They explain how the crowd moves in the chupinazo of San Fermín and why a misfortune does not occur

Year after year, watch the mass chupinazo on television that starts the San Fermín festivities in Pamplona causes the same impression. How can all these people fit in the Consistorial Square – a smaller one in the reality of what appears in the images – without bruising pushes or, worse still, dragged by a human avalanche? A team of physicists from the University of Lyon (France) and that of Navarra have conducted a novel study to know how the crowd moves in that reduced space. The findings, based on four years of observations, point out that these collective movements are not chaotic, but can be predictable from a certain density. The work, published Wednesday in the prestigious magazine ‘Nature‘, can help avoid a misfortune in very busy reduced environments, such as festivals or concerts.

The idea of ​​the study occurred to Iker Zuriguel, from the University of Navarra, after listening to a talk from his colleague Denis Bartolo, from the University of Lyon, about the physics of fluid mechanics applied to the exit of the Boston Marathon. “I taught him some videos of YouTube of the Chupinazo, who did not know what it was, and convinced him to apply his model in Pamplona,” he says. «In El Chupinazo about 600 people congregate in a 50 -by -20 -meter square, with an average density of six people per square meter. It is repeated every year in the same place, which makes it an incredible laboratory to investigate pedestrian dynamics, ”he adds.

Nine cameras

The team placed nine cameras in different parts of the square to record Los Chupinazos from 2019 to 2024, with the exception of the two years in which there were no parties for the Pandemia stop of the COVID-19. When analyzing the images, they found that the crowd does not move chaotically as thought, but does “with a periodic movement, such as the pendulum of a cuco clock, orbital,” explains Zuriguel. This movement “can be in the direction of the clock needles or the opposite. Even in one part of the square there can be regions (groups of people who move at the same time) who move in one direction and elsewhere, in another ».

The greater the density, the larger these regions will be. For groups of 500 people, they have a typical ten -meter size. Of course, they do not form a perfect circle, but sometimes move forward a few meters, backwards, to the right … «The important thing is the frequency of oscillation: they take to make an entire return (around a specific point ) 18 seconds, which has to do with the size of the square, ”says the author. It is very curious when musicians break into the square and it is divided into two, each with their behavior.

The researchers compared their results with the images of the Love Parade de Duisburg Electronic Festival in 2010, during which several hundred people were injured and 21 died in a human stampede. They discovered that when the multitude of Duisburg reached a density similar to that of the San Fermín festivities, the same oscillations were observed.

Does this mean that in Pamplona there may be danger? «Yes, whenever there are so many people there is, but the difference is that in Duisburg there was only one entrance and an exit, while here the square gives five streets and another annexed square. I think this is precisely what makes a misfortune never occurred, ”says the physicist.

The study results apply from four people per square meter, «what makes sense. Pedestrians are free to do what we want in low densities, in high densities, we move as sand granites or water molecules, we end up doing what the rest does, ”says the researcher. «Four people per square meter is already a lot of physical contact. And six don’t even tell you, imagine them in a shower, ”he adds.

The author believes that the technique used to detect movements in San Fermín can be applied to anticipate the behavior of other crowds in confined spaces. As he says, in Pamplona there has never been a great accident but “these movements that we have seen make the system more dangerous and you have to take it into account,” he says. In similar situations, “measures can be taken such as preparing ambulances or being prepared to act if any unexpected problem,” he adds.