On Nov 6, 3:51 am, Geoff wrote:
On Mon, 05 Nov 2007 05:45:06 -0800, wrote:
On Nov 5, 5:02 am, Geoff wrote:
On Sun, 04 Nov 2007 03:31:03 -0800, wrote:

I note that you conveniently snipped out my point about the jet fuel
burning outside the building.

But unless the temperature is very high, it will not PROPAGATE, which
was most likely the case.

Sure it will, it just takes more to ignite. Given sufficient heat flux, it
will propagate. Flame spread is a series of ignitions. Given enough energy,
and oxygen, it will burn.

And given enough energy and confinement, deuterium nuclei will fuse. I
guess the point is, given enough of anything, anything's possible.

Having done a number of cone calorimeter tests on
furniture foam, including that used in aircraft (and hundreds of flame
psread and ignition tests on wood), not only does it burn, it continues to
do so after ignition. The heat flux for flame spread will vary by
orientation, but some data points I could lay my hands on quickly:
V Babrauskas and Wetterlund did a number of cone calorimeter tests and
lateral flamse spread tests in the ASTM 1321 LIFT apparatus as part of the
Surofic fire test series. Fire retardent PU foam had a minimum ignition
flux of around 3KW/m2.

ROTFL! That's 0.3 W/cm^2...that's nonsense.

Kevlar covered PU foam was better at around 13kW/m2 -
to be expected as the kevlar (or wool) retards the ignition of the
vapourising PU foam. Wool forms an insulating char layer, which is one
reason it is often used for auditorium seating. For more specific info on
furiture foam and ignition, see Chen's thesis in the University of
Canterbury.
More specifically on flame spread, babruaskas even provides nice pictures
of burning foam in the flame spread testing rig.
Babrauskas, V. Wetterlund I. Comparative data from LIFT and cone
calorimetertests on 6 products including flame flux measurements, Publ SP,
Sweden. SP report 1999:14.
If you really want to get into it, I suggest Babrauskas' book "the ignition
handbook" for some further light reading. About $200 well spent if you are
interested in the field.

I suggest you buy a basic physics book and learn about things like
power and energy; then, when you have a grasp of the basic underlying
physics, you can move along to some specific applications.

I woudl also be surprised if the furnitreu and carpets
were especially fire resistant, unless it was required by the building
code. Given the sprinkler system, there isn't much point from a fire
engineering perspective.
There is PLENTY of other fuel (beside the jet fuel) in an office - paper,

Modern offices are not loaded with paper like they were years ago. And
the paper that is there is usually inside filing cabinets etc.; it's
certainly not "readily available".

You haven't seen my desk recently (mind you, neither have I...:-)

Ok, so you may be a slob, but the point is that office buildings
generally don't have anywhere near the paper laying around that they
had 10 to 15 years ago or so.

desks, wooden fittings, panelling, softboard ceiling tiles, etc. 3) Even if there was an adequate supply of readily combustible fuel
present, 56 minutes is not enough time to develop a fire intense
enough or large enough in extent to weaken the steel enough, given the
thermal mass of steel and concrete present (every floor had hundreds
of thousands of kg of steel and over one million kg of concrete).

Sure it is. The floors were supported on relatively lightweight trusses,
whcih have a lot of expeosed area (high surface to cross section ratio)-
this means it will heat up fast.

Not a chance. Too much thermal mass there. Way too much. You can't
selectively heat what you want without heating everything else in the
vicinity, e.g., concrete. Look up the Stefan-Boltzmann law. Hot
surfaces start radiating away huge amounts of power to the
surroundings...the power scales as T^4.

a 610UB will reach 500 deg C in around 9 minutes in a "standard" fire, at
which point it has around 20% of the original strecnght.

I think for the steel used in the WTC towers the number was about 700
degrees centigrade for 80% reduction in strength.

In any case, the WTC towers had several hundred thousand kg of steel
and over a million kg of concrete per floor. Your uninformed pedantry
and hand-waving notwithstanding, in order to raise the temperature of
this kind of thermal mass to 700 degrees centigrade, you have to
release over 3E12 J of energy (and this is neglecting losses - a
ridiculously generous constraint). To release this kind of energy in
56 minutes would require a specially designed apparatus, e.g., about a
dozen blowers the size of jet engines, to feed enough air to the
fire.

Steel starts to
weaken around 300 deg C. If you want the exact figures, it will have to
wait until Monday when I am back at work.

I already looked it up. It losses about 10% at 300 degrees C. Nowhere
near enough, and it's doubtful the fire even reached that temp over
any appreciable area in the first place.

See below

More importanly for the WTC collapse was the connections of the trusses at
each end - to the central core and the vertical columns at the preimeter.
These failed (rather than the trusses) so theends failed in sear, so the
collapesed straight down - hence the pancake.

Well, IIRC, that's not what NIST is claiming. In fact they're claiming
an inferno of 1000 degrees centigrade, and that's pure nonsense.

A house fire will easily get to well over 800 deg C. Flashover is at around
600 deg C, which is when all combustibles in the room spontaneously ignite.

You've got a steel and concrete building with approximately 2E6 kg of
thermal mass per floor, little or no "readily available" fuel, and
little airflow.

You cannot reach temperatures anywhere near the 600 to 700 degree
centigrade range in 56 minutes under these conditions. You'd have to
rig up some kind of high tech blast furnace.

the head flux to the floor is around 20kW/m2 at that time. There is a well
known ad promoting fire safety showing the effect of a ciggie lighting a
sofa, curtains to flashover in a few minutes. That is a house, which has a
comparably lower fuel load than an office (circa 400MJ/m2 vs 800 MJ /m2
typical). There is no reason why the WTC would be much cooler.

The temperature of fires in buildings has been very well researched, as it
has a significant effect on the structure (duh!) and also the premature
failure of gypsum plasterboard. The initial research was started by
Margaret Law in the UK in the 1960s at BRE (IIRC), so it is nothing new. A
major early publication was from Marguesson (sp) in Sweden with a number of
real fire tests. Depending on the fuel load and openings, temperatures
ranged up to 1200 deg C.

Sorry but you won't do it in 56 minutes, at least not over any kind of
an area.

There has been significant research into fires in commercial buildings,
given the huge market and money at stake. BHP, a major Australian steel
manufacturer did a huge number of tests in the 1980s. The Building Reserch
Establishment (BRE) in the UK built a 6 story steel office tower in an old
airship hanger at Cardington for a well known series of full scale fire
tests. A couple of friends were involved in them. These tests were fully
instrumented, so the temperatures of the members and at a number of points
around the building were recorded, and much of it has been published over
the years as it formed the basis for a lot of research and verification of
theories and methods.
An office mockup test at Cardington gave an average temperature of 900 deg
and a maximum of 1200 deg C. The unprotected steel reached 813-1150 deg C,
which is PLENTY hot enough to turn it into cooked spagetti.http://guardian.150m.com/fire/small/...m(abouthalfway down the page)
I could probably get the actual test data if I asked for it.

Sorry but you won't do it in 56 minutes.

Wanna bet? Plenty of scientific evidence says otherwise. The WTC fires were
much more severe any conventional fire for a building of the type =
multiple starts, much extra fuel, no suppression, etc.



A well known accidental fire was Broadgate in the UK. It was a conventional
office building with steel framing, concrete slabs on steel beams. The
building was under construction and hadn't had the fire rating applied.. A
fire broke out in a site shed, and was enough to severely deform the beams
and columns. The building didn't collapse due to moment redistrbution of
the load, thanks to the design of the building, with welded and pinned
joints and multiple columns. The WTC was different, with the central core
and perimeter columns, it relied on the connections at each end of the
trusses. When either the connections failed, or the trusses twisted so the
load was no longer correctly supported, it was all over.
The temperature was estimated to be around 1100 deg C for the Broadgate
fire.
More info on real fires and temperatures at:http://www.modernsteel.com/Uploads/I...7_01_fire.pdfh......
I suggest Andy Buchanan's fine bookhttp://www.amazon.com/Structural-Design-Safety-Andrew-Buchanan/dp/047...

A key difference between the WTC and natural fires was the development of
the fire. In a normal fire, it will start at a single point of ignition -
say an overheated computer, and spread through the floor as neighboring
items ignite until

...

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It is impossible to debate with an insane fanatic who thinks the green
men did it.