Deco Gasses

[Hetland]

I'm looking to take advanced nitrox/deco procedures soon, and am slowly building up my gear collection so that I can take the classes with the least amount of borrowed/rented gear as possible. In the long run I'm looking to do wreck penetration, and longer dives at depth, so I'll likely take cavern (for the overhead) first, then wreck or maybe even cave if I get snake-bit.

I'll also save some typing on everyone's end and state that I am in no way interested in doing deco dives without the cert. I understand that's how it was done in the old days, but I also understand that I don't know what I don't know, and that's what good instructors are for.

My inquiry is about pure oxygen as a deco gas. Is that what most people with similar diving interests are using? It seems like the time you save using 100% is significantly offset by the work required to keep tanks, valves and regs oxygen clean. If 100% is not the most common mix, what mix is, and if it's North of 40%, what extra gear issues do you have maintaining a system that's safe for say 80% vs. 100%? How often do you re-clean your tanks, valves and regs to maintain oxygen compatibility?

Why does this matter now? It probably doesn't. I know the instructor can answer this question when the time comes, and I have a reg I can use for deco gas up to 40% now. I imagine that in training, I'll be using less than 100% anyway, but I'd very much appreciate the thoughts of experienced deco divers.

 

[rjack321]

Anything >40% requires O2 cleaning, 50%, 80%, 100% doesn't matter.
Anything <40% isn't really going to accelerate your decompression (depends but practically speaking not much).

Its also still fairly common to make <40% nitrox by partial pressure which requires the tank & valve to be clean.

O2 cleaning isn't very hard.

 

[Rhone Man]

My inquiry is about pure oxygen as a deco gas. Is that what most people with similar diving interests are using? It seems like the time you save using 100% is significantly offset by the work required to keep tanks, valves and regs oxygen clean.

Makes a pretty big difference. There may be a mathematical formulae that I don't know, but I would estimate that using pure O2 rather than air on your final stop probably cuts deco time at that stop by about 55%?

 

[tasdiver]

My inquiry is about pure oxygen as a deco gas. Is that what most people with similar diving interests are using? It seems like the time you save using 100% is significantly offset by the work required to keep tanks, valves and regs oxygen clean. If 100% is not the most common mix, what mix is, and if it's North of 40%, what extra gear issues do you have maintaining a system that's safe for say 80% vs. 100%? How often do you re-clean your tanks, valves and regs to maintain oxygen compatibility?

I use O2 and 50% and it all depends on the dive. For most of my OW tech stuff I use 50%, it gets me on a richer gas sooner and starts the offgassing process quicker. Plus it's not a problem carrying the deco bottle and doing the switch in OW. In the caves I use O2. The bottle is waiting for me somewhere around 20ffw (cavern area) and I do not have to deal with switching to my deco gas and stowing a stage reg

I have 2 aluminum 40 deco bottles. One is dedicated to 50% and the other to 02. I do the same with my deco regs and 1 backup (spare).

 

[Captain12Pk]

Yes, for Tech 1 level dives, oxygen is the primary deco gas. Beyond T1, you will begin adding more deco gasses, such as EAN50. No agency that I'm aware of teaches the use of an EAN80. Either way, you'll want to have this equipment O2 cleaned and keep it clean. Each year at visual time, or any time that I have reason to believe that any contaminants have been picked up, it gets checked and cleaned again as necessary.
Yes your instructor will cover all of this, and I can't imagine he or she would let you train with O2. It creates an unnecessary cost and potential hazard.

Happy diving

 

[Jax]

If cleaning the regs to O2 service isn't that hard, why do manufacturers sell "O2" clean regs?

What does O2 cleaning on regs entail?

 

[Rhone Man]

What does O2 cleaning on regs entail?

(i) Breaking them open, (ii) cleaning them thoroughly to remove all hydrocarbons, (iii) replacing all rubber seals with viton, (iv) lube dynamic parts use an oxygen compatible lubricant, (v) reassemble, (vi) all preferably in a clean room.

The only hard step is (v). Do not try this if you don't know how to disassemble and reassemble your model of regulator. I did the TDI O2 servicing technician course in a single afternoon.

 

[Jax]

Yes your instructor will cover all of this, and I can't imagine he or she would let you train with O2. It creates an unnecessary cost and potential hazard.

Happy diving

I am sure this is true, but one may start assembling the necessary O2 cleaned equipment before the class, I assume?

Using O2 clean regs and such with Nitrox < 40% is not a problem, right? Especially when the method of blending is partial pressure and the bottles are O2 clean anyway.

 

[netmage]

Yes, for Tech 1 level dives, oxygen is the primary deco gas. Beyond T1, you will begin adding more deco gasses, such as EAN50. No agency that I'm aware of teaches the use of an EAN80. Either way, you'll want to have this equipment O2 cleaned and keep it clean. Each year at visual time, or any time that I have reason to believe that any contaminants have been picked up, it gets checked and cleaned again as necessary.
Yes your instructor will cover all of this, and I can't imagine he or she would let you train with O2. It creates an unnecessary cost and potential hazard.

Happy diving

It's not common, and usually footnote in some locales where wave action can make a hang or drift @ 20' cumbersome... IANTD had tables calling for it...

I like to use something richer than 50, but leaner than O2 for my rich bailout bottle on tech dives... Just so I can get onto something richer sooner otherwise my profile would be extremely long on something like 21/35 or move to a bend\mend profile.

 

[FireInMyBones]

100% is the primary deco gas. After that is 50%.

Beyond that would be adding Helium to your 50% for coming off of real deep dives as to not spike your Nitrogen levels (isobaric counter diffusion).