The effectiveness of emergency medical services (EMS) depends on the existing infrastructure and allocation of medical resources. The response time for ambulances is in general considered a critical factor to the survival of EMS patients. EMS is a challenging task due to the spatial distribution of the population and geographical layout in the urban area. The spatial configuration of ambulance fleets and hospitals should be assessed to provide an efficient service. Additionally, EMS plays a critical role in disaster situations. In this research, the effect of disasters is considered as the disturbance to the EMS system. The objective of this research is to assess the service area of EMS after a disaster. In this study, the deviation of service area before and after the disaster on the transportation infrastructure is evaluated. Multi-layer perceptron (MLP) was used to predict EMS demand in usual conditions, and a loss estimation tool is used to model the disaster triggered demand. Given the usual and disaster triggered EMS demand, location of ad hoc EMS facilities were determined using cluster analysis, and the reachability of the facilities to individual demand points were evaluated using service area analysis. The proposed approach serves as an assessment methodology and also a planning tool for the preparedness of future disaster occurrences.