At what oxygen percent level does a human typically lose consciousness?

A human typically loses consciousness at around 17% oxygen levels due to the body's physiological response to decreased oxygen availability. The normal atmospheric oxygen level is roughly 21%. When the oxygen concentration drops to about 17%, the blood can no longer deliver sufficient oxygen to the brain and other vital organs, leading to oxygen deprivation.

At this reduced oxygen level, individuals may start to feel symptoms such as confusion, dizziness, or shortness of breath as the body struggles to function properly without adequate oxygen. Continuing exposure to levels below this can result in more severe symptoms and unconsciousness.

The other options represent levels that do not typically lead to immediate unconsciousness. For instance, 21% is normal atmospheric oxygen, while levels like 15% and 10% are increasingly critical but tend to affect consciousness and bodily functions at a more advanced stage.