To prevent<unk> , a pure oxygen (O2) atmosphere was used in early space flights to eliminate nitrogen in the blood. There are major fire hazards associated with using pure O2 as a breathing gas, which was central to the death of three astronauts in a fire during a ground test with Apollo 1. Nonetheless NASA continued to use a nominally pure oxygen atmosphere throughout the Apollo Program but switched to air for the follow-on Space Transport System "Space Shuttle". Russian cosmonauts used pure oxygen before changing to a higher-pressure nitrox mixture, leading to incompatibility problems in 1975 on the Apollo-Soyuz Test Project. Space suits are often pressurized to several psi lower than stations' capsules or shuttles and since they still use pure O2, an acclimation period is common in the airlock to remove nitrogen and other gases from the bloodstream.
Ebullism
Enamel pearl
Black hairy tongue
Omphalolith
Hamartia 
Aphalangia
Amastia
Caviar tongue