The International Atomic Energy Agency (IAEA) produced this scale of nuclear emergencies/disasters.
It states, "The INES Scale is a worldwide tool for communicating to the public in a consistent way the safety significance of nuclear and radiological events.
Just like information on earthquakes or temperature would be difficult to understand without the Richter or Celsius scales, the INES Scale explains the significance of events from a range of activities, including industrial and medical use of radiation sources, operations at nuclear facilities and transport of radioactive material.
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 ten times greater for each increase in level on the scale. Events without safety significance are called “deviations” and are classified Below Scale / Level 0."