How a Peaceful Crowd Turns Into a Lethal Stampede

Few things are as bafflingly tragic as the mass death that can occur when a crowd of people becomes overcome by panic and stampedes within a confined space. As I’ve written earlier, in many cases of mass panic individual members of a crowd do not themselves act irrationally. However, in the case of a stampede the crowd truly seems to leave its senses, becoming a heaving mass in which rational behavior by an individual becomes impossible. The result can be truly horrific — in some cases, over 1,000 people have died in the ensuing crush.

Compounding the awfulness is the fact that in many cases the stampede is triggered by no actual danger. It seems that, in certain settings, a crowd that grows to a critical density reaches a critical state at which the slightest twitch is sufficient to send it into a stampede — like a supercooled drop of water that just needs the tiniest seed to instantly freeze.

The toll in human lives is immense: in the past decade there have been over 100 stampede events resulting in mass fatalities.  Yet there has been surprisingly little study has been done into the phenomenon. I was delighted, then, to learn via @bengoldacre of an absolutely fascinating new paper from Ed Hsu and colleagues at Johns Hopkins:  “Epidemiological Characteristics of Human Stampedes.” I emailed Dr. Hsu and he sent me copies of the paper, along with another, “Human Stampedes: A Systematic Review Historical and Peer-Reviewed Sources,” that further elaborated his team’s findings.

The papers are chockablock with intriguing findings, but here are some of the highlights:

• The force of just 6 or 7 people pushing in the same direction can generate up to 1000 lbs of force — enough to bend steel railings and topple brick walls.
• People tend to die standing up. When the pushing stops and the bodies covering them are removed, they tend to remain standing.
• People die when the pressure is applied to their bodies in a front to back direction, causing “ventilatory failure.” When the pressure is applied to their side, they often survive, presumably because their rib cages are still able to expand and draw breath.
• Those who study stampedes draw a distinction between escape panic — “headlong rush away from something” — and a a craze — “a rush toward something believed to be gratifying.” In one of the earliest recorded stampedes, 1389 people died at a coronation ceremony for Tsar Alexander II of Russia when a rumor circulated through the crowd that souvenirs were in short supply, causing people to rush forward en masse.
• 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. Is the number increasing because of humanity’s increasing urbanization and growing population size, or merely an artifact of improved communication technology? As the authors unsurprisingly observe, more study is needed.