Nitrox tables

[pilot fish]

For most recreational dives you dont want to exceed a ppo of 1.4. High oxygen contents and the pressure of deeper diving dont go together so well. The last thing you want to do is push your limit and experience Oxygen toxicity underwater.

That much I know so far, just read about it, but why is it bad, exactly? If you get too much nitrogen the bubbles get larger in your blood 'but what is the physical effects of going too deep on nitrox? is it just oxygen toxicity, convulsion, etc?

 

[wedivebc]

You are way more advanced than I. Question: why can you not exceed 110ft on 32% mixture? What is the chemistry of it? I said to someone that asked me that, it had to do with oxygen toxicity but Im not sure EXACTLY why.

Put your hand on a stack of bibles and promise you won't use info gleaned here as a substitute for training and take a nitrox course.
Now on to your question. Oxygen has toxic properties in higher concentrations. That means as the ambient pressure goes up the o2 concentration (PO2) that you are breathing goes up. As your PO2 reaches 1.6 the risk on central nervous system toxicity (CNS) increases. If you calculate 110 ft into atmospheres absolute (ATA) you get 1.334 ATA now multiply that by .32 which is the fraction of oxygen in your breathing gas (nitrox) and you get 1.39 which is getting close to the upper limit (1.6).
I agree with Kraken and other who say don't disregard the benefits of knowledge and try to just rely on a computer for your nitrox diving. It is very important to understand the big picture.

 

[The Kraken]

You'd need to get to the physics of diving forum to become educated properly in the physics of diving and Oxy toxicity of the central nervous system, but it in very simple terms, studies have shown that an Oxy PP of 1.6 is about the maximum sustainable at a specific depth before the possiblity of a convulsion becomes very real.

But, O2 is transferred through the air sacs in the lungs at a certain rate. I believe the ambient pressure has something to do with that . . . not that knowledgeable from the physical aspect.

It's that partial pressure that get's ya hurt.

A EAN32 at 33 FSW has a partial pressure of .64. An increase to a depth of 99 FSW would give you an ATA (Atmosphere Absolute) of 4.0. To get your PPO for this depth with a 32% mix, you would multiply your mix percentage times your ATA for a resulting PPO2 of 1.28 . . . still a safe dive.

When you take the same mix, 32%, down to the max recommended recreational depth of 132 fSW (5 ATA) you get a resulting PPO2 of 1.6.

Technical divers actually dive with LESS oxygen in their mix to avoid oxygen toxicity at depth. For example, if you were to set your PPO2 at a safe 1.4, to dive at 231 FSW (8 ATA), your optimum oxygen content would be 17.5%.

Following that, divers will incorporate helium in their mix to reduce the PP of nitrogen equal to that of about 4 ATA to reduce the nitrogen narcossis potential.

It goes on and on . . .

It's a great deal more than just simply increased bottom times.

 

[jbd]

but I won't like it. I HATE TABLES!!

Tables are really quite simple to use and you should have learned the mechanics of using them in your OW class. They work the same way for nitrox.

The computer is only doing what the tables do although they do recalculate the same info while you under water so you don't get the square profile penalty if you in fact do a multi- level dive. Even if you are going to rely on computers you should have some reasonable understanding of what is going on---tables help you understand this.

 

[pilot fish]

Put your hand on a stack of bibles and promise you won't use info gleaned here as a substitute for training and take a nitrox course.
Now on to your question. Oxygen has toxic properties in higher concentrations. That means as the ambient pressure goes up the o2 concentration (PO2) that you are breathing goes up. As your PO2 reaches 1.6 the risk on central nervous system toxicity (CNS) increases. If you calculate 110 ft into atmospheres absolute (ATA) you get 1.334 ATA now multiply that by .32 which is the fraction of oxygen in your breathing gas (nitrox) and you get 1.39 which is getting close to the upper limit (1.6).
I agree with Kraken and other who say don't disregard the benefits of knowledge and try to just rely on a computer for your nitrox diving. It is very important to understand the big picture.

I am taking a nitrox course -just saw the video several times and am reading the book, and messing with the damn tables You answered my question

 

[scubatoys]

You are way more advanced than I. Question: why can you not exceed 110ft on 32% mixture? What is the chemistry of it? I said to someone that asked me that, it had to do with oxygen toxicity but Im not sure EXACTLY why.

Some agencies, and some computers say do not exceede a PPO of 1.6, some 1.4. So depending on the computer, or agency, on a 32 mix you should not go past 130... others say 110. Just depends on how conservative you want to be.

I've never heard a report of O2 tox in dives up to 1.6... and the is the default PO2 for the Aeris Computers.

Now a quick overview of what that means... Right now you are under pressure... and not just your job and your relationship... atmospheric pressure. In the amount of 1 atmosphere. Since you are breathing 21% (or .21) Oxygen, your partial pressure of O2 as you read this is .21 atmospheres. If you were breathing pure O2, your partial pressure of oxygen would be 1.0.

So if I have a tank of .32 and I take it to 33 feet I am under 2 atmospheres of pressure - my percentage of O2 is .32, so my pressure of oxygen is .64. At 66 feet, or 3 atm, my PO2 is .96, and at 4 atm it is 1.28, and at 5 atm, it is 1.6. So if you are trying to stay below 1.6 ata of oxygen pressure - don't exceede 132 feet, or 5 atms.

This is based on Dalton's law of gasses. In case you want some more reading on it - check out Daltons Gas Law.

If you exceede these depths, you could suffer CNS O2 Tox. (central nervous system oxygen tox.) In bad layman terms, your taking in so much O2 with each breath, your body does not handle it and goes into convulsions to burn off the excess O2. It's really not the seizures and convulsions that are bad for you.... it's spitting out a regulator at 140 feet that proves to be kinda' unhealthy.

Make sense??

So do I plan on tables?? Actually no. I understand people have a very hard time with dive tables, that's why I wrote the Computerized Table Tutor Software.

Based on testing everyone from new divers to instructor candidates and instructors doing cross overs, I've seen many more human errors in calculating tables than I have ever seen in computer errors...

But I also dive with a backup computer. And yes... I trust them. I don't rebalance my checkbook with pencil and paper, I let quicken do it. And when doing multi-level dives, it would be practically impossible to do calculations to determine allowable times unless you spend the entire dive tracking depth and time for each level.

So I hate to admit it... but I just punch in my nitrox level, set a max depth alarm at 110 feet, and simply don't let the big number hit zero on the computer. Simplistic?? Yea... But it's how I've done it for the last 2000 dives.

 

[pilot fish]

You'd need to get to the physics of diving forum to become educated properly in the physics of diving and Oxy toxicity of the central nervous system, but it in very simple terms, studies have shown that an Oxy PP of 1.6 is about the maximum sustainable at a specific depth before the possiblity of a convulsion becomes very real.

But, O2 is transferred through the air sacs in the lungs at a certain rate. I believe the ambient pressure has something to do with that . . . not that knowledgeable from the physical aspect.

It's that partial pressure that get's ya hurt.

A EAN32 at 33 FSW has a partial pressure of .64. An increase to a depth of 99 FSW would give you an ATA (Atmosphere Absolute) of 4.0. To get your PPO for this depth with a 32% mix, you would multiply your mix percentage times your ATA for a resulting PPO2 of 1.28 . . . still a safe dive.

When you take the same mix, 32%, down to the max recommended recreational depth of 132 fSW (5 ATA) you get a resulting PPO2 of 1.6.

Technical divers actually dive with LESS oxygen in their mix to avoid oxygen toxicity at depth. For example, if you were to set your PPO2 at a safe 1.4, to dive at 231 FSW (8 ATA), your optimum oxygen content would be 17.5%.

Following that, divers will incorporate helium in their mix to set the PP of nitrogen equal to that of about 4 ATA to reduce the nitrogen narcossis potential.

It goes on and on . . .

It's a great deal more than just simply increased bottom times.

gulp, yeah, yeah, what he said. I'm wayyyyyyyyyyyyyyyyyyy over my head.

 

[The Kraken]

No you're not. It's just new. You're still relatively new to diving and now you're getting into something that's a bit more advanced.

I have several formulae that I've put together in a spread sheet that I can send you if you'd like.

It's kind of fun to learn how to take a mix, convert it to an EAD (equivalent air depth) and play with air charts.

Learning more about the PPO and percentages of daily allowable exposure at different depths can actually make multilevel diving a lot easier.

One of these days I've GOT TO take the advanced course!!!

 

[pilot fish]

Some agencies, and some computers say do not exceede a PPO of 1.6, some 1.4. So depending on the computer, or agency, on a 32 mix you should not go past 130... others say 110. Just depends on how conservative you want to be.

I've never heard a report of O2 tox in dives up to 1.6... and the is the default PO2 for the Aeris Computers.

Now a quick overview of what that means... Right now you are under pressure... and not just your job and your relationship... atmospheric pressure. In the amount of 1 atmosphere. Since you are breathing 21% (or .21) Oxygen, your partial pressure of O2 as you read this is .21 atmospheres. If you were breathing pure O2, your partial pressure of oxygen would be 1.0.

So if I have a tank of .32 and I take it to 33 feet I am under 2 atmospheres of pressure - my percentage of O2 is .32, so my pressure of oxygen is .64. At 66 feet, or 3 atm, my PO2 is .96, and at 4 atm it is 1.28, and at 5 atm, it is 1.6. So if you are trying to stay below 1.6 ata of oxygen pressure - don't exceede 132 feet, or 5 atms.

This is based on Dalton's law of gasses. In case you want some more reading on it - check out Daltons Gas Law.

If you exceede these depths, you could suffer CNS O2 Tox. (central nervous system oxygen tox.) In bad layman terms, your taking in so much O2 with each breath, your body does not handle it and goes into convulsions to burn off the excess O2. It's really not the seizures and convulsions that are bad for you.... it's spitting out a regulator at 140 feet that proves to be kinda' unhealthy.

Make sense??

So do I plan on tables?? Actually no. I understand people have a very hard time with dive tables, that's why I wrote the Computerized Table Tutor Software.

Based on testing everyone from new divers to instructor candidates and instructors doing cross overs, I've seen many more human errors in calculating tables than I have ever seen in computer errors...

But I also dive with a backup computer. And yes... I trust them. I don't rebalance my checkbook with pencil and paper, I let quicken do it. And when doing multi-level dives, it would be practically impossible to do calculations to determine allowable times unless you spend the entire dive tracking depth and time for each level.

So I hate to admit it... but I just punch in my nitrox level, set a max depth alarm at 110 feet, and simply don't let the big number hit zero on the computer. Simplistic?? Yea... But it's how I've done it for the last 2000 dives.

huminah huminah. Yeah, of course. You just enlightened me to reset my max depth alarm on my puter when, and if, I use nitrox. If you don't look at the tables prior to a dive, have never seen anyone check tables prior to dive, how do you know what the max is ?Is it 110 ft on all recreational blends?

 

[pilot fish]

No you're not. It's just new. You're still relatively new to diving and now you're getting into something that's a bit more advanced.

I have several formulae that I've put together in a spread sheet that I can send you if you'd like.

It's kind of fun to learn how to take a mix, convert it to an EAD (equivalent air depth) and play with air charts.

Learning more about the PPO and percentages of daily allowable exposure at different depths can actually make multilevel diving a lot easier.

One of these days I've GOT TO take the advanced course!!!

You're kidding of course? You're OW, not AOW?