WHAT OTHER GASES CAN WE USE?
When we think about diving gases, most people think; air, oxygen, Nitrox, and maybe helium and Trimix. But what about all the other gases? Why don't we use them while diving? Let's talk about that. First of all, what is wrong with air? Well, the percentage of oxygen in air becomes toxic at depth, and nitrogen (the other main component of air) becomes very narcotic at depth. Most people start to feel it's effects at about 30 m / 100 ft. We want to dive deep with a clear mind, so air is not ideal.
Now, what exactly are our other options?Right now we'll start by talking about just pure elemental gases. The only elements the are in gas form at room temperature are: Hydrogen, Helium, Nitrogen, Oxygen, Fluorine, Neon, Chlorine, Argon, Krypton, Xenon and Radon. Straight away we can eliminate three of these. Pure Fluorine and Chlorine are both poisonous to us, and Radon is radioactive. That leaves us with eight elements to talk about.
Oxygen is essential for life, so any mix we choose needs to have some amount of oxygen in it. However 100% oxygen is toxic past 6 m / 20 ft , so we need to dilute that oxygen with something else. Looking at the other gases, if our goal is something better than air, so something less narcotic than Nitrogen, lets compare narcotic levels of other gases.
Narcotic Level
He
Ne
H
N
Ar
Kr
Xe
1
1.83
3.8
4.26
0.43
0.14
0.039
If we look at our chart we see Nitrogen is represented by 1, as it is our base narcotic level. It would take 1.83 times the amount of Hydrogen to reach the same narcotic effect as Nitrogen. It would take 3.8 times the amount of Neon, and 4.26 times the amount of Helium. So these are all gases that we would want to use. On the other side of the table, we see it would take less than half (0.43 times) the amount of Argon to reach the same narcosis effect as Nitrogen. It would take Krypton 0.14 times the amount, and finally Xenon would only be 0.039 times the amount! That means, that if most people start to feel narcosis at 30 m / 100 ft using 79% Nitrogen (air), it would only take 1.18 m / 3.9 ft of depth to feel narcosis using a 79% Xenon, 21% Oxygen mix. That's crazy!
That leaves us with only three gases that are "better than" Nitrogen in terms of narcosis; Helium, Neon and Hydrogen.
Before we continue talking about gases, we need to talk about a few key things. First is tissue solubility. Tissue solubility is how well, or fast, a gas dissolves into and out of a tissue. A high solubility is fast, a low solubility is slow. Next we should quickly note that gases in liquids do not follow Dalton's Law. Gas entering a tissue is dictated by how much of that particular gas is already in a tissue, not by the amount of other gases already present. This can lead to tissue over saturation while mixing gases. Finally we need to review what a partial pressure is. A partial pressure is the hypothetical pressure of a gas if it alone occupied the entire volume of the original mixture (the total pressure of a gas mix is the sum of the partial pressures of all gases present, as per Dalton’s law).
We'll talk about Oxygen first, as it is essential for life, so any gas mix we use will need Oxygen. Although we need Oxygen to survive, a partial pressure higher than 1.6 can cause convulsions, which under water can lead to death. That means pure oxygen cannot be breathed past 6 m / 20 ft. Ideally we want to keep our partial pressure of Oxygen at 1.4, however we can lower that if necessary. We need a minimum partial pressure of 0.16 to survive. Overall Oxygen is a fairly inexpensive gas, and is generally readily available.
Next is Nitrogen. Nitrogen is also readily available and for the most part, you wouldn't pay for it, you'd just use the Nitrogen in the air around us. It has a moderate density so is fairly easy to breathe. It has a pretty moderate tissue solubility as well, however as we have already discussed it is more narcotic than would be ideal.
On our narcotic scale above, next is Hydrogen. Hydrogen is very light and easy to breathe, and it also has a high tissue solubility. As we already saw it is less narcotic that Nitrogen. However it does still become narcotic at about 150 m / 495 ft. While most divers are aware of Nitrogen's narcotic effect, which is usually compared to being drunk, Hydrogen has a very unique narcosis, which has been described as similar to being on LSD, causing hallucinations. The biggest issue with Hydrogen is not its narcotic effects however. The biggest
issue is unlike Nitrogen, Helium and Neon, it is not a noble gas. For those of you forgetting your elementary school science, that means it is reactive, particularly to Oxygen. Combined with more that 4% Oxygen it is explosive. This means the shallowest we can dive it while maintaining a high enough partial pressure of Oxygen to keep us conscious is 30 m / 100 ft. Because of this, if we were to dive with it we would also need a travel gas mixture to get us down to 30 m / 100 ft, as well as a switching mixture, because even in your lungs it is still reactive. If you just took a breath of a mix with more than 4% Oxygen then switched to a Hydrogen mix, that Oxygen would still be in your lungs.
After Hydrogen is Neon. Neon is a noble gas, so in non-reactive. It has a moderate density, so at depth deeper than 155 m / 511 ft it can become harder to breathe. However because of this density it is also warmer than air, which can be very helpful for long deep dives. It has a very low solubility, so it takes a long time to both enter and leave our tissues. It doesn't product narcosis until about 365 m / 1200 ft. The reason Neon isn't used in recreational diving however is the price. Neon is incredibly expensive, costing about 83 times the amount of Oxygen. To put that in perspective, a 60 CF tank of pure Oxygen would cost about $65. For Neon, that would cost about $5,393.
Finally we have Helium. Helium is what is commonly used in recreational tech diving. It is a noble gas, with low tissue solubility. It is very light and easy to breathe, however because of its lightness it is very cold. While using Helium divers need a separate drysuit inflation bottle. Also because of its lightness it can distort speech while using comms. It produces almost no narcosis, however at depths greater than 120 m / 396 ft it can cause HPNS, (high pressure nervous syndrome). Symptoms of HPNS are nervous tremors, nausea, fatigue, and impaired thinking, which underwater are very dangerous. The reason divers still use it, is because they mix it with Nitrogen. Nitrogen is a natural depressant and helps eliminate HPNS.
As we can see, each gas has positive and negative elements. Because our best option is to mix gases. Trimix, a mix of Oxygen, Nitrogen and Helium is the best option for recreational divers, however in commercial and military setting tests are being run on other mixtures, so maybe one day we'll have more options.