INES classification and what it means

What is the purpose of the INES?

The International Nuclear and Radiation Events Scale (INES) is a worldwide tool used to communicate the safety significance of nuclear and radiological events to technical communities and the public.

The scale was designed by an international group of experts in 1989 and further developed by the International Atomic Energy Agency (IAEA) in conjunction with the Organization for Economic Co-Operation and Development’s Nuclear Energy Agency (OECD/NEA) and more than 60 Member States, including Canada.

Who uses the INES?

The scale allows the Canadian Nuclear safety Commission (CNSC) and regulatory agencies in the 60 Member States of the International Atomic Energy Agency (IAEA) to classify events involving radioactive materials.

Since its inception in 1990, the INES has been adapted to meet the growing needs for communicating all significant events associated with nuclear reactors, processing facilities, the transport, storage and use of radioactive material and radiation sources for medical, industrial and research applications. The current version of the INES manual was adopted on July 1, 2008.

In October 2008, the IAEA General Conference of Member States endorsed the updated INES.

What does it mean?

Events are classified at seven levels: levels 1–3 are "incidents" and levels 4–7 are "accidents".

These levels consider three areas of impact:

  • people and the environment
  • radiological barriers and controls
  • defence in depth

The scale is designed so that the severity of an event is about 10 times greater for each increase in level on the scale.

Events without safety significance are called "deviations" and are classified Below Scale/Level 0.

Events are classified at seven levels: Levels 1–3  are “incidents” and Levels 4–7 are “accidents”
Source: IAEA (click to enlarge)

Consequences to people and the environment are measured by assessing the amounts and types of radioactive releases that can impact members of the public in general and the environment.

Consequences relating to radiological barriers and controls are assessed by looking at impacts on both workers and facilities.

Degradation to the defence in depth of the facilities is measured by assessing the successive barriers between radioactive material and the environment, such as safety systems and technical and administrative procedures.

General description levels

General Discription Levels
Source: IAEA (click to enlarge)

Who classifies the event?

In Canada, the CNSC is responsible for assigning INES ratings to Canadian events.

This is the case for each IAEA Member State, where an organization designated by the local government is responsible for assigning INES ratings to events which may occur in that Member State.

The IAEA provides tools and training to help each Member State’s designated agency discharge this responsibility.

The IAEA also manages a database of events and distributes the information at the international level.

What are examples of events classified on the INES?

Some examples of events at nuclear facilities are:

Examples of Events at Nuclear Facilities
Source: IAEA (click to enlarge)

Read the IAEA International Nuclear and Radiation Events Scale (INES) brochure (PDF)