A mass casualty incident (MCI) is an event in which the number of injured or ill patients exceeds the ability of the initial responding emergency medical resources to provide adequate care using normal procedures. MCIs are defined not only by the number of patients, but also by the severity of injuries, the need for specialized resources, and the impact on the overall emergency response system. These incidents require the use of an incident management system, organized triage, and coordinated response among multiple agencies.

In Broward County, a mass casualty incident is typically declared when there are five or more patients involved, or when the incident requires additional EMS units, multiple patient transports, or hospital notifications beyond routine response. Declaring an MCI early allows responders to manage resources efficiently, establish command and control, and prioritize patient care to improve outcomes and maintain responder safety.