Death by Oxygen

by Adrienne Montgomerie

Flying high in the sky where the air is thin, fighter pilots wear oxygen masks to make sure they can breathe. But oxygen can be deadly. It's a tight balance.

Oxygen to Live

The air we breathe is actually mostly nitrogen (close to 4/5 of it). Only about 1/5 of the air outside is oxygen.* And what we breathe out still has quite a lot of oxygen in it. Our bodies only use about 1/4 of it.
We breathe O₂: it has two atoms of oxygen in every molecule. Add an oxygen atom, and we get O₃: ozone. High up in Earth's atmosphere, a thin layer of ozone protects us from too much harmful solar radiation (the UV in sunshine).

Oxygen to Kill

Oxygen is also used to clean water. The O₃ of ozone quickly breaks down into O₂. The free oxygen atom oxidizes cells and other pollutants in the water.
Oxidation happens when a substance joins with oxygen and turns into another substance. Rust is oxidation, so is an avocado turning brown. In cells, oxidation happens when oxygen burns through membranes and joins with the DNA inside.
Antioxidants prevent oxidation in cells, or at least slow it down. Vitamins C and E and others do this work, but with questionable results.

Can’t Live With It, Can’t Live Without It

When the air has less than 6% oxygen, humans can't get enough to live. But getting too much oxygen can be deadly too. When there's much more that 21% oxygen in the air, some of that oxygen binds to proteins in the lungs, interferes with the central nervous system, and messes with the eyes. It can lead to death. So doctors and nurses are very careful to not give patients too much.
Breathing is necessary, and oxidation is a natural process linked to aging. So, in some sense, oxygen will be the death of you.

---

*There's another 1% or so of outside air that is made up of carbon dioxide and argon (mostly), plus some other gases.

Photo courtesy of Defence Imagery, CC0 Pixabay.