Regarding breathing O2 at the surface: That would indeed lead to much faster off-gassing (as the nitrogen gradient between tissue and breathing gas is about 0.8bar lower) but the amount of time saved once more depend on which tissue is controlling the limit. To see the effect in the mathematica notebook, in the assignment to “values”, replace the f-> 0.79 by f->0.

]]>I’d like to see the effect of breathing O2 at the surface on the no-fly time (NFT).

Would it be possible to start with a substantial dive (say: 20min@40m) to preload the compartments and then calculate the NFT for different scenarios?

First would be 21% O2 (= plain air) for reference, then some steps like

10 minutes of 100% O2,

20 minutes of 100% O2,

30 minutes … ,

up to 4 hours (that probably requires a large O2 tank)?

Some sources state that they have had no adverse effects using a 1:4 ratio, so that every 1 minute of O2 would cut 4 minutes off the NFT (starting with 24h).

My mathematica knowledge is “I believe it is a modelling program with mathematics included”, so that isn’t the swiftest way to go for me.

Would it be possible to add the NFT to subsurface? I tried to fake it with a dive at altitude and some superextended deco stop @3m on O2, no conclusive result so far.

Kind regards

André

what I tried to say in my post is exactly that even if you ” just let the user make his own NDL GF settings whatever they find appropriate” it turns out that the influence of GFlow on the NDL is almost not there.

BTW, an easy regularisation is to say that the minimal depth to apply GFlow something like 0.1m. That resolves the singularity in the formula and automatically makes sure that GFhigh is responsible for the NDL. And obviously yields a smooth transition.

]]>The problem though, is all NDL dives eventually become decompression dives. So you need a transition from NDL GF mode to Deco GF mode. Take a look at the dive log of a computer that does this, and you will see as the deco begins, the transition to initial stops will come on with rush. Rather quickly the plan has gone from no deco, to 2 or 3 levels of required deco with extra minutes of deco time needed. However, that blended approach, is not proportional to the underlying needs of decompression, and not respecting the divers wishes per his GF settings.

Others might argue that GF Lo creating early stops in NDL mode, is doing exactly what has been asked of it – to lower the maximum saturation pressures accordingly and insert early stops.

That’s the compromise when trying to use GF in NDL mode. Some programs will go to the trouble to try to silently blend that transition into the ascent (those that “look” to show no GF Lo influence). Other programs just let the user make his own NDL GF settings whatever they find appropriate.

]]>This seems to well beyond what can be explained by rounding and is much more into the domain of different interpretations of a corner case of the algorithm.

I was faced with this exact dilemma during the implementation of own diving computer and although at first blush it seems reasonable enough to just not worry about the discrepancy, at the end of the day the code had to implement one approach or the other and I just can’t help feeling uncomfortable with an arbitrary choice.

]]>GF 80/80

ostc planner : no stops

gap diveplanner : no stops

pastodeco : no stops

mvplan : no stops

Rerunning the simulation with GF 30/80

ostc planner : no stops

gap diveplanner : no stops

pastodeco : 1min at 6m et 1min at 3m

mvplan : 2min at 6m et 1min at 3m

So it seems like both OSTC planner and GAP diveplanner fall into the “GF low only applies to deco dives” camp.

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