1.4.2 National Institute of Standards and Technology, November 2008

2002). In May 2002, FEMA published the World Trade Center Building Performance Study (FEMA, 2002). The purpose of the study was “to examine the damage caused by the events, collect data, develop an understanding of the response of each affected building, identify causes of observed behavior, and suggest studies that should be performed.” The FEMA Report was inconclusive as to the cause of WTC 7’s collapse, but it proposed a number of scenarios for further investigation. Based on the fact that the east penthouse fell approximately 7 seconds before the rest of the building fell, the FEMA Report suggested that the collapse initiated on the east side of the building on the interior, most likely at the transfer trusses between floors 5 and 7. FEMA also suggested that there were not enough combustibles on these floors to sufficiently weaken the structural members. Thus, FEMA hypothesized that diesel fuel stored in the lower levels of the building was somehow pumped and discharged through severed pipes and this somehow fed fires for several hours. The report noted that its best hypothesis had “only a low probability of occurrence” and that further investigation was needed. NIST would later rule out the diesel fuel hypothesis.

1.4.2 National Institute of Standards and Technology, November 2008

NIST began a more in-depth investigation into the collapse of WTC 1, WTC 2, and WTC 7 in August 2002. This effort was conducted under the mandate of the National Construction Safety Team Act (NCSTA), which was signed into law on October 1, 2002. NIST put its WTC 7 investigation on hold in 2005 to focus on completing its report on the collapse of WTC 1 and WTC 2 that year. Eventually, in November 2008, NIST released its final report on WTC 7 (NIST, 2008, NCSTAR 1A). Below is a moderately detailed description of NIST’s collapse initiation hypothesis, which will be examined in the following chapters.

1.4.2.1 Floors with Fires The NIST report provides photographic evidence of fires occurring on Floors 7 to 9, 11 to 13, 19, 22, 29, and 30 (NIST, 2008, NCSTAR 1A). The report states that fires on the four upper floors (19, 22, 29, and 30) were of relatively short duration and inconsequential in terms of causing the collapse. The NIST report claims that the fire on the 12th floor in the northeast corner of the building was primarily responsible for initiating the collapse by causing heat-induced failures of the 13th floor structure.