On October 24, 1960 the second stage of the first R-16 ICBM ignited on the pad, igniting the first stage and causing the whole rocket to explode. 126 people died, including Soviet Stratigic Missile Forces Commander-in-Chief Mitrofan Nedelin and Chief Designer Boris Konoplev. The rocket's Chief Designer, Mikhail Yangel, himself only just missed being killed, having walked into a bunker to smoke a cigarette 30 seconds before the explosion. The cause of the accident was later found to be a poorly designed second-stage control system which lacked sufficient on-pad safeguards. The heavy death toll resulted from complete neglect of safety rules.
The incident was very effectively covered up during the Cold War and the story did not emerge in the West until the 1990s.