PPO2 maximum safe value: 1.4, 1.6

[Rhone Man]

Lots of opinions on this. Keeping at ppO2 of 1.4 or below will almost certainly keep you safe from what is a very bad risk.

But when I was in Europe diving to a max of 1.5 (and for some people 1.6) was pretty standard for recreational dives, the theory being you only spend a small part of your dive at max depth, and for most of it you will have a much lower ppO2. Plus few recreational dives are long enough to give you serious exposure.

But (i) the onset of oxygen toxicity is inherently unpredictable, and (ii) is likely to have severe consequences if it happens. So unless you are manic about those extra minutes, it is probably no bad thing to play it safe knowing you'll go home safely to your family after diving.

 

[tbone1004]

I totally agree that the contents should be analyzed after filling and just before attaching the reg, but three times? At the station I fill, analyze, and mark the tank with mix, MOD, date and initials. At the site, I analyze to verify that the tank is correctly marked, assemble the gear and set the mix on my computer. Why should I analyze more than that?

if you're doing you're own filling and the bottles aren't going straight to the car the third one applies. I.e. if you are blending the day before, you should analyze before you leave just to make sure everything is OK, and you obviously have to analyze when you finish filling to make sure it worked properly.

 

[tursiops]

I'm not aware of a link between narcosis and O2 tox; in fact, I believe there was speculation that narcosis had some countering effect on O2. CNS suppression versus stimulation (uppers and downers). Hence, why the rate of O2 tox on deep air was quite low (given bottom time and very high ppO2). Just speculation and lore...

I didn't say it very well. When your narcosis is a "dark narc" and you get anxious, perhaps panicked, you breathe harder and shallower and your CO2 goes up. But I said CO2 separately, so that would cover it.

I think the speculation on N2 mitigating O2 toxicity is still rampant, which is not the same thing as still valid.

 

[NAM001]

I look at it as a sped limit sign. limit is 70 but you must modify that max for weather conditions. CNS exposure points sky rocket at about 1.65, there abouts. so that for me is the absolute statistical limit., Not personal but statistical. .2 less provides a buffer between you and that limit. The other conditions as noted like many repeditive dives and lengthy dives have to reduce that base 1.6 also. This prosses of thought is lacking int he basic nitrox classes. I think they consider the 2/10 buffer being adaquate for 99.9% of rec dives being done, including boat trips of 5 dives a day for 2-3 days. MOst of that planning is done by the boat in hte established SI's that are set. The divers are normally left out of the process and have no idea why the madnndatory 1.5 hr SI's are set.

That is essential my understanding and what I got from my course. And I appreciate this approach. Instead of a "black line in a grey area" with a hard MOD, the instructor attempted to give me the information to make an informed decision and skills to modify it as personal and dive site conditions changed.

 

[CuzzA]

@dumpsterDiver is this the one? If so, that's one hell of a price and I wonder about the quality.

http://www.ebay.com/itm/Scuba-Scuba...3660psi-Max-/311424817795?hash=item48825d9a83

The only issue is my pony is DIN. If you own this one do you know if you can remove one of the yoke valves and use a DIN? I think Piranha sells DIN to 1/4" female NPT for ~$40.

Edit: It almost looks like a quick disconnect in the picture.

 

[fsardone]

Hello,
If I understand your history correctly, you are now undertaking open water training. You are not yet certified.
Please allow me to tell you there is no substitute for time under water.

Please take the time to build up some experience, then go deeper than 18 mt/60 feet whatever is called the OWD limit, but not before getting additional training.

Looks like you are looking to race in Moto GP and you are not yet going around on a bike on your own.
There is nothing wrong in looking forward to training but you do not take courses because you need c-cards, you train to acquire skills. I have been diving for years without cards (not needed/required when I started 30+ years ago) I trained from my father (when he started c-card did not even exist) but I dove for 10+ years before moving to technical (I am slow).

You are trying to assess the limits for ppO2 diving before being certified for OWD.

As many have told you max ppO2 is 1.6 only for non working phases of the dive. PADI and other agencies recommend max ppO2 to 1.4. Some tech agencies to lower ppO2 by 0.1 for each stressor (cold, work, dark) starting from 1.4 ... for the deep part of the dive (using trimix this is possible without increasing the narcotic level).

So get your OW CC find a buddy and have fun within 18 mt (Air is the best gas for this unless you are looking to stay there 60+ minutes but you will run out of gas on a 12l/S80). When you are at ease with your trim and buoyancy control, weighting (and have worked out a few inconvenient that will happen) keep training to acquire skills and not CC.

Please do not take this as a way to tell you off. But in the few years I have been diving I saw a few accidents and near misses that could have been avoided if the diver had learned to walk before attempting to race track race. Build water time with knowledgeable buddies and progress with instructors.

Above all have fun!

 

[dumpsterDiver]

@dumpsterDiver is this the one? If so, that's one hell of a price and I wonder about the quality.

http://www.ebay.com/itm/Scuba-Scuba...3660psi-Max-/311424817795?hash=item48825d9a83

The only issue is my pony is DIN. If you own this one do you know if you can remove one of the yoke valves and use a DIN? I think Piranha sells DIN to 1/4" female NPT for ~$40.

Edit: It almost looks like a quick disconnect in the picture.

Yeah I think someone on here mentioned they got it and it was decent. It is very inexpensive. If I didn't have three (normal ones) already, I would buy it. Not sure what i would do about the DIN pony... That might be an issue..? If you had a convertible valve on the pony, you could stick the yoke conversion plug in ... kinda a pain, but would work

 

[WarrenZ]

Din Fill adapter?

 

[tbone1004]

just use a din-yoke fill adapter. All divers with their own din tanks should own at least one of them and they're quite cheap.

 

[kensuf]

So.. The thing to consider is that when we consider oxygen exposure, we're concerned with dose (PO2) and duration (time). O2 exposure is analogous to taking medicines, you can take one advil a day for a month and probably be OK, but if you take 30 advils in a day you'd be in a world of hurt.

Now, one of the main reasons to advocate for a lower PO2 is to provide you with a buffer zone for contingencies. What if you accidentally drop 10'-20' deeper than you planned, thus giving you a higher dose? What if some event happens that delays you and extends your duration?

1.4 max PO2 for recreational diving (no-decompression diving) gives you a pretty wide margin for error. If you're doing multiple dives, like on a live-a-board, or deco diving, I'd drop to 1.2 or lower.