Experiences with nitrogen narcosis

Discussions about nitrogen narcosis

The topic of nitrogen narcosis always leads to very heated discussions. We would like to shed light on some of these questions here – without claiming to proclaim universally valid truths. But of course the argumentation refers to scientific findings on the subject – the studies we mention here are all discussed in more detail on the previous page.

Is oxygen narcotic?

One question that is often discussed is whether the oxygen content in the gas should be counted as narcotic or not. Do we have to assume that oxygen makes the narcosis worse or less bad? Is oxygen narcotic or not?

According to the theory of fat solubility, oxygen – an extremely fat-soluble gas – should be narcotic. At the same time, however, oxygen is metabolized, which means that it may not accumulate at the synapses in sufficient quantities for a narcosis.

Unfortunately, it is impossible to directly measure the narcotic effect of oxygen under high pressure, as toxicity sets a limit long before a possible narcotic effect. However, indications can be gleaned from some studies on nitrox.

One example of this is an experiment in a pressure chamber in which 10 test subjects breathed either air or EAN40 in a pressure chamber. During a simulated dive to 30m, a CFFF test was carried out beforehand, on arrival at depth, after 20 minutes (directly before the ascent), on reaching the surface and 30 minutes after the dive. The result: In both groups, alertness increases at the beginning of the dive, with nitrox significantly more than with air. Towards the end, and also afterwards on the surface, it then decreases significantly – with Nitrox, however, significantly less than with air, and after diving you immediately reach a normal level again.

If one wants to understand this decreasing alertness as a sign of narcosis, one can read this study as an indication that nitrox is less narcotic than air – and consequently that oxygen is probably not narcotic, or at least not as strong as nitrogen.

There are also recent studies of brain waves in subjects who have breathed air at normal pressure and pure oxygen at normal and elevated pressure, which indicate that at elevated pressure, breathing pure oxygen causes different changes in brain activity than those known to occur when breathing air and may be associated with the narcotic effect.

However, the question is really much less relevant in practice than one would expect from the heated debates: one may believe that one feels less narcosis at 40m with an EAN28 than with air. With the 7% difference, it might be difficult to prove more than a placebo effect – but since there is no harm in using an EAN28, anyone who likes it can simply do so. On the other hand, when it comes to determining the EAD in a trimix, the difference between assuming O2 is or is not narcotic is so small that the whole discussion is rather academic.

Can you train for nitrogen narcosis?

Many divers report that they are experienced enough to no longer have a narcosis – they are convinced that it can be trained away. But is that really the case?

In fact, there is at least some evidence that experience helps in different ways to cope with being narked. In the psychomotor skills study, those with more diving experience performed better – an indication that dealing with high pressures can perhaps actually be trained. In the breathing gas comparison study, the results of the test subjects, all experienced divers, were also better than in the shallow water narcosis study, in which less experienced divers took part.

In addition, studies on brain chemistry have shown changes after repeated exposure to high pN2. However, it is not clear whether this is actually a sign of habituation and what effects it has on the skills relevant underwater.

What you can train is how to deal with intoxication. You can get used to not being quite so clear-headed. And above all, you can train your own diving skills so that they work without thinking – as we have also seen in the psychomotor skills study, mechanical skills are largely retained.

Is nitrogen narcosis stronger in dark and cold waters?

Divers in particular, who also spend a lot of time in deep lakes, often describe how the narcosis is something completely different in the cold and dark than in warm, light-flooded waters. What’s the story?

First of all, no differences can be proven under different diving conditions – at least if you believe the “environmental conditions study”. But: In this study, no really dark and cold conditions were tested.

Now there are two things that can actually have an influence here.

Firstly, you usually dive in cold water in a dry suit, and often with a twin tank. So you have to move more equipment than in a thin neoprene – and that is a little more strenuous. However, exertion in combination with the increasingly dense breathing gas at depth can cause the CO2 level to rise – and this in turn feels quite oppressive: CO2 is highly narcotic, and it also triggers a reaction that is definitely suspected of turning a “mild, euphoric” deep dive into an unpleasant, bad one. The air hunger associated with an increased CO2 level, the feeling of breathlessness, can intensify worrying feelings. So it really can have a physiological cause – which doesn’t just play a role in the cold, but also in other exertions, e.g. when you have to fight against a slight current.

On the other hand, you can well imagine that darkness in combination with depth is simply somewhat unsettling. The same narcosis can therefore simply feel different. But that doesn’t necessarily make it stronger, you just perceive it differently.

Can you do anything about nitrogen narcosis?

If you can’t actually get used to the narcosis and it is very dependent on your daily form, is there anything you can do to minimize the risk?

Strictly speaking, there is only one thing to do: keep the pN2 below the threshold that becomes problematic. And there are two ways to do this: you can replace some of the nitrogen with helium, or you can stay shallower.

Of course, there can be no hard limit here; as we have seen, the effect of narcosis sets in gradually and becomes stronger and stronger with higher pN2. Perhaps a useful guideline is the following: If you really want to be careful – up to 30m the narcosis is not particularly limiting for most people in most situations. In the range between 30m and 40m, most people feel a noticeable effect, and it is already worth thinking carefully about the possible consequences and, if it becomes uncomfortable, to get shallower immediately or to think about alternative breathing gases. From 40m the effects increase significantly. Dives to these depths are possible with air and are also made. But they absolutely require an informed decision, caution, and the knowledge that if in doubt, choosing a different breathing gas will be the safer option. And above all, you shouldn’t try to turn the maximum depth that can be dived with air into a test of courage or a baptism of fire.

Want to talk about narcosis?

“I am personally quite receptive to nitrogen rapture. I like it and fear it like doom . . . . L’ivresse des grandes profondeurs has one salient advantage over alcohol: no hangover. If one is able to escape from its zone, the brain clears instantly and there are no horrors in the morning.
I can’t read reports about a record dive without wanting to ask the champion how drunk he was.”
(Jacques Cousteau: The silent world)

“(…) when you hear that noise, you’ve been fucked up on air, you’ve been deep on air. It’s called the ‘wah-wah’ “ (Bob Raimo)

The good old nitrogen narcosis. For some a threat, for others a wonderful moment. Sometimes that changes from one day to the next.
“Nitrogen rapture” sounds dangerous. But “being a bit narked”, and even more beautiful “l’ivresse des grandes profondeurs” – I would now rather consider that a beautiful experience.

These differences in description correspond to the differences in experience. A nitrogen narcosis begins – the first few times, when you are still quite inexperienced – somewhat frighteningly. You no longer feel quite so normal, but you are still under water!
Only when “being under water” is no longer threatening can the deep dive become a pleasant experience. You know that you have the situation under control, even if you feel somehow narked. Then you enjoy it, and when it’s time, you go back up again. The time until then actually increases with experience.
That’s what I usually mean by “nitrogen narcosis”. My depth for this is around 40-55m.

Then there is the nitrogen narcosis which becomes unpleasant. You notice that it’s harder to breathe, your perception is blurred, you find it all somehow quite threatening – then you should get up. Even when you hear beautiful singing. A few of the very old who survived tell of the “wah-wah”, the sound of unconsciousness flooding in. When you hear it, it was really too deep. And if you can still talk about it, you’re lucky.
I now prefer to stay at depths where I know that survival is not a matter of luck. What depth is that? None of your business. But no, it’s not 30m…

Because very little is known from the various studies about how divers experience their own personal deep dive, we are collecting articles on this topic.

Would you like to tell us how you are doing in depth? With pleasure! We collect reports that we can compile and share – with your name or anonymously, whichever you prefer.