The NIST Investigation

Thus, rather than pursuing the most likely hypothesis for WTC 7’s destruction, FEMA posited a hypothesis that it found no evidence for; that involved an unprecedented cause; and that it acknowledged had “only a low probability of occurrence.”

Amid a growing sense that the FEMA Building Performance Study was insufficient for the task of conducting a full-scale investigation, NIST began planning its own investigation in October 2001 to eventually succeed FEMA’s. The NIST investigation was announced on August 21, 2002, and was scheduled to take 24 months.

Although a new agency was assuming the task of investigating the World Trade Center destruction, a number of key members of the FEMA Building Performance Study would come to have principal roles in the NIST investigation. Some of them included:

■ Therese McAllister and John Gross, who became Co-Project Leaders of the most important part of the NIST investigation,

“Structural Fire Response and Collapse

Analysis.” McAllister had been the editor of the FEMA Building Performance Study and the Chapter Leader of the report’s introduction. Gross had been a contributing author to the introduction.

■ Ronald Hamburger, whose firm was awarded the most important contract related to WTC 1 and WTC 2: a study of the thermal-structural response of the buildings to the fires. Hamburger had been the Chapter Leader of FEMA’s chapter on WTC 1 and WTC 2. As discussed above, Hamburger initially thought that “charges had been placed in the building” but apparently ruled out this hypothesis when he

learned it was not compatible with the official account. ■ Ramon Gilsanz, whose firm was awarded the most important contract related to WTC 7: the development of structural models and collapse hypotheses for WTC 7. Gilsanz had been the Chapter Leader of FEMA’s chapter on WTC 7. COMMON

MISUNDERSTANDINGS

“WTC 7 collapsed because of the diesel fuel fires.” 5 Although this was a leading hypothesis for several years, FEMA and NIST found no evidence to support it and NIST eventually ruled it out, stating, “Diesel fuel fires did not play a role in the collapse of WTC 7.” “WTC 7 collapsed because of a massive, extremely hot fire. It was a raging inferno.” 6 NIST concluded that the fires in WTC 7 were not unusual or extreme. In its final report it stated: “The fires in WTC 7 were similar to those that have occurred in several tall buildings where automatic sprinklers did not function or were not present.” The thermal expansion of beams that initiated the collapse occurred “at temperatures hundreds of degrees below those typically considered in design practice for establishing structural fire resistance ratings.”

In its final plan, released in August 2002, NIST acknowledged that fire had never caused the total collapse of a high-rise building prior to September 11, 2001. Nonetheless, it pursued its hypothesis confidently, even going so far as to declare it as fact: “The WTC Towers and WTC 7 are the only known cases of total structural collapse in high-rise buildings where fire played a role.”

NIST’s first progress report in December 2002 did not discuss hypotheses in any detail. In May 2003, it released a second progress report, which laid out three leading hypotheses for the destruction of WTC 1 and WTC 2. One was FEMA’s “pancake theory” involving the failure of floor connections. Another suggested that the floor connections held strong, which then allowed the sagging floors to pull the exterior columns inward until they buckled. This would become the main initiating mechanism in NIST’s probable collapse sequence (see Table 2). The third hypothesis posited direct fire-induced column failure. The May 2003 progress report, however, did not explore hypotheses for the destruction of WTC 7.

In June 2004, NIST released a third, much more extensive progress report containing interim findings and a working hypothesis for the destruction of WTC 1 and WTC 2 — and this time WTC 7. Although the working hypothesis for WTC 1 and WTC 2 described the overall sequence of events from airplane impact to collapse initiation in relatively clear steps, NIST did not settle on an initiating mechanism or on a location in either building where it might have occurred. In regard to WTC 7, NIST suggested that an initial local failure somewhere below Floor 13, caused by fire and/or structural damage, triggered a column failure and subsequent vertical progression of failures up to the east penthouse. The resulting damage, NIST hypothesized, set off a horizontal progression of failures across the lower floors, resulting in disproportionate collapse of the entire building.