Nitrox - 1.40 or 1.60 PO2?

[Bismark]

OK, OK, I have my SSI Enriched Air Nitrox DVD (c) 2004 in my computer. Couldn't find the book.

The DVD states that the CNS Oxygen Toxicity threshold appears to be 1.1, and the risk increases above 1.4. So all these technical discussions are very interesting, but I,as a recreational diver, will stay within the limits suggested by my training which is 1.4. As I understand, the OP was speaking of recreational EAN use. So recreational EAN use is germane to the thread. I fear that some of the more intricate points made might have a reverse effect and possibly confuse a diver not as knowledgeable as some of these very intelligent and experienced posters.

That would be sad, as one of us might have to dive after someone, and not with him/her.

I disagree with your approach. You are making a black and white distinction between technical diving and recreational diving in respect to CNS limits where such a distinction does not exist. You have also chosen to simply repeat what one diving manual suggests which does nothing more than tell us what SSI's position on the matter is. This stuff is not rocket science and suggesting that recreational divers do not need to understand the issue further that what is suggested in your manual is doing a disservice to divers. If you are smart enough to pass your open water exam you can understand this topic much more than just "trust me on the limits" as presented by SSI, or many other agencies for that matter. I believe that is important that we treat divers as intelligent thinking individuals and do no "dumb down" topics such as this. (With the exception of Nereas of course......) Telling someone just to keep their PP02 within the 1.1 to 1.4 limits is a "trust me" approach and not one to which I subscribe in my learning and teaching.

 

[Bismark]

Could someone contact the mods and tell them that Nereas is off his meds again........

 

[HowardE]

It seems to me that having the wrong information in these debates isn't all bad.

 

[kadleck]

Could someone contact the mods and tell them that Nereas is off his meds again........

 

[wve]

To each his own no matter how much they talk about it no one has ever suffered a hit at 1.6 or below and even with a number above it they had to be in that environment for 30 minutes or more and be working really heard! Lost I can find was a 30 minute exposure at 1.7 with heavy exercise! So with that in mind lets all drive 25mph! After all we kill 50 thousand people every year and if we had Zero tolerance we really would have a bad economy! Or lets keep all people off the Black Diamond slop, look at poor Sony! The benefit Vs risk is true of every dive and no one should ever dive beyond their ability! But we will see more and more orgs. and operators requiring, unnecessarily, enforcing some rule they read on the Board! Until I see hard core evidence that it is a risk I will set my computer to 1.6 hard bottom and dive that MOD profile! I think this is a good topic so that just maybe people diving VooDoo Gas will do their own home work and not just take someones word for it!

You and I don't disagree, and I hope you don't think I am advocating driving 25 mph!

There are no hard numbers one can rely upon -- even 1.6! The risk is a continuum with no hard shoulder.

I don't know for sure, but I bet that most computers actually calculate oxygen toxicity units. The max is often set by the programmers to 300 units daily, but if one is making only one or two dives, Hamilton and others have shown that people can tolerate levels 2 to 3 times that amount.

So my main point is that if you stay within the limits set by most computers and agency guidelines, you will already be diving pretty conservatively. I don't see a strong need to make it even more conservative (eg, set your limit to 1.2).

My second, minor point is that recreational Nitrox divers like me who do the usual reef tours and vacation-type wreck dives are not likely to even approach those limits because we are optimizing the length of our dives. That is, the limiting factor of our dives is nearly always the amount of gas we have, not concerns about nitrogen or oxygen toxicity.

 

[rstofer]

A question each diver should be considering is to what depth/ata ppO2 he would be willing to go to in order to rescue another diver in an emergency. Do you treat the 1.4ata (or 1.2ata or 1.6ata or whatever your "magic number" is) as a solid floor below which you will not descend in even an emergency?

That's a very deep question! It clearly depends on who's emergency it is. For a family member, there is no floor. For an insta-buddy above 1.6ata? I'll send flowers.

Richard

 

[Papa_Bear]

Emergencies???! The Data shows the possibility of a hit below your MOD if your working hard at time and depth! It becomes a crap shot with high stakes and a personal decision and something you should discuss with your buddy instant or not! On a boat or resort what about dissimilar gas or mix? MOD has to be to the higher mix buddy! The price is great and so is the margin, so plan your dive and dive your plan and if an emergency happens stop and read your gauges! I would push the envelope to MY comfort and experience not yours!

 

[Thalassamania]

In an emergency, with no prior exposure, and planning on a very short exposure (< 5 mins.) I'd be willing to risk 3.0, but then I've done that many times in a chamber. I would not recommend that sort of exposure to anyone who has not had that sort of prior testing (and yes, I know, you can't completely trust the tests, there's day to day variation).

 

[Bismark]

In an emergency, with no prior exposure, and planning on a very short exposure (< 5 mins.) I'd be willing to risk 3.0, but then I've done that many times in a chamber. I would not recommend that sort of exposure to anyone who has not had that sort of prior testing (and yes, I know, you can't completely trust the tests, there's day to day variation).

I would probably do the same thing, maybe not quite to 3.0, but that would be one nerve-wracking 5 minutes........ Let's just make sure our dive plans and buddies do not require this......

 

[Thalassamania]

You betchum. But I do believe in having a "bottom line" so that I'm not thinking about as the crash clock is running. Similary you need to make decisions about blood without gloves and rescue breathing without a mask, etc. Make your decisions now, not in the heat of the moment.