On diving with Hydrogen: exploring the limits of diving

Hydrogen is the lightest element, being the first element on the periodic table. It is also the lightest gas and is used in many fields for various purposes. Of course, as this is a diving blog, so we are going to focus on its applications in the diving sector.

When in its gaseous form, two hydrogen atoms bond together to form dihydrogen or H2.

In diving, hydrogen is only used experimentally, and at significantly greater depths -I will go over the exact reasons why later on in this article-

First, we must ask ourselves why we would want to dive with hydrogen.

Going deep, blends of nitrogen and oxygen become increasingly narcotic, whose potency is reduced by reducing the proportions of both gases by introducing helium into the mix. Helium has a lower narcotic potency than both Oxygen and Nitrogen, which allows us to go deeper with reduced adverse effects (up to a certain depth). This sounds like a great solution until we hit the limitations of helium: Firstly, it is a finite resource that will run out one day, and its cost constantly increases as supplies dwindle, it is therefore quite expensive to dive with helium. Secondly, at a depth of around 150m, another physiological phenomenon, called High-Pressure Nervous Syndrome (or HPNS for short) appears: it is characterized by tremors, jerking, and dizziness (among other various symptoms). HPNS appears to be characteristic of Helium-containing blends and become increasingly significant beyond 300m.

To answer those two issues, there have been trial dives using hydrogen, to see if there was potential to use it as a "renewable" source (as it can be extracted from water), and without the threat of HPNS.

Properties of Hydrogen

Hydrogen has multiple properties that make it interesting to use as a breathing gas, let's go over some of them:

Reduced density: As mentioned before, Hydrogen is the first element on the period table, which makes it the lightest element to exist. Consequently, it is also the least dense gas under normal conditions.

As we go deeper, the gas we breathe becomes denser as we breathe it at a higher pressure (i.e. there is "more" gas in each breath). The more dense a gas becomes, the more effort is required to breathe it. This can become a significant issue at depth beyond recreational limits, where every effort is multiplied. To breathe Hydrogen instead of Helium (or Nitrogen) means significantly reducing this breathing effort.

Less Narcotic: There have been attempts to rank the narcotic potency of multiple gases on a scale, using Nitrogen (N2) as a reference, which has a narcotic potency of 1. By comparison, Hydrogen (H2) has a narcotic potency of 0.6, and although it is more narcotic than Helium (which has a potency of 0.2 on the scale), it is still less than that of Nitrogen which is a great advantage. A theory for the reduced narcotic potency of Hydrogen is that it has considerably lower lipid solubility, although that exact mechanism for narcosis is still debated.

Having the presence of anesthetic gas (such as hydrogen in this case) in a Helium-containing blend reduces the onset and potency of the signs and symptoms of HPNS.

Although extremely rarely Talked about, there is a physiological phenomenon known as Hydrogen Narcosis, which is exactly what it is called: narcosis induced by breathing Hydrogen. It is only experienced mainly by ultra-deep divers.

Problems and risks of Hydrogen

First, let's talk about the most obvious issue: reactivity. Hydrogen is reactive and poses the threat of exploding. It is especially so in mixes containing more than 4% Oxygen. There is an "easy" solution to this: to breathe hydrox (hydrogen-oxygen mix), the diver must first descend to a depth where he can safely breathe a mix containing only 4% oxygen (40m/130 feet for example). Only then, can the diver switch to the hydrox blend. This prevents extra oxygen that might still be present in the diver's lungs from interacting with the hydrogen mixture.

Experiments have shown that exposition to a partial pressure of 25 atmospheres of hydrogen and beyond, divers will develop intense narcosis, akin to psychotic-like disorders (hallucinations, delirium, etc...).

see Abraini, Jacques & David, HélèneN & Vallée, Nicolas & Risso, Jean-Jacques. (2016). Theoretical considerations on the ultimate depth that could be reached by saturation human divers. Med Gas Res 6(2):119-121.

Another issue we have to consider is the sheer logistics of using hydrogen. Although extracting hydrogen from water is simple enough, it can get more complex on a bigger scale, on top of storing it, which requires specialized equipment, which might not be available to everyone.

To recap

Introducing hydrogen into your gas blend makes it:

• Less dense, easier to breathe
• Increase narcotic potency relative to helium
• Decrease narcotic potency relative to Nitrogen
• Reduce the onset and potency of signs and symptoms of HPNS
• May pose additional narcotic issues at greater depths