Researchers in the Department of Applied Physics and Mathematics at the Universidad de Navarra have demonstrated for the first time, with real experiments, what happens in a jam of people when there is pushing, a phenomenon that  had not been measured in any previous study.

The experiments -carried out in collaboration with the School of Architecture and the Sports Service of the academic centre- used pressure sensors and three cameras to record what happens when a group of people -one hundred volunteers in this case- try to exit at the same time through a door. The experiments were carried out with doors measuring 68 cm and 75 cm, and ten recordings were made in situations of no pressure, intermediate pressure and high pressure.

The results obtained indicate that the more the pushing, the greater the pressure in the exit and the more jams produced. "And not only that," explains Iker Zuriguel, the researcher who directed the experiment, "but also there is a gradual increase in the difficulty of undoing the jams. In fact, we prove that, with pressure, the probability of occurrence of jams of over a second of duration is multiplied by ten. This is a very important matter, if we take into account that jams of three or four seconds can imply life-or-death risk for the people involved."

The group in the Granular Media Laboratory of the Universidad de Navarra have been working for several years on the way in which different agents behave when exiting an enclosure - from the grains or particles in storage tanks, to flocks of sheep-, but until now there had been no extrapolation to people. "The practical application of this study is broad, but perhaps one of the most urgent measures could be that of modifying the current norms concerning exits from enclosures, which are designed and calculated without talking into account the determinant factor of pressure."

Same time, but more accidents

The video recordings, for the first time with real people, suggest that, besides taking into account the time of evacuation from an enclosure, it is fundamental to consider the frequency with which jams occur during the process: "Existing studies until now centre exclusively on the time that it takes to evacuate a space, but in similar time spans very different circumstances can develop, as is observed in the videos we have taken. Jams that show up as small jumps in the graph can translate into lesser or greater accidents, some of which could potentially even result in death."

To date the group in the Department of Physics at the Universidad de Navarra

has carried out over 600 evacuations with sheep. With these experiments they have proved the usefulness of placing an obstacle in front of the exit door to diminish the pushing pressure. The next step will be to demonstrate the same utility with people, a finding that would have important practical applications in all types of enclosed spaces.

The study, published in the scientific journal Physical Review E, was undertaken in collaboration with the Consejo Nacional de Investigaciones Científicas y Técnicas de Argentina (Conicet) and the Faculty of Veterinary Science at the Universidad de Zaragoza.