END Calcutaion question

[skdvr]

I have been reading Exploration and Mixed Gas Diving Encyclopedia and I am a bit confused when it comes to calculating END or EAD. Just the differnece between END and EAD has be confused at the moment too. I thought that they were the same thing but I guess not. I am going to try to explain this the best I can so please bear with me. In this book it shows to calculate EAD us the following formula.

EAD = FN2 x Depth + 33 / .79 - 33

That pretty much made sense to me because it is the same thing as what was tought to me in PADI Nitrox.

Then I got the the END formula which really threw me for a loop because it is as follows.

END = Target END + 33 x .79 / (depth + 33)

The first part of it really threw me off because I thought I was supposed to be calculating END and it is asking me to input my target END. well after looking at it a little further it is giving you the FN2 for what ever your target END is. I do not really understand why they call it a END formula when you are not calculating END.

So then at this point I am still thinking that EAD and END are still actually the same thing, but I went onto my trusty laptop where I keep a conglomerate of scuba info. From lists of books I want to read, tank charts, Owners manuals, and of course formulas. The following is a formula that I had for calculating END, that I saved last year. I really have no idea where I got it from but after some google searching it seems to be a faily common formula now.

END = (Depth + 33) x (1 - FHe) - 33

Which is obviously only subtracting out the He and counting O2 as a narcotic as well.

So my question is.

What formula do you use? Does IANTD still teach the EAD formula that I posted above for use with Trimix? Is the last END formula that I posed actually used at all? I guess all I am asking or trying to ask is what do you guys use? In the IANTD tables they all seemed to be based off the above EAD formula, so my assumption is that is what is taught since I just bought this book last year this time.

Thanks for any and all help...

Phil

[scububa]

FIrst of all, as written in your post, the first formula is not mathmatically correct. (Order of operation would have 33 divided by .79 and that added to the product of Depth and Nitrogen fraction.)

EAD = [ (FN2) (D+33) / .79 ] - 33

So, you are looking at FN2 over .79.

You are normalizing to .79 (air % of N within)

If FN2 = .79, then the ratio is 1 and you are 'same as' (equivalent to)

If FN2 > .79, then ratio is above 1 and you are, at a depth, with more N, equivalently deeper than with air

If FN2 < .79 then ration is below 1 and you are, with less N, equivalently shallower.

[skdvr]

FIrst of all, as written in your post, the first formula is not mathmatically correct. (Order of operation would have 33 divided by .79 and that added to the product of Depth and Nitrogen fraction.)

EAD = [ (FN2) (D+33) / .79 ] - 33

So, you are looking at FN2 over .79.

You are normalizing to .79 (air % of N within)

If FN2 = .79, then the ratio is 1 and you are 'same as' (equivalent to)

If FN2 > .79, then ratio is above 1 and you are, at a depth, with more N, equivalently deeper than with air

If FN2 < .79 then ration is below 1 and you are, with less N, equivalently shallower.

Thank you for the correction...

I am not following the rest of it though. Can you speak (type) a little slower please....:D

Phil

[b1gcountry]

Phil-

I think you're a little confused on a couple of things.

EAD-equivalent air depth, which is used when you are diving a nitrox mix other than air, but still want to use air tables. The concept is that your body absorbs nitrogen based on the partial pressure of N2 you are breathing at depth. If you lower the percentage of N2 in your mix, you will have to go deeper to absorb N2 at the same rate.

For example, if you are breathing 32% at 100', you are breathing a ppN2 of 2.72 ({100+33}/33*.68). If you were diving air, you would only have to be at 80' to reach the same ppN2 ({80+33}/33*.79). This means that theoretically, you could plan your decompression for a dive to 100' on 32% the same way you would plan an air dive to 80'.

The formula you quoted solves for the equivalent air depth, with the true depth, fO2, and fN2 as givens.

END- I've heard people call this equivalent nitrogen depth, or equivalent narcotic depth. I believe a lot of people originally discounted the oxygen in their calculations, but as more people started thinking it should be included, they changed the acronym (and the associated calculations) from nitrogen depth to narcotic depth. This is not as clearcut as EAD as you've seen, because their are two ways of approaching this calculation.

The first way is common for people who like standard mixes. The first thing you do is decide upon a planned depth, and mix. You can then use these to solve for the amount of narcosis you will be feeling. Assuming O2 is narcotic, the calculation is pretty much just finding the partial pressure of everything that isn't He, and converting to depth. For example, if I'm planning a dive on the SS Wisconsin, I'll plan on a max depth of 120', and I would use 25/25. The ambient pressure is 4.6ata (120+33 /33). Subtracting out the ppHe, you get 3.5ata (4.6ata * .75). This is equivalent to 82' (3.5ata*33 - 33). This is conceptually what you are doing, but you can simplify the calculations, and you get the formula you quoted:
equivalent narcotic depth = (planned depth + 33) * (1-fHe) - 33

The same calculation ignoring the narcotic potential of O2 is
= (planned depth + 33) * fN2/.79 - 33


The second way to calculate END is common among people who like to use best mix calculations. Instead of using the mix as a constant, they instead use the amount of narcosis they find acceptable as the constant, and then solve for the fHe they need to use. So if you decide that 100' is an acceptable narcosis level, that's 4 ata. For the same dive on the Wisconsin, you are going to 120' (4.6ata), and want to hit 4ata or less. You need a mix that will cut narcosis by 87% (4.0ata/4.6ata). This means you need 13% He or more. Again, the simpler formula is the one you provided:

Target fHe = 1 - (Target Narcotic Depth + 33) / (Planned Depth + 33)


So yes, there are two formulas. One is truly the END, and the second is really a best mix calculation you can use to acheive a planned END.

Tom

[skdvr]

Thanks Tom...

What confused me is that from other things that I have read it appeared that most were figuring O2 as a narcotic, but when looking at the IANTD tables it appears that they are figured without O2 as a narcotic. Now their tables do not start until 150ft for trimix but here is an example using IANTD C-3706 for an END with 1.4 PO2 to a depth of 150ft and a END of 80ft you would use 25/26.

So if you figure it with the EAD formula that I have above you end up with.

EAD = .49FN2 x 183 = 89.67/.79 = 113.51 - 33 = 80.51ft.

The END formula that you posted for not counting O2 is the same as mine for EAD right?

So Tom when you plan Trimix dives do you count in the O2 as narcotic? I am assuming that you do.

Obviously I will do what ever is taught, when ever I take a class. I am just looking to see if IANTD's tables may be using an older (less conservative) approach to planning.

Thanks
Phil

[scububa]

Sorry, I got 'family tasked' and then Joan took the computer.

Tom did a better job and I am not trimix trained, but I intended on continuing...

Yes, I thought EAD was normalizing EANx to allow the use of air tables and air experience.

With EANx, we are dealing with narc at a level we deal with with air or less. Oxtox limits the use of EANx below what were use to with air. So the trade is between Nitrogen loading and Oxtox (depth).

Now, I am getting into being less sure, but with Trimix, we are working deeper (usually) or, at least for Normoxic, working to be clearer headed deep. The Nitrogen Narcosis I thought was better defined as INERT GAS Narcosis. So, I thought END was normalizing the inert gas content to what we know about nitrogen alone.

1 = FO2 + FN2 + FHe
Then by picking a set point, say we don't want to be more narced than 100 ft., we can calculate the correct mix. O2 is set first to control Oxtox for planned depth. This leaves

1 - FO2 = FN2 + FHe

Then by picking the 'narc limit' and knowing the planned depth (partial pressure), you calculate the FN2. The remainder is then FHe.

I have read about the He and the O2 also being factors in narcosis or nervous system anomolies, but I thought N2 was the heavy hitter, washing out the others, for the most part.

So, three things need to be balanced or traded. Oxtox, inert gas absorbtion, and narcosis.

My thought is that you control Oxtox with the FO2, then manage the narcosis with FN2 and make up the difference with FHe. Then when you dive, you have to control the on/off gassing of both inert gasses.

I'd never post this on another board for all the BS that would follow. I am hoping here that I will get philosophically straightened out more gently without all the 'learning to dive on the inet' stuff. I am just begining to think about starting trimix training, so the subject has my interest. I have several books, but while they show the tables, calcs and mixes, they don't do much of anything in terms of addressing the trade offs and rational.

[skdvr]

I will see what I can find, but I remember reading that O2 is more soluble in lipids than N2 is which makes if more Narcotic. Twice as much if I remember correctly. BUT you are also metabolizing the O2.

The narcotic effect of He is there but it is pretty much nothing. Again I do not remember what exactly but I think it was like 5 times less narcotic than N2. At least that it what is sticking in my head.

I felt the same way about being BASHED over my internet head asking somewhere else.

I really need to get Physiology and Medicine of Diving (http://www.amazon.com/Physiology-Medicine-Diving-Peter-Bennett/dp/070201589X) it is supposed to be a great book, I am just not sure if it would be way over my head or not. Probably...

Phil

[steve2281]

Phil-

I think you're a little confused on a couple of things.

EAD-equivalent air depth, which is used when you are diving a nitrox mix other than air, but still want to use air tables. The concept is that your body absorbs nitrogen based on the partial pressure of N2 you are breathing at depth. If you lower the percentage of N2 in your mix, you will have to go deeper to absorb N2 at the same rate.

For example, if you are breathing 32% at 100', you are breathing a ppN2 of 2.72 ({100+33}/33*.68). If you were diving air, you would only have to be at 80' to reach the same ppN2 ({80+33}/33*.79). This means that theoretically, you could plan your decompression for a dive to 100' on 32% the same way you would plan an air dive to 80'.

The formula you quoted solves for the equivalent air depth, with the true depth, fO2, and fN2 as givens.

END- I've heard people call this equivalent nitrogen depth, or equivalent narcotic depth. I believe a lot of people originally discounted the oxygen in their calculations, but as more people started thinking it should be included, they changed the acronym (and the associated calculations) from nitrogen depth to narcotic depth. This is not as clearcut as EAD as you've seen, because their are two ways of approaching this calculation.

The first way is common for people who like standard mixes. The first thing you do is decide upon a planned depth, and mix. You can then use these to solve for the amount of narcosis you will be feeling. Assuming O2 is narcotic, the calculation is pretty much just finding the partial pressure of everything that isn't He, and converting to depth. For example, if I'm planning a dive on the SS Wisconsin, I'll plan on a max depth of 120', and I would use 25/25. The ambient pressure is 4.6ata (120+33 /33). Subtracting out the ppHe, you get 3.5ata (4.6ata * .75). This is equivalent to 82' (3.5ata*33 - 33). This is conceptually what you are doing, but you can simplify the calculations, and you get the formula you quoted:
equivalent narcotic depth = (planned depth + 33) * (1-fHe) - 33

The same calculation ignoring the narcotic potential of O2 is
= (planned depth + 33) * fN2/.79 - 33


The second way to calculate END is common among people who like to use best mix calculations. Instead of using the mix as a constant, they instead use the amount of narcosis they find acceptable as the constant, and then solve for the fHe they need to use. So if you decide that 100' is an acceptable narcosis level, that's 4 ata. For the same dive on the Wisconsin, you are going to 120' (4.6ata), and want to hit 4ata or less. You need a mix that will cut narcosis by 87% (4.0ata/4.6ata). This means you need 13% He or more. Again, the simpler formula is the one you provided:

Target fHe = 1 - (Target Narcotic Depth + 33) / (Planned Depth + 33)


So yes, there are two formulas. One is truly the END, and the second is really a best mix calculation you can use to acheive a planned END.

Tom

A very good resposne and exactly the wasy I understand the difference between EAD and END depth.

What is absurb to me is the way Iantd goes about figuring turn pressures with dissimilar cylinders. RMV,SFR, two or three other charts; why not just figure it the way most cave divers do it: smallest cylinders are the control, and when either diver reaches 1/3 cu ft of the smallest cylinders the dive is turned. Don't even need SAC or RMV other than perhaps in the planning stage??? Over my head. Any thoughts?

[scububa]

I am quick to agree that IANTD goes heavy on the charts. To me, doing a calculation method is easier, but others aren't as comfortable with that. (I don't fall for the easier to make a mistake after seeing the way people make mistakes with tables.)

But, smallest cyclinder, alone, is not sufficient. If you have the smallest cylinder and I am the hoover, your 1/3rd for you to come out at max penetration is fine for you, but the other 1/3rd isn't enough for me. And without a lot of on the fly math for burn rate of remaining gas and a big knife, probably we both are in trouble as I suck into your 1/3rd. (If my tanks are enough bigger, I won't necessarily hit 1/3. Then as you turn the dive, I lose all gas.)

The smallest cyclinder will be in control, but not at a simple 1/3 turn.

[skdvr]

OK so here are a few links. This one (http://archive.rubicon-foundation.org/dspace/bitstream/123456789/2810/1/734806.pdf) talks about a study where there find the narcotic effects of O2 to be the same as N2

And yet another (http://divemar.com/divermag/archives/dec96/divedoctor_Dec96.html) that says the O2 is nothing to worry about.

I think I am starting to go crazy....

Phil

[skip]

I do not include the O2 in my END calculations. Some do. I have not had a problem at depth with narcosis and see no good reason to include the O2 - it's not really narcotic in the general mix of things. But many disagree with me and do include it in the END calculations.

As for IANTD's RMV and SFR, whatevers, I suspect it's primarily for planning purposes - how much will this particular dive require with sufficient reserves? If you want 20 minutes on the bottom at 260 feet, then you best make sure you have the gas to do the dive before you are in the water calculating turn pressures!

Cave divers do all those calculations and tables and charts too - when they are planning a deep cave dive (or long exploration dive) involving travel mixes and deco.

-skip

[skip]

But, smallest cyclinder, alone, is not sufficient. If you have the smallest cylinder and I am the hoover, your 1/3rd for you to come out at max penetration is fine for you, but the other 1/3rd isn't enough for me. And without a lot of on the fly math for burn rate of remaining gas and a big knife, probably we both are in trouble as I suck into your 1/3rd. (If my tanks are enough bigger, I won't necessarily hit 1/3. Then as you turn the dive, I lose all gas.)

The smallest cyclinder will be in control, but not at a simple 1/3 turn.

but that's not how it works...the one with the smaller doubles calculates thirds in terms of cubic feet (not psi) and that is how much the buddy can use too, no matter how big his/her tanks and no matter the RMV. Why is RMV not important? Let's say the one with the smaller tanks had 210cf total, so 1/3 is 70cf. So the one with bigger tanks can also use only 70cf. The "hoover" can only use 70 cf on the way in. So the hoover blows all gas at max penetration (used 70cf). Buddy, not being a hoover has used less, say 60cf of the 70 available. That leaves buddy with 150cf for both to exit. Hoover only used 70 to get in and now has 70 from buddy to get out (keep your cool and you will survive - no panic, no heavy breathing, stay calm on exit). Also remember the 1/3's rule is the least conservative and a 1/4's rule may be better in many conditions.

-skip

[skip]

OK so here are a few links. This one (http://archive.rubicon-foundation.org/dspace/bitstream/123456789/2810/1/734806.pdf) talks about a study where there find the narcotic effects of O2 to be the same as N2

And yet another (http://divemar.com/divermag/archives/dec96/divedoctor_Dec96.html) that says the O2 is nothing to worry about.

I think I am starting to go crazy....

Phil

The first one says O2 became narcotic at high partial pressures (1.65).
The second one says basing O2 narcosis on physical property of O2 is incorrect method.

We don't do PPO2 above 1.4, so yes, O2 is narcotic if you push it to high PP's, but No it's not narcotic if you keep it 1.4 or less (below 1.65 according to the article. Unless I missed something, that's how I understood the articles.

I do wonder about extended O2 consumption. Since the Oxygen clock is both PP and Time dependent, does O2 become narcotic at lower PP's if maxing out the daily does limit? Well, there are some things we just don't know yet.

skip


skip

[steve2281]

I am quick to agree that IANTD goes heavy on the charts. To me, doing a calculation method is easier, but others aren't as comfortable with that. (I don't fall for the easier to make a mistake after seeing the way people make mistakes with tables.)

But, smallest cyclinder, alone, is not sufficient. If you have the smallest cylinder and I am the hoover, your 1/3rd for you to come out at max penetration is fine for you, but the other 1/3rd isn't enough for me. And without a lot of on the fly math for burn rate of remaining gas and a big knife, probably we both are in trouble as I suck into your 1/3rd. (If my tanks are enough bigger, I won't necessarily hit 1/3. Then as you turn the dive, I lose all gas.)

The smallest cyclinder will be in control, but not at a simple 1/3 turn.

Here is a discussion over on the Deco Stop about iantd gas matching dissimilar tanks. Read all of it. http://thedecostop.com/forums/showthread.php?t=26955&highlight=iantd&page=3

Here is another link to the proper way to figure dissimilar tank turn pressures. http://www.cavediveflorida.com/gas_match.htm

Yes, it is a simple as turning at 1/3 the smallest tanks; EVERYONE turns at 1/3 volume used of the smallest tanks. A guy with dual LP 120's might turn the dive at 3300 psi depending on who he's diving with.

[skdvr]

The first one says O2 became narcotic at high partial pressures (1.65).

skip
Yeah, I am not sure about it. The way that I was reading is that O2 at 1.65 ATA was just their test pressure and they saw a 10% decline in arithmetic skills and had to get N2 to 6.3 ATA while keeping O2 constant before they could see the same 10% decline in arithmetic ability.

So I dont think that they are saying that O2 is not narcotic until 1.65 ATA, I think that they are saying that its narcotic effects kick in much sooner than N2 (about 4 times faster).

BUT, reading the whole thing kind of confuses me. So it is very likely that I am reading it wrong...

Thanks for the input Skip....

Phil

[skdvr]

I went ahead a started a thread on TDS just asking about the O2 narcotic thing...

Just incase anyone wants to follow along.
http://thedecostop.com/forums/showthread.php?t=42284

Phil

[scububa]

but that's not how it works...the one with the smaller doubles calculates thirds in terms of cubic feet (not psi) and that is how much the buddy can use too, no matter how big his/her tanks and no matter the RMV. Why is RMV not important? Let's say the one with the smaller tanks had 210cf total, so 1/3 is 70cf. So the one with bigger tanks can also use only 70cf. The "hoover" can only use 70 cf on the way in. So the hoover blows all gas at max penetration (used 70cf). Buddy, not being a hoover has used less, say 60cf of the 70 available. That leaves buddy with 150cf for both to exit. Hoover only used 70 to get in and now has 70 from buddy to get out (keep your cool and you will survive - no panic, no heavy breathing, stay calm on exit). Also remember the 1/3's rule is the least conservative and a 1/4's rule may be better in many conditions.

-skip

I think that we are saying the same thing. I guess I should have said that the smallest cylinder will 'probably' be the controlling factor by way of having to have 1/3 plus the equivalent hoover 1/3. Each set has to have a minimum of 1/3 of each guys requirement to exit and turns are set accordingly. And, I didn't mean to imply psi control, but volume (cf) control factored back to PSI. The smaller cylinders will have to turn before a 'standard' 1/3. (Which, btw, is what all the various charts questioned are doing.)

I started to add a comment about 1/3 being on the edge. But, after following the thread on TDS, I didn't want to hijack the original END too far off line. But, I agree with what you say and was attempting to say the same.

[skip]

Yeah, I am not sure about it. The way that I was reading is that O2 at 1.65 ATA was just their test pressure and they saw a 10% decline in arithmetic skills and had to get N2 to 6.3 ATA while keeping O2 constant before they could see the same 10% decline in arithmetic ability.

So I dont think that they are saying that O2 is not narcotic until 1.65 ATA, I think that they are saying that its narcotic effects kick in much sooner than N2 (about 4 times faster).

BUT, reading the whole thing kind of confuses me. So it is very likely that I am reading it wrong...

Thanks for the input Skip....

Phil

They did not get the effect at lower PPO2, the control value of 0.25. It's pretty dense reading, but they can not claim there's an O2 narcosis effect at lower PPO2's because they didn't test lower values. The effect seemed very small to me. They report "statistical significance," but did not report a magnitude value, which is really needed to give some real-world generalizability. The 10% increase in speed and errors in doing math does not seem like much to me. Means were like 25 problems correct/done dropping to 22/23 problems correct/done and that's their "narcotic" effect.

And since we don't dive 1.65 PPO2's, it seems to me that we have a case of science and theory showing us narcosis, while in real life the effect is too small to be "significant." I'm also not convinced that O2 is more narcotic than N2...in real life. It is in science though. The PPN2 of 1.65 is nothing at all, no narcosis, but they only tested N2 at 1.3ata and 8ata (PPN2's of 2.3 and 6.3). A PPO2 of 6.3 would be killer! So yes, O2 at 1.65pp is more narcotic than N2 at 6.3pp, but we don't breath the kind of PP's they are talking about in the article.

I ignore O2 in END calculations (and EAD), keep the PPN2 around 3.15, and have had no problems with narcosis. As an "experiment," I dove to 240 feet on "lite" helium and couldn't remember much of anything - my buddy told me stuff I swear did not happen. Then we did the same dive on proper helium mix and the difference was night and day - I remembered everything.

I've also had equipment malfunction at 310 feet and during O2 deco and solved the problems just fine. I'm thinking that given the science and that 10% effect, maybe I was 10% slower in removing the inflator hose from the leaky inflator, or 10% slower in repairing the deco reg mouthpiece when it came apart....oh wait, the article said NO EFFECT on physical tasks, only on the math problems! good reason to get those skills practiced over and over until muscle memory takes over and no thought is needed!

skip

[b1gcountry]

Dang, this is the most activity on a thread since I joined!

Phil-
If you want to go halves on the deco for divers, let me know. I'll throw in my share just to read it and you can keep it on your shelf.

Jim-
Yes on everything you said. ppO2s are most important. Then fHe. You manage everything else with your ascent profile/gas switches.

Steve-
I got what you meant the first time. A third of my starting supply isn't necessarily a third of your starting supply, but I don't want to get sidetracked on thirds...


As to the narcotic effects of O2, I remember the same tests Phil was talking about in regards to the lipid solubility. O2 is way more soluble than N2, which theoretically makes it more narcotic. BUT it is also metabolized by the body, which theoretically makes it less narcotic. As far as the science goes, I think there's just too much going on to really understand what is going on in the body theoretically.

However, I do know that when I dive EAN32 to 100', I'm just as narc'd as I am diving air to 100'. If oxygen wasn't narcotic, then I should be more clear-headed diving nitrox, but I really haven't found this to be the case. Doing the calculations, EAN32 at 100' has the same ppN2 as air at 80'. I think I would notice some difference if N2 was the only contributing factor. I've got to believe that O2 plays at least some part.

As far as calculations go, it really doesn't matter. Running the numbers for a couple common mixes:
25/25 @ 150' END = 104'/83'
21/35 @ 150' END = 86'/69'
18/45 @ 200' END = 95'/76'
15/55 @ 250' END = 94'/75'

So using one method over another only gives you about a 15-20' difference in narcosis levels. It's also pretty consistent, so you can get pretty much the same result by just adjusting your results up or down by 20' to see what the other formula would give you. I think the O2-As-Narcotic formula is easier to use. I can do it in my head. In the end, you're just picking an arbitrary narcosis level anyway, so the end result is going to be the same if you use formula 1 with an END of 120', or formula 2 with an END of 100'. Why not just go with what's easiest?

Once you start diving trimix, you KNOW you are going to have deco, and you KNOW you are going to have an expensive fill. Once you accept that, the difference 5-10% He, and 2-3% O2 makes is what maybe $15 more for a fill, and 5min more at 20'. If I'm going through the trouble and expense of a deep dive, I don't want to just reduce narcosis, I'm going to eliminate it.

Tom