Rec Trimix

[JeffG]

awesome a pissing match..
i saw this comming....
just remember dont pee INTO the wind

LOL

 

[Kevrumbo]

I just got done having a very interesting and productive discussion by PM with another SBer on another subject. My point there was that, to develop a really valid algorithm for dealing with a given situation, you need DATA -- you really need to know what the most likely failures would be in order to know where to start diagnosing and treating them. The data aren't there.

And that's true for so much of this. The data just aren't there. Too much of what we discuss is purely anecdotal.

I had a bad narcosis experience at 100 feet in poor viz and low light. It has left me reluctant to return to those depths under those conditions. But are the conditions really relevant? Or is it simply that those conditions create the challenges that make the narcosis-related reduced function more obvious, sooner? I heard a story from my GUE instructor about a narcosis event at 100 feet (on air) where he was completely unaware of the fact that his inability to complete a task was related to narcosis, until he ascended and was then able to complete the task. This was a diver with many, many times my experience and training, and narcosis got to him.

The diver who says you can learn to deal with it makes me suspicious. I deal with a lot of people in the ER who think they can drive when they're intoxicated, until some combination of events proves that they can't, either.

If a rec triox class properly trains people in the buoyancy, team skills, problem solving AND gas management skills to dive the 80 to 130 range using helium, is there anything wrong with it? Before I make routine trips to those depths in our waters, I would want something to breathe that didn't have the effects I experienced before. If I can't afford the gas, I won't do the dives . . . I'll just stay shallower, where I can think. Other people may make different decisions, and it's up to them. I personally think GUE has a good point, but again that's based on anecdotal experience.

Empirical Long Term Studies are still on going with the US Navy, with regard to the RGBM "Bubble Model" (at least that what Weinke likes to tout for his proprietary algorithm). NAUI has a set of Recreational and Technical Tables utilizing this model and I've been using an on-the-fly derivation of it for Triox Dives in the 80-110' depths, the so called "Tech-reational" Range. http://www.rgbmdiving.com/site/rgbmhis.htm
I'm confident that this model will be soon be scientifically validated. . .

 

[gcbryan]

I just got done having a very interesting and productive discussion by PM with another SBer on another subject. My point there was that, to develop a really valid algorithm for dealing with a given situation, you need DATA -- you really need to know what the most likely failures would be in order to know where to start diagnosing and treating them. The data aren't there.

And that's true for so much of this. The data just aren't there. Too much of what we discuss is purely anecdotal.

I had a bad narcosis experience at 100 feet in poor viz and low light. It has left me reluctant to return to those depths under those conditions. But are the conditions really relevant? Or is it simply that those conditions create the challenges that make the narcosis-related reduced function more obvious, sooner? I heard a story from my GUE instructor about a narcosis event at 100 feet (on air) where he was completely unaware of the fact that his inability to complete a task was related to narcosis, until he ascended and was then able to complete the task. This was a diver with many, many times my experience and training, and narcosis got to him.

The diver who says you can learn to deal with it makes me suspicious. I deal with a lot of people in the ER who think they can drive when they're intoxicated, until some combination of events proves that they can't, either.

If a rec triox class properly trains people in the buoyancy, team skills, problem solving AND gas management skills to dive the 80 to 130 range using helium, is there anything wrong with it? Before I make routine trips to those depths in our waters, I would want something to breathe that didn't have the effects I experienced before. If I can't afford the gas, I won't do the dives . . . I'll just stay shallower, where I can think. Other people may make different decisions, and it's up to them. I personally think GUE has a good point, but again that's based on anecdotal experience.

I agree there is no data and that the evidence is anecdotal, including my observations. My take on narcosis is this...everyone is affected by the narcotic effect of nitrogen and that is determined by depth (partial pressure of nitrogen). To me this effect should more or less remain constant from dive to dive at the same partial pressure. The difference from dive to dive is an added component let's call it anxiety. When the two mix this is really what people are talking about when they refer to being "narced" one day and not another.

You can't learn to manage the narcotic effect of nitrogen, it is what it is. Experience usually reduces the anxiety component but on a bad day (not enough sleep, stress, etc.) that component can elevate even for an experienced deeper diver.

People who drink shouldn't be driving and divers probably shouldn't do deep wreck penetrations on air. I assume you can have a glass of wine with dinner and still safely go on a walk after dinner and within reason I believe a diver can go somewhat deep on air and be able to deal with most problems in an OW environment.

In your situation it was the poor viz and low light that created some anxiety which mixed with the constant level of narcosis present at 100 fsw. Poor viz and low light didn't increase the narcotic effect of nitrogen. It only increased your anxiety. I guarantee that if you do 10 dives in a row to 100 fsw under similar conditions that will remove the anxiety component. You may then find that an objectionable level of narcosis for you isn't found until let's say 140 fsw assuming you do 10 more dives at 110,120,130 fsw.

I know your instructor is an excellent diver but when an instructor represents an agency where air/nitrox is poison below 100 fsw then their experiences tend to fall in with their belief systems in my opinion.

With all due respect I have always found it hard to believe that anyone was significantly "narced" at 100 fsw if they were in conditions where they had a bit of prior experience. Experience reduces the unpleasant effect and exercise increases the effect so with experience and without going deep where there is current for one to struggle against I believe it's reasonable to go significantly below 100 fsw in an open water environment.

This is just my take on it though.

 

[grazie42]

I´m not even sure what the question is anymore...
Is the question at what END, people become narced?
When some He is reasonable to add to your mix based on some reasonable level of risk?
Or when we, as individuals feel He should be added and how much?

The level of impairment due to narcosis is individual and varies from dive to dive. I guess that´s what gcbryan calls the "anxiety effect". It´s up to every diver to find the "point" where the costs and hassle of adding He is offset by the reduction of impairment. There seems little point in calling people names because their "point" is at xft rather than yft...

I will dive air to ~130ft on wrecks in cold, dark waters but I´ll only do progressive penetration and if I go "far" into a wreck I´ll add He. For OW in those conditions I wont go further than 150ft...

The above are only "rules of thumb" and I will dive whatever mix I deem prudent for whatever dive I choose to do. For me, the mix I´ll end up taking on a dive, is the least narcotic mix of those suggested by everyone on the dive...

 

[Marlinspike]

My point was that it is safer to stick to what works for you rather than dive a profile just because "those guys on the internet" are doing it.

I would rather have an overconservative profile than an untested one. Mixed gas diving is a do-it-yourself lab experiment. You get the c-card, you get some gas, and you go dive. If you get bent or feel tingly, add more deco the next time.

Ahh...much more clear. I agree with your first two sentences. The second two are still dribble though. Mixed gas diving has a good safety record UNLESS you start pushing the envelope and not following well accepted and tested models.

~Marlinspike

 

[do it easy]

Ahh...much more clear. I agree with your first two sentences. The second two are still dribble though. Mixed gas diving has a good safety record UNLESS you start pushing the envelope and not following well accepted and tested models.

~Marlinspike

That dribble is just an obscure way to say that one MIGHT come to a point in their diving career where spending 2 hours on deco is too risky for the dive. That's the point they might start shaving time and pushing the gradients, or maybe just do a shorter, shallower, safer dive. The risk/reward balance is different for everyone, whether it's 35 END or 350 FFW.

 

[Marlinspike]

That dribble is just an obscure way to say that one MIGHT come to a point in their diving career where spending 2 hours on deco is too risky for the dive. That's the point they might start shaving time and pushing the gradients, or maybe just do a shorter, shallower, safer dive. The risk/reward balance is different for everyone, whether it's 35 END or 350 FFW.

There is a HUGE difference between cutting deco time with potentially much higher risk, and the opposite end of the descision continuum, a shorter shallower dive. I think I see what you are attempting to say, but the message is being lost in the lines you are trying to draw between short shallow dives and blowing off deco time, risking a big hit.

~Marlinspike

 

[do it easy]

I don't think that the difference is that huge- if a diver isn't willing to shave time off and experiment, then they will have to do stick to the dives they know are safe-shorter, shallower dives.

If they are planning on experimenting, hopefully they don't just go from 100' to 450' in one dive. I would hope that they would get the proper training and then gradually test the waters.

 

[TheRedHead]

HERE'S some more interesting data on this subject - because the answer is all about the different compartments, for example, this sentance from the text:

"In lipid tissue, the outward flux of nitrogen from bubbles exceeds the inward flux of helium, whether the exchange of gases in the tissue is limited by perfusion or diffusion."

Yes, but Floater's premise is the inward flux of helium being the same as the inward flux of nitrogen.

 

[TheRedHead]

If a rec triox class properly trains people in the buoyancy, team skills, problem solving AND gas management skills to dive the 80 to 130 range using helium, is there anything wrong with it?

Not if that's what you want to do. My instructor made the argument that you incur a deco obligation faster on He so why use it when you can do dives in the 80-100 ft range safely on Nitrox? Nitrox is cheaper too. The average recreational diver does not have the skills to dive Trimix and the name rec trimix is a misnomer.