Experimental and modeling study on evacuation behaviors considering small groups under different visibility

The evacuation of crowd mixed by individuals and social groups with low visibility under fire has attracted increasing attention. A series of evacuation experiments were conducted in a room under different visibility conditions. Critical results regarding the movement speed, evacuation time and typical behavior, were collected. The results show that evacuation with group can be more advantageous than individual evacuation under limited visibility with 9%-transparency eyepatches. Two movement modes of groups for evacuation are found in limited visibility, including the leadership mode and cooperative mode. To capture and evaluate the influence of group behaviors on crowd evacuation, we propose an extended floor field cellular automaton model to perform such phenomena, which is validated with the comparison of experimental results. The characteristics of two movement modes for groups are explored with multiple cases considering the effects of factors such as the occupant density, familiarity of exits and number of group members. The results show that the cooperative mode is superior to the leadership mode for groups when the occupant density is between 0.05 and 0.08 ped/cell without the familiarity of exits and the exits trigger, and it is adverse when the density is less than 0.02 ped/cell. In addition, the occupant density has an obvious effect on the evacuation distance between the members of groups when people are familiar with the exits. This study can be reference to the verification of egress-related computational models and fire safety engineering design.