The terms emergency and disaster often are used interchangeably. This common use of terms can be confusing. It is easiest to understand the terms emergency and disaster as being at two ends of a scale, in which the size of an incident and the resources to deal with the incident are matched to varying degrees.

Emergencies are usually small-scale, localized incidents which are resolved quickly using local resources.

Disasters are typically large-scale and cross geographic, political, and academic boundaries. Disasters require a level of response and recovery greater than local communities can provide.