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Diving with 100% Oxygen

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I’m sitting here looking at regulators online, thinking to myself ” do I need to buy another one”?. Here is the answer – pure O2.

Last season I completed my Advanced Nitrox/Helitrox/Deco procedure course. This season I am using this training, as I continue  to gain  experience in the field of technical diving. I have completed my third deco dive since my training.

Sea to Sky

When taking an advanced nitrox course you learn about PPO2, and oxygen toxicity. If PPO2’s get too high, or with cumulative dives, this gradually builds up in your system, and is a risk to a diver. I am not a science guy, so I don’t understand the theory or physiology of oxygen in the body, but here is what is causing me pause. Below 20 feet, pure oxygen becomes toxic; quickly! Any other nitrox also has its MOD ( Maximum Operating Depth), but for 100% oxygen, it is very shallow.


Diving with just oxygen, or diving with any other single deco mix does not give me great concern, you know what you have and the depth you need  to be to use it safely. Where I am stuck is diving with two deco mixes, commonly my 50% and my 100%. What if I mix them up? Grabbing 50% at 20 feet when it has an MOD of 70 feet is no issue, but grabbing 100% at 70 feet when it has an MOD of 20 feet, is a problem. Not a, “oops I dropped my reel” problem, more a oops, I could  just drown problem. I have taken the training, I have practiced gas switching, from confirming the mix and depth with myself and my buddy before breathing it. I analyze and mark my bottles appropriately. If I am not sure, I analyze again, I have selected a regulator of my sets that I have designated for my O2 regulator. I have a green adjustment knob on the second stage of that regulator,  and I have put 2 zip ties on the hose of that regulator so in blind conditions I can identify it,  I have even gone so far as to put Hello Kitty tape on the hose right next to the second stage to identify it. If nothing else works, at least Hello Kitty will save me. But here I am, contemplating spending X dollars on a brand new regulator, that I don’t need,  but its all green, with a green hose and a green mouthpiece and green, and despite being green everything, I would still add Hello Kitty for safety.

I have no real solution here, this is a matter of confidence and practice and experience. As I gain more in all of them, I will be more comfortable. I guess the real take away from this thought process, for me at least, is that it is good to have a healthy respect for diving, and the risk that is involved, at all levels. I believe that if we do not stop and have these questions and conversations with ourselves from time to time, then we have possibly become complacent. It’s not that every single time you don dive gear you need to have a deep conversation with yourself, if you did you might find yourself short on dive buddies; but it is important that when those concerns, or voices pop into your head, that you take stock in them and work through them, seek advice, maybe get some extra training, to be confident and safe.


La Galigo

About Author

Matthew lives in Kingston Ontario at the gateway of the Thousand Islands. He is fortunate to have the St Lawrence River and Lake Ontario in his backyard. He can be found most of the time in these waters. Matthew began diving in  2011, and completed his open water training in Loreto MX Diving in the Sea of Cortez. Matthew has since completed his Dive Master, Cavern Course, Intro to Cave Diving and has logged over 300 dives. Matthew has also completed Advanced Nitrox, Deco Procedures, and Helitrox Training

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Dive Curacao

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