International Nuclear and Radiological Event Scale

Compared to earthquakes, where the event intensity can be quantitatively evaluated, the level of severity of a human-made disaster, such as a nuclear accident, is more subject to interpretation.

A number of criteria and indicators are defined to assure coherent reporting of nuclear events by different official authorities.

But the most pressing item identified by Smythe is that INES conflates magnitude with intensity; a distinction long made by seismologists to compare earthquakes.

By analogy, a nuclear incident with a high magnitude (e.g. a core meltdown) may not result in an intense radioactive contamination, as the incident at the Swiss research reactor in Lucens shows – yet it resides in INES category 4, together with the Windscale fire of 1957, which caused significant contamination outside of its facility.

The factor of 20 assures that both the INES and the NAMS scales reside in a similar range, aiding a comparison between accidents.

The NAMS scale still does not take into account the radioactive contamination of liquids such as an ocean, sea, river or groundwater pollution in proximity to any nuclear power plant.

The estimation of magnitude seems to be related to the problematic definition of a radiological equivalence between different types of involved isotopes and the variety of paths by which activity might eventually be ingested,[46] e.g. eating fish or through the food chain.