to prevent further structural damage.

Ulshafer: We're concerned that the cold water on the hot steel will cause further contraction and expansion and then give us a collapse. We're gonna let the building cool down normally and then probably go up there for final extinguishment some time tomorrow.

I don't think anyone at the time thought the entire building could possibly collapse. If there was such a concern, obviously the entire surrounding area should have been evacuated, just like they did with WTC 7. But this was not done, as you can also see firefighters standing around near the base of the building, for example at 1:30 in the video. So this supports your point of a total collapse due to fire being an "unknown unknown" at the time, nobody seemed to be even thinking of it at the time.

But this raises a question, though... If total collapse due to fire of a tall building was an "unknown unknown" before it happened for the first time at 5:20PM on September 11th, how was it predicted on that day?
 
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Jeffrey Orling

Senior Member
That seems like a good way of putting it. About the collapse concerns regarding One Meridian, I think the concern there was that some concrete floors might collapse due to the expansion and contraction of the steel frame. It's discussed at around 3:30 in this video:

Source: https://www.youtube.com/watch?v=SiwW7rnIB5A




I don't think anyone at the time thought the entire building could possibly collapse. If there was such a concern, obviously the entire surrounding area should have been evacuated, just like they did with WTC 7. But this was not done, as you can also see firefighters standing around near the base of the building, for example at 1:30 in the video. So this supports your point of a total collapse due to fire being an "unknown unknown" at the time, nobody seemed to be even thinking of it at the time.

But this raises a question, though... If total collapse due to fire of a tall building was an "unknown unknown" before it happened for the first time at 5:20PM on September 11th, how was it predicted on that day?
7WTC was an odd duck of a design and no garden variety high rise:
It was a 40 story tower erected of a functioning sub station and required a number truss transfers to redirect axial loads which would go right through the sub station​
it had a column free floor space outside the core​
it had an exterior moment frame supported by trusses at 27 locations for the entire perimeter​

The design was a bit of a Rube Goldberg approach... and rather that a design that isolated area structurally, the structure was all linked laterally by the transfers.... which in the end were the reason for the global collapse.
 

benthamitemetric

Senior Member
But this raises a question, though... If total collapse due to fire of a tall building was an "unknown unknown" before it happened for the first time at 5:20PM on September 11th, how was it predicted on that day?
It would all be so mysterious and steeped in necessary conspiracy except for the fact that WTC7 was the third time that fire brought down a high rise building, and the firefighters on scene had literally just watched the first and second times with their own eyes. That shouldn't be hard to understand, but, even if it were, I've already shown you that is exactly why the on-scene commander thought WTC7 could collapse. Again, here's the press release that FDNY Chief Daniel Nigro issued on September 23, 2007 ahead of the release of the NIST report:

Release date: September 23, 2007

Regarding WTC 7: The long-awaited US Government NIST (National Institute of Standards and Technology) report on the collapse of WTC 7 is due to be published at the end of this year (although it has been delayed already a few times [ adding fuel to the conspiracy theorists fires!]). That report should explain the cause and mechanics of the collapse in great detail. Early on the afternoon of September 11th 2001, following the collapse of WTC 1 & 2, I feared a collapse of WTC 7 (as did many on my staff).

The reasons are as follows:

1 - Although prior to that day high-rise structures had never collapsed, The collapse of WTC 1 & 2 showed that certain high-rise structures subjected to damage from impact and from fire will collapse.
2. The collapse of WTC 1 damaged portions of the lower floors of WTC 7.
3. WTC 7, we knew, was built on a small number of large columns providing an open Atrium on the lower levels.
4. numerous fires on many floors of WTC 7 burned without sufficient water supply to attack them.

For these reasons I made the decision (without consulting the owner, the mayor or anyone else - as ranking fire officer, that decision was my responsibility) to clear a collapse zone surrounding the building and to stop all activity within that zone. Approximately three hours after that order was given, WTC 7 collapsed.

Conspiracy theories abound and I believe firmly that all of them are without merit.

Regards, Dan Nigro
Chief of Department FDNY (retired)

(Emphases added.)
(Statement preserved here.)

Why are we having this conversation again?
 
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