Re-Evaluating My GF

[Graeme Fraser]

I finally made it through this. All I can say is wow, just wow.

I'm with you on that! Like a car crash; you know you shouldn't look, but just can't help yourself. Surprising when even very intelligent people don't seam to realise that their rants are forever online for all to see. Glad I'm not that smart

 

[Celt]

So, I guess my question wasn't so stupid after all. Using MultiDeco, I got a run time of 90 minutes with Buhlmann ZH-L16C 100/100 and 113 minutes with VPM-B nominal.

definitely not when I'm using Buhlmann ZHL16/C any chance you could give me a break down of the 90 min run time

 

[scubadada]

definitely not when I'm using Buhlmann ZHL16/C any chance you could give me a break down of the 90 min run time

 

[Celt]

View attachment 508748

Great thank you.

 

[TrimixToo]

I'm with you on that! Like a car crash; you know you shouldn't look, but just can't help yourself. Surprising when even very intelligent people don't seam to realise that their rants are forever online for all to see. Glad I'm not that smart

It's one of *at least three* (perhaps four) Simon/Ross train wrecks in different places. Simon has the patience of a saint and the tenacity of a bulldog...Ross just keeps playing the knight in the Monty Python movie, over and over.


(I like MultiDeco, very much. IMO, Ross would serve himself best by just quietly supporting his best product.)

 

[J-Vo]

Quel Trimix pour quelle plongée : exemples et (…) - Club de plongée d Aix les bains, lac du Bourget (Savoie)

Interesting (even through Google Translate) comparison of GF to COMEX tables. I would be grateful to get @Dr Simon Mitchell 's input on it.

 

[leadduck]

I don't think that one has gas switches though. It's an interesting question because by strictly Haldanean model if you ride your chosen M-value line continuously, you're off-gassing most efficiently the whole time. Until you change the gas.

Even with gas switches, you’re still off-gassing at max efficiency.

Hmmm... I wonder if integral supersaturation is the correct measure here... That graph does look counter-intuitive.

According to Wikipedia, "Efficiency is the (often measurable) ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without waste."

"Without waste" means that efficiency is about finding a good spot in a cost-benefit trade-off; it does not mean "maximize speed without regard to cost." In the context of decompression, I'd say efficiency means finding the ascent with smallest DCS risk for a given TTS; or equivalently the ascent with shortest TTS for a given DCS risk. The concept of Pareto efficiency makes sense here.

A useful metric for DCS risk comparison is integral supersaturation. Probabilistic decompression models use ISS. Finding the ascent that really minimizes ISS for a given TTS is a problem of calculus of variations, which is quite tricky and not available in dive computers or planning software.

Following the ceiling calculated by the Bühlmann model is much easier, but is not equivalent. It limits the peak supersaturation, but ignores time and does not minimize integral supersaturation. In some trivial situations this is obvious: when decompressing with 100% oxygen, following the ceiling will only increase DCS risk but not improve off-gassing. But also after a gas switch from 18/45 to EAN50 as shown above, there are solutions that reduce ISS without increasing TTS.

 

[J-Vo]

But also after a gas switch from 18/45 to EAN50 as shown above, there are solutions that reduce ISS without increasing TTS.

This only makes since with regard to the He. Once you throw in the N2 loading in parallel your increasing your TTS. Some compartments may even begin on gassing N2 at the switch.

EDIT: (Typo)

 

[boulderjohn]

The last couple pages of this article might be helpful.

 

[dmaziuk]

What I wonder is, if for helium the models give right answers for wrong reasons, does that also extend to ISS calculations.