Scrubbing with EANx

[1_T_Submariner]

The Bakers Dozen - 13 reasons why we do not use 80/20. by George Irvine

Thanks for the link. Lots of sarcastic personal opinoins in there but, I get the point.

 

[1_T_Submariner]

Not to hijack the thread, but George's diabtribe misses the point of 80/20. For those of us who have neither a booster nor an unlimited supply of full-pressurized oxygen tanks, 80/20 is sometimes what you get when you have top off with an EAN40 continuous blend in order to get the needed volume.

It's not that I can't maintain my buoyancy, it's that my oxygen tanks decrease in pressure every time I transfill into my deco bottle. At some point, you've got to top off with EAN40 to get enough volume.

If you're George Irvine and can afford to get a $5,000 booster or new, fully pressurized oxygen cylinders every time you need to fill your deco bottles, then I guess you can have it perfect every time. The rest of us have to deal with real physics, and we can't realistically plan a deco dive with only 500 PSI of 100% O2 in our deco bottles.

Back to the question of the OP, in the world of recreational diving profiles there is no proven benefit of even a gas as rich as EAN40 in reducing risk of DCI.

Thanks for the explanation of Reality. I wasn't thinking about you tranfilling your own tanks. That makes a lot of sense to me.

Sorry about the Hijack.

 

[paddler3d]

To the OP, if your question was more about safety vs. curiosity, I got a lesson the other day about 'minimum deco' by some DIR folks.

Google that and you'll find some tables. Also try and search the threads about this.

If you wanting to expand your diving experience by diving with pony bottles, so on so forth, I do know a few divers who carry bottle of 50/50 (MOD of 70) and simply switch over to that at 70.

 

[Reg Braithwaite]

The Bakers Dozen - 13 reasons why we do not use 80/20. by George Irvine

Reading George's reasons I get the impression he is arguing with the strawman that 80/20 is used to avoid buoyancy issues doing a stop at 20'. And reading "Deco for Divers," the author points out that 80/20 is an optimum mix if you buy into a certain Buhlmann model of decompression and ignore or disbelieve certain theories about bubble models and oxygen windows.

I would find an argument that addresses this directly interesting to read.

 

[Don Burke]

I was poking around in DecoPlanner and found that if you have your heart set on carrying one deco bottle, you can get a significant time advantage by first planning the entire dive on your backgas, then adding a deco gas with an MOD that is the same as the depth of the deepest stop the program came up with on the backgas only dive. That will get the diver out of the water quite a bit faster than 100%. It only saves a few minutes compared to using EAN50, so I never tried it.

For no-stop profiles, a second gas that would come to 1.6 ATM oxygen at the deepest depth of the dive might be a slight help. That would let it serve as a bailout gas as well. I would be more worried about the diver getting the idea that he was bulletproof, so I would not do it.

 

[PfcAJ]

If you're George Irvine and can afford to get a $5,000 booster or new, fully pressurized oxygen cylinders every time you need to fill your deco bottles, then I guess you can have it perfect every time. The rest of us have to deal with real physics, and we can't realistically plan a deco dive with only 500 PSI of 100% O2 in our deco bottles.

So you'd like to have 100%, but can't afford it? So you compromise with something less than optimum. Why not skip a dive one day and get a full bottle of o2 instead so you benefit in the long run?

 

[rjack321]

If you're George Irvine and can afford to get a $5,000 booster or new, fully pressurized oxygen cylinders every time you need to fill your deco bottles, then I guess you can have it perfect every time. The rest of us have to deal with real physics, and we can't realistically plan a deco dive with only 500 PSI of 100% O2 in our deco bottles.

Buy a couple more cylinders to transfill out of. I have 4x 125cf O2 bottles so its pretty easy to get a 2000psi fill in an AL40. Then use up the dregs continuous blending 32% for other recreational dives.

2000psi of O2 in an AL40 is plenty for 20-25min dives into the 200-220ft range (with 50% along as well).

If I have a big project I can get my O2 bottle boosted to 3k at a shop. Although boosters are easily available for less than $5k, I've considered getting one but its not necessary.

Dragging along and breathing 20% of exactly what I'm trying to eliminate (N2) is counterproductive.

 

[rjack321]

And reading "Deco for Divers," the author points out that 80/20 is an optimum mix if you buy into a certain Buhlmann model of decompression and ignore or disbelieve certain theories about bubble models and oxygen windows.

Its more a function of the deco someone who's brought a full AL80 of 80% on a 200ft dive is likely to do. In other words, if you need that much "shallow" gas its probably because you haven't spread your deco time across multiple gases and are doing a buhlmann profile.

Do the gas choice(s) come first or the profile choice?

 

[jtivat]

Not to hijack the thread, but George's diabtribe misses the point of 80/20. For those of us who have neither a booster nor an unlimited supply of full-pressurized oxygen tanks, 80/20 is sometimes what you get when you have top off with an EAN40 continuous blend in order to get the needed volume.

It's not that I can't maintain my buoyancy, it's that my oxygen tanks decrease in pressure every time I transfill into my deco bottle. At some point, you've got to top off with EAN40 to get enough volume.

If you're George Irvine and can afford to get a $5,000 booster or new, fully pressurized oxygen cylinders every time you need to fill your deco bottles, then I guess you can have it perfect every time. The rest of us have to deal with real physics, and we can't realistically plan a deco dive with only 500 PSI of 100% O2 in our deco bottles.

Back to the question of the OP, in the world of recreational diving profiles there is no proven benefit of even a gas as rich as EAN40 in reducing risk of DCI.

We have been diving a long time with no booster. I can get 2200psi of O2 into a 40 with no booster and that it plenty of gas to do a 270' dive with a 20' BT.

 

[Doc Harry]

We have been diving a long time with no booster. I can get 2200psi of O2 into a 40 with no booster and that it plenty of gas to do a 270' dive with a 20' BT.

And how many time can you do that before there's not enough pressure left to get the required volume?

Buy a couple more cylinders to transfill out of. I have 4x 125cf O2 bottles so its pretty easy to get a 2000psi fill in an AL40. Then use up the dregs continuous blending 32% for other recreational dives.

2000psi of O2 in an AL40 is plenty for 20-25min dives into the 200-220ft range (with 50% along as well).

If I have a big project I can get my O2 bottle boosted to 3k at a shop. Although boosters are easily available for less than $5k, I've considered getting one but its not necessary.

Dragging along and breathing 20% of exactly what I'm trying to eliminate (N2) is counterproductive.

I have three O2 cylinders. One by one, as the pressure drops, they are relegated to continuing blending. But eventually the pressure in the other two drop and you just can't get the needed volume. At some point you've to go top off with EAN40. I could just keep ordering new O2 cylidners, but at some point I'm gonna have 10 cylinders strapped to the wall with 500 PSI, all waiting to be drained as I blend EAN into my doubles.

Sometimes you can plan your gas around your dive, but other times you've got to tweak the dive plan around the available gas.