Reports of the Federal Building and Fire
Investigation of the World Trade Center Disaster

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NIST NCSTAR 1-7: Occupant Behavior, Egress, and Emergency Communication

This report describes the occupant evacuation of World Trade Center (WTC) 1 and WTC 2 on September 11, 2001. Multiple sources of information were collected and analyzed: over 1,000 new
interviews with survivors (including 803 telephone interviews, 225 face-to-face interviews, and 5 focus groups); over 700 published interviews; 9-1-1 emergency calls; transcripts of emergency communications, historical building design drawings, memoranda, and calculations; formal complaints filed with the Occupational Safety and Health Administration; and other relevant materials. The egress system, including stairwells and elevators, was described and compared to requirement of both contemporary and current code requirements. This report documents the emergency procedures, both as they were designed to be implemented, as well as how they were actually implemented on September 11, 2001.

The population in WTC 1 and WTC 2 on September 11, 2001, at 8:46:30 a.m. was enumerated and described, where the characteristics of the population were relevant to the subsequent evacuation, including training, experience, mobility status, among others. The progress of the evacuation of both towers was described in a quasi-chronological manner from 8:46:30 a.m. when WTC 1 was attacked, until 10:28:22 a.m., when WTC 1 collapsed.

Causal models were built to explore the sources of evacuation initiation delay (why people did not immediately start to leave the building) as well as normalized stairwell evacuation time (how long the average occupant spent in the stairwells per floor). Issues identified as contributing to either speeding or aiding the evacuation process were explored. Egress simulations provided context for estimating how long WTC 1 and WTC 2 would have taken to evacuate with different populations, using different models, and subject to different damage to the building.

• NIST NCSTAR 1-7: Occupant Behavior, Egress, and Emergency Communication
  • NIST NCSTAR 1-7A:  Analysis of Published Accounts of the World Trade Center Evacuation
  • NIST NCSTAR 1-7B: Technical Documentation for Survey Administration: Questionnaires, Interviews, and Focus Groups

 

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Last updated:  November 2008