On April 4, 1999, three workers were killed when the oil refinery in Pančevo was hit by NATO airstrikes.[9] Subsequently, 80,000 tons of oil ignited into flames, and the concentration of carcinogens over Pančevo rose 10,500 times higher than local laws allowed at the time.[10] On the same day, one civilian was killed after airstrikes struck electric heating plants in Belgrade.[11]