A team of scientists and engineers at the Commerce Department's National Institute of Standards and Technology (NIST) that is investigating the collapse of New York City's World Trade Center 7 (WTC 7) building expects to release its draft report for public comment by the end of the year. WTC 7 was a 47-story office building adjacent to the WTC towers (WTC 1 and 2) that collapsed following the terrorist attacks of Sept. 11, 2001. WTC 7 collapsed later that afternoon.
NIST's investigation of WTC 7 includes an extremely complex analysis that incorporates detailed information about the building's structure and construction, as well as data about fires, damage sustained from falling WTC 1 debris and other technical factors to determine its probable collapse sequence.
"We are proceeding as quickly as possible while rigorously testing and evaluating a wide range of scenarios to reach the most definitive conclusion possible," said Shyam Sunder, WTC lead investigator for NIST. "The WTC 7 investigation is in some respects just as challenging, if not more so, than the study of the towers. However, the current study does benefit greatly from the significant technological advances achieved and lessons learned from our work on the towers."
The NIST investigation team initially worked simultaneously on both the WTC towers and WTC 7 collapses. In June 2004, the team shifted to full-time study of the towers to develop needed simulation methods and other research tools and to expedite completion of the WTC towers report. Work resumed on the WTC 7 study in October 2005.
The current NIST working collapse hypothesis for WTC 7 is described in the June 2004 Progress Report on the Federal Building and Fire Safety Investigation of the World Trade Center Disaster (Volume 1, page 17, as well as Appendix L), as follows:
An initial local failure occurred at the lower floors (below floor 13) of the building due to fire and/or debris induced structural damage of a critical column (the initiating event) which supported a large span floor bay with an area of about 2,000 square feet;
Vertical progression of the initial local failure occurred up to the east penthouse, as the large floor bays were unable to redistribute the loads, bringing down the interior structure below the east penthouse; and
Horizontal progression of the failure across the lower floors (in the region of floors 5 and 7, that were much thicker than the rest of the floors), triggered by damage due to the vertical failure, resulting in a disproportionate collapse of the entire structure.
This hypothesis may be supported or modified, or new hypotheses may be developed, through the course of the continuing investigation. NIST also is considering whether hypothetical blast events could have played a role in initiating the collapse. While NIST has found no evidence of a blast or controlled demolition event, NIST would like to determine the magnitude of hypothetical blast scenarios that could have led to the structural failure of one or more critical elements.
Updated information with the specific date for the public release of the NIST team's draft report will be posted on the WTC investigation Web site, http://wtc.nist.gov.