The Official Account
In its Final Report on WTC 7,  issued in November 2008, NIST finally acknowledged that WTC 7 had entered into free fall for more than two seconds. NIST continued to say, however, that WTC 7 was brought down by fire, with no aid from explosives.
The Best Evidence
Scientific analysis  shows that a free-fall collapse of a steel-framed building could not be produced by fire, that is, without explosives (a fact that NIST’s lead investigator, Shyam Sunder acknowledged  in his discussions of NIST’s Draft Report for Public Comment in August 2008).
References for WTC 7 Point 3
- NIST NCSTAR 1A, Final Report on the Collapse of World Trade Center Building 7, November 2008, p. 45 (pdf: 87).
- Chandler, “WTC7: NIST Finally Admits Freefall (Part III),” January 2, 2009, at 1:19 minutes.
This analysis has been confirmed by NIST itself, in “Questions and Answers about the NIST WTC 7 Investigation,” NIST, August 2008 (originally at www.nist.gov/public_affairs/factsheet/wtc_qa_082108.html). This version of the document, which was posted at NIST’s website at the time its Draft version of its WTC 7 report was published, has been replaced by a version that was updated September 17, 2010, in which NIST continues to acknowledge a 2.25-second stage of “gravitational acceleration (free fall).”
- Sunder said: “A free fall time would be [the fall time of] an object that has no structural components below it. … The … time that it took … for those 17 floors to disappear [was roughly 40 percent longer than free fall]. And that is not at all unusual, because there was structural resistance that was provided in this particular case. And you had a sequence of structural failures that had to take place. Everything was not instantaneous” (“WTC 7 Technical Briefing,” NIST, August 26, 2008). Although NIST originally had a video and a transcript of this briefing at its Internet website, it removed both of them. However, the video is now available at Vimeo. Also available is its transcript, under the title “NIST Technical Briefing on Its Final Draft Report on WTC 7 for Public Comment.”