Science News has an intriguing article on how physicists have applied models of fluid dynamics to successfully understand dangerous crowd stampedes.
The joint German-Saudi team were prompted to conduct the research by the tragic events of 2006 where hundreds were killed during a mass stampede during the Hajj, the annual pilgrimage to Mecca.
Various physical models have been applied quite successfully in understanding crowd behaviour. We reported on one using a model of magnetism back in 2005.
These models work because, perhaps surprisingly, many different types of complex system seem to share higher-level or emergent properties: from atoms to neurons to people to telephone networks, and so on.
When trying to understand potentially life-threatening situations like crowd panic or stampede, it would be unethical to do large scale experiments, but these sort of models could be used to understand how they occur.
The researchers simulated crowd behaviour using models from fluid dynamics and compared their predictions with video of the stampede during the 2006 pilgrimage and found that it could accurately model crowd panic.
In normal conditions, pedestrians tend to spontaneously fall into ordered patterns, such as lanes going in opposite directions, previous research had shown. As crowds get denser, stop-and-go patterns begin to propagate in waves, as is typical for cars on heavily trafficked highways. But in critical situations‚Äîas when cars get into gridlock‚Äîpeople can break out in panics that result in random patterns of motion, similar to the turbulence of water in the wake of a boat. Crowd members can get squeezed and asphyxiated or fall and be trampled.
These sorts of models can be life-saving as they enable crowd control measures to be tested in the most dangerous conditions without putting anyone at risk.
The full paper is available online as a pdf file.