On 26 April 1986, reactor number 4 at the Chernobyl Nuclear Power Plant exploded. The accident released at least 100 times more radiation than the bombs dropped on Nagasaki and Hiroshima in Japan, and is considered to be the worst nuclear accident in the history of humanity. It is classified as a level 7 incident, the highest level on the International Nuclear Event Scale. The only other incident to be categorized at this level is the Fukushima Daiichi nuclear disaster of 2011.
In the days, months and years that followed, over half a million civilians and military personnel (“liquidators”) were involved in the decontamination process to avert a potential second catastrophe.