Welcome to brain Stuff from how stuff works. Hey, brain stuff, it's Christian Seger. Imagine you're waiting in line with hundreds of other people to get Josh Clark from stuff you should know as autograph. Your bodies start getting jammed together, no longer being able to choose where to go. The crowd begins acting like a fluid, and by that point it's too late. You're in danger. People ignore the emergency exits,
creating a bottleneck and knocking one another over. You feel pressure on all sides and you can't lift your arms. You're pulled off your feet. Some people below you crawl then die. Within three minutes, there are a hundred corpses on the floor and you're struggling to breathe as the air is squeezed out of your lungs. People generally try to be decent and calm and behave rationally, except maybe on YouTube comments. Even in a crisis, they'll try to
make safe decisions. But they can only do this based on what they know, and crowds are a condition and of everyday urban life, a necessary inconvenience of city living. We pass in and out of them all the time on subways and sidewalks. Crowd crushes, or also referred to as crush accidents that killed ten or more people, have happened on at least forty four recorded occasions since n
that's one every four months, and they happen everywhere. Multiple crowd crushes have occurred with the Hajj in Mecca, Saudi Arabia, where hundreds were killed on at least nine occasions. Much of the information in this episode actually comes from an excellent October article from The Guardian by Leo Benedictus. So we've got two types of crowds to look at. The first is low density, and it's the low risk type of crowd, moving crowds with a density of up the
four people per square meter. Those are usually safe. People have enough room then to decisions and act accordingly. But the second type of crowd, those are high density crowds, and they are high risk. There's been an increase in the frequency of high density crowds lately because we're trying to service more people in less time. High density crowds are measured by at least six people per square meter. Reports show that crowd disasters have more than doubled in
the past two decades. In the developed world, these are most likely to occur at rock concerts and soccer games. They also happen at religious events like the Hodge. One of the best documented crowd disasters in the US happened in nineteen seventy nine at a concert by The Who in Cincinnati. High density crowds are a mass of complex agents that respond based on their limited choices in their exposure to products in their environment like heat. For instance,
physical contact in these high density crowds causes waves. Every time there's physical contact between members. These shock waves can lift people off their feet and even propel them about three meters or ten feet. One researcher even studies mosh pits by standing in the middle to witness crowd dynamics produced by shock waves. Within high density crowds, there are two types of dangers you want to watch out for. Type one is what's referred to as progressive crowd collapse.
One person falls over and they deny their body as something for the others to lean against. This creates a domino effect where the adjacent people fall on top of them or are knocked over trying to help. The hole gets larger and more people are forced in and fall. This often happens when a large crowd is moving steadily through a confined route. Now, this actually happened to me at a bouncing soul show in Luckily someone picked me
up and saved my life. Type two. The other one you want to watch out for is the crowd crush. When people are squeezed so much by a crowd that they can't inflate their lungs, they'll die from compressive asphyxiation. This typically happens when too many people push into a confined area. Often those who die are the ones against the wall. Now, maybe you've also heard talk of stampedes. The mass media's idea of mass panic or a stampede
is actually misleading. Again, most of the evidence shows that people take sensible action when they have their right information. They're only crushed or crushing when they have no choice in the matter and they don't know what's going on because they're too far from the epicenter. Actually, stampedes themselves are unlikely to kill you. The word stampede suggests that people are causing havoc while they're running away, but the real problem is when people can't move at all, but
train These events as mob psychology or crazes is. It's misleading and it's false. Most people move in crowd patterns and flows, but humans don't have the capability to transmit information about the physical dynamics of their crowd the same way ants can, for instance. Unfortunately, there isn't much of a record of information in the crowd control industry to provide analysis, but there are some technologies being developed to
try to help. In two thousand thirteen, a team of UK and Saudi Arabia researchers developed an artificial intelligence system that uses body heat readings to monitor the build up of crowds and congestion. It uses infrared and black and white images to interpret the crowds changing density. Then it processes this information and acts like a human spotter, pointing out high density crowd situations. Also in eleven, a German researcher developed a system that observes when people sway slowly
from side to side to keep their balance. This is another indicator of high density crowds. The system detects any sudden increased in symmetrical movements that suggested as a congestion issue, and it highlights the area in red, so you're probably asking right now, what should I do if I'm in a crowd disaster. There's some simple efforts that you can take. Look ahead and listen to the crowds noise. If the crowd starts to surge, wait for it, and then move
with it and sideways. Check out the brainstuff channel on YouTube, and for more on this and thousands of other topics, visit how stuff works dot com