FIRE AND MATERIALS Fire Mater. (2011) Published online in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/fam.1080 The World Trade Center evacuation study: Factors associated with initiation and length of time for evacuation Robyn R. M. Gershon 1, ∗, †, ‡ , Lori A. Magda 1,§ , Halley E. M. Riley 1,¶ and Martin F. Sherman 2,‡ 1 Mailman School of Public Health, Columbia University, 722 West 168th Street, Room 938, New York, NY 10032, U.S.A. 2 Department of Psychology, Loyola University Maryland, Baltimore, MD, U.S.A. SUMMARY 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. Received 24 August 2010; Accepted 19 October 2010 KEY WORDS: high-rise evacuation; evacuation time; emergency preparedness; pre-evacuation delay; organizational safety climate INTRODUCTION The magnitude and severity of 11 September 2001 attack resulted in the need to effect a rapid and full evacuation of the World Trade Center (WTC) complex, including the two super skyscrapers, WTC Towers 1 and 2. The process is considered to have been successful, with a large majority of occupants below the point of impact able to evacuate [1]. Both structural and organizational changes that were made in the aftermath of the 1993 WTC bombing facilitated a more timely egress in 2001. ∗ Correspondence to: R. R. M. Gershon, Mailman School of Public Health, Columbia University, 722 West 168th Street, New York, NY 10032, U.S.A. † E-mail: rg405@columbia.edu ‡ Professor. § Data Manager. ¶ Project Coordinator. Copyright  2011 John Wiley & Sons, Ltd.