Riding GF99 instead of mandatory/safety stops

[L13]

In my case I am diving most of the time 50/60 so I would make sure that GF99<60 all the time. Thank you

If @EFX is right about how GF99 is calculated, you would have to reduce GF99 << 60 before each gas switch to prevent it from exceeding 60 immediately after the switch.

 

[BlueTrin]

If @EFX is right about how GF99 is calculated, you would have to reduce GF99 << 60 before each gas switch to prevent it from exceeding 60 immediately after the switch.

Are you saying he’s not right?

 

[LFMarm]

If @EFX is right about how GF99 is calculated, you would have to reduce GF99 << 60 before each gas switch to prevent it from exceeding 60 immediately after the switch.

I don’t know who is right. Just on pure logic, if this statement is true, then the same applies also to following deco stops (squared profile): if you switch your gas while at a stop, your GF99 might exceed the line between GF_low and GF_high, which means you are out of your chosen conservatism.

 

[L13]

If @EFX is right about how GF99 is calculated, you would have to reduce GF99 << 60 before each gas switch to prevent it from exceeding 60 immediately after the switch.

Are you saying he’s not right?

Yes.

Gas transport (to determine tissue inert gas loading) is calculated using partial pressures.

GF's are calculated using total inert tissue pressure, and total ambient pressure (as well as M-value based on depth pressure and gas mix).

 

[L13]

I don’t know who is right. Just on pure logic, if this statement is true, then the same applies also to following deco stops (squared profile): if you switch your gas while at a stop, your GF99 might exceed the line between GF_low and GF_high, which means you are out of your chosen conservatism.

Exactly.

Changing your deco gas does not change your GF (and unless Shearwater did something very weird, does not change your GF99). If the GF99 equation used inert ambient partial pressure, instead of ambient total pressure, it would.

 

[inquis]

Can you safely follow GF99 and forget about discrete deco stop as long as GF99 is always below your accepted conservatism?

If you're talking about riding the instantaneous ceiling (GF99 == GF Line over time), maybe? The issue is that testing is severely lacking when making such continuous ascents. TBH, I wonder if *any* testing has employed continuous ascents. Plus, the various reasons previously laid out for staged/stepped stops make a ton of sense (task loading, etc.).

I am diving most of the time 50/60 so I would make sure that GF99<60 all the time.

Ok, but how much under 60? If you just keep it locked at 60 (i.e., ascend a little when it drops to 59), then you're effectively running GF 60/60. I know of no deco scientists who run equal GF factors. That said, 60 is pretty conservative. Judgement call.

Back to some of the statements made early in the thread (I think it was this thread!): the Navy's algorithm has the allowable supersaturation parallel the ambient pressure. Doolette runs GFLow = 0.83 * GFHigh to approximately achieve that with the Buhlmann+GF algorithm. Mitchell's GFLow is under his GFHigh. I'm sure some people run equal factors; again, judgement call. I'm personally inclined to mirror the experts' practice for normal dives, and perhaps resort to equal GF factors in an emergency when I need to shallow up quickly.

ETA: Just clued into the first part of your statement I quoted. if you're following GF 50/60, that answers the question of "how much under 60", and is in line with the experts' practices, though more conservative than I think they run. Not necessarily a bad thing.

 

[BlueTrin]

I am with @inquis for continuous ascent, unless you can find that people have tried that and tested it, you wouldn’t know if it is a safe practice.

But at the same time, since people fudge a GF factor over Buhlman it’s likely that you’d find a GF Hi/Lo that’d work for you unless something is fundamentally broken with continuous ascent? (only ranting here because well you probably just need to gather more data to know? Maybe try to find some papers/test data?)

Disclaimer: I don’t know much about all of this tbh

 

[kaylee_ann]

I even have a ton of bags of popcorn, and didn't think to make one before reading the whole thread. Smh.

 

[dmaziuk]

What would be the point of that?

The point would be that Haldane's tables did not count inspired inert gas separately, that only started with Workman. Finding out why that was, and figuring out why his reason does not apply to ambient pressure in Earth atmosphere, is left as an exercise to the reader.

Yes, we could do it. There's just no point, exactly as you say.

 

[dmaziuk]

I don’t know who is right. Just on pure logic, if this statement is true, then the same applies also to following deco stops (squared profile): if you switch your gas while at a stop, your GF99 might exceed the line between GF_low and GF_high, which means you are out of your chosen conservatism.

If your computer calculates GF99 relative to the phase of the Moon in the House of Jupiter, your mileage will of course vary. But if you're calculating it relative to your current conservatism setting: GF Low..GF High, then at a stop your controlling tissue is at its M-value and its current overpressure is right on the line between GF Low and GF High and dropping. If you switch to a lower N2% gas, it will be dropping faster.