Need Formula Help - Nitrox

[furby076]

So I just got my Nitrox certification and I want to make a sheet I can carry around with the formulas. I am terrible with math (remembering formulas) so want to check my formulas before I take them. Your help would be greatly appreciated:

Calculating Maximum Operating Depth (MOD)
1. Pata = PO2 limit / FO2
2. D fsw = (Pata – 1atm)x33 fsw / atm

Calculating Best Mix

1. Pata = (D fsw / (33fsw/atm)) +1atm
2. FO2 = PO2limit / Pata

Calculating Equiv Air Depth
1. Pata = (D fsw / (33 fsw /atm)) +1atm
2. D fsw = (P ata – 1 atm) x33 fsw/atm

I feel I am missing something and am not confident my above notes

 

[Mr Carcharodon]

Point 1: Stick to 32%.

MOD:110 fsw.

EAD: depth*0.8

Forget best mix.

Not a lot to remember.

See and you thought it was complicated.

 

[gcbryan]

So I just got my Nitrox certification and I want to make a sheet I can carry around with the formulas. I am terrible with math (remembering formulas) so want to check my formulas before I take them. Your help would be greatly appreciated:

Calculating Maximum Operating Depth (MOD)
1. Pata = PO2 limit / FO2
2. D fsw = (Pata – 1atm)x33 fsw / atm

s

You don't need the last part.../atm

1.4/.32 = 4.375
(4.375 -1) x 33 = 111.375 which is your MOD.

 

[elan]

Like Mr Carcharodon said, stick to the standard mixes,

32 works fine down to the 110 ft. I remember the 32 and air tables as I use them often. You are not going to use those formulas during the dive anyways.

 

[Walter]

Here is an Excel spread sheet you can print and stick in your logbook. View attachment Nitrox Formulas 1.xls

Here is an Excel spread sheet that will do the calculations for you. View attachment Nitrox & RMV calcs.xls

I love using best mix.

 

[Crowley]

Best mix is ... well ... er best.

Not always available in many locations - here we have a standard mix from a membrane system that is supposed to be 32% but varies between 28 and 34 which is not a problem for the dives we do here.

Rather than keep the formulas, decide what is your pp02 "limit" - i.e. 1.4 ata (as per PADI) or 1.6 ata or whatever and make a sheet which tells you maximum operating depth for each blend. It's much easier to refer to. I haven't checked, but I assume Walter's spreadsheet will provide you with exactly that.

Cheers

C.

 

[TSandM]

Well, there are really two approaches to Nitrox -- adapt the dive to your mix, or adapt your mix to the dive. The second suffers from two issues: You may not be able to DO the dive you planned, in which case your "best mix" is no longer best for the dive you end up able to do (for example, getting blown off the deep wreck you had in mind, and diving a shallower site). And the advantage you gain from using Nitrox is diminished more and more as you lean out the mix to go deeper.

I use the approach others have mentioned. I dive 32% all the time; I know the NDLs on it for various depths, I know the MOD. I just don't do dives that go below that on that gas. It limits me very little.

 

[RTee]

I considered myself bit of a dinosaur as I first started scuba diving where everything seemed so much simpler...but not necessarily safer. However, having spent the biggest part of my life doing mental dead reckoning in a helicopter cockpit, I always enjoyed knowing some rules of thumbs as it facilitated my flight planning and other aspect of flying (instrument flying in this case when you equate your rate of turns to lead distances for an arc that you are trying to intercept and follow or a radial you want to intercept from an arc based on how many radials per nautical miles, etc).

All that to say that knowing some formulas (I also keep a cheet sheet in my logbook) greatly assist me when i am planning my dive. When I took my Nitrox course, my instructor...a very keen 23- 24 instructor ensured I knew and understood those formulas as they cam to play during our briefing session....MOD, COD, EAD, SAC, etc to determine what would be the limiting factor for that very specific dive. Diving single 80 cf tank at the time, I could then tell him that based on these numbers that we would transbribe to our slates, we might only be able to achieve a 25 mins bottom time at 100 ft using EAN 32 due to my gaz consumption even though such mix would allow me 32 mins bottom time, MOD 111.375 (1.4) and contingency of 132 (1.6) , etc....

As for other uses of such formulas...I find that it is not every LDS that offers EAN. Therefore, if I have my set of doubles top up with air then I can come up with the O2 percentage of the mix and find all the applicable numbers pertaining to it.

Last but not least reciting some of those formulas with some examples at night seems to help my bed warmer falling asleep which can be very handy specially if you forgot to take the garbage out that very same morning...

 

[RTee]

...I meant 30 mins instead of 32....Gee I just realized that reciting those formulas also put me to sleep....lol

 

[SkimFisher]

Even though I have the info available to me, I do as the others have mentioned here and stick to one mix.

If you have an iPhone - check out Nitrox Tools. It comes in handy.