Proceedings of the 11 th International Fire Science & Engineering Conference, Interflam 2007, 3-5 th September 2007, Royal Holloway College, University of London, UK, Volume 2, pp. 1435-1442. ISBN 978 0 9541216-9-3, 2007. INVESTIGATING THE IMPACT OF OCCUPANT RESPONSE TIME ON COMPUTER SIMULATIONS OF THE WTC NORTH TOWER EVACUATION Galea, E.R., Sharp, G, Lawrence P.J., and Dixon A. Fire Safety Engineering Group The University of Greenwich London SE10 9LS, UK http://fseg.gre.ac.uk/ ABSTRACT This work explores the impact of response time distributions on high-rise building evacuation. The analysis utilises response times extracted from printed accounts and interviews of evacuees from the WTC North Tower evacuation of 11 September 2001. Evacuation simulations produced using these “real” response time distributions are compared with simulations produced using instant and engineering response time distributions. Results suggest that while typical engineering approximations to the response time distribution may produce reasonable evacuation times for up to 90% of the building population, using this approach may underestimate total evacuation times by as much as 61%. These observations are applicable to situations involving large high-rise buildings in which travel times are generally expected to be greater than response times. INTRODUCTION The evacuation of the World Trade Centre (WTC) towers [1] is of fundamental importance to the future design of high-rise buildings. The attack on the WTC towers brought home to the world the importance of providing adequate and robust means of evacuation in high-rise buildings. In this paper we explore the impact of occupant response time on the evacuation of the North Tower of the World Trade Centre (WTC1). In an earlier study [2], the buildingEXODUS evacuation model [3,4] was used to investigate the evacuation of WTC1. This analysis made use of a generalised response time distribution based on data derived from a study of published accounts of WTC survivors [5,6]. NIST have also investigated certain aspects of the WTC investigation using a variety of evacuation modelling tools [1]. The simulations undertaken by NIST utilised an instant response time distribution and so did not accurately represent the initial movements and potentially the subsequent evacuation evolution. In a more recent paper [7], the authors returned to their earlier WTC1 simulations using more reliable data than was available at the time of the original analysis. This involved more accurate information relating to the building geometry, building population size and fire fighter performance capabilities. The paper explores several ‘what-if’ scenarios centred on the tragedy including what would have happened had the building been fully occupied at the time of the attack and what would have happened had a single staircase survived linking those above the impact zone with the ground. The paper also used the WTC evacuation scenario to explore generic issues associated with the practical limits of building size that can be expected to be efficiently evacuated using stairs alone. In this paper we return to the previous simulations of the evacuation of WTC1 using an improved set of occupant response. THE EVENT