In 1957 Mayak was the site of the Kyshtym disaster, which at the time was the worst nuclear accident in history. During this catastrophe, a poorly maintained storage tank exploded, releasing 20 million curies (740 PBq) in the form of 50–100 tons of high-level radioactive waste. The resulting radioactive cloud contaminated an expansive territory of more than (a nine-mile radius) in the eastern Urals, causing sickness and death from radiation poisoning.