GFHi - practical meaning?

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I know the replies here are more referencing deco dives when suggesting GF85 as being 'ballsie', but it seems that on basic rec computers, at least for the 1st dive they mimic GF95 (my observation with my Perdix vs my Mares RGBM. Not sure what it's like with repetitive dives yet). With this being used by people mostly ignorant of deco stress ( eg. riding NDLs), why are not more divers heading to the chambers? As was mentioned in another thread, rec divers are often experiencing more dec stress than deco divers, so shouldn't these computers be even more conservative of at least GF85?.

On a dive within recreational limits the faster tissues are the limiting factor, from what I recall the faster tissues can tolerate a higher level of supersaturation. On a deco dive you typically have slower tissue compartments as the limiting factor, which may not be able to tolerate that same amount of supersaturation. In addition, how you set GF-Low also plays a role in whether you bend or not.

I'd also argue that while rec dives may experience a higher level of supersaturation, they in fact experience less deco-stress overall as their integral super-saturation is much lower.

I know that for me, on a typical 200 ft dive in coldish (45-55) water I am comfortable exiting with a SurfGF of 85. For a dive with high stress or a lot of work on the bottom I'll extend my last stop until I feel good getting out of the water. I'll also add that while not an athlete I don't consider myself old or fat :D
 
I'd also argue that while rec dives may experience a higher level of supersaturation, they in fact experience less deco-stress overall as their integral super-saturation is much lower.
Is there a way that we can compute ISS from our dive computer output after the fact?
I can look at a spreadsheet and plot out values for various compartments, but it would be nice to fit a curve to a dive and look at that data somehow...
 
Most of my questions in the OP have been answered Recreational Ascent Rate in the last 15 feet

I know the replies here are more referencing deco dives when suggesting GF85 as being 'ballsie', but it seems that on basic rec computers, at least for the 1st dive they mimic GF95 (my observation with my Perdix vs my Mares RGBM. Not sure what it's like with repetitive dives yet). With this being used by people mostly ignorant of deco stress ( eg. riding NDLs), why are not more divers heading to the chambers? As was mentioned in another thread, rec divers are often experiencing more dec stress than deco divers, so shouldn't these computers be even more conservative of at least GF85?.

I don't think the actual GFHi setting (in Rec) is too relevant*; it's what your surface with (SurfGF) that is (certainly relatively, probably absolutely). And from what we've seen on threads between Tec and Rec there appears to be convergence on that number roughly close to 70.

*that then leads to the question for Rec; is how you arrive at a SurfGF/GF_Current(aka 99) (on the surface) important? I don't think it is that much because of where stops would be ... here's my (amateur) thoughts on that quoted from this thread: What's your SurfGF and how does it compare to your (Rec) GFHi?

FWIW I'm diving with 99/99 for GF. My SurfGF is usually in the 50's, sometimes 60's, seldom in the 70's. Which mean's I am diving a reverse GF*. In practical terms it's probably averaging 80/55. I tend to take it very easy from 10m and shallower, and super-slow from my 6m SS (5 min) to the surface. On deeper squarish dives to ~40m, gas isn't an issue, so as long as I achieve my SurfGF I'm not too worried about seeing NDL=0. It's dives with a shallower average depth that I need to check I've got enough gas to get my SurfGF down even though NDL is farther from the limit; with 50bar reserve, my NDL and gas limits intersect at an average depth of 16m on GFHi of 99 (SAC is 1bar/min for AL80).

I wanted to somehow assess the wisdom of this seemingly aggressive GFHi and for the occasional dives where NDL get's pushed below 5min remaining. Here's my thought process:

At max Rec depths (or slightly beyond) on Air, a 40m dive for 20min produces stops from 9m for GFLo's between 60-83 with 24-27mins of deco using a GFHi of 70. GFLo83+ is 6m stop depth.

Reducing the deco time to something closer to 'light' deco, say a 40m dive for 15mins, with a GFHi of 70, a GFLo of 65+ results in 12min of total deco starting at 6m. With a GFHi of 60, 6m stops are produced from GFLo of 70+

Given GLo has less of an effect on the depth of the first stop as max depth becomes shallower, at 30m for 25min produces 15mins of deco starting from 6m for GFLo 53+

To me, this reinforces SurfGF targeting, long SS and super slow ascent as per Recreational Ascent Rate in the last 15 feet

That in turn (perhaps) defocuses NDL at depth ... because:

The difference between GFHi of 90 & 99 is 3 mins at 30m, 2min at 40m. Between GFHi 80 & 99 it's 6 and 3mins respectively. i.e. not massive differences at depth and it's just a question of gas supply and time availability at/near SS depths. Secondly there's seems almost/no difference between doing what I'm doing and say very 'light-deco' on a lower GFHi and a higher GFLo provided I'm slow from 10m and shallower.

re Reverse GFs: *The question of whether the actual (self adjusted) m_value line I'm following is a reverse hockey-stick (like merely padding the SS), or is a modified linear mayn't be too relevant for Rec depths.

(p.s. I realise/agree on a NDL dive GFLo plays no effective role).

Thoughts? Holes in my logic? and who else dives a similar NDL/SurfGF style?

Having said all that, that general comment for Rec might additionally also seem to hold true if for all Rec profiles the above comment re ISS from @njdiverjoe holds true (assuming Tec and Rec generally surface with the same GF).
 
Is there a way that we can compute ISS from our dive computer output after the fact?
I can look at a spreadsheet and plot out values for various compartments, but it would be nice to fit a curve to a dive and look at that data somehow...

As far as I know there isn't any off the shelf software that can accomplish that. If you find out otherwise I would like to know as well!
 
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You might be able to do something yourself. If you have a graph of the ss (supersaturation) take three x,y points from the graph and plug them into "Equation Generator". Equation generator is a free app on the net. Equation generator will create an equation for the line on the graph. Take that equation and plug it into another free app on the net (equation solver), solving for the integral to get your result.
 
A GF/Hi of 85 means that a friend of mine ends up in the recompression chamber because he was 15% off the maximum and succumbed to other factors that the computer was not aware of (being cold, overweight, 40+, in bad aerobic shape, carrying heavy gear and so on).

A GFHi of 85 means VVAL, DCIEM, and ZH-L16 all agree on your friend's chances of ending in a recompression chamber: Fraedrich follow-up – The Theoretical Diver -- nothing more nor less.

It also means that if you actually in deco, then your leading tissue compartment's gas loading upon surfacing can be back-calculated from Buhlmann's "ceiling" reduced by GFHi: pin the ceiling at the surface and calculate tolerated tissue overpressures for that depth -- keeping in mind that IRL you may never actually reach that calculated value after all the off-gassing done at previous stop.

On a no-stop dive direct ascent to the surface will keep it at or below that value; if you do your safety stop it's always guaranteed to be the latter.
 
You might be able to do something yourself. If you have a graph of the ss (supersaturation) take three x,y points from the graph and plug them into "Equation Generator". Equation generator is a free app on the net. Equation generator will create an equation for the line on the graph. Take that equation and plug it into another free app on the net (equation solver), solving for the integral to get your result.
For those interested, Microsoft Excel will also generate your equation. Highlight your points, and click Insert. Pick "2-D Line". After line-graphing your points (not just three, but as many as you want), right-click on the line. From the drop-down menu, choose "Add Trendline". A window will appear on the right of your screen listing six different types of equations to fit to your line. Use the one that fits best (don't forget the option of increasing the order of polynomial equations), and then click the box that says "Display Equation on Chart."

Now I've got to go find Equation Solver and figure out how to use that to generate an ISS. If anyone wants to chime in, that would be great! If my line graph of supersaturation yields a result like y = .35x² + .9x (yeah, I know - way too simple an equation), I assume y will be my desired ISS result. But what does "x" represent? Excel's equation generator isn't generating an integral equation, but rather (in this case) a polynomial one. Where is my thinking going wrong?
 
What is "integral supersaturation" anyway? E.g. Dr. Doolette back in 2011 used the term for "representative fast (τ = 10 minutes) and slow (τ = 160 minutes) compartments and their sum for each of 504,271 hypothetical dive profiles" -- I'm assuming we're not talking about simulating half a mil hypothetical profiles in an Excel spreadsheet?
 
What is "integral supersaturation" anyway? E.g. Dr. Doolette back in 2011 used the term for "representative fast (τ = 10 minutes) and slow (τ = 160 minutes) compartments and their sum for each of 504,271 hypothetical dive profiles" -- I'm assuming we're not talking about simulating half a mil hypothetical profiles in an Excel spreadsheet?

It's simply a measure of the total supersaturation exposure for the entire dive profile. In the paper you reference they look at the integral supersaturation of the two different compartments and how it changes with respect to the 504,271 hypothetical dive profiles.
 
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