Trimix advantage for recreational diving below 130ft. Reference to literature wanted.

[walkonmars]

Hi folks,

Just wondering if you have any recent references or threads that detail advantages of using trimix for recreational diving below 130ft.
I'm not a tech-diver but only a nitrox diver and a home partial pressure blender of nitrox.
I am a small time welder and own numerous gas cylinders for work and hobbies so helium for me is readily available.
My motivations to home-blend nitrox was the convenience of not having to go to a shop 20 miles away. Driving 20 miles in traffic takes an hour each way on bad days from my home location.

I have read in some internet posts that diving with less nitrogen has no disadvantages for shallow depths. The details and quantitative examples are never posted at the location I see these claims.
One issue is the unforeseen narcosis effects. I don't recall ever being having narcosis even at wreck dives to 120ft. My worry is that I actually was "narced" because on those deep dives I have trouble recalling details I normally expect to remember. My guess is that a person gets improved situational awareness even at depths 80 and 90 feet.

I'm not asking to do tech diving without taking training. I just want to find out details of using Trimix at shallow depths (below 130 ft).
My expectation is that a person can take better speargun shots at fish, notice more lobsters and catch more details during a dive using trimix.
Can I assume if I mix a 20% to 30% helium blend with 30% O2 and use standard nitrox tables and computer algorithms I can be OK?

Thanks for your kind help.

T

 

[kwinter]

First, if you're diving "below 130 ft", that's deeper rather than more shallow. Second, every individual's threshhold for narcosis is different, and the same person may react differently from one day to the next.

All that being said, there might be some benefit of helium for some people at shallow depths if they feel they normally are narced. I really doubt you would notice any difference at all if you don't notice any narcosis at 130 feet. And no-decompression limits might be different. Helium is a funny gas. A little bit will reduce decompression time, but adding more will eventually increase it. Helium has to offgas just like nitrogen.

Bottom line is that what you propose is expensive, foolish to do without more training about the science of it, and probably totally unnecessary.
But it makes for an interesting first post.

 

[bl6394]

Hi folks,

<snip>
I'm not asking to do tech diving without taking training. I just want to find out details of using Trimix at shallow depths (below 130 ft).
My expectation is that a person can take better speargun shots at fish, notice more lobsters and catch more details during a dive using trimix.
Can I assume if I mix a 20% to 30% helium blend with 30% O2 and use standard nitrox tables and computer algorithms I can be OK?

Thanks for your kind help.

T

No - you can't assume that using standard nitrox tables and computer algorithms will be OK. Helium is a "faster" gas than nitrogen. I.e. faster to dissolve into your tissues and faster to come out. Using nitrox tables / algorithms will fail to account for the different properties of the mix.

Furthermore - you'll find diving trimix is less tolerant of poor technique. In the case of a no stop recreational dive - an excessively rapid ascent might get you bent.

I think there is a place for recreational trimix - but please consider getting appropriate training! An example of this training might be the recreational trimix class from IANTD. Recreational Trimix Diver - IANTD - World Headquarters.

Also - since you mention having access to helium - it might be that you intend to mix your own trimix. I'd strongly encourage you to consider taking a blending class prior to doing so. It will make you aware of the challenges and concerns associated with partial pressure blending: fill rates, labeling and analysis requirements, mixing calculations, hazards of high pressure O2, etc...

I believe that without additional training - you are creating considerable risk - both to yourself and others.

Regards,

Bjorn

 

[walkonmars]

Thanks for the input. Sorry, I actually meant shallower than 130ft.
In order to keep the post short, I didn't want to tell too much useless info. I can mix batches of 30% (in a 80Cu.ft. tank) for around $20, anyway.
Also, I'm probably a little more technically adept than I'm claiming now. I'm not pretending to be a technical diver (nor do I want to go to that level) but just want references to articles, threads or data to justify trimix at (<130ft) use if money is not a concern.
In regard to narcosis, I don't believe it is a physical state like an on-off switch. I'm believing it can creep up slowly on divers to varying degrees based on conditions. I probably have been in a milder state without knowing.
Giving an example from Vance Harlow's "Oxygen Hacker's Companion", an experienced wreck diver mixed up a batch of trimix for a 120ft penetration dive he had previously done over 500 times on air. The amount of additional details he noted on the trimix dive were far greater than other previous dives.
We can probably combat the major part of narcosis on nitrox, anyway. I still want information for tri-mix use if it helps the recreational diver at any level.
I understand helium has a higher diffusion constant and therefore faster diffusion rates both in and out of body tissue. Foolish to use without info, yes. So can I get some literature references? (Please don't say "take a class.")
Thanks.

 

[lowviz]

...//... I'm not pretending to be a technical diver (nor do I want to go to that level) but just want references to articles, threads or data to justify trimix ...//...

Troll.

 

[bl6394]

Thanks for the input. Sorry, I actually meant shallower than 130ft.
<snip>
We can probably combat the major part of narcosis on nitrox, anyway. I still want information for tri-mix use if it helps the recreational diver at any level.
<snip>
Thanks.

Yes - diving trimix could minimize narcosis and ease the work of breathing at recreational depths.

But - no offense - but you have a fundamental lack of information about trimix and the effects of these gasses on your body. Since both Nitrogen and oxygen are both considered narcotic - enriched air (nitrox) does not combat any part of nitrogen narcosis.

I own the Oxy Hacker's companion - and I believe it's possible if you were to carefully read and understand the book - you may be able to partial pressure blend Helium and Oxygen without an oxygen fire. You may approximate something like a 30/30 mix.

However, I'm not convinced that you understand the effects that a higher PPO2 will have on your body (oxygen toxicity) or that you know how to calculate the MOD of the gas you just blended. I'm not sure you know what different grades of helium are available and what grades should be used for breathing gases. I'm not sure you are aware of the thermal properties of this mix - and what will happen if you use it to fill your drysuit in colder water. I'm not sure you will properly mark or analyze your gas - so that you know what you are diving - and you are sure no one else breathes this mix by mistake. This line of uncertainty goes on and on...

I can't refer you to a reference (article, book, literature) - because learning to dive trimix is not generally a DIY proposition. Obviously - years earlier - divers did learn how to dive trimix without classes... And some of these divers made costly mistakes.

I would encourage you to think very carefully before you embarked on a self taught trimix diving experiment.

Bjorn

 

[walkonmars]

Thanks Bjorn.
OK, OK, you got me.
From the PADI EAN Diving Manual, "...theoretically, oxygen has about the same narcotic potential as nitrogen. Further, studies have found little difference between the narcotic effects of nitrogen and oxygen."
So I assumed incorrectly that the enriched air reduces your potential for narcosis.
My motivation is knowing that something is not right on deeper dives (shallow for a tech). Perhaps not during but after the dive. I have had only a handful of dives beyond 110 ft and all of them are blurry memories in spite of dive buddies and instructors and my own limited memory that I was "normal". Normal in the sense that I was checking gauges, tracking buddies, reacting correctly and being aware of surroundings.
If there was a way to lessen the narcosis effect, it would be nice to recall more details during dives or remain more alert even at the shallow depths of 80-100 feet. Lacking details on a deep dive is like seeing a movie after 4 beers. (Can you even recall the plot to the movie?)
Where I am, the local islands can get to the 70-100+ range after jumping off the boat. We are advised to not go deep but the less traveled places have better game and less "trampled" environs. If a person can gain a small, conscious advantage, they should at least ask to see how obtainable it can be. I believe more most accidents are diver error rather than equipment.
(Also, I'm not going for any tech cert any time soon because my girlfriend just got certified a month ago. We just want to dive recreational and if I dove without her, my next tank would be laced with CO at 50%, "murder-mix 50".)
Thanks for your cautions and useful info.

 

[DevonDiver]

If you have a problem with narcosis below a given depth, then you have two options; (1) stay shallower and (2) use a normoxic trimix blend. There are suitable courses available for recreational trimix (normoxic).

You simply retain the depth you are narcosis-free at, as your Equivalent Narcotic Depth and blend accordingly.

Equivalent narcotic depth - Wikipedia, the free encyclopedia

Technical Diving: Equivalent Narcotic Depth Notes

The narcosis of trimix and the calculation of END

Lloyd Borrett - Interests - Scuba Diving - Equivalent Narcotic Depth (END) Calculator

As others have mentioned, helium isn't a forgiving gas. It'll bend you much quicker if your foundational skills are flawed - because it doesn't tolerate fast ascents. Get properly trained, because you could easily hurt yourself otherwise. Trimix isn't nitrox...

 

[Agility]

the intro to understanding trimix is in Mark Powell's Deco for Divers: Decompression Theory and Physiology: Mark Powell: 9781905492077: Amazon.com: Books but that only gives a rough outline of the problems.

 

[TSandM]

I'm not sure what information you are asking for.

I am one of a group that does not dive below 100 feet without helium. I use 25/25 for dives in the 100 to 130 range. I am way more clearheaded that way, and don't have the feeling of impending doom that often hits me around 100 feet on Nitrox, in our dark waters.

Helium's effect on decompression is controversial. Some schools believe that, because it is a fast diffusing gas, you need longer decompressions with it. Others believe that, because it is so poorly soluble, using the same schedules as Nitrox may even be more conservative than you need to be. I think everyone agrees that helium will come out of solution into bubbles easily if ascents are not controlled, so it is a unforgiving gas if you can't slow your ascent in the shallows.

I don't know of any "literature" on the use of helium in deeper recreational depths. I just know a lot of people who do it.