Mass Casualty/Multi-Casualty Incidents (MCI)

A Mass Casualty Incident (MCI) or Multi-Casualty Incident is any event where the number of injured individuals overwhelms the usual emergency response capabilities of a community.

Because resources and capabilities vary across regions, EMS agencies and hospitals may define a MCI differently, and some may also classify MCIs by numbers. 

 For example: 

  • A motor vehicle accident with five injured patients that occurs in an urban setting where there are multiple hospitals and EMS units may not add additional stress to the system. 

  • The same motor vehicle accident with five injured patients that occurs in a rural setting with one EMS unit and one hospital could exceed available resources, making it an MCI. 

 
Disasters are NOT just large MCIs
 

Although both events can cause a surge in demand, disasters are more severe than MCIs.

MCIs strain the system, but operations can often be adjusted to meet needs.

Disasters often go beyond stretching local resources. They overwhelm or break existing systems. Disasters may require outside assistance and coordinated response at local, state, or even federal levels.

Written by Dennis Ren

Last updated: 5/30/2025

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