| New building evacuation data |
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| Written by Barry Scholes, Managing Director Evac+Chair International Ltd, July 2005 | |
In December 2004 the Building Disaster Assessment Group (BEDAG) of the UK office of the Deputy Prime Minister published its report on the evacuation of the World Trade Center (WTC) disaster in September 2001. The research is extensively reported in 116 pages and gives new insight into human behaviour1.
Unlike routine fire and evacuation drills, which most of us experience every six months and where each of us exits the building as individuals, in this study many individuals formed groups that physically and psychologically supported the weakest. Many women discarded inappropriate footwear that had caused sprains and others assisted the more seriously injured due to burns or long bone fractures, as well as the blind and other disabled groups.Evacuation timesAccording to Fruin's Law an able-bodied person can descend stairs at 0.7m per second. The recommendation for Sports Grounds is 0.82m per second, based on the UK Green Guide. This is based on analysis of large crowds exiting stadiums with many exits and wide openings. However, where conventional buildings are concerned, progress can be impeded due to the number of people on a staircase at any one time; this can vary for able-bodied persons to 0.5m per second. In the WTC, the BEDAG analysis estimates that the mean stair descent rates in WTC1 (North Tower) were as low as 0.33m per second and in WTC2 (South Tower) this was slightly better at 0.49m per second. These figures support the view that occupants in WTC2 started to evacuate that tower prior to it being hit by the second aircraft.A further explanation for this was that the elevators were heavily used prior to the assault on this building. This had two positive contributions to the evacuation. Firstly, it helped clear large numbers of people and, secondly, eased congestion on the stairs, making moving on the stairs more efficient. However, sadly a significant number of people also delayed their evacuation - with fatal consequences whilst waiting for elevators to return to their floor. Many observers relate how they allowed ascending fire-fighters stairway priority, delaying their own evacuation time. One evacuee was John Abruzzo, who worked on the 69th floor of Tower 1. He and his ten colleagues were lucky to escape. When the first aeroplane hit the tower that day, they rushed to the stairwell. However, Abruzzo is a C5-6 quadriplegic who relies on an electric wheelchair for mobility. He recalls how on that tragic day many seemingly ordinary people did extraordinary deeds. " There was no debate on whether I would be brought down or not by these people. It was more or less a collective decision," says Abruzzo. With the use of a special evacuation mobility device designed for the physically disabled, called the Evac-Chair Emergency Wheelchair, Abruzzo was able to make an escape to safety. It took an hour-and-a-half to get down 69 floors. Although it is designed for one person to guide it, three or four people handled the device while heading downstairs, rotating positions as necessary. His average speed of descent was much slower in that the mean was approximately one floor every 90 seconds. Reading his personal account of what took place during his assisted descent with the Evac+Chair, delays were a hybrid of:
Summary of eventsWTC1 was hit by American Airlines Flight 11 at 8.46am. The impact was centred on the north face of the building between the 94th and 98th floors. WTC2 was hit by United Airlines Flight 175 at 9.03am on the south face of the building between the 78th and 84th floors. WTC2 collapsed at 9.59am and WTC1 collapsed at 10.28am. It is estimated that 1,432 building occupants perished in WTC1 and 599 in WTC2. However, a further 753 lost their lives on that day, including those in the aircraft and the emergency services (data from USA Today). Further information Reference |
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