Isobaric Counter Diffusion (ICD)

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Searcaigh

Seahorse Wrangler
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Following reading a recent post of diving the Arch in the Blue Hole at Dahab and watching the video in the post I was a bit confused as to why EAN32 was being used as the first deco gas.

I decided to establish a new thread on this subject rather than hijack the original tread.

From what I understand about ICD a change from the bottom gas 18/30 to EAN32 could result in DCS as the N2 difference is 16% which is more than the ideal.

Or am I incorrect?

I've always used EAN50 when changing from 18/40
 
MultiDeco really whinges at you if you change the nitrogen levels too much.

I look at the ICD logic like this:
Going from 18/40 (= 42% nitrogen) to 32% (=78% nitrogen) seems that you're going to get a lot of helium replaced with nitrogen.
Doing the same with 50% (=50% N2) will be more effective as the nitrogen content's not changing much, but there's a big change in O2.
 
My understanding is ICD isn't really an issue until you are deeper than about 100M. I'm sure there is a shallower and longer threshold as well (like 250 feet for a two hour bottom time or something). But if you are still in the normoxic range, it is probably mostly academic.
 
Does anyone have any knowledge of recreational teck divers getting an ICD hit?
What peer reviewed evidence is there to suggest it is anything but academic?
 
Following reading a recent post of diving the Arch in the Blue Hole at Dahab and watching the video in the post I was a bit confused as to why EAN32 was being used as the first deco gas.

I decided to establish a new thread on this subject rather than hijack the original tread.

From what I understand about ICD a change from the bottom gas 18/30 to EAN32 could result in DCS as the N2 difference is 16% which is more than the ideal.

Or am I incorrect?

I've always used EAN50 when changing from 18/40
While you are correct, that change is outside the parameters and wouldn't be an ideal choice, I was taught and have always learned that IBCD is of little concern with normoxic dives of nominal length.
 
My understanding is ICD isn't really an issue until you are deeper than about 100M.

The depth threshold to start thinking about ICD is 80m for TDI.
 
I witnessed a hypoxic class using 36% for travel/deco to "avoid carrying the extra bottle" on the final dive they were switching from 10/70 to 36% at 120' (fresh water at altitude). That caught my eye as a little aggressive, but they didn't have any problems with ICD. I have no idea why they where using 10/70 for a dive to 280' in open circuit
 
I witnessed a hypoxic class using 36% for travel/deco to "avoid carrying the extra bottle" on the final dive they were switching from 10/70 to 36% at 120' (fresh water at altitude). That caught my eye as a little aggressive, but they didn't have any problems with ICD. I have no idea why they where using 10/70 for a dive to 280' in open circuit
Was that a bounce dive to 95m/280' where they just used 32% and 80%? i.e. only two deco cylinders.
 
Was that a bounce dive to 95m/280' where they just used 32% and 80%? i.e. only two deco cylinders.

10/70 on the bottom, 36% and 100% for deco. If memory serves me well, 15 minute bottom time. but I'm not sure. I only no the mixes as I was curious about not taking 3 bottles. Personally, one of the big learning curves of Hypoxic was managing 3 and 4 deco bottles. I thought the instructor was doing them a disservice by avoiding it..


Edit: typo
 
10/70 on the bottom, 36% and 100% for deco. If memory serves me well, 15 minute bottom time. bit I'm not sure. I only no the mixes as I was curious about not taking 3 bottles. Personally, one of the big learning curves of Hypoxic was managing 3 and 4 deco bottles. I thought the instructor was doing them a disservice by avoiding it.
Looney toons.

Delete either of those two bottles and you’re REALLY in a pickle. Too much space between the 36% bottle and oxygen.
 
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