CONCEPT OF MAJOR RISK
According to the International Organisation for Standardization (ISO), the risk would be defined as a "combination of the probability of an event and its consequences". RISK is thus the probability that an accidental phenomenon produces in a given point of the effects of a given potential gravity, during one given period.
Consequently, a potentially dangerous event, the HAZARD , is not transformed into RISK only if it applies to a zone where human, economic or environmental STAKES are in presence and this zone has a certain degree of VULNERABILITY.
of a zone or a given point is the appreciation of
the sensitivity of the targets present in the zone at a type of effect
given (intensity of seism, volume of precipitations, concentration of
toxic product, etc.).
Two same risks values can thus result from completely opposite components:
In fact, the major characteristic of a risk is mainly given by the importance of the damage which it is likely to generate:
hazards of everyday life (domestic accidents, road accidents) are not,
in general, sources of major risk;
It is necessary for that to take into account simultaneously two types of damage:
MAJOR RISK would thus be characterized by the two following criteria:
Only two categories of phenomena can fully be associated to such description:
risks, among which one can distinguish: