Was Column 79 the Achilles' Heel of WTC7?

[Thomas B]

In hindsight, what do you think the firefighters could have done with regards to WTC7 to have shown "greater urgency"?

A firefighter / chief who thought that uncontrolled fires generally burn themselves out, causing local collapses (floors, sections) at worst, before 2008 (the publication of the NIST report), will feel "greater urgency" about getting fires under control after 2008, since there seems to be more at stake, i.e., the total collapse of whole skyscrapers.

If firefighters had known then (on 9/11) what they know now, they might have spent those three hours (from 2:30 onwards) working very deliberately (and with great urgency) to get water to the building (from the Hudson) in hopes of avoiding further thermal expansion. Remember that in the days and weeks after 9/11 a lot of water was eventually poured on the site. So the water problem did get fixed. I'm saying they would have worked to the last second -- i.e., up to the moment of collapse -- to expedite this solution.

Obviously, they would also be very wary of actually entering the building. But some effort to avoid the complete collapse of the building (knowing that the relevant effort to be made is to reduce the temperature of the steel, i.e., get water on the fires) would surely have made sense, if they had known the mechanism that eventually brought the building down.

 

[Gamolon]

they should have developed ad-hoc "creative solutions" that would have allowed them to extinguish a burning 40-storey building with no water mains within a few hours; the fact that they didn't is attributed to them being stupid and lazy, I think?

if he can answer this question, he should apply for a job as NYPD fire chief

I mean seriously.

Taking all that Thomas B has stated in this thread and others, he thinks the following should be a result of what happened to WTC7:

1. Make sure that another source of water is available if main water lines supplying the current fire being fought are severed/debilitated for whatever reason
2. Determine whether a single point of failure is present within a building that could cause a complete collapse and then focus fire fighting efforts on that area

 

[Thomas B]

How would a firefighter determine an Achilles' Heel of a particular building during a fire?

They wouldn't, that's my point. They would only know that buildings are likely to have one. And the way you avoid it coming into play is to put out the fires. So instead of containing fires in particular sections of buildings and letting them burn out (which is one approved method), they might feel some urgency about actually extinguishing them. After all, it's now known to be possible that the fire is located around a C79-type location in the building, i.e., the Achilles heel.

 

[Gamolon]

A firefighter / chief who thought that uncontrolled fires generally burn themselves out, causing local collapses (floors, sections) at worst, before 2008 (the publication of the NIST report), will feel "greater urgency" about getting fires under control after 2008, since there seems to be more at stake, i.e., the total collapse of whole skyscrapers.

If firefighters had known then (on 9/11) what they know now, they might have spent those three hours (from 2:30 onwards) working very deliberately (and with great urgency) to get water to the building (from the Hudson) in hopes of avoiding further thermal expansion. Remember that in the days and weeks after 9/11 a lot of water was eventually poured on the site. So the water problem did get fixed. I'm saying they would have worked to the last second -- i.e., up to the moment of collapse -- to expedite this solution.

Obviously, they would also be very wary of actually entering the building. But some effort to avoid the complete collapse of the building (knowing that the relevant effort to be made is to reduce the temperature of the steel, i.e., get water on the fires) would surely have made sense, if they had known the mechanism that eventually brought the building down.

 

[Thomas B]

I mean seriously.

Taking all that Thomas B has stated in this thread and others, he thinks the following should be a result of what happened to WTC7:

1. Make sure that another source of water is available if main water lines supplying the current fire being fought are severed/debilitated for whatever reason
2. Determine whether a single point of failure is present within a building that could cause a complete collapse and then focus fire fighting efforts on that area

As I say above, 2. is not what I'm saying. I am indeed saying that after 9/11 firefighters should (and probably do) feel greater urgency about 1 when prioritizing their operations.

 

[Gamolon]

If firefighters had known then (on 9/11) what they know now, they might have spent those three hours (from 2:30 onwards) working very deliberately (and with great urgency) to get water to the building (from the Hudson) in hopes of avoiding further thermal expansion.

Avoiding thermal expansion where? Everywhere in a building? You keep bringing up single column failure causing a complete collapse and now it's just "thermal expansion" in general.

 

[Thomas B]

Avoiding thermal expansion where? Everywhere in a building? You keep bringing up single column failure causing a complete collapse and now it's just "thermal expansion" in general.

The mechanism of thermal expansion is induced by fire. So you focus on the fires, obviously. Or am I misunderstanding your question?

 

[Gamolon]

They would only know that buildings are likely to have one.

How would they know?

Or is this just going to be a general assumption that ALL BUILDINGS may possibly have a structural Achilles' Heel that may cause a total collapse if it fails?

 

[Gamolon]

The mechanism of thermal expansion is induced by fire. So you focus on the fires, obviously.

Isn't that what firefighters do now? Focus on the fires?

 

[Thomas B]

Or is this just going to be a general assumption that ALL BUILDINGS may possibly have a structural Achilles' Heel that may cause a total collapse if it fails?

The NIST report goes to some length to say that WTC7 was built entirely up to standard and performed as could be expected. So maybe buildings designed after 2008 could be counted on not to fail (though I don't think the codes have changed sufficiently yet). As the advisory board meeting I sometimes also cite suggests, 9/11 challenged some standing assumptions about "burn out" and fire protection. So, yes, I would think this is a shift in presumptions about all skyscrapers -- unless there's some way to rule it out in some cases. (Like maybe this only goes for steel-framed buildings. Etc.)

 

[Thomas B]

Isn't that what firefighters do now? Focus on the fires?

I'm not sure you've been following the discussion. They focus on the fires, after they've focused on the people they are primarily concerned about. They also sometimes (as in the case WTC7) abandon buildings and let them burn and focus on clearing the area.

 

[Gamolon]

The mechanism of thermal expansion is induced by fire. So you focus on the fires, obviously.

But you made this statement in the other thread (the potion I put in red in particular):

"Sure, but there must be a list of buildings that fire departments now must approach as at risk of total collapse if a fire starts in them. It will be important to put those fires out since there's a chance they happen to be near a "critical column". I don't think fire fighters thought they were saving skyscrapers from total collapse before 9/11. That's what I mean by "greater urgency"."

You want firefighters to know ahead of time if a building has a possible Achilles' Heel that they need to focus on.

 

[Gamolon]

I'm not sure you've been following the discussion. They focus on the fires,

Oh, I'm following the discussion all right.

See my post above.

 

[Thomas B]

You want firefighters to know ahead of time if a building has a possible Achilles' Heel that they need to focus on.

My view is that, in light of NIST's findings, the game plan for fighting fires in buildings that are similar to WTC7 is likely to have changed. What was allowed to happen under the extra-ordinary circumstances on 9/11 would, hopefully, be deliberately prevented from happening in the case of an "ordinary" office fire. There's nothing in NIST's findings to suggest that the mere ordinariness of the cause of the fire would rule out the vulnerability that ultimately explained the collapse of WTC7.

 

[Miss VocalCord]

Obviously, they would also be very wary of actually entering the building. But some effort to avoid the complete collapse of the building (knowing that the relevant effort to be made is to reduce the temperature of the steel, i.e., get water on the fires) would surely have made sense, if they had known the mechanism that eventually brought the building down.

They couldn't because they were simply lacking the materials for doing so:

They didn't have equipment, hose, standpipe kits, tools, and enough handie talkies for conducting
operations inside the building

Page 302 (346)

 

[Thomas B]

They couldn't because they were simply lacking the materials for doing so:

Page 302 (346)

Right. I'm saying they would focus on getting that equipment with somewhat greater urgency, knowing that they had a real shot at saving the building if they could get the fires out (or at least reduced) over the next few hours.

Instead, not knowing how to avoid the collapse, they focused their efforts on clearing the area, moving rescue crews off WTC1 and WTC6 (and presumably on to WTC2, which, I'm guessing was sufficiently, out of harms way should a collapse occur.)

Presumably they were already working on getting water from the Hudson. They would just have made this a greater priority if they thought they had a real shot of WTC7 not collapsing.

It's understandable that they didn't, since they didn't know what was killing the building.

 

[Gamolon]

My view is that, in light of NIST's findings, the game plan for fighting fires in buildings that are similar to WTC7 is likely to have changed.

Similar to WTC7 in what sense? That is was a building that completely collapsed due to "single column failure induced by fire".

Are you suggesting that structural engineers go through every existing building to run computer simulations to try and determine which of them could be susceptible to total collapse in this manner? All to come up with a list of these possible total collapse prone buildings for firefighters?

 

[Thomas B]

Similar to WTC7 in what sense?

There's a clue in NIST's name. Buildings are built according to standards. So firefighters approach residential and commercial buildings, skyscrapers and walk-ups, refineries and parking-garages differently, but each class of building is expected to behave in a "standard" way. Our expectations of steel-framed commercial skyscrapers that have been built "to code" changed a little as a result of 9/11.

 

[Thomas B]

By the way, I'm really interested in the pushback against this "greater urgency" remark of mine. Why is it so important to debunk the idea that 9/11 changed the way firefighters approach skyscrapers? How does it make the truthers' case stronger if NIST's report had an effect on firefighters' sense of urgency about the potential for total progressive collapse?

 

[econ41]

Let's remember that the topic if this thread is:

Was Column 79 the Achilles' Heel of WTC7?

You @Thomas B posted the OP - referencing an earlier finding by NIST that removal of Column 79 would cause global collapse.

You then asked some OP questions:
(a) Does anyone know whether NIST has said something directly about this?
(b) ... did NIST say that they had identified a particular point of vulnerability in an otherwise strong building?
(c) ...if the fires had not lingered around column 79 quite as long,...would the building still be standing?
(d) Given only uncontrolled fire in the building, what was the developing probability of global collapse after N hours?
(e) And was it simply identical to the likelihood of removing lateral support around column 79 over the height of a few floors?
(f) Also, [what explains] the relatively symmetrical nature of the collapse, i.e., that it fell more or less straight down,...?
(g) Does anyone know NIST's view on this?

@FatPhil gave what I regard as the best answer so far to the actual OP question when he responded at post #2:

One of the columns was going to be the one with the lowest safety factor. One of the kids in class is going to be the shortest. These are just truisms.

Now @FatPhil is correct that for any collapse something will fail first. It is a truism.

So what is YOUR real concern @Thomas B? Because "Achilles' Heel" sounds derogatory. It implies weakness, a fault, a flaw in the design and possible some issue of culpable negligence.

I suggest that the normal meaning of"Achilles' Heel" is derogatory. It is used to indicate a weakness that should NOT be present. BUT you seem to be using it to mean the "weakest link" that triggers failure irrespective of the level of trauma applied. Whether or not it goes beyond the intended use or "design spec" for the object. So I will continue this post using the term "Achilles' Heel" with that meaning. "Achilles' Heel" == "Weakest Link".

Let me make some bare assertions - backed by career competence is the underlying topics:

1) Column 79 was, without doubt, the Achilles' Heel (i.e. the "weak link" and trigger) of the failure of WTC7 on 9/11.
2) The 9/11 failure resulted from a gross fire situation well outside the scope of scenarios that the building was designed for.
3) Column 79 was NOT an Achilles' Heel, NOT a "weak link", in normal operating conditions for the building.
4) In my partially informed opinion Column 79 would have not been an Achilles' Heel, trigger point for failure, under fire conditions as designed for.

And, a statement of philosophy that identifies what I assert should be the frame of reference for this type of discussion:
5) Building design including fire protection aspects is an evolving field of learning. The three WTC fires and collapses were unique in several ways. As have been other high rise fires. The whole industry learns from experiences. Those experiences work their way into regulatory codes and the "prevailing design wisdom" of the industry. Some experiences from 9/11 may have "worked their way" into contemporary building management.

Too much of this debate and parallel debates on concurrent threads are forgetting the dynamics of evolutionary progress. Aspects of discussion are confused between backwards implied allocation of 'blame' and suggestions as to forward progress.

Your claims @Thomas B seem to imply hindsight allocation of blame. I see no cause for blame. I see a few issues where we here, and the industry at large, can benefit from learning. Other threads may be more appropriate for discussion of the broader topic.

@FatPhil correctly identified the truism. The next question is "Does the reality that WTC7 had a specific "Achilles' Heel" when subjected to gross trauma beyond the design envelope suggest the need for improvements in standards?" Other questions may flow from affirmative answer to that preliminary question.

And THAT debate of that question surely acts at a higher level than current discussions.

Has your OP question been answered @Thomas B

You asked "Was Column 79 the Achilles' Heel of WTC7?"

My response: "Yes - under gross trauma Col 79 was an "Achilles' Heel"

Do you want to change the topic to discuss further ramifications?

Do you agree or disagree with my summary?

 

[Thomas B]

You asked "Was Column 79 the Achilles' Heel of WTC7?"

My response: "Yes - under gross trauma Col 79 was an "Achilles' Heel"

I have a clarifying question about what you mean by "gross trauma beyond the design envelope". According to NIST, the collapse was intiated by the collapse of floor 13 at column 79 due to thermal expansion caused by fire. The fires on floors 11, 12, and 13 were first observed after 2:00 PM (see page 20-21).

https://nvlpubs.nist.gov/nistpubs/Legacy/NCSTAR/ncstar1a.pdf

Does this mean that office fires on those three floors, burning for three hours, were "beyond the design envelope" and in themselves constitute "gross trauma"?

(We're not here considering the reasons that the fires would burn that long, just that the same fires, burning for just over three hours, would bring down the building even if nothing else had happened that day to WTC1 and WTC2, etc.)

Or are you saying that other aspects of the damage done on 9/11 were necessary? And three-hour office fires on three floors 11, 12 and 13 around column 79 would not bring the building down?

If the latter, I would not say you're describing an "Achilles' Heel" in the sense I'm asking about.

As I read the report, WTC7 was vulnerable to specifically those fires, and nothing else would have been needed to bring it down. Whereas the same fires, located elsewhere in the building would be survivable -- probably easily. That's the sense in which column 79 was the Achilles Heel of the building. (It was a disproportionate point of vulnerability in an otherwise very strong building.) And it suggests that the collapse was very unfortunate, i.e., very unlikely.

I'm not assigning blame.

 

[econ41]

I have a clarifying question about what you mean by "gross trauma beyond the design envelope". According to NIST, the collapse was intiated by the collapse of floor 13 at column 79 due to thermal expansion caused by fire. The fires on floors 11, 12, and 13 were first observed after 2:00 PM (see page 20-21).

https://nvlpubs.nist.gov/nistpubs/Legacy/NCSTAR/ncstar1a.pdf

Does this mean that office fires on those three floors, burning for three hours, were "beyond the design envelope" and in themselves constitute "gross trauma"?

I am, as always, trying to help you understand the issues. And I have several times referred to "levels of vulnerability" and "Design Envelope" is fundamental. I'll try to explain further:

When designing a building the architects and engineers have a range of standard requirements to satisfy. And a lot of projector site-specific ones. Some examples include questions of floor loading - average load in pounds per sq foot and maximum point load. How many bathrooms are required for the expected population? Escape paths and capacity of stairways. Hundreds of details which @Jeffrey Orling understands far better than I - he has practised as an architect in NYC.

The "Design Envelope" factors relevant to THIS discussion include:
(a) WTC7 was a high rise steel-framed structure. Steel frames are vulnerable to fire more than other materials. A point I've identified several times.
(b) Steel framed high rise buildings are designed to a "fire rating" expressed in hours. The time needed for occupants to escape. And for "active fire fighting" operations to be started. Three hours as I understand for WTC 7.
(c) WTC 7 had sprinklers installed as part of the provision for fire-rating.
(d) Fire rating also assumes issues such as dual or multiple initiation points. Does it assume a single point of fire initiation or two? Or more? One is normal. Two may be required. I don't know what it was for WTC7. But we do know that WTC 7 floors were seen on 6-7 floors very early in the event.

So the WTC 7 fires were well in excess of what the design allowed for. You already know (i) water supply failed therefore early failure of sprinkler systems; (ii) Early identification of multiple floors on fire - details of little significance but check if you need; (iii) and - the big decision - NO active fire fighting.

So the WTC 7 fires were well outside what was designed for. Do you agree?

If you do I can continue with my explanation.

If you disagree - we should try to resolve what you don't understand.

BUT the rest of your questions and confusion cannot be resolved until we agree on the foundations AND follow legitimate explanations.

I note that you still won't answer my questions. Specifically this one: "Do you agree or disagree with my summary?"

(We're not here considering the reasons that the fires would burn that long, just that the same fires, burning for just over three hours, would bring down the building even if nothing else had happened that day to WTC1 and WTC2, etc.)

Or are you saying that other aspects of the damage done on 9/11 were necessary? And three-hour office fires on three floors 11, 12 and 13 around column 79 would not bring the building down?

No I am not trying to follow YOUR confusion. I"m trying to present you with a reasonable framework for responses to your legitimate concerns.

Please read what I posted and respond to what I said.

I'm not assigning blame.

Then stop it. Decide that we are looking forward for positive suggestions.

 

[econ41]

I would not say you're describing an "Achilles' Heel" in the sense I'm asking about.

Then stop being coy and evasive. DEFINE how you understand "Achilles' Heel"
I said "I suggest that the normal meaning of"Achilles' Heel" is derogatory. It is used to indicate a weakness that should NOT be present."
<< Meaning "A".

"BUT you seem to be using it to mean the "weakest link" that triggers failure irrespective of the level of trauma applied."
<< Meaning "B"

Which one do you want?

 

[Thomas B]

I note that you still won't answer my questions. Specifically this one: "Do you agree or disagree with my summary?"

Before agreeing or disagreeing with your summary I have to understand it. That was the purpose of my clarifying question.

It's still not clear to me what you think the design envelope was. Do you think the building was designed to survive (that is, not collapse because of) one three-story, three-hour fire? (I gather you think it might make a difference whether it has one, two, or three ignition points. Feel free to specify.) Was it designed to survive such a fire anywhere in the building? Or were certain areas (knowingly)* designed in a way that made the building more vulnerable to total collapse if the fire started there?

If there's something I might disagree with it's this:

(c) WTC 7 had sprinklers installed as part of the provision for fire-rating.

As we've discussed before (more recently here), this was taken up by the WTC7 investigation's advisory board:

Q: If fires start in a building and there is no firefighting effort, is the building expected to come down? Or would it be expected that the building would remain standing after the fires have burned out?

A: Buildings are currently designed based upon E119 test results for building components and subassemblies. [...] This would provide sufficient time for people to evacuate and for automatic sprinklers or manual firefighting efforts to control the fire. [...] The assumption is that the system as a whole will survive that exposure. The implicit assumption is that when there is a situation where the sprinklers do not function, there would be burnout of the building contents without collapse. [... But] The science has not evolved to the point of designing to meet the performance objective of burnout without collapse.

https://www.nist.gov/system/files/documents/2017/05/09/NCSTACMeetingMinutes121807.pdf

To me this suggests that the design envelope did not assume that the sprinklers would work and that the fire ratings depended on estimates of how much fuel there would be for the fires.

It seems that the "implicit assumption" that the building would survive was part of the "design envelope". But the events of 9/11 have revealed that the science needed to "evolve".

Does that seem right?

Edit: sorry, I keep changing my mind about this. I think it would have to be a known weakness if it is part the design envelope.

 

[Thomas B]

DEFINE how you understand "Achilles' Heel"

a disproportionate point of vulnerability in an otherwise very strong building.

That is, a trauma that would not cause total collapse if applied at any other point in the structure would cause collapse if applied at the "heel" (in this case column 79).

 

[Mendel]

By the way, I'm really interested in the pushback against this "greater urgency" remark of mine. Why is it so important to debunk the idea that 9/11 changed the way firefighters approach skyscrapers? How does it make the truthers' case stronger if NIST's report had an effect on firefighters' sense of urgency about the potential for total progressive collapse?

You've developed the "urgency" idea in another thread ĺ https://www.metabunk.org/threads/can-skyscrapers-fall-over-on-their-side.12394/ ) and then brought it here; it is off topic in both.

The idea that something could/should have been done to "save the building" that was not done on 9/11 aligns with the idea that there was a conspiracy aimed at destroying that building.

The idea is also insulting to the moral integrity and the firefighting expertise of the FDNY, and since it is not based on expertise (original or cited) on your part, I find it itself immoral.

To be super clear: your proposal that "urgency" was the only thing lacking at the FDNY suggests that the FDNY had the means to contain the WTC7 fire(s) but did not; it is a speculation that lacks any kind of evidence to support it, and goes against common sense.

 

[Gamolon]

It's still not clear to me what you think the design envelope was.

https://www.nist.gov/system/files/documents/2017/05/09/NCSTACMeetingMinutes121807.pdf

From page three of the document you linked previously (linked above):

A: Buildings are currently designed based upon E119 test results for building components and subassemblies. In the E119 test, components of a building are subjected to prescribed standard time-temperature exposure and a rating is assigned (e.g., 1 hour, 2 hour, etc.). If the walls, floors, and ceilings were intact before the fire and if doors are closed, the fire is presumed to be contained in the room of origin for some period of time that is roughly related to the fire ratings of these partitions. This would provide sufficient time for people to evacuate and for automatic sprinklers or manual firefighting efforts to control the fire. This containment would also limit the intensity and duration of the fire such that significant loss of strength of the fire-related structural components should not occur. The assumption is that the system as a whole will survive that exposure. The implicit assumption is that when there is a situation where the sprinklers do not function, there would be burnout of the building contents without collapse. It is not surprising that different buildings will react differently when exposed to normal building fires. Buildings designed more conservatively, such as those with more compartmentation, smaller floor spans, more massive structural elements, and greater redundancy in the structural system will perform better than a structure that has large, open floor plans with few compartments preventing the spread of the fire.

I think it would have to be a known weakness if it is part the design envelope.

Continuation of the paragraph quoted above:

The science has not evolved to the point of designing to meet the performance objective of burnout without collapse. This was a recommendation made in the final report on the Investigation of the Collapse of the WTC Towers. There was also a code change proposal to require providing for burnout without collapse that was submitted to the International Code Council (ICC) 2006/2007 code cycle but was not approved. Two proposals on burnout without collapse have been submitted for the 2007/2008 code cycle. If either of these proposals is approved, design for burnout without collapse would be built-in to all buildings, not on a case-by-case approach

This document was from 2008. This should answer your question about WTC7 being designed within the "envelope" (first paragraph) at the time it was designed and the recommended changes to design parameters after the analysis (second paragraph).

 

[Mendel]

The mechanism of thermal expansion is induced by fire. So you focus on the fires, obviously.

Isn't that what firefighters do now? Focus on the fires?

If there was a gas tank outside a burning building, the fire fighters would divert some of their effort away from fighting the fire and towards cooling that gas tank, because their priority is to keep that tank from exploding. Similarly, nearby (intact) buildings may have water applied to them to prevent the fire from propagating. Often, this is more important than to "save" a building that is a write-off already.

The fact that column 79 was not in itself critical, but merely "the weakest link", precludes a similar strategy for the WTC7 scenario: if they had used available water (which was scarce anyway, and would still have been scarce if pumped from the river) to cool some structural elements down (supposing they could have accessed them), other elements exposed to the fires would have expanded more and caused the building to fail. (That's the biggest problem with the "Achilles heel" metaphor: just because that column failed first, it wasn't the only vulnerability; but the heel was the only vulnerability for Achilles.)

So the basic decision process remains the same: every fire chief tries to recognize the time when fighting the fire becomes pointless, and shifts their focus from fighting the fire to keeping the fire from spreading elsewhere while protecting their crews and the bystanders. This shift in focus is not uncommon at all.

 

[Gamolon]

Edit: sorry, I keep changing my mind about this. I think it would have to be a known weakness if it is part the design envelope.

Honestly Thomas B?

The only thing I'm taking away from your recent statements in these threads is that you want to assign blame to someone (or multiple groups) for the complete collapse of WTC7. Whether the firefighters weren't urgent enough or didn't do enough to fight the fires or that it was a design flaw that was missed by the engineers who designed the building.

I have the impression that you think these supposed design flaws were purposely exploited to make WTC7 completely collapse.

This wreaks of conspiracy thinking in my opinion.

 

[Jeffrey Orling]

I think building a high rise over a sub station meany load transfer structures, which if compromised, could result (and did) in destruction spreading across the foot print. This was not a design flaw and the only way to make the project work. Having multiple floors collapse undermined the trusses. A single column failure without multiple floor collapses would not be fatal.

 

[Gamolon]

Edit: sorry, I keep changing my mind about this. I think it would have to be a known weakness if it is part the design envelope.

This right here is what I am talking about.

Do you think someone deliberately missed this known weakness or Achilles' Heel?

 

[Mendel]

It seems that the "implicit assumption" that the building would survive was part of the "design envelope". But the events of 9/11 have revealed that the science needed to "evolve".

The WTC7 fire exceeded the design envelope.

Not all catastrophes can/should be designed for (e.g. truck bomb).
Or do you think "science needs to evolve" after the Oklahoma City bombing?

 

[Thomas B]

I don't have time to do all your comments justice at the moment. But I'll try tomorrow. Remember that NIST identified a hitherto unknown mechanism of progressive collapse when explaining WTC7:

This study has identified thermal expansion as a new phenomenon that can cause structural collapse. For the first time we have shown that fire can induce a progressive collapse. (P. 3)

https://www.nist.gov/system/files/documents/2017/05/09/RemarksSunderAug212008briefing.pdf

This means that, while the FDNY was concerned that the building would collapse, it doesn't seem likely that they knew that it was the fires that would cause it. They appear to have thought that the building was fatally wounded by the debris from the previous collapses.

This is one reason that they felt no urgency about the fires. They thought the building was doomed for other reasons and didn't know about the "new phenomenon" of fire-induced progressive collapse.

In hindsight, however, we now know that the fires killed WTC7. As far I can tell, this new phenomenon also identified a hitherto unknown vulnerability in the building. An "Achilles' Heel".

 

[Mendel]

I don't have time to do all your comments justice at the moment. But I'll try tomorrow. Remember that NIST identified a hitherto unknown mechanism of progressive collapse when explaining WTC7:

https://www.nist.gov/system/files/documents/2017/05/09/RemarksSunderAug212008briefing.pdf

This means that, while the FDNY was concerned that the building would collapse, it doesn't seem likely that they knew that it was the fires that would cause it. They appear to have thought that the building was fatally wounded by the debris from the previous collapses.

Speculation.

This is one reason that they felt no urgency about the fires. They thought the building was doomed for other reasons and didn't know about the "new phenomenon" of fire-induced progressive collapse.

Speculation.

"Fire-induced collapse" is not a new phenomenon per se, roofs especially collapse all the time, and the size of the building perimeter that was cleared off seems suitable (and proved to be!) to accommodate collapse.

In hindsight, however, we now know that the fires killed WTC7. As far I can tell, this new phenomenon also identified a hitherto unknown vulnerability in the building. An "Achilles' Heel".

Yes.

The issue we disagree on is whether this knowledge would've made any difference in the FDNY strategy, especially since steel frame buildings don't tip over. And that's the issue that's a) off topic, b) lacks evidence = c) more speculation.

 

[econ41]

Before agreeing or disagreeing with your summary I have to understand it. That was the purpose of my clarifying question.

Which I have answered.

 

[econ41]

It's still not clear to me what you think the design envelope was.

Despite me having several times listed the key aspects. So let's drop the expression "design envelope" - I see that @Gamolon is also not clear on the simple couple of points I am trying to make so we can agree on what we are discussing. Your "cross-thread" references are not helping either.

SO:
1) The topic of this thread is YOUR OP question "Was Column 79 the Achilles' Heel of WTC7?
2) I asked you to define it - SOP you ignored my suggestions BUT offered a partial definition. We can still work on the definition when we need to.
3) The WTC 7 was:
(a) A steel-framed high rise tower with the known vulnerability of steel frames to fire;
(b) It was designed with a three hour "fire rating" to allow time for commencement of active fire fighting;
(c) The design included the provision of sprinklers;

Do you @Thomas B agree with those three factors listed as 3(a), 3(b) and 3(c)?

4) On 9/11:
(a) The sprinklers were compromised and not effective because of the failure of supply water mains.
(b) There was a deliberate decision to not undertake "active fire fighting"

Do you, @Thomas B, agree that those two statements 4(a) and 4(b) are true?

IF so do you @Thomas B accept that the fires were not fought as was planned for in the building design?

IF we agree to those base-level issues we have reached the stage where we can "draw a line" to separate "Fire was fought as per building design" from "Fire was NOT fought as per design".


And THAT much is all we need AT THIS STAGE explanation. All of your detailed objections can be addressed ONCE we agree on what we are debating.

I'll take a risk and deal with ONE of your derail attempts:

Do you think the building was designed to survive (that is, not collapse because of) one three-story, three-hour fire?

No. I have never mentioned "three-storey". I have been explicitly clear that the three hour is the time to start active fire fighting. Obviously it must presume still standing. Equally obviously it would be beyond three hours before the risk of collapse arose.

This document was from 2008. This should answer your question about WTC7 being designed within the "envelope" (first paragraph) at the time it was designed and the recommended changes to design parameters after the analysis (second paragraph).

@Gamolon - we - you and I - are using "Design Envelope" with different meanings. I use it to describe the total set of design parameters. i.e. the package or "envelope" encompassing all design parameters. The aspect you refer to is just one of those parameters. Since @Thomas B is reluctant to accept the "envelope or package of ALL design parameters" - I'll stop using the term to avoid further confusion.

 

[Thomas B]

The design included the provision of sprinklers;

Do you @Thomas B agree ... ?

If there's something I might disagree with it's this.

You sometimes seem to just re-ask quesstions that I've explicitly disagreed with, without engaging with my objections. I do not agree that the structural design of the building assumed that sprinklers would work. My understanding of the design principles is that the fire rating of the steel structure (including fire insulation) assumes that there are no functional sprinklers and no firefighting.

Also, my understanding is not that the building is expected to collapse after the rated time. Rather, the fuel is expected to be exhausted after that time, burned out.

Also, it's not the whole building, but the local components that are fire rated. That is, a building could burn for 24 hours without exceeding the design envelope as long as the fires are exhausting themselves and moving on from office to office, floor to floor. The structure heating up and cooling locally within the fire-rated time.

These are all pre-9/11 understanding of structural response to fire, of course. NIST explicitly said that the science had to "evolve" on this in light of the events of 9/11, not least the collapse of WTC7.

 

[Thomas B]

The fact that column 79 was not in itself critical, but merely "the weakest link", precludes a similar strategy for the WTC7 scenario: if they had used available water (which was scarce anyway, and would still have been scarce if pumped from the river) to cool some structural elements down (supposing they could have accessed them), other elements exposed to the fires would have expanded more and caused the building to fail.

This is very different from my understanding of NIST's collapse sequence. They do in fact describe the column as "critical" and it's not my sense that if the 13th-floor girder at C79 had not walked off then another girder somewhere else would have. (The fires in the building were not causing the whole thing to expand uniformly. The thermal expansion was local. It only caused the initiating collapse of floor 13; the subsequent progressive collapse was mechanical.) And it's not my sense that all the shear-connections between columns and floors in the building were such that, if any one of them fails, then the whole building comes down. There seems to have been something special about C79 around the 13th floor.

(That's the biggest problem with the "Achilles heel" metaphor: just because that column failed first, it wasn't the only vulnerability; but the heel was the only vulnerability for Achilles.)

We agree on the meaning of "Achilles Heel" (a uniquely vulnerable point). Your answer to the OP is no. Mine, at the moment, is yes.

 

[Miss VocalCord]

This means that, while the FDNY was concerned that the building would collapse, it doesn't seem likely that they knew that it was the fires that would cause it. They appear to have thought that the building was fatally wounded by the debris from the previous collapses.

Speculation.

It isn't complete speculation if you look at the reasons why they decided to give up any efforts on WTC7:

• The WTC 7 building had sustained damage from debris falling into it, and they were not sure
about the structural stability of the building.
• The building had large fires burning on at least six floors. Any one of these six fires would have
been considered a large incident during normal FDNY operations.
• There was no water immediately available for fighting the fires.
• They didn't have equipment, hose, standpipe kits, tools, and enough handie talkies for conducting
operations inside the building.
• The reports that WTC 7 was making loud noises as it burned indicated to them that it might be
unstable.

Page 302 (346)
So they were concerned about both the structural damage and the fires still ongoing.

 

[Thomas B]

There are few general issues in your responses that I'm not going to get into now, but which I might start separate threads on at some point. They don't really address the technical question of this thread, but they do seem to be a barrier to thinking dispassionately about it. That's interesting, but there's no need derail this thread with them. A few quick comments to see what I mean:

The idea is also insulting to the moral integrity and the firefighting expertise of the FDNY, and since it is not based on expertise (original or cited) on your part, I find it itself immoral.

The idea that it might be immoral to question a fire department's actions from a layperson's perspective is very strange to me. Like any government agency (and like any organization whatsoever) it is capable of everything from well-intentioned mistake to outright corruption. The citizens and journalists who try to hold them accountable will always be non-experts. So I simply don't share this morality of critique at all.

Also, since we're talking about the wisdom of hindsight, and an "evolving" (NIST's word) science, informed by the very events we're talking about, you seem to be saying that firefighters would find it insulting to have to learn from unprecedented events. Most of what I'm talking about (the evolving sense of "urgency" for example, but also the existence of vulnerabilities in steel-framed skyscrapers) are things that I grant the firefighters couldn't have known at the time.

Speculation.
Speculation.

This is interesting. I think of those same passages as acts of deduction. I am not, for example, "speculating" that the FDNY didn't know that fire was killing the buildings. I'm deducing it from the fact that NIST only discovered the possibility that fire could cause total progressive collapse during their investigations, which were published seven years later. They explicitly say that "for the first time" they've shown that this can happen. Since the FDNY did worry that the buildings would collapse, but couldn't have known that fire would be the reason (a "new phenomenon" that was discovered only afterwards), they must have had other reasons. The natural one to suppose they had in mind is the structural damage caused by the debris. (See also @Miss VocalCord's comment #79.)

This wreaks of conspiracy thinking in my opinion.

I raised this question too. I think a thread devoted to this would be interesting. I want to understand how identifying C79 as the Achilles Heel gives credence to the conspiracy theories. I'll think about this some more and start a thread.