International audience The catastrophic events of these last years such as the catastrophe ofAZF in 2001 or the various terrorist attacks lead to an evolution of the concept of risk by integrating dimensions of crisis and threat. The damages which result from this are not present on a delimited area but impact the whole society. The crisis organizations are destabilized by the unusual features of these situations. The managers must anticipate these situations as soon as possible; react efficiently and in a fast way in order to avoid the consequences of the crisis. However, the decision makers need a fast, clear and structured expertise allowing a reduction of uncertainties related to the crisis and to increase the knowledge about the situation. The objective of this paper is to present, after a state of the art on the crises, amethodology of decision-making aid to help the competent authorities through the assessment of a potential of crisis usable in vigilance and during the emergency phase.