Related questions on Metaculus:

• Will there be a major nuclear or radiological accident before 1 January 2022?

The International Nuclear and Radiological Event Scale (INES) was introduced in 1990 by the International Atomic Energy Agency (IAEA) in order to enable prompt communication of safety-significant information in case of nuclear accidents.

The scale is intended to be logarithmic, similar to the moment magnitude scale that is used to describe the comparative magnitude of earthquakes. Each increasing level represents an accident approximately ten times more severe than the previous level.

Compared to earthquakes, where the event intensity can be quantitatively evaluated, the level of severity of a man-made disaster, such as a nuclear accident, is more subject to interpretation. Because of the difficulty of interpreting, the INES level of an incident is assigned well after the incident occurs.

The INES scale consists of eight levels, with level seven - 'Major Accidents' - being the most serious. A level seven event involves a major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures.

To date, there have been two level seven Major Accidents: the Chernobyl disaster that began on 26 April 1986, and the Fukushima Daiichi nuclear disaster, a series of events beginning on 11 March 2011.

As INES ratings are not assigned by a central body, high-profile nuclear incidents are sometimes assigned INES ratings by the operator, by the formal body of the country, but also by scientific institutes, international authorities or other experts which may lead to confusion as to the actual severity.