The overcrowding of Emergency Departments (EDs) is a well-known problem that has been analyzed on multiple occasions. Queuing theory and simulation have been applied extensively to specific ED situations, such as staff planning, waiting time reduction and capacity investment. However, there are remaining problems in the EDs that need more study. One of them is the ambulance diversion, which may cause a delay in the treatment of urgent patients therefore jeopardizing their welfare. Since ED are complex system and setting the diversion state in EDs is a subjective decision, a detailed modeling and analysis of cause and effects of such a decision is beneficial. In this research, we build a case-study and analyze the impact of diversion policies in various performance measures of the ED through a designed experiment using a discrete-event simulation model.