Modeling the Evacuation of the World Trade Center Towers on September 11, 2001

Multiple evacuation models were used to simulate different WTC tower evacuations, subject to a number of assumptions. The goal of the modeling was to frame an understanding of actual evacuation findings on September 11, 2001. Simulations demonstrated that a phased evacuation (occupants of the emergency floor, the occupants on the floor above, and the occupants on the floor below were to evacuate to three floors below the emergency floor) would have taken between 4 min to complete (without delays in evacuation initiation) and 11 min to complete (with evacuation initiation delays between 0 min and 10 min). Total evacuation of a tower assuming a full occupant load would have required from 92 min to 142 min. NIST estimated that approximately 14,000 occupants would have been unable to evacuate from WTC 1 and WTC 2 on September 11, 2001 had the starting building population in each tower been 19,800, i.e., a full occupant load without visitors.