Planner Question

[Mal Bridgeman]

Originally Posted by milldog

I know the symptoms of an O2 hit and the last thing that sticks in my mind was the metallic taste to the mix before the hit, but it was only tremors and not convulsions I also know that i could go to a ppO2 of 1.8 before i get the symptoms and feel the effects, how do i know because i tested the theory. (but thats just me)

Your one-time test flies in the face of what I believe

In this document there is a passage....

"In any diving situation, oxygen tolerance is reduced by exercise, breathing resistance, any other factors that might cause an increase in CO2, anxiety, extremes of temperature in either direction, and other presumably lesser factors. These are possible to monitor and avoid, but another major factor is individual variation. These occur for different individuals, and for the same individual at different times. This is discouraging, because we know very little about how to predict or even detect these individual susceptibilities."

which is why I would tend to dive lower ppO2's.....it seems you get away with it till you don't and since "it's not necessary to remind this audience that drowning can spoil your whole day" I'll stick with that!

Rgrds
Mal

[Clare Gledhill]

Originally Posted by milldog

I know the symptoms of an O2 hit and the last thing that sticks in my mind was the metallic taste to the mix before the hit, but it was only tremors and not convulsions I also know that i could go to a ppO2 of 1.8 before i get the symptoms and feel the effects, how do i know because i tested the theory. (but thats just me)

Graham - the most comprehensive study of oxygen use in divers found that there was no correlation between what a single diver could stand from one day to the next. We think that we know enough to state that it is time, dose dependent but measures are highly unreliable and will be affected by work, cold, dehydration , CO2 or H2O2 production or other physical stresses. You cannot therefore rely on past experience to suggest what your personal limits are. Remember also that sometimes the first 'symptom' is convulsions.

[milldog]

It wasn't a test of personnel limits more as to the actual symptoms before the hit and i know that a strong metallic taste is one of the last symptoms, I'm not saying we should all use 1.75 etc etc as always you jump the gun again.

m*** will happily dive a ppO2 of 1.75 i wouldn't but back to the question how do you come to a 1.4 or 1.2 ppO2

perhaps i didn't explain the question fully, perhaps i should look more at the post before all these gods start the cross burning


EDIT just for record i dive 1.4 on the bottom and 1.6 for the deco with safety of 10%

Graham

[milldog]

Originally Posted by Clare Gledhill

Graham - the most comprehensive study of oxygen use in divers found that there was no correlation between what a single diver could stand from one day to the next. We think that we know enough to state that it is time, dose dependent but measures are highly unreliable and will be affected by work, cold, dehydration , CO2 or H2O2 production or other physical stresses. You cannot therefore rely on past experience to suggest what your personal limits are. Remember also that sometimes the first 'symptom' is convulsions.

I know this thats why i dont do Deco on the fly and have the whole group doing the same. You could end up putting someone in the pot! i use my computer and gary uses his we meet up at 6 meters,

But thats the topic of another thread

Graham

[Clare Gledhill]

Originally Posted by milldog

I'm not saying we should all use 1.75 etc etc as always you jump the gun again.

Graham - I am not suggesting that you dive 1.75 or are telling anyone else to. But...

Originally Posted by Milldog

i know that a strong metallic taste is one of the last symptoms,

This is simply not true. Symptoms may appear in any order - or not at all. Do not rely on them to indicate what is happening or what would happen on another occasion.

I know this thats why i dont do Deco on the fly and have the whole group doing the same. You could end up putting someone in the pot! i use my computer and gary uses his we meet up at 6 meters,

I think you may be confusing my answers which relate to PPO2 and Oxygen Toxicity issues, and thoughts on decompression requirements.

[Janos]

Originally Posted by milldog

HOW do you get to a ppO2 of 1.0, 1.2, 1.4, 1.1 what drove you to that decision, did you work it out what's best for the body or is it just what you have been told and follow it without question.

The main reason for me is that it makes bugger all difference on the bottom. Running a setpoint of 1.2 compared to 1.5 is like being 3m deeper throughout the dive. Ok, it makes a difference on stops, but very little to decompression requirements. Try running a few plans at different ppO2s and see (remember to switch back to a higher ppO2 on the surface

Originally Posted by milldog

also if we use a ppO2 of 2.5 for the chamber why not push the deco to 1.75? or is it that this is the max you are allowed and you follow it.

I know the symptoms of an O2 hit and the last thing that sticks in my mind was the metallic taste to the mix before the hit, but it was only tremors and not convulsions I also know that i could go to a ppO2 of 1.8 before i get the symptoms and feel the effects, how do i know because i tested the theory. (but thats just me)

Because a hit in the chamber is unlikely to be fatal, whereas a hit underwater almost certainly will be. Also, you haven't tested the theory. You need to have a sample size of thousands of cases to have any sort of reliability.

Just because something has worked once for you, or even dozens of times, it doesn't mean that it's sensible. You could have a 1 in 100 chance of having a hit (ie dying) but based on your evidence you wouldn't know.

Originally Posted by milldog

so how do you come to your set points a, work it out or b, use what you have been told, follow computer defaults ???

I look at all the evidence I can find and assess it. Where there is doubt, I choose the most conservative path. What happens if I do the dive at 1.2 instead of 1.4? I do an extra ten minutes of deco. So what. Big deal. I'm not fussed.

If I was doing 10 hour runtimes then yes, I might consider a more risky strategy, but for my dives I'm not fussed.

Janos

[Janos]

Originally Posted by Clare Gledhill

This is simply not true. Symptoms may appear in any order - or not at all. Do not rely on them to indicate what is happening or what would happen on another occasion.

Indeed. I was teaching this last Wednesday as part of the BSAC Nitrox cross-over lessons. Symptoms (including convulsions) can appear in any order.

Also, when I was being recompressed a couple of years back I had an interesting chat with the chamber tech. about toxing and a surprising number of people do tox. I can't quite remember what it was but it's not a problem as you're dry and there's a nurse by your side.

Janos

[milldog]

thanks Janos for that i have been told that RB divers use 1.2 for the bottom and push that to 1.6 for the deco,

on comparison have you looked at the time differences between using 1.2 and 1.4 as the bottom times and stop times were they greater? and do you feel better or worse after the dive ?

Another thought if you use 1.2 or 1.0 (as has been mentioned) on the bottom and then go to 1.6 for the deco what measures do you put in place to stop a large N spike. wouldn't it be better to keep the difference closer 1.4 to 1.6 or even 1.5 to 1.6.


graham

[MarkP]

Originally Posted by milldog

also if we use a ppO2 of 2.5 for the chamber why not push the deco to 1.75? or is it that this is the max you are allowed and you follow it.

Seriously? No, you can't be serious.

Actually, there was once a well known and very experienced technical diver / instructor who said "You get away with it until you don't". I think that sums up diving high PO2 quite nicely.

Regards,

Mark

[Mal Bridgeman]

Originally Posted by milldog

It wasn't a test of personnel limits more as to the actual symptoms before the hit and i know that a strong metallic taste is one of the last symptoms, I'm not saying we should all use 1.75 etc etc as always you jump the gun again.

m*** will happily dive a ppO2 of 1.75 i wouldn't but back to the question how do you come to a 1.4 or 1.2 ppO2

perhaps i didn't explain the question fully, perhaps i should look more at the post before all these gods start the cross burning


EDIT just for record i dive 1.4 on the bottom and 1.6 for the deco

Graham

Ok you've lost me...

In your earlier post you seemed to suggest there were only two routes to determine O2 toxicity tolerance. One was to test it on yourself and the other was to blindly follow someone else's advice.

I would suggest that the two options are flawed which is what I tried to explain.

Firstly, that a test on yourself is unreliable since you cannot accurately re-create the circumstances of your test every time you need to rely on the results and as the paper I linked to pointed out, it varies in the same person in the same circumstances on different times for unknown reasons. That, to me, is pretty scarey.

Secondly, you seem to imply with the word "blindly" that "following someone else's advice" is inherently wrong or ill informed. I am not sure I agree fully with that but fortunately, there is a third route which is to take counsel from a number of reliable sources so you can form an opinion based on the experience and knowledge of others and blend that with your own knowlege & experience.

That's what I have done and is why I now prefer to dive lower ppO2's than I previously would have.

HTH
Mal