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NIST's World Trade Center Investigation: Improving the Future Safety of Buildings, Occupants, and First Responders

The collapse of New York City's World Trade Center (WTC) on Sept. 11, 2001, was the worst building disaster in recorded history, killing some 2,800 people and causing estimated insured losses in excess of $50 billion. More than 400 fire and emergency responders were among those killed, the largest loss of life for this group in a single incident.

The National Institute of Standards and Technology (NIST) is leading a building and fire safety investigation to study the structural failure and subsequent progressive collapse of several WTC buildings following the terrorist attacks. The investigation of WTC Buildings 1 and 2 (the "Twin Towers") and WTC Building 7 will focus on the building construction, the materials used, and the technical conditions that contributed to the outcome of the disaster.

The results of the investigation will serve as the 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; and improved public safety.

First-Hand Accounts

As part of the NIST investigation, interviews were conducted in person, by telephone, and through focus groups to get first-hand accounts of the events of Sept. 11, from people who were inside the WTC buildings. Over 400 people were interviewed face-to-face, including occupants near the floors of impact and in elevators or lobbies; people with disabilities who were inside the WTC buildings; first responders; and people with safety responsibilities such as floor wardens and fire safety directors. Families of the victims, who communicated with loved ones inside the Twin Towers before they collapsed, were interviewed to determine the nature of the environment above the floors of impact.

Additionally, some 800 occupants and persons with responsibilities in WTC 1 and 2 were interviewed by telephone. Finally, specific issues were investigated with six focus groups involving people from both WTC 1 and WTC 2.

Improving Evacuation Safety, Practices

In total, this effort will yield data on the role of occupant behavior and evacuation technologies and practices for tall buildings, including decision-making and situation awareness, time-constrained evacuation strategies, communications, the role of floor wardens and fire safety directors, and issues concerning people with disabilities. Additionally, NIST will seek specific observations of fire and smoke conditions and/or structural damage from within the building.

Improving Fire Service Safety, Practices

NIST built upon work done by the Fire Department of New York and McKinsey & Company in examining how the response and safety of the fire service in responding to fires in tall buildings could be improved. NIST will use the data to:

  • fully document what happened during the response by the fire services to the attacks on the World Trade Center, up to the time of collapse of WTC 7;
  • identify issues that need to be addressed in changes to practice, standards, and codes;
  • identify alternative practices and/or technologies that may address these issues; and
  • identify research and development needs that advance the safety of the fire service in responding to massive fires in tall buildings.

Additional information:

Web site:

E-mail: wtc [at] (wtc[at]nist[dot]gov)

Postal mail:

NIST World Trade Center Investigation Team

100 Bureau Drive, Stop 8610

Gaithersburg, MD 20899-8610

Created May 27, 2010, Updated March 15, 2018