After three explosions and a fire in four days, the situation at Japan's earthquake-stricken Fukushima Daiichi nuclear plant grew more serious Tuesday, chasing all but a handful of workers from the site ad raising fears of a far more dangerous radiation threat. The latest incidents, an explosion Tuesday at the plant's No.2 reactor and a fire in a cooling pond used for nuclear fuel at the No.4 reactor, briefly pushed radiation levels at the plant to about 167 times the average annual dose of radiation, according to details released by the International Atomic Energy Agency. That dose would quickly dissipate with distance from the plant, and radiation quickly fell back to levels where it posed no immediate public health threat, Chief Cabinet Secretary Yukio Edano said. But the deteriorating situation and concerns about a potential shift in wind direction, that could loft radiation toward populated areas prompted authorities to warn people as far as 18.6 miles away from the plant to stay inside. There is still a very high risk of further radioactive material coming out, according to Prime Minister Naoto Kan, asking people to remain calm!