
When Crowds Try to Flee for Their Lives - 7402
http://www.atlasobscura.com/articles/what-happens-when-crowds-try-to-flee-for-their-lives
======
lkozma
One of the best explanations I've read of this phenomenon was on reddit:

[https://np.reddit.com/r/worldnews/comments/3pcvfb/saudi_arab...](https://np.reddit.com/r/worldnews/comments/3pcvfb/saudi_arabia_hajj_disaster_death_toll_at_least/cw5vxtm/)

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nxc18
This gives me a new appreciation for the panic bars
([https://en.m.wikipedia.org/wiki/Crash_bar](https://en.m.wikipedia.org/wiki/Crash_bar))
I've been seeing my entire life. I only recently discovered (thanks to a well-
hidden tag on one) that they are fire safety devices, but this article makes
it clear how important they are in crowd safety for building-type venues.

Presumably not launching fireworks into the ceiling and limiting crowd sizes
are the other steps that would be taken in this particular situation.

It really is sad that people have to relearn fire safety lessons over and
over. (Note that none of this applies to outdoor crowds, which is obviously a
much harder problem when scaled up)

~~~
sytse
"At first security guards thought patrons were trying to leave without paying
and blocked exits, trapping victims inside." One other thing to improve is to
have people pay up front. This would have prevented the guards from closing
the exits. If you have a tab apparently sometimes people try to do a mass
break out.

Another great thing is to always have people leave through the fire exits to
get them familiar with them (I think they do this in the UK).

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chiph
I'm surprised they didn't mention the fire at The Station club, where 100
people died in the fire because they couldn't get out in time. Mostly because
they headed back to the door they came in (a behavior mentioned in the
article)

[https://en.wikipedia.org/wiki/The_Station_nightclub_fire](https://en.wikipedia.org/wiki/The_Station_nightclub_fire)

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lisper
Some technical resources:

[http://www.vfdb.de/download/TB_13_01_Crowd_densities.pdf](http://www.vfdb.de/download/TB_13_01_Crowd_densities.pdf)

[http://www.gkstill.com/Support/crowd-
density/CrowdDensity-1....](http://www.gkstill.com/Support/crowd-
density/CrowdDensity-1.html)

[http://www.gkstill.com/Support/crowd-
flow/MovingDensity.html](http://www.gkstill.com/Support/crowd-
flow/MovingDensity.html)

And one very dramatic video:

[https://www.youtube.com/watch?v=eu4DlwE0Bu8](https://www.youtube.com/watch?v=eu4DlwE0Bu8)

Viewer discretion advised.

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CaptainZapp
Absolutely mandatory reading on the subject:

[http://www.newyorker.com/magazine/2011/02/07/crush-
point](http://www.newyorker.com/magazine/2011/02/07/crush-point)

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pasta
One thing that is used to prevent bad situations is to place wide round
columns before the exits. This will direct the flow around the columns
creating a little more time for people behind the column to go thought the
exit and remove some pressure of the people in front of the columns.

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amelius
So is there any action which, if taken by a minority of people, could avert
disaster? How big should this minority be?

~~~
lisper
Nope. Once a crowd reaches a certain density you're pretty much just screwed.
It's just physics at that point. You can't even get out (that's part of the
problem). The best you can do is to never get yourself into a super-dense
crowd situation in the first place.

~~~
amelius
As far as I can tell, all research on this topic assumes that all people
behave in the same way. So it would be interesting to investigate how to
change this.

~~~
lisper
People in a super-dense crowd behave in the same way because they have no
choice. A super-dense crowd is essentially an incompressible fluid with people
as the constituent particles. If everyone stood perfectly still everyone would
be fine, but that is not a stable situation. One person tries to move, but
they can't because they are packed in so tightly. There is nowhere to move to.
So that person's movements are transmitted directly to their neighbors. Again,
if _all_ of those neighbors just ignored the fact that there was someone
wriggling next to them and continued standing perfectly still, they might be
able to contain the problem, but that's not what happens. Some of the
neighbors of the initial mover respond to the movement by trying to move
themselves. As long as the average number of people responding to movement by
moving by moving themselves is >1, the movement will inexorably amplify and
spread.

~~~
amelius
> People in a super-dense crowd behave in the same way because they have no
> choice.

Yes, it seems like all research focuses on the situation where it is already
too late (perhaps because the fluid equations are easier to handle).

I'd like to see some simulations where:

1\. Half of the people refuse to move.

2\. Half of the people start moving in the opposite direction.

3\. Half of the people stand still and try to hold hands with other people (of
that group), effectively blocking other people.

~~~
lisper
> Half of the people refuse to move.

When someone shoves you, you can't "refuse" to move. Momentum has to be
conserved somehow.

> Half of the people start moving in the opposite direction.

Which half?

If you can somehow split the crowd cleanly and get the two halves moving away
from each other that might help, but this is usually not possible. And getting
a randomly selected half to move in a different direction than the crowd as a
whole is simply not possible, again because of physics. A dense crowd is
essentially an incompressible fluid. All of the particles in a local area have
to be moving in the same direction.

> Half of the people stand still and try to hold hands with other people (of
> that group), effectively blocking other people.

You really don't have a good mental model of what a dense crowd is like.
There's no need to hold hands. You are already pressed up against neighbors on
all sides of you. In a dense crowd you are going to remain stationary relative
to your neighbors whether you like it or not. That is the root of the problem.

~~~
amelius
> You really don't have a good mental model of what a dense crowd is like.

And you are clinging to much to your crowd-as-a-fluid abstraction.
Abstractions often don't hold up in the real world, especially if you actively
try to break them. Further, yes, if you squash people hard enough they behave
like a fluid, but what can we do at or before the state-transition?

~~~
lisper
> what can we do at or before the state-transition?

Get the hell out of there as fast as you can while you still can.

~~~
simonh
That's what everybody else is doing. The suggestion above to try and work your
way to the edge of the crown seems sensible, even if that edge isn't in the
direction of the exit. I've been in dense crowds but noticed that there is
sometimes a significant gap between the crowd and the walls.

~~~
munificent
I think the main point is that you "get the hell out of there" where "there"
is _the crowd itself_ not _whatever the crowd is trying to move away from_.

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joshstrange
Reminds me of the
[https://en.wikipedia.org/wiki/Hillsborough_disaster](https://en.wikipedia.org/wiki/Hillsborough_disaster)

