Abstract
Although some experimental evidence showed that an obstacle placed in front of a door allows making people’s evacuations faster, the efficacy of such a solution has been debated for over 15 years. Researchers are split between those who found the obstacle beneficial and those who could not find a significant difference without it. One of the reasons for the several conclusions lies in the variety of the experiments performed so far, both in terms of competitiveness among participants, geometrical configuration and number of participants. In this work, two unique datasets relative to evacuations with/without obstacle and comprising low and high competitiveness are analyzed using state-of-the-art definitions for crowd dynamics. In particular, the so-called congestion level is employed to measure the smoothness of collective motion. Results for extreme conditions show that, on the overall, the obstacle does not reduce density and congestion level and it could rather slightly increase it. From this perspective, the obstacle was found simply shifting the dangerous spots from the area in front of the exit to the regions between the obstacle and the wall. On the other side, it was however confirmed, that the obstacle can stabilize longitudinal crowd waves, thus reducing the risk of trampling, which could be as important (in terms of safety) as improving the evacuation time. However, under urgent, competitive, but non-extreme conditions, the obstacle generally had a positive effect, helping channeling the flow of pedestrians through the exit while facilitating their interactions.
Highlights
Concerning obstacle distance (Fig. 17c), it is found again that, at least for the cases investigated here, differences in flow rate are not important
The variations in crowd collective motion caused by placing a circular obstacle in front of an exit during evacuation have been studied by means of supervised experiments
Trajectories extracted from video analysis have been used in the numerical analysis which focused on classical and novel quantities employed in the frame of pedestrian dynamics
Summary
This work is based on two separate experimental trials which have been already described in other publications. To allow recreating conditions similar to a real emergency evacuation while ensuring the safety of participants, a second set of experiments was performed by involving professionally trained soldiers of the Spanish army. In this second experimental campaign (details on these experiments are given in26) 181 soldiers were recruited as participants. To ensure safety and avoid that injuries would occur (which, for instance, are not rare in airplane evacuation tests32,33), officers were supervising the experiments and could stop them at any moment should a dangerous situation occur This occurred a couple of times and those executions had to be stopped as some participants got their arm trapped at the doorjamb or were about to fall down. In addition to the video camera providing tracking information, in the experiments with soldiers a pressure sensor was mounted on the doorjamb (technical details are provided in27), allowing to measure the pressure exerted on the wall from the evacuating crowd
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