Recreational Helium?

[Tomeck]

I believe that trimix can be the recreationnal diving.

 

[AndyNZ]

Correct me if I am wrong, but I am under the impression that because helium is lighter than nitrogen, it on gasses and off gasses much faster. That property makes it desirable during long deco dives, but also makes it less "forgiving" than nitrogen. For example you may be able to spend more time on the bottom and less time at each stop, but that your ascent rate and stop times MUST be followed with more accuracy, otherwise your risk of dcs increases.

I would have thought the primary argument for introducing Helium in to breathing mixes would be it's reduced narcotic effect, not it's on/off gassing properties.

Shallower than 30m, I don't see a lot of point in Helium. If I had the time/money for the course and gas, I probably would use it on some of our more tricky wreck penetration dives in the 30-40m range.

These dives aren't really "recreational" dives, though.... dark, murky water and penetrating beyond the light zone.

I yet remain to be convinced of the need for Helium in breathing mixes for recreational dives in the 30-40m range. Just my opinion, mind you.

 

[Reg Braithwaite]

Correct me if I am wrong, but I am under the impression that because helium is lighter than nitrogen, it on gasses and off gasses much faster. That property makes it desirable during long deco dives, but also makes it less "forgiving" than nitrogen. For example you may be able to spend more time on the bottom and less time at each stop, but that your ascent rate and stop times MUST be followed with more accuracy, otherwise your risk of dcs increases.

There's also the whole question of He being less narcotic than N2, which is very attractive even on dives that do not involve deco, and He being lighter than N2, which makes it easier to breathe at depth. But as you say, the speed of off-gassing is a reason to think very carefully before considering something like this "recreational."

 

[Reg Braithwaite]

If I had the time/money for the course and gas, I probably would use it on some of our more tricky wreck penetration dives in the 30-40m range.

These dives aren't really "recreational" dives, though.... dark, murky water and penetrating beyond the light zone..

Maybe I should have used the phrase "no-deco." The other agencies suggest you need some experience before taking their "recreational" trimix courses. I was just wondering whether TDI had such a thing under wraps somewhere or had a strong opinion against it.

 

[seaducer]

There's also the whole question of He being less narcotic than N2, which is very attractive even on dives that do not involve deco, and He being lighter than N2, which makes it easier to breathe at depth. But as you say, the speed of off-gassing is a reason to think very carefully before considering something like this "recreational."

I've read alot of conflicting information on whether or not oxygen is as narcotic as nitrogen, so I am not sure you are really gaining much with helium. A diver who experiences less narc on helium may be feeling placebo. Or maybe not, I don't know, just throwing it out there...

 

[AndyNZ]

Maybe I should have used the phrase "no-deco." The other agencies suggest you need some experience before taking their "recreational" trimix courses. I was just wondering whether TDI had such a thing under wraps somewhere or had a strong opinion against it.

Fair enough - I've got no idea of the stance TDI have on it! I'd certainly use it for non-deco dives if the dive was "complex".

I've read alot of conflicting information on whether or not oxygen is as narcotic as nitrogen, so I am not sure you are really gaining much with helium. A diver who experiences less narc on helium may be feeling placebo. Or maybe not, I don't know, just throwing it out there...

You do actually gain quite a lot with helium. Have a look at the results of the Meyer-Overton study, which shows a number of things... Oxygen is slightly more narcotic than Nitrogen, Carbon Dioxide is about as narcotic as Nitrous Oxide (laughing gas) and Helium is significantly less narcotic than either Nitrogen or Oxygen.

 

[Reg Braithwaite]

I've read alot of conflicting information on whether or not oxygen is as narcotic as nitrogen, so I am not sure you are really gaining much with helium. A diver who experiences less narc on helium may be feeling placebo. Or maybe not, I don't know, just throwing it out there...

Well, consider a dive to 35m (115 feet) like The Tiller, which is 114' to the mud. If we plan to do the dive on 30/30 (PO2 of just under 1.4), what benefit does the He supposedly offer?

If you believe O2 is not narcotic, the Equivalent "Narcotic" Depth of the dive is 12.8m (42'). If you believe that O2 is narcotic, then the Equivalent "Narcotic" Depth is 21.5m (71').

Seems like it's still nice to have the option of reducing the narcotic effect from 114' to 71'.

How's my math? Did I get the calculations correct from my arm-char??

 

[wedivebc]

I've read alot of conflicting information on whether or not oxygen is as narcotic as nitrogen, so I am not sure you are really gaining much with helium. A diver who experiences less narc on helium may be feeling placebo. Or maybe not, I don't know, just throwing it out there...

No helium significantly reduces narcosis regardless of your position on oxygen narcosis. My feeling is helium is expensive, and getting harder to aquire both by cost and by gas suppliers recent policies. Helium is a tool that is very useful in deeper dives and aids in certain deco schedules but to just throw some HE in a tank so you can go a little deeper for a very short time seems a waste.
One agency has 2 levels of recreational trimix with a depth limitation of 160ft. It also allows minimal deco. Who are they trying to kid? It is an attempt by a tech agency to grab a few more levels of certification where if someone wanted to perform those types of profiles they should do it properly with double tanks, a high PO2 deco gas and proper preparation and training to spend more than a couple of minutes at those depths.

 

[AndyNZ]

Here's the results of Meyer-Overton study for reference.... they argued (in 1908, I think!) that the narcotic effect of a gas was proportional to the solubility of the gas. In these results, a higher number means more narcotic..

Gas Bunsen Solubility Coefficient in Olive Oil, 22Ž°C, ata-1

Helium 0.015
Hydrogen 0.042
Nitrogen 0.052
Oxygen 0.11
Argon 0.15
Krypton 0.44
Carbon Dioxide 1.34
Nitrous Oxide 1.56
Xenon 1.9

 

[seaducer]

You do actually gain quite a lot with helium. Have a look at the results of the Meyer-Overton study, which shows a number of things... Oxygen is slightly more narcotic than Nitrogen, Carbon Dioxide is about as narcotic as Nitrous Oxide (laughing gas) and Helium is significantly less narcotic than either Nitrogen or Oxygen.

I had heard helium was less narcotic, just curious about whether or not the effect is reduced, depending on how much narc comes from O2 versus N2.

Cool, thanks for the info...