Modeling of building evacuation using ladders

Existing research and tools used for building evacuation planning do not take into account the common practice of using ladders for rescue operations. The ladders provide a simple and practical way of creating additional exits with a potential to significantly reduce the evacuation time. Use of ladders is critical in case of severe disasters and when some normal exits get blocked. To our knowledge, this paper presents the first systematic planning approach for optimal placement of a limited number of available ladders. We first propose modifications to the existing models of buildings to incorporate ladders and ladder points (locations in the building where ladders can be placed). Next, we develop optimization formulations to solve the following evacuation planning problems when a limited number of ladders are available: (i) optimal deployment of a given number of ladders to minimize evacuation time and (ii) finding minimum number of ladders along with their locations necessary to evacuate a building in a given evacuation time. These problems, posed as integer linear programming formulations, are applied to two case studies to demonstrate the importance of using ladders. The results show that evacuation plans can be significantly improved by optimally placing ladders at the selected ladder points.