why helium?

[wedivebc]

I just read those posts. Can someone explain the difference to me between ongassing and solubility? I thought ongassing involved diffussion/solubility of the biomass. Just trying to learn something here!

Yes ongassing is the dissolution of gasses in tissue and is therefore affected by the solubility of the gas. My understanding is the transport of gasses is by both perfusion (tranport directly from arterial blood supply) and diffusion (gas transported by contact with adjacent tissue with a higher gradient). I think most dissolved tissue (single phase) models are known as parallel model and consider perfusion as the transport medium. I am sure there are others but I know DCIEM tables consider both perfusion (blood into tissue) and diffusion (tissue into tissue).
Accoring to the chart here Henry's law - Wikipedia, the free encyclopedia He is only slightly less soluble than N2 in water but we also know it is much less soluble in other tissues such as lipids. How this effects the human body I am still unsure but this oversimplification

b. Yes it goes in and out faster but it is also less soluble. Imagine a glass of warm water. Dump sugar into it and the sugar dissolves. Dump sand into it and the sand doesn't dissolve. N2 = sugar. He = sand.

is not an accurate analogy. In fact I am really bothered by the drones who chant "heluim can't hurt you, helium is your friend". I can assure you helium coming out of solution and forming bubbles can do as much if not more harm than N2 especially in recreational profiles where shorter time at depth means faster tissue is more likely involved.
The current trend is to teach new divers that in the event of an OOA emergency the surface is a viable option. Although when diving air we can often get away with this but with the faster nature of helium I am concerned the cavilier attitude toward helium is going to land someone in a wheelchair or worse.

 

[TSandM]

The current trend is to teach new divers that in the event of an OOA emergency the surface is a viable option. Although when diving air we can often get away with this but with the faster nature of helium I am concerned the cavilier attitude toward helium is going to land someone in a wheelchair or worse.

I am not aware of any class which certifies you to dive helium that doesn't spend significant time teaching problem solving underwater. I've taken two recreational helium classes, and I will say that BOTH of them spent 99% of their time like a tech class, handling failures and maintaining our equilibrium (literally and figuratively) under stress in midwater. So I don't think the teaching that new divers get is really pertinent to how people are going to behave or the skills they are going to have while diving helium.

 

[wedivebc]

I am not aware of any class which certifies you to dive helium that doesn't spend significant time teaching problem solving underwater. I've taken two recreational helium classes, and I will say that BOTH of them spent 99% of their time like a tech class, handling failures and maintaining our equilibrium (literally and figuratively) under stress in midwater. So I don't think the teaching that new divers get is really pertinent to how people are going to behave or the skills they are going to have while diving helium.

That may be. Why do we call it recreational trimix and some agencies also have advanced recreational trimix?
I think if we aren't diving completely redundant systems which allow problem solving independant of a either a buddy or the surface we have no business diving trimix. Am I correct that your rec trimix training standards allow single tank with no redundant gas other than a buddy?
I for one think this is irresponsible and is minimizing the dangers involved with a gas that is still not as well understood as nitrogen. I feel trimix diving and its inherent dangers is a whole order of magnitude more complex than diving air or nitrox and should not be treated casually. I realize you had very intensive training but as long as you are diving with a single tank you are trusting your life to a buddy who may or may not be there when you need them.

 

[TSandM]

I believe GUE's standards still permit taking Rec Triox in a single tank, but none of us did, nor do I intend to do any dives where I would use helium on a single tank. And GUE's Rec Triox standards presuppose you have passed Fundies, which implies a certain degree of stability in the water, tolerance for task loading, and dependable team skills.

 

[Bismark]

That may be. Why do we call it recreational trimix and some agencies also have advanced recreational trimix?
I think if we aren't diving completely redundant systems which allow problem solving independant of a either a buddy or the surface we have no business diving trimix. Am I correct that your rec trimix training standards allow single tank with no redundant gas other than a buddy?
I for one think this is irresponsible and is minimizing the dangers involved with a gas that is still not as well understood as nitrogen. I feel trimix diving and its inherent dangers is a whole order of magnitude more complex than diving air or nitrox and should not be treated casually. I realize you had very intensive training but as long as you are diving with a single tank you are trusting your life to a buddy who may or may not be there when you need them.

Wow, a lot of assumptions in this one paragraph.

First, I believe they refer to it as recreational trimix because depth limits for the class are the same as recreational diving limits (or less) meaning, 130'.

Second, I am guessing that your reference to "completely redundant systems" that you are referring to independent doubles. I can see this is going to be another argument but I am not sure how independent doubles or doubles with an isolation manifold make any difference in using trimix. Looks like we have another point of contention here.

While I am definitely not dismissing the fact that trimix diving can be more complicated than air or nitrox diving, it doesn't need to be. Absolutely the diver requires more education and definitely the diver requires more skill (particularly with ascent rates and deep stops) but at that point one can make the comparison between diving trimix today and diving nitrox 10-15 years ago. There are clearly other factors to consider when diving nitrox than diving air but divers as a community seem to have been able to incorporate them into training and education and the "devil gas" of 15 years ago is now looked upon quite differently. And in my opinion, this is also what should happen with Helium, albeit with tigher educational and training and skill standards.

Finally, I have to take issue with your last comment about diving with a single tank and trusting your life to your buddy. Yowza, I don't know where to start with that one. I think you can probably guess my leanings in this so that entire point is a non event. I don't dive with buddies I don't trust and I don't dive with people with anything other than the same gas in their tanks (singles or doubles) as me. Yes I do trust my life to my buddies and they trust me with theirs. Problem solved.

 

[limeyx]

Nick, read these excerpts from Bruce Wienke:


Nick, the article above may help you understand where the NAUI Tech divers are coming from (especially in that current TDS thread:11. . .

Thanks for the links Kevin. I honestly have no idea where most NAUI divers are coming from since their story seems to be

"Oh, we use 100% O2 instead of 50% to avoid ICD" then I say
"Oh, so you guys dont promote using 50% first then adding 100%"
and they reply "Oh no, we can definitely use 50% as long as we talk with our instrucor and 'understand the risks' " whatever that is supposed to mean. Too much complexity for me.

My comments in quotes on He, are what "some" people believe, and NAUI does seem to think less He is better for the short bottom times.

My view is different. I will use He whenever I can, and dive it with no penalty compared to air (except using deep stops) and I actually think He is easier to offgass than air mixes (or lower He mixes) and I'm far less worried about it than air.

I have no issue doing a 45 min dive at approx 80-90 feet average on 18/45 for instance, and having no ill effects. Obviously 1 data point does not make a trend, but ...

 

[limeyx]

Wow, a lot of assumptions in this one paragraph.

.......

Finally, I have to take issue with your last comment about diving with a single tank and trusting your life to your buddy. Yowza, I don't know where to start with that one. I think you can probably guess my leanings in this so that entire point is a non event. I don't dive with buddies I don't trust and I don't dive with people with anything other than the same gas in their tanks (singles or doubles) as me. Yes I do trust my life to my buddies and they trust me with theirs. Problem solved.

it's just a different way of thinking that comes out of the way things used to be, and the way they sadly probably still are in a lot of areas.

Yes, N2 may be "well understood" -- it's understood (by a lot of people) that it's not very good for you at high pressures when diving, and Helium has a lot of properties that make it much better as long as you have reasonable skills and treat it right.

I have no problem diving 30/30 or 25/25 the same way I'd dive nitrox honestly.

 

[Bismark]

Okay, so now I am replying to my own post.......... I thought I better expand a bit on the buddy thing Dave.

It appears to me that your presupposition (is that a word actually?) is that when you said "diving with a single tank you are trusting your life to a buddy who may or may not be there when you need them" is that problems that may be encountered underwater can be solved with a redundant gas supply. I would posit that while an OOG incident is indeed an emergency, it is far from the only thing that can go wrong. I think what most people are missing with the whole "super buddy" approach that certain approaches to diving ;-) advocate is that the extra brain power in solving problems present when you have one or even better two buddies with the same training and skill level helps solve any problem you may encounter that much more easily. This does include OOG obviously, but it is not limited to that. I know in my business world how valuable having someone of comparable background is to solving problems and it is no different underwater. One might argue "what if" and create any sort of scenario where you "lose" your buddy, but most of those scenarios are predicated on accepting certain conditions that I would not. In fact, it might be a useful exercise for anyone to come up with a situation (other than a true lightning strike) where this is not the case?? Finally, like I mentioned in my post above, diving HE, whether for any type of diving requires a higher standard of skills. As far as I know, these skills are prerequisites of the GUE rec triox course and for good reason. With the proper skill and knowlege base, diving trimix recreationally becomes a viable and practical alternative to air and nitrox. (please let's discount the economic factors to save us some more posts back and forth)

 

[wedivebc]

Wow, a lot of assumptions in this one paragraph.

First, I believe they refer to it as recreational trimix because depth limits for the class are the same as recreational diving limits (or less) meaning, 130'.

Second, I am guessing that your reference to "completely redundant systems" that you are referring to independent doubles. I can see this is going to be another argument but I am not sure how independent doubles or doubles with an isolation manifold make any difference in using trimix. Looks like we have another point of contention here.

.

Now who's assumptin'. I never said anything about independants.

 

[limeyx]

Now who's assumptin'. I never said anything about independants.

Well, manifolded doubles dont fit the criteria. I dont know enough about rebreathers but since those divers have to carry bailout gas, I am guessing they aren't "fully redundant" surface-supplied -- someone still has to change the T-bottle.

Maybe you could let us know what you were meaning ?