What defines a Mass Casualty Incident (MCI)?

• A. An incident with a single patient.
• B. A routine medical call.
• C. An incident that requires only EMS response.
• D. An event where patient numbers exceed available resources, such as a bus crash.

Answer: (D)

Mass casualty incidents are defined by the number and/or severity of victims that overwhelm the available resources, requiring a coordinated, multi-agency response beyond routine operations. The defining point is the demand on care and logistics exceeds what normal first-response units can handle, which triggers disaster plans, triage, and mutual aid. A bus crash is a classic example because you can have many injured people with varying needs, and standard EMS resources alone typically aren’t enough, so you activate additional help and incident command.

If there is a single patient or a routine medical call, it stays within normal EMS capacity. Even if many patients are involved, the situation becomes an MCI only when the system is strained beyond its usual capabilities and requires a broader, scaled response.