418 Dive Log Australasia JUNE 2026.pdf

occur underwater, can lead to drowning. At the surface, the air we breathe has a harmless level of oxygen, but if we breathe it from a scuba cylinder at 60m, we are inhaling seven times as much oxygen with each breath as we do on land. Problem #2 The second issue with air is that it is dense and, like all gases, it becomes denser the more we breathe. This means the deeper we go, the harder it is to breathe, and our scuba regulators and the surrounding water pressure just increase the level of difficulty. In other words, we can’t fill our lungs or empty them without expending much more effort. Problem #3 This leads to the third issue. The primary consequence of reduced breathing efficiency is that we retain more carbon dioxide (CO2) in our lungs and bloodstream. A greater level of CO2 in our body not only makes us more likely to experience oxygen toxicity convulsions, but it also triggers our automatic emergency response system, the final phase of which is panic, the diver’s worst enemy. Problem #4 Underwater, a trained deep diver with a clear head will identify the process that is causing the onset of anxiety, cease all activity and take a series of deep full breaths to bring the CO2 in their bloodstream down to a manageable level. However, the fourth problem with going deeper is that the further you go, the less likely it is that you will be able to think clearly. This is because two of the three main gases present in your body, carbon dioxide and nitrogen, both have something called anaesthetic potential, which means they can knock you unconscious. In scuba diving, we have a name for this effect. We call it narcosis. As you go deeper, the level of each gas increases, and the anaesthetic effect of each gas on your central nervous system rises accordingly. Simon Pridmore is the author of Technically Speaking, a short series of books about technical diving.

Alcohol also has anaesthetic potential, and the effects of narcosis are similar to alcohol in that they are dose-related. The deeper we go and the longer we stay down, the worse we are affected. Just like the more we drink, the drunker we get. The subjective symptoms may differ, but objectively they are the same. Narcosis initially makes us overconfident, relaxed, inattentive and less able to respond to an emergency in a timely or rational manner. Then, as we get more “narked”, anxiety, poor decision-making, panic and stupor follow. Just Don’t Do It We no longer live in the 1970s. We now have techniques, strategies, breathing gases, equipment configurations and training options to enable any diver who wants to explore deeper than the conventional training agency limits to go wherever they want, and safely. Deep diving using air and a single cylinder is pointless, unnecessary and can be fatal. Just don’t do it!

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DIVE LOG Australasia #418.June ‘ 26

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