June 11, 2008
If You Can’t Take the Heat, Get Out of the Kitchen
A critical missing element in the National Institute of Standards and Technology (NIST) report on the collapse of the World Trade Center towers1 is the absence of any reference to the three-dimensional thermal conductivity properties of the structural steel network in those buildings, commonly referred to as the heat sink.2 Thermal conductivity "is the intrinsic property of a material which relates its ability to conduct [transfer] heat."3 Considering that each tower was made up of approximately 100,000 tons4 of inter-connective steel, and "steel has a high thermal conductivity",5 this neglect by NIST to analyze the towers’ heat sink properties nullifies NIST’s mission to determine why and how the towers collapsed.
Each tower edifice was a network of inter-connective steel. The perimeter walls of each tower consisted of 236 structural steel columns (59 columns per side) secured at each floor by steel spandrel plates that ran horizontally along the buildings.6 The perimeter columns and spandrel plates in the upper floors of the buildings were tempered, increasing their resistance to weakening by fire.7
The core of each tower consisted of 47 structural steel box columns8 connected to each other by large square girders and cross-braced by I-beams about two feet deep.9
Each floor assembly was a composite unit consisting of a corrugated steel pan, into which was poured four-inch thick, lightweight cast-in-place concrete,10 riveted and spot-welded to primary double trusses below (the towers also had transverse trusses that ran perpendicular to the double trusses, creating a very strong and highly interconnected egg crate-like structure11). The steel pans provided a thermal connection not only to the truss system,12 but to the perimeter walls and cores that they spanned.13
The towers were therefore part of an interconnected steel framework that would have transferred heat away from hot areas to cooler areas, the heat initially dissipating upwards through the buildings via the steel network.
An explanation of why NIST failed to carry out an examination of the towers’ heat sink properties is explainable when one delves into the empirical testing NIST performed on samples of steel from the aircraft impact area of one of the towers.
NIST examined 170 sampled areas belonging to 16 affected perimeter steel columns from WTC 1 (North Tower) to determine the temperatures reached by those steel columns.14 NIST analyzed paint cracking caused by thermal expansion on the 170 steel samples and found that of the 170 samples tested 167 came back with temperatures no greater than 250 ºC.15 The remaining three samples reached temperatures no greater than 600 ºC.16 In a May 7, 2003 progress update NIST affirmed, "NIST has nearly 250 pieces of steel recovered from the WTC site—a number adequate for the purposes of this investigation."17 However between the 2003 progress update and the 2005 Final Report Underwriters Laboratories (UL) had tested, on behalf of NIST, models of the WTC floor assemblies for the purpose of investigating the pancake hypothesis for the towers’ collapse.18
The UL results were not what NIST expected. The steel in the tests performed very well, despite experiencing heavier loads and longer burn times than in the towers.19 This was a problem for NIST, so in one swift stroke NIST contradicted its 2003 progress update where it considered "adequate" the 250 pieces of steel recovered from the WTC site by saying, "NIST did not generalize these results, since the examined columns represented only 3 percent of the perimeter columns and 1 percent of the core columns from the fire floors".20 NIST then proceeded to scrap the pancake hypothesis and moved on to a new hypothesis, this time using computer simulation models.
The empirical tests conducted by UL confirmed that the temperatures the WTC structural steel would have reached were well within the safety margins. This should not have been a surprise to NIST nor anyone else with a rudimentary grasp of the heat sink effect and a little knowledge of the weakening heat points of structural steel. With such relatively low temperatures being arrived at there was no way that NIST was going to incorporate into its reports any calculations of the towers’ heat sink capabilities. Such calculations would only confirm the low temperatures NIST found in its analysis of the 170 samples it tested.
Structural steel begins to weaken at 300ºC,21 with impending failure occurring at temperatures ranging between 538 ºC and 593 ºC.22 As was reported by NIST in their empirical analysis of the maximum temperatures found in 167 of the 170 WTC affected steel samples tested, the temperatures were determined to be no higher then 250 ºC (482 ºF), which is 50 ºC below the minimum necessary to cause any weakening in structural steel.
If indeed the fires in the towers were burning as hot as NIST claimed they were (thereby critically weakening the structural steel), then the results for the 170 area samples tested would have had dramatically different results. Instead of finding maximum temperatures no greater than 600 ºC in only three samples out of the 170 tested, with the remaining 167 samples recording maximum temperatures no greater than 250 ºC, NIST should have come up with a more realistic tally, such as three samples showing temperatures no greater than 600 ºC, with the remaining 167 samples approaching temperatures anywhere between 538 ºC and 593 ºC., the impending failure temperature range for structural steel.
2. For those who are curious on this matter, search for the following terms in the NIST 2005 Final Report cited above: "heat sink", "thermal" and "conductivity". Thermal conductivity is only discussed in reference to one-dimensional heat-flow (http://wtc.nist.gov/NISTNCSTAR1-3.pdf, p. 122-124) and SFRMs (spray-applied fire resistive materials and other fire retardant materials), nothing however about the heat sink properties of the three-dimensional, inter-connective structural steel network itself). Also see http://911research.wtc7.net/essays/nist/#conduction on NIST's failure to address the towers' heat sink properties.
4. http://wtc.nist.gov/NISTNCSTAR1CollapseofTowers.pdf, page 67.
5.Cote, A. E., editor, Fire Protection Handbook, 17th Edition, Quincy, Maine: National Fire Protection Association, 1992, p. 6-63.
8. http://wtc.nist.gov/NISTNCSTAR1-3.pdf, page 10.
10. http://wtc.nist.gov/NISTNCSTAR1CollapseofTowers.pdf, page 10.
16. The temperature at which structural steel loses half its strength. See NIST NCSTAR 1A, Final Report on the Collapse of World Trade Center Building 7 , page 54.
22. Cote, A. E., editor, Fire Protection Handbook, 17th Edition, Quincy, Maine: National Fire Protection Association, 1992, p. 6-66.