favorite deco blends

[aue-mike]

The heliox 50 use is still "experimental." We treat it just like EANx 50 solely as an added safety factor. However, logic and physics lead us to believe it will result in a cleaner decompression. It is hard to quantify how much better it is as many of the programs are behind the curve. We have discussed this with various experts and we have yet to determine a way to model it accurately. We are currently at a point in our tables that there is nothing left to crank back on so we are trying to find ways to expand the safety margin within current table parameters.

Cheers,
Mike

 

[Divesherpa]

Question for you AUE Mike, and I mean this with all due respect as I am fairly new.
If ascending from 240ffw and not switching until 70ffw, then again at 20ffw, would you not have a much larger gap than if switching at 110ffw then 30ffw?
Also on the point of 50% then 100%, what about the difference at 30ft?
I guess I just need to get a CCR.
Anyone want to make a donation?
Thanks again for the helpful words.

 

[aue-mike]

Not at all, if you are diving mix. The bottom mix I would be using is typically based on a 1.2-1.3 PPO2 and a 100fsw END. Even at 110fsw, the bottom mix would produce a much lower PPN2 than would the EANx 36. It would be better to stay on the mix.

Several years ago (and depending who you listen to, still to this day) many believed helium to be "hard" to deco from and it was recommended to get off mix as soon as possible. Well, logic and real-life scenarios (including tens of thousands of man-dives amongst various groups) have revealed that this was extremely flawed. People were getting on air at 180fsw or EANx at 110fsw and doing more harm than good. You are basically polluting yourself with nitrogen. Consider nitrogen the enemy and then devise your dive plan in a way as to supress that enemy to the greatest extent possible.

You are right about the gap in the EANx 50 at 30fsw. This happens between any two gasses. However, if you want to get the greatest benefit you employ the best two gasses. You do lose some benefit, but your PPO2 (of EANx 50) is still higher than EANx 36, and your PPN2 is still much lower than EANx 36 at your 30fsw (or 40fsw, etc.) stop. This is extremely important in your shallow stops as you want to rid yourself of nitrogen. The gap you need to worry about is between the two deco gasses and not the gap between bottom gas and first deco gas as the helium displaces the nitrogen there.

Sure, you can deco on EANx 36 and EANx 80, but if you want to optimize efficiency, safety, and your short- and long-term diving health, you need to optimize your breathing gasses. If you do, you come out of the water with less "residue" and you can safely get back in the water after a shorter interval.

Cheers,

 

[Lost Yooper]

Originally posted by Green_Manelishi
To sum it up, the deco is occuring DEEPER with a switch at
70ft to 50%, but is it ultimately, all things factored in, occuring
BETTER?

GM,

All things being equal, the total deco times are not significantly different (50% alone shows a slightly faster deco than O2 alone) , so I guess neither is better than the other in terms of quality deco. I like the offgassing at deeper depths, so I can get it over with in the event of an emergency. I wouldn't have any particular problem with taking just O2 or just 50% for simple dives, but I choose to take just 50% which isn't uncommon among technical divers. It just depends on what you want to do, I guess. There's certainly nothing wrong with taking just O2 for sure.
I make it a habit to stay at 70' for 5mins whether the program tells me to or not. That is one of my conservation factors that I throw into my dives -- like a safety stop. Then we plan for the deepest dive possible and only hit that depth for a minute or two (most of the dive taking place 15' or so shallower) as another conservation measure. I keep the programs to a minimal conservation and just throw in my own safeties.

Take care.

Mike

 

[aue-mike]

As far as my mentioning two bottles, I was referring to bringing both EANx 50 and 100% O2. For shallow stuff where there is minimal to no mandatory deco obligation, I generally take just 100%. As you know, the greatest pressure change occurs near the surface and with 100% O2 you can make sure your system is "purged" before surfacing. Again, I am talking about minimal mandatory deco.

By ascending slowly and starting deeper, you should not really need to stay for any period of time in deeper water. I generally do half-depth stops (e.g., max depth of 120 - stop at 60, then 30, etc.) for only a minute or two just to let the body catch up before continuing the slow, steady ascent. Staying any longer than that really has no benefit for these light dives, but to each their own. Do what works for you and remember, decompression is all theoretical

Cheers,

 

[Lost Yooper]

Just as a side note to the discussion here, there can be other variables that may effect your gas choice (50% and O2) for the "less complicated" dives. Some people may have easier access to O2 fills, or some may be able to get reliable 50% fills considerably cheaper. The cost of an O2 fill may be a consideration. Having O2 kicking around isn't a bad idea if you need it on the surface too. Then, in the case of GM's friend, sensitivity may play a factor.
Some people who do a lot of repetitive deco diving in a week, may very well wish to cut back on high doses of PPO2 as a matter of saving their lungs. Yet another consideration may be the back gas you're using. If it's a rich mix of nitrox, then 50% would be less desirable than O2 for deco. These are just a few variables that may be considered in using a particular deco procedure.

I don't think there is a particular advantage or disadvantage to taking one or the other as far as quality deco is concerned for "less complicated" dives. Both techniques have their merits, so it may come down to other variables to help someone choose their mix. I am going to look into that 50/50 heliox.

Take care.

Mike

PS. It is important, IMO, to get use to using standard mixes in your diving. We have standard mixes we use for a range of depths, and the deco gasses stay the same. This way, you will learn how those gasses affect you; memorize what the deco looks like; be familiar with filling those mixes; and you'll be able to use gas specific deco tanks that are marked accordingly. Just thought I'd throw that in.

 

[100days-a-year]

Kudos to the Mikes.Standardized mixes are much easier.I tried the heliox on the programs that would allow it.Mostly they actually added time,guess they are behind a bit.Wander how hard it would be to integrate deco to a real time u/w doppler machine.How much does a surface model cost now?That would take all the guess work out the equation.Or a lot of it.

 

[padiscubapro]

aue mike-

I should clarify when I said I switch to 32% or 36% quite often those mixes are just a higher Fo2 trimix, the composition really depends on what my bottom mix was (and If im using a travel gas its some type of hypoxic gas), many times I use 32tx18 or 36tx14 so the n2 is never higher than 50% (my next deco gas), I want to help the He along without penalizing myself with n2 loading (factoring in ascent, switch times and some deep stops I have at least 5 mins on this gas, probably more) time.. plus in the event I lose my 50/50 bottle I'll have another reasonable substitution.

 

[aue-mike]

padiscubapro-
that should be your third deco gas for dives past 330fsw or so. We typically use something like a 35/20/45 for our deep deco gas. It helps produce a cleaner deco on deep dives instead of coming off a real high He mix to nada.

When I saw 32/36 and 80 I assumed these were the "standard" agency deco mixes, and I think this was the reason the thread developed.

There is no problem with using a deep trimix for deco. However, one should still shoot for the 50/50 as you ascend. With your deep trimix deco, yes, you limit the PPN2, but you still need the other component of a high PPO2 that is relatively efficient over a variety of shallow depths.

Of course the "ideal" solution would be to have an ideal mix for every deco depth, but that is not very practical. Also, we do not take a third deco mix unless the dive warrants it (that is, the depth is below 330fsw) as it just adds to task/gear loading. We like to keep it simple and taking an extra bottle for only a few minutes of benefit just doesn't cut it. The open water, ocean dives we do that frequently have swift currents and dynamic temperature and visibility demand enough from us as it is.

FWIW, with our deco profiles, we can still blow away the constant PPO2 rebreather divers - even with only two deco gasses.

Cheers,

 

[Norm]

Divesherpa I'm with your associates in Gainesville....if I'm doing 'true' deco I abide by the 50/50, 100% rule. The DIR gang has proven this to me beyond doubt. JMO
Norm:doctor: