Putting the YouDoo in VooDoo gas!


I don’t know about you but when I started to dive, I was told I should breathe air. Same with you right? It is a good question to ask of yourself, what should I breathe underwater?

Lets delve briefly in to physiology, we are beings designed to breathe air at a partial pressure of 1 bar. Arguments sake .21 vs .79 O2 & N2. A misconception is that we breathe a percentage, we don’t… we breathe a partial pressure. As we climb a mountain the makeup of the gas is the same but the atmospheric pressure drops causing altitude sickness as an example. This relationship is inverted in SCUBA as we are increasing the pressure on a given gas by taking it deeper….

OK so we know now that there is no correct gas to breathe underwater. What can we do? I guess the most sensible approach would be to assess the benefits of gasses and their risks also.

Each of these areas deserve post of their own and would make this post lengthy and laborious to read. I intend to mention them and their implications but if you want to know more, get in touch and book a class..


O2 is what we need to survive, we know we cant have too little or we become Hypoxic, equally too much and we become Hyperoxic. This is the big scare for divers as high partial pressures can lead to CNS toxicity and we convulse.

The problem here is that as we go deeper the PO2 increases. Limits are set at 1.4 for recreational dives


Most are familiar with narcosis and decompression obligations associated with Nitrogen. As we dive our bodies adjust to the surrounding pressure and we equalise to it. Coming up we need to make sure we have not accumulated too much and if we have we need to make stops. It is narcotic but strangely not as much as Oxygen if we were to compare notes

CO2-(carbon dioxide)

A byproduct of respiration, we really don’t want it hanging around. It is very dense and twenty times more narcotic than N2….. It truly is our most dangerous gas underwater and can lead to everything from narcosis to Hypercapnia


Helium is amazing in all but its price! very low narcotic potential, low density and inert. Helium is the best choice you can make in deeper diving to insulate from all the main physiological risks associated with the above. It is expensive…

Where is the safe Zone?

Through the use of set points and responsible approaches to NDL limits GUE has developed a suite of gasses that are not only tiered over varying depth ranges, they can be interchanged and re mixed into each other. Let’s look at things one by one…

If we run the T formula calculations 30 meters on 32% would run at 1.28 PO2, way under the threshold for CNS troubles at its deepest usable depth. All GUE bottom mixes run closer to this 1.2 set point than recommended industry limits.

N2 is reduced significantly by the addition of more Oxygen and thus we have longer times allowed at depth. This means shorter surface intervals and less physiological stress from decompression obligations. Looking good so far…

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CO2 and He I want to tackle together. Any Air or Nitrox mix will get more dense as we increase depth and pressure. At 30m you can only ventilate half the amount of gas you can at the surface which can lead to a lot of problems with retention and as mentioned above a host of other problems from CNS to Hypercapnia.

This video is well worth watching as Simon Mitchell discusses Respiratory failure in Technical diving. In this he deals with density and problems within to our sport. It may surprise you how shallow the depth is that we are above the recommended gram per litre of CO2 in Air/ Nitrox mixes.

In order to compensate for this density, when dives are hard or deep it would make sense to limit the density, limit the narcotic value and limit the Nitrogen retained so we can decompress in less time. This is where Helium comes in. It solves all the issues we have talked about. It really is a miracle gas for deep dives.

Helium, the real cost!

We know He is expensive, it is the main reasoning for the continuation of deep air courses and the evolution of rebreather technologies along with consumption.

I want to ask a question at this point. How much do you spend on a trip out diving? Boat fees, travel, accommodation, dive gear….. the list goes on. How much is your safety and enjoyment worth on that dive?

I know plenty of people who won’t pay the extra $7 for a Nitrox fill & plenty that will dive Air to 50+ meters knowing that they have an unacceptable risk from density, narcosis and obligations. It is all down to money…

The reality is that a major contributing factor in diver accidents is inappropriate breathing choices & WOB. People have DIED because of this so when we are gauging the value of Helium, it is important to remember things in perspective. Don’t be cheap, you are cheating yourself….

The safest gasses are familiar, easy to remember and easy to blend. Stay tuned for our next post and I will show you how to make and mix gasses affordably and easily. As well as this we will see how to make open circuit Helium based mixes far more affordable.

For those who will call me rich and a zealot, here are a few photos that show I was not always GUE and have learned many lessons on my journey here. I want this post to trigger some brain cells and get divers to think about their choices under water and enhance their own safety. I don’t want to hear of anyone else suffering from lack of understanding and we should all be open and promote a culture that shares information of this nature.

Anon 13th Century, Latin - “it is better and more useful to meet a problem in time than to seek a remedy after the damage is done.”

Russell Hughes