An expert on crowd dynamics shares his advice on how to survive a crush of people. Two tips: Don't put a backpack on the ground — and protect your ribs so you can breathe.
Lack of oxygen is the killer in crowds, so preserve space around your chest
People often ask me, "Why do we die in a crowd? What's the cause of death?" Well, the cause is not enough oxygen. You're so densely packed that your lungs don't have enough space to do their job, and to keep you breathing. That's one thing that is superuseful that people should be aware of: The problem is going to be breathing.
If you can maintain sufficient space for you to breathe, you're going to be OK. Put your arms out just in front of your chest and hold them there. In this position, you would have some space, just a little bit, to push for half a centimeter or just 1 centimeter — enough for you to keep breathing. It's not going to be comfortable. You're going to be feeling really bad, but at least you'll survive.
Don't push. Move with the crowd
In a crowd, everything is about chain reactions. When you push your neighbors, they're going to push their own neighbors and it eventually hits an obstacle. Then the pushing is amplified — and it's going to come back to you. If you feel a push, don't push back. Don't amplify this wave. Just go with the flow. It's not going to be comfortable, you're not going to like it, but it's the best way to behave in this situation. Don't add pressure in the system.
In the worst moments, you have multiple pushing waves at once. This is what we call crowd turbulence. You don't want to be where two waves cross, because the pressures come from opposite directions, and that's really dangerous. When we observe crowd turbulence, we see death, a tragedy.
Learn to detect crowd density
Density is really the critical variable, that's the first thing we measure. It's expressed as the number of people per square meter, and there are some thresholds: Below five people per square meter [about 10.7 square feet], it's fine. Maybe not comfortable, but it's fine. Above six persons per square meter, it starts becoming dangerous.
Eight people per square meter: Most of the time there are injuries or worse. It's superuseful to have a sense of that density, but it's not intuitive. Here's a tip: If you feel that people are touching you on both shoulders or on several places on your body at the same time, the density is probably around six or above. If you still have time and can move, get away. That's an alarm signal.
If a crowd gets unsafe, look out for others
Helping behaviors and altruistic behaviors are kind of contagious in crowds. The same applies to individualistic or selfish behaviors. If you try to help your neighbors, they're going to help you, or they're going to help their own neighbors. If this spreads, it creates a positive, helping atmosphere. It's going to make things less bad. So definitely, helping behavior is something you should adopt.
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