How can Fukushima crisis be rated as severe as Chernobyl?

Some specialists are questioning the usefulness of an international scale for measuring the severity of nuclear accidents – a scale that now rates the Fukushima Daiichi crisis in Japan as equal to Chernobyl.

They note that even by the most dire estimates Fukushima has released only one-tenth the radiation that Chernobyl did. Moreover, they suggest that scale is not intended to help politicians and the public decide how to act – it was designed by engineers for engineers, and is even flawed in that respect, they say.

Officials at two Japanese agencies that oversee the nuclear industry jointly announced they were elevating the severity of the crisis on the International Atomic Energy Agency's (IAEA) severity index from 5 to 7, the maximum ranking.

But the scale "doesn't trigger anything," says David Ropeik, who heads Ropeik & Associates, a risk-management consulting firm in Concord, Mass. "Here it is being used, and it's demonstrating that it can't even categorize things that precisely."

It's more than a quibble over numbers, he says. Instead, it's about uncertainty and confusion among a public already stressed by the effects to themselves and their loved ones of the quake and tsunami. "To the extent that this tool is adding to that, it's making things worse," he says.

What the scale measures

The scale was developed in Chernobyl's aftermath.

"People felt there needs to be some kind of way to explain the safety significance of events associated with radiological accidents," including events at nuclear plants, says Olli Heinonen, a senior fellow at Harvard University's Belfer Center for Science and International Affairs in Cambridge, Mass.

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