A mass casualty incident involves how many individuals?

• A. 100+ individuals
• B. 10-99 individuals
• C. 1-9 individuals
• D. 500+ individuals

Answer: (A)

A mass casualty incident is defined by the number of victims that overwhelms local emergency resources, requiring a formal, multi-agency response. In many health and EMS teaching frameworks, when the casualty count reaches about 100 or more, the event is categorized as a mass casualty incident. This threshold matters because it signals the need to activate incident command, establish triage and treatment areas, and request mutual aid and hospital surge capacity beyond routine operations. Smaller events, even with several casualties, are typically managed within the normal EMS framework and may not necessitate the full mass casualty response. Very large events—hundreds to thousands of victims—also fall under the MCI umbrella, but the commonly cited educational threshold to label something as a mass casualty is 100 or more.