On Jan. 27, 1967, the crew of Apollo 1 was killed when a fire broke out in their pure oxygen-soaked capsule during a routine pre-launch test. The dangers of an oxygen fire should have been obvious to NASA. It was obvious to the Apollo spacecraft's builder, North American Aviation, who recommended the space agency not run tests with a highly pressurized spacecraft.
It was also a danger the Soviet space agency knew well. In the early days of their training, cosmonaut hopeful Valentin Bondarenko was killed in an eerily similar accident to the Apollo 1 crew.
Cosmonaut training in the 1960s wasn't all that different from the astronauts' training at NASA. Neither nation's space program was sure how men would react to orbital flight and each went to great lengths to prepare its men, both mentally and physically, for the anticipated stresses. For the cosmonauts, the mental training included time spent in an isolation chamber the cosmonaut trainees called the Chamber of Silence.
The Chamber was a spartan room with minimal furnishings: a steel bed, a wooden table, a seat identical to the Vostok capsule's, toilet facilities, an open-coil hot plate, and a limited amount of water for both washing and cooking. Cosmonauts also had leisure materials. Mind games were posted on the walls, and some men were given books or drawing materials. That was it. As the "Chamber of Silence" moniker suggests, sensory deprivation was part of the test. The room was mounted on rubber shock absorbers that muffled any vibrations from movement outside, and the 16-inch thick walls absorbed all outside sounds.