Help me to understand what happened

[ginti]

In my opinion, "deep" for air starts at 50m. Until 50m, diving with air and light deco is NOT technical diving, it is fully recreational, and safe enough for anyone who has got proper training for it.

Hi @Angelo Farina, I am particularly interested in understanding your opinion. But first, let me share my experience.

I have never liked diving deeper than 30/35m in air. At 40m, I have always felt a bit anxious, and I could never understand why. The thing is that, being in this slight anxious state, problem management could become an issue. I am not saying this is totally critical: I had a free flow regulator accident at 40m, and although it was stressing (first and only time in my life I did a "real" S-drill), I managed it pretty well. But I am not sure if I could manage other kinds of problem, especially if I need to think a lot. To give an idea, I will NEVER go that deep inside a cave with air/nitrox, because the solution to an issue might not be as straightforward as "do an S-drill and ascent with your buddy".

Then I tried trimix - it is another dimension, literally. I enjoyed all the (very few) dives that I did, and I feel no difference between being at 20/30m with air and being at 40/50m with trimix. In the end, we dive for fun, so if I enjoy it more with trimix, and if it is as safe or safer than with air - I'll do it. Helium is a bit of a penalty in terms of decompression, so if you want to stay for a long time at depth, and you don't want to do long deco (long deco in my opinion is a bad idea), you need deco-gas and gas-switches, which actually introduce some risks. Solution? More experience and more training, specifically what you called technical training. [I usually avoid oxygen as a deco gas, in part for the reason you mentioned; I think oxygen makes sense for long shallow dives - which I have never done, and I am not sure if I will ever do... maybe in caves?]

Now, this is a personal experience and I cannot say that it can apply to everyone. But I would be surprised to know that other people feel nothing at 40m, and even at 50m, since these effects start at the surface and increase gradually with depth. Since your opinion is apparently very different from mine, I am particularly interested in understanding it.

So here we are to my questions for you:
- how do you define "safe enough"? when a dive at those depths is not safe anymore?
- what does the "proper training" you mentioned include? what are the key skills that must not lack to do dive with air at those depths?

Thanks

 

[Angelo Farina]

First of all, since many years I do not dive at more than 35m, well within NDL. Going deeper in plain air is too risky for a father who is responsible of maintaining wife and sons.
My last deep dive (around 52m, on the Portofino's cape) was done in January 1990, together with my wife. She was already pregnant at the time since a couple of weeks, but of course we discovered this later.
So the anwer to "what is safe enough" changes dramatically depending on life's circumstances.
During the first 15 years of my diving career (1975-1990) we did not have access easily to trimix. It was very expensive, we did know that it was the way for going deeper, but diving in air down 50-55m with short deco (20 min max) was considered absolutely normal here, and we were trained for this. The standard tank was a 10+10 liters with two independent regs. A pony tank was added for caves, etc.
All this was considered reasonably safe.
Personally I did always feel good down to 50 m. Only beyond 50m I had some effect of narchosis. My wife instead had such a limit at 60m (females are apparently better suited for deep air, as they breath much less). However we have seen many other divers starting having problems at 35-40 m.
We did also meet Raimondo Bucher, he had no problem up to 90m, and could go beyond 100m.
We are not all built the same...
So I usually kept my diving within my confort zone, 50m max.
You correctly respect your confort zone, and it is correct to switch to trimix for going deeper, if you can find it easily at a reasonable price (which was impossible at our times).
I never used trimix. But I had used it when young, if it was available.
However, if available in quantity, I had used it also for deco, avoiding switching to an highly oxygenated deco mixture.
As said, I witnessed many bad reactions to abrupt gas switching. I tend to avoid it, if possible.
In some cases I used a CC oxygen rebreather for deco. Not for shortening it, I did always follow the standard US Navy tables, but simply because my back tank was almost empty.
This for me was "plan B". We used to leave a couple of ARO CC rebreathers hanging under the Zodiac at 6m, in case we did arrive at the deco stop short of air...
As said, all these things were considered "safe enough" in the eighties, when I and my wife were young instructors, fearing nothing, and always searching to extend our limits.
As soon as we converted to be parents, the concept of "safe enough" changed drastically for both of us...

 

[ginti]

You correctly respect your confort zone, and it is correct to switch to trimix for going deeper, if you can find it easily at a reasonable price (which was impossible at our times).

Not easily, and not at a cheap price; but it's the only way I really enjoy it, so there is no purpose in going at those depths without trimix for me

All this was considered reasonably safe.

I think this sentence is very important. I believe that we all are influenced by some factors around us, including the culture. The culture evolves with time, and it is particularly important to make it evolve in the right direction. But this is not always the case unfortunately.

Nowadays we know way better than we do NOT understand anything about human physiology. Hence, we should be more conservatives. In 2020, we tend to be more conservative on the paper, e.g. today the rec limit is 40m for most agencies, except for some old-style ones like the french federation. But less with training, and this is probably not good.

I am also in favour, in general, with gas mix, because it seems to me that physiologists are suggesting to do so. There are many other factos behind narcosis (for instance, hypercapnia). But I agree with you that the use of more gases introduces new complications, and we should have a more in-depth training.

Anyway, understand what to change and how o do it is very complex, and would require an entire new thread; better not go too much off topic here.

I just add a last comment, because I think that the evolution of training may have played a role in this accident. I have the feeling that, today, instructors tend to exagerate some physiological aspects, such as oxygen toxicity***. Consequently, more susceptible students can overeact to the environmental factors related to this "exagerated topics", consciounsly or unconsciously. Here the guy might have be so worried about OT to have developed this inconscious reaction... The OP said that the course was well done, so maybe in this case this inconscious reaction (if it was the cause of the problme) may have been caused by the inexperience and pressure on the diver, as said by other before me.

***On the other hand, very often some critical factors are not considered as much as they should.

 

[Angelo Farina]

I did use pure oxygen without any toxicity symptoms down to 12m, that is twice the currently recommended max depth, so also I think that the risk of oxygen toxicity is currently being over-rated.
However, as said, I have seen several cases of convulsions triggered from switching from Nitrox to Pure Oxygen using military-grade rebreathers. Not complete CNS blackouts, just a set of convulsions lasting 30s, and then everything was back to normal.
Those guys (COMSUBIN, the Italian navy seals) seemed to be accepting this as an unavoidable consequence of using their Caimano IV SC rebreathers.
In ensure you that those guys are heavily skinned, and that no psychological effect could have been the cause of their convulsions.
So, reading the original post, where the diver reported convulsions after switching to an highly-oxygenated mixture, I did recall this experience, as the symptoms were the same.
And my experience with those military rebreathers is the main reason for which I always tried to avoid as much as possible those abrupt gas switching procedures...
Modern rebreathers are another world: if working properly, they modify smoothly and continuously the gas mixture, and avoid any sudden variation of oxygen content, so they are not so prone causing these nasty effects.