Nitrox Tables Vs. EAD (Long Post)

[KilgoreTrout]

I am in the process of developing a dive log and planning program for my beloved Mac OS X. I have successfully completed a dive planner by integrating Navy Air No-D tables into the software. (Please no comments about my choice, honestly they were the closest to my computer at the time.) Are the navy tables the same as the NOAA tables?

Having just completed a Nitrox Class last week, I decided that it would be fairly simple to update the program to plan for Nitrox mixtures. I planned to do this using by calculating the Equivalent Air Depth (EAD) and then running it back through my tables. In the process of implementing this, I ran into some issues between the tables that I would like to discuss. BTW, I am using NOAA Nitrox tables (I was told they were the same/compatible).

More Background:

The EAD Equation I'm using:

EAD = (((fsw+33)(1-%O2))/0.79)-33
(Corrected 5/18/2003 11:12EST)

This equation is solely looking at nitrogen levels. Therefore, I have added a Max Operating Depth check in the program which simply changes the max depth is you have exceeded it.

The problem:

I ran this profile: 150'@%36 for 100 min.

Of course this won't work, so the MOD got automatically changed to 95.33' and the No-D limit was changed to 40 minutes.

Next I ran: 92'@%36 for 150min.

Of course the No-D limit needs to change, but it went to 50 minutes.

EAD=68.26' No-D limit on Air at 70' is 50 minutes.

This is only one example. I found several other spots like this in the table yesterday.

So, my question is why is there a discrepancy? I realize that the easiest and safest solution is to remove the EAN section of my program. Should I be looking at PO2 at every depth?

But this brings up the question of which method is more correct. Tables or EAD? What method does most software use (I realize there are more advanced computational methods, but I don't have those)? I just see people on a dive boat using EAD because they have air tables with them and running into the same issue without even knowing it.

Can anyone with more experience in the matter shed some light on the subject?

 

[omar]

KilgoreTrout asked...
The EAD Equation I'm using:

EAD = (((fsw-33)(1-%O2))/0.79)-33

So, my question is why is there a discrepancy?

The correct EAD formula is:
EAD = (((fsw+33)(1-%O2))/0.79)-33

Try this and make sure your lookup routine is correct...

As you noticed this equation is just finding the equivalent depth for the same partial pressure of nitrogen. Not the best appraoch in my opinion.

omar

 

[KilgoreTrout]

That IS what I am using. I must have gotten ahead of myself when I typed that post.

I agree that it is probably not the best approach. Do you have any recommendations for other methods?

Thanks for catching that.

 

[Braunbehrens]

KilgoreTrout once bubbled...
I am in the process of developing a dive log and planning program for my beloved Mac OS X. I have successfully completed a dive planner by integrating Navy Air No-D tables into the software. (Please no comments about my choice, honestly they were the closest to my computer at the time.) Are the navy tables the same as the NOAA tables?

First, let me congratulate you on your choice of computing platform. OS X is incredible, sometimes I forget how happy I am with it, then I realize I haven't rebooted in weeks.

The Navy tables have some problems, so I'm not sure I'd be using those. Why don't you use a program like decoplanner to generate the tables. This would give you a better starting point. There are other programs out there as well.

Unfortunately deoplanner doesn't work on the Mac, unless you are running virtual PC and winblows.

Having just completed a Nitrox Class last week, I decided that it would be fairly simple to update the program to plan for Nitrox mixtures.

Wouldn't it be easier to simply have a cheat sheet so that when you plan a nitrox dive to 80 ft, you know that it's equivalent to a 60ft air dive?

I planned to do this using by calculating the Equivalent Air Depth (EAD) and then running it back through my tables. In the process of implementing this, I ran into some issues between the tables that I would like to discuss. BTW, I am using NOAA Nitrox tables (I was told they were the same/compatible).

More Background:

The EAD Equation I'm using:

EAD = (((fsw+33)(1-%O2))/0.79)-33
(Corrected 5/18/2003 11:12EST)

This equation is solely looking at nitrogen levels. Therefore, I have added a Max Operating Depth check in the program which simply changes the max depth is you have exceeded it.

The problem:

I ran this profile: 150'@%36 for 100 min.

Of course this won't work, so the MOD got automatically changed to 95.33' and the No-D limit was changed to 40 minutes.

.36 x 4 ATA or so, you are running a max PO2 of 1.4?

Next I ran: 92'@%36 for 150min.

Of course the No-D limit needs to change, but it went to 50 minutes.

EAD=68.26' No-D limit on Air at 70' is 50 minutes.

I don't understand your problem. Sounds like your program did the right thing to keep you out of serious deco.

This is only one example. I found several other spots like this in the table yesterday.

So, my question is why is there a discrepancy? I realize that the easiest and safest solution is to remove the EAN section of my program. Should I be looking at PO2 at every depth?

I'd like to help, but maybe I'm being dense here, I don't get the problem

But this brings up the question of which method is more correct. Tables or EAD?

EAD is going to be closer, but if you are using air tables to start with then you are just deriving your results from tables anyway. Anytime you use tables the results are going to be slightly scewed to accomodate 10 ft increments in depth.

Let me clarify this. Let's say that the air table says you have 50 mn at 70 ft. Now you want to do a dive to 85 ft. When you calculate the EAD and go to your table, it will have to look up the next deeper depth that matches the EAD. The table doesn't have a NDL number for 63.4 ft. So it used the one for 70 ft. Is this the problem you were mentioning above?

What method does most software use (I realize there are more advanced computational methods, but I don't have those)? I just see people on a dive boat using EAD because they have air tables with them and running into the same issue without even knowing it.

Can anyone with more experience in the matter shed some light on the subject? [/B]

Like I said, I'd like to help, but not sure exactly what the problem is. I derive all my profiles from air tables, including deco profiles. I use simple methods to shape the curve of the deco and account for any nitrox or trimix. All I carry along with me is a set of air tables.

Deco isn't that precise anyway. It's not like if you do 60 for 60 you'll be fine but if you do 62 for 62 you'll get bent. Even though most computers would like to make you think so.

 

[KilgoreTrout]

92'@%36->100'@#36 has a No-D limit of 40min. EAD=68' -> 70' = 50min No-D.

That is my main worry. By the 36 table, I should be doing a stop at 10' for 10min if I dive for 50min@100'. I realize that this is not rocket science. So many factors exist that change deco, blah blah blah... I just don't like the idea of a 10minute jump.

All I want in this program is to do basic planning. I will update it in the future whenever I get into more technical diving. I wouldn't feel comfortable doing it now.

I have other tables, but you can imagine the tedium required to enter the values from those tables, let alone get all of them working correctly. The EAD approach, though not ideal, is much easier. One table, infinite variety of mixes with one simple equation.

Creating a cheat sheet would be one method, but tricky for all varieties nitrox. I could stick to 32 & 36 but I would be limiting the program (and why do that?).

What about this... [Thinking out loud...]

If EAN>21 then
EAD = (((fsw+33)(1-%O2))/0.79)-30
else
EAD = (((fsw+33)(1-%O2))/0.79)-33

This makes things more conservative (which doesn't hurt my feelings) but doesn't screw with air dives.

Which tables would you recommend? (and out of curiousity, why?)

BTW, I'm glad to see there are OS X people on this board. Know anything about programming? Do you want to see this in it's current state? I would love feedback on it.

Thanks.

 

[Braunbehrens]

I see your problem now. You're getting a 10mn stop in one table, and your ean to air table gives you a no stop dive.

Well, we could make things more complicated ;-) ... I think that any dive needs a minimum of stops. There is no "no deco" dive. That's why I make a 1 mn stop at 40, 30, 20 on every dive. At 10 I either make a stop, or I ascend at 2 ft per minute if I have time and gas etc.

Looking at deco planner, 70 ft at 21% for 50 mn gives you 10 mn of stops. Setting the values differently gives you 15 mn of stops.

At 40 mn I still get 5 mn worth of stops.

Howevere, decoplanner tends to give stops anyway, and 5 mn of stops is probably a NDL dive if you looked at at table. 70 for 20 still gives me 3 mn of stops.

It looks like your program may be looking the wrong way when looking up the EAD.

In other words, when you get an EAD of 64 it looks at the table for 60 fsw, instead of 70 fsw.

Any chance that may be happening?

I'd be happy to look at your code, I have delved into programming on a couple of occasions, but in the end I always felt that the UI was too much of a pain to code. The "meat" of the coding was always more fun anyway. I think the first thing I ever wrote was a game of "life" on the commodore 64. Now that's a loong time ago. Never did get it to work.

 

[Cave Diver]

KilgoreTrout once bubbled...
92'@%36->100'@#36 has a No-D limit of 40min. EAD=68' -> 70' = 50min No-D.

First thing I would check is to make sure that 40 min is the correct NDL for 100' on EANx 36. This seems to be extremely high to me. What table are you getting this NDL from?

Looking at a set of Navy Air Tables, I agree on with the NDL of 50 minutes for a 70' dive on air and that 68' is the EAD for EANx 36.

Comparing that to my IANTD 36% tables you have an NDL of 75 minutes for that same 70' dive, but are only allowed 25 minutes of NDL at the 100' mark.

Using an IANTD Air table, it shows an NDL of 35 minutes for a 70' dive.

Since the Navy air table NDL is almost smack dab in the middle of the IANTD air and 36% table for the same depth, I would submit that it is not being as conservative for this dive. BTW, the 30, 32, and 34 IANTD tables all show a 51 minute NDL for 70'.

Secondly, I would like to know which agency your course was through? If it was an IANTD course, there are copies of all of the tables (21, 26, 28,30, 32, 34, 36, 38 and 40) in the back of the course book.

 

[Cave Diver]

Braunbehrens once bubbled...
I think the first thing I ever wrote was a game of "life" on the commodore 64. Now that's a loong time ago. Never did get it to work.

Wow! I remember those days! My first major programming accomplishment on a C-64 was to create one of those text based adventure games where you typed in instructions and it moved you from place to place and provided feedback to you based on your current location. (Anyone remember Zork?)

It took a lot of work to get it all figured out, but the sense of accomplishment was worth it.

 

[KilgoreTrout]

Here is a copy of the program.

http://homepage.mac.com/clathan/FileSharing7.html

The .dmg file is the program build (I coded it in 10.2.6 but it may work in previous versions?) The file called scuba.m is the meat of the code. I have XML property lists called Log.plist, plan.plist, NoD.plist, RNT.plist and SI.plist in the contents of the program bundle. The last three (you guessed it) are the table. They are basically matrices.

If you can't decifer the code, no worries. I mainly want input from someone else. Most people I know (especially mac owners) aren't divers so I can't get decent input.

To answer other questions, the class was both IANTD & Padi. An odd one night class. I didn't buy the book since the instructor had NOAA tables for me and since I own the NOAA dive manual, I'm not worried about it.

The NOAA %36 NDL for 100' is 40min. I have included the aforementioned table.

35min NDL at 70'? The NOAA Air table gives 50min NDL at 70'! It appears that the IANTD tables are way conservative (not a bad thing).

It appears that this should spin off another topic... Which set of tables do you use, NOAA, NAUI, PADI, IANTD, Navy, etc... Or are most people relying on software now?

BTW, my first programming experience was with TURTLE. I was 3 yrs old! Never had a C64, but did have a "Tommy Tutor Computer" that I was able to code some BASIC. Very fun stuff.

Good Night.

 

[KilgoreTrout]

Don't know what happened...