Should TDI Helitrox replace AN+DP?

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Modern research seems to give us new reasons why Helium should be used for dives deeper than 100.

Basically what GI3 was saying 15+ yrs ago was correct all along.
The "old school" like Chatterton is wrong about narcosis (you cant adapt), they were wrong about density (WOB and CO2 are very important). And they were wrong about helium being "more difficult" than air.

AN/DP on air sticks around and might even become more popular due to the price of helium. Wouldn't be the first time money was put in front of science and safety. Won't be the last I'm sure
 
Basically what GI3 was saying 15+ yrs ago was correct all along.

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Even if you happen to be one of those who can manage Narcosis,

These people dont really exist. Pull an OOA on your camera wielding buddy, or get tangled in some line on a wreck or a crab pot, or work hard when the current doesnt behave as expected - his (or her) performance is going to go to hell fast right when you need them to be "on their game"
 
IIRC, IANTD Advanced Recreational Trimix certifies you to 51m / 170ft, whereas Advanced Nitrox is only to 42m / 140ft, isn't it? Anyway, the classes are almost the same. So it makes sense for the student to take ART instead of AN no matter what he's diving after class.

I’m not sure about IANTD as the OP specifically mentioned TDI Helitrox vs AN/DP. The depth limit for both of the TDI courses is 45m.

If I was looking for more depth I’d go straight to TDI trimix from AN/DP and skip helitrox entirely, if for no other reason than to save the gas cost during AN/DP. If I was simply looking for a shallower END with no desire to go deeper, I’d go helitrox in lieu. This is within the scope of TDI only.

In this case, neither applies to me, but I can see that being the thought process of a potential student. My personal feeling is get on helium early.
 
These people dont really exist. Pull an OOA on your camera wielding buddy, or get tangled in some line on a wreck or a crab pot, or work hard when the current doesnt behave as expected - his (or her) performance is going to go to hell fast right when you need them to be "on their game"

Narcosis is a very real phenomenon. My question is why have Helium at 100ft and not at 107ft or at 109 ft? How can Narosis follow such even numbers like 100' with two zeros in the end? Obviously different people are getting Narced at different depths due to a variety of factors and we are rounding them up right?
 
Narcosis is a very real phenomenon. My question is why have Helium at 100ft and not at 107ft or at 109 ft? How can Narosis follow such even numbers like 100' with two zeros in the end? Obviously different people are getting Narced at different depths due to a variety of factors and we are rounding them up right?
My guess is that like simple numbers. I'm curious however if there is a non-linear relationship between narcosis and depth. Is there a tipping point around the END of 100 feet where the narcotic effect appears to increase more rapidly than increases in depth? Or is this even possible to determine other than empirical observations? Yes, narcosis exists, but how to quantify?
 
Narcosis is a very real phenomenon. My question is why have Helium at 100ft and not at 107ft or at 109 ft? How can Narosis follow such even numbers like 100' with two zeros in the end? Obviously different people are getting Narced at different depths due to a variety of factors and we are rounding them up right?

Simplicity. MOD for 50% is actually 73', for example, but we just call it 70 to keep it simple and a hair more conservative. Likewise, essentially everyone feels some noticeable narcotic effect at 100'. It may vary person to person, day to day, but I'd be willing to bet people who aren't even the slightest bit impaired at 100' are rare or even nonexistent. 100 is a nice, round number as well, so it's easy to remember. It also aligns nicely with new gas density guidelines, but I don't know that that would've been a deciding factor when it was established.
 
My guess is that like simple numbers. I'm curious however if there is a non-linear relationship between narcosis and depth. Is there a tipping point around the END of 100 feet where the narcotic effect appears to increase more rapidly then increases in depth. Or is this even possible to determine other than empirical observations. Yes, narcosis exists, but how to quantify?
I'd wager such a tipping point exists because ppN2 and density driven Co2 are both increasing and acting synergistically.

Back in the olden days (think Exley era) people planned for much deeper ENDs on trimix, 130ft, 150+ft END for 250-350ft dives. This is all talked about quite extensively in Caverns Measureless to Man.

Its also clear they were hella impaired, and it didnt take long for cave country divers to realize that helium wasnt such a big bad boogyman and planning for 130+ft ENDs on big risky deep dives was foolish. Well if a 130ft END is bad at 300ft why is a 130ft END at 130ft somehow ok? And duh recreational triox was born.

The proverbial "tough new England" wreck diver took a lot longer to come around.
 
No it enhances it. Hyperoxic mixes are very handy in certain situations. I like 30/20 when doing work inside the spiraled grove or Duane.
 
Before my UTD days, I had approached PSAI for their Narcosis Management courses. They were the only agency training divers in Narcosis Management in various depth increments like

Level 1 - 100'
Level 2 - 130'
Level 3 - 150'
Level 4 - 180'
Level 5 - 200'

I asked PSAI how do you "manage" Narcosis. The reply that I got was as follows. Areas worthy of attention have been underlined (by me.)

I may be able to help explain the Narcosis Management course. Generally, students begin at Level I (100fsw/30m). It’s not that you are incapable of diving at that depth. Rather, it’s just the opposite. After substantial classroom work you will perform dives at Level I for you to establish your baseline performance. From here, with each increasing depth level, you can objectively assess your performance at depth. If you do enough levels, you will reach a depth in which you will experience broad failures in performing the assigned dive tasks. You will then “learn” your practical air-depth limits.

These dive tasks are practical in nature. Primarily they are DATA, which is Depth, remaining Air, dive Time, and general dive Awareness (dive plan, buddy awareness, potential water hazards, etc.).

It may help to know that Inert Gas Narcosis is nothing more than a form anesthesia. Forget all the other nonsense. If you go deep enough, you will simply go to sleep and drown. Some do not handle even mild to moderate (typical recreational depths) narcosis-anesthesia very well and will show loss of concentration, poor judgement, and act in seemingly illogical ways. This deterioration in mental capacity can become dangerous, long before you would “fall asleep” at great depth.

Each individual has his own unique limitations. The 130fsw/40m air limit can be relatively safe with proper training for many divers, but this certainly is not the case for all divers. Obviously some, but not many, have had success in diving much deeper. Increasingly, agencies are encouraging lesser depths for recreational limits in part due to public’s lack of interest in proper training and in refusing to build depth experience incrementally.

Now this is important, you cannot teach somebody to dive to some arbitrary depth. Their limits are fairly fixed. If somebody is already having problems at 130fsw/40m, he is never going to “learn” to dive to 180fws/55m. In our experience, continuous accommodation training (developing tolerance) very seldom nets more than about 1 atm. (30 fsw/9m) in working depth, if even that much! You pretty much are what you are AND do not change much, if any.

We DO NOT recommend or encourage anybody to perform dives that are beyond the limits of their formal depth training and certification.

The ideas expressed were not a huge departure from my own views. I had seen some people act very slow even at 110 feet while others would do very complex tasks like operating DSLR camera with strobes, manipulating through the menu to select aperture, shutter speed, strobe power and putting it all in synch at 150' without too much challenge.

Now if we are going to standardize a gas for various depth ranges, are we going to standardize based on the guy who is operating DSLR at 150' or are we going to use the guy who is losing his mind at 110? The funniest thing is that the guy who loses his mind at 110 feet may not be convinced that he is acting slow at depth. This means that you really can not be a judge of your own self. This is why GUE/UTD standard gases make sense because if you add one irrational person into a dive team then the whole team gets compromised. Similarly, sticking to GUE/UTD standard gases meant that almost everyone is surfacing alive no matter where they are on their personal narcosis tolerance level.

I had the opportunity to discuss Narcosis very briefly with John Chatterton. It was never my impression that he was suggesting constant exposure to Narcosis as a way of developing tolerance. He was critical of standardizing gases due to a totally different reason. To him, making conservative rules that would apply to a vast population was often a substitute for more in depth knowledge. He wanted all his students to understand various components that factor into narcosis and none of those would be necessary if the technical diving population was being trained to switch to Helium at the lowest common denominator. He was of the opinion that WOB (Work of breathing) has a lot to do with how Narced you would be and managing WOB was one of the fundamental aspects of Narcosis management in his view. So there was a skill or technique to diving deep while maintaining brain function and it was not repeated and constant exposure.

He was coming from the background of commercial diving and commercial divers often dive solo. Knowing ones own limits and how one would respond to Narcosis on an individual level was of greater importance than throwing away that knowledge to become part of a "team." He mentions that he is comfortable diving to 200' on air as long as the dive permits him control of all factors that effect narcosis. He says that he has used Helium shallower than 200' when dive was complex or factors effecting narcosis were outside his control etc but there was no "one size fits all dives" approach in his mindset. Instead a fundamental part of the training of a technical diver in his view was to understand what would work, where.

So yes for what it is worth, this was a huge departure from my own UTD/DIR mindset.
 
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