Twenty-nine years ago, on April 26, 1986, the world witnessed the worst human made and humanitarian disaster effects of which are still being felt today. An explosion and fire at Reactor No. 4 of the Chernobyl nuclear power plant released large quantities of radioactive particles into the atmosphere which spread over western parts of the USSR and Europe. The Chernobyl disaster was the worst nuclear power plant accident in history in terms of costs and casualties. It is one of only two classified as a level 7 event (the maximum classification) on the International Nuclear Event Scale, the other being the Fukushima disaster in 2011.