Re:How One of the Deadliest Hajj Accidents Unfolded
by visakanv on Tuesday September 06, 2016 @02:47PM
(#12438298)
I once saw a reddit comment that explained it really, really well: https://np.reddit.com/r/worldnews/comments/3pcvfb/saudi_arab...
Re:How One of the Deadliest Hajj Accidents Unfolded
by Analemma_ on Tuesday September 06, 2016 @03:31PM
(#12438656)
There's also a good New Yorker article that made a lot of the same points, but in the form of a longform article, if you prefer that: http://www.newyorker.com/magazine/2011/02/07/crush-point. The bottom line is that past a certain "person density", crowds are actually governed by a lot of the same laws as fluid dynamics. When you introduce a "wall" in front of the flow, the people at the back don't even know it because they're too far away to notice. They can't know to "stop" any more than water at the back of a pipe can suddenly stop if the water ahead of it encounters an obstacle.
Re:How One of the Deadliest Hajj Accidents Unfolded
by cloudjacker on Tuesday September 06, 2016 @11:34PM
(#12440827)
60% water, checks out
Re:How One of the Deadliest Hajj Accidents Unfolded
by mmanfrin on Tuesday September 06, 2016 @02:48PM
(#12438312)
The problem is that people don't stop immediately. You stop, the person behind you stops just a little bit later, the person behind them a little bit later than that. As you're walking the gaps in between people shrink. Finally the person in front of you stops, you try to stop but the person behind you is close and bumps in to you a bit as you try to stop, you bump the person ahead of you who has stopped because they can't move forward, which squeezes the person ahead of him. Repeat for thousands of people and you have a collection of tiny small bumps and pushes that squeeze people to the point of death.
Re:How One of the Deadliest Hajj Accidents Unfolded
by mkaziz on Tuesday September 06, 2016 @02:42PM
(#12438264)
Thinking about the sheer numbers might help imagining the mechanics. 2 million pilgrims crowded into very specific places at or near Makkah that year. For reference, the population of Chicago is 2.7 million.
Re:How One of the Deadliest Hajj Accidents Unfolded
by ihsw on Wednesday September 07, 2016 @09:38AM
(#12443243)
> I would hope that with most people having cell phones nowadays, which gives them the ability to more easily regroup after separation, it should be a priority in cases like this to urge people to not form chains and to devalue staying with their group if it affects the flow of traffic.
While true, the reception at such events is usually non-existent due to the sheer volume of people with devices. Even with a healthy quantity of cellular base stations or wifi access points, there will still be serious issues and connections will be spotty at best.
Re:How One of the Deadliest Hajj Accidents Unfolded
by lisper on Tuesday September 06, 2016 @04:03PM
(#12438889)
> as long as everybody obeys that simple rule of movement, this should never happen.
That's true, but beyond a certain density this is no longer possible because there is no space between you and the next person.
Here's a video that shows this phenomenon in rather graphic detail (warning: disturbing imagery):
Re:How One of the Deadliest Hajj Accidents Unfolded
by mbrameld on Tuesday September 06, 2016 @03:43PM
(#12438738)
At a certain density a crowd of people starts behaving more like a fluid than a group of individuals.
Re:How One of the Deadliest Hajj Accidents Unfolded
by semi-extrinsic on Tuesday September 06, 2016 @05:03PM
(#12439276)
And the GP has rediscovered that viscosity is much higher for a fluid made up of long-chained molecules (think motor oil) than a fluid made up of short-chained ones (think gasoline).
Re:How One of the Deadliest Hajj Accidents Unfolded
by noobermin on Tuesday September 06, 2016 @05:24PM
(#12439400)
>Under normal conditions, when people walking in front of you stop, you stop also so you don't bump into them. Makes sense, right?
By that logic, there should be no car crashes.
Re:How One of the Deadliest Hajj Accidents Unfolded
by duaneb on Tuesday September 06, 2016 @07:04PM
(#12439888)
> By that logic, there should be no car crashes.
Under normal conditions with rational drivers, there shouldn't be any car crashes. It's when the assumptions fail—distractions, obstacles in the middle of the road, weather, inebriation—that people crash.
Under normal conditions, when people walking in front of you stop, you stop also so you don't bump into them. Makes sense, right?
So you would think that as long as everybody obeys that simple rule of movement, this should never happen.
But having been caught in a much less serious "crush" once, I know it's not that simple.
In my case, I was at a similar event -- religious in nature, lots of people from all around the world, and mostly traveling in groups -- and although everybody was polite and non-aggressive, as groups traveled through the crowds, nobody wanted to be separated from their groups, and that caused major issues.
For instance, a lot of groups traveled while holding hands in an effort to remain together. But imagine how much more difficult it is for a bunch of worm-like people chains to travel through a crowd than it is for discrete individuals to do so.
The surge I was caught in was little more than a momentary push forward, but it was very scary to lose control over my ability to move freely.
I would hope that with most people having cell phones nowadays, which gives them the ability to more easily regroup after separation, it should be a priority in cases like this to urge people to not form chains and to devalue staying with their group if it affects the flow of traffic.