http://wtc.nist.gov/
"In response to the WTC tragedy, the National Institute of Standards and Technology conducted a 3-year building and fire safety investigation to study the factors contributing to the probable cause (or causes) of post-impact collapse of the WTC Towers (WTC 1 and 2) and WTC 7; expanded its research in areas of high-priority need such as prevention of progressive collapse, fire resistance design and retrofit of structures, and fire resistive coatings for structural steel; and is reaching out to the building and fire safety communities to pave the way for timely, expedited considerations of recommendations stemmng from the investigation." [Architecture & Building]
