Question Isobaric counter diffusion in CC

[wedivebc]

Correct, though even on my Meg *which does have a 3L bottle*, I don't use that 3L bottle for dil, instead using it for inflation, and have it in a rack for boat diving with twin LP50's that I use for dilout. I wouldn't use an onboard 3L bottle for diluent on that deep of a dive, that bottle is far better off being used for inflation.

I want to apologise for misunderstanding your intent of the post. I knew you were a meg diver as am I. Using "dilout" on a meg was never part of my training and I assumed you were carrying extra dil in order to perform dil flushes for cell validation. Sorry for the confusion. I now understand your intent.

 

[mr_v]

I want to apologise for misunderstanding your intent of the post. I knew you were a meg diver as am I. Using "dilout" on a meg was never part of my training and I assumed you were carrying extra dil in order to perform dil flushes for cell validation. Sorry for the confusion. I now understand your intent.

Interesting that you've mentioned that training aspect. How did your instructor teach cell validation in situation when multiple gases are available?

 

[wedivebc]

Interesting that you've mentioned that training aspect. How did your instructor teach cell validation in situation when multiple gases are available?

Cell validation is taught in basic CCR. It hardly seems appropriate to explicitly teach the basic skill using multiple gases since the principal applies the same way regardless of the gas being used.

 

[LFMarm]

Thanks to a ton of suggestions from @inquis, I did some more calculations to compare the most relevant case studies on ICD.

The cases are:

• Biophysical basis for inner ear decompression sickness - Doolette, Mitchell (2003) Biophysical basis for inner ear decompression sickness - PubMed
  • Bottom mix 8/60, bottom depth 110m, bottom time 25 min, set point 1.3 bar, switch to air at 30m
  • Calculated inner ear tissue tension (my own calculation):
    • Tissue tension 8.7 bar (He 5.7 bar, N2 3.0 bar)
    • Inspired pressure change at the time of dil switch: 𝚫He -1.8 bar, 𝚫N2 +2.2 bar
  • Outcome: 1/1 cases of DCS
• Safe inner ear gas tensions for switch from helium to air breathing during decompression - Doolette, Gerth (2013) https://diving-rov-specialists.com/...as-tensions-for-switch-from-helium-to-air.pdf
  • Bottom mix 16/84, bottom depth 67m, bottom time 61 min, set point 1.3 bar, switch to air at 30m
  • Calculated inner ear tissue tension (my own calculation):
    • Tissue tension 6.3 bar (He 6.3 bar, N2 0 bar)
    • Inspired pressure change at the time of dil switch: 𝚫He -2.7 bar, 𝚫N2 +3.2 bar
  • Outcome: 0/27 cases of DCS

My calculations assume 18 m/min descent, inner ear half time of 8.8 min, ignoring offgassing during ascent before dil switch.

Based on this I think that:

• The deltas on inspired pressures of He and N2 at the time of dil switch, seem comparable between the 2 cases. This is a bit counterintuitive to me as all the empirical rules on ICD were based on the ratio of these deltas
• The total inner ear tissue tension is significantly different between the 2 cases (6.3 bar vs 8.7 bar)

Unless somebody finds some holes in these calculations and conclusions, I plan to check all my big dives against the total tissue tension and not be concerned about ICD if the tissue tension is below 6.3 bar (which is the case for all my dives so far and planned). Here is the comparison for the 100m dive planned at the beginning of this thread:

• Bottom mix 11/74, bottom depth 100m, bottom time 12 min, set point 0.7 bar during descent, 1.2 at the bottom and 1.3 on ascent, switch to 21/35 at 52m
• Calculated inner ear tissue tension (my own calculation):
  • Tissue tension 5.0 bar (He 4.2 bar, N2 0.8 bar)
  • Inspired pressure change at the time of dil switch: 𝚫He -1.9 bar, 𝚫N2 +1.9 bar
• Outcome: hopefully no DCS given it's much lower tissue loading than the 2013 study