NIST report contradicts itself on the 'high temperatures' present. Let's take a look at their mess (NIST's report is in quoted text, the critique is in bold)
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Imagined Heat
The Report repeatedly makes claims that amazingly high fire temperatures were extant in the Towers, without any evidence. The Report itself contains evidence contradicting the claims.
"Observations of paint cracking due to thermal expansion. Of the more than 170 areas examined on 16 perimeter column panels, only three columns had evidence that the steel reached temperatures above 250 ºC: east face, floor 98, inner web; east face, floor 92, inner web; and north face, floor 98, floor truss connector. Only two core column specimens had sufficient paint remaining to make such an analysis, and their temperatures did not reach 250 ºC. ... Using metallographic analysis, NIST determined that there was no evidence that any of the samples had reached temperatures above 600 ºC. (p 90/140) "
The highest temperatures estimated for the samples was 250 ºC (482 ºF). That's consistent with the results of fire tests in uninsulated steel-framed parking garages, which showed maximum steel temperatures of 360 ºC (680 ºF). How interesting then, that NIST's sagging truss model has the truss heated to 700 ºC (1292 ºF).
"A floor section was modeled to investigate failure modes and sequences of failures under combined gravity and thermal loads. The floor section was heated to 700 ºC (with a linear thermal gradient through the slab thickness from 700 ºC to 300 ºC at the top surface of the slab) over a period of 30 min. Initially the thermal expansion of the floor pushed the columns outward, but with increased temperatures, the floor sagged and the columns were pulled inward. (p 98/148) "
Where does NIST get the idea that steel temperatures should be more than 450 degrees Celsius (or 842 degrees Fahrenheit) higher than their own evidence indicates? This passage provides some insight into their experimental method.
"A spray burner generating 1.9 MW or 3.4 MW of power was ignited in a 23 ft by 11.8 ft by 12.5 ft high compartment. The temperatures near the ceiling approached 900 ºC. (p 123/173)"
1.9 to 3.4 MW (megawatts) is the heat output of about 500 wood stoves -- that in a living-room-sized space!
"The jet fuel greatly accelerated the fire growth. Only about 60 percent of the combustible mass of the rubblized workstations was consumed. The near-ceiling temperatures varied between 800 ºC and 1,100 ºC. (p 125-6/175-6) "
Temperatures of 800 ºC to 1,100 ºC (1472 ºF to 2012 ºF) are normally observed only for brief times in building fires, in a phenomenon known as flashover. Flashover occurs when uncombusted gases accumulate near the ceilings and then suddenly ignite. Since flame consumes the pre-heated fuel-air mixture in an instant, very high temperatures are produced for a few seconds. Note that this temperature range includes the 900 ºC recorded using the megawatt super-burner, so they must have had to pour on quite a lot of jet fuel.
The first section of the Report describing the fires deceptively implies that 1,000 ºC (1832 ºF) temperatures (rarely seen in even momentary flashovers) were sustained, and that they were in the building's core.
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The article goes on, complete with some good graphics. You might want to take a look:
http://911research.wtc7.net/essays/nist/index.html
