Where: Baikonur Cosmodrome (also known as Tyuratam), Soviet Union
When: Oct. 24, 1960
What Happened: Fuel valves in the second stage of the Soviet's R-16 ICBM prototype were inadvertently opened, and hypergolic propellants mixed and burned into the first stage causing a massive explosion at the launch pad. The number of personnel and visitors in close proximity to the launch pad exceeded safe limits given that technicians were performing repairs on a fully-fueled rocket. At least 74 people died from the fireball and toxic gases, and approximately 50 more died later from the injuries received that day. Marshal of Artillery Mitrofan Nedelin, who was personally in charge of the R-16 Program, was at the launch pad and one of the 74 killed.