On the third day of Japan’s nuclear crisis, officials upgraded the number of imperiled nuclear plants to four and said another explosion was possible. Partial meltdowns have presumably occurred at two facilities, they say. At a third plant, near the northeastern city of Sendai, increased radiation was detected, though it’s not yet clear where it’s coming from. The fourth facility, 75 miles north of Tokyo, is experiencing cooling problems. At Fukushima, the hardest-hit plant, Japan has already been through the worst nuclear plant incident since Chernobyl; radiation exposure has been detected in at least 22 nearby residents. Meanwhile, government officials have predicted that the death toll in one region alone will reach 10,000 and have dispatched 100,000 troops, half Japan’s active military force, to respond to the humanitarian crisis.