Nitrox tables/math

[NJMike]

Okay, I'd like to go back to the original post by frogman159....

I printed out your post and did the dives last night. You did correct the rounding error on dive 2 - rounding PPO2 down instead of up, resulting in a 5% difference in accumulated O2.

But I get different ending pressure groups (EPG) for dives 2, 3 and 4. I did the dives both ways - using the equivalent air depth (EAD) as well as the enriched dive tables for EANx32 and 36.

For dive 2, using the RDP and an EAD of 42', I get a EPG of 'M'; using the enriched table I get 'L'.
For dive 3, using the RDP and an EAD of 38', I get 'I'. I get the same answer with the enriched table.
For dive 4, only using the RDP I get 'L'.

Frogman, can you check these? If anyone else sees my mistake, please chime in!

 

[Chernish]

I think you simply forgot to take the begining groups into account:

Finish dive 1 with group L; wait 1 hour; group becomes C
Begin dive 2 with group C; using the EANx 36 tables, you have to add 21 minutes to the real bottom time at 18m : 40+21=61 -> Finish Dive 2 with group O

And so on and so forth

Cheers!

 

[NJMike]

Chernish, you have given me something to look at. I have not been adding RNT to come up with an ending pressure group. I have just checked the problems in the PADI Nitrox book and they do not go that far in the answers.

I do not have an OW book to go back and review the proper use of the tables. Being out of diving for a while, then coming back in the age of computers has contributed to my forgetting how the tables worked. Thanks!

But even so, your answers do not agree with those of the frogman. He says that dive 2 ends up as R; you say O. I followed your reasoning and can see how you got O.

 

[frogman159]

Chernish, you have given me something to look at. I have not been adding RNT to come up with an ending pressure group. I have just checked the problems in the PADI Nitrox book and they do not go that far in the answers.

I do not have an OW book to go back and review the proper use of the tables. Being out of diving for a while, then coming back in the age of computers has contributed to my forgetting how the tables worked. Thanks!

But even so, your answers do not agree with those of the frogman. He says that dive 2 ends up as R; you say O. I followed your reasoning and can see how you got O.

Sorry for the delay,
We agree after dive 1 and the first 1hr surface interval we are "C" divers.

Dive 2 is 60ft, but I changed gas to Nitrox 36%, therefore the equivalent air depth is 42ft

On page 2 of the air dive planner, 42ft will round up to 50ft, now follow column C till it intersects with 50ft- You'll see that will indicate you have 17min of Residual nitrogren and a Max dive time of 63 minutes.

Flip back to page 1, remember 60ft is now equivalent to 42ft, which round to 50. Follow the 50ft column down to 40minutes for the dive time PLUS 17 minutes of residual nitrogen time so New dive time = 57minutes. 50ft for 57 minutes makes you an R diver when you come up from dive 2.

 

[frogman159]

I think you simply forgot to take the begining groups into account:

Finish dive 1 with group L; wait 1 hour; group becomes C
Begin dive 2 with group C; using the EANx 36 tables, you have to add 21 minutes to the real bottom time at 18m : 40+21=61 -> Finish Dive 2 with group O

And so on and so forth

Cheers!

My EAN36 table column C @ 60' gives a RNT of 20, max dive time of 95-

So I get 60minutes of bottom time at 60' I come up with Group O also when i use the EAN36 table- I think Padi revised this tables in 2003, that may account for our slight discrepancies if you have an older table.

I figured my orignal with Equivalent Air Depths and the PADI Air RDP. Which is why our groups are a little different, But it is intresting this was brought up- it appears using EAD and the Air RDP is a more conservative approach.

 

[NJMike]

I just bought the Nitrox book with the course....so I hope I have newer tables. My air RDP is about 2 years old.

I think the issue is very clear. I was out of diving for 30 years. Got back into it in 2006. I immediately bought a dive computer. The dive computer is so awesome that I never did go back and do an adequate review of all the book work. Some I did, but not using the tables (since I had the new, awesome computer . ) But now I have been reminded how RNT is used in dive planning.

So this has been a great discussion and I thank you and chernish for answering me!

 

[NJMike]

BTW, frogman159, I'm doing my nitrox certification next month down in Jupiter, FL. When did you say you were doing yours?

 

[frogman159]

BTW, frogman159, I'm doing my nitrox certification next month down in Jupiter, FL. When did you say you were doing yours?

Bonaire at the end of March

 

[NJMike]

Sweet. I just googled the RDP and did a review on using the tables. I'm planning on 4 dives off Jupiter and 1 at Epcot's Living Seas aquarium during the week I'm down there.