Nitrox - What do you dive PO2 - 1.4, 1.5 or 1.6?

[uncfnp]

Assuming that you are always mindful of your dive computer data and not just waiting till an alarm goes off. You have two choices. Either dive a leaner mix or set you computer 1.5 to give you that little extra leeway when needed knowing that you want to be less that 1.4 for most of the dive.

That is what I do. I set my computer to 1.5.

read your profile and you're Advanced Nitrox certified. Did you take Staged Deco with that class?

Not yet. One reason I don't need that Petrel just yet. SM cave is next on my agenda then possibly a formal deco class.

 

[TONY CHANEY]

I set my mix for sand at 1.5 The majority of the dive will be at 1.4 or less. NOw I did on one occasion hit 1.78 on 32% because I did not watch the depth gage while on the Oriskani. Once i saw i was past i beet feet up to ppo2 1.0 for a while. That distraction was what the 1.4-1.6 buffer was for. Others I am sure MIGHT say that explains a lot about me. Hmmmmm

Why did you pick a 32% mix to dive on a ship that has a sand depth of 220 fsw and the flight deck is 145ft deep, the Hangar Bay is at 175ft? Just asking.

 

[ddmattos]

That is what I do. I set my computer to 1.5.

Not yet. One reason I don't need that Petrel just yet. SM cave is next on my agenda then possibly a formal deco class.

Just asking since it's not uncommon to do both courses simultaneously.
Also, since your looking for max bottom times, a formal deco class would be a valuable tool to have.

 

[uncfnp]

Just asking since it's not uncommon to do both courses simultaneously.
Also, since your looking for max bottom times, a formal deco class would be a valuable tool to have.

No problem. Yes, Ad Nitrox and Deco are usually taken together and I recommend that approach. But I never seem to do anything the normal way and this path is the best for me.

 

[NAM001]

Its fair of you to ask. I can take the hit.... 32 is what was available. there was no plan to go below mod. I was looking for something preticular ( the rifle boots and helmet) on the ship. Not only did i not see them I did not watch my depth. My fault .... no justifiable excuses.... Next thing I knew I was seeing flight deck and i looked at the depth gage and I was at 1.79 ppo2. Didnt need to ask why ow how i just went back up perhaps 90 ft. Each dive is a learning experience. I thnk i can still look at the predator to see the profile. This is not say that not seeing the gum ect. was not affected by being narced to some degree. One would be a fool to deny the possibility.

Why did you pick a 32% mix to dive on a ship that has a sand depth of 220 fsw and the flight deck is 145ft deep, the Hangar Bay is at 175ft? Just asking.

 

[TONY CHANEY]

Very nice reply and I fully understand.

 

[Jandee]

Had a chance to dive Devils Throat in Cozumel, 120 feet At the end of the swim through. Diving N32. I was told my the shop owner, not a DM or instructor I would be fine if I went up to MOD right away. Maybe I would of been OK but why take a chance, stick to 1.4.

 

[redacted]

Had a chance to dive Devils Throat in Cozumel, 120 feet At the end of the swim through. Diving N32. I was told my the shop owner, not a DM or instructor I would be fine if I went up to MOD right away. Maybe I would of been OK but why take a chance, stick to 1.4.

I believe the exit is more like 128 ft so you would have been getting pretty close to the old standard of 1.6. So, did you make the dive but not go through the throat or did you pass on the dive?

BTW, I believe there have been O2 hits recorded at less than 1.4 so even that may have a bit of "chance" associated.

Why use EAN for the first dive in Coz anyway. You are probably better of with air for the first dive and EAN36 for the 2nd.

 

[BRT]

Had a chance to dive Devils Throat in Cozumel, 120 feet At the end of the swim through. Diving N32. I was told my the shop owner, not a DM or instructor I would be fine if I went up to MOD right away. Maybe I would of been OK but why take a chance, stick to 1.4.

Us too. Why risk it?

 

[GDI]

The standard debate, ppO2 pressure vs ppO2 exposure. What % do we use and at what pp?

If you had the chance to really graph this out you might actually find that the CNS clock at say Ean28 vs a Ean36 for example is not too far apart with a delta of 8% difference. What do you get with a 10% delta?

In this thread the mixes (standard mindset) of 32 % to 36% (range 30%-36%) and the 50% group are being discussed. This is mainly because many who learn EAN diving get locked into these %'s and never think of anything different or anything to best make their dive plan the safest it could be, possibly. I was instructed this as being best and thus assume to follow the norm.....

I recommend to run a software program comparing the algorithms of different mixes. Compare the CNS totals, the PPo2 by pressure and by time exposures. See what the algorithms illustrate. Cavet is that in diver physiology one day to another and one diver to another is a variable, so consider your graph to be at best a educated guess of averages.

Doing this your thinking may change to question why bother with a gas pushing a 1.4 or even a 1.6. Why not go even lower say to a 1.0 or 1.2 as your max (conservative mindset of course). Maybe you will find it best to go higher as in for deco?

Question:
1. Is it better to come on a gas sooner (@ lower ppO2 but deeper depth) or of a higher ppO2 (shallower depth) to ensure better off-gassing?
2. Is it best to dive the highest possible EAN% for a given dive plan? and
3. In having two different available EAN% mixtures what % is best to dive the first dive and which % is recommended to dive on the second dive, the higher of the two or lower?

One thing I have not read discussed here (maybe I missed it, its a good thread afterall) is what advantage does EAN diving actually give you when considering a diver's RMV/SAC rate and the volume of gas available to breathe? The ppO2 by pressure is an effect caused by AtA/bar depth. The ppO2 exposure clock does have a impact based on a diver's RMV/SAC or the amount of time a diver breathes the gas. ( of course the ppO2 at depth plays into this as well, basic Dalton)

Often divers are simply told that EAN diving will give them more allowable bottom time and some greater level of safety. Myth vs fact often intermixed. The cylinder used for a diving gas is the same size in volume whether on air or EAN. Your lungs work on a breathing volume (RMV/SAC) . Enjoy your course when you take it.
As for me I'm just stirring the pot