On Sept. 30, 1999, Japan's worst nuclear accident happened in a facility northeast of Tokyo. Three workers at a uranium-processing plant in Tokaimura, then the center of the Japanese nuclear-power industry, improperly mixed a uranium solution. A blue flash heralded trouble. As TIME wrote, "One [worker] was knocked unconscious. Within minutes, the others were nauseated, and their hands and faces were burned bright crimson." Two ended up dying, and hundreds were exposed to various levels of radiation.