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Comment by psychoslave | Hacker News Reader

So, that's all very interesting. Do we also have some studies on how to avoid gathering people in such z dense level that all possibilities of that kind of dramatic outcome can occurs.

Also note that not all crowds are the same. I went to some metal concerts where the moves would exhibits very different moves, including less packed and steal, split in in very highly packed borders before an abrupt run and merge, as well as creating protection circle around someone who falls on the ground. I actually didn't witnessed any major crowd incident in such a concert, so I would be interested to have statistics about outcomes of a crowd panic in a metal concert vs in a cinema for example.

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Seems to me that formal studies would have more of an effect looking at how to manage crowds that are already too dense without making things worse. If you want to avoid the density in the first place, you decide on a maximum density within a central perimeter, and also manage density appropriately along the ingress routes. That way you don't just push the unsafe densities into the outer side of the perimeter. And you set your desired densities low enough to both avoid dangerous situations inside the central perimeter, and allow the central crowd to get out if there is a fire/etc. inside it.

Essentially if you want a max density in area A, you enforce some other max densities in the area several times larger than A.

I would imagine that if anyone has done the work to study this, it’s the Saudis for the Hajj, since they are managing the largest human migration to a single point. (I believe there are larger migrations like China’s Lunar New Year, but those are more diffuse since it’s more people to hometowns.)

Studies will also no doubt be done on the currently unfolding Maha Kumbh Mela in India, which has to be breaking some records for largest human gathering.

I admittedly don’t know very much about that festival.

One interesting thing about Hajj is that not only is travel to a specific place mandated but also travel in a specific path and direction; you need to walk around the Kaaba seven times and walking between the hills of Safa and Marwah seven times.

Given the Kaaba is only 12m x 10.5m its a very small place to concentrate people in.

If you can have a circle pit then the density is probably less than 9 people per square meter.

Crowd density is certainly the key here. Over a certain density crowds move like a liquid. Under a certain density crowds get much more difficult to model.

This is not new in any way, btw. This paper seems to specifically address the running of the bulls.

https://www.science.org/doi/10.1126/science.aat9891

But if anything, this study at least shows that we're getting closer to understanding and managing the dangers of large, dense crowds in a way that can actually be applied

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