Speaker 1: Welcome to brain Stuff from how stuff works. Hey, brain stuff,
Speaker 1: it's Christian Seger. Imagine you're waiting in line with hundreds
Speaker 1: of other people to get Josh Clark from stuff you
Speaker 1: should know as autograph. Your bodies start getting jammed together,
Speaker 1: no longer being able to choose where to go. The
Speaker 1: crowd begins acting like a fluid, and by that point
Speaker 1: it's too late. You're in danger. People ignore the emergency exits,
Speaker 1: creating a bottleneck and knocking one another over. You feel
Speaker 1: pressure on all sides and you can't lift your arms.
Speaker 1: You're pulled off your feet. Some people below you crawl
Speaker 1: then die. Within three minutes, there are a hundred corpses
Speaker 1: on the floor and you're struggling to breathe as the
Speaker 1: air is squeezed out of your lungs. People generally try
Speaker 1: to be decent and calm and behave rationally, except maybe
Speaker 1: on YouTube comments. Even in a crisis, they'll try to
Speaker 1: make safe decisions. But they can only do this based
Speaker 1: on what they know, and crowds are a condition and
Speaker 1: of everyday urban life, a necessary inconvenience of city living.
Speaker 1: We pass in and out of them all the time
Speaker 1: on subways and sidewalks. Crowd crushes, or also referred to
Speaker 1: as crush accidents that killed ten or more people, have
Speaker 1: happened on at least forty four recorded occasions since n
Speaker 1: that's one every four months, and they happen everywhere. Multiple
Speaker 1: crowd crushes have occurred with the Hajj in Mecca, Saudi Arabia,
Speaker 1: where hundreds were killed on at least nine occasions. Much
Speaker 1: of the information in this episode actually comes from an
Speaker 1: excellent October article from The Guardian by Leo Benedictus. So
Speaker 1: we've got two types of crowds to look at. The
Speaker 1: first is low density, and it's the low risk type
Speaker 1: of crowd, moving crowds with a density of up the
Speaker 1: four people per square meter. Those are usually safe. People
Speaker 1: have enough room then to decisions and act accordingly. But
Speaker 1: the second type of crowd, those are high density crowds,
Speaker 1: and they are high risk. There's been an increase in
Speaker 1: the frequency of high density crowds lately because we're trying
Speaker 1: to service more people in less time. High density crowds
Speaker 1: are measured by at least six people per square meter.
Speaker 1: Reports show that crowd disasters have more than doubled in
Speaker 1: the past two decades. In the developed world, these are
Speaker 1: most likely to occur at rock concerts and soccer games.
Speaker 1: They also happen at religious events like the Hodge. One
Speaker 1: of the best documented crowd disasters in the US happened
Speaker 1: in nineteen seventy nine at a concert by The Who
Speaker 1: in Cincinnati. High density crowds are a mass of complex
Speaker 1: agents that respond based on their limited choices in their
Speaker 1: exposure to products in their environment like heat. For instance,
Speaker 1: physical contact in these high density crowds causes waves. Every
Speaker 1: time there's physical contact between members. These shock waves can
Speaker 1: lift people off their feet and even propel them about
Speaker 1: three meters or ten feet. One researcher even studies mosh
Speaker 1: pits by standing in the middle to witness crowd dynamics
Speaker 1: produced by shock waves. Within high density crowds, there are
Speaker 1: two types of dangers you want to watch out for.
Speaker 1: Type one is what's referred to as progressive crowd collapse.
Speaker 1: One person falls over and they deny their body as
Speaker 1: something for the others to lean against. This creates a
Speaker 1: domino effect where the adjacent people fall on top of
Speaker 1: them or are knocked over trying to help. The hole
Speaker 1: gets larger and more people are forced in and fall.
Speaker 1: This often happens when a large crowd is moving steadily
Speaker 1: through a confined route. Now, this actually happened to me
Speaker 1: at a bouncing soul show in Luckily someone picked me
Speaker 1: up and saved my life. Type two. The other one
Speaker 1: you want to watch out for is the crowd crush.
Speaker 1: When people are squeezed so much by a crowd that
Speaker 1: they can't inflate their lungs, they'll die from compressive asphyxiation.
Speaker 1: This typically happens when too many people push into a
Speaker 1: confined area. Often those who die are the ones against
Speaker 1: the wall. Now, maybe you've also heard talk of stampedes.
Speaker 1: The mass media's idea of mass panic or a stampede
Speaker 1: is actually misleading. Again, most of the evidence shows that
Speaker 1: people take sensible action when they have their right information.
Speaker 1: They're only crushed or crushing when they have no choice
Speaker 1: in the matter and they don't know what's going on
Speaker 1: because they're too far from the epicenter. Actually, stampedes themselves
Speaker 1: are unlikely to kill you. The word stampede suggests that
Speaker 1: people are causing havoc while they're running away, but the
Speaker 1: real problem is when people can't move at all, but
Speaker 1: train These events as mob psychology or crazes is. It's
Speaker 1: misleading and it's false. Most people move in crowd patterns
Speaker 1: and flows, but humans don't have the capability to transmit
Speaker 1: information about the physical dynamics of their crowd the same
Speaker 1: way ants can, for instance. Unfortunately, there isn't much of
Speaker 1: a record of information in the crowd control industry to
Speaker 1: provide analysis, but there are some technologies being developed to
Speaker 1: try to help. In two thousand thirteen, a team of
Speaker 1: UK and Saudi Arabia researchers developed an artificial intelligence system
Speaker 1: that uses body heat readings to monitor the build up
Speaker 1: of crowds and congestion. It uses infrared and black and
Speaker 1: white images to interpret the crowds changing density. Then it
Speaker 1: processes this information and acts like a human spotter, pointing
Speaker 1: out high density crowd situations. Also in eleven, a German
Speaker 1: researcher developed a system that observes when people sway slowly
Speaker 1: from side to side to keep their balance. This is
Speaker 1: another indicator of high density crowds. The system detects any
Speaker 1: sudden increased in symmetrical movements that suggested as a congestion issue,
Speaker 1: and it highlights the area in red, so you're probably
Speaker 1: asking right now, what should I do if I'm in
Speaker 1: a crowd disaster. There's some simple efforts that you can take.
Speaker 1: Look ahead and listen to the crowds noise. If the
Speaker 1: crowd starts to surge, wait for it, and then move
Speaker 1: with it and sideways. Check out the brainstuff channel on YouTube,
Speaker 1: and for more on this and thousands of other topics,
Speaker 1: visit how stuff works dot com