Optimization of emergency shelter layout with consideration of toxic gas leakage based on a cell transmission model

The layout and site selection of emergency shelters have a significant impact on the efficiency of large-scale crowd evacuation. However, during the actual evacuation process, there may be factors that affect the capacity of evacuation routes. This paper considers the problem of decreased road capacity due to toxic gas effects. By extending the Cell Transmission Model (CTM) and incorporating additional constraints, a linear programming model for emergency evacuation traffic was developed. Based on an improved CTM, this study examines the impact of different emergency shelter layouts in the Tianjin Port area. The results indicate that under the actual conditions at Tianjin Port, the evacuation efficiency differs by 22.43% between scenarios with and without the presence of toxic gases. A reasonable layout of additional shelters can improve evacuation efficiency by up to 45.33%. However, if the number of shelters is excessively increased, it could exacerbate congestion and reduce evacuation efficiency by up to 59.81% under the influence of toxic gases. The value of this study lies in its establishment of a model that can more accurately assess evacuation risks under the influence of toxic gases and inform the strategic placement of emergency shelters.