Common characteristic of disaster situations. Definition, criteria and classification

• A disaster is a serious disruption of the functioning of a community or society that exceeds its ability to cope with its own resources, so that external assistance is needed.
• It arises when a hazard meets a vulnerable population with too little capacity or too few measures to reduce the risk.
• Common features: sudden onset, collective community-wide level, damaged infrastructure, loss of hospitals and healthcare services, a disrupted recovery environment, vulnerable people.
• Entry criteria (EM-DAT): 10 or more people killed, 100 or more affected, a declared state of emergency, or a call for international assistance. Any one is enough.
• Classification: two generic groups, natural and technological (plus complex disasters such as famine). Natural disasters are split into geophysical, meteorological, hydrological, climatological and biological sub-groups.

Disasters occur at the collective, community-wide level. They permanently reshape the communities where they happen.

• Infrastructure may be damaged.
• The people affected are often left without hospitals and healthcare services.
• The recovery environment is disrupted and unfamiliar.
• People go through the painful realisation that nothing will be exactly the same again, and they are vulnerable.
• Some members of the community will move away.

The characteristics usually listed in short form are: sudden onset, damage to infrastructure and human life, severity, unpredictability, and people becoming vulnerable.

The definition used for a disaster is often as varied as the discipline using it, because of the multidisciplinary nature of disaster.

The WHO definition

The World Health Organization (WHO) defines a disaster as "a sudden ecological phenomenon of sufficient magnitude to require external assistance".

The emergency medicine definition

A more focused definition, often used by practitioners of emergency medicine, says a disaster exists when the number of patients presenting within a given time period is such that the emergency department cannot provide care for them without external assistance.

The EM-DAT definition

A disaster can also be defined as "a serious disruption in the functioning of the community or a society causing widespread material, economic, social or environmental losses which exceed the ability of the affected society to cope using its own resources". A disaster results from the combination of hazard, vulnerability and insufficient capacity or measures to reduce the potential chances of risk. A disaster happens when a hazard impacts on a vulnerable population and causes damage and disruption.

What all definitions share

• Disasters are not defined by a specific number of casualties but by the event itself and the venue in which it occurs.
• Disasters tend to be caused by nature or by humans themselves.
• In all definitions, a disaster is something outside the normal experience of daily life that requires a change from the daily management style and thinking.

EM-DAT (Emergency Events Database) data include the following main information.

When a disaster occurs, the related information is entered at three different levels: the event/disaster level, the country (or countries) level, and the source level.

For a disaster to be entered into the database, at least one of the following criteria must be fulfilled:

1. Deaths: ten (10) or more people reported killed.
2. Affected: one hundred (100) or more people reported affected (injured or made homeless).
3. Declaration: the country declares a state of emergency.
4. International assistance: the country makes a call (appeal) for international assistance.

Secondary criteria are taken into account when figures are missing. An example of a secondary criterion is a consequence of an earthquake, such as the disruption of electrical power.

EM-DAT distinguishes two generic categories of disaster: natural and technological. The natural category is divided into 5 sub-groups, which cover 15 disaster types and more than 30 sub-types. The technological category is divided into 3 sub-groups, which cover 15 disaster types. Each group therefore covers different disaster main types, and each main type has different sub-types.

Natural disasters can be divided into six groups (biological, geophysical, meteorological, hydrological, climatological and extra-terrestrial), and four important divisions are atmospheric, terrestrial, aquatic and biological.

Floods, volcanoes and wildfires are examples of natural disasters. A natural disaster is a catastrophic event caused by natural forces.

The sub-types in the classification tree are:

• Biologicalepidemic (viral, bacterial, parasitic, fungal and prion infectious disease), insect infestation, animal stampede.
• Geophysicalearthquake; volcano; mass movement (dry) with rockfall, landslide, avalanche and subsidence.
• Hydrologicalflood (general flood, flash flood, storm surge or coastal flood); mass movement (wet) with rockfall, landslide, avalanche and subsidence.
• Meteorologicalstorm (tropical cyclone, extra-tropical cyclone, local storm).
• Climatologicalextreme temperature (heat wave, cold wave, extreme winter condition), drought, wildfire (forest fire, land fire).

The hydrological and meteorological groups together make up the hydro-meteorological group in the diagram.

A technological, or man-made, disaster is a harmful event caused by human actions or mistakes. The EM-DAT table groups them into three sub-groups:

The same grouping is often taught in broader terms:

• Industrial accidentschemical spills, nuclear incidents, industrial explosions.
• Transportation accidentsplane crashes, train derailments, shipwrecks.
• Environmental pollutioncontamination of air, water or soil.
• Terrorist attacksbombings, chemical attacks, cyber-terrorism.
• Armed conflictswars and civil unrest.

A third category, complex disasters, was added in EM-DAT for specific events such as famine that are not directly linked to a natural hazard.