Nitrox Tables Vs. EAD (Long Post)

[Cave Diver]

Okay, that would appear to be part of the problem. If you are using NOAA tables for the 36% computation and Navy Air tables for the EAD, that could explain the discrepency of 10 minutes between the two.

Different tables often have different NDL's.

My suggestion would be using a NOAA Air Table when doing your EAD calculation if you are using the NOAA 36 Table and see if that clears it up.

 

[KilgoreTrout]

I was told (and everything I've seen) that the NOAA tables are the same as the Navy tables. I haven't held them side by side yet, but for this particular case it is true.

I am aware that different tables could be incompatible. I.e. a G group in one table being an F or H group in another.

I will hunt down a Navy nitrox table to see if this does clear things up. Its just I don't have one handy.

Thanks for your help.

 

[Braunbehrens]

I haven't had time to look at your program yet, however, I would use a fairly aggressive table if I were you. The reason is that it's always easier to err on the side of conservative (i.e. do a couple of stops on the way up). If you have a very conservative table, you may find yourself riding the edge of it all the time, and then you won't know when you've gone too far over the line.

Just my .02

 

[DIR Tec Diver]

Also a good idea to limit your pp02 to 1.3, to also err on the side of caution. Many people slip into the idea that high o2 concentrations in the mix do so many wonderful things for you, when in actualaty there is little gain in few percentages of 02.

One example of a difference in my Vytec and using Decoplanner is when I dove in Cyprus at the Zenobia. I used decoplanner to plan the dive, and then left my Vytec in normal Nitrox mode to compare. Decoplanner had me out of the water 14 minutes before the Vytec would allow, and of course I was completely clean. I analyzed the profiles and data from the computer and the decoplanner, and doing things like this really have helped me understand decompression better as well as what is happening to the body. I should also mention that my profile was very conservative, as the previous post mentioned if you are riding the edge long enough you will get cut (or bent as the case may be).

If people use NOAA, NAVY and other tables and interchange them, you will get into trouble. To the best of my knowledge there is no interchangeability between them, and the conversions I have seen have obvious flaws in them, and most all diving agencies directly advise not to cross match tables.

 

[Big-t-2538]

Cave Diver once bubbled...


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?

I was pretty sure that using a max ppo2 of 1.4 that the MOD for EANx is 95ft, or am I just an idiot with my math????

 

[Big-t-2538]

Cave Diver once bubbled...


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?)

Zork, Gorf, Choplifter, and Zaxxon....all wonderful C-64 games

 

[DIR Tec Diver]

1.4 divided by .36 gives you 3.888888 ATA or 29 meters, round down for conservatism and 28m is good to go.

You can also do the opposite if you don't know the EANx percent appropriate.

PP02 desired divided by ATA

in this case 1.4 divided by 3.8 gives you .368 round down for conservatism 36%

 

[KilgoreTrout]

You are right, the MOD is around 95'. But the trick is that you round up to 100' for the table. 1.4/0.36=3.88 -> 3.88*33-33=95.04' (Same as below but different units) (1m=3.28ft)

That is where the 40min@100' on %36 comes from.

I will compare the NOAA/Navy tables more. They do appear to be the SAME EXACT table. I will go line by line to compare.

I have the NOAA Air and EAN36 tables, and this EAD-EAN36 conversion problem happens using NOAA tables only. I know that it would happen with ANY set of tables.

It is beginning to sound like this is not the best method of planning a dive. I will probably just limit my program to 32 & 36 and just enter in the tables manually. I just wanted this to work with any mix. If I get a trained monkey (I've been THIS CLOSE to buying one) I may enter more tables in, but the tedium is not something I look forward to.

I will keep searching for algorithms that I can use to calculate exposure/no-d limits. I have seen a couple papers floating around online, but I hesitate to use just any formula I find unless I can tell if it is well thought out and accurate (as possible).

Thanks and Good Day.

 

[Charlie99]

A good air to nitrox depth conversion table is at
http://www.gooddiving.com/Doc/EquivalentNitrox.pdf


This takes the even 10' air depths, and shows the equivalent nitrox depths for various mixes. This way you don't have the round off problem you have run into.

For example, it shows that for EAN32, 80' air depth is equivalent to 98' on EAN32, so you can dive 98' max for 30 minutes or whatever the 80' NDL is on the air tables you are using.

Although the NAVY/NOAA tables are more liberal than PADI for 1st dvies, if you are doing repetitive dives, you will generally get more total bottom time using the PADI tables, since they are calculated for a 60 half time of outgassing, while the Navy/NOAA tables use 120 minutes.

Charlie