Error 130 dives on Fake Nitrox

[tursiops]

“Suppose you are doing NDL diving with a GF-hi of 95, because you like long dives. But you've also noticed that now and then, perhaps on the third dive of the day you surface with an aching shoulder and an itchy chest. Maybe GF-hi 95 is too aggressive. Drop back to 85 and see if that helps. If it does, maybe bump it back up to 99 and s÷ if that is still ok.And you need many dives to sort this out”
You wrote this ^^^^^
I don’t see anything about stopping diving, getting on O2 and calling DAN.
You mention dropping back to 85 and trying again.
Then you say if it seems ok to bump it back up to 99 and see if it’s still OK.
Are you nuts??

You are trying to hard to make this an issue. I was discussing what to do about GFs, NOT what to do about DCS.
Sorry, 99 was a typo; I meant 90...that is, edge back up from 85 if 85 sems OK. (I changed it from 99 to 90 in the post)

 

[crofrog]

Pain in joints, skin itching...

View attachment 875305

Sleepiness / fatigue

 

[tursiops]

Sleepiness / fatigue

Yep, this is my first symptom.
I DM'ed for a while with a shop that did dives on the west coast of Oahu to a wreck at 90 ft. The dives were all on air. Most of the dives were to my NDL, often working harder than I'd like to get don't-dive-very-often-customers up to the safety stop and then doing air-sharing on the hang bar. Second dive on a modest reef, not deep, not near NDL. I was often exhausted after the two dives, and sometime would have to pull off the road and snooze as I drove home. I don't feel that way on 90-ft dives anymore, but now I don't use air, I stay away from NDL, and I now dive 70/85 instead of my old Oceanic GF 95 (approx).

 

[OctopusLover]

Well, it's funny the conversation has ended up into preventing "mild DCS".

Let me offer my own strategy that I'm frankly surprised isn't more common: dynamic long safety stops driven by Shearwater Gf99.

I don't do 3 mins at 5 meters. I ascend until Gf99 is at 40-50%. This is usually above 5 meters. Then I keep ascending to keep Gf99 at that value until I either hit the surface or SurfGf is 60% and I can't be bothered.

Effectively, I treat every dive as a deco dive with a GfHi of 60. Believe it or not, this procedure takes 5~ minutes and routinely takes my SurfGf from 75-80% to 60%, whereas a normal safety stop would barely reduce it.

Since I started doing this, I feel nothing even after 4 dives a day on liveaboards, routinely hitting <5 minutes NDL with my GfHi at 85.

 

[LFMarm]

Well, it's funny the conversation has ended up into preventing "mild DCS".

Let me offer my own strategy that I'm frankly surprised isn't more common: dynamic long safety stops driven by Shearwater Gf99.

I don't do 3 mins at 5 meters. I ascend until Gf99 is at 40-50%. This is usually above 5 meters. Then I keep ascending to keep Gf99 at that value until I either hit the surface or SurfGf is 60% and I can't be bothered.

Effectively, I treat every dive as a deco dive with a GfHi of 60. Believe it or not, this procedure takes 5~ minutes and routinely takes my SurfGf from 75-80% to 60%, whereas a normal safety stop would barely reduce it.

Since I started doing this, I feel nothing even after 4 dives a day on liveaboards, routinely hitting <5 minutes NDL with my GfHi at 85.

I do the same but dive even more conservative GFs — starting with 50/60 for low exposure dives (PrT<31) and reducing GFs to follow the XVal 2.3% Isorisk curve from Doolette / NEDU until reaching the lowest GFs I use 33/40 for saturation dives (PrT>43).

If dive conditions allow, I lower SurfGF even more by spending longer time shallow.

While this is still empirical (I don’t plan to test my DCS tolerance by pushing GFs), it uses the NEDU Isorisk curves for 2.3% risk so it’s somewhat based on human physiology.

Using this approach I never felt tired even after long decks decos. I am sure I could be more aggressive but don’t feel the need for the ropes of diving I do.

 

[Stoo]

And this, boys and girls, is EXACTLY why you analyze every tank, every dive. If you're diving nitrox, you should own your own analyzer and you need to take it with you when you travel. That way you don't need to take the DMs word for what you're breathing, and you don't need to wait to use the boat's analyzer that's shared between 16 people.

 

[LI-er]

The diver in question probably did most of his dives in a group setting, and the dive times were limited by the biggest air hogs of the bunch. If this diver did more on their own, and experienced longer dives as a general rule, odds are they would have run into a problem.

If he logged his dives it would be easy enough to figure out if this was the case.

You can't change the laws of physics Captain. - Scotty circa star date 3021

 

[justinthedeeps]

Lots of people could probably do this and not get bent (though not all...)
The military counts on it (or did?)

People play around with helium like this too and end up dead
There was a high profile tragedy with someones repetitively diving 10/50 and telling the computers it was 10/20

 

[OctopusLover]

And this, boys and girls, is EXACTLY why you analyze every tank, every dive. If you're diving nitrox, you should own your own analyzer and you need to take it with you when you travel. That way you don't need to take the DMs word for what you're breathing, and you don't need to wait to use the boat's analyzer that's shared between 16 people.

Not sure you've understood the situation. This diver never thought they were using Nitrox, never analysed a tank or had anyone analyse it for them. They knew they were on air, just the computer was misconfigured all along.

The diver in question probably did most of his dives in a group setting, and the dive times were limited by the biggest air hogs of the bunch. If this diver did more on their own, and experienced longer dives as a general rule, odds are they would have run into a problem.

If he logged his dives it would be easy enough to figure out if this was the case.

You can't change the laws of physics Captain. - Scotty circa star date 3021

Well, no. They explicitly mentioned this was far from the first time they dove in a group where everyone else was on Nitrox (they had done many liveaboards) and had never felt them being on air was in any way a problem (the irony lol). They in fact seemed confused as to why everyone else cared about Nitrox when they were on air and doing the same as Nitrox divers. They quoted people explaining to them that "they dove Nitrox for extra safety", and didn't really seem to grasp that there were any functional differences beyond this extra safety.

My theory is that every safety stop this person did when diving with Nitrox groups, was actually a deco stop and if they had ever emergency ascended towards the end of the dive they'd have had DCS symptoms.

 

[LI-er]

Well, no. They explicitly mentioned this was far from the first time they dove in a group where everyone else was on Nitrox

Well, yes. Like I figured, most of his dives were in group situations, so the dives were probably limited by the diver with the most rapid gas consumption. "Far from the first time" is roughly equal to "much or most of the time".