Request for opinions about standardizing on EAN80

[doctormike]

Hi,


Right now I have two AL40 deco cylinders, which are marked and filled with EAN50 and 100% O2. I was thinking of relabeling them both for EAN 80 (as was taught in my tech class) so as to standardize and make the logistics easier, but I know that there is some controversy about this. I am interested in your opinions.


I'm doing "light" deco - i.e. not very long profiles, deco limited to about 30 minutes maximum, single deco gas dives. I'm not planning on trimix training at this point.


I have seen a number of SB threads about EAN80 vs 100% O2 as a single deco gas. I have read a lot of this material, including George Irvine's strong critique of EAN80 from a while back, and the issue of the oxygen window. I also understand that some divers use EAN80 to compensate for difficulty holding the 20 foot stop in heavy seas. Also, a bottle of 100% O2 is handy for surface use in case of DCS. Looking at my typical profiles, it seems that there is slight advantage in run time for 80 vs 100, and usually a moderate advantage when compared to EAN50.


So I have two questions.


1) Leaving aside the deco issues, are there safety reasons for standardizing on EAN80 when compared to 100% O2? I understand that the standard pure O2 fill (without a booster) of an aluminum tank with a service pressure of 3000 PSI is about 2200, but then again, you need less gas volume in most profiles. Tank accidents and fires are rare, but does having 100% vs 80% make any difference?


2) Do any of you feel that there is a significant advantage of EAN80 in terms of oxygen injury (CNS clock, vascular perfusion, pulmonary injury)? Air breaks? Anything else...?

 

[lee stroke]

It really doesn’t matter, use whatever works for your profile that you are diving. I use O2 pump to 3500 without any problem. If I have a odd profile I might be using a lower 02 but that is to add some Helium to it.

 

[boulderjohn]

First, the benefits touted for the oxygen window went out that window a while ago. The theory behind that has pretty much been forgotten.

To me, the big difference lies not so much in the mathematics of it all but more in where you are diving. If you are in a place where it is easy to get O2 fills, then I don't see any reason to do otherwise. I just completed teaching a class for which we had enough O2 fills to get us through to the last dive. If we had done any more dives, though, we would not have been able to do it. We were out on the prairie making our mixes using an O2 supply bottle in the back of a van, with no booster within hundreds of miles. Our next step would have been topping off a final mix, and 80% would have been nice indeed.

 

[doctormike]

First, the benefits touted for the oxygen window went out that window a while ago. The theory behind that has pretty much been forgotten.

To me, the big difference lies not so much in the mathematics of it all but more in where you are diving. If you are in a place where it is easy to get O2 fills, then I don't see any reason to do otherwise. I just completed teaching a class for which we had enough O2 fills to get us through to the last dive. If we had done any more dives, though, we would not have been able to do it. We were out on the prairie making our mixes using an O2 supply bottle in the back of a van, with no booster within hundreds of miles. Our next step would have been topping off a final mix, and 80% would have been nice indeed.

Thanks! My LDS can do O2 fills, so that's an option. But I can also get EAN80 just as easily.

 

[Superlyte27]

If you can get 100% regularly, there's NO REASON to get EAN80.

 

[doctormike]

If you can get 100% regularly, there's NO REASON to get EAN80.

Thanks! So no advantage in terms of operational safety or O2 exposure?

Standardize on 100% and fill both bottles with that, getting rid of the EAN50?

 

[dumpsterDiver]

There is the issue of contamination. If you just get oxygen, it is less likely to be contaminated, versus air from a compressor which might not be so clean one out of 50 times?

 

[doctormike]

There is the issue of contamination. If you just get oxygen, it is less likely to be contaminated, versus air from a compressor which might not be so clean one out of 50 times?

Good point, I hadn't thought of that. I do trust my LDS to mix clean nitrox, but if there is no big downside to O2 that's another vote in it's favor... especially if I have to get fills elsewhere.

 

[PfcAJ]

You need the 50%. You've got a gas that you can switch to at 70ft which really impacts minimum gas volumes when compared to 30 or 20ft.

I'd keep what you've got.

100% is the most efficient deco gas. Divers also have less bubbles post oxygen deco when compared to other gases (gf held constant). its useful on the surface for dcs. 80% involves 2 fill whips, oxygen involves 1, reducing chance of contamination. Less of a concern IMO with things like 50% as the o2 pressures are much lower. Lots of drawbacks for 80%.

 

[JohnnyC]

The only operational safety issue would be if you can't hold a 6m stop. EANx80 MOD is 10m. If you have buoyancy issues such that you would need the extra MOD safety factor because you can't hold a 6m stop without a 4m swing, you probably shouldn't be doing technical diving.

That being said, the amount of time difference in a deco obligation running EANx80 vs. O2 isn't much when diving in the realm where a single AL40 is enough gas for your deco. If you're using 2 AL40's worth of EANx80, you should probably be reevaluating your dive plans and your deco obligations.

Just as an example, a 45m deep, 30min bottom time using air as backgas, using EANx80 gets you out in 76 minutes running VPM +3. Using O2 gets you out in 80 minutes for same depth and bottom time. It actually takes longer with O2 because you can't make the switch until 6m so you're doing the rest of your stops through 9m on air. Of course 4 minutes is nothing.

Now, add 50% into the mix with the O2 and you're on deco gas substantially sooner (in this case 15 minutes, this can be substantial in cold water). Keep the 50%, keep the O2. Forget the 80%, not worth the hassle.