On a scale of 1 to 7...

The Japanese authorities have classified the event at Fukushima Daiichi Unit 1 as a level 4 "accident with local consequences" on the International Nuclear and Radiological Event Scale (INES). The scale is used to consistently communicate the safety significance of events associated with sources of radiation. The scale runs from 0 (deviation -- no safety significance) to 7 (major accident).

The 1979 Three Mile Island accident in Pennsylvania was a level 5 ("accident with wider consequences"). The 1986 Chernobyl disaster was a level 7 ("major accident).

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