OXTOX limits - MOD, PPO2 or CNS Clock?

[DiveNav]

......Again... This is not "THE LAW" - but a guideline. 45 minutes at 1.6 doesn't mean that 46 minutes will cause tox.

My question would be ...what about if you cross the 1.6 threshold? and go to 1.65 .. or 1.7?
Immediate tox? Or after a while?

Not that I am planning to do that any time soon ... but I would like to know so we can fine tune our algorithm.

 

[DiveNav]

Is the "Time" on your chart below really in Hours?

It seems so

 

[HowardE]

My question would be ...what about if you cross the 1.6 threshold? and go to 1.65 .. or 1.7?
Immediate tox? Or after a while?

Not that I am planning to do that any time soon ... but I would like to know so we can fine tune our algorithm.

Absolutely not. That is the point of this thread. People are under exactly that impression and this is why this discussion started.

 

[ScubaFeenD]

Im really glad someone started this thread; it has been an interesting read.

I have to say that I tend to agree with HowardE that the way MOD and ppO2 is taught is not optimal. 1.6 is clearly not an absolute limit, while 1.4 is not necessarily safe even though it feels like that is the way it is taught. It harbors both unrealistic understandings of the physiology, unsubstantiated fears, and complacency about ppO2 of 1.4. Now that I think about it, its all taught pretty poorly :-/

 

[HowardE]

I'm not endorsing a cavalier attitude toward PO2, but just for people to take a realistic approach to MOD's and what it means to exceed 1.6 in an emergency. I still plan my dives to be below 1.4 PPO2 for the working portion, and use 1.6 as a max PPO2 for deco. But there's more to it than that, and that is what I wanted to express.

 

[ScubaFeenD]

I'm not endorsing a cavalier attitude toward PO2, but just for people to take a realistic approach to MOD's and what it means to exceed 1.6 in an emergency. I still plan my dives to be below 1.4 PPO2 for the working portion, and use 1.6 as a max PPO2 for deco. But there's more to it than that, and that is what I wanted to express.

Indeed. Its sad that real education has taken a back seat to the "just do this" approach.

 

[Jax]

And who said that?

So, if the recommended limit for 1.5atm is 83minutes and the one for 1.6atm is 45min, I just can't see why the limit for 1.601atm should be 0min .... human body doesn't work like that ... in fact I think I saw the table below somewhere ...

My question would be ...what about if you cross the 1.6 threshold? and go to 1.65 .. or 1.7?
Immediate tox? Or after a while?

Not that I am planning to do that any time soon ... but I would like to know so we can fine tune our algorithm.

Im really glad someone started this thread; it has been an interesting read.

I have to say that I tend to agree with HowardE that the way MOD and ppO2 is taught is not optimal. 1.6 is clearly not an absolute limit, while 1.4 is not necessarily safe even though it feels like that is the way it is taught. It harbors both unrealistic understandings of the physiology, unsubstantiated fears, and complacency about ppO2 of 1.4. Now that I think about it, its all taught pretty poorly :-/

Indeed. Its sad that real education has taken a back seat to the "just do this" approach.

Interesting . . . Nothing I've read has ever done a "just do this" approach. All of it (1) gives history that a PPO₂ of 1.6 atm was the recommended safe level; (2) that time and further study lowered the recommend safe level to 1.4, and (3) that all of these had further, unknown factors of individual physiology that would affect what was safe and what was not. The books and papers go on to further say that risk increases exponentially from 1.4 with the severest curve at 1.6.

 

[jtivat]

Taking the issue further, even on a 60 foot dive with a 36% mix, you could easily say that you are causing a massive increase in the creation of "free radicals" in your body....as many of us take large amounts of vitamin C and E , etc., in an attempt to limit concentrations of free radicals in our bodies, the idea that extensive nitrox use is actually quite unhealthy ( metabolically), may be worth considering.
The WKPP direction for this issue was always using normoxic trimix, as the "healthier" alternative to nitrox.

Regards,
Dan V

Interesting my Normoxic Trimix instructor was Gary Taylor and he did a lot of talking about this issue. He wrote a few papers on free radicals and Ox Tox and was a big believer in the use of antioxidants to help. But I really have never heard anyone else talk about this issue over the year. Do you have any info on this?

Thanks

 

[HowardE]

Interesting . . . Nothing I've read has ever done a "just do this" approach. All of it (1) gives history that a PPO₂ of 1.6 atm was the recommended safe level; (2) that time and further study lowered the recommend safe level to 1.4, and (3) that all of these had further, unknown factors of individual physiology that would affect what was safe and what was not. The books and papers go on to further say that risk increases exponentially from 1.4 with the severest curve at 1.6.

Yeah, the risk increases, because the time "allowable" decreases. Not to mention that if you're already at 50% of your daily limit... your 45 minutes at 1.6 becomes 22 minutes. The clock runs quickly at high PO2's. The point is. It's not immediate if you cross 1.6. It's not like, "if you violate the MOD - you will tox"

which... if you carry the equation further... you can see that in recreational diving... it's extremely difficult to run out your clock. Certainly for tech diving... it's more of a possibility, especially when you plan deco segments at high PO2's, or even rebreather dives, where you can run at 1.3 or 1.4 or even 1.5 PO2 the whole dive.

 

[Jax]

Yeah, the risk increases, because the time "allowable" decreases. Not to mention that if you're already at 50% of your daily limit... your 45 minutes at 1.6 becomes 22 minutes. The clock runs quickly at high PO2's. The point is. It's not immediate if you cross 1.6. It's not like, "if you violate the MOD - you will tox"

You're the only one that has ever made that statement, Howard.