The September 29 stampede at Mumbai’s Elphinstone Road station which claimed 23 lives and left scores injured is a stark reminder that high-density crowds can be lethal. While mass gatherings are usually safe, stampedes have been known to occur during pilgrimages; at music concerts, sporting events, protest rallies; and even on discount sale days such as Black Friday. Many think that if people just acted rationally they wouldn’t be crushed to death. But research into crowd dynamics shows it’s not panic that kills.

In a populous country such as India, crowds are inevitable. But heeding the warning signs of the formation of high-density crowds can be the difference between life and death. So, here we explain the science behind high-density crowds and provide tips to escape a stampede.

First of all, remember that, contrary to myth, it is not injuries from being trampled upon that kills people in a stampede but asphyxiation. Also, not every stampede results in fatalities.

Looking for warning signs

A high-density crowd is when there are six or more people per square meter, six being the minimum. In high-density crowds, people are squeezed together so tightly they can no longer choose where to go and begin to resemble the movement of a fluid. Such crowds can develop pressure waves that can exceed 1,000 pounds of force. These waves can travel through the group causing it to lose control.

High-density crowds can kill when they either result in a crowd crush or a progressive crowd collapse.

A crowd crush is when people are jammed together so tightly that they can no longer inflate their lungs and they gradually die of asphyxiation or suffocation. The people who die in crowd crushes are usually those against the wall. Crowd crushes happen when an ever-increasing number of people try to fit into a confined space, trying to get in or out.

A progressive crowd collapse occurs when one person suddenly falls because of the pressure exerted by the crowd or by slipping. Adjacent people are denied the support of the fallen person’s body, which they were leaning against, even as they are still under pressure from the other side. This ultimately results in a domino effect, knocking over the adjacent people as well.

The result is a hole: more and more people are forced into creating a pile of bodies atop each other until the pressure eases. This usually happens when a large, tightly packed crowd is moving forward steadily through a confined space.

Keith Still, professor of crowd science at Manchester Metropolitan University, United Kingdom, writes on his website:

“Crowd forces can reach levels that almost impossible to resist or control. Virtually all crowd deaths are due to compressive asphyxia and not the ‘trampling’ reported by the news media. Evidence of bent steel railings after several fatal crowd incidents show that forces of more than 1,000 pounds occurred. Forces are due to pushing, and the domino effect of people leaning against each other.”

A video by HowStuffWorks illustrates how high-density crowds can be lethal.

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Escaping a high-density crowd

Stay on your feet. Your best chance of making it out alive is if you are standing upright. Do not bend to pick up anything you may have dropped or dislodged such as a phone, wallet or a shoe. If your child has stumbled, pick them up immediately.

Your best chance of making it out alive is if you are standing upright. Do not bend to pick up anything you may have dropped or dislodged such as a phone, wallet or a shoe. If your child has stumbled, pick them up immediately. Keep your hands by your chest, like a boxer. This ensures mobility and creates an air pocket that protects your lungs.

This ensures mobility and creates an air pocket that protects your lungs. Stop talking and listen for signs of distress from people at the front of the crowd.

from people at the front of the crowd. Be aware of the ground you are on . Uneven or wet surfaces increase the chances of a progressive crowd collapse.

. Uneven or wet surfaces increase the chances of a progressive crowd collapse. Do not push against the crowd or try to move in the direction against it. Move sideways. Conserve your energy, do not yell.

Conserve your energy, do not yell. Note all the exits. Take the path of least resistance , not necessarily the main exit.

, not necessarily the main exit. Avoid barricades, railings and walls that you can be pinned against.

that you can be pinned against. If you fall and can’t get up, turn on your side, protect your head with your hands and draw in your legs. Lying on your stomach or back will leave your lungs exposed.

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This article first appeared on Boomlive.