Basic Disaster Concepts

Disaster: A serious disruption of the functioning of a society with widespread human, material, or environmental losses which can exceed the ability of affected community or area to cope using its own resources. "Natural" disasters involve largely geological and climatic hazards. In human-made disasters, the principal direct causes are identifiable human actions.

Disaster Incident: A natural or human-made event that can cause a disaster with severe negative effects on human life, property, and activities. 

Disaster Category


Sudden Onset

Tsunami, Flood, Earthquake, Hurricane, Wildfire, Volcanic Eruption, Landslide


Drought, Famine, Environmental Degradation, Desertification, Deforestation, Pest Infestation


System Failure/Accident (wreck, derailment), Spillage, Explosion, Fire

Wars & Civil Strife

Terrorism, Insurgency, Armed Aggression

Epidemics, Pandemics

Water/Food-Borne Diseases, Person-To-Person Diseases, Vector-Borne Diseases

Vulnerability or Risk: The measure of the negative cultural, social, economic, and environmental factors and unsafe conditions that put people at risk of a disaster when a hazard occurs. See Top Disaster Risks on menu.

Disaster Size


Low (I)

Affects 1-30 households, assistance provided by local teams and churches.

Medium (II)

Affect 50-200 households, involves entire community or several communities with district response.

High (III)

Large area, usually eligible for presidential declaration. Massive response by state and federal agencies.

Catastrophic (IV)

Large number of deaths or injuries, extensive property damage, severe impact on national security.


Disaster Phases 



Activities designed to plan for high risk disasters, minimize loss of life and damage, plan for the temporary removal of people and property from a threatened location, facilitate timely and effective rescue, relief, and recovery.  It also includes education, training, and certification, communications systems, and other preparation activities.


The time period during which the disaster happens. It may be days, weeks, or, in rare situations, months. 


The time-frame when extraordinary measures are taken to search and find survivors; provide medical assistance; support human needs of shelter, water, and food; and protect property.


The operations for cleanup of structures and roads,  restoration of communications and power, and removal and disposal of debris.


Actions taken prior or after a disaster to identify risks, take risk reduction activities such as zoning flood plains for park land and wildlife habitat areas, clearing debris from streams and rivers, modifying or moving buildings.  After a disaster, mitigation may impact where and how rebuilding activities are undertaken.


Actions taken to re-establish a community after a period of rehabilitation subsequent to a disaster - including construction of permanent housing, full restoration of services, complete resumption of the pre-disaster state.

Disaster Management:
The policy and administrative decisions and operational activities which pertain to the various stages of disaster at all levels.