In July, during the opening ceremony of the San Fermín Festival reporting the imminent start of the Taurus race in Pamplona, Spain, more than 5,000 people are in the central square of the city. The crowd begins the morning dressed in white. At noon, a large part of their clothes was dyed in pink by the fluid blood.
Participants in the event described the noisy crushing of people Denis BartoloPhysicist at the normal superior school in Lyon, in France, who did not dare to foot on the place itself. “The density of people is so high that it is not only that you feel uncomfortable,” he said that he was told. “It becomes painful, as you can feel pressure on your chest.”
In several years, he filmed and studied the event in order to perhaps one day to help prevent Stampeds that can become fatal in major public events. In an article published Wednesday In the newspaper Nature, Dr. Bartolo and his colleagues say that it may be possible to predict the spontaneous movement of a large crowd in a confined space once the density of people crosses a critical threshold.
Studying large, densely wrapped crowds is notoriously difficult. “You can’t just invite a thousand people to participate in an experience,” said Dr. Bartolo. Even if he could, “I could not know how to guarantee their security,” he added.
This is why the San Fermín festival was so attractive. This implies thousands of people who bring together predictably and relatively calmly, each year.
Dr. Bartolo and his colleagues set up cameras on the upper balconies of two buildings on the opposite sides of the square to film the participants below. “If you take a look at the video, the dynamics seem to be erratic, chaotic, turbulent,” he said. But he wondered if he could disentangle an organizational principle that govern the movements of the crowd.
The analysis of the images presented a challenge similar to the study of the flow of water. “Of course, you cannot detect the position of each water molecule. It’s impossible, ”said Dr. Bartolo. And yet, there are mathematical techniques in the field of fluid dynamics that allow researchers to measure the flow of a material by inspecting its direction and speed. Dr. Bartolo applied these same methods at the San Fermín festival.
The crowd turned out to be less chaotic than they seemed. Instead, researchers have detected circular oscillations in people’s sea. “We are talking about hundreds, if not thousands of people, all according to the same circular trajectory in synchronization,” said Dr. Bartolo.
In addition, the orbital movements, in which each person draws a raw circle from their individual starting point in the crowd, took 18 seconds to finish in this special place. The timing was so reliable that Dr. Bartolo said “You can define your clock” on the dynamics of this crowd, even if the movements may seem random.
The research team then applied what they had learned to a deadly stampede. They examined surveillance images From the 2010 love parade to Duisburg, Germany, where 21 died and hundreds of others were injured in a jostle. “And we detected the same oscillations”, which emerged just before the deadly scramble, said Dr. Bartolo.
When the researchers built a mathematical model of crowd mechanics, they found that above a critical density of people, these circular movements emerge spontaneously. They do not depend on an internal or external force, like people who are actively growing.
As a security precaution, Dr. Bartolo suggests monitoring the crowds densely packed for these orbital movements. Detecting them can offer a prior warning to the emergence of dangerous and uncontrolled movements. By grabbing oscillations when they are small, he says that the event organizers could ask the crowd to disperse or stay still, before the orbits grow and lead people crushed or trampled.
“We are not yet quite there”, Analisa QuainiA computer mathematician at the University of Houston who was not involved in the study, said these real applications. It is one thing to have a well -lit place filmed with high quality cameras. But granular night safety images, for example, may not reveal revealing circular movements.
However, Dr. Quaini qualified the search for significant contribution to understanding the collective behavior of large dense crowds.
“It’s a huge effort,” she said. “And one day, we can use it in a practical setting.”