Radiation Exposure Fears Grow After Blast, Fire In Japan Nuclear Crisis

The threat of radiation exposure rose Tuesday following an explosion and fire at the Fukushima Daiichi nuclear plant which prompted officials to warn people in a 19-mile radius to stay indoors.

"Please do not go outside. Please stay indoors. Please close windows and make your homes airtight. Don't turn on ventilators. Please hang your laundry indoors," Chief Cabinet Secretary Edano said to the residents in the danger zone. "These are figures that potentially affect health. There is no mistake about that."

The International Atomic Energy Agency said radiation dose rates of up to 400 millisievert per hour had been reported at the Fukushima power plant site. That compares with a normal background level of about 3 millisieverts.

According to the Associated Press, the warning covered about 140,000 people near the plant, which was damaged by the earthquake and tsunami that struck northern Japan last week.

Hours after the explosion and fire, elevated levels of radiation were detected in Tokyo, 175 miles away, though government officials said there was no health risk there, according to the Associated Press.

The explosion, which occurred at 6:10 a.m. local time Tuesday came shortly after the International Atomic Energy Agency announced that the reactors at the Fukushima Daiichi plant were shut down.

While the previous explosions at Fukushima Daiichi reactors Nos. 1 and 3 were hydrogen blasts caused by a buildup of steam in the reactor units, the new blast at reactor No. 2 has officials very concerned.

This time, the roof did not blow off and it's now believed the trapped pressure cracked the containment vessel around the reactor's core - allowing radioactive material to seep out.

"It is likely that the level of radiation increased sharply due to a fire at Unit 4," Edano said. "Now we are talking about levels that can damage human health. These are readings taken near the area where we believe the releases are happening. Far away, the levels should be lower."

Also, Japanese officials told the International Atomic Energy Agency that the fire at unit 4 was "a pool where nuclear fuel is kept cool," the Associated Press reported.

The blaze has since been extinguished.

And for the first time, nearly 800 workers at the plant were told to leave.

Katsaki Mitsui, an expert at Japan's Institute of Applied Technology told NHK TV that it's a "very serious" situation around the plant.

"I don't think you're going to see acute deaths or something like that, even with it [radiation levels] so high. I would not walk around," he said.