What happens if you breathe pure oxygen: take a look at Divers Alert Network guidelines. Scuba equipment works by forcing compressed air into the lungs at the same pressure as the pressure of the surrounding water. The deeper you dive, the more air you use. For every 33 feet / 10 meters that you descend, the pressure of the water increases in one atmosphere.
There is something called oxygen toxicity. As its partial pressure increases, oxygen becomes increasingly toxic. For example, under normal atmospheric conditions, you are breathing about 0.2 atm of oxygen (21% oxygen at 1 atm). Once you go to a single atmosphere partial pressure, you will still be able to live, but you will have a limited time. Safe limits for recreational dives are 1.4 bar O2 or normal air at a pressure of 7 atmospheres. Even then, you’re starting to get into the nerve zone. 1.6 is considered just silly.
As compensation, deep divers will breathe gas mixtures with lower O2 levels. A 10% O2 mix will allow you to go much deeper. But you will also pass out if you try to breathe it within 30 feet. Because 30 feet is 1 atm of water pressure plus 1 atm of air pressure = 2 atm. 10% O2 x 2 atm = 0.2 atm of oxygen, or just what you breathe normally in the atmosphere.
You probably can survive about 24 hours in 100% oxygen at atmospheric pressure. To live longer, you have to reduce the pressure.
What the Body Does With the Nitrogen We Inhale?
Yes, most of the air is made up of nitrogen (78%). But we don’t need it, we need oxygen, so what does our body do with it?
Well, just as we inhale it, we exhale it since the body does not require it so it does not process it.
From the capillaries, the pulmonary alveoli also receive the main waste product of cellular respiration, carbon dioxide. Through expiration (expulsion of air from the lungs) this gaseous compound is released outside our body. At this stage, the gaseous composition of the air that entered through the airways changes.
Exhaled air contains the same percentage of nitrogen (78%), but the levels of carbon dioxide (4%) and water vapor (2%) increase. Logically, the amount of oxygen expelled decreases. This helps us to reduce the concentration of oxygen and also prevents us from breathing pure oxygen, since pure oxygen could harm us.
Could We Live in an Atmosphere With Oxygen but Without Nitrogen?
So, if our bodies do not absorb nitrogen, we could do without it, right? Unless the lungs evolve in such a way that they can absorb all the oxygen without collapsing, no.
The nitrogen that we inhale serves to keep the pressure in the lungs stable. That is, it prevents them from shrinking. Without nitrogen the lungs will collapse. Why?
In an atmosphere of pure oxygen, oxygen is rapidly absorbed and the sacks where the simple diffusion of oxygen and carbon dioxide occurs – shrink. This happens because the external pressure is greater than the internal one. There would be nothing left inside the alveoli except a little carbon dioxide.