why helium?

[wedivebc]

Okay, so for a 20-30 minute dive to 200' where you have oodles of gas in OC, particularly if you carry a stage (which sounds like you are doing essentially) what is the advantage of a RB? Sounds like you are carrying the same amount of bailout gas as I would.

For a 20-30 minute dive yes I am probably carrying the same bailout gas as you. For deeper dives probably less (if team bailout used)
I am also using about 3-4 cuft of helium and I am also gradually replacing trimix with oxygen as I ascend so I only have to worry about ICD issues with regard to my bailout where I might push it a little more than I would normally.
I am breathing warm moist gas that my body does not have to reheat on every breath and I am carrying less weight on my back when I am out of the water. Should I decide to alter my dive plan I still have the optimal mix for the revised plan (within bailout parameters) and I never have some DIRF wannabe come up and tell me how I should be confiured:mooner: unlike when I dove independant doubles and had some obviously DIR kid come up and tell me I was going to die. I was too interested in getting in the water to try to educate him but diving RB means never having to explain yourself.
For square profiles the deco advantage of CCR is minimal in fact sometimes a well thought out deco plan can benefit from OC deco but in most of the diving I do, shore, cave, multilevel the fixed setpoint will provide lots of deco benefits.

 

[wedivebc]

...double post

 

[bletso]

Okay, so now I have another question: I don't dive a CCR so please help me with this one. What do RB divers do for bailout gas for a dive to say, 200' with, say a deco of 35 minutes? Do you actually carry enough bailout gas for the ascent and the deco (different bail out gases?) assuming the **** hits the fan at the last minute of the dive?

Yes, most of us do. The real big advantage of the rebreather vis-a-vis longer deep dives is I can carry my whole weekend's worth of gas on my back. The deco stages are plumbed in as off board deco gas/es. The stages serve to purge the system with the deco mix and that is all, just a few breaths per dive.

If something goes awry at the end of the last dive, I can go OC and complete my deco obligations. Rebreathers are beautiful!!!!! It also cuts down on the cost of gas necessary to do the dives.

I dive trimix on most dives over 30 MFW. A 40 cf trimix will last me a couple of weekends easily.
Dale

 

[Kevrumbo]

. . .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 ...

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

<snip>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.

Dave and Nick, I would agree while adding one subtle caveat due to an incident I had a few years ago using 30/30 Triox on repetitive NDL dives on backgas only, using Ratio/Minimum Deco Rules: at the end of three dives of max depths 100'/30m, 60'/18/ and 40'/12m, with 90 to 120min SIT, I developed a case of the chokes. Obviously there was an overloading of my lungs as a bubble filter due to what I believe now was excess residual helium. Dives were nominal multi-level progressions, with no ascent spikes or bouncing buoyancy problems that I can recall. . .

Long story short --I now always take an AL40 of Oxygen on Triox Repetitive Dives, and breath it at the safety stop on the next-to-last or last dive of the day (haven't had any similar post-dive dyspnea/shortness-of-breath symptoms since). . .

 

[bletso]

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.

Absolutely correct!! NO ONE should be diving helium with the surface option mentality. Whenever I dive helium, I always tote the O2. It is just part of my kit.

It (helium based diving) requires a much more knowledgeable, and disciplined personality. i.e. Cave and or technical

Dale

 

[DiveBandit]

Call me old school, but when I learned to dive in the 80's, diving to a P02 of 2.0 was not uncommon, and I know more than a few divers who dove hotter P02's than that. It was lowered to 1.4 over the years because they found it to be a safer overall P02 for the masses. I'm all for safety, so I'm not against using 1.4. However, I think this whole argument over deep air is a little inaccurate. To say that deep air diving in certain situations isn't a good idea would be accurate. To say it's simply a bad idea period is simply wrong. I dive 220' in a low flow cave on air often. There isn't anything crazy about it. I'm not sure I'd dive that deep on air if I was in open ocean with current, but in a low flow cave it works fine for me. I carry stage bottles for back-ups and I deco on 100% and I've never been bent, and I've never oxtox'd. Same goes for the 3 divers that dive that deep with me. Yes, I agree it's not for everyone, but when I hear these arguments that anything deeper than 130' on air is stupid, or unsmart, or crazy, Etc. It simply isn't 100% correct. I think you simply need to progressively dive to whatever depth you feel comfortable with. For me, I believe that my "oxtox on air" line in the sand probably sits somewhere below 230', but I personally don't feel comfortable going any deeper than 220' and thats just me. I'm certainly not trying to make a blanket statement that everybody can dive to 220', but I am saying that a blanket statement that anything past 130' on air is crazy is simply not accurate.

That said, I would add that at some point I would like to get trimix certified simply because where I want to dive and what I want to see are at depths that require a mix that has less than 21%. I also want to try heliox and normoxic first - not because I'm made of money, but so I can learn about diving helium and experience it. There's nothing wrong with that is there.

Ok, My fire suit is on - Flame away if you must.

EDIT: in case the question comes up. 220' is a turning point. We only spend a minute or two at most at that depth.

 

[Mike Edmonston]

EDIT: in case the question comes up. 220' is a turning point. We only spend a minute or two at most at that depth.

The kaliedoscope of colors must be amazing at that depth, you could always bring some "Iron Butterfly" on an MP3 player to get the full effect...

 

[Meng_Tze]

WOW that is 7.7 ata. Which is a PO2 of 1.61 and PN2 of 6. Not flaming , but that is a lot. Kudos if you can handle that. I know I can't.

 

[Bismark]

Call me old school, but when I learned to dive in the 80's, diving to a P02 of 2.0 was not uncommon, and I know more than a few divers who dove hotter P02's than that. It was lowered to 1.4 over the years because they found it to be a safer overall P02 for the masses. I'm all for safety, so I'm not against using 1.4. However, I think this whole argument over deep air is a little inaccurate. To say that deep air diving in certain situations isn't a good idea would be accurate. To say it's simply a bad idea period is simply wrong. I dive 220' in a low flow cave on air often. There isn't anything crazy about it. I'm not sure I'd dive that deep on air if I was in open ocean with current, but in a low flow cave it works fine for me. I carry stage bottles for back-ups and I deco on 100% and I've never been bent, and I've never oxtox'd. Same goes for the 3 divers that dive that deep with me. Yes, I agree it's not for everyone, but when I hear these arguments that anything deeper than 130' on air is stupid, or unsmart, or crazy, Etc. It simply isn't 100% correct. I think you simply need to progressively dive to whatever depth you feel comfortable with. For me, I believe that my "oxtox on air" line in the sand probably sits somewhere below 230', but I personally don't feel comfortable going any deeper than 220' and thats just me. I'm certainly not trying to make a blanket statement that everybody can dive to 220', but I am saying that a blanket statement that anything past 130' on air is crazy is simply not accurate.

That said, I would add that at some point I would like to get trimix certified simply because where I want to dive and what I want to see are at depths that require a mix that has less than 21%. I also want to try heliox and normoxic first - not because I'm made of money, but so I can learn about diving helium and experience it. There's nothing wrong with that is there.

Ok, My fire suit is on - Flame away if you must.

EDIT: in case the question comes up. 220' is a turning point. We only spend a minute or two at most at that depth.

For the sake of clarification, please answer for me the following questions:

1) At what point do you believe narcosis begins to affect your ability to make timely and correct decisions?
2)Do you think your ability to react to an emergency is impaired with narcosis or not?
3)How do you reconcile the accepted science regarding narcosis with your decisions?

I am truly interested in your rationale here. Of course your decisions are your own and I don't intend to change your mind because it is not my right to do so. However, I am trying to understand the mindset of those who share the same opinion you do
regarding this. Personally I believe your approach is no different from that made by my rugby buddies who feel "good enough to drive" after several (many several) drinks. How do you personally reconcile that comparison with what you chose to do.

Again, interested in your point of view. Not a flame. We can agree to disagree.

 

[limeyx]

Dave and Nick, I would agree while adding one subtle caveat due to an incident I had a few years ago using 30/30 Triox on repetitive NDL dives on backgas only, using Ratio/Minimum Deco Rules: at the end of three dives of max depths 100'/30m, 60'/18/ and 40'/12m, with 90 to 120min SIT, I developed a case of the chokes. Obviously there was an overloading of my lungs as a bubble filter due to what I believe now was excess residual helium. Dives were nominal multi-level progressions, with no ascent spikes or bouncing buoyancy problems that I can recall. . .

Long story short --I now always take an AL40 of Oxygen on Triox Repetitive Dives, and breath it at the safety stop on the next-to-last or last dive of the day (haven't had any similar post-dive dyspnea/shortness-of-breath symptoms since). . .

Interesting, definitely something to consider. I have not had that experience but I dont do a huge amount of helium no or min deco diving, just usually last dive of the day if we have some gas left, or first dive of the day if it's going to be a bit deeper than the others.

Do you have the profiles handy ?