Trouble understanding nitrox po2

[Scubadives]

Thanks for all the responses. I re read the book "Naui Nitrox Diver" 2008. Although it talks multiple times about single dive exposure limits from NOAA, it only stated on page 39 that your mainly limited to NDL, and gas supply; even the most deticated and determined diver would possibly exceed the 24 hour limit by diving 7 square profile dives to 90 feet/50 min with a SI of 2:39 min.

It might be somewhere else in the book, but I have been through it 3 times already.

Ok so now I know there is a way to calculate the % of clock used, anyone know the formula?
Im sure it is something like; the max po2 for that dive, then you refrence the noaa chart and convert some minutes to a percentage?

Can I use something like this, get the % from each dive, and add them to my 24 hour clock?

anaspides.net/documents/scuba_diving_documents/NOAA%20CNS%20Percentage%20Table.pdf

 

[Scubadives]

Found it
To calculate this we use a CNS table:

PO2 Maximum Single Exposure
(minutes) Maximum 24 hour Exposure
(minutes)
1.6 45 150
1.5 120 180
1.4 150 180
1.3 180 210
1.2 210 240
1.1 240 270
1.0 300 300
0.9 360 360
0.8 450 450
0.7 570 570
0.6 720 720

To calculate the CNS% do this:
CNS% = Time spent / Maximum Single Exposure (for used PO2)

For example let's say we did a dive to 21msw/70fsw for 50 minutes using EAN32. What's the CNS%?

Let's start by finding our our PO2.
PO2 = FO2 * Pata => PO2 = 0.32 * 3.1 ATA = 0.99 ATA
We always round the ATA up and look it up in the table.

Our maximum single exposure time is 300 minutes.
CNS% = 50 min / 300 min = 16.7%
So our accumulated CNS% is 16.7%

If we do multilevel diving we have to calculate CNS% for every segment of the dive and add them together.

Also doing a surface interval longer then 90 minutes will lower the CNS clock with 50%.



Wheww. Thanks all for the help, did not think it would be so hard to find it.

 

[Scubadives]

Now that my mind is clear.....er I will properly introduce myself. I got OW cert in 97, did a few gulf dives, then joined my fire departments search and rescue dive team. We went through search and recovery training a few years later, beacuse at that time that was the only specific course availiable. A few years after that I became the dive team leader, and took over all training, and maint of the truck,and eq. In 2008 in attempt to follow NFPA standards we convinced the boss to send us all to get our AOW cert, which we did. I have many many pool dives to 20 feet in training, and a few tens of dives in rivers, and ponds. I recently went through my nitrox class, in preperation of a few dives on our vacation to orange beach, AL in May. My future plans is to get enough money to send all my guys throught the PSDC which is new to our area, and is alot more geared to what we do. If the funds allow, I might persue Master diver. I also am about to purchase a UW housing for my Cannon 1200IS camera, just hope the gulf waters are clear enough this time to allow any kind of picture instead of just silt and darkness

 

[DiveNav]

......Ok so now I know there is a way to calculate the % of clock used, anyone know the formula? ....

Google is your friend --> See Baker Paper.

Let me ask you something ..... once you know the formula what will you do? Bring a calculator/notebbok with you on the boat? It might get wet

Maybe you should just get a dive computer .... if they get wet they don't break :blinking:

Alberto (aka eDiver)

 

[knotical]

Google is your friend --> See Baker Paper.

That's a good article, but the URL you posted seems to require a log-in. Another source is:
http://www.shearwater.com/tools/sof...perty=FileName&toolscontext.stepinput.id=3540

 

[muddiver]

Google is your friend --> See Baker Paper.

Let me ask you something ..... once you know the formula what will you do? Bring a calculator/notebbok with you on the boat? It might get wet

Maybe you should just get a dive computer .... if they get wet they don't break :blinking:

Alberto (aka eDiver)

All the rebreather divers I know cary a caculator, clip board and check lists. Just buy a cheap caculator if you are so remiss with your gear that it will get wet.

 

[Thalassamania]

I have a good calculator (HP50G) and a cheap calculator (HP35S) in a ziplock, in a dry box (OK, I like RPN).

 

[Trace Malinowski]

When diving standard nitrox mixtures of Nitrox 32 and Nitrox 36, you can also keep track of your Equivalent Air Depths, CNS%, and OTU's fairly accurately when tables aren't available with the following calculations:

Equivalent Air Depths
EAD of Nitrox 32 = 20% reduction of depth

EAD of Nitrox 36 = 25% reduction of depth

CNS%

Bottom Time + Safety Stop Time / 2

OTU's

Bottom Time + Safety Stop Time X 1.5