In March 1990, the IAEA and the OECD/NEA introduced the international nuclear event scale (INES) to help the public and the press to understand easily and consistently the safety significance of events occurring at nuclear installations. After the trial application was developed and completed, it has been in full use since 1992. At present, approximately 60 countries around the world are using this system for nuclear events. Korea has been operating the INES system since 1993.
The event scale is divided into 7 levels according to the safety significance in the INES. Event level 1~3 are termed "Incident" and higher than 4 "Accident". In general, the standard of event scale evaluation is whether the event has radioactive influence on the plant employees/residents or not, and the event having no influence is classified into "Incident." Also, the INES defines the event having no safety significance as "Deviation," (Below Scale, Level 0) and the event having nothing to do with a safety as "Out of Scale."