Request for opinions about standardizing on EAN80

[waterpirate]

Sooo,

My take on the dives you are making put me on 70% for a single deco gas in 1 al40 even if getting into 90 minute run times on vplanner +2. After hours of comparing schedules it occurred to me that the meaningful stops occur in terms of time starting at 40 feet. Not counting running stops. That meant to me that I wanted to be at 1.6 for deco gas starting at the first meaningful stop at 40fsw. Ergo 70%. Easy to blend, easy to deal with. I would not ever consider using 100% in the ocean, to unpredictable with to much time at 10fsw in the washing machine.
YMMV
Eric

 

[lee stroke]

Not sure why you would ever be at 10 feet doing deco on O2. Most divers I know do it all at 20 and then a ten minute float up to the surface.

 

[boulderjohn]

It sounds like you are minimizing any and all risk of O2 exposure, whether CNS clock or OTUs. I couldn't disagree more.

I have no idea what your reply has to do with what I wrote.

I'm not sure what you mean... could you explain this a little more?

The term "oxygen window" has several different meanings in different contexts. Mark Powell identifies three different uses for the phrase his book Deco for Divers. I am assuming in the context of this discussion that the usage was in relation to the concept that at the time the diver was breathing a high PPO2, it created an "oxygen vacancy" that increased the ability of the body to eliminate nitrogen. Powell accurately pointed out that this theory violated Dalton's Law. If you read the one and only article on which the theory was based with a critical eye, the single paragraph in which the idea occurs leaps out at you, since there was absolutely nothing in the previous data to justify the conclusion. Nevertheless, it was held to be gospel in some circles, and dive profiles were tweaked to increase the time spent at the highest PPO2s. As I understand it, that concept has been pretty much abandoned by all agencies that once embraced it. The famous S-curve is no more.

 

[Nasser]

The term "oxygen window" has several different meanings in different contexts. Mark Powell identifies three different uses for the phrase his book Deco for Divers. I am assuming in the context of this discussion that the usage was in relation to the concept that at the time the diver was breathing a high PPO2, it created an "oxygen vacancy" that increased the ability of the body to eliminate nitrogen. Powell accurately pointed out that this theory violated Dalton's Law. If you read the one and only article on which the theory was based with a critical eye, the single paragraph in which the idea occurs leaps out at you, since there was absolutely nothing in the previous data to justify the conclusion. Nevertheless, it was held to be gospel in some circles, and dive profiles were tweaked to increase the time spent at the highest PPO2s. As I understand it, that concept has been pretty much abandoned by all agencies that once embraced it. The famous S-curve is no more.

Ok I see what you mean.

Yes, when you mentioned O2 window, Mark Powell's definition with respect to accelerated deco came to my mind as well. My understanding of it is that by increasing the gradient between the tissue tensions and the inspired inert-gas pressure this would result in a faster rate of off-gassing. The oxygen window in this context being this increased gradient which is achieved by switching to a deco gas with a higher O2 content (or full O2) and thus a lower or no Nitrogen content.

 

[boulderjohn]

Ok I see what you mean.

Yes, when you mentioned O2 window, Mark Powell's definition with respect to accelerated deco came to my mind as well. My understanding of it is that by increasing the gradient between the tissue tensions and the inspired inert-gas pressure this would result in a faster rate of off-gassing. The oxygen window in this context being this increased gradient which is achieved by switching to a deco gas with a higher O2 content (or full O2) and thus a lower or no Nitrogen content.

Yes, that is the definition used by some people. Unfortunately, that concept is often confused by the very different definition used by others. It's hard to tell what people actually mean when they use the phrase "oxygen window" unless they supply more information.

 

[Redshift]

Even without the "oxygen window", a higher partial pressure differential is beneficial.
But there may be some added advantage of breathing high PO2. O2 saturation of haemoglobin is rapidly reached, but at higher pressures, the solubility in plasma is increased, taking more oxygen even to poorly-perfused tissues. That can happen with EAN80, but it's 20% less than with O2.

 

[karstdvr]

That can happen with EAN80, but it's 20% less than with O2.

From the literature I have seen it is more of partial pressure issue, so comparing O2 and EAN80 at the same depth is not a fair comparison. From what I have seen O2 at 20' and EAN80 at 30', do not have equal ratios,but there is a diminishing return,such that both function well. I think with all dives a need to analyze the plan and assess deco gas needs,because not all scenarios are equal. Did a dive once where the deco gas needed was EAN 60,because to deco in warmer spring water versus very cold lake water, this gas was needed.

 

[Germie]

First, if you put a dive with let’s say 15minutes bottomtime at 100m depth in your decoplanner, you will see that there is almost no difference in divetime when using an 80% or an 100%.
And you will see that the CNS loading is almost half when using 80% over 100%.
So if you find cns loading important, then choose the 80%

But then, if you read 1 of the explanations of oxygen window, then it means how bigger the gradient between tissueloading and the gas you are breathing, the faster offgassing is. That means oxygen is more efficient than 80%.

Yes, in courses you are not allowed to make dives over 80% cns. Then you are learned about airbreaks. How you make them, 12-5-12, 25-6-25, or whatever (it depends on agency), is learned in courses. But doing airbreaks can be controversy too, back to backgas? Back to first decogas? Back to travelgas? When doing airbreaks and back to what gas? There is not 1 answer right. If you don’t want to think about airbreaks, then take an 80%, normally you don’t have problems with too much cns. But if you think I want to use oxygen, then you have to think about doing airbreaks or not and how. Not too difficult and I still prefer oxygen over 80%.

But you do not talk about depths of 100m, but shallower. You speak about 2 alu40 stages with 2 different decogases. You want to go back to 1 decogas.
First question: is that possible for your dives? Ali40 is not big. Ever calculated how much deco you can have as maximum out of 1 ali40? Or do you want to take the 2 ali40’s with both same gas? Then there is absolutely no reason to go back to just 1 gas.

Then, why a 100% or 80% over an 50%? If I can do a dive with just 1 decogas, I would prefer to take a 50%.

But I think in your case with just 2 small stages I would stay with 50% and 100%. I don’t see a reason to get to 80%. And if divecenters only fill 80% I don’t see a problem to use that, but that is just when they don’t want to fill 100%.

I use 50%-100% most times. Some prefer 40%-80%. Theoretically there is a chance that using 40% over 50% means you can stay 30-60 seconds longer on bottom and still have the 1/3 reserve. If you don't want to use only 'standardgases', then you can think about it. It is all about what plan you make.

Oxygen is theoretically the most ‘clean’ gas, it is just decanted from a buffer to your cylinder. With 80% there is a possibility that the air from the compressor is contaminated (not clean enough for use with pure oxygen to hold cylinders in oxygenservice). Not as much you will get ill, but that you have to clean cylinders again.

I have used on 100+m dives 80% and 100% as last decogas, with both decogases I came up safe. My personal choice is 100%.

 

[doctormike]

But you do not talk about depths of 100m, but shallower. You speak about 2 alu40 stages with 2 different decogases. You want to go back to 1 decogas.

Hey, thanks for the reply! Yes, most of the issues that you mentioned with very deep dives wouldn't apply to me..

First question: is that possible for your dives? Ali40 is not big. Ever calculated how much deco you can have as maximum out of 1 ali40? Or do you want to take the 2 ali40’s with both same gas? Then there is absolutely no reason to go back to just 1 gas.

Yes, when I plan dives with MultiDeco, I limit my profiles by the amount of deco gas I carry in an AL40, and by the amount of back gas I would need in a lost gas scenario. I wouldn't ever carry two bottles with the same gas, that would give me the same issue that I'm trying to avoid, with respect to the large camera rig. If I was planning a dive where I needed more deco gas, I would get an AL80.

Then, why a 100% or 80% over an 50%? If I can do a dive with just 1 decogas, I would prefer to take a 50%.

I'm sort of coming to that conclusion, after having run a bunch of profiles for my typical dives. Also, the EAN50 tank serves above MOD as a bit of extra redundancy as well.

 

[Centrals]

The 100% could come handy on the surface.
I normally dive with 50% and 100% but if I only have one deco gas then my choice is also 50%.