How to Prevent a Crowd Crush

The death of a Wal-Mart security guard in New York on Black Friday has Americans lamenting the human condition. The shoppers at the Valley Stream store have been called "rabid," "pathetic" "savages" with "no souls." There have been calls for criminal prosecutions against these "animals." Wal-Mart, meanwhile, has claimed it prepared for the crush by bringing on outside security and additional sales staff. "Despite all of our precautions," said Wal-Mart executive Hank Mullany in a thrillingly passive turn of phrase, "this unfortunate event occurred."

"How could you know something like that would happen?" one worker told the New York Times. "No one expected something like that." But for people who study crowd crushes, there was nothing surprising about what happened at Wal-Mart. It was reminiscent of many tragedies that have come before, at soccer stadiums, concerts and Ikea stores, which only makes it more awful. "We know exactly how crowds work," says G. Keith Still, a crowd management expert who has helped plan high-density events around the world, including the annual pilgrimage of Muslims to Mecca in Saudi Arabia. There is, he says, no excuse for these kinds of accidents. "It's stupidity. It's ignorance. But the consequence is human life."

Mobs are not mystical, it turns out. "All types of crowds, even relatively small gatherings, can quickly become dangerous if not carefully managed," John Fruin, a traffic engineer specializing in crowd safety, wrote in a recent National Fire Protection Association handbook.

The investigation into the death of Jdimytai Damour, 34, is ongoing, and now that the lawsuits have begun (Damour's family has sued Wal-Mart, Green Acres Mall and other companies connected to the event), the major players have gone dark. The family's attorney, Jordan Hecht, did not return a call requesting comment, and a Wal-Mart spokesperson said he could not elaborate beyond the vague statements the company has already made.

But here is what we do know about crowds, generally speaking, and none of it is as malicious as we might expect.

1. Competition kills.

It's possible to have bargain bonanzas without casualties. But it's imperative to make the process fair and predictable. If, for example, people wait in a snaked line with ropes or are given numbers, then they know in advance who goes first — and do not feel the need to compete when the doors open. "Allow those who have waited longest to get in first," says Still. "Let them in one at a time. Then everyone knows it's a fair system. Very quickly you see that people's behavior adapts."

Police have said that the Wal-Mart incident may have happened after people who were waiting in their cars tried to rush the doors, past people who had been waiting outside.

The most notorious example of this problem, called a "craze" by crowd management experts, happened at a Who concert in 1979. A crowd of 18,000 fans had gathered outside the Cincinnati Coliseum to see the band. Seats were on a first-come, first-served basis. When the opening band began to play, the fans thought the show was beginning without them. There were only two doors open, and the crowd rushed toward them. Eleven people died.

2. Crowds are deaf and dumb.

It often looks like a crowd has intentionally trampled the victims. But what usually happens is that the people in the rear of a crowd do not know that someone in front has fallen. They still have room to move, unlike the people in front, so they continue to press forward. The compounding pressure can bend steel like it's made of rubber. "It only takes five people to push against one to break a rib, collapse a lung or smash a child's head," says Still. Most stampede victims (including the Wal-Mart worker) die of asphyxiation — they literally cannot breathe due to the pressure of the crowd.

At an outdoor 2000 Pearl Jam concert in Denmark, nine people were killed when the fans in back surged forward — despite band members' pleas to step back.

3. Physics matter most of all.

When crowds are moving, there should be no more than two to four people per square meter to prevent injury. It's a simple mathematical reality. Otherwise, people do not have enough room to recover from being jostled. Someone can easily fall. Then someone else will lean down to help that person and get sucked down, too. The pile up begins, absorbing the growing pressure of all the people coming from behind.

Once a crush begins, it's very hard to reverse the flow. So it's essential that event organizers preserve enough space anywhere the crowd may flow. At Hillsborough Stadium in the U.K. in 1989, a terrace became packed with fans, causing a railing to give way. In all, 96 people died. On the terrace, there were 8.4 people per square meter, according to studies of photographs taken before the railing collapsed.

Many huge crowds passed into stores without incident on Black Friday. "Disney World does this every day," notes Nassau County Police Commissioner Lawrence Mulvey. "People aren't inherently interested in hurting each other." But managing crowds is not something people do well without knowledge and training. Mulvey says that his department met with local retailers, including Wal-Mart, two weeks before Black Friday to remind them that they needed to provide their own security. "We patrol the parking lot, the exteriors, but each individual store is responsible for their own security," says Det. Sgt. Anthony Repalone. "We can't be at every retail store, especially on Black Friday."

The department is planning another meeting with stores for mid-December to share crowd-management strategies and try to prevent future fiascos. So far, Mulvey says, Wal-Mart has been very cooperative in the investigation into Damour's death. "We will continue to work with local law enforcement officials so that together we can implement even stronger safety measures going forward," Mullany, the Wal-Mart executive, said in a statement on Dec. 3.