Review: TDI Normoxic Trimix with John Chatterton, November 2019

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I have had a few discussions with deep air divers. No one believes that Helium is bad. That is one point that everyone can agree. The point of departure is at what depth should it be introduced? Should that depths be fixed or should it vary depending on the nature of the dive, the work that is being performed, individual disposition to Narcosis etc?

The first school of thought is the 100' ft mark. In other words, if you are diving U-352 AT 115' depth, which is the single most common dive in North Carolina, done repeatedly by new recreational divers, then you should be on Helium! If you are diving a deep reef in Bonaire at 112 ft then you should be doing that on Helium as well. This view is supported by scientific recommendation based on gas density but tens of thousands of divers are already diving in excess of that scientific recommendation so on one hand there is academics and then there is real world. Modern science recommends drinking eight glasses of water each day. How many of us are keeping a count? Science recommends 7-9 hours of sleep every single day. I can not recall the last time I had that much sleep in one go. Scientific recommendations give us an ideal to strive for and then reality hits us in the belly.

I have had a few discussions with old school divers who were doing technical diving before Trimix became a thing. I have been told that diver proficiency plays a large role in making certain diving related functions autonomic and ingrained. Once these functions become reflexive instead of deliberated and thought out, impact of narcosis on those specific functions is also reduced. Other factors that can aid in reducing the impact of Narcosis are reducing the exertion level and thus managing the work of breathing etc. I have never done that type of diving so I do not have much personal experience to argue for or against such methods but it is easy to see that there used to be a technique to deep air diving when that was the only option. Then Helium came and the age of Trimix began. All those methods and techniques that collectively constituted the Narcosis Management became politically incorrect. Any attempt to study those also became frowned upon and instructors who are explaining those today are not looked at favorably.
 
The techniques used for narcosis management are things that should be taught anyways. Streamlining, managing exertion, proper buoyancy, reading flow/current, recognizing when to kick vs pull and glide, etc. I don't think anyone discounts their value.

You can still get narced on trimix with poor form and efficiency. I've seen it happen firsthand. So in my opinion, proper gas choice and diver proficiency go hand in hand. You can't substitute one for the other without giving up your safety margin.

A quick recreational dip to 115 on nitrox is one thing. Is it a bit out of ideal scientific guidelines? Sure. Would it be nicer on mix? Definitely. But it's not outrageously risky. But what Chatterton is teaching (air beyond 50m) is, in my opinion, like teaching people techniques to safely drive without a seatbelt.
 
Excellent questions!


That brings me to your second question. Did I *have* to wear the bottles on both sides vs. one side? I don't know: I never asked. My guess is, John wouldn't blink an eye. The beauty of total self-reliance is you don't really care what your buddy does, as long as it's not actively harmful to others. It won't affect you unless you want it to. The deeper question is, though: why are you taking this class from this instructor? You don't take TDI Trimix from John Chatterton to learn about helium half-lives or END calculations. You take it to understand his diving philosophy and see it in action. Conversely, you don't take GUE Tech 1 to learn about helium half-lives or END calculations. You take it to understand *their* diving philosophy and see it in action. Would you ask your GUE instructor if you had to wear your deco bottles on one side or are they open to wearing them on both sides? No: it's an affront to the class *and* the instructor. I feel the same way about the reverse.

I Think your GUE instructor will tell you why you should wear your deco bottle(s) at your left side. Maybe he will let you dive with a deco bottle at your right side if you really want. But If he/she let you dive with a deco bottle at the right I know what will happen... Your buddy will have 2 unfixable failures and will be out of gas. And you have to deploy your longhose. :)
 
Back to the OP, I think you talked about taking a stage of 21/35 on an air dive to demonstrate the difference back to back. I have thought about doing that but decided I had no idea what the risk might be, imagining a whole load of He rushing into tissues while the N2 only gradually left, so concerned about ICD. Was this risk discussed? Is there a convincing argument as to why it is ok?

Interesting questions.

No, this did not come up. A few random thoughts off the top of my head:

According to my TDI book, ICD isn’t an issue at normoxic depths, even at the end of a dive switching at deco time. This was *early* in the dive and at a much shallower depth than hypoxic depths, with much less saturated tissues. Plus, this is not terribly far off from travel gas use. And I have heard of lots of other divers doing this in Trimix classes. (Sure, normalization of deviance.)

Im not saying this should be part of your normal routine. Just like I’m not saying *air* should be part of your normal routine. I *never* use air at *any* depth. But a class is *not* routine. It’s the most controlled 165’ dive I could do while still getting wet. Given that, it was an opportunity to safely push beyond the limits. Think race car driver on a skid pad: you don’t *want* to lose control of your car ever, but if you can’t guarantee that it won’t happen, it would be wise to be familiar with the process in controlled conditions.

In my opinion, technical diving is like race car driving. For me, not Formula One, but not daily commute, either. In my opinion safe and controlled training in marginal (and beyond-marginal) conditions is prudent. We do zero-viz training for the same reason. Not so you can intentionally enter those conditions. But so you can be aware of the situation and have the skills to deal with it. I hope to never experience narcosis ever again. I hope to never dive air again. But even with those precautions it is not impossible for narcosis to occur. And I’ll understand the signs in advance, as well as the experience of having dealt with it. For me, I consider that valuable.
 
I can’t imagine doing a dive to 130ft on air (deepest I’ve been and I had a major case of what I refer to as “mush brain.”) and being asked to perform a valve drill or something else complicated. I’m doing AN/DP/Helitrox this year (150ft max) and a number of people have questioned adding He for such “shallow” depths. For me it’s a safety factor as well as wanting to enjoy/better remember the wrecks I dive. I start feeling narced at 115ft or so.
 
on the dive with 36% deco gas what were your other gasses?
depth & time for that?

Sorry I got confused about which dive was which and all the different gases going on
 
I'm still intrigued by the follow the ceiling not the stop depth concept if it's ok to discuss out with the course.

FWIW on the deep air debate, I started diving years, before mix, and only got involved in tech diving just before mix became commonplace.

So whilst my group were qualified to dive it deep air was the norm, down to 70m in quarries for practice/acclimatisation and wrecks in up to 60m of water, obviously the structure was usually at 50-55m.

Narcosis was apparent but not debilitating and varied depending on the circs, but we were still capable of completing tasks at depth, it was a regrettable era of "artefact recovery" which often required team work and mental/physical dexterity. Usually it was dark and sub 12-14 degrees.

The one negative that I don't remember, and that no one else really ever mentioned was a significant issue with gas density.

Obviously you could feel the additional resistance but it was never at a level that caused concerns in terms of ventilation rate, either that or the narcosis covered it up! Not saying it didn't play it's part but it didn't feel.like a limiting factor.

At that time in the UK Poseidon Jetstreams were the reg of choice for the discerning tech diver.
 
I'm still intrigued by the follow the ceiling not the stop depth concept if it's ok to discuss out with the course.

The did not follow the ceiling, they followed their stop depth. However, because the ceiling at the end of a stop is higher than the stop depth/below the next ceiling, OP says it was encouraged to cut your stop time short and ascend to the next ceiling by the end of the stop time.

Basically, you follow the stop until about a minute before your stop time is over, then ascend to your next stop, because technically the ceiling is higher than the stop depth by the end of the stop.
 
The one negative that I don't remember
I snorted when I read this - good stuff!

At that time in the UK Poseidon Jetstreams were the reg of choice for the discerning tech diver.
They are still popular even if the GUE crowd bangs on them and the price (at least on this side of the pond) makes you faint. Plus getting good parts & service is a pita. If I dove in Swedish water temps more (uff its cold there!) I would seriously consider switching.
 
They do them with sensible reg hose connections now too!

What's the benefit to moving up quicker than waiting out the stop tho?
 
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