The recent crowd tragedy where more than 150 people died at a Halloween get together in Seoul following similar recent disasters in Indonesia and Houston have prompted the need for authorities to factor in the inherent risks in crowding and manage these events better. The WIRED features Martyn Amos, a professor at Northumbria University who studies crowds in this article to understand how exactly crowds can be dangerous. It is not so much the unruly behavior nor did people in Seoul die of a stampede.
“Amos says safe crowds act like a gas; people are like particles that can move around freely. But add too many people—about five or six for every square meter—and the crowd transforms to become more like a liquid. “Where the crowd is a fluid, that’s where we’ve got the potential for problems,” he says. “You’re essentially a particle at the mercy of physics.”
A small push from the back of the crowd can grow stronger as it ripples through the group like a wave. If it eventually reaches a person next to an obstruction, like a wall, fence, or immovable pack of people, that wave has nowhere to go. Without an outlet, that force can now crush the people in its path. In the Itaewon incident, a collapse in the crowd may have caused the obstruction, with one or more people falling in the densely packed group. And when people are trapped, Amos says, the force of the crowd can hem them in and prevent others from pulling them out.
Ultimately, people die in crowd crushes from asphyxiation, Amos says. When a person breathes out, their chest cavity contracts. But when they try to breathe in again, the force of people around them can be too strong, making it impossible for their chest to expand and take in new air. Five people pushing on one person can create a 3,000-newton force, says Amos, or the equivalent of 674 pounds, which can break a person’s ribs.
Take the 1989 Hillsborough disaster, a crush that resulted in 97 deaths at Hillsborough Stadium in England. The strength of the crowd broke steel barriers, a feat that required forces on them to exceed 4,500 newtons, Amos says. Gil Fried, an attorney and professor at the University of West Florida with an expertise in crowd management, says metal railings were also twisted after a 1993 incident at the University of Wisconsin-Madison’s Camp Randall Stadium. That destruction was the result of more than 1,000 pounds of pressure per square inch.
The US Centers for Disease Control and Prevention offers recommendations for surviving a crowd crush. One is to take a boxer’s stance, with feet apart and knees slightly bent, one in front of the other, and hands up. This may keep people from falling or having their arms pinned. Another is to move with the flow of the crowd instead of against it. Experts also encourage people not to waste breath screaming, and they caution against bending over to pick up dropped items.
But there’s little else individuals can do to protect themselves once the crowd’s pressure builds. Those on the outer edges of a crowd often have no idea their movements are crushing others in the group.
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