January 27 , 1967 Apollo 1

Apollo 1 was scheduled to launch on February 21, 1967. Its three-man crew of Virgil Grissom, Roger Chaffee and Edward White were sealed in their capsule on the launchpad on January 27th when an electrical fire broke out. The pure oxygen atmosphere of the module turned the capsule into an immediate inferno, asphyxiating the crew immediately.