Once again, a stampede has turned a large celebration into a tragedy. Just four months after 21 people died at the Love Parade in Duisburg, Germany, more than 350 were killed and a similar number injured yesterday at a festival in Cambodia. The terrible irony of stampedes is that for decades engineers and sociologists have been studying how to design spaces so that crowds don’t turn deadly, yet the number of incidents only continues to grow. As I pointed out recently, there were only 24 such tragedies around the world in the 1980s; in the last decade, there have been well over 100.
Part of the problem is likely that growing affluence around the world, together with improved communication and transportation, means that it’s easier for large crowds to assemble. But another factor may be that the general public has erroneous ideas about what a stampede actually looks like, how it can turn deadly, and what one can do should one occur. Maybe if more people were aware of what a potentially dangerous situation looked like, they could take steps to defuse it. So: what does a real-life stampede look like?
Well, let me start with what it’s usually not. The word “stampede” usually conjures of images of frantic running — cattle trampling over a prairie, or a crowd of people running pell-mell. In fact, the crowds at Phnom Penh last night, like those at Duisburg in July, were so dense that running or even walking would have been impossible. The critical density at which this kind of disaster becomes likely is about 10 people per square meter, at which point individuals are pushed together shoulder-to-shoulder and front-to-back. They might be stationary, or moving together towards a common destination. Then something causes a change in their momentum — either to get them moving if they’re at rest, or to stop them if they’re moving. Oftentimes the trigger is psychological: a rumor sweeps through the crowd, or a loud noise is heard. Already anxious and at the edge of panic due to uncomfortably close crowding, people panic and begin shoving.
But the problem doesn’t need to start with panic. The sheer force of people moving into an already-crowded area can cause sufficient pressure to cause fatalities, which then triggers further panic, shoving, and more death. Contrary to the common idea that people die when they fall down and trampled, most people die standing up, as the pressure on their rib cages makes it impossible to breath. They’re squeezed to death like a boa constrictor’s prey.
After I blogged about the Love Parade stampede, several readers wrote in and said that they had been on the scene, and that there had been no panic at all — people had been slowly crushed merely by the remorseless crush of the crowd. Some news outlets have reported that the Cambodian tragedy began when some of the revelers collapsed, triggering panic among those nearby. Perhaps these first fatalities were a result of simple mechanical force, which quickly worsened once the crowd realized how desperate their situation had become.
So if you find yourself in the middle of a stampede, what should you do? Unfortunately, once you’re surrounded by the remorseless pressure of hundreds of other bodies, you may be physically incapable of any action at all. A crowd that’s only 6 or 7 people deep can exert 1000 pounds of pressure, enough to topple brick walls and bend metal stanchions. It has been suggested that some people have survived stampedes because they were turned sideways to the press of the crowd, so that their shoulders absorbed the force rather than their ribcage, and they were still able to breathe. But while I’d keep this tidbit in mind, I wouldn’t count on it as a life saver.
Really, the only thing you can practically do is to keep your wits about you, and start to think critically about your situation once the crowd around you becomes so dense that it becomes hard to move. It’s a natural human tendency to get caught up in the emotion of a crowd, and I’m sure that for most of the celebration the revelers at the Cambodian festival were swept up in a common euphoria. Even while having fun, though, it’s worth keeping a small, sober part of your brain alert to potential trouble. If you can’t get out easily, it’s time to start moving for the exit.