At the Mayak Industrial Reprocessing Complex in Russia s southern Urals, a storage tank holding nitrate acetate salts exploded in 1957, releasing a massive amount of radioactive material over 20,000 square kilometers, forcing the evacuation of 272,000 people. In September 1994, an explosion at Indonesia s Serpong research reactor was triggered by the ignition of methane gas that had seeped from a storage room and exploded when a worker lit a cigarette.