Rapture of the Deep – or Narcosis perhaps?

Without intending to sound like a broken record, my Malin Head dive trip was cancelled AGAIN this weekend. That’s 2 weeks in a row by the way. It was very disappointing, but I find it cathartic to share my dismay with my many, many readers; or something … maybe.

It can be such a shame that diving requires the sea. I am considering creating a movement in which the majority of famous shipwrecks, including The Titanic, will be shipped to a purpose built quarry within walking distance from my house.

Titanic in Vobster

More on that in a future post perhaps.

As my original dive plan was scuppered, I had to formulate an alternative; in other words - Strangford Lough. I visit The Alastor shipwreck in The Lough far more than I would like, but it’s a pretty cool dive, I work some skills into the outing, and it’s better than not diving. Any diving is better than not diving in my book.

My planned Malin Head dive buddy, ‘DIR Dave’, and his many Halcyon Scout back-up lights, agreed to come along for the grand expedition, on the site I’ve dived about 50 times.

Dave arrived on schedule; we loaded my jeep with far too many twinsets, unnecessary stage bottles, Wifebuddy’s can light, and headed to the dive site.

We were both diving air, and brought a stage bottle along for a bit of a skills circuit. Checks done, we shuffled down the shoreline and went for a dive.

The visibility was excellent, which was both weird and exciting; as it’s usually appalling. Once we arrived at the wreck I spent the first 5 minutes laughing to myself as to how (relatively) clear the water was; about 8m in every direction.

The clear(er) visibility made the dive very different from my usual weekly experience in The Lough. I was even able to get a few pictures, in which you can actually determine the content. 

The wreck lies in 20m-25m of water depending on the tide; on this particular dive we maxed out at 21m. Usually, on the journey from the shore out to the wreck, I have a ‘moment’ at 16m.

The moment The Rapture takes hold!

In standard visibility, 16m is where the dark is; natural light is eradicated and the poor visibility amplifies the effect, shrouding the diver in murk. My ‘moment’ consists of a mental slapping, as my brain chooses to remind me I’m under water, in the dark, relying on a piece of plastic to feed me the life blood, which is my air supply.

The cause is simple; The Rapture of the Deep, scientifically known as Narcosis.

What is Narcosis?

Narcosis is the effect on the mind of a diver caused by breathing from scuba at depth. Nitrogen is the main player in this as it makes up the greatest proportion of air, 79% roughly.

As a diver descends, the partial pressure of nitrogen increases to a point where it causes an undesirable mind state.

Although often referred to as “nitrogen narcosis” it may not be accurate, as oxygen and other gases present in air are considered narcotic at depth. Carbon Dioxide is also narcotic; often caused by exertion or poor breathing techniques.

Narcosis is expected to occur at 30m, but it can be accentuated by diving conditions, or the diver in question, resulting in narcosis at shallower depths.

Effects of Narcosis

Narcosis when scuba diving can have different effects depending on the individual. Most divers refer to it as a ‘drunken feeling.’

I know divers that dive ‘deep’ on air, and have described elation, lack of fear, the inability to complete basic tasks, or simply don’t care about anything anymore; including their air supply.

The drunken comparison seems quite accurate; after a bottle of vodka i approach a level of invincibility Wolverine couldn't look at. I'm equally as hard too. I don't drink Vodka anymore, it appears to inhibit my ability to get the claws to come out.

When I get a narcosis ‘hit’ I tend to get a little perplexed. I would rather get the ‘happy-happy’ feeling most divers talk about, but no; I get certain doom. That seems a little unfair to me.

How to cure narcosis

The only way to truly remove narcosis from a dive is to stay shallow, or replace the nitrogen in air with the inert gas Helium.

Helium has no narcotic effects and is less dense, which has a positive impact on the work of breathing of a diver. An improved work of breathing also helps reduce carbon dioxide levels.

Narcosis Management

Divers cannot develop a tolerance for narcosis, fact; although some divers claim that it can be managed.

I’m not sure if I personally “manage” narcosis, but I have experienced the symptoms, and understand the process. This helps keep me calm if the rapture takes hold, and I know that if I ascend slowly, the partial pressure will drop alleviating the undesirable experience.

Keeping on top of skills helps. Muscle memory is a great tool, so if things ever go a bit mental at depth, a diver is more likely to be able to deal with it, if skills are rehearsed regularly.


Ironically, on the dive in this post, I didn’t receive my customary “iffy” moment at 16m. I think the good visibility helped.

Dave, on the other hand, explained (post dive) he did experience narcosis; and I recalled him signalling he was disorientated as we reached the bow of the wreck.

At that stage of the dive a signal wasn’t really necessary to be honest, as he had finned off the wreck entirely and began investigating the sea bed quite emphatically.

I must confess I was slightly amused at the time; although equally concerned of course … ahem.

As a precaution, we ascended 5m onto the upper deck, and all was well with the world. Dave signalled ‘OK’ and we continued on with the dive.

The dive concluded with some fabulous stage handling and gas switching, but was marred by an absolute abomination of smb deployment on my part. I would love to write that off as narcosis, unfortunately I was only at 6m when the smb began fighting me.

What can I say? I need practice.


Narcosis is part of scuba diving. The only definitive way to avoid narcosis is to keep your diving shallow, or dive Trimix.

  • Have you experienced The Rapture of the Deep?

  • How do you cope with narcosis?

  • Do you think a rich Nitrox helps fight narcosis?

  • Share your experiences in the comments section below. 


  1. Hi Andy

    You ask an interesting question: "Do you think a rich Nitrox helps fight narcosis?" I don't have an opinion (sorry), but would like to relate what other divers on my Trimix course mentioned after one of the dives.

    We'd ascended from 50-odd metres on TMX18/40 and switched to EAN32 at 30 metres. Of the five of us that were underwater, three said they felt narcosis increase after the gas switch. With a PO2max of 1.4bar, we weren't going to get any richer FO2, at that depth.

    I guess this points toward rich EANx not helping reduce narcosis much?



  2. Jeez buddy, that's an ongoing argument amongst many divers at the moment. There are many factors at play in that situation that could be argued.

    When you guys switched the partial pressure of nitrogen changed from 1.68 to 3.12. The increase could explain the increase in narcosis.

    There is also the argument that oxygen should be considered narcotic, you switched from 18% to 32% - that may also have contributed.

    Work of breathing would also have increased as nitrox a denser mix than trimix, may also be a contributing factor.

    Isobaric counter diffusion maybe?

    In all honesty, I have no idea mate! My knowledge of trimix is quite limited as I'm new to it, but I have been privvy to such discussions and opinions vary.

    Personally, I've only switched from trimix 20/20 to eanx 50 at 21m. I don't remember thinking I got narc'd all of a sudden; but then would I? :)

    In short, I don't think O2 is narcotic, what you guys experienced probably had more to do with Other factors, I just dont have the knowledge.

    Very interesting, cheers for posting! If you ever find out from someone sensible let me know. ;)


Thanks for commenting, I appreciate it!

Safe diving buddy.