(CNN) -- The explosion Tuesday at Japan's Fukushima Daiichi nuclear plant has elevated the situation there to a "serious accident" on a level just below Chernobyl, a French nuclear official said, referring to an international scale that rates the severity of such incidents.
The International Nuclear and Radiological Event Scale -- or INES -- goes from Level 1, which indicates very little danger to the general population, to Level 7, a "major accident" in which there's been a large release of radioactive material and there will be widespread health and environmental effects.
"It's clear we are at Level 6, that's to say we're at a level in between what happened at Three Mile Island and Chernobyl," Andre-Claude Lacoste, president of France's nuclear safety authority, told reporters Tuesday.
Japanese nuclear authorities initially rated the incident at Level 4, according to Greg Webb of the International Atomic Energy Agency. Level 4 is characterized as a minor release of radioactive material that necessitates only measures to control food due to contamination. But in the latest information about the explosion, Japanese authorities did not give it a rating, Webb said, and the IAEA is not putting a number on it either.
Whatever the level, many experts warn that it's too early, and there's too little information, to determine what it means for the people who live in the region near the Daiichi plant.
"We don't know enough to assess the long-term or short-term effects of this," said Dr. Kirby Kemper, a noted nuclear physicist, physics professor and vice president of research at Florida State University.
Based on information from Japanese authorities, Kemper said it appears the radioactive material that has been released has mostly dissipated into the atmosphere. However, he said, authorities would have to test the soil for contamination in the 20-kilometer radius that was evacuated around the plant before anyone could return home. CNN
