Subsurface mobile general question

Robert Helling helling at
Sun Nov 14 14:07:51 PST 2021

Hi Poltsi,

> On 14. Nov 2021, at 22:44, Paul-Erik Törrönen via subsurface <subsurface at> wrote:
> When CCR, you're mainly interested in the consumption of O2 as noted previously. The diluent is not really telling since it is mainly a function of your profile as you use diluent to equalize the pressure in the loop. A serrated profile (lot's of ups and down) == large volume of diluent used because of addition to loop when going down, then dumping it when ascending.

I can see that the amount of O2 used divided by total dive time could be of interest. But it’s definitely something else than SAC and thus should not be mixed with it. For example, in any statistics when you have both CCR and OC dives, it would make zero sense to combine the two. So even if we computed this number, it should not be displayed as SAC or stored as such. Let alone the number with an ambient pressure correction like the SAC makes zero sense for a CCR.

> Of course this also happens to O2 also, but what would be interesting to see is how/when your consumption of O2 changes due to increased work.

I meant more the other way around: If you diluent also contains O2, you underestimate the O2 consumption if you only use the pressure drop in the O2 cylinder.

So here is a question I have: For a typical CCR dive, what is the ratio between used O2 and used diluent? I understand this depends on how often descend and how often you flush but what is a ballpark type figure?

I vaguely recall, there was a discussion on this list a while ago is there is any hope of doing a decent prediction of how much gas is used in a CCR dive but if I remember correctly the consensus was no, nothing that would be of any use.

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