Hajj provides critical insights in crowd control
German researchers use the physics of fluids to predict dangerous crowd conditions; “thermometer of chaos” helped prevent Hajj deaths in 2007
Longtime readers may have guessed that we are not of the Muslim faith, but that does not mean that there is nothing to learn from the Islamic religious tradition, both theologically and temporally. In fact, scientists are finding that the most important Muslim rite — the Hajj, or pilgrimage to Mecca — holds important insights for crowd control studies. Every year, millions of Muslims descend on the holy city for a week of prayer and reflection, and quite often stampedes result both from general panic and religious fervor. Last year, for instance, 345 people were killed and 289 injured. These tragedies, however, may soon be a thing of the past thanks to some ingenious work in the physics of fluids.
How it was done: Using video recordings of the 2006 stampede, physicists at Dresden University of Technology in Germany created visual-recognition software to track and measure the motion of individuals in the crowd. Under normal conditions, Science News reported, pedestrians move in orderly patterns such as walking in lanes moving in opposite directions. As crowds develop, stop and go traffic develop in a wave pattern, as seen in car traffic jams. “But in critical situations … people can break out in panics that result in random patterns of motion, similar to the turbulence of water in the wake of a boat.” By looking at the video from last year’s tragedy, the Dresden researchers were able to identify the factor that correlated with such outbreaks: crowd pressure, a function of crowd density and change in the velocity of the flow. Call it “a thermometer of chaos.”
The results are “remarkable,” said Hani Mahmassani, a traffic-dynamics expert at the University of Maryland at College Park who has advised the Saudi government on Hajj-related issues. “It sheds incredible light on the anatomy of a major crowd disaster.” Still, there is much work to be done, he said, especially in the psychology of panic. Those interested in such work will have plenty of raw data to work with. According to Salim Al-Bosta, a civil engineer in the Saudi government, image-recognition software is now an integral part of the government’s crowd control system, with software notifying officials when crowd pressure in Mecca reaches a critical stage.
