Search

A social force model is developed in this paper to study the crowd evacuation when a terrorist attack occurs in the public place. The persons in the model are divided into two groups—terrorists and pedestrians. On one hand, each terrorist chooses the nearest pedestrian as the target. Once the distance between him and his target is small enough, the terrorist will launch attacks on his target and the target will be killed with a certain probability. On the other hand, each pedestrian tries to avoid the terrorists and reach the exits. An emergency exit choice strategy which emphasizes the security risk factor is developed for pedestrians. The main simulation results are summarized as follows. First, the number of deaths in the terrorist attack increases with the number of terrorists and with the density of pedestrians. If the number of exits decreases, the death toll will become more sensitive to the change of the density of pedestrians. Second, adding the number of exits can significantly reduce casualties. Third, more pedestrians will be killed and the evacuation speed will be reduced if terrorists start the attack from the positions of the exits. Fourth, the emergency exit choice strategy has an advantage over the ordinary exit choice strategy in daily life for reducing casualties. The more unbalanced the terrorists’ initial distribution around the exits is, the more noticeable this advantage will be. Fifth, the number of deaths will decrease obviously if at least half of the exits are available and safe. Our study is valuable for developing an effective evacuation scheme to reduce casualties in a terrorist attack. [ABSTRACT FROM AUTHOR]

Understanding human decision making during emergency evacuations is important. It is because decision making is crucial at each stage of the evacuation (e.g. route choice, exit choice, path finding, etc.). Previous studies have examined the influence of social interaction and environmental factors on exit choice. However, researches on the decision-making behaviour and risk attitude towards such selection at the individual level is still limited. To fill this knowledge gap, we designed a series of virtual evacuation scenarios to examine the exit choice behaviour and decision-making attitude in uncertainty risk scenarios in different smoke conditions. Data collection was implemented by an online stated preference survey. The results revealed a systematic and pattern preference in exit choice regardless of the decisions made by experienced evacuees. The weighted uncertainty risk for individuals was determined by considering the smoke height and smoke appearance frequency. The weighting function between the subjective and objective entities exhibited an S shape. In addition, the function was estimated using an empirical equation. A decision maker's attitude towards uncertain risk in evacuation scenarios was observed to be a rank- and reference-dependent preference rather than being fully rational. The results of the experiments conducted in virtual environment well agreed with the cumulative prospect theory. This research demonstrates the feasibility of using virtual environment for evacuation experiment which can total avoid the risk of stampede while the individual decision-making behaviours can still be captured. • A series of virtual evacuation scenarios were designed and conducted to examine the exit choice behaviour and decision-making attitude of the participants under uncertain risk. • The study revealed a systematic and pattern preference in exit choice regardless of the decisions made by experienced evacuees. • The weighting function between the subjective and objective entities exhibited an S shape, and the function was estimated by an empirical equation. • A decision maker's attitude towards uncertainty risk in pedestrian evacuation was observed to be a rank- and reference-dependent preference rather than being fully rational. [ABSTRACT FROM AUTHOR]

The research of crowd evacuation plays the predominant role of guaranteeing the controllability of the stampede disaster and decreasing accidents casualties. Herd behavior is one of the characteristic crowd evacuation behaviors, which has the definite influence on evacuees' decision-making and evacuation efficiency. In this paper, the crowd evacuation observation experiments were conducted to investigate herd behavior by considered 16 working conditions, including change the number of participants, alter urgency levels and set barrier. The participant allotment and crowd movement time on different sides and exits are obtained. The judgment area and crowd density are proposed to understand the herd behavior and choices of decision maker. The critical states of herd behavior in direction and exit choices are confirmed according to the video observation and data analysis. The results indicate that herd behavior moderately leads to the different distribution and movement time of the experimental crowd. Decision maker does not present herd behavior when crowd density is relatively high or low. When crowd density in direction choice judgment area is within the range of [1/12, 1/6] (person/m2), and the crowd density in exit choice judgment area is within the range of [1/27, 2/27] (person/m2), decision maker basically triggers herd behavior. This study provides insight into the critical state of herd behavior which deepens the understanding of crowd evacuation and contributes to the reference of the crowd accident management. • Investigating herd behavior by conducting the crowd evacuation experiments. • Putting forward the critical state of the crowd herd behavior in decision-making. • Determining judgment area and crowd density to estimate herding choice. • Implementing participant allotment and movement time of experimental participants. [ABSTRACT FROM AUTHOR]