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The physics of stampedes

With all the statements regarding the culture of mendicancy and how the establishment (read: government, media moguls, corporations) exploits the masses, perhaps the empathy for the stampede victims will increase if I echo the statement that buildings such as the ULTRA are designed with the assumption that the crowds flowing through its exits do like fluid through a pipe, and that according to David J. Low, a civil engineer in Scotland:

"This traditional approach assumes that the crowd is made up of identical, unthinking elements...A fluid particle cannot experience fear or pain, cannot have a preferred motion, cannot make decisions and cannot stumble and fall. [boston.com]"
The lack (or the absence) of a security plan and the choice of venue aside, emotions played a huge part in the tragedy that transpired last Saturday. Partly panic-driven, as a bomb scare was reported, but it was motivated more by the chance to get the prize (it was said that the host handpicks ten contenders for the million-peso pot, but gives at least a hundred pesos for a joke). Even harmless tricks such as throwing caps (e.g. April Boy Regino concerts) or posters (e.g. mall tours for movie promotions) can incite a mob and it is even suggested that performers should be aware of this responsibility.

The geek in me tried to understand the physics of stampedes in as little time as possible. While the rest of the blogosphere elicited the whole spectrum of emotions on the Saturday accident, I wanted to view it in another perspective, that which assumes less of the they're-ordinary-people-who-wanted-to-get-out-of-the-vicious-cycle-of-poverty and the-system-is-to-blame-for-what's-happening-now.

In a way, yes, the crowds behaved under the laws of fluid dynamics, like the flow of water meeting a vertical obstacle at one end. In a commentary about the stampedes that usually happen during the Haj, neo-neocon posited:
The situation, as far as I can determine, is a bit analogous to the elements that go into a tsunami, strangely enough. That is, a huge and extremely powerful force (in the case of crowds, the moving people; in the case of tsunamis, the moving water) is initially spread out horizontally. Then, some sort of blockage impedes that horizontal movement and converts it, at least partially, into a vertical one.
It's a situation you can almost see everyday if you ride the MRT during rush hour: the crowd mills around the entrance to the car--not your usual falling-in-line routine back in grade school, in the shape of an arch. Years ago I commuted daily from Cubao to Makati and found that by positioning myself directly in front of the train door, I have the same chance of, and even lesser than, entering the train door if I sneak myself from the left or right of it. And in desperate times when I know that I will be late, these latter positions work to my advantage. I guess most people think likewise.

Increase the panic level of that MRT scenario a thousand times or ten and you have a Wowowee situation. People wanted to enter the stadium at once, but the entrance is narrow. All the left, right and central positions are occupied and the last people to join are pushing the ones near the entrance. And that may be where the verticality of the movement came in. The weak ones near the entrance may have given in--the old, the women, the children--forming the human base of the stampede from where the latter ones step on to get inside, dying with a force of almost half a ton from compressive asphyxia as more bodies pile up. This is of course, assuming that the casualties are concentrated at the entrance (I can't find any details on this from the news).

The guard rail giving in was also expected. Due to leaning and pushing, it became a set of toothpicks or a stack of cards against a crowd of fifty or sixty (?) thousand. From an Australian study, under a simulated panic, a "crowd" of five is capable of developing a force of 3430 newtons, a force a third of a ton against a guardrail. Multiply it ten thousand times and the force is unimaginable, short of releasing a TNT in the center of the city.

I could go on and on, but what is the point of this entry?

There is science in crowd management, and it doesn't hurt if we understand it, however complex it may be, it only boils down to two things: crowds behave like fluid flow (from placidity to turbulence) and emotions play a decisive role in how people behave in crowds.

I almost wanted to agree with the benevolence of a radio announcer I heard last Saturday afternoon, except for the air he had put upon himself so high--these people only knew that they wanted to get in and won't know about crowd management. Somebody had to be responsible for them and that somebody was not there.

Knowing what a mess the tragedy made out of us (we're in the New York Times!), stampedes are a global phenomenon, and it is not confined to the Third World or "only in the Philippines." I'm not schadenfreuding about it (the closest term I can think of), but let's look beyond the national self-esteem and let's get back to work. My only fear is that after all the pinpointing has subsided and this tragedy has lost its top spot to another tragedy or scandal, we haven't learned our lesson well and are bound to repeat it in the future.

*Stampede model lifted here.

**I've been planning to revive my Skythologies series. What a way to start.

“The physics of stampedes”

  1. Anonymous aa Says:

    wow, you beat me to it. =)

  2. Anonymous Paolo Says:

    Thats a very good assesment of what happened!

  3. Anonymous ade Says:

    "found that by positioning myself directly in front of the train door, I have the same chance of, and even lesser than, entering the train door if I sneak myself from the left or right of it."

    I figured that one out too. hehehe.

    anyway, interesting post. explains a LOT. :)

  4. Anonymous sky Says:

    aa: great minds think alike! hehehe.

    paolo: thanks, though it's a hurried post.

    ade: thanks for visiting too. everyday we encounter such crowds. observe how people behave and it may save your life someday.

  5. Anonymous juned Says:

    Interesting and informative post. I hope you do not mind I linked your article in one of my posts.

  6. Anonymous DJB Says:

    I think the fluid gas model of a crowd is useful with stampedes corresponding to turbulent flow being marked by a "phase transition" at a "critical point" -- like the sudden boiling of water, and the level of emotion--panic, fear, anger, corresponding to the temperature. There is another approach from Game Theory I was looking at but haven't written up: The Tragedy of the Commons.

  7. Anonymous mariko Says:

    you may want to check out the papers here:


  8. Anonymous coleen Says:

    kaya pala sa singapore ang mga MRT doors ine-encourage na ang papasok pumuwesto sa gilid, ang mga lalabas sa gitna.

  9. Anonymous banzai cat Says:

    Excellent analysis of the stampede, man. Hope you won't mind if I cite you in a future post. :-)