Nitrox and PO2

[Kriterian]

I wasn't sure where to post this, so I hope this is an ok spot.

I'm about to take my Nitrox course in a few days, and I've already read the book/answered the questions/watched the dvd. In the appendix of the book is a section for doing the formulas yourself vs. using the supplied EAN table. I'm trying to do the actual PO2 formula, and I'm not sure if it's my math that's messing me up.

Here is the formula I'm using:

PO2 = ( d + 33 / 33 ) x FO2

Example) What is the actual partial pressure of oxygen (PO2) for an EAN37 dive to 68 fsw?

So I'm trying to do this:

Depth (68) + 33 = 101
101 / 33 = 3.060606
3.06 x FO2 (37) = 113.242424

What am I doing wrong exactly? I'm assuming that the answer would be 1.13 but how does the decimal move? Thanks for any stupid reminders of basic algebra you have to provide but it's been way to long since I took math.

EDIT:
BAH! Using the same thing I discovered in the next problem, helped me figure this one out. Just had to convert FO2 to a decimal sooooo

68+33 / 33 = 3.0606
3.0606 x .37 = 1.13

So the PO2 = 1.13

 

[Kriterian]

I need help with another one, since I atleast remember the "order of operations" and MOD (maximum operating depth) isn't coming out right either.

Here is my formula:

MOD = [ 33 x (PO2/FO2) ] - 33


Sooooo, the example = What is the MOD in salt water of EAN30 with a limiting PO2 of 1.4?

Plugging in to the brackets, since multiplication and division it doesn't matter the order would be : 33 x (1.4/30)

That would be 1.54 and when you subtract 33 you get a negative number (-31.46) which doesn't make sense because it should be a positive number in feet.

<sigh>

I guess what I need to do is get my scientific calculator out and just plug it in with all the paranthesis etc, but I'd like to know what I'm screwing up atleast.

Thanks again,


EDIT:

Ok I think I got this one. I wasn't converted FO2 into a decimal number sooooo

[ 33 x 1.4 / .30 ] - 33 would be....

121 feet

 

[triton94949]

Its better if you figure these out for yourself.

There are some general formulae that you should always remember, which are algebraically intuitive, if you are good with algebra (algebra was invented by the Arabs, by the way, just like numerals).

The general formula for total absolute pressure:

P (total) ATAs = Depth in fsw / 33 ft per ATA + 1 ATA

or P ATAs = Depth in ffw / 34 ft per ATA + 1 ATA

Example: P is unknown; Depth is 95 fsw:
95 fsw / 33 fsw per ATA + 1 ATA = 3.88 ATAs

The general formula for partial pressure of a gas:

ppG = %G x P (total) ATAs

Example: Depth is 95 fsw; %O2 is 36%; solve for ppO2 at 95 fsw for EAN36:
P = 95 fsw / 33 fsw per ATA + 1 ATA = 3.88 ATAs (just like above! the arabic numerals are working consistently today!)

ppO2 = 36% x 3.88 ATAs = 0.36 x 3.88 = 1.40 ATAs

This is the maximum ppO2 that most modern courses will teach you is safe for NDL diving. Therefore this example has told you that the MOD of EAN36 is 95 fsw.

Now, you try it... .

 

[bedmund]

Remember, the fractions of O2 need to have the decimal point moved over two spots - ie. 36% O2 is .36



edit: Oh I see you got that after I posted. Good job.

 

[Kriterian]

Its better if you figure these out for yourself.

There are some general formulae that you should always remember, which are algebraically intuitive, if you are good with algebra (algebra was invented by the Arabs, by the way, just like numerals).

I finally figured it out, but I'd like to thank Google and BSAC. Google for showing me some BSAC website, and the BSAC website for showing me a mathmatical example. Then I was able to figure out my math mistakes.

 

[Kriterian]

Remember, the fractions of O2 need to have the decimal point moved over two spots - ie. 36% O2 is .36



edit: Oh I see you got that after I posted. Good job.

Thanks for taking a look though, and the support. I had nothing better to do while waiting on replies so I dove back in and tried it again, hehe.

 

[triton94949]

If you remember that EAN36 (aka NOAA Nitrox 2) is ideal to 95 ft, and that EAN32 (aka NOAA Nitrox 1) is ok to 110 ft, then you have learned the main benefit from nitrox.

You also need to learn how to operate an O2 analyzer and how to log your nitrox tanks when you pick them up.

Shallower than 50 ft is where air diving is generally better. Between 50 ft and 95 ft EAN36 is best. If you must go deeper than 95 ft, then EAN32 will get you to 110 ft. Generally it makes sense to keep your diving shallower than 95 ft however, and to breathe nitrox when your planned depth is deeper than 50 ft.

The main benefit to nitrox is lower N2 accumulation compared with air. A secondary benefit to nitrox is more efficient off-gassing during your ascent and safety stop of the accumulated N2 from your dive. As a result, with nitrox you can dive more than compared with air. That makes nitrox a perfect gas for vacation resort diving, where you might dive 3 or more dives in a day, for several days in a row.

 

[The Kraken]

Kriterian,
Take your formulae and play with them and manipulate them as much as you can. The more you understand the inter-relationships of the different variables the better nitrox diver you'll be.

 

[Tobagoman]

One easy way to remember this is that a fraction is a portion of 1, while a percentage is a portion of 100.

 

[WellBelowH2O]

Between 50 ft and 95 ft EAN36 is best. If you must go deeper than 95 ft, then EAN32 will get you to 110 ft. Generally it makes sense to keep your diving shallower than 95 ft however, and to breathe nitrox when your planned depth is deeper than 50 ft.

Unless, of course, you wanted to max out your nitrox benefits, where your best bet is to go 40% until 82 feet using a p02 of 1.4.

hehe... your post just reminded me of the "what is the best mixture using a 40% max" type questions on the nitrox test.