## Breathing gas mixtures : how divers achieve to go deeper. When I started practicing [scuba diving](Scuba%20diving.md), I was fascinated by the divers who was going very deep. With the naivety of a beginner, I just didn't think about how it could be done. Then, I succeed my first certification, that allowed me to go only at -20 m deep. This is where I started to see that the next -20 m will not be that easy to reach without some theoretical knowledge about breathing gas. After ~30 dives, I wanted to progress in scuba diving and succeed a "level 2 certification", which allow me, among others, to dive assisted with a max operating depth of -40 m. I take advantage of this certification \(which require 10 dives of diverse exercises\) to pass a [[Nitrox]] certification. Here it is! My first breath of a gas mixture enriched with oxygen! And what a room for improvement: when some of my instructors have been diving deeper than -100 m, my personal record is -36 m and I'm already concerned by gas mixture! This only increased my interest about the gas blending subject in scuba diving : if you want to go deeper, using different gas mixtures is vital. So here's what I've learned about this field. ## Why do we even need to breathe gas mixture? TL;DR : to avoid accidents due to bio-physic and bio-chemical reaction of our organism when subject to a higher pressure mostly caused by the nitrogen. The air we're breathing every day \(the same that is in our tank by default in scuba diving\) is composed of ~78% of [nitrogen](https://en.wikipedia.org/wiki/Nitrogen), ~21% of [oxygen](https://en.wikipedia.org/wiki/Oxygen) and ~1% of other more rare gases like [argon](https://en.wikipedia.org/wiki/Argon). There's two main accident we want to avoid in scuba diving that can justify the need of gas mixture : * [Decompression sickness](Decompression%20sickness.md) * [Nitrogen narcosis](Nitrogen%20narcosis.md) ## Gas mixing to underweight nitrogen Theses popular accidents often occur because of the nitrogen. This gas seems to cause too many threats when diving deep. So one of the main reason we change the gas mixture is to underweight nitrogen, at first, in profit of oxygen. The most popular of these is the [Nitrox](Nitrox.md). But for professionnal divers and to achieve deepest dives, we even need to underweight the oxygen with gas mix like [Trimix](Trimix.md). For now, the world record for deep dive in water (and also theoric, using an hyperbaric chamber at -701m) at -520m was made using a gas mix called "[Hydreliox](https://en.wikipedia.org/wiki/Hydreliox)", which only have 0.8% of oxygen but 50.2% of helium and 49% of hydrogen. 😮