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How can physics models prevent deadly stampedes at mass gatherings?

The death of at least 56 people in a in Nzérékoré, Guinea, is the latest example of how quickly mass gatherings can turn catastrophic.

From a to a or a , history—both recent and ancient—is filled with such tragedies.

While these events often seem unpredictable, physics models can help understand how stampedes form, says Max Bi, an associate professor of physics at Northeastern University.

"Â鶹ÒùÔºics provides valuable tools to model pedestrian dynamics and analyze crowd behavior, offering actionable strategies to improve public safety," Bi says.

Some of the deadliest modern crowd crushes have occurred during the hajj, the annual Islamic pilgrimage to Mecca, Saudi Arabia. In 1990, a claimed 1,426 lives, while a resulted in over 2,400 fatalities.

Understanding human movement

To simulate crowd movement, physicists studying active matter—a field focused on collective behavior—often simplify individuals into particles or marbles.

In 1995, physicists Dirk Helbrig and Peter Molnar introduced the that mathematically describes pedestrian movement based on three "social forces" internally motivating each individual.

According to their research, in typical situations people try to reach their destination in the most comfortable way—for example, without detours and in the shortest time possible. Every crowd member tries to avoid collisions with obstacles such as walls of buildings, fences or other individuals.

"We're uncomfortable getting too close to people, so we kind of try to keep a certain distance," Bi says.

People don't look behind them

People tend to be attracted by actions, window displays or street artists in front of them, according to the social forces model, and don't pay attention to things happening behind them.

"You don't care about what people are doing behind you, whether they are going in the same direction or opposite direction," Bi says. "If you already see people in front of you going toward the exit, you would tend to follow them."

When a crowd reaches a constriction—an exit, a bridge or a staircase—its movement slows down. In life-threatening situations or in a rush, if people are not getting through the exit fast enough, Bi says, the crowd's physical pressure grows.
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Don't panic; try to stay calm

The area becomes jam-packed, and an exit can get blocked. Panic reduces individuals' ability to adapt to the movements of others, Bi says, leading to collisions.

"That's when stampedes typically tend to happen," he says.

If somebody loses their footing and falls down, they risk being trampled as the crowd's collective push continues.

Research shows the dangerous pressure generated by a crowd can get so intense that it can bend steel barriers or push down brick walls.

Pushed against the floor or a wall by such force, Bi says, individuals can suffocate as chest compression prevents breathing.

"You end up losing air," Bi says.

How to survive a stampede

His tips to maximize one's chances of survival in a stampede are:

• Stay calm: Panicking exacerbates crowd pressure and reduces individual control.
• Protect your chest: Use your arms to create a protective space in front of you to prevent chest compression.
• Move with the flow: Do not fight the direction of crowd movement; instead, move diagonally to navigate toward the edges.
• Avoid walls and barriers: These locations often become high-pressure zones where individuals are pinned.

What precautions should be taken?

If you fall, Bi says, protect your head and curl into a fetal position to minimize injury. Try to get up as soon as possible by holding on to stable objects or individuals.

While individuals can take precautions, Bi says, designers of venues, event planners and authorities play a critical role in preventing such tragedies.

Planners should ensure sufficient exits, he says, and eliminate chokepoints. Wider exits help distribute pressure, and clearly marked signage can promote calm, steady movement. Trained personnel can manage crowd flow, while strategically placed obstacles can disperse density and guide crowds toward exits.

Additionally, regulating access to high-density zones can prevent dangerous surges, reducing the likelihood of stampedes.