The 9/11 Forum

no_body wrote:Hi Trippy

I think you are an obfuscater, are you really trying to shed some light on this?.

Because what you're saying merely clouds the issue.

Don't be too hasty. Trippy is merely offering plausible explanations, in this case how a large expulsion of smoke could occur and coincide with a loud sound and roughly with the onset of collapse. A partial floor collapse internally may (help) precipitate global collapse and is a means of blowing a lot of air out very quickly, probably in a turbulent fashion, which may account for part of the sound. Doesn't mean it's so, and I still don't know the particulars of the argument.

no_body wrote:Hi Trippy

I think you are an obfuscater, are you really trying to shed some light on this?.

Because what you're saying merely clouds the issue.

Humans can distinguish between near field and far field sounds, low frequencies travel further, an analogy can be made with visual experience.

This is psychoacoustics!

If you don't want to hear the loud bang as the tower begins to drop then you won't hear it!

All this stuff about gale force winds has no relevance because the distant boom coincides with the onset of the collapse, so the building has hardly moved at all.

I'll thank you to keep your unfounded adhominem attacks to yourself thankyou very much.

If you disagree with some part of my calculations, come up with something better, but petty name calling is both unwarranted and unwelcome.

David B. Benson wrote:Trippy --- The ordinary office floors in question were 12 feet = 3.6576 meters apart.

I had 13 feet in my head for some reason.

David B. Benson wrote:Also, about 40% of the core was voids for elevators, stairs, HVAC and utility shafts.

And the windows represented what percentage of each face?

Trippy wrote:And the windows represented what percentage of each face?

I think there is enough information in NIST's NCSTAR1-2A to determine that.

But in the core, note that air can escape both up and down, pressurizing both above and below and escaping through the various broken windows from floor 92 up to and including at least 104.

And by the way, the quarter inch glass breaks at about 0.5 psi.

David B. Benson wrote:

Trippy wrote:And the windows represented what percentage of each face?

I think there is enough information in NIST's NCSTAR1-2A to determine that.

At this stage, however, I lack the time to delve that deeply into it.

David B. Benson wrote:But in the core, note that air can escape both up and down, pressurizing both above and below and escaping through the various broken windows from floor 92 up to and including at least 104.

And by the way, the quarter inch glass breaks at about 0.5 psi.

The calculations I posted don't consider over-pressure, and are based on the assumption that all of the windows were previously broken by the fire - this may seem like an odd thing to assume, however i'm sure you can see how it works in favour of the conspiracy theorist, but, I do recall seeing somere testimony from FDNY officers that as well as falling bodies, falling glass presented a hazard, and glass does tend to shatter when fires are involved.

It's getting tetchy

The loud distant bang occurs before the top block has moved a foot. Bang then puffs of smoke that's the sequence.

Your calculations are therefore OT, and do nothing other than obfuscate, this is my opinion of your contribution and not an ad-hominem. My goodness do calm down .

If you'd kindly keep your comments on topic (and kindly ask DBB to do the same) then your contribution would be gratefully received. This is not about how fast air escapes from floors AFAIK.

David B. Benson wrote:But in the core, note that air can escape both up and down, pressurizing both above and below and escaping through the various broken windows from floor 92 up to and including at least 104.

And by the way, the quarter inch glass breaks at about 0.5 psi.

It occurs to me that there's a fairly straightforward way of taking this into account - simply add the perimeter available for the air to escape through the core to the perimeter of the building available for air to escape through, which will allow you to calculate a new velocity based on a new apeture size, except this time it will be the velocity of the air escaping into the core, as well as out through the windows.

no_body wrote:It's getting tetchy

As tends to happen when, without substance, you accuse someone of being fundamentally dishonest.

no_body wrote:The loud distant bang occurs before the top block has moved a foot. Bang then puffs of smoke that's the sequence.

You're assuming that the motion of the floors inside the top block is reflected by the motion of the roofline of the top block.

of course you can justify this assumption... Right?

no_body wrote:Your calculations are therefore OT, and do nothing other than obfuscate, this is my opinion of your contribution and not an ad-hominem. My goodness do calm down .

My calculations were precisely on topic as they address a point raised by you in your post, which you claim supports your hypothesis - namely the expulsion of fire and smoke.

And you didn't address my post, you addressed me, you precisely stated that I was an obfuscater, not that I was obfuscating. To accuse me of being an obfuscater is to accuse me of being a liar.

Shall I suggest that you are a liar and see how far I get?

no_body wrote:If you'd kindly keep your comments on topic (and kindly ask DBB to do the same) then your contribution would be gratefully received. This is not about how fast air escapes from floors AFAIK.

You made it about how fast the air escapes when you claimed that there was no possible explanation for the expulsion of air and smoke from the floor in question, other than controled demolition.

no_body wrote:It's getting tetchy

A bit. It's not helpful to call someone an obfuscator for suggesting a possible explanation. You'll get a lot of that here.

The loud distant bang occurs before the top block has moved a foot. Bang then puffs of smoke that's the sequence.

A partial floor collapse could occur without the top block moving. Don't know what it would sound like, and I think Trippy was not talking partial, but it is worth considering.

Your calculations are therefore OT, and do nothing other than obfuscate, this is my opinion of your contribution and not an ad-hominem. My goodness do calm down .

IF a partial floor collapse did occur at precisely the time of the bang, it could be very much on topic. However, I've contributed much to the off-topic posting and will stop. I do appreciate your assistance on the distance.

Bear in mind that the presentation of an idea does not necessitate its acceptance and argumentation is almost inevitable for anything that isn't trivial. I'm neither arguing pro or con, having still not considered the material, but rather that debate is appropriate.

no_body, how does the sound intensity of the bang compare to the ensuing collapse? I know, I could watch the video...

The ensuing collapse has more bottom end - low frequencies.
You can see it on the sonograph in the video.

Someone who obfuscates is an obfuscater.

I'm merely asking that the discussion stays on topic and is not distracted.

I would characterise the sound as explosive, short with a rapid attack, with a reverberation from the hard, surrounding city scape, a report. Not a partial floor collapse IMO, it's too loud and the steel of the perimeter would further reduce the high frequencies we'd surely get more of a dull thud with a partial floor collapse.

David B. Benson wrote:

Trippy wrote:And the windows represented what percentage of each face?

I think there is enough information in NIST's NCSTAR1-2A to determine that.

But in the core, note that air can escape both up and down, pressurizing both above and below and escaping through the various broken windows from floor 92 up to and including at least 104.

And by the way, the quarter inch glass breaks at about 0.5 psi.

FYI.
Taking into account the reduced volume, and the fact that the perimeter columns were 1'-2" in the appropriate ddirection, and the void space in the cores, yields a cross sectional area of 1,067 m^2 - both window space and core void space to escape, and gives us a flow velocity of 15.2 m/s which is still Force 7 on the Beaufort Scale.

Whole trees in motion. Effort needed to walk against the wind. Swaying of skyscrapers may be felt, especially by people on upper floors.

So I stand by what i've said regarding the expulsion of fire.

And OWE, these firgures are for full, rather than partial collapse, and represent an average value (as teh floor falls further, the volume decreases, but so does the size of the apeture the air has to escape through).

no_body wrote:The ensuing collapse has more bottom end - low frequencies.
You can see it on the sonograph in the video.

Right, as would be expected, because the high frequencies attenuate faster than the low ones, as I believe I have already mentioned, and, as you pointed out, the steel attenuates the high frequencies more than the short ones.

no_body wrote:Someone who obfuscates is an obfuscater.

This is the third time you have stated or implied that I am a liar.

no_body wrote:I'm merely asking that the discussion stays on topic and is not distracted.

[/quote]
It is, I am endeavouring to address points you yourself have raised - or are you saying that the expulsion of fire and smoke from the building is off topic and no longer relevant to your argument?

Watched the video. It's very hard for me to hear the sound in question. I'll probably need to listen many times to pick it out, so it's almost like not having watched yet at all. At least I know what's being presented.

I would characterise the sound as explosive, short with a rapid attack, with a reverberation from the hard, surrounding city scape, a report.

OK, a report is a different thing and perhaps not what would be expected from rapid expulsion, subsonic. Nevertheless, I confess I haven't distinguished a report from the ambient noise yet and that may be my so-so ears. As best I can tell, this sound occurs very near visible initiation. There are a lot of perimeter columns breaking (not buckling) around that time, breakage crosses the west wall in under a second, from the estimates I've seen. This is the sort of thing that might issue a report.

Just sayin' - not obfuscatin'!

As to partial or full, I was opting for partial because the large smoke expulsion occurs on the far side only - if we're talking about the same thing.

I fail to see how a discussion about possible (loud) internal action prior to descent is off-topic. After all, isn't that exactly the premise of the thread? Unseen loud noise at initiation? It can be argued that the characteristics of a floor collapse or perimeter breakage don't match those exhibited in the recording and that may be how it goes. But skipping straight to any conclusion is premature, isn't it?

The white rectangular object (search light?) on the NW corner begins to move simultaneously with the bang,

There is a small burst from the NW face at the corner floor 101?, which also coincides with the bang as does some black smoke explosively ejected further up floor 106?. We have multiple events and a single sound - a bang, and the building begins to fall, what happens next isn't really relevant is it?

The mast has already begun moving about a meter? (guessing) at bang time, then the first linear expulsions along the N and NW face occur more or less as the bang ends,

I hardly think it has anything to do with 'gale force winds' and 'forest fires' (IMO)

OWE
Yes it is difficult to hear through all the noise, you have to train your ear to hear it, but it is present on the sono graph.

I felt the discussion was veering into how much air was being expelled, which has nothing to do with this (IMO)
This is a single sound, do all the columns 'break, in unison? something sure does go bang tho'

Edit AFAIC it's not about finding 'smoking guns' it's about gathering evidence, so - loud report observed at the onset of the collapse.

More to follow