International Nuclear and Radiological Event Scale

Source: IAEA
International Nuclear and Radiological Event Scale (pdf)

“The INES Scale is a worldwide tool for communicating to the public in a consistent way the safety significance of nuclear and radiological events.

“Events are classified on the scale at seven levels: Levels 1-3 are called “incidents” and Levels 4-7 “accidents.” The scale is designed so that the severity of an event is about 10 times greater for each increase in level on the scale.”

Chernobyl – 1986- Category 7
Three Mile Island, USA – 1979 – Category 5
Fukushima I-1, Japan – 2011 – Category 4