40% Nitrox

[chillyinCanada]

We may simply be dealing with a different language interpretation here.

 

[rhwestfall]

We may simply be dealing with a different language interpretation here.

plausible...

 

[FullThrottle]

"Our chief weapon is surprise! And fear..."

 

[Hartattack]

"Our chief weapon is surprise! And fear..."

This made me lol.

 

[12th Man]

 

[Larryjd1]

"Our chief weapon is surprise! And fear..."

“No one expects the Spanish Inquisition! Our chief weapon is surprise, fear and surprise; two chief weapons, fear, surprise, and ruthless efficiency! Er, among our chief weapons are: fear, surprise, ruthless efficiency, and near fanatical devotion to the Pope! Um, I'll come in again...”

Thanks for the Monty Python reminder! A truly funny Show!

 

[Errol Kalayci]

Why would you want to use 40% Nitrox?

Why push a high po2?

For me, I stick with 32% for everything less than 100 feet and add helium whenever possible to make work of breathing much easier, no narcosis at all, lower chance of CO2 build up and arguably better decompression (even non-decompression dives I feel way better). Using 32% in 100 feet or less takes all the guess work out and gives you a very good understanding of how decompression works and able to do in your head your no deco limits if computer fails. 32% at 100 feet would be a PO2 of 4atax.32= 1.28 at which I do not believe there has ever been cns toxicity event, especially in sport diving. Adding more oxygen really saves nothing from decompression standpoint and increases chance of cns tox event with the higher PO2. Oxygen is arguably more narcotic than nitrogen by looking at it scientifically all though no practical way to prove if it is, or is not. Assume at least as narcotic.

Changing Nitrox percentages each time decreases a divers comfort with it and increases complexity for no reason. Best Mix I believe is non-sense for a bottom gas, better to follow standard gas selection within a depth range so that you address concerns of O2, work of breathing, narcosis and deco once and know your good to go thereafter at that depth or less. By picking 32% you are good if your dive depth changes while on boat if wreck is full of other dive boat or people want a different wreck, you know your good to 100'. If you went with higher O2 and depth increases from that planned, may not be able to dive or put yourself at increased risk. Sure, if I asked for 32% and gas analysis came out to 34.2% (note I always record O2% to one decimal so clear that was analysis not what was requested) I would likely accept it if diving plans allow it, or may have them fix it. I have never dove 40% and see no reason why I ever would. I do use 50% Nitrox for a 70 foot deco gas when I can't add helium to make it 50/15 which eliminates the possibility of me getting inner-ear isobaric counter diffusion hit - which sucks- take my word for that!

For me personally, I almost always have helium in my tanks on any dive regardless of depth as typically go for 30/30. If I am feeling cheap or more likely helium scarce for another diver, blow 32% on top and I still have a nice mix like 32/15 for example which I treat like 32% Nitrox but reap benefits of the added helium. Been doing this recreational nitrox since 1994 after coming from deep diving in the morning and topping up tanks by adding O2 to raise O2% in mix and use whatever helium was still in my dive tanks and felt so much better kept doing it ever since and started just filling my recreational tanks with 30/30. All of the foregoing is just my opinion, and my personal dive approach and does not reflect any agency under which I train divers.

 

[BlueTrin]

Why would you want to use 40% Nitrox?

Why push a high po2?

For me, I stick with 32% for everything less than 100 feet and add helium whenever possible to make work of breathing much easier, no narcosis at all, lower chance of CO2 build up and arguably better decompression (even non-decompression dives I feel way better). Using 32% in 100 feet or less takes all the guess work out and gives you a very good understanding of how decompression works and able to do in your head your no deco limits if computer fails. 32% at 100 feet would be a PO2 of 4atax.32= 1.28 at which I do not believe there has ever been cns toxicity event, especially in sport diving. Adding more oxygen really saves nothing from decompression standpoint and increases chance of cns tox event with the higher PO2. Oxygen is arguably more narcotic than nitrogen by looking at it scientifically all though no practical way to prove if it is, or is not. Assume at least as narcotic.

Changing Nitrox percentages each time decreases a divers comfort with it and increases complexity for no reason. Best Mix I believe is non-sense for a bottom gas, better to follow standard gas selection within a depth range so that you address concerns of O2, work of breathing, narcosis and deco once and know your good to go thereafter at that depth or less. By picking 32% you are good if your dive depth changes while on boat if wreck is full of other dive boat or people want a different wreck, you know your good to 100'. If you went with higher O2 and depth increases from that planned, may not be able to dive or put yourself at increased risk. Sure, if I asked for 32% and gas analysis came out to 34.2% (note I always record O2% to one decimal so clear that was analysis not what was requested) I would likely accept it if diving plans allow it, or may have them fix it. I have never dove 40% and see no reason why I ever would. I do use 50% Nitrox for a 70 foot deco gas when I can't add helium to make it 50/15 which eliminates the possibility of me getting inner-ear isobaric counter diffusion hit - which sucks- take my word for that!

For me personally, I almost always have helium in my tanks on any dive regardless of depth as typically go for 30/30. If I am feeling cheap or more likely helium scarce for another diver, blow 32% on top and I still have a nice mix like 32/15 for example which I treat like 32% Nitrox but reap benefits of the added helium. Been doing this recreational nitrox since 1994 after coming from deep diving in the morning and topping up tanks by adding O2 to raise O2% in mix and use whatever helium was still in my dive tanks and felt so much better kept doing it ever since and started just filling my recreational tanks with 30/30. All of the foregoing is just my opinion, and my personal dive approach and does not reflect any agency under which I train divers.

Isn’t it expensive to always fill with 30/30 ?

 

[jlcnuke]

Isn’t it expensive to always fill with 30/30 ?

30/30 here is $0.60/cu ft, so $48 for an AL80. Nitrox for ~1/5th of that cost. With the prices of helium everywhere (as far as I'm aware) being pretty high these days, that'd be some relatively expensive diving.

 

[boulderjohn]

30/30 here is $0.60/cu ft, so $48 for an AL80. Nitrox for ~1/5th of that cost. With the prices of helium everywhere (as far as I'm aware) being pretty high these days, that'd be some relatively expensive diving.

I am able to get both oxygen and helium at good prices--pretty rare these days. I provide it to friends and students as a service, and I charge a little more than it costs me for the gas in order to factor in my other costs. Unless you are doing it yourself, you can't get it any cheaper than you can get it from me. I would charge about $30 for the helium and oxygen in an AL 80 of 30/30. After that, they would have to get it topped off with air, which might cost $10, for a total of $40.

That cost is primarily helium. Depending upon the mix, I would only charge about $4 for the oxygen portion of a nitrox fill, for a total of $14.

So, yes, diving 30/30 for a typical recreational dive is quite expensive.