Why people die standing up in a crush
The phrase "crowd crush" brings up an image: people are running, someone falls, and the rest run over them. Accounts of real disasters show something different. Bodies are often found standing or wedged in a passageway: there was nowhere to fall. The cause of death listed most often is chest compression. To breathe in, the ribs need room to expand, but there is no room.
A person in the middle of a crush often doesn't understand what's happening: she's standing there, surrounded by people, and no one is attacking her. But those farther back can't see anything and keep pressing forward - they think the line is simply moving slowly.
What matters isn't the crowd's mood but the number of bodies in a given area. With 3 people per square meter, you can walk at your own pace. Beyond that, space runs out, and the crowd behaves like a viscous fluid: currents, waves, and pressure appear, and you lose your own path. The boundaries are approximate, but this is the general scale.
- 6 or more per m²: you're carried along, your feet don't choose
- 5 per m²: arms pinned, your neighbor sets your step
- 4 per m²: you can move only with everyone else
- 3 or fewer: you can turn and move around freely
How a steady flow turns into waves
The dangerous state begins before the crush itself. Researchers analyzing video from the 2006 Hajj described a sequence: first, a dense but steady flow; then jerky movement, as the crowd moves and stops; then what they called crowd turbulence - people are tossed sideways and backward for no visible reason.
The mechanism is simple. When bodies are in contact, a push is no longer absorbed: it travels through people as through a dense medium, combines with other pushes, and returns as a wave. No one is running or panicking, yet the force is already enough to bend steel barriers - this has been documented after real crowd crushes. And if one person falls, neighbors topple after them, and the entire mass bears down on the person who fell.
- FlowIt's crowded, but everyone moves steadily. It looks like an ordinary line.
- JerksThe crowd moves in jolts: a few steps - stop, then again.
- WavesYou're swayed sideways and backward, and your feet move on their own.
- CollapseSomeone falls, neighbors topple after them, and there's no air to breathe.
That's why the word "panic" is almost always unnecessary in reports. People in a crowd crush usually don't lose their heads: they pull each other out, lift children above them, shout back, "Stop." It's just that physics doesn't ask permission, and those at the back can't hear the shouting.
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Sources
- Helbing, Johansson, Al-Abideen, "Dynamics of crowd disasters: An empirical study" (2007)
- John Fruin's work on pedestrian flow density levels