On 11 September 2001, one of the largest workplace evacuations in the U.S. history took place. The evacuation was largely successful: an estimated 87% of all occupants in World Trade Center (WTC) Towers 1 and 2 exited in less than two hours. Evacuation times, however, were highly variable and not entirely explained by the engineering parameters of the buildings. To understand the complexity of factors that potentially influenced the evacuation time on 11 September, 2001, an interdisciplinary research study was conducted by public health scientists from the Mailman School of Public Health at the Columbia University in the New York City. Analysis of survey data collected from a sample of 1444 evacuees identified several facilitators and barriers to length of time to initiate and fully evacuate from WTC Towers 1 and 2. At the individual level, these included sociodemographic and occupational variables, health status, sensory cues, risk perception, delaying behaviors, and following a group or an emergent leader. At the organizational level, factors included emergency preparedness safety climate variables. Structural (environmental) factors included egress route barriers, poor signage, congestion, and communication system failures. Many factors identified in the study are modifiable. Therefore, these data have the potential to inform high-rise preparedness and response policies and procedures. Copyright © 2011 John Wiley & Sons, Ltd.