A discrete time evacuation model designed for safety of building egress

The crowd safety is closely related to the evacuation capability of building egress. In order to ascertain the capability of building egress, it's necessary to define the relationship between density and crowd-flow rate. In this paper a discrete time evacuation model (DTEM) for a building with single egress is put forward. The empirical relationship between density and velocity has been summarized and then the crowd-flow rate as a function of density is deduced. The influence of crowd density on evacuation process was considered in the model. In DTEM, the evacuation process can be divided into different phases according to the characteristics of the building, the evacuation time is discrete. The density of the crowd and the number of the evacuees can be determined at any time during the evacuation process. The model was used to research type C building; it was proved that the efficiency cannot be improved when the width of the egress is increased to a special value. Furthermore, it was also proved that the characteristics of crowd density are similar during the whole process, although the evacuation time is different corresponding to different relationship between density and velocity. Finally, the model can define the optimum width of egress in the case. Based on the results, DTEM shows great value in dealing with building up the egress design.