Understanding Enriched Air Nitrox

Question: What is missing from the table above? Time

Question:What does the RDP calculate? Time

Now that you know the EAD (49fsw), Move to the AIR RDP to calculate time at depth.

Question: What is your NDL at 50fsw on the Air RDP?

Answer: 80 minutes. 80 minutes becomes your NDL for a 30% mix at 60fsw, presuming this is your first dive.

Let’s say you performed the dive to 60fsw on 30% Nitrox for only 50 minutes.

Question: What will your Pressure Group be at the end of the 50 minute dive?

Answer: P

After a 1 hour surface interval, your Pressure Group becomes: E

You enter your second dive in Pressure Group E.

See, nothing new here.. Once you find the EAD from the EAD Table for the Depth and mix of Oxygen you will be diving, it’s onto the Air RDP to calculate the time.

Let’s run through the first scenario of your scheduled four dives. As a reminder they are to the depths:

(1st) 100fsw, (2nd) 80fsw, (3rd) 60fsw and finally (4th) 40fsw.

Let us presume you have 32% Nitrox in all four of your cylinders. I understand there is a table made specifically for 32%. For the purpose of learning the EAD Table, we will use the EAD table.

Looking at your EAD Chart to find your EAD for the mix and depth of your first dive.

Question: What is the EAD for 32% to 100fsw?

Answer: 81fsw

Question: What is the PPO?

Answer: PPO=1.29

As a thought.. In my planning I would calculate for 90 feet as well. Just in case you did not quite reach 100fsw, you would be credited with some time and that credit may prove handy.

You use the EAD tables to determine your EAD. Once you have your EAD, you move over to the AIR tables.

Question: What is your NDL?

Answer: 25 minutes

Where did you get 25 minutes from? The AIR RDP under the 90fsw column. The black box at the bottom of that column reads 25.

Question: Why did you use the 90fsw column on the AIR RDP and not the 80fsw?

Answer: Your EAD on the EAD Chart showed a dive to 100fsw on EAN32 is equivalent to a depth of 81fsw on air. Since you round UP, 81 becomes 90.

If we were to take a detour for just a second. Loot at the NDL for 32% on the Nitrox RDP for 32%, what is the NDL?

Answer: 30 minutes

You see, if you were to use the 80fsw column on the AIR RDP vs the 90fsw, you would have 30 minutes. See why I mentioned above why planning the next lower depth? What if you never quite reached 100fsw, your AIR depth would have you using the 80fsw column instead of the 90fsw and you would have most likely gained 5 minutes to your NDL.

Let’s stick with our 100fsw plan for now and continue the example.

Now that you know the NDL is 25 minutes, How many minutes would you like to spend at depth?

Let’s plan for 15 minutes.

Question: What Pressure group do you end your dive to 100fsw for 15 minutes on EAN32?

Answer: H

Let’s plan to spend 1 hour on the surface interval

Question: What pressure group are you in after a 1 hr surface interval?

Answer: B

You will enter the water for your second dive to 80fsw as a Pressure Group B.

Turning the AIR RDP over to table 3 the Repetitive Dive Timetable, let’s calculate the amount of time we have to spend at our next depth of 80fsw on 32% EAN.

Question: What is the EAD to 80fsw on EAN 32%?

Answer: 64fsw

We obtained the answer by going back to the EAD table and locating the EAD for a dive depth of 80fsw under the 32% section. Now that you have the EAD, move back to the AIR table and calculate your RNT for a depth to 64fsw with a Pressure Group of B.

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