Japan hikes nuke workers' legal radiation dose

TOKYO - Japan has raised the maximum radiation dose allowed for nuclear workers, citing the urgent need to prevent a crisis at a tsunami-stricken power plant from worsening.

Despite the increase, surging radiation levels forced emergency workers to temporarily withdraw from the crippled Fukushima Dai-ichi nuclear plant on Wednesday, losing time in their struggle to cool overheating fuel in reactors crippled by last week's devastating earthquake and tsunami.

The Ministry of Health Labor and Welfare raised the maximum allowable exposure for nuclear workers to 250 millisieverts from 100 millisieverts. It described the move as "unavoidable due to the circumstances."

According to CBS News medical correspondent Dr. Jon LaPook, radiation can damage human cells. A chest X-ray emits about one-tenth of a millisievert.

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Nuclear plant workers are typically limited to 20 millisieverts a year, LaPook reports. One hundred millisieverts in one dose can increase the risk of cancer, and 100 to 500 can cause bone marrow damage, leading to infection and death.

Reports say radiation levels were as high as 400 millisieverts an hour at the Fukushima Dai-ichi plant on Tuesday. But they fell dramatically -- first to 11.9, then to 0.6.

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To put this in perspective: in Chernobyl, among people who became sick the radiation dose ranged from 800 to 1.6 million millisieverts - much higher than what's being measured so far in Japan.