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  • Hey there and welcome to BrainStuff. Welcome, welcome. I'm Josh Clark, and you're you, and

  • that is wonderful. Let's talk about crowd crushes.

  • Have you ever been standing in a crowd before? Say you were waiting for Weird Al to come

  • out from backstage after a show. And then suddenly he does, and all of a sudden it seems

  • like all the people around you multiply exponentially. And as far as you can see, you're surrounded

  • by people. And all of them start to press forward. And you, against your own will, are

  • propelled forward. And you're pushed into the person in front of you, and you propel

  • them forward. And you stop and think, "Uh oh!"

  • Well if you thought that, you were thinking very clearly. Because you were in a very dangerous

  • situation: something called a high density crowd. A high density crowd is one where there's

  • 6 or more people per square meter. It can get a lot more packed than that, but that's

  • the lowest level threshold. The reason that's the threshold is because, when you have 6

  • people per square meter, individuals in the crowd start to lose their ability to move

  • on their own accord. Things get more and more packed, and the crowd tends to behave a lot

  • like a fluid.

  • So there's a couple of ways that you can actually die in a high density crowd. The first one

  • is called a crowd crush. When you first start to get to about 6 people per square meter,

  • the individuals lose their ability to move around. The next step is that you lose your

  • ability to move your arms from your sides. And as people pack in further and further,

  • the pressure from all sides keeps your lungs from inflating and deflating, which means

  • you lose your ability to breathe.

  • What's amazing (and horrific) is that people suffocate in crowds because they're squeezed

  • so tightly by the people pressing against them. That's a crowd crush.

  • Another way you can die in a crowd is what's called progressive crowd collapse. So, say

  • you have a bunch of people crowded together in a high density crowd. And one of them falls

  • down. That creates a hole in this crowd, and the people who were formerly leaning against

  • this person who just fell down start to fall down. And so on and so forth. A domino effect

  • is created. People start to pile up and the ones on the bottom are literally pressed to

  • death by the humans who have piled up on top them.

  • So why don't people just get up and go, get out of the crowd? Well, the short answer is,

  • they can't.

  • One mark for humanity is that crowd researchers have shown that when individuals are given

  • information - say, something like, "Oh, someone ahead is being crushed to death" - they respond

  • positively by, say, backing up and alleviating the pressure on the crowd in front.

  • The problem is humans aren't ants. We don't transmit information through crowds like ants

  • do. And so people end up dying in crowd crushes and progressive crowd collapses because the

  • people in the back are pushing forward.

  • Another common misconception are mass panics and stampedes. There's this idea that people

  • stampede over one another and that's how deaths occur in crowd crushes. This is really off

  • point. In fact, if you have enough room to rush out over your fellow humans to get from

  • Point A to Point B, there's probably enough room for those fellow humans to get out of

  • the way. So, stampedes really don't cost any lives whatsoever. That's not the problem with

  • crowd crushes.

  • And the same with mass panics. Very rarely do entire crowds panic and move in a panicked

  • way. In fact, you can suffocate in a crowd crush in a very calm crowd that's just entered

  • a bottleneck in a narrow corridor, and trying to get out of an exit. People just quietly

  • die pinned up against their fellow human beings who are leaving the place.

  • So, crowd researchers are using computers now to predict high density crowds, and stop

  • them before they turn fatal. They're using video feeds fed into artificial intelligence,

  • which analyze crowds for things like increases in body heat, or people swaying from side

  • to side, which is a telltale sign that they're no longer moving on their own volition.

  • What do you do if you find yourself in a crowd? Well, get out. That's the best thing you can

  • do. But, as you're entering a crowd, crowd researchers suggest that you pay attention,

  • stop talking, and listen ahead for people calling for help, or saying "Move back!" or

  • any other indication that there's a crowd crush going on. In that case, get back as

  • far as you can.

  • If you find yourself in a crowd, and it starts to surge forward, follow the crowd movement,

  • but move to the side as much as possible. Just stay out of crowds. How about that?

  • Have you ever been in a crowd crush or a crowded situation where you thought, "Uh oh?" Let

  • us know in the comments section below. And while you're down there, go ahead and subscribe

  • to BrainStuff. And head on over to HowStuffWorks.com for even more cool stuff like this.

Hey there and welcome to BrainStuff. Welcome, welcome. I'm Josh Clark, and you're you, and

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