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How Coöperation Can Slow Emergency Evacuations

Want to get out of a burning building but can’t see an exit? Don’t follow the crowd, say complexity scientists who have modeled the behavior of mass evacuations.

In a fire, the obvious strategy is to leave the area by the nearest fire exit. Consequently, crowd behaviour specialists exercise a great deal of thought about how best to indicate fire exits, whether with a steady or flashing green light, for example. 

But what if the exits are not visible? What then is the best strategy for getting out? There are essentially two options–to make your own way to the exit, regardless of what others are doing; or to follow somebody else or a bigger group in the hope that you’ll do better together than alone. 

Last year, a group from Finland studied this question by watching how people attempted to get out of a corridor with two exits. It turns out, they said, that those who acted selfishly tended to get out more quickly. By contrast, those who cooperated by following others or forming groups with a leader, got out more slowly.

That’s a worrying result not least because the best evidence from real evacuations is that people do tend to cooperate with each other.

It also raises an interesting question: why should cooperation work against escapees? Today, Emilio Cirillo and Adrian Muntean at the Eindhoven University of Technology in the Netherlands provide an answer.

These guys have simulated the behaviour of a crowd escaping from a corridor with two doors. In various runs, they varied the number in the crowd from 100 to 10,000 and also the individuals’ propensity to follow each other, from no tendency at all, so they follow a random walk, to a high tendency in which individuals form into large groups. 

Cirillo and Muntean say that when the grouping tendency is close to zero, individuals tend to form only small groups and this does not effect the rate at which people find an exit. 

However, as the grouping tendency grows, the rate at which people can exit drops dramatically. Cirillo and Muntean suggest that this is because of pile ups at the doorways. 

The results give some insight into the Finish discovery but there may be other effects at work too that the model does not capture, such as disagreement between individuals which slow down a group.

The bottom line seems to be that if you ever need to escape from a building but can’t see an exit, don’t follow the crowd. That way lies disaster. 

Ref: arxiv.org/abs/1203.4852: Dynamics Of Pedestrians In Regions With No Visibility – A Lattice Model Without Exclusion

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