Should I do a nitrox course?

The other day, I came across a question on a divers’ chat room.

The question was: “My boyfriend is doing a nitrox course. Should I do the course with him? I don’t need it as I always have at least 1500 psi left in my tank at the end of a dive when he is down to 500psi.”

There is so much to unravel in this question.

By far the greatest benefit of diving with nitrox rather than air is the fact that with nitrox you are breathing less nitrogen than if you were breathing air. The difference is 68%* of each breath rather than 79%.

Therefore the nitrogen level in your body builds up more slowly during a nitrox dive than during an air dive. This means that, if you are using nitrox AND if your computer is set to nitrox, it will take more time for you to arrive at your no decompression limit than if you were breathing air.

If you are typically doing dives on air where your dive time is dictated by your no decompression limit rather than your air supply, then switching to nitrox will give you longer dives.

However, if you are typically ending your dives when you run low on air and still have plenty of no decompression time remaining, then switching to nitrox will make no difference at all to your dive time. Switching to nitrox has absolutely no effect on how quickly you use up your breathing gas. There are plenty of techniques that will help you reduce your consumption rate, but that is a separate discussion – (my Scuba Confidential book has a whole chapter on it).

So, should you do a nitrox course?


1. As you gain more diving experience you will reach the point where you no longer use your breathing gas up as fast as you did in the beginning and you start doing deeper and more challenging dives. At this point, you will want to use nitrox to give you more time at depth.

2. If your diving partner is using nitrox, then it is good for both of you to be on nitrox, so that your computer profiles match more closely. If one of you is using nitrox and the other is using air, then, especially if you are doing multiple dives in a day, your no decompression time remaining figures will be very different.

3. At some point in your diving lives, you will start doing extended dive trips. Using nitrox on trips like these can give you extended dive time as I described, which can be valuable especially on later dives in the day when your no decompression time on air may be quite short. Or using nitrox can help you add an element of caution to your diving – see below.

If you are older or out of shape (or both), or if you are any age or shape and just want to dive conservatively, especially if you are on a trip where you will be doing multiple dives over multiple days in a remote area far from a recompression chamber, then a great technique is to use nitrox and have your computer set to air.

You will not benefit from the extra no decompression time that diving with nitrox can offer, but you will be building in a margin of safety as far as decompression sickness is concerned on every dive, as your computer thinks you are breathing 79% nitrogen with each breath, whereas in fact you are breathing only 68%*.

This is a completely safe procedure to follow as long as you never exceed the maximum operating depth (MOD) of the nitrox*. This maximum depth depends on what maximum PO2 you choose and set in your computer: as follows:

Max PO2 = 1.4 / MOD = 110ft (33m)*

Max PO2 = 1.5 / MOD = 120ft (36m)*

Max PO2 = 1.6 / MOD = 130ft (39m)*

So, as I said, diving with nitrox will not reduce your consumption rate, nor will it make you less susceptible to narcosis, even though you are breathing less nitrogen. Oxygen is narcotic too.

However, another claim made for nitrox, that you are less tired after a nitrox diving day than after an air diving day, is a matter of debate. Scientific experiments have failed to find any objective proof that this is the case, but I remember when I ran liveaboard trips in the past and everyone was using air, some divers found it hard to keep their eyes open during dinner and by 8pm we were all in bed.

Nowadays, when everyone is using nitrox, the chatting and story telling goes on long after the crew have cleared the dishes.

I notice the difference. See if you do too.

*I am assuming that nitrox is nitrox 32 / EAN32, as it almost always is in recreational diving circles these days.