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Interim Findings from NIST World Trade Center Building and Fire Safety Investigation Identify Issues with Current Standards, Codes and Practices

The Commerce Department's National Institute of Standards and Technology (NIST) today issued its second major progress report on the agency's federal building and fire safety investigation into the World Trade Center (WTC) disaster of Sept. 11, 2001. At a press briefing in New York City, lead investigator Shyam Sunder said that the NIST investigation team identified a series of issues about test methods, standards, codes and emergency operations currently used for buildings that merit further analysis as the investigation moves toward completion.

The NIST investigation's goal is to recommend improvements in the way people design, construct, maintain and use buildings, especially high-rises.

Sunder explained that the findings released today may be revised and additional findings will be included in the team's final report, scheduled for release as a draft document in December 2004. He also stated that NIST is not making any recommendations at this time. All recommendations will be made in the final report.Key findings in the second interim report are summarized in the attached fact sheet. The report includes:

  • A comprehensive summary of interim findings and accomplishments for each of the independent investigation objectives.
  • A working hypothesis for the collapse of WTC 1 and WTC 2 (the towers) that identifies the chronological sequence of major collapse events and allows for different possible load redistribution paths and damage scenarios currently under analysis. The hypothesis will be refined on the basis of these analyses to determine the most probable collapse sequence for each building.
  • A working hypothesis for the collapse of the 47-story WTC 7 based on an initiating event, a vertical progression at the east side of the building, a subsequent horizontal progression from the east to the west side of the building, and global collapse.
  • Key visual observations on the building, fire and smoke conditions in all three WTC buildings (the WTC towers and WTC 7) from analysis of a large collection of photographic and videographic images.
  • A summary of major progress in building comprehensive models for analyzing the most probable collapse sequence, from aircraft impact to collapse initiation, and simplified analytical models with results to supplement those from detailed models.
  • Results from experimental work to (1) analyze the recovered WTC structural steel, (2) support the fire dynamics and thermal modeling, and (3) conduct fire endurance testing of typical floor systems of the WTC towers based on the current standard (known as ASTM E 119).
  • Reports on the inventory and identification of the steels recovered from the WTC buildings, and on the contemporaneous (1960s era) structural steel and welding specifications used to construct the WTC towers.
  • First-person interviews of nearly 1,200 WTC occupants, first responders and families of victims to collect data on occupant behavior, evacuation and emergency response with some early results from analysis of that data.
  • A review of the New York City 9-1-1 tapes and logs and the transcripts of about 500 interviews with Fire Department of New York (FDNY) employees involved in WTC emergency response activities (the analysis of this material is still in progress).
  • Preliminary analysis of emergency responder communication tapes recorded by the Port Authority, including the high-rise radio repeater, and by the New York Police Department (NYPD), including internal department operations.
  • Analysis of building and fire codes and practices, including: a review of available documents related to the design, construction, operation, maintenance and modifications to the three WTC buildings; and a comparison of selected building regulatory and code requirements.
  • Analysis of the design, capabilities and performance of the installed active fire protection systems for all three WTC buildings (i.e., fire alarm, sprinkler, and smoke management systems) with documentation of the fire history of the WTC towers.
  • Progress on both the research and development and the dissemination and technical assistance programs related to the WTC investigation.
  • Seventeen appendices with detailed interim reports on specific technical tasks within the eight investigation projects where significant progress has been made.

The complete report, including appendices, is available on the comprehensive NIST WTC investigation Web site,

As a non-regulatory agency of the U.S. Department of Commerce's Technology Administration, NIST develops and promotes measurement, standards and technology to enhance productivity, facilitate trade and improve the quality of life.

Released June 18, 2004, Updated January 7, 2021