 Incidents had also occurred in the Soviet space program , but due to the government 's policy of secrecy , these were not disclosed to the West until well after the Apollo 1 fire . Cosmonaut Valentin Bondarenko died on March 23 , 1961 , from burns sustained in a fire while participating in a 15 @-@ day endurance experiment in a high @-@ oxygen isolation chamber , less than three weeks before the first Vostok manned space flight ; this was disclosed on January 28 , 1986 . 
