Question Isobaric counter diffusion in CC

[flymolo]

Where did you get the mixes 11/74 and 40% from?

3 dil switches? Who teaches that?

 

[flymolo]

Why would you ever switch your DIL to 100%. That seems like a terrible idea in the ocean

 

[inquis]

Why would you ever switch your DIL to 100%. That seems like a terrible idea in the ocean

I suspect he meant an O2 flush at 6m.

 

[Snusmumrik]

Why would you ever switch your DIL to 100%. That seems like a terrible idea in the ocean

Presume switch to pure O2 is not a switch, but loop flush.

 

[flymolo]

Presume switch to pure O2 is not a switch, but loop flush.

Nope, I don’t think so

• Switching through all gases (11/74, 21/35, 40/0, 100/0): 100 min

Given the increased complexity and higher potential for ICD, on such a dive I would likely go for the second option and sacrifice 11 min of longer deco compared to the optimal gas switches. For dives with significantly longer deco, I may opt for the option of switching to all available gases and get a 10% acceleration on deco.

 

[sea_ledford]

I just checked the speed up in deco from doing dil switches for the 100m example dive. Here are the total dive times:

• Keeping bottom gas as dil for the whole dive (SP 1.3): 115 min
• Loop flush with oxygen at 6m (SP 1.3 until that point): 111 min
• Switching through all gases (11/74, 21/35, 40/0, 100/0): 100 min

Given the increased complexity and higher potential for ICD, on such a dive I would likely go for the second option and sacrifice 11 min of longer deco compared to the optimal gas switches. For dives with significantly longer deco, I may opt for the option of switching to all available gases and get a 10% acceleration on deco.

Thanks everyone for sharing their perspective.

This all seems to be very biased toward thinking the gas programed into your computer is what is actually happening. If I'm on the loop with a 10/80 dil, it is not 10/80 as I ascend until I do an O2 flush at 20'. Even with a perfect ascent, and needing to add no dil, your inspired gas will increase in PO2 and decrease in PHe as you add O2 on ascent.

Your first example would only be realistic if you did a dill flush with 10/80 at every stop. I would think the reality of the dive would be similar to option 3.

The only time switching dil make sense to me would be if you weren't going to the surface, but instead were ascending to a shallower depth and staying there for awhile and would need to add dil with normal depth variations.

Anyone have a Liberty that would be willing to share a clean deco ascent with Po2 and PHe on the graph?

 

[tbone1004]

One thing that has not been mentioned yet and should be.

When you get into these really long run times and the cells are hot and humid, you need to be able to perform cell validation. Cell validation is done with dil flushes to ensure that the cells are responding predictably and to check for current limitation. You can certainly do this by dil flushing with whatever you have plugged in but I really couldn't be bothered if my cells are accurate below a ppO2 of 1.0 when I'm on deco, I really want to know what they're doing in the 1.3-1.6 range and by doing the gas switch and doing a dil flush you are validating that the cells can still read up to 1.5-1.6 and that they are doing it correctly. This is risk mitigation for oxtox on the ascent. To each their own, but I won't run a ppO2 up above about 1.3 unless I can get a dil flush in and make sure the cells still get up there, if they can't get it up, then at least you aren't trying to get it up and do the funky chicken.

 

[flymolo]

One thing that has not been mentioned yet and should be.

When you get into these really long run times and the cells are hot and humid, you need to be able to perform cell validation. Cell validation is done with dil flushes to ensure that the cells are responding predictably and to check for current limitation. You can certainly do this by dil flushing with whatever you have plugged in but I really couldn't be bothered if my cells are accurate below a ppO2 of 1.0 when I'm on deco, I really want to know what they're doing in the 1.3-1.6 range and by doing the gas switch and doing a dil flush you are validating that the cells can still read up to 1.5-1.6 and that they are doing it correctly. This is risk mitigation for oxtox on the ascent. To each their own, but I won't run a ppO2 up above about 1.3 unless I can get a dil flush in and make sure the cells still get up there, if they can't get it up, then at least you aren't trying to get it up and do the funky chicken.

If you are doing "really long runtimes" are you really flushing your po2 up to 1.4 and above on deco? I sort of doubt it.

What is a "really long runtime" that people are actually doing in the ocean that necessitates dil flushing to validate cells on deco?

 

[mr_v]

@flymolo, I am with @tbone1004 on the procedure he described with a slight modification: I check the cells if there is excess moisture in the loop. Dive time > 2.5 hrs or "gargling noises" is a moisture presence indicator.

I typically don't switch DIL but will check the cells with the gas that can confirm linearity in ~1.3-1.6 PPO2 range. The procedure should be a no-brainer for anyone diving CC.

 

[flymolo]

i don't think i would do that unless i suspected something was off, but then again i usually check cells for current limiting at the start of the descent and i don't really run my po2s above 1.3 anyways

linearity checks are done on land since i can barely do the math above water