PPO2 maximum safe value: 1.4, 1.6

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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...

Nonetheless, there are other effects on the body caused by being in-water under hyperbaric conditions that provoke CNS hits. Hence, the higher incidence of O2 tox in-water versus in dry chamber at equal ppO2.
 
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I don't see the value in permanently marking a tank or choosing one mix for every dive. You plan a dive, choose the best mix, request the mix, analyze the mix, label it and dive your plan, repeat. If you can't get partial pressure blends where you dive you do the same aforementioned procedure except when planning your dive you choose a banked mix that doesn't exceed 1.4 ppo2. That's it. If you don't trust the operations analyzer then buy your own to double check for discrepancies. Cootwo from DiveNav seems like a solid option.

I don't want to derail the thread too much, but I do have a question for the board. What are your thoughts on permanently marking a bailout or pony bottle and using enriched air? Being that this tank is likely not going to be drained and filled over the course of several dives or even months of diving I can see some pre planning being implemented to have a more permanent approach. If I recall, I've read some people recommend only air in a bailout bottle, but let's say where you dive ranges from 60-100 feet with a hard bottom, does anyone see an issue with filling your tank with a mix of say 32%? This keeps you well below 1.4 ppo2 which I think is advantageous considering if you're going to your bailout you're probably exerting more effort and increasing the possibility of an ox tox. Also, if you've done some rock bottom calculations so your carrying the appropriate sized cylinder and can actually make a typical ascent with stops and you're typically a repetitive dive diver the extra O2 may offer some help to prevent lower level/sub clinical DCS. Honestly, I don't know how much of a difference 32% would make over 21% in that regard, so I'd like to hear more.
 
Honestly, I don't know how much of a difference 32% would make over 21% in that regard, so I'd like to hear more.

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Here's one place to start learning about that discussion: http://www.scubaboard.com/community/threads/enhanced-air-does-it-help-fatigue.519006/
 
I don't see the value in permanently marking a tank or choosing one mix for every dive. You plan a dive, choose the best mix, request the mix, analyze the mix, label it and dive your plan, repeat.
The reason for permanently labeling tanks is because then no confusion can arise. Labeling only makes sense for 'dangerous' mixes (for instance 100% oxygen, dangerous at depth more than 6m) as far as I'am concerned. Meaning in particular stage tanks. Imo there's no need for labeling back gas, not even with a green/yellow Nitrox sticker. It makes sense for complex decodives, not so much for the local quarry dives.
 
I don't see the value in permanently marking a tank or choosing one mix for every dive. You plan a dive, choose the best mix, request the mix, analyze the mix, label it and dive your plan, repeat. If you can't get partial pressure blends where you dive you do the same aforementioned procedure except when planning your dive you choose a banked mix that doesn't exceed 1.4 ppo2. That's it. If you don't trust the operations analyzer then buy your own to double check for discrepancies. Cootwo from DiveNav seems like a solid option.

I don't want to derail the thread too much, but I do have a question for the board. What are your thoughts on permanently marking a bailout or pony bottle and using enriched air? Being that this tank is likely not going to be drained and filled over the course of several dives or even months of diving I can see some pre planning being implemented to have a more permanent approach. If I recall, I've read some people recommend only air in a bailout bottle, but let's say where you dive ranges from 60-100 feet with a hard bottom, does anyone see an issue with filling your tank with a mix of say 32%? This keeps you well below 1.4 ppo2 which I think is advantageous considering if you're going to your bailout you're probably exerting more effort and increasing the possibility of an ox tox. Also, if you've done some rock bottom calculations so your carrying the appropriate sized cylinder and can actually make a typical ascent with stops and you're typically a repetitive dive diver the extra O2 may offer some help to prevent lower level/sub clinical DCS. Honestly, I don't know how much of a difference 32% would make over 21% in that regard, so I'd like to hear more.

your premise is wrong. A pony bottle will be checked and turned on and off and might freeflow a little here or there or leak, MORE than a normal tank because it is used 4-5 or more times per day. Also, as the pony slowly loses pressure, this reduces the volume available for emergency. If you carry a small pony, it is more better ... to try to keep it close to full... PLUS it might be nice to actually practice using the pony for an ascent. say on the last dive of the day.. Also the pony valve gets used/worn out a lot more than other tanks, so i often have leakage issues with storage.

So... i am quite often using an equalizer whip on the boat to top off the pony from the main tank before the first dive of the day on the boat. Generally, I prefer to have the pony filled with air, but in practice.. if i am not diving past recreational depths, it will be filled with some nitrox.

Personally, I think air is best, because if you should think you feel oxygen toxicity coming on, you could switch to the pony and press the up button and bail out to 30 ft less depth pretty quick.

I saw some super cheap (yoke) whips on Ebay.. with a gage.. A whip with a guage is very useful on the boat for balancing tanks out and keeping the pony filled..
 
Good points. I haven't used my pony enough to experience the issues you mentioned, but it makes perfect sense. I also hadn't thought about switching to your bailout "if" you felt the tox coming. I'll have to check out those whips. Got a link?
 
Personally, I think air is best, because if you should think you feel oxygen toxicity coming on, you could switch to the pony and press the up button and bail out to 30 ft less depth pretty quick.

Riiiiight. So we have someone that has no clue about O2, that is gonna "feel oxygen toxicity coming on" when using some low % nitrox, and switching to air is totally gonna solve it. Because he totally cannot ascend to lower the pO2, assuming he's able to sense it in the first place.
 
Riiiiight. So we have someone that has no clue about O2, that is gonna "feel oxygen toxicity coming on" when using some low % nitrox, and switching to air is totally gonna solve it. Because he totally cannot ascend to lower the pO2, assuming he's able to sense it in the first place.


Chances are .... you won't have much warning with an oxygen hit... from what i have been told/taught .... but I like to think it might be one more tool in the box... Also.. if you ONLY fill the pony with air AND you totally screw up the nitrox mix in your main tank (or the particular nitrox tank is contaminated) it could be beneficial to have separate air source. Over all minor considerations..I concede.
 

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