But what is the minimum amount of oxygen we can tolerate? This is not a subject that comes up much for divers, since we generally operate at increased pressures. The maximum safe partial pressure of oxygen is the well-known 1.4 ATA – the most oxygen our bodies can safely cope with. There is also another problem with any such hypoxic ( < 21% O2 ) mix. So simply replacing oxygen with nitrogen is not a workable solution. You would probably be completely incapacitated by this – i.e. However, the PN2 of this mix at that depth is about 7.9, almost double the recommended limit. Plugging 15% O2 into the calculator gives a max depth of 275 feet. First, we can try what might be called hypoxic Nitrox: reducing the oxygen content of air to EAN15, for example. To go deeper than 190 feet without risking oxygen toxicity, we need to reduce the fraction of O2 in our mix. Since the advent of Trimix and modern technical diving protocols, few people dive this way any more. The dangers of “deep air” were well known, and accepted as part of the game. There was a time before such limits became known and accepted that divers routinely exceeded these figures, diving to 250 feet ( PO2 = 1.8 ) and well beyond on air, the only gas available. You could also use a maximum PO2 of 1.6 instead of 1.4 in these calculations I am being conservative here. In other words, although you are safe from oxygen toxicity, you are also probably narc’ed out of your skull, and very likely to do something stupid and get yourself killed. Using the Nitrox Mix Calculator and a maximum safe PO2 of 1.4 ATA, we calculate that the maximum usable depth for air is 187 feet, which we will round off to 190 feet. The “least” and therefore deepest Nitrox mix is good old air – EAN21, 21% oxygen and 79% nitrogen. How Not Toįrom the previous section on Nitrox, we can see that higher Nitrox mixes have shallower usable depths. This next section should be considered nothing more than “thinking out loud.” It is in no way a reference on mixed-gas technical diving, it is just a bunch of hypothetical calculations that have nothing to do with the real world.

But I do have an engineering degree, curiosity, and half a brain. I’m not a “Tech” diver I’m not interested in going deep enough to actually need such gas mixes, and I’ve never taken a formal class in such things. If Nitrox will not take you deeper than air, what will? I touched on a couple of possibilities previously – Trimix and Heliox, but I did not explain what they are, or how they work.

Sea sickness we need to go deeper