GlossaryEmergency management
Mass-casualty incident
A mass-casualty incident (MCI) is an event whose patient needs exceed the capacity of the usual available medical resources and procedures.
A mass-casualty incident (MCI) is an event whose patient needs exceed the capacity of the usual available medical resources and procedures. It describes the relationship between demand and response capacity. It is not defined by one universal patient count, and “casualty” does not mean every affected person has died.
Why capacity matters
The World Health Organization's overview describes a sudden patient surge overwhelming local medical resources. U.S. response agencies apply their own incident plans and activation criteria, so a national or international explanatory definition does not replace a local MCI protocol.
A dispatch declaration can initiate coordinated resources while patient numbers are still being assessed. It should not automatically be interpreted as a final casualty tally. Later incident, transport, and hospital records may describe different stages and populations.
Example
Hypothetical example: A remote community has several patients from one collision and requests additional ambulances because its immediately available resources are insufficient. A larger urban system could have different resources available for the same number of patients.
The example shows why capacity and severity matter alongside count. It does not supply a threshold that all communities must use. The local MCI declaration describes an operational need, not a statement that a particular number of deaths occurred.
Common confusion
A mass-casualty incident and a mass-fatality incident concern different needs. One term cannot be substituted for the other merely because an event is large.
An emergency declaration is also a separate governmental action. MCI activation does not automatically establish a legal disaster declaration.
Reading local reports
Look for the activation criteria, estimated and final patient totals, severity categories, and mutual-aid records. Separate people assessed from people transported. A response can use MCI arrangements without every initially reported person ultimately needing transport or hospitalization.