Although discrete event simulation models are known as classic cost-effective tools for analysis of healthcare systems, they are barely suited to represent a strategic level of emergency department (ED). This study applies discrete-event simulation combined with the system dynamics approach to present a comprehensive integrated safety simulation investigation of fast track and ED improvement strategies. By embedding a fast track process logic in the base model of ED discrete event simulation, different strategies have been proposed to evaluate the impact of each scenario. Integration of the base simulation model with system dynamics simulation approaches can articulate the main interconnected and sensitive variables affecting ED key performance index. The integrated model presents the impact of sensitive policy parameters for evaluation of fast track strategy optimization including human resources adjustment, ED resources modification and environmental modification strategies. The main contribution of the proposed integrated safety simulation paradigm is to couple the macroscopic level of safety dynamics analysis with the microscopic discrete level simulation. The results comprise the main model with the scenarios tested by the suggested approach to investigate the ED optimized performance levels. The research results have been validated and indicated that the fast track strategy optimization using the integrated safety simulation could play a significant role in facilitating patient flow without requiring any additional resources.