Experienced gas swichers

[Bigcape]

I am having a total brain lock-up!

I have been using computers toooooo long now i am going back to the tables and just realized that I have either forgotten how to do repetitive dives or the answer to this question is wrong in the book.

Here goes:


A diver completes a 70 foot dive for 30 minutes, using air. One hour later she plans a 60 foot dive using Nitrox-II. What is her maximum actual bottom time to avoid stage decompression?

 

[do it easy]

I get about 60 minutes, but she would have to do the 3 minute safety stop and stay out of the water for 3 hours (the WXYZ rules).

Anyhow, it depends on the tables that you are using... I used the PADI air tables AKA the RPD. I don't have nitrox tables, so I calculated the EAD, which introduces rounding. This is just a guess, but using the PADI nitrox tables, the anwer would probably be about 1.5 hours.

 

[PerroneFord]

Vplanner says 165 minutes set at +2 conservatism for dive #2. For what that's worth.

 

[Bigcape]

I get about 60 minutes, but she would have to do the 3 minute safety stop and stay out of the water for 3 hours (the WXYZ rules).

Anyhow, it depends on the tables that you are using... I used the PADI air tables AKA the RPD. I don't have nitrox tables, so I calculated the EAD, which introduces rounding. This is just a guess, but using the PADI nitrox tables, the anwer would probably be about 1.5 hours.

Ah, you worked it backwards using the EAD of nitrox and kept it all in the AIR table.....Very Very Smart.smart.

However I am trying to flip between tables and it is kicking my arse!!

 

[Bigcape]

Vplanner says 165 minutes set at +2 conservatism for dive #2. For what that's worth.

here are my choices:


a. 62 mins

b. 30 mins

c. 60 mins

d. 20 mins

 

[PerroneFord]

In our nitrox class, we just did EAD conversion and ran air tables. Usually simpler than carrying around a bunch of tables. If I was doing it by hand, that's the way I'd do it. But for non-class work, if I am diving nitrox on 60-70ft dives, I'm really not all that worried about NDLs. I'd need large doubles to even get close.

 

[Bigcape]

I figured it out........the resulting group designation of the gas you just used is the ENTRY point to the next table!!!

Im gonna try the EAD methode and convert and see how it works out.

 

[do it easy]

So what is the answer? And how much more time do you get using the nitrox tables give? It sounds like they might be about the same.

 

[Bigcape]

No I didnt figure it out. I just thought i did

 

[Bigcape]

Air equivalent is one thing but Actual allowed time at bottom with a new mix is different........apples and oranges