 The environment within the astronauts ' pressure suits was not changed . Because of the rapid drop in cabin ( and suit ) pressures during ascent , decompression sickness was likely unless the nitrogen had been purged from the astronauts ' tissues before launch . They would still breathe pure oxygen , starting several hours before launch , until they removed their helmets on orbit . Avoiding the " bends " was considered worth the residual risk of an oxygen @-@ accelerated fire within a suit . 
