nitrox MOD/TOD

[wedivebc]

i.e. let's say 4 deg c (37 f ????)watertemperature, phisycally unfit divers with about 60 pounds of overweight.

i.

This diver should limit their ppo2 to .21 :huh:

 

[victor]

My legs started to tingle so I thought to myself "self move your legs they are tired from being in position so long" so I did and went back to the damn gobbie. Then a little alarm went off in the back of my head that said "holy **** I'm starting to tox, I had that happen in the chamber once on my yearly O2 tolerance test just before I did the funky chicken". I then put actually used my inflator as the up button so as to not exert myself and the tingle went away at 60 feet.

When we learn to go deeper we are shown what being narced is like. For most the surprise of being unable to solve simple problems hits home and we remember what can happen.
Maybe there should be an equivalent for O2 TOX hit.
I doubt whether most certified divers would know what the early symptoms are until it hit them. That's to late, frequently fatal from what I have read so far as spitting out the reg is normal. :jpshakehe

 

[cerich]

When we learn to go deeper we are shown what being narced is like. For most the surprise of being unable to solve simple problems hits home and we remember what can happen.
Maybe there should be an equivalent for O2 TOX hit.
I doubt whether most certified divers would know what the early symptoms are until it hit them. That's to late, frequently fatal from what I have read so far as spitting out the reg is normal. :jpshakehe

It isn't that simple, it can manifest itself differently on different days, exposure etc.

Simply put don't push it.

 

[victor]

It isn't that simple, it can manifest itself differently on different days, exposure etc.

Simply put don't push it.

Cerich
This is why I am not sure that nitrox is such a good idea.
In situations where 33m is as deep as you can go without a shovel then it's safe to use 32%.
What about a wall situation, where even experienced divers can make mistakes and slip deeper than they intended. How many divers can honestly say that they have never dropped below their planned max depth. Diving with a video camera chasing that elusive eel, that hidden cave that's just down round that corner.
You can recognise signs of being narced, you get some warning, maybe not enough to always save you, but time for you or your buddy to do something about it.

From what I have read an O2 tox hit can come with little or no warning. The effects can be catrastrophic. Is an extra 5 minutes bottom time or a 20 minute shorter surface interval worth this risk.

As I have said I will be taking the course and I will decide after that whether I will dive with it or not, and if I do, what precautions I feel are necessary.

 

[cerich]

Nitrox is a proven method for recreational divers to use. That's why there is a course. At the end of they day a dive is responsible for their own safety.

 

[Kim]

How many divers can honestly say that they have never dropped below their planned max depth.

I would hope most - or at least if you mean by accident. I can honestly say that in around 60 Nitrox dives I have only ever broken my TOD once - by 2m for 2 minutes to take a picture of a leopard shark. As my TOD was computed using 1.4 PPO2 and was 33m and as the MOD was 39m I don't see it as a problem. I can honestly say that that was the only time and I was fully aware when I did it. Other 'accidents' I would also know as I download all my dive data from my Vyper so would see instantly afterwards even if I wasn't aware at the time. Personally I like to be aware of my depth at all times, but especially when I'm at the deepest portion of the dive or anywhere close to a limit.

 

[TSandM]

I think what's coming out in this discussion is what comes out from time to time in discussion of the NDLs, and that is that none of these numbers is cut in stone. Just as susceptibility to DCS varies from person to person and from day to day, susceptibility to oxygen toxicity varies, too. There is a ppO2 where nobody toxes, and a ppO2 where most everybody would, and in between there is a large grey area of increasing -- but not exactly quantifiable -- risk. Where you draw the line depends on how much risk you are willing to take. The agencies have picked their numbers -- IANTD says it's okay to go to 1.6 and stay there, NAUI says 1.4. It's up to me to decide which I want to use. I think it's also incumbent upon me to tell my buddy what gas I'm diving, so he can decide if he's comfortable going to that depth with me on that gas, since he's the one who's going to have to try and rescue me if I tox.

 

[Jason B]

I think what's coming out in this discussion is what comes out from time to time in discussion of the NDLs, and that is that none of these numbers is cut in stone. Just as susceptibility to DCS varies from person to person and from day to day, susceptibility to oxygen toxicity varies, too. There is a ppO2 where nobody toxes, and a ppO2 where most everybody would, and in between there is a large grey area of increasing -- but not exactly quantifiable -- risk. Where you draw the line depends on how much risk you are willing to take. The agencies have picked their numbers -- IANTD says it's okay to go to 1.6 and stay there, NAUI says 1.4. It's up to me to decide which I want to use. I think it's also incumbent upon me to tell my buddy what gas I'm diving, so he can decide if he's comfortable going to that depth with me on that gas, since he's the one who's going to have to try and rescue me if I tox.

Nice post.

 

[Kim]

IANTD says it's okay to go to 1.6 and stay there, NAUI says 1.4.

Actually, to be clear, IANTD also now recommends 1.4 as the limit for rec divers (I think) - although their Nitrox tables (or at least the ones I have which are 5 years old) use 1.6 for the limits.

 

[H2Andy]

one further thing that struck me:

percentage of oxygen means nothing. PPO2 means everything.

you could have 21% 02 and die ... if you exceed a safe PPO2 (let's say 1.6)

and you could have 100% O2 and be fine ... if you don't exceed a safe PPO2 (let's say 1.6)

it's the partial pressure that matters, not the percentage in the mix. and partial
pressure has everything to do with depth.

alas, it's not a line ... 1.6 is safe ... for most people ... most of the time ...
some people used to go to 1.8 ... and be ok, most of the time ...
1.4 seems to be safe for the most people, almost all of the time .... and so on...

it's not a line ... it's a gray zone anywhere from 1.4 (acceptably safe) to
2.0 (unnaceptably risky) -- or whatever labels you want to use