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November 22, 2004 

To: The National Construction Safety Team Advisory Committee 

NCST Advisory Committee 

 100 Bureau Drive, Stop 8610 

 Gaithersburg, MD 20899-8610 

 NCSTAC@nist.gov

From: James G. Quintiere 

RE: NIST conclusions on the WTC collapse mechanism reported on October 19, 

2004 

The October surprise in the NIST investigation was the assertion that all of the core 

column insulation was knocked off by the airplane impacts. To a lesser extent, reliance 

on NYNJPA audit insulation data solidified the NIST assertion that the failure of the core 

columns, and not the trusses, were to blame for the collapses of the South and North 

towers. That audit information was reported by NIST to have the fire floors of the north 

tower with truss insulation thicknesses as an average of 2.5 inches up to 4 inches instead 

of the prescribed 1.5 inches. 

NIST needs to produce demonstrable and clear substantive information to support this 

rationale for its conclusions. The core-damage theory was put forth by the Weidlinger 

group in the Silverstein civil suit, and I heard it expressed at a local ASME meeting over 

a year ago by a NIST staffer. Therefore, I think it is incumbent on NIST to explain when 

and how they came to this conclusion. This collapse mechanism conclusion has profound 

influence on the recommendations brought from this investigation. The airplane-caused 

column collapse theory yields significantly, and almost diametrically, opposed 

recommendations than the fire induced truss collapse mechanism. 
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NIST needs to validate its conclusion by addressing the following: 

1. The NYNJPA North tower insulation data needs to be authenticated. There is a 

long saga on the insulation coverage of the truss assemblies, and it should not end 

with an audit report that contains data that are extraordinary. The claim that up to 

4 inches of insulation was sprayed onto 1-inch diameter truss elements needs 

testimony, photographic corroboration, or other tangible evidence to establish the 

accuracy of this information. 

2. It needs to be clearly demonstrated how the core column insulation was removed. 

This cannot simply be based on an assumption or an extrapolation from impact 

calculations. It is too important to the conclusions to have modeling as the sole 

basis. Sandia has been experimenting with airplane crashes into buildings. Have 

they been consulted for supporting information or assistance? NIST needs to live 

up to the Daubert-rulling in civil case law, and demonstrate a clear methodology 

for their conclusion that the insulation was removed. 

Finally, NIST needs to clarify inconsistencies that appear in their public information to 

date. These inconsistencies and apparent weakness lead me to question their collapse 

theory, and place the collapse cause more on the lack of sufficient truss insulation. 

1. NIST metallurgical analyses show no core columns from the fire floors reached 

temperatures above 250 C. It is claimed that this information is consistent with 

computer modeling. Moreover, I was pleased to see that after many inquiries for 

microscopic analysis of the steel debris, it was done and reported in the October 

briefing. The importance of forensic evidence to document the temperatures 
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reached of the steel cannot be overlooked. First, its consistency with the 

modeling has little significance since the modeling cannot have that level of 

detailed accuracy precise fire effects around the core columns. Secondly, the core 

column theory requires that the columns got sufficiently hot, say 500 C, and 

tangible evidence from metallurgical analysis is crucial in supporting the NIST 

conclusion. Unfortunately, that evidence has not been found by NIST. Thirdly, 

as a consequence, this crucial lack of evidence must indict the selling of the WTC 

steel debris before an investigation could be launched. Will NIST speak to this as 

they now have future investigative authority? 

2. NIST computations show that floor truss assemblies can fail at temperature 

measured in the UL tests. UL fire tests showed for 1⁄2 and 3⁄4-inch insulation that 

steel truss temperatures exceeded 1300 F (704 C) in roughly 58 minutes and 62-

76 minutes, respectively. They reached average temperatures of 1110 F (593 C) 

in 66 and 66-86 minutes, respectively. My own data with Isolatek indicate that 

individual web elements can reach 593 C in about 35 to 50 minutes, respectively 

for 1⁄2 and 3⁄4 inches. NIST’s model for a single WTC truss (which is more 

accurate than the impact computations), predicts a truss would fail at the column 

connections at these temperatures. The NIST model for a single truss and its 

connection shows that the truss fails at the interior column seat connection, and 

‘walks off” the seat. This occurs at 650 C. The web diagonals begin to buckle at 

340 C, and the exterior columns bow inward at 560 C causing the truss to act as a 

catenary. Other independent work done by Usmani et al, and Burgess et al., show 
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similar results. If one floor falls on the floor below while both are heated by fire, 

can the impacted floor carry the load? Is this a plausible global collapse 

mechanism? To me, this means that truss failure is likely, at least in the South 

tower; and in the North if the PA audit data are wrong. Collapses of the floors 

were seen in both of the towers well up to 20 minutes before the buildings 

collapsed. This indicates the presence of the floor collapse mechanism. 

Incidently, the NIST scaling criterion used for the 1⁄2-scaling in the UL tests 

should be examined, as it is thermally not to scale. The shorter truss members 

will cause lower temperatures as the web transfers heat into the concrete floor. 

3. NIST has relied on state-of-the-art computer models that are at the forefront of 

their technologies. However, these models have not been proven 

comprehensively for less complex incidents than the WTC. Will NIST continue 

to invest in these modeling technologies, or are they proven and ready for general 

use? If they are ready, will NIST advocate their use in design, or will NIST 

continue to perform research to improve them? If the latter is true, will NIST 

articulate the uncertain aspects of the modeling, and comment on how they bear 

on the investigation’s conclusions? 

4. NIST has used workstations fire experiments as a basis for their modeling. The 

stated fuel load is 4 lbs/ft2 and this loading has been questioned, as it appears very 

low in the spectrum of office loadings. Because our students are conducting a 

scale model experiment of the 96th floor of the North tower, it forced us to 
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examine this loading. While we could not pursue our information in depth, I can 

relate some major concerns. NIST experimental photographs of the office 

modules show little paper, and NIST has told me that the paper load was reported 

as light. I was told by a WTC inspector that the load was heavy, storage areas 

were overloaded and floors were continually cited for having paper stacked on the 

window sills; a furniture installer of the Marsh floors gave me information that 

showed extensive file cabinets surrounding the cubicles and these were not 

included in the NIST fire experiments – he, too, said that the Marsh office spaces 

were heavy in paper; an anonymous Marsh employee said that the Marsh 

company were paper “hogs”, and a family member said it was heavy as well. The 

fuel loading is crucial to the duration and the temperatures of the fires. A light 

fuel load in the modeling will lead to low temperatures and this would affect the 

overall results. 

It is imperative that NIST get the cause of the WTC tower collapses correct. The 

legacy of its victims bears on future fire safety. The protection of buildings in fire 

and terrorists attacks will be impacted by these conclusions, so they need to be right. 

The Advisory Panel plays a clear role to sign off on these conclusions. I know of 

others that feel the NIST conclusions need, in the least, clarity, and in the main, more 

support. However, we are few in number, and it falls on you to insure the public that 

they got it right. 
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Recommendations that should come from this study are submitted in no priority 

order as suggestions for your consideration: 

1. Experimental studies to establish temperatures and fire duration characteristic of 

modern facilities including office large plan spaces, places assembly, and 

underground structures should be undertaken to validate models and establish 

design methods. The current correlations are incomplete in terms of fuel type and 

building type. 

2. The standard time-temperature structural fire tests should be examined in light of 

computational methods. Data for the tests yielding temperature and deflection 

should be integrated with computations to extrapolate to actual assemblies used in 

practice. 

3. Sensor technologies integrated with alarm monitoring for building performance 

should be integrated into the emergency response network for assessing the nature 

of the hazard. 

4. Forensic techniques and standards should be established to assess failure 

information from structural debris. The elimination of the steel structure from the 

WTC site should be fully addressed, and its consequences fully stated. 

5. Fire and disaster planning should include full and proper analyses for safe egress 

and effective response. Responders and building planners need to have the 

benefit of analyses that quantitatively address these facets. Real time modeling of 

the fire effects based on sensor information are possible and should be integrated 

into special building designs and response actions. 
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6. Novel techniques need to be investigated to rescue people and to fight high-rise 

fires. 

7. Current codes weaknesses, in light the WTC collapses, need to be fully addressed. 

Issues of lightweight construction designs that are vulnerable to catastrophic 

collapse of a structure need particular attention. 

8. A nationally supported infrastructure is needed to insure that objective scientific 

input is placed into the code consensus process to bring fire safety to a proper 

level of engineering analyses. The current code process is lacking in scientific 

underpinning, and the WTC disaster should stand for change in this direction, 

especially if the scientific community cannot render a clear and decisive verdict.