TO BREATH WE NEED

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air and  not only oxygen.
MAJOR  PARTS. OF   AIR :  (% by volume).
Nitrogen (N2) 78.084; Oxygen (O2) 20.9474 ; Argon (Ar) 0.9340; Carbon dioxide (Co2) 0.0314; Neon (Ne) 0.01818; Helium (He) 0.000524: Krypton (Kr) 0.0000114; Ammonia (NH3) o - trace;
Iodine (I2) 0.00001; Xenon (Xe) 0.00000087; Hydrogen (H2) 0.00005; Methane (CH4) 0.0002; Nitrous oxide (N2O) 0.00005; Ozone (O3) 0.000007; Sulfur dioxide SO2) 0-0.0001;
Nitrogen dioxide (NO2) 0-0.000002; Carbon monoxide (CO) 0 - trace; Water vapor (H2O) 0.1-1.0.
NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION (1976).
To be safe to breath we need all of above elements with certain proportion. The individual nose passages timely control composition of this elements for each individual body..But, we have to use our  nose for breathing..

On the photo: The  Multi -position  bar.