Triox for the masses

[Brian Gilpin]

helium ongasses (and offgasses) from tissues faster. a "recreational trimix" dive within the "NDLs" runs a higher risk of DCS if someone tried a CESA. it requires mandatory safety stops (deco stops) and slow ascent rates. training and equipment needs to take into account the fact that a direct ascent to the surface is less acceptable than in normal recreational diving.

Not having taken the class I dont understand the basic physics but I do understand what you are saying. I thought He would reduce risk of DCS and narcosis. Apparently this is not true as regards DCS then? How much extra risk is there within normal GUE ascent rates? How about in case of a more rapid ascent. Are we talking about a minor additional risk or a significant one?

 

[mer]

Pros of He:
- Decreased density = decrease work of breathing (regs breath easier) = less CO2 buildup
- Decreased CO2 buildup = less CO2 narcosis (CO2 is VERY narcotic) or chance of CO2 induced confusion/fatigue/unconsciousness
- Decreased nitrogen narcosis (nitrox is arguably as narcotic as air)
- More efficient decompression (less risk of DCS theoretically) due to faster in and faster out IF MINIMUM DECO DONE
- Roughly same advantage of bottom time OR increase saftey factor as 32% EAN
- Smaller buoyancy swing of tanks during dive
- Reduced red blood rigidity (maybe)
- Amuzing donald duck voice

Cons of He:
- Cost
- Not widely available (yet )
- Expensive He analyzers, or relying on math
- Cannot inflate suit with it (thermal conductivity), must add additional suit inflation system

Skill concerns:
- Planning of dive is not all that much different than a nitrox dive
- Buoyancy must be controlled, especially during ascent (due to absorption/offgasing occuring quickly) -- practically eliminates the CESA, minimum deco is important
- Since CESA is eliminated, must have the skills to handle problems on the bottom

My guess is that it is cost, and desire to get sufficient buoyancy and problem management skills that will keep it from being as popular nitrox.

FYI - GUE ascent rates are 30fpm deep, and 10fpm (or less) from first deep stop, last 10 feet verrrry slow. For specifics, that's what fundamentals and the rec triox class are for.

 

[detroit diver]

Call me a cynic...I think that is the last of their concerns.

Okay, you're a cynic!

Seriously, I think this is one area where they might have to play it safe. Nitrox can't do any more potential harm than air (using the same profiles), but helium has the potential to bend the "average" diver. If I were advising an agency that doesn't train for buoyancy control, I'd tell them to stay as far away from helium as they could.

 

[lamont]

Not having taken the class I dont understand the basic physics but I do understand what you are saying. I thought He would reduce risk of DCS and narcosis. Apparently this is not true as regards DCS then? How much extra risk is there within normal GUE ascent rates? How about in case of a more rapid ascent. Are we talking about a minor additional risk or a significant one?

I think that's probably all debatable.

I'll throw in my $0.02 and then grab some popcorn...

To first order, He and N2 are the same as far as DCS goes. V-planner tends to extend deco stops when you substitute N2 with He which suggests its model thinks that He is "worse" for deco. A lot of people have had success with substituting 50/50 for EAN50 as the 70 fsw gas though without modifying their profiles and 'feel better' when they get out suggesting that He is "better". There's some evidence that subclinical DCS and post-dive fatigue may be due to N2's effect on red blood cells and that He has less of an effect, suggesting that He is "better". And since He has faster halftimes and saturates faster it tends to be "worse" on shorter dives and "better" on longer dives.

 

[JeffG]

My guess is that it is cost, and desire to get sufficient buoyancy and problem management skills that will keep it from being as popular nitrox.

It (Helium) needs to solve a problem before it is widely accepted. The majority of divers are WWW (warm water wimps) and do nice colorful reef dives. Helium really doesn't solve any problems for them.

For the rest of the recreational divers (>100ft-120ft...cold water..etc etc) , it would be hard to quantify and because of that I think it would be a hard sell. So taken as a whole, Helium for recreational depths will always be a niche market. IMO

 

[JeffG]

If I were advising an agency that doesn't train for buoyancy control, I'd tell them to stay as far away from helium as they could.

Thats exactly what they will do. Helium will be the next "voodoo" gas.

 

[detroit diver]

Not having taken the class I dont understand the basic physics but I do understand what you are saying. I thought He would reduce risk of DCS and narcosis. Apparently this is not true as regards DCS then? How much extra risk is there within normal GUE ascent rates? How about in case of a more rapid ascent. Are we talking about a minor additional risk or a significant one?

Brian,

Using proper ascent rates, He will certainly reduce narcosis (because it displaces nitrogen), and will not cause higher rates of DCS. GUE teaches these proper rates of ascent and hammers on buoyancy control.

On the other hand, rapid ascents are not feasible with He because the tissues need time to purge themselves of the higher amount of HE that they have taken up (remember, He is taken up into the tissues at a much faster rate than N). While everyone is different, my guess is that your additional risk would depend on where your rapid ascent started from, and how fast you were rising. (Not unlike nitrogen, just more of it in your system to possibly cause a problem.)

 

[mer]

It (Helium) needs to solve a problem before it is widely accepted. The majority of divers are WWW (warm water wimps) and do nice colorful reef dives. Helium really doesn't solve any problems for them.

Narcosis, effects of CO2, and decompression efficiency are not problems for them?

 

[JeffG]

Narcosis, effects of CO2, and decompression efficiency are not problems for them?

I doubt it. They probably have bigger issues to worry about, such as running out of gas and doing an air share with the DM.

 

[mer]

I doubt it. They probably have bigger issues to worry about, such as running out of gas and doing an air share with the DM.

Most of the *regular* warm water divers I've seen (ie Bonaire) seem pretty good at not running out of gas, (although they don't tyically carry the reserves that I would nor hold smooth shallower stops.)

I would say that most of them have enough dive basics down for the narcosis, CO2 build up and decompression implications to be bigger factors.

To play devil's advocate:
Does narcosis or CO2 build up help the problem of them not checking their SPG frequently enough, or being clear headed enough to navigate back to the ascent line? In a current?