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The International Nuclear and Radiological Event Scale

What is INES?

INES is a tool for promptly and consistently communicating to the public the safety significance of events associated with sources of ionizing radiation.

What is the purpose of INES?

The primary purpose of INES is to facilitate communication and understanding between the technical community, the media and the public on the safety significance of events. The aim is to keep the public as well as nuclear authorities accurately informed on the occurrence and consequences of reported events.

Scope of INES

The INES scale applies to any event associated with the use, storage and transport of radioactive material and radiation sources, whether or not the event occurs at a facility; this includes events involving the loss or theft of radioactive sources or packages and the discovery of orphan sources, such as sources being discovered in scrap metal.

INES is also used for the rating of events resulting in actual exposure of workers and the public in medical, research and educational institutions.

The scale does not cover the actual or potential consequences for patients exposed as part of a medical procedure.

INES is intended for use in civil, i.e. non-military applications and only relates to the safety aspects of an event.

It is not appropriate to use INES to assess or to compare safety performance between facilities, organizations or countries.

Description of INES

INES uses a numerical rating to explain the significance of events associated with sources of ionizing radiation.

Events are rated at seven levels: Levels 1–3 are “incidents” and Levels 4–7 “accidents”. The scale is designed such that the severity of an event is approximately ten times greater for each increase in level of the scale. These levels consider 3 areas of impact:

  • People and the environment
  • Radiological barriers and control
  • Defense in depth

Events without safety significance are rated as Below Scale/Level 0. Events that have no safety relevance with respect to radiation or nuclear safety are not rated on the scale.


INES Rating Interactive Learning Tool

The INES Rating Interactive Learning Tool (INES-RILT) is a tool aimed to assist users in understanding and applying the INES methodology.

The tool follows the structure of the INES User's Manual which facilitates the task of rating the safety significance of events using the scale. The INES User’s Manual includes additional guidance and clarification, as well as provides examples and comments on the ongoing use of INES.

The tool leads the user through the description of the scale, through detailed definitions of the levels and through criteria for each level in regard to the impact of the events to people and the environment, radiological barriers and controls at facilities, and the impact on the defence in depth areas.

The purpose of INES-RILT is to:

  • Provide initial on-line training to participants unable to attend training course
  • Provide a refresher course for those already trained

Although the interactive tool is primarily for the use of those already acquainted with INES, senior management of the operating organisations and regulatory bodies may also find the tool to be practical and user friendly in its presentation in comparison with the more technically presented INES User's Manual.

INES Guidelines and good practices

This publication is the first to provide guidance on establishing or improving a national framework for the effective use of INES during event communication.

Participation in INES

Participation in INES is voluntary and open to all IAEA Member States. Member States are invited to officially designate INES National Officers via official channels. INES National Officers represent their countries in the biennial INES technical meetings and participate in discussions and decisions on the application of the scale.


INES was developed in 1990 by international experts convened jointly by the IAEA and the Nuclear Energy Agency of the Organization for Economic Co-operation and Development (OECD/NEA). Initially the scale was applied to classify events at nuclear power plants, then extended and adapted to enable it to be applied to all installations associated with the civil nuclear industry. More recently, it has been extended and adapted further to meet the growing need for communication of the significance of all events associated with the use, storage and transport of radioactive material and radiation sources.


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| Last update: Thursday, 17 November, 2016.