GF LO

[cathal]

Adding 2 or 3 minutes to a 3 min "obligation" is doubling your deco for basically no effort at all.
Adding 2 or 3 mins to 4 hours of deco is not a substantive change.

I will always stay longer than required if its meaningful and helpful.

Agreed. As a general point on this issue and to paraphrase Dr.Dolette, adding extra time to your shallow stops is the cheapest form of dive insurance there is.

 

[Capt Jim Wyatt]

despite what my student tried to tell you at Ginnie I’m typically running a 50/75 or 50/80 -Ben

Roger that @DiveTucson --

 

[kensuf]

These last few posts have been reassuring. Because while I don't have a fraction of the experience @kensuf has, the comment below seems slightly backwards. After noting that with short deco he'll pad an extra few minutes (prompting my estimate of what his actual surfacing GF99 might be), he then noted that with long deco obligations, he'll stick right with the plan:

Now I understand a reluctance to spend any more time than you have to in deco, especially on a long dive. But I don't understand why GFLo 80 with three minutes of padding (e.g, surfacing GF of 74) is desirable for short deco, but on a long dive (with even more filling of slow tissues that are not as resistant to kissing the M-factor as fast tissues might be), one not only doesn't pad, but chooses a higher GF as well?
I'm not picking on you, @kensuf . I just don't understand the logic, beyond "I feel fine". If 85 is your comfort zone, then so be it. But if something is making you wait to 74 on an easy dive, then why is 85 okay when your loading is greater? I understand a reluctance to add 30 min of deco to get to 74, but then why bother with it on a short dive?

If there's some doubt prompting you to add 3 min when it's easy, it seems like normalization of deviance to skip it when the price is higher, e.g., 30 cu ft more oxygen. Help me understand how you chose this.

And you're not alone: @rjack321 does the same thing, I think:

I don't get it.

The 80 is my GF hi on short dives. The GF lo is 50.

I think we mostly all agree that straight Buhlmann is too aggressive and increases the risk of DCI. So, let's start off with saying that a GF Hi of 100 is a bit too aggressive for almost all dives, except maybe in an emergency where the risk of certain death is greater than the risk of getting bent.

Remember, GF hi is based on padding the M values as established by the stock generic Buhlmann algorithm. The lower your GF hi, the greater the padding.

GF 50/100 - 90' for 50 minutes:
30' - 1 minute
20' - 1 minute * switch to O2
10' - 1 minute

GF 50/95 - 90' for 50 minutes:
30' - 1 minute
20' - 1 minute * switch to O2
10' - 2 minutes

GF 50/90 - 90' for 50 minutes:
30' - 1 minute
20' - 1 minute * switch to O2
10' - 3 minutes

GF 50/85 - 90' for 50 minutes:
30' - 1 minute
20' - 1 minute * switch to O2
10' - 4 minutes

GF 50/80 - 90' for 50 minutes:
30' - 1 minute
20' - 2 minutes * switch to O2
10' - 5 minutes

GF 50/75 - 90' for 50 minutes:
30' - 1 minute
20' - 2 minutes * switch to O2
10' - 6 minutes

It seems silly, but personally on a dive with this kind of profile, I feel better sitting until my SurfGF is 80 than 85. Total difference in time is 2 whole minutes, not a big deal in the grand scheme of things, but the deco is more than double a SurfGF of 100.

Now let's look at what happens when the deco obligations start getting longer and longer.

Let's say a dive profile (50 minutes @250') running straight Buhlmann calls for a total run-time of 211 minutes, with 72 minutes at 20' and 10'. Same dive profile, but with 50/85 calls for total run-time of 237 minutes with 85 minutes at 20' and 10' (a padding of nearly 30 minutes total deco and a bakers dozen extra minutes at 20' and 10'). And same profile with 50/80, 245 minutes total r/t, 90 minutes total at 20' and 10' (+34 minutes total / +18 minutes shallow).

Running straight Buhlmann on a dive like that will likely leave me a pretzel, and while running 50/80 on a dive like that will leave me fine, I've also personally found that 50/85 on a dive like that will also leave me fine.

Summary: On a really short deco, I personally prefer to be more conservative because I feel better. On a really long deco, where the padding enabled via GF gets further away from the Buhlmann M-values, I feel fine running a slightly higher slope.

 

[rddvet]

Well it appears I jinxed myself by posting about my gf. Did about 80 minutes scooter dive at ginnie on ccr gf 50/70 and 30/30 diluent about 15 minutes. Ive got mild skin bends and some visual disturbances. Good news is this morning before the dive I had a consult to close my pfo

 

[Jack Hammer]

I pad short deco by a few minutes simply because I don't like riding the edge a hypothetical line of where deco is "required" versus not necessary.

 

[grantctobin]

Well it appears I jinxed myself by posting about my gf. Did about 80 minutes scooter dive at ginnie on ccr gf 50/70 and 30/30 diluent about 15 minutes. Ive got mild skin bends and some visual disturbances. Good news is this morning before the dive I had a consult to close my pfo

Gnar, especially on mild dive. You going w Doug?

 

[rddvet]

Gnar, especially on mild dive. You going w Doug?

That's what makes no f'ing sense. My average dive for the past couple years averages 30 minutes of deco, especially swimming. This was a lazy scooter dive, minimal exertion, and minimal deco comparatively. It's just proof that no matter what you set your gfs or how you dive, there's so many other factors that play into it that it's a crap shoot. Especially when you add the pfo into it. I looked at my logs and it's been about 2.5 years since I had any major symptoms till today.
I went to Dr Ebersole to get the echo to diagnose it and would love for him to close it, but he and the hospital he would do it at are out of network. So my out of pocket costs would be $28,600. So I came up to gainesville to see a cardiologist who's done quite a few cave divers. Dr Ebersole was prepared to do it anytime I wanted with no additional testing. The gainesville cardiologist requires a sedated Transesophageal Echocardiogram prior to scheduling the closure. So I've got to set that up, then after set up the closure. I think since Dr Ebersole's research focuses on divers and pfo's he doesnt require the additional test, whereas most cardiologists aren't doing a million closures for dive reasons and so take extra precautions. Not a huge deal in the grand scheme of things. Of course now my wife (while we were at my appointment) got a call of a job offer that likely will offer insurance that's in network for Dr Ebersole. If so, then I'm probably just going to go to him.

 

[Capt Jim Wyatt]

Good luck @rddvet

 

[Couv]

Good luck @rddvet

Ditto.

 

[kensuf]

That's what makes no f'ing sense. My average dive for the past couple years averages 30 minutes of deco, especially swimming. This was a lazy scooter dive, minimal exertion, and minimal deco comparatively. It's just proof that no matter what you set your gfs or how you dive, there's so many other factors that play into it that it's a crap shoot. Especially when you add the pfo into it. I looked at my logs and it's been about 2.5 years since I had any major symptoms till today.
I went to Dr Ebersole to get the echo to diagnose it and would love for him to close it, but he and the hospital he would do it at are out of network. So my out of pocket costs would be $28,600. So I came up to gainesville to see a cardiologist who's done quite a few cave divers. Dr Ebersole was prepared to do it anytime I wanted with no additional testing. The gainesville cardiologist requires a sedated Transesophageal Echocardiogram prior to scheduling the closure. So I've got to set that up, then after set up the closure. I think since Dr Ebersole's research focuses on divers and pfo's he doesnt require the additional test, whereas most cardiologists aren't doing a million closures for dive reasons and so take extra precautions. Not a huge deal in the grand scheme of things. Of course now my wife (while we were at my appointment) got a call of a job offer that likely will offer insurance that's in network for Dr Ebersole. If so, then I'm probably just going to go to him.

Just get it done and quit dicking around with it.