Nitrox to Air

[asckar]

I plan on diving the U-853 in a couple of weeks and my plan is for the first dive - to 110 feet - to be breating EAN32. My plan for the second dive is with air (since I only have one nitrox tank). My question is when do I transfer to the air Repetative Dive Table? I'm thinking that as soon as I surface I use the regular air table to determine my SI using the air equivelent of my first dive (aka: 90 feet for an actual depth of 110 on EAN 32) and continue with the air table from that point on. Is this correct?

 

[Atticus]

The numbers on the surface interval tables should be the same on both sets of tables. I just verified this using PADI's 32% and Air tables.

On another note, if you do both dives to the same depth then your partial pressure of nitrogen on the second dive will be greater than on the first dive (think of the EAD of the first dive compared to the second). This violates the deepest dive first rule.

I haven't always followed that rule myself, but if I may suggest - doing the first dive on air and the second dive on 32% will be a little easier on your body. (Some may debate this, but this is the standard line from pretty much all the agencies).

Whatever you do, have a great dive!

 

[matt_unique]

I plan on diving the U-853 in a couple of weeks and my plan is for the first dive - to 110 feet - to be breating EAN32. My plan for the second dive is with air (since I only have one nitrox tank). My question is when do I transfer to the air Repetative Dive Table? I'm thinking that as soon as I surface I use the regular air table to determine my SI using the air equivelent of my first dive (aka: 90 feet for an actual depth of 110 on EAN 32) and continue with the air table from that point on. Is this correct?

A few things to suggest - 110' is a bit too shallow a plan to dive this wreck. The top of the hull is at 118', conning tower 95', and the sand is 125'. Give or take a few feet depending upon the tide of course. 32% at 118' gets you a 1.46 pp02. I would suggest a "cooler" mix to stay at 1.4 or lower for your bottom gas - such as 30% EAN. If you plan to descend over the side to check out the bottom features I would suggest a mix no richer than 29%.

When you say you have just one Nitrox tank....do you mean you have one 02 cleaned tank and one tank that is not 02 cleaned? Do you have access to a shop that does premix Nitrox fills? If yes you could get your other tank filled with premix Nitrox without having to worry about an 02 cleaning.

You could of course just use EAD and use your air table for both dives.

I'll be diving the U853 Mem Day Weekend weather permitting. I have visited her 11 times to date though next weekend will be the first for this year. I always wonder how she has changed over the winter.

Have a great time - it's a short dive on a single tank and non deco but well worth it. You using a pony as well? Just curious.

--Matt

 

[Diver0001]

I plan on diving the U-853 in a couple of weeks and my plan is for the first dive - to 110 feet - to be breating EAN32. My plan for the second dive is with air (since I only have one nitrox tank). My question is when do I transfer to the air Repetative Dive Table? I'm thinking that as soon as I surface I use the regular air table to determine my SI using the air equivelent of my first dive (aka: 90 feet for an actual depth of 110 on EAN 32) and continue with the air table from that point on. Is this correct?

You can do two things:

The first is to use the Air table for both dives and use the EAD concept to calculate your EAN32 dive.

The second is to use the EAN32 table to calculate the first dive and the Air table to calculate the second dive. If you do this then you need to use the Air table to work out your RNT for the second dive. For example, if you made a 100ft dive for 20 min on the EAN32 table then you would come out a K. Transfer the K to the Air table and do your SIT and your RNT calcs for your Air dive with the Air table. You can do this because the group designations on all the DSAT tables mean the same thing. A K on the EAN32 table means the same thing as a K on the Air table.

In other words as a general rule if you're going to change tables when switching EANx mixes for repetative dives then you use the table for the *next* dive for calculating the RNT each time.

R..

 

[Diver0001]

I haven't always followed that rule myself, but if I may suggest - doing the first dive on air and the second dive on 32% will be a little easier on your body. (Some may debate this, but this is the standard line from pretty much all the agencies).

Whatever you do, have a great dive!

This is a good point. I think his (potential) total bottom time for the day may be longer this way too..... I haven't worked it out but that's my gut feeling.

R..

 

[Don Burke]

This is a good point. I think his (potential) total bottom time for the day may be longer this way too..... I haven't worked it out but that's my gut feeling...

The tables tend to give longer times when the dive with the deeper EAD is done first, so I would expect so.

 

[StSomewhere]

What tables are you working from? The IANTD EAN tables are interchangable between mixes and dives, you can do one dive on the 32% table, get your pressure group from the surface interval and transfer to another mix/table for the next dive. I realize that's not the case with tables from different agencies.

 

[pete340]

What tables are you working from? The IANTD EAN tables are interchangable between mixes and dives, you can do one dive on the 32% table, get your pressure group from the surface interval and transfer to another mix/table for the next dive. I realize that's not the case with tables from different agencies.

That's also the case for PADI tables. Of course, that doesn't mean you can mix tables from different agencies.

 

[StSomewhere]

Thanks Pete. I thought there was some specific issue of *when* to transfer between tables with the PADI tables but I can't seem to find mine right now see if I remember correctly.

 

[latitude]

Thanks Pete. I thought there was some specific issue of *when* to transfer between tables with the PADI tables but I can't seem to find mine right now see if I remember correctly.

For the PADI tables (Air, EANX32, EANx36), the pressure groups are interchangeable anywhere. Take a look at the table 2 on each of the cards, they're all identical. Just make sure you go to table 3 for whatever depth/mix you're going to use on your NEXT dive to figure RNT for THAT depth/mix. I usually stay on the same table 2 as I just worked table 1. For your example, I'd use the 32 table for my first dive and SI to get and ending pressure group, then grab the air table #3 and figure RNT and adjusted NDL for the 2nd dive.

I never thought about doing the deepest dive EAD wise first... It makes sense to me, but I don't recal ever being taught/told to do that... Seems the 21% first then your NITROX mix is the way to go for 2 dives to the same depth with differing mixes...