Ever since I have tried to determine the minimum blood oxygen percentage which will just keep an average human conscious. It seems to be about 65 to 70 %. Does anyone out there have a more accurate figure? Climbers of Everest should know.
Mountain climbers are conditioned to tolerate low oxygen environment, however a normal earthling will experience difficulties if the O2 level gets down around 85%. The brain and eyes need an enormous amount of oxygen so the initial effects will be impaired vision and cognitive function. The effects are insidious with primarily a feeling of warmth and euphoria, and an affected person will have difficulty recognising they are in a hypoxic state.