Nitrox tables/math

[tstormdiver]

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

I personally use 21%, yes I know,... even a bit more accurate at 20.9%. There are some, to keep it simple that go with 20%.

 

[crpntr133]

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.

Then throw in the fact that air becomes "toxic" at around 210'. Some will argue this point to be deeper. At either rate you will probably be narced out of your mind.

 

[tstormdiver]

At either rate you will probably be narced out of your mind.

Actually,.... I get that way at about 95ft (especially in cold waters).

 

[williama]

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?

The 100% Oxygen Exposure guideline is for a 24 hour period of diving. (Starting at 9 AM and ending at 9 AM the next day) You can dive morning, noon, evening and still get to start at 0% the next day at 9 AM.

Please keep in mind that the recommendations/materials are a guide for Enriched Air Diving within Recreational Limits. Also it's recommended just like every maximum that you stay well within it, the manual recommends stopping at 90%. There are more factors than just math to consider like diver fitness and exertion during the dive.

If you decide to continue your training that's when you'll learn about other theory's on how to manage Oxygen Exposure which include surface interval credit and some deco dives that are well beyond the 100% listed on that table.

Good luck on your test and that would be the only time to to shoot for 100%!!!

 

[scubadiver888]

I'm taking my EANx course this weekend. To prepare for it I have been doing the same thing as frogman159. I have been going through my log books and taking days I did repetitive diving on air but changing things for if I was diving on EAN32 or EAN36. I've also tried taking dives where I was too deep for EAN36 initially and doing dive 1 and 2 on EAN32 then dive 3 on EAN36.

One question... The fourth dive for frogman159 was on air at 40' for 50min. He put the oxygen exposure at N/A. Shouldn't it be O2pp for air at 40' is 0.46, round up to 0.6 (the lowest my tables go). DSAT table has 36 min = 5% and 72 min = 10% so add 10%? I plan on asking my instructor but I wonder what everyone here has to say.

 

[williama]

One question... The fourth dive for frogman159 was on air at 40' for 50min. He put the oxygen exposure at N/A. Shouldn't it be O2pp for air at 40' is 0.46, round up to 0.6 (the lowest my tables go). DSAT table has 36 min = 5% and 72 min = 10% so add 10%? I plan on asking my instructor but I wonder what everyone here has to say.

It's funny you should ask this because the same point in the manual that says to round up also has a note that shows 0.5 ata or less do not add to your oxygen exposure.

That's great to hear you are using your previous dives for practice. It's also a good idea to plan some future repetitive dive trips on Air, EAN32/36 and then on the highest possible mix for that dive "best mix". This will let you compare when Enriched Air is beneficial for extending bottom time and when it doesn't make sense to dive the highest mix because the benefit may only be a couple of minutes and you are pushing the Oxygen Exposure.

Now go make your instructor work by asking them all these tough questions

 

[frogman159]

It's funny you should ask this because the same point in the manual that says to round up also has a note that shows 0.5 ata or less do not add to your oxygen exposure.

Exactly where I got this from. Pg 74

 

[Dan Weidert]

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.

Since he is using PADI, wouldnt the MOD be calculated at 1.4 with the contingency depth being 1.6?

Dan

 

[tstormdiver]

Good point. Yes, it probably is. I was just going through the mathematical absolute maximum of 1.6 PPO.

 

[splicer]

I did the EAN course in Kauai last February and sweated through all the math formulas (phew, haven't done math in a long time). Now relying on my computer, setting the mix at 32%, the dive profile gives a maximum depth of 107'. If the first dive is going to fluctuate between 120-90 should I be diving with 21% for the first dive then 32% for the second shallower dive? I opted for EAN cause my wife is not a diver and I kept falling asleep at dinner when I dove with air (you know blowing bubbles in my soup).