The usefulness of deco training without trimix

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To put some things into a perspective regarding "limits".
Doing CMAS AN/DP, or, did theory part, next month doing dive part. Under CMAS. no such thing as AN/DP, it's all under Advanced nitrox title.
Excerpt from CMAS standards:
Oxygen pP: bottom 1.4, deco 1.6, up to 100% O2.
No time limit, depth limit depends on your current level, CMAS*,**,etc. Planing depth limit 50 meters.
No limit on number of gases, practical limit is back gas and one deco gas ( put by instructor), can expand with experience.
Gas planing and management within team and with external support.
OTU and CNS limits are implicit.
Regarding my number of dives, as I said before, "big" dives are done with mentors, I am not stupid enough to try and do them without "umbrella" of instructor oversight.
Since all divers in my club are always under "peer review", no diver is allowed to progress, unless deemed ready.
 
I'm wondering whether AN/DP (or the equivalent PADI courses) provide a certification and skills that are useful by themselves for real dives, or if they are better understood as stepping stones to trimix certification.
I cannot speak with regard to AN/DP. I can speak with regard to the PADI Tec 40/45/50 sequence. These courses provide training and experience that is useful for real dives. That is what they are primarily intended to do. If you successfully complete the courses, you are trained and credentialled to use 2 deco gases, including up to 100% O2.
Much of the question revolves around whether or not there are dive teams, trips, and LOBs organized to work within the relatively narrow depth range where decompression is required but trimix is perhaps not.
Off the coast of North Carolina there are a number of dives in the 130-185 ft range, which are best conducted as deco dives, but which do not require trimix. You are free to use trimix, of course, and there are users on SB who would argue that trimix should be used (I am not one of them), on these dives. What is critical is being able to plan the dive, and select and use appropriate deco gases. You will get that in the 40/45/50 sequence.

I have done a number of deco dives in the St. Lawrence staying at 160 and below, on air. I have dove the Oriskany to the hanger deck (~175 feet) on air, with appropriate deco gases.

Yes, I am trimix certified. But, the skills and knowledge that I use tghe most were acquired in 40/45/50 (or, in my case, Tec Apprentice / Tec Deep, the 2-course predecessor to the 40/45/50 sequence). Frankly, I seldom use mix, i.e. only on dives below 200 feet. I value the ability to use mix, for those less frequent dives when it is required. But, franky the training was simplistic relative to the rigors of the primary sequence.
 
Yes, I am trimix certified. But, the skills and knowledge that I use tghe most were acquired in 40/45/50
And that makes total sense because in the PADI sequence, the skills and knowledge build throughout the course sequence. That is why someone crossing over at the trimix level from another agency must still learn the materials in the Tec 40/45/60 sequence. The trimix course assumes you have that knowledge. It repeats the key skills, but it assumes you have the knowledge and just builds on it.
 
I am starting to think about taking some tech training as a step towards my goals of wreck diving in the Great Lakes.

I'm wondering whether AN/DP (or the equivalent PADI courses) provide a certification and skills that are useful by themselves for real dives, or if they are better understood as stepping stones to trimix certification.

Much of the question revolves around whether or not there are dive teams, trips, and LOBs organized to work within the relatively narrow depth range where decompression is required but trimix is perhaps not.

I took my initial technical training and my trimix training years apart. Where I live you need to take a shovel with you if you want to dive deeper than about 50 meters so trimix training was not high on my agenda.

However, wreck diving WAS high on my agenda and when you're diving to wrecks at 30 or 40 meters and you've paid €125 for the boat ride to get there then you don't want to make two short dives on a day. I remember my first dive on a wreck after I finished certifying. I was the first person in the water and the last person out. Everyone else had done a bottom time of about 20 minutes. My bottom time was 50 minutes and the whole dive took 87 minutes. I remember it like it was yesterday. Just being able to do that dive justified the expense and effort I put in to reaching that point. As an aside I realized that I needed to find buddies who could do that too because at the time they weren't easy to find. This was not an easy process.

My initial training was also a stepping stone to some other activities, notably, ice diving without the limitation of being tied to a rope. IANTD ice diving sees the environment under the ice like a big cave, to put it in a nutshell.

That was my initial motivation. During and especially after my initial technical training I felt an ENORMOUS sense of relief because I no longer felt any time pressure from the NDL. I felt like I had somehow been freed of some kind of mental schakels and my diving became much more structured, much more under control and much LESS stressful, especially with respect to the aspect of time than it had ever been before that.

Aside from that I learned a number of new skills, a boat-load of "tips and tricks" and picked up on a mindset related to gear, safety and risk management that I benefit from in ways that sometimes don't even have to do with diving.

I don't want to make it sound too romantic but taking ... whatever it was called?... Advanced Nitrox and deco procedures or whatever it was called, transformed my diving and opened up all kinds of avenues for further development that had previously seemed unattainable.

These days, I pretty much do three things on a routine basis. I train novice divers, which involves a lot of shallow diving where the NDL doesn't even ping on the radar.... I do these pretty much on a weekly basis. For "fun" I make technical dives that are (mostly) our weekday evening splashes..... usually they're not that long (60-80 min) and involve swimming to points close to shore, including some interesting wrecks. These dives mostly require decompression within the 30 minute range, sometimes more but not that often... and I take 1 trip a year (most years) to somewhere tropical and dive my buttocks off for a week but remain within (or barely over) the NDL's.

I feel very lucky indeed to be in a position to do all three of those things. As for trimix. I'm glad I did it and I'm happy to make the odd deep dive but for local diving to a maximum depth of 50m I seldom use it. I have much more benefit from the technical nitrox training.

R..
 
I am starting to think about taking some tech training as a step towards my goals of wreck diving in the Great Lakes.

I'm wondering whether AN/DP (or the equivalent PADI courses) provide a certification and skills that are useful by themselves for real dives, or if they are better understood as stepping stones to trimix certification.

Much of the question revolves around whether or not there are dive teams, trips, and LOBs organized to work within the relatively narrow depth range where decompression is required but trimix is perhaps not.
IMHO, an Advanced Nitrox/Decompression Procedures with a Helitrox option course would be a better intermediate stepping stone, and together with a DPV/Scooter class offers greater Open Circuit utility & economy for the wrecks in the 30m to 40m range (wreck interests later with dives deeper or longer, then I would consider changing to a CCR Trimix training path).

Along with understanding the controversies and learning how to apply the various deco algorithms, it's probably just as important to understand the problem of Gas Density/Work-of-Breathing & CO2 Retention/Hypercapnia effects of breathing bottom gases like Air & Nitrox at 40m depth and deeper, and why you should consider using Helium blended mixes especially if anticipating physical exertion at depth (example would be continuously finning hard against a constant current at depth without the aid of a DPV). Below is a great summary and short article link of the current research:
Hello,

As clearly illustrated by the discussion above there are multiple risks in breathing air at progressively greater depths, but with one exception (see below) there are few data defining clear thresholds at which the "big three" risks (narcosis, oxygen toxicity, gas density and CO2 retention) become intolerable. Indeed, as has been pointed out, there is strong evidence that there is considerable variability (both between and within individuals) in the expression of these problems.

Arguably, of these risks, the one with a threshold that is now best defined by data is the risk of CO2 retention due to rising gas density. As pointed out by Kev, the relevant data were compiled by Gavin Anthony of QinetiQ from a database of test dives, and we published those data together last year. To summarise, when gas density exceeded 6g/L during modest work (100 - 125 watts) underwater there was a sharp inflection in the risk (to over 40% of dives) of developing dangerously high levels of body CO2. 6g/L corresponds to use of air at about 40m.

Right there we now have a strong evidence-based argument for avoiding use of air deeper than recommended by the recreational training agencies. I would remind you that development of a high CO2 level is also a significant risk factor for oxygen toxicity. So, using deep air has been clearly demonstrated to increase the risk of CO2 retention, which in turn also indisputably increases the risk of another catastrophic complication.

Yes, I know that many vocal divers have used air at great depths. That, of itself, is not a valid justification of the practice in the face of hard evidence that it is dangerous. These people are a self selected population of survivors, and are around to talk about it, but the ones that died doing it are not.

Simon
Advanced Knowledge Series: The Gas Density Conundrum

Here's an example of a Standard Mix Open Circuit MOD look-up table, taking into account ppO2, END and Gas Density:
MOD ranges of
UTD Standard Mixes @ 1.2ATA ppO2:

Eanx32: 28m
25/25: 38m
21/35: 47m
18/45: 57m
15/55: 70m
12/60 (or 10/70): 90m
10/70: 110m

So at a bottom gas working ppO2 of 1.2 ATA, the END of the Standard Mixes list above are all at 30m or less and with Gas Densities less than 6 g/L.
 
http://cavediveflorida.com/Rum_House.htm

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