Any reported cases of Ox Tox between 1.4 and 1.6?

[davehicks]

I got bent at least three times last year, doing multiple single tank, nitrox dives and I go up to 1.6 and follow a computer.

I hope that proves I'm "right" on this issue. LOL

Sounds like I'm making a joke, but two of them were skin bends that hurt for a few days and the other was more serious - significant back pain that developed within 5 minutes of surfacing.

I "treated" myself for the back hit by going back down to about 38 feet (where I got instant and complete pain relief) and then spent 20 -25 minutes coming up, all done on the remaining nitrox in my tank- this happened on the first (only) dive of the day.

That is actually kinda funny now that I think about it; not only did a single tank have enough gas to get me bent (after I did a safety stop no less) but I had enough left over in the same tank to do a redneck deco (IWR) treatment. I came up feeling fine and drove in to a beach picnic and then went snorkeling afterwards, however I was using a large steel tank - maybe a 120.

Yeah use a computer.

Maybe see a doctor. You should not be getting bent that often even if you are being less than careful.

 

[justinthedeeps]

It can't be simple ppO2 numbers, 10+ other personal and situational factors strongly affect both DCS and toxicities

Is someone relaxed at 80 metres on air safer than someone jellyfishing on nitrox at 40 metres? Anecdotally some old timers might agree, but where is the data? It doesn't exist

Experienced photography divers in the tropics (e.g. Lembeh, Anilao) go into NDL/deco on single EAN32 AL80s all of the time, even on ScubaPros at '90/90' or whatever, lots of time sitting relatively still in the ~25 metre depth range. I don't think any of them have ever toxed (?)

Rebreather divers do 300% CNS dives quite regularly on 3+ hour dives with minimum ppO2's of 1.3 and extended (2+ hour) phases of 1.4 and 1.6, throw in some token 'air breaks' because otherwise it's boring as hell sitting there so long not toxing

 

[rjack321]

Is someone relaxed at 80 metres on air safer than someone jellyfishing on nitrox at 40 metres? Anecdotally some old timers might agree, but where is the data? It doesn't exist

Actually it does, although not for those exact gases. Deeper is quantitively more risky for any given set of GFs

 

[rsingler]

I got bent at least three times last year, doing multiple single tank, nitrox dives and I go up to 1.6 and follow a computer.

I think the focus on O2 is not relevant. Ox tox is the "other" gas from the bends, of course.
So my question would be: what were your gradient factors? And if you're not using a computer with GF, but rather "Conservative, Normal, High", or I, II, III, then after three hits I'd really recommend a Shearwater.

 

[rob.mwpropane]

@johndiver999 if you're getting bent why not adjust the dive to suit your body? Maybe move slower, more conservative settings? Honest question, not trying to point fingers. Lots of people get bent, but its obviously a sign something isn't right, yeah?

 

[flymolo]

throw in some token 'air breaks' because otherwise it's boring as hell sitting there so long

Is this tongue in cheek or are you saying air breaks aren’t necessary

 

[johndiver999]

I think the focus on O2 is not relevant. Ox tox is the "other" gas from the bends, of course.
So my question would be: what were your gradient factors? And if you're not using a computer with GF, but rather "Conservative, Normal, High", or I, II, III, then after three hits I'd really recommend a Shearwater.

It is some model of an old oceanic computer. I have several, Don't think it has any adjustments, I just try to set the alarm at 1.6, generally punch in one percent less oxygen (to be safe - and to make the chamber operator laugh if I really need a ride) and I don't violate it and come up slower than prescribed from 50 feet and generally add a minute or two of a safety stop after it says "all clear". I've also been trying to breath left over nitrox for 10 minutes on portions of the surface interval - when convenient.

On the other hand, I often do three pretty aggressive dives in a day with exposures on one side or the other of the NDL.

 

[GF99/99]

First off, I'm not looking to start a 1.4 vs 1.6 debate! The conventional wisdom of 1.2-1.4 for diving and 1.6 for deco is perfectly sound.

I've been poking around on this subject for a while now though, and what I can't find is how exactly the 1.4 idea came about. I know there are loads of cases of Ox Tox at 1.8 and above, and that it's known to be really insidious. There's a great anecdote in The Last Dive about a diver who thought 2.0+ was fine, he actually got away with it for a dozens of dives before it finally bit him and he didn't come back up.

Are there any documented cases in literature, or even just well known examples, where divers had a seizure somewhere below 1.6? Or has theory just advanced to the point where we can say that odds are, it will bite someone sooner or later?

I am not entirely sure what you are trying to get at with your question. Reason I say this is because your forgetting the time factor. Remember its your exposure duration in relation to the O2 level is that causing O2 toxicity. You can have an o2 tox diving 1.0 in theory. When I do 500min cave dives ill rack up 100%+ CNS sometimes and that is diving between 0.5-1.0 (almost never am above 1.0 unless I'm on deco)
Perfect example, my dive a couple days ago 92% CNS

So to answer your question where does the 1.4 idea come from, my thoughts were always because of time (I am just assuming this). If you look are "XYZ" agencies CNS clock you will see that as you increase the PPO2 your CNS starts to rack up exponentially, especially between 1.6-2.0 its actually pretty crazy quickly it can sky rocket at these PO2's. So I am assuming most adopted 1.4 as a reasonable balance that gives you lots of time to dive at 1.4 while still keeping a very low CNS. And then where does 1.6 on deco come from. Well same thing, it is a balance where you still get very effective deco off gassing but for your "average" technical diver your still not racking up crazy amounts of CNS. In addition if I remember correctly there were some papers also showing supporting evidence that CO2 and high CNS can be linked to O2 convulsions, hence when if your going to be on a high Po2 it is on deco where you are not on the "working" phase of the dive.

To answer your question about documented cases, well I am sure if you look there are cases, especially in the CC world. But as I mentioned earlier time plays just as much of factor as the Po2. So I don't know how relevant just looking only at the PO2 is. Not to over exaggerate but theory diving at 1.8 for 5min would be safer than diving at 1.2 for 500min.

For your question about biting someone sooner or later. Well that is almost impossible to say. Way to many uncontrolled "human body" variable to determine when someone will have an O2 tox incident.

On a side note and I think @crofrog first started to elude to it was that running high Po2's is not necessarily always a good thing and I am not to sure why so many have this fixation with diving 1.6. Not to open up a can or worms but I do a lot of sub 150m diving and on deco I mostly just run 1.4. Alot of my dives end up with 300min+ of deco and if you run your dive plan through "XYZ" deco software you will see that running 1.4 on your unit only gives you maybe 15min more of deco vs. running 1.6 and doubling your CNS

Perfect example of a typical 180m dive I would do:
Running 1.4 for deco; Dive time 323min with 187% CNS

Exact same thing but running 1.6 on deco; Dive time 306min with 433% CNS

Save 17min of deco but racked up 246% more CNS. 17min more in the water for a dive like that in the grand scheme of things is nothing compared to the risk of O2 tox.

 

[johndiver999]

@johndiver999 if you're getting bent why not adjust the dive to suit your body? Maybe move slower, more conservative settings? Honest question, not trying to point fingers. Lots of people get bent, but its obviously a sign something isn't right, yeah?

I'm trying to extend my stops, be aware of my exertion level, generally move around during the stop, try to make sure we have oxygen on the boat, etc.

 

[scubadada]

I got bent at least three times last year, doing multiple single tank, nitrox dives...

It is some model of an old oceanic computer...

...On the other hand, I often do three pretty aggressive dives in a day with exposures on one side or the other of the NDL.

As one of my computers, I have been diving an Oceanic running DSAT since 2002. I changed my backup to a Dive Rite Nitek Q in 2016 to learn Buhlmann.and switched to a Shearwater Teric in 2019.

DSAT runs reasonably close to a GF high of 95 so is liberal/aggressive for both no stop and light deco diving. I also dive aggressively. I used to do the equivalent of an adaptive safety stop when close to NDL and padded my safety stop. With my Teric, I simply follow SurfGF and have not surfaced with a GF above 80.

I have never been bent. Personally, I would be extremely concerned if I was bent once, let alone 3 times. It sounds like you need to make changes in you dive profiles before something disastrous happens. Consulting a dive physician would be a good idea.