Who's using 100% O2 for deco?

[MXGratefulDiver]

So, you're saying the reason to use 100% is because everyone else is . . . ?

That's actually a valid reason ... if one of your goals is to make a deco schedule that's compatible with your dive buddies ...

... Bob (Grateful Diver)

 

[MXGratefulDiver]

In many places 200 bar of 100% O2 simply is NOT possible because of lack of a booster pump. You have to decide if you want 120 bars of O2 or 200 bar of 75/80%.
Stroke!! I don't give a toss.

Places that use nitrogen separation systems ... such as PSA or membrane ... to produce O2 will not be able to produce 100% O2 ... because those systems will generally also pass argon and CO2 molecules, which will represent (at best) about 5% of what you're breathing. In many parts of the world ... where medical or aviation-grade oxygen is not available ... it's just not practical to produce O2 at levels higher than about 90%.

... Bob (Grateful Diver)

 

[Jax]

Well, that misses some of the reasons many of us standardize on particular gases. That's different than the "why O2" question.

(1) If everyone has the same deco gas(es), it means we get to deco together. Since gas switches are probably the most dangerous part of a "tech dive", I know *I* (and all those I dive with) want to be together with the team for all the decompression. If one person shows up with 80% and another with O2, we're going to be doing our switches (and deco) apart. For some of us, that's a non-starter.

(2) Picking a small set of gases let's you minimize one of the variables in decompression (i.e. gas choice). This leads to a better understanding of how you personally deal with varying deco schedules. If you use different gases all the time, you don't get to build up that inventory of constrained experience.

(3) Standardizing on gases can allow you to standardize on decompression schedules (e.g. Ratio Deco). Again, that just means minimizing deco variables (you are now holding constant the type of ascent and gases used for a particular depth/BT combination). Doing so can help you hone in faster as to what works and doesn't work deco-wise for your personal physiology.

Those are just some of the reasons many of us choose NOT to vary what deco gases we use on a whim.

As to why O2, for me it mostly comes down to: (1) no inert component, (2) fitting in with other deeper deco gas choices, (3) standardization, (4) ease of access (no blending required), and (5) a good personal history with it.

Finally someone gets around to stating the 'real' reasons 100% is so common.

While I understand "if we are all the same, we can swap the same or share in emergency", I still see that some will be thrown for a loop should something 'non-standard' happen. I also recognize that y'all plan for that.

However, as DevonDiver said, one uses what one has available. The thought of filling a 40cf only two thirds full, just to stick to the 100%, causes niggles. . . . I'd rather carry max capacity of 80% than to dive with a partial fill bottle.

Remember, though, that I occurr only a few minutes of deco time, not the bazillions of hours the rest of y'all do.

 

[Jax]

Thinking back to that "we all switch gases at the same time" . . . What is the big deal in that?

If I am coming up from depth, my buddies know and respect my PDIS stop(s). If, at my 30ft stop, I swap gas, we do the gas swap drill and no big deal. Then at the 20ft stop, they do their gas swap drill. I'm not seeing that could wrap anyone around an axle because we don't do it at the same time.

:help: Anyone? Is this a standardization comfort thing?

 

[Gilldiver]

If 100% is available, then 21-99% is available as well <100%

No, it is not.

There are still is a lot of this globe where you can get only air and100% O2 . The wreckers I go with have been using 100% boat supplied for about 25 years now. Roll a 200 of welding O2 onto the boat, put on a high flow O2 welding regulator and drop a 5/16th hose down to 20&#8217; with 2 to 4 2nd stages on 10&#8217; whips.

Nowadays, we will plan for our dives on back gas plus one deco gas that we carry. If we miss the up line to the boat and 100% O2 whips (never happened to me but it is planned for), we do a drift deco on what we carry. If we make it back to the boat and the 100%, we use it as the 2nd deco gas and get out of the water quicker.

80% is a gas you make when you only have an air compressor and O2 at delivered pressures of 2200-2400 psi as you put in 2250 psi of O2 and top with air to 3000psi. If you are making a number of bottles of 80% get 3 or 4- 300 cubic foot bottles of O2 and cascade them. Forget the BS about safety in seas, it is because you don&#8217;t have access to a booster. But if you have a large bottle of O2, either live with using a bottle of O2 filled to 2000psi and take a larger bottle (say a 60 or an 80@2000 instead of a 40@3000), just put a large 2000psi bottle on the boat and use whips, or live with using 80%. Your deco gasses are tools in your tool box. Sometimes, you need to use a different tool than the one you would like to use, but that it&#8217;s no reason not to learn how to use all of your tools.

 

[MXGratefulDiver]

Thinking back to that "we all switch gases at the same time" . . . What is the big deal in that?

If I am coming up from depth, my buddies know and respect my PDIS stop(s). If, at my 30ft stop, I swap gas, we do the gas swap drill and no big deal. Then at the 20ft stop, they do their gas swap drill. I'm not seeing that could wrap anyone around an axle because we don't do it at the same time.

:help: Anyone? Is this a standardization comfort thing?

It's more about keeping your deco schedules compatible than about comfort. When I do a deco dive with someone on a rebreather, we have to add a bit of complexity to the deco schedule, due to the fact that she's on a constant PO2, while I have to make manual switches. And that's just one variable. If you add a third team member ... or if two OC divers using different deco gases, the complexity could be multiple times what I experience with my CCR friend, depending on how many deco gasses are being used.

Planning and sticking to a deco schedule becomes much simpler if everyone uses the same gasses ... and keeping your deco schedule simple makes it more manageable ... which is a very desireable thing for both comfort and safety ...

... Bob (Grateful Diver)

 

[Jaydubya]

On my last trip one buddy had 32%, one had 78% and I had 100%. We were all decoing at different levels for different amounts of times. The gas choice was just a matter of convenience since those are the gases we had in our bottles. If we had been diving deep with multiple stages it would have had major cluster potential. There's something to be said for the team using the same gas, especially on deeper dives.

 

[Tortuga68]

No, it is not. There are still is a lot of this globe where you can get only air and 100% O2

If you have both, why can't you transfill to make a partial pressure nitrox blend somewhere in the 21-99% range? That's what I do

 

[Dive Bug Bit Me]

On my last trip one buddy had 32%, one had 78% and I had 100%. We were all decoing at different levels for different amounts of times. The gas choice was just a matter of convenience since those are the gases we had in our bottles. If we had been diving deep with multiple stages it would have had major cluster potential. There's something to be said for the team using the same gas, especially on deeper dives.

Planning is just so much simpler with all on the same gas, that way I know my buddies plan and he knows mine (particularly relevant if something goes wrong or we overstay at depth). I tend to follow what my buddies are doing in terms of gas selection. Last 5 deco dives I have used 100% (guess its my buddies favorite deco gas). Just for Irvine, the last time I dived with GUE divers (Tech 1) they insisted on deco with 50% from 70ft. That makes for a long hang in 42F water.

Surprisingly if I am given a choice I will tend towards 80% for the benefits of changing sooner and being a little more forgiving (anything that reduces risk is OK by me). Interestingly I just ran 80% and 100% on I-deco (30 /80 gradients, last stop at 20ft) for a 55 min dive to 100ft on air. 80% had the shorter run time (by one minute).

Advantage to 80% in the above scenario (in addition to the shorter run time) is that your CNS loading is only 32% compared to 51% on O2. Point is that there are some situations where 80% can give a more optimal outcome.

 

[gsk3]

The last time I dived with GUE divers (Tech 1) they insisted on deco with 50% from 70ft. That makes for a long hang in 42F water.

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