Not really an unbiased study.....they were selling the training, of course they say it works.
The problem is that you can learn how narcoses feel. This is by doing diving quite a lot. But you never know when narcoses will happen. This is the shape of the day.
I never felt any narcoses myself till I started diving with trimix. Then I knew I also have it.
I know now that it normally starts for me between 40 and 44m. Not that I cannot dive there anymore, but a little bit tunnelvision. But you cannot see it in reactiontime and thinking time. This is normally.
But I have had some dives where it started at 38m already.
I am not that sensative for narcoses that I cannot do deep air dives. I can dive without problems to 60-65m. BUt, again, sometimes I feel I don't have to go deeper, so sometimes it is better not to go that deep (and this is the risk of deep air diving). Have done these depths several times. (Yes I am a cmas 3* diver as well which is a deep air cert to these depths).
But not all divers can do it. Some divers cannot handle narcoses anymore at 42m. And this is the problem. A lot can do, but you cannot say every diver can go to 60m without problems.
The shape of the day, the temperature, darkness or not, all are things that can change the narcoses that time. Since I have a ccr, mix is better for me
A very nice story about narcoses I had years ago. Went to 43m on a winter day, water 6 degrees C, air temperature below zero. Wow, I was in love of some stupid rocks, the rocks where so beautifull, really beautifull. I recognised narcoses as I had done that dive a lot of times. But this times the rockes were sooo nice. After the dive we talked about that and decided to do the dive again. It was really a dive I will remember, the rockes were very beautifull, not only stupid rocks anymore. They were bigger, better shaped, more colorfull, etc than normal. We did the second dive, went to 53m depth on air. Nothing happened, it was just a normal dive.
Narcoses can change during the dive also. If you go down fast, it will onset more intense due to the delta P. The body is taking N2 faster than if you go down slower. If you wait for a few minutes, the narcoses will slow down. And then you can have a normal dive. But the risk is that you must be able to calm that few minutes.
On 1 of my dives over 100m depth on oc (I now only do it normally on ccr), I asked for a trimix with a quite low end. I got a mix with an end of 45m. Not what I asked. The diveshopowner said: can you handle 45m on air? I said yes, I can. For oc fun dives I will never take trimix for such shallow depths. So I accepted the mix. We went down very fast. I was at 103m, my hand were tingling, a very nice feeling, but it is narcoses. I also thought I have narcoses at 103m depth. 103m depth is not a depth to make mistakes. So I aborded the dive. The reaction of the divecenter: why did you not wait 1-2 minutes, then you would have felt better because of the delta P. Yes, that is true, but at that moment I could not find the rest to wait. It is 103m depth, so you don't want to wait and if you don't feel calm, better go up.
So I will never accept a mix again that is different from a mix I asked.
I think a divecenter must never decide what gas you are diving. 45m on air can be handled by most divers without problems. But if a diver want to dive a trimix, no problem, please do it. Deep air is still done a lot and I see it is coming back due to the helium prices. I dove a lot deep air before I had a ccr. With a ccr it is much more easier to dive a trimix due to better prices.
From my deep dives, I know that I am at depth still able to do some calculations, I can still use a reel. But of course I also have (some) narcoses. But the tests with calculations don't work for every diver. I have made calculations for a short time at 74m depth, just to know if I could do it. With a diver who had trimix to watch me. Such depths are never safe on air, even not if there is an agency that teaches 'narcoses management to 73m'. At such depths it is not only the narcoses, but also the PO2. Maybe I better can not tell such things, but I also tell it as a way that people can learn and think about things. This deep air dive to a full trimix depth did not cause any problems, but there are a lot of things that can easy turn such a thing into a real accident. So I will not advice to do it, and I will not do it again. It was quite a long time ago, also before my ccr career.
I am a trimix instructor, so can automatically also teach the extended range/technical diver to 54m depth or so. I have never done this. If a students wants to learn diving with 2 decogases I will say do a normoxic trimix course. The course is more or less the same and you will be able to dive a little bit deeper but also with a trimix for safety/narcoses. But for me as instructor there is another important thing: if I teach deep air, I am responsable, even if I take a mix in my ccr. So that is the main reason I don't teach. But I get the question to teach it a little bit more now due to the helium prices.
The problem with deep air is what is the limit? 40m? 45m? 50m? (I believe 50m is the bsac limit), 60m? (the old cmas limit till a few years ago), 63m? (the older cmas limit that was about 10 years ago), 73m? (the psai narcoses management limit). This answer is difficult. What water, current, temperature, darkness, etc?
But thee is a question were a lot of divers will lie about. If you can go to a nice wreck at 60m, but you can only do it on air, will you go? A lot of people will say no here, but will do it if they can and stay there where not helium is available.
But no, you cannot adapt to narcoses, you can learn how it feels, so you know better what to do. But the shape of the day will be the biggest reason for narcoses or not. And if you want to do a lot of deep air dives, maybe you can think about a ccr (with a ccr deep air is more dangerous than oc) and dive a mix.
I am happy with my ccr. I have done stupid things in the past, I am also human, but due to these things I can tell about experiences I had.
