Government Investigates Structural Failure of WTC

Oct. 24, 2002
The federal government wants to know why three of the buildings at the World Trade Center suffered complete structural collapse on Sept. 11 and is willing to spend time and money to find out.

The Commerce Department's National Institute of Standards and Technology (NIST) is spending $16 million and 24 months to conduct a federal building and fire safety investigation examining structural failure and subsequent progressive collapse of several World Trade Center (WTC) buildings following the terrorist attacks of Sept. 11.

The study of WTC Buildings 1 and 2 ("The Twin Towers") and WTC Building 7 will focus on the building construction, the materials used and all of the technical conditions that contributed to the outcome of the WTC disaster.

NIST already has completed much of the planning work for the investigation and recent passage of an emergency supplemental appropriations bill now enables NIST to move ahead with the study.

"Many people, including technical experts, industry leaders and families of victims, have pressed for a broad-based federal investigation of the building collapses at the World Trade Center," said NIST Director Arden Bement Jr. "The lessons to be learned from this investigation and the companion research and development program are critical to understanding what core reforms are needed to make tall buildings safer nationwide, enhancing the safety of fire and emergency responders, better protecting occupants and property, and providing better emergency response capabilities and procedures for future disasters."

NIST has extensive experience and expertise in conducting disaster investigations following structural/construction failures, fires and natural disasters, including earthquakes, hurricanes and tornadoes. A fact sheet detailing this background and listing past NIST investigations is available online at

In addition to the investigation, NIST is planning to conduct two related programs concurrently:

  • A multiyear research and development program to provide the technical basis for improved building and fire codes, standards and practices; and
  • An industry-led dissemination and technical assistance program that will provide practical guidance and tools to better prepare facility owners, contractors, designers and emergency personnel to respond to future disasters.

NIST hopes the investigation will serve as a basis for:

  • Improvements in the way buildings are designed, constructed, maintained and used;
  • Improved tools and guidance for industry and safety officials;
  • Revisions to codes, standards, and practices;
  • Improved public safety.

The primary objectives of the investigation include:

  • Determine why and how WTC 1 and 2 collapsed following the initial impacts of the aircraft and why and how WTC 7 collapsed;
  • Determine why the injuries and fatalities were so high or low depending on location, including all technical aspects of fire protection, occupant behavior, evacuation and emergency response;
  • Determine what procedures and practices were used in the design, construction, operation and maintenance of WTC 1, 2 and 7;
  • Identify, as specifically as possible, areas in building and fire codes, standards and practices that are still in use and warrant revision.

The results of the investigation could stimulate major changes in both U.S. building and fire codes and in engineering practice, despite the unique design features of the buildings or circumstances under which they collapsed. The lessons derived from the investigation will be applicable to a broad range of buildings types, not just the specific buildings that are studied. The WTC Towers and WTC 7 are the only known cases of total structural collapse in high-rise buildings where fires played a significant role. These building collapses provide a unique source of information to understand the complexities associated with the dynamics of building fires and the collapse vulnerability of buildings to fires. Through the analysis of that information, the investigation will provide an excellent case study to apply and gain experience in the use of general methodologies for fire safety design and retrofit of structures.

In addition, NIST hopes to learn more about:

  • The ability of open-web steel trussed joists to withstand the thermal environment present in large fires. Joists are used in commercial and institutional buildings nationwide.
  • The behavior of fireproofing materials and the fire performance of connections used in steel structures.
  • Possible mechanisms - not considered previously - that could initiate progressive collapse in buildings as a result of fires and impact loads, and the critical role of pivotal components such as transfer girders and floor diaphragms.
  • The mechanical and metallurgical behavior of different grades of structural steel in these buildings (using steel recovered from the WTC site that is being stored at NIST).
About the Author

Sandy Smith

Sandy Smith is the former content director of EHS Today, and is currently the EHSQ content & community lead at Intelex Technologies Inc. She has written about occupational safety and health and environmental issues since 1990.

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