Karlek's Blog

NIST agrees.

At a press briefing in New York City on April 5, the National Institute of Standards and Technology
(NIST) presented its analysis of how the World Trade Center (WTC) towers collapsed after two
aircraft were flown into the buildings by terrorists on Sept. 11, 2001. The study is the most detailed
examination of a building failure ever conducted.
“Like most building collapses, these events were the result of a combination of factors,” said Shyam
Sunder, lead investigator for the agency’s building and fire safety investigation into the WTC disaster.
“While the buildings were able to withstand the initial impact of the aircraft, the resulting fires that spread
through the towers weakened support columns and floors that had fireproofing dislodged by the impacts.
This eventually led to collapse as the perimeter columns were pulled inward by the sagging floors and
buckled.”
The probable collapse sequences update and finalize hypotheses released by NIST last October. The
sequences are supported by extensive computer modeling and the evidence held by NIST, including
photographs and videos, recovered steel, eyewitness accounts and emergency communication records.
Additionally, this information was used to document a variety of factors affecting the performance of the
buildings, the efforts of emergency responders and the ability of occupants to escape prior to the collapses.
In turn, NIST has identified a number of future practices and technologies that potentially could have
enhanced building performance and life safety capabilities on 9-11 had they been available for
implementation.