Nitrox tables/math

[frogman159]

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).

I'll qualify my answer with the fact I'm new at this..But here's my $.02

Option 1: If your a gambling man you COULD go to 120' on EAN32 and your pp02 would still be below 1.6- I wouldn't do it however.

Option 2: You could drop to EAN30 which would keep your ppO2 below 1.4 Doing this would get you an extra 3 minutes of bottom time- Not worth it in my opinion.

Option 3: You could stay at like 100 to 90ft max on EAN32- This would get you extra bottom time and keep your ppo2 within acceptable limits.

Option 4: Just dive air with your computer

I would choose either option 3 or 4 for the first dive, If going to 120, then option 4 and depending on how much surface interval and the depth of dive 2 - would determine if I went with EAN on that dive or just air on that one too.

I'm sure others will chime in

 

[--tom--]

Now relying on my computer, setting the mix at 32%, the dive profile gives a maximum depth of 107'. QUOTE]

You are probably diving a Suunto Computer that rounds your O2 up (so if you get a mix of say 32.8% you still punch in 32) and it calculates as 33% @ 1.4.

 

[splicer]

I looked at the profile on my Suunto Mosquito which I now use as a backup. I use the Sherwood Insight now so I'll go dig it out of storage and see how it compares. Thanks for the input.

 

[williama]

I'm sure others will chime in

Excellent feedback! No need for me to chime in.

 

[marcbs]

What an excellent discussion. I took my nitrox course last year and am re-reading the book for next month's trip. Question-on page 75 of the PADI Enriched Air Diving coursebook-bullet point 3-last sentence-reads "that below 40 feet air has an oxygen partial pressure greater than 0.5 ata." It looks like the air 02 column on the DSAT EAD Table for Nitrox reads that below 40 feet air has a partial pressure below 0.5 ata. A misprint??

 

[Dan Weidert]

What an excellent discussion. I took my nitrox course last year and am re-reading the book for next month's trip. Question-on page 75 of the PADI Enriched Air Diving coursebook-bullet point 3-last sentence-reads "that below 40 feet air has an oxygen partial pressure greater than 0.5 ata." It looks like the air 02 column on the DSAT EAD Table for Nitrox reads that below 40 feet air has a partial pressure below 0.5 ata. A misprint??

If we assume air is 21% O2
Then ppO2 at depth = ata times .21
If we pick a depth over 40 feet, say 41, we get [(41/33)+1] times .21
which equals 2.24 times .21
which equals 0.47

A diver would have to get to 46 feet to get a ppO2 of 0.5 ata (0.5019 ata) (assuming 21% O2 and that I can still do algebra)

Dan

 

[mark99]

What an excellent discussion. I took my nitrox course last year and am re-reading the book for next month's trip. Question-on page 75 of the PADI Enriched Air Diving coursebook-bullet point 3-last sentence-reads "that below 40 feet air has an oxygen partial pressure greater than 0.5 ata." It looks like the air 02 column on the DSAT EAD Table for Nitrox reads that below 40 feet air has a partial pressure below 0.5 ata. A misprint??

I think you're supposed to read "below 40 feet" is referring to the next entry in the table, i.e. 50 feet- where the O2 partial pressure is greater than 0.5 ata- namely 0.53 ata per the table. You can see that the O2 partial pressure in the table at 40 feet is listed as 0.46.

 

[NJMike]

I'm taking the PADI Nitrox course next month in Jupiter, Florida while on a week long business trip. I'll be doing two days of diving in the ocean plus Epcot's Living Seas Aquarium.

marcbs, that's one of two spots I marked in the book to ask the instructor about. I wasn't sure if it was a misprint or I was 'mis'ing something!

This is a great discussion. I'm going to print out the pages so that I can read them tonight while I'm at the library doing some practice nitrox problems.

There is definitely a chance here to misunderstand something...since 'below' usually means 'less than' .... but in this case it may mean 'deeper than' ?

 

[splicer]

I looked at the profile on my Suunto Mosquito which I now use as a backup. I use the Sherwood Insight now so I'll go dig it out of storage and see how it compares. Thanks for the input.

Okay, I dug my gauges out of the attic (which need annual service anyway) and ran through the dive profiles on the Insight computer using 32%. at 120 ft. NDL was 13 min., at 130 ft. NDL was 10 min. and 132 was the maximum depth. Interesting eh.

 

[--tom--]

Okay, I dug my gauges out of the attic (which need annual service anyway) and ran through the dive profiles on the Insight computer using 32%. at 120 ft. NDL was 13 min., at 130 ft. NDL was 10 min. and 132 was the maximum depth. Interesting eh.

So your Mosquito is set for 1.4 PPO, and it rounds up the O2%.

Your Insight does not round the O2, and is set for 1.6 PPO. So everything matches.

We have too much fun (and/or free time) here.