To ensure that the nature and severity of an incident in a nuclear power plant could be described in the same way everywhere, the International Atomic Energy Agency (IAEA) worked with the Organisation for Economic Cooperation and Development (OECD) to develop an international scale of events for nuclear installations.

Today, the INES scale is used globally and comprises seven levels.

ENSI classifies events according to this scale and reports the accident assessment to the IAEA. An accident is an event in which an installation deviates from its intended operation and its safety is impaired.