Nitrox tables/math

frogman159 · Jan 18, 2009

I'm studying for my PADI nitrox cert, and I want to challenge myself with difficult profiles to make sure I have a solid grasp at the tables and math. I was hoping someone with a bit of experience can check to see if I'm on the right track for this profile, assuming this was 1 day of diving. I was changing up gases to make it harder, this is theoretical so assume this was all that these were the gases available.

I used PADI EAD's all SI are 1 hr

dive 1:
EAN32 70ft, 30min; MOD= 110' PPo2=1.0; CNS Clock= 10% End L

dive 2:
EAN36 Start C, 60ft, 40min; MOD=90' PPo2= 1.01; CNStot= 10%+15%= 25% End R

dive 3
EAN32 Start F, 50ft, 40min; MOD= 110' PPo2= .80; CNStot= 25%+10%= 35% End Q

dive 4
Air Start F, 40ft, 50min; MOD= 130; PPo2=.46; CNStot= 35%+ N/A= 35% End S

I figure if I can handle this, I've got it down
Thanks in advance :coffee:

solowgregg · Jan 18, 2009

As far as your profile (by which I mean using your EAD tables) your calculations are correct sir... Well done

williama · Jan 21, 2009

frogman159:
I'm studying for my PADI nitrox cert, and I want to challenge myself with difficult profiles to make sure I have a solid grasp at the tables and math. I was hoping someone with a bit of experience can check to see if I'm on the right track for this profile, assuming this was 1 day of diving. I was changing up gases to make it harder, this is theoretical so assume this was all that these were the gases available.

I used PADI EAD's all SI are 1 hr

dive 1:
EAN32 70ft, 30min; MOD= 110' PPo2=1.0; CNS Clock= 10% End L

dive 2:
EAN36 Start C, 60ft, 40min; MOD=90' PPo2= 1.01; CNStot= 10%+15%= 25% End R

dive 3
EAN32 Start F, 50ft, 40min; MOD= 110' PPo2= .80; CNStot= 25%+10%= 35% End Q

dive 4
Air Start F, 40ft, 50min; MOD= 130; PPo2=.46; CNStot= 35%+ N/A= 35% End S

I figure if I can handle this, I've got it down
Thanks in advance

I am very happy to see you posting this and your instructor will certainly appreciate your additional practice.

-your pressure groups are good
-your oxygen exposure % is off by a little bit. Please take a look again at Dive2 and keep in mind the guidelines for that table are to use the exact O2pp or round up.

Some additional feedback

-list your EAD
-do not put the MOD for air at 130'. Take out the calculator and figure it out.
(I don't like to use air deeper than 60' but I do know the MOD is much deeper.

tstormdiver · Jan 21, 2009

MOD, at 1.6 PPO, for air depends on how you like to represent the % of O2 in air. For 20% O2 It is about 231 fsw. If you consider it to be 21% O2 then it is about 218 fsw. Not saying that in any way it's safe, but mathematically that is the depths.

frogman159 · Jan 21, 2009

williama:
-your oxygen exposure % is off by a little bit. Please take a look again at Dive2 and keep in mind the guidelines for that table are to use the exact O2pp or round up.

I see the error, I rounded 1.01 down to 1 and it should have went to 1.1 making my CNS clock 5% higher. Thanks for that.

1 question about the CNS clock- The book says its your oxygen exposure for 24hrs, but if you reach 100%, you shouldn't dive for 12 hrs. So....

Lets say you dive my example between 9am to 4pm- your CNStot= 40% then you do the exact same thing on day 2.

At 9am day 2 what is your starting CNStot?

The book says there is no surface interval credit, but there is mention of that 12hr if @100% rule. This leads me to believe- 1. Day 2 9am I start at 0% (12hrs passed), 2. Day 2 I start at 40% and by the end I'm at 80%, so by day 3 I can't dive cause according to the rules, it'll keep rolling over unless a wait 24hrs, this doesn't seem right.

williama · Jan 21, 2009

frogman159:
I see the error, I rounded 1.01 down to 1 and it should have went to 1.1 making my CNS clock 5% higher. Thanks for that.

1 question about the CNS clock- The book says its your oxygen exposure for 24hrs, but if you reach 100%, you shouldn't dive for 12 hrs. So....

Lets say you dive my example between 9am to 4pm- your CNStot= 40% then you do the exact same thing on day 2.

At 9am day 2 what is your starting CNStot?

The book says there is no surface interval credit, but there is mention of that 12hr if @100% rule. This leads me to believe- 1. Day 2 9am I start at 0% (12hrs passed), 2. Day 2 I start at 40% and by the end I'm at 80%, so by day 3 I can't dive cause according to the rules, it'll keep rolling over unless a wait 24hrs, this doesn't seem right.

You start a 0% every morning at 9 am(or every 24hrs).

The 12hr break is if you exceed the 100%.

If you add a couple of night dives to your previous plan and exceed the 100% at 2 AM then you would have to wait until 2 pm to start your diving instead of 9am.

frogman159 · Jan 22, 2009

williama:
You start a 0% every morning at 9 am(or every 24hrs).

The 12hr break is if you exceed the 100%.

If you add a couple of night dives to your previous plan and exceed the 100% at 2 AM then you would have to wait until 2 pm to start your diving instead of 9am.

But I dove all afternoon- The O2 accumulated all day till 4pm (when I stopped diving) has not elapsed 24 hrs- 24hrs would be 4pm on day 2.

At 9am wouldn't I at least have the o2 from the afternoon probably day 1 dives 2,3,4?

jtivat · Jan 22, 2009

frogman159:
But I dove all afternoon- The O2 accumulated all day till 4pm (when I stopped diving) has not elapsed 24 hrs- 24hrs would be 4pm on day 2.

At 9am wouldn't I at least have the o2 from the afternoon probably day 1 dives 2,3,4?

Well I know you are doing math to pass a class. However in the real world even an hour SI will run you CNS clock down some. Get your hands on the NOAA charts or a copy of V-Planner or similar program.

When I run your dives through V-Planner I get a total CNS of 12.2%.

Tortuga68 · Jan 22, 2009

tstormdiver:
MOD, at 1.6 PPO, for air depends on how you like to represent the % of O2 in air. For 20% O2 It is about 231 fsw. If you consider it to be 21% O2 then it is about 218 fsw

Please explain why you would use 20% instead of 21%?

frogman159 · Jan 22, 2009

jtivat:
Well I know you are doing math to pass a class. However in the real world even an hour SI will run you CNS clock down some.

I would think so

- Which is a discrepancy in the PADI materials, on one hand they say there is no appreciable SI credit, only after 24hrs....ok fine so your O2 hangs around for 24hrs......

Yet they then say if your at 100% as in full-no more, its OK to dive after 12hrs- This would imply a SI credit of some kind would occur, yet they don't tell you what that credit is

guess that's what I'm getting at.

I'm going to be doing some repetitive diving on vacation soon, and I intend to follow the tables- Can't afford trade my air computer for a nitrox one right now. So to be safe I want to do it "by the book"

Nitrox tables/math

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