{"id":1298,"date":"2022-01-20T13:03:17","date_gmt":"2022-01-20T13:03:17","guid":{"rendered":"https:\/\/punkfish-academy.com\/expand-boundaries"},"modified":"2026-01-28T14:02:03","modified_gmt":"2026-01-28T14:02:03","slug":"boundary-expanding","status":"publish","type":"page","link":"https:\/\/punkfish-academy.com\/en\/boundary-expanding\/","title":{"rendered":"Expanding boundaries with Nitrox"},"content":{"rendered":"

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Pushing limits – diving longer with Nitrox
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No-decompression limits and saturation with air and Nitrox<\/h2>\n

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If you look at the no-decompression tables for air and various nitrox mixtures, it is clearly visible that you can simply dive longer with nitrox – provided your own breathing allows it. Nevertheless, you still saturate with nitrogen, it just takes a little longer. If you take advantage of the new limits of Nitrox, the dive will be longer, but not safer.
This is exactly what we will look at here, step by step.<\/p>\n

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Here we would like to look at a dive to 30m and compare how the safety advantage of using an EAN32 instead of air on the same dive is – and also how far you can extend the dive by doing so.<\/p>\n

In the first picture you can see a typical dive profile:
You reach the 30m maximum depth within three minutes and stay there until the no-decompression limit. According to the table, that’s 20 minutes at 30m, so we’ll just plan for that. We go up slowly, taking 5 minutes until we are back at 10m. We stay there for another 10 minutes and then return to the surface with a safety stop.<\/p>\n<\/div>\n

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Below the profile you can see the heatmap for this dive. This tells you which tissues are currently saturating, which are desaturating, and how oversaturated they are. The top line corresponds to the fastest tissue, the bottom to the slowest. What is important here is the moment when the surface is reached again. In this example, the middle tissues are at their saturation limit here (the redder, the more borderline).<\/p>\n

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The schematic below shows exactly the same dive, but now with an EAN32. We look at the decompression phase, surfacing, and most importantly, how supersaturated you arrive at the surface. Even the middle tissues are far from the orange or red range, not even 50% of the M values are reached,
As you can clearly see here, you actually come out of the water much less oversaturated, so you would have made your dive safer.<\/p>\n

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Things get different when you use nitrox to extend the no-stop time. Although in this plan you can stay at 30m for 32 minutes instead of 20 – but then you come out of the water just as saturated as in the shorter dive with air. This dive is just as “risky” as the one with air.<\/p>\n

Nitrox is a great thing, sure. Taking in less nitrogen is so good that you’re happy to put up with a little oxidative stress for it. But it doesn’t make the dive safer per se: if you push the limits with it, you come out of the water just as oversaturated and have also exposed yourself to higher oxygen pressures. A little distance from what the models and computers say you’re allowed to do might actually be a good idea.<\/p>\n

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You can also create such profiles yourself with Subsurface – open source, free, can only be used for planning on a PC, great: Subsurface Dive Planner<\/a><\/p>\n

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Optimize gases and times: Calculation games<\/h2>\n

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Of course we can find tables and technical aids for everything. The Analyzer simply displays the MOD, we can read EADs from a table, apps calculate the best mix for us… So why still calculate yourself?
Maybe just because we can. But maybe also because it’s good to be able to at least roughly estimate what can be true and what isn’t, and where it becomes dangerous. The app is not there when you decide underwater whether you want to risk going 2m deeper or not.
We would like to show you here how to calculate important values yourself. A few small tools will help: You don’t have to do the calculations yourself, but can observe how the results change when you change the depth or oxygen content. <\/p>\n

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Dalton’s Diamond – or: How am I supposed to remember all the formulas?<\/span><\/h3>\n

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Who feels like me: Too many characters at once just don’t stick in the brain. You don’t even need it, if you remember the one important context…<\/p>\n

It’s always about three things: The ambient pressure – i.e. the depth you are at. Then the percentage of oxygen in the gas, what percentage does the mixture have. And, of course, it’s all about the partial pressure of oxygen.<\/p>\n

These three units are connected to each other. What’s really easy to remember is that pO2 increases as pressure increases, and it increases in proportion to pressure. P, the pressure, times fO2, the oxygen content in a gas, gives pO2, the partial pressure of oxygen.<\/p>\n

P x fO2 = pO2<\/p>\n

So far, so simple, right? Depending on what you are looking for, you can fill two of the placeholders with values and calculate the third.<\/p>\n

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To remember, you can use “Dalton’s Diamond” – and because it’s not only about oxygen, but about any gas, we just take g for gas instead of O2.<\/p>\n

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Calculate MOD<\/h3>\n

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How deep can I go with my mix? Maximum Operating Depth (MOD) is the maximum operating depth of a gas. The limit is reached when the oxygen partial pressure pO2 becomes too high. For normal dives, 1.4 bar pO2 is considered an acceptable limit, but some also opt for 1.3 bar or 1.6 bar for use as decompression gas. <\/p>\n

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We always calculate the MOD for a specific gas that we already have, so we know the oxygen content. Let’s assume that we measured 32% – this corresponds to a proportion of 0.32. And we know the pO2, i.e. the 1.4 bar that we do not want to exceed.
We have to use these values: We divide the 1.4 bar by the oxygen content in the gas – in this case 0.32 – and obtain the total pressure at which our mixture reaches the oxygen partial pressure of 1.4 bar. In the example, this would be 4.37 bar. <\/p>\n

So far, so simple. 4.37 bar pressure prevails at 33.7m, something like that (every 10m one bar, and one that is already there at the surface…). That would be, rounded to the safe side, a MOD of 33m.<\/p>\n

Far too complicated? Then just use the MOD calculator \ud83d\ude42 <\/p>\n

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