Dive plan: Taking into account isobaric counterdiffusion

Tue Jan 2 07:30:23 PST 2018

On 02/01/2018 16:24, Robert Helling wrote:
> Hi,
>
>> On 2. Jan 2018, at 14:53, Stefan Fuchs <sfuchs at gmx.de 
>> <mailto:sfuchs at gmx.de>> wrote:
>>
>> I am personally interested in this topic so I started to play with 
>> your patch and this is my feedback:
>> - +1 for implementings.th <http://s.th/>. regarding ICD / IBCD
>> - Ok with choosing this 5% rule of thumbs from IANTD unless someone 
>> clearly shows us that there is a MUCH better approach or e.g. a kind 
>> of 2nd/3rd/... limit we could consider additionally
>> - No real idea where else we could put this code other than in the 
>> plannernotes.c
>> Ok, this was the easy part, now the more difficult items:
>> - I already expected people to give negative feedback regarding 
>> cluttering the UI/output - and I would have understood this.
>> Always adding this additional column in the dive plan table with some 
>> complex info which is needed by almost nobody really doesn't look 
>> that nice. So we need to look for a clever solution for this. I 
>> already see a few options:
>> x Only show this column for Tx dives (not too difficult but still it 
>> could happen that s.o. want's NOT to see the info)
>> x Prefs option to switch it on/off (yeah, also cluttering the UI)
>> x Don't print ICD info into plan/table but only show it as a tool tip 
>> when hovering over the gas in the plan (complex, maybe even not possible)
>>
>
> I also like the idea of displaying the info on ICD (and I am happy to 
> hear that there is some sort of limit that at least some people agree on).
>
> I am not sure, the dive notes/written dive plan are the best location 
> for the display, though, in particular since those notes are supposed 
> to be printed on wet notes (and during the dive this is not relevant 
> information). Wouldn’t it be better to make this an event in the 
> profile or modify the gas change event accordingly (including the 
> percentage information and maybe using a different icon if the change 
> is above the threshold)?
>
> What do you think?
>
> Best
> Robert

Thank you, Stefan and Robert,

The current implementation only supplies the ICD information for OC dive 
plans that include trimix. I understand the argument about adding to the 
profile listing of the dive plan. What if one makes a separate paragraph 
at the bottom of the dive plan by adding a  small HTML table? Something 
like:

CNS: 78% OTU: 164 Deco model: Bühlmann ZHL-16C with GFLow = 33% and 
GFHigh = 66% ATM pressure: 899mbar (931m) Isobaric counterdiffusion 
information *Time    Gas change **ΔN₂ **Max ΔN₂* 12:13    11/55 -> 21/42 
         3.0%      2.6% 12:27    21/42 -> 33/31         3.0%      3.0% 
12:38    33/31 -> EAN55       5.0%       5.8% Gas consumption (based on 
SAC 21|15ℓ/min): 933ℓ/84bar of EAN55 (383ℓ/35bar in planned ascent) 
2506ℓ/110bar of (11/55) (676ℓ/30bar in planned ascent)  — Minimum gas 
(based on 2.0xSAC/+1min at 115m): 1864ℓ/79bar/Δ:+51bar 1200ℓ/105bar of 
EAN80 (1200ℓ/108bar in planned ascent)  — Warning: not enough reserve 
for gas sharing on ascent! 836ℓ/79bar of (21/42) (371ℓ/36bar in planned 
ascent) 683ℓ/62bar of (33/27) (683ℓ/65bar in planned ascent) 0ℓ/0bar of 
oxygen I am not sure the alignment of this table will be ok in your mail 
browsers, but you will get the idea, I am sure. The table will only show 
for OC trimix dives. Having to hover over the profile to get the ICD 
information requires a lot of work for the user to get some very simple 
but critical information. My feeling is that the info, when relevant, 
should be immediately and prominently available. We have had some 
serious injuries by ignorant divers who dived to 80m with trimix and who 
then used air as a deco gas. Crazy. Therefore I regard the ICD info as 
critical.

I do not think one should go so far as to say "you are above the limit" 
and provide a YES or NO decision with respect to ICD. As with so many 
diving decisions, these are based on experience and track record, rather 
than hard scientific facts. My preference would be to show deltaN2 and 
Max_deltaN2 and allow the diver to make the decision of whether the 
differences in gas mixtures are within limits or not. (For instance the 
first change in the "table" above has deltaN2 of 3.0%, which is 0.4% 
more than Max_deltaN2. I *personally* would be happy with that 
difference, even though the difference is slightly larger than the 
maximal value of 2.6% because gas composition is also affected by gas 
mixes that allow accommodating failure of a deco gas during ascent, so 
there are competing factors that affect gas mixtures during the dive).

Please comment on these ideas!

Kind regards,

willem

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