Jeff Wise, the author of Extreme Fear: The Science of Your Mind in Danger, guest-blogged for us earlier this year about road fear. This time, he turns his attention to another interesting phenomenon: crowd panic.
When Crowds Panic
By Jeff Wise
The recent deaths at the annual Love Parade music festival in Duisburg, Germany, can be counted among the most perplexing form of tragedy: one that unfolds entirely as a result of the normal psychology of healthy human beings. When crowds reach a critical density, they automatically become vulnerable to a contagion of blind fear that overwhelms any attempt at rational behavior. The paradox of terror is that the subconscious fear response, which evolved over millions of years to keep us safe, can itself pose a terrible danger in the 21st century. If anything, the advent of modern technology seems to have left us even more vulnerable to fatal stampedes, as mass transportation and instant communication make it easier to bring large crowds together.
The toll in human lives can be immense: in the past decade there have been more than 100 stampede events resulting in mass fatalities, with the worst, Iraq’s Baghdad Bridge stampede in 2005, killing nearly 1,000 people. Just as a forest fire needs a critical density of dry timber in order to reach the blowout stage, a crowd must reach a critical density in order to become dangerous. Crowds will continue to grow in size or density until there are about 10 people per square meter – that’s 2,600 people in an area the size of a tennis court.
What happens next has been examined in a fascinating pair of recent papers by Ed Hsu and colleagues at Johns Hopkins. According to Hsu et al., there are two major ways that things can go wrong. One is a “turbulent stampede” that takes place when two crowds merge from different directions or a stationary crowd is induced to panic. The other, a “unidirectional stampede,” occurs when a crowd reacts to a sudden positive or negative change in force. A positive change in force might occur when a crowd is stopped by a barricade or a narrowing in a passageway; a negative force is the release of constraining pressure, as for instance might occur when a gate is opened. Based on preliminary accounts, the deaths that occurred at Duisburg were a result of a positive force that occurred when security guards shut a gate at the end of a tunnel.
Once panic takes hold, individual free will goes out the window and the mass as a whole becomes subject to a collective crowd psychology. Not only do people in such situations show a tendency to mimic the behavior of those around them, but the sheer physical force of the crowd can become irresistible, capable of bending sturdy steel stanchions and knocking down brick walls. One particularly gruesome aspect of stampedes is that these factors can cause victims to overlook perfectly good exits, as for instance occurred in the Station nightclub fire in Rhode Island in 2001.
People tend to die standing up. When the pushing stops and the bodies covering them are removed, they tend to remain standing. The proximate cause of death is pressure applied to their bodies in a front to back direction, causing “ventilatory failure.” When the pressure is applied to their sides, they often survive, presumably because their rib cages are still able to expand and draw breath.
The deadliest single event is the pilgrimage to Mecca, particularly the “stoning the devil” event, which can draw crowds of up to 3 million people. Lethal stampedes occurred in 1990, 1994, 2004, and 2006.
For years, as Hsu et al point out, engineers and psychologists have been working to model crowd behavior and to figure out how to design spaces so that stampedes are prevented. Yet every year lethal stampedes become more common. In the ’80s, there were 24 incidents reported in the media; in the ’90s,? 62; in the 2000s, up to 2007, there were 129.
What should you do if you find yourself in a potential stampede situation? Once the panic has begun, very little, due to the enormous forces at work. Your best bet is to stay alert whenever in a large crowd. Take note of exits and other escape routes, and when the density becomes high enough to seem dangerous, move away from the center. Ask yourself: do I really need to be here? Perhaps the greatest irony of stampedes is that, in retrospect, the attraction that brought the crowd together seldom seems important enough to merit any deaths at all.