An experimental study of the impact of an obstacle on the escape efficiency by using mice under high competition

Crowd dynamics is an area of interest for scientists as a series of accidents caused by crowd within the last decades. Interestingly, some previous experiments and simulations have suggested that the presence of an obstacle in front of an outlet may improve the flow rate. A number of experiments were conducted to drive the mice to pass through an exit, with or without an obstacle before it. The impact of the obstacle on the efficiency of evacuation was studied under two typical geometry conditions, i.e., The setting I and the setting II. The setting I is an area of 1.5 m wide and 80 cm long and the setting II is a laterally confined space compared with Setting I. For evacuation at Setting I, a benchmarking study without the obstacle was conducted and the average evacuation time per mouse is 4.7s±0.44s. Further study was conducted by placing a 3.2 cm-obstacle at varying distances of 3 cm-6 cm and the quickest evacuation time per mouse is reduced to 3s±0.09s, around reduce by 36% compared with no obstacle condition. The presence of an obstacle before an exit improves the flow rate, which is consistent with the previous finding in silo flow and crowd flow. For evacuation at Setting II, similarly, a benchmarking study without obstacle was conducted and the average evacuation time per mouse is 3.9s±0.36s. When the 3.2 cm-obstacle was placed at varying distances from 4 cm to 10 cm, the average evacuation time per mouse increases to 4.9s±0.28s, around 26% higher than no obstacle condition. Further experiments were conducted at Setting II by using a 2 cm-diameter at varying distances from 4 cm to 8 cm and the presence of 2-cm obstacle still increases the evacuation time. The study reveals that the presence of an obstacle in front of an exit can improve or deteriorate the evacuation efficiency depending on the surrounded geometry. The time intervals of two consecutive mice and the burst sizes are also studied.