Subsurface mobile general question

[Jan Mulder]

Robert,

On 15-11-2021 10:33, Robert.Helling wrote:
> Jan,
>
>> On 15. Nov 2021, at 09:11, Jan Mulder via subsurface 
>> <subsurface at subsurface-divelog.org> wrote:
>>
>> The idea that there is a ratio between diluent use and O2 use is 
>> flawed. The main driver for O2 use is time and workload, and for 
>> diluent its the dive profile.
>>
>>
>
> this is clear. I was asking to get an understanding how bad the error 
> is to ignore that O2 is not only contained in the O2 bottle but also 
> in diluent. I guess you would want to know how much O2 your body 
> consumes during the dive. The true number would be the sum of the O2 
> from the O2 cylinder plus the O2 contained in the diluent minus the O2 
> that was released from the loop to the water.  How bad is the 
> approximation that takes into account only the O2 from the O2 
> cylinder? If it’s a few percent, I would make sense to compute and 
> display that number. If the error is bigger probably less so.

I think that the approximation to only take into account the O2 from the 
O2 cylinder is a good one with only small error.

I dive a mCCR (Kiss Classic) and adding diluent to the loop is a very 
explicit action by the diver. I only add diluent to the loop when 
descending (and than only when the loop volume is too low, and the pO2 
is as high as I want it to be). In other words. The diluent plays a very 
limited role in the pO2 management.

In the mCCR, the O2 from the O2 cylinder is added automatically using a 
bleed orifice that constantly puts the amount of O2 into the loop that 
is close to your metabolized O2. Obviously, the metabolized O2 also 
depends on workload, but heavy workload on any CCR is a bad idea (as the 
scrubber will not be able to get all the produced CO2 out of the mix). 
So, the mCCR diver sets the amount of O2 bleeded into the loop based on 
the "normal" workload. And a nice side effect of this, is that in a very 
relaxed deco phase of the dive with low workload, the pO2 rises.

And I agree with Anton that a model that can determine how much loop 
volume is metabolized and how much is wasted can be interesting, but 
primarily from academic point of view.

--jan
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