Seven years after 9/11, the world continues to remember the terrorist attacks on the World Trade Center -- and learn from them. Based on an analysis of what happened, researchers from the Universities of Greenwich, Ulster and Liverpool have produced a thesis on high-rise evacuations in emergencies. The study that took three-and-a-half years to complete will be available to experts and emergency operations leaders in the future. It will, its authors believe, improve safety in high-rise buildings worldwide.

Interviews with 271 survivors generated 6,000 pages of first hand accounts of what it was like as they tried to leave the twin towers. This vast database is known as HEED (High-rise Evacuation Evaluation Database). “Together, these personal stories paint a comprehensive picture of what happened and why. What influenced evacuees’ behaviour? What was going through their minds when they made key decisions?” said Project Director Professor Ed Galea of the University of Greenwich.

In theory, the Twin Towers had the most comprehensive evacuation procedures, but many failed when the attack happened. The study found that more that half the occupants delayed their departure to carry out tasks at hand, some taking up to eight minutes. Those trying to seek information on what had happened took between 1.5 and 2.6 times longer to evacuate, reducing their chances of survival.

Stairway congestion was the main cause of delay. According to research projections, had the North Tower been fully occupied with 25,000 people rather than the 8,000 who turned up, some 7,592 would have died, much more than the actual 1,462 fatalities. One of the conclusions: for buildings above a critical population and height, stairs alone will not be sufficient for safe, quick evacuation.

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