origin of the constant values in the EAD and PO2 formula calculations ?

Hello,

Can some one explain me or tell me a web link in which is explained
the origin or source of the formulas for calculating:

EAD= (((1-O2%) x (Depth+10) )/ 0.79)-10

0.79 comes from where?

PO2=(((Depth+10))/10)x 02%

this formula comes from where?

I would like to understand where these formulas come from.

Thanks,

Mario

"Mario" <marmagi@hotmail.com> wrote ...

> Can some one explain me or tell me a web link in which is explained
> the origin or source of the formulas for calculating:
>
> EAD= (((1-O2%) x (Depth+10) )/ 0.79)-10
>
> 0.79 comes from where?
>
> PO2=(((Depth+10))/10)x 02%
>
> this formula comes from where?
>
> I would like to understand where these formulas come from.

Your basic diving course and the Nitrox course should explain it.

The 0.79 comes from the N content of ordinary air, around 21% O2, 79% N

The Depth + 10 =MUST= be in metres, the +10 (then / 10) gives you the
additional 1 BAR pressure of the atmosphere to give you the absolute
pressure at depth. e.g. 10m of water gives you (10 + 10) / 10 = 2 BAR
absolute.

HTH, do the course

Keith L

"Mario" <marmagi@hotmail.com> wrote in message
news:472db9ab.0408090113.5dc1cb28@posting.google.c om...
> Hello,
>
> Can some one explain me or tell me a web link in which is explained
> the origin or source of the formulas for calculating:
>
> EAD= (((1-O2%) x (Depth+10) )/ 0.79)-10

That's the formula in meters. Most here are more likely to do the formula
in feet.

> 0.79 comes from where?

That's the partial pressure of nitrogen at 1 atmosphere

> PO2=(((Depth+10))/10)x 02%

> this formula comes from where?

The partial pressure of O2, and other gasses as well, varies with depth.
The sum of all partial pressures will always equal the the total pressure.
In the formulas you've shown, the gas is presumed to consist only of
nitrogen and oxygen at .79 and .21 percent respectively for air. At 10
meters, approximately 2 atmospheres, you're talking partial pressures of
1.58 and .42 which, you'll note, add to 2 atmospheres.

Lee

On 9 Aug 2004 02:13:55 -0700, marmagi@hotmail.com (Mario) wrote:

>Hello,
>
>Can some one explain me or tell me a web link in which is explained
>the origin or source of the formulas for calculating:
>
>EAD= (((1-O2%) x (Depth+10) )/ 0.79)-10
>
>0.79 comes from where?
>
>PO2=(((Depth+10))/10)x 02%
>
>this formula comes from where?
>
>I would like to understand where these formulas come from.
>

It is all Dalton's Law which you should have been taught in your basic
scuba and Nitrox courses
--
Pete

news 'at' melbourne 'dot' me 'dot' uk

On 9 Aug 2004 02:13:55 -0700, marmagi@hotmail.com (Mario) wrote:

Just responding to UKRS, not getting into all that cross posting
shite.

>Can some one explain me or tell me a web link in which is explained
>the origin or source of the formulas for calculating:

So, that tells me (i) you haven't done the Nitrox course or (ii) you
weren't listening. These are observations, not jibes, so please don't
call me any names.

For this to make sense, you need to know about partial pressure and
fractions of gasses.

"The total pressure of a mixture of gases equals the sum of the
pressures that each would exert if it were present alone" - John
Dalton

The fraction of a gas is the amount of gas that makes up the whole gas
for example, air is basically made up of 79% Nitrogen and 21% Oxygen.
This is represented as a fraction of Nitrogen (FN2) of 0.79 and a
fraction of Oxygen (FO2) of 0.21bar which when added together makes up
the 1 bar of atmospheric pressure (at the surface).

The partial pressure of a gas is the amount of pressure that the
fraction of the gas exerts as part of the pressure exerted by the
whole gas. For example, the ppO2 (or PO2) of air at the surface is
the same as the FO2 which is 0.21bar. If we now descend to 10m the
ambient pressure increases from 1 to 2 bar which means that the air we
were breathing at the surface has doubled in density. Therefore, the
ppO2 has become 2 x 0.21bar = 0.42bar.

The main difference between gas fractions and partial pressure is that
for any given gas, the fraction of the component gasses stay constant,
whilst the partial pressure is a function of the gas fraction and the
pressure exerted by the whole gas on the surrounding environment..


>EAD= (((1-O2%) x (Depth+10) )/ 0.79)-10

>0.79 comes from where?

It is the fraction of Nitrogen (N2) in air. Air tables are based on
the fraction of N2 inspired (FN2). The EAD principal is derived from
the fact that when using a Nitrox mix (EANx) the diver is inspiring
less nitrogen than if the diver was breathing air. It is possible to
use Air tables to plan dives conducted using Nitrox by working out the
partial pressure of N2 (ppN2) we are breathing and translating it to
the depth we would be at if we were breathing air and the ppN2 was the
same.

For example, if we were breathing a Nitrox32 (EAN32) mix, the FN2
would be 0.68bar. If we were at 20m, the ppN2 would be 0.68 * 3 =
2.04bar. If the same dive was to be conducted with air, the ppN2
would be 0.79 * 3 = 2.37bar. Clearly we would be inspiring less N2
with the Nitrox mix. Next, we work out what the depth would be if we
were inspiring the same amount of N2 when breathing air as we are with
our EAN32 at 20m to do this we use Dalton's triangle.

ppN2
------------------
FN2 | Depth (bar absolute)

The ppN2 is 2.04bar, the FN2 is 0.79 so the Depth is 2.04 / 0.79 =
2.58. When, when converted to a depth (-1 * 10) is 15.8 or 16m.
Therefore, based on the inspired N2, our 20m dive on EAN32 is the same
as a 16m dive when breathing air.

To get the EAD formula above, we need to put the two steps together.
For example, the ppN2 of the gas we are breathing (EAN32) is obtained
by taking the FN2 and working out the ppN2 by multiplying pressure of
the water at the current depth and adding another 1 bar for the
atmosphere.

i.e. (1-FO2) * ((Depth/10) + 1)

In the above example, the ppN2 is 2.04 which is (1-0.32) * ((20/10) +
1).

Next, we need to divide by the FN2 of air to give us the ambient
pressure we would be at if we were breathing air to inspire the same
amount of N2.

(1-FO2) * ((Depth/10) + 1)
----------------------------------------
0.79.


Finally, we need to convert the pressure to a depth by removing the
atmospheric pressure (1 bar) and converting pressure to depth (*10)

So, the final equation is


( (1-FO2) * ((Depth/10) + 1) )
( ---------------------------------------- - 1 ) * 10
( 0.79. )


We can easily convert this equation to the one you posted by working
with depths and not atmospheric pressures. In my equation above, we
convert depths to pressure and then back. Your equation is a
simplified version of mine (EAD= (((1-O2%) x (Depth+10) )/ 0.79)-10)

>PO2=(((Depth+10))/10)x 02%
>
>this formula comes from where?

John Dalton (see above). The principal is that you can find either
the ppO2, FO2 or Depth (represented as an absolute pressure - i.e.
[Depth + 10]/10) if you know two of the values.

i.e.

ppO2 = FO2 * Depth
Depth = ppO2/FO2
FO2 = ppO2/Depth

In your example, (Depth + 10) /10 is the absolute pressure in bar and
O2% is the fraction of O2.

The Dalton equations are usually represented as the triangle (see
above) where you cover up the value you require and crunch the
remaining two values


>I would like to understand where these formulas come from.

Some really clever blokes that worked out some pretty fundamental
things about how gasses behave under pressure.

Oh and BTW, none of this accounts for changes in temperature.

Christ I am bored this afternoon!

Laz

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A foolproof method for sculpting an Elephant:
First, get a huge block of marble. Then, chip away
everything that doesn't look like an Elephant.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Change "nospam" to "ntlworld" to reply.

0.79 is the partial pressure of nitrogen at sea level. You use this formula
to calculate your equivalent air depth or your equivalent narcotic depth
depending on what type of diving your doing. You use the EAD to determine
what air depth your diving when your diving a nirtox mixture. However the
formula is more correctly written
EAD= [FN2 / .79 x (depth mswa)] - 10 msw

your PO2 formula is used to determine your oxygen partial pressure at a
given depth. This is very important to know since exposure to high practical
pressure of oxygen can kill you in a hurry. On the flip side of that
prolonged exposure to lower oxygen partial pressure > .55ata and < 1ata can
also cause some rather unpleasant side effects. The long and the short of
this is it is very important to track your oxygen exposure and if you have
not been trained in the proper use of breathing gases other than air you
shouldn't use them or you will probably kill your self


"Mario" <marmagi@hotmail.com> wrote in message
news:472db9ab.0408090113.5dc1cb28@posting.google.c om...
> Hello,
>
> Can some one explain me or tell me a web link in which is explained
> the origin or source of the formulas for calculating:
>
> EAD= (((1-O2%) x (Depth+10) )/ 0.79)-10
>
> 0.79 comes from where?
>
> PO2=(((Depth+10))/10)x 02%
>
> this formula comes from where?
>
> I would like to understand where these formulas come from.
>
> Thanks,
>
> Mario

On 9 Aug 2004 02:13:55 -0700, marmagi@hotmail.com (Mario) wrote:

>Hello,
>
>Can some one explain me or tell me a web link in which is explained
>the origin or source of the formulas for calculating:
>
>EAD= (((1-O2%) x (Depth+10) )/ 0.79)-10
>
>0.79 comes from where?

Percentage of nitrogen in the atmosphere. You are converting to an
equivalent AIR number, so you need to factor for the composition of
AIR.

>PO2=(((Depth+10))/10)x 02%
>
>this formula comes from where?

Let's say EAN50 at 30m, plus 10 would be 40. 40/10=4.0 4.0*0.50=2

In the metric system, depth=bar*10, so 30m would equal 3bar. You need
to add one to get to 4bar because of the 1ata surface pressure. You
are adding 10 instead of 1 because you are using the simplistic
formula of working directly with depth.

The formula would be just as accurate if changed to
"PO2=(Depth/10+1)x 02%" where you convert depth to pressure. That's
how we do it in the Imperial system... 100ft/33=3.03+1=4.03*0.50=2.06

Close enough.

>I would like to understand where these formulas come from.

Take a class.

You've been on this forum for over a year asking the most very basic
questions. You've claimed to have been certified many years ago, yet
you continue to ask questions that indicate a complete lack of
understanding of the most basic concepts.



--- Rich
http://richlockyer.tripod.com/

I blame the instructors.

They either can't teach properly, or if they have a student who simply can't
do the maths, then they haven't got the balls to be honest and fail
someone!


"Keith Lawrence" <false@nospam.com> wrote in message
news:411742de$0$58823$5a6aecb4@news.aaisp.net.uk.. .
> "Mario" <marmagi@hotmail.com> wrote ...
>
> > Can some one explain me or tell me a web link in which is explained
> > the origin or source of the formulas for calculating:
> >
> > EAD= (((1-O2%) x (Depth+10) )/ 0.79)-10
> >
> > 0.79 comes from where?
> >
> > PO2=(((Depth+10))/10)x 02%
> >
> > this formula comes from where?
> >
> > I would like to understand where these formulas come from.
>
> Your basic diving course and the Nitrox course should explain it.
>
> The 0.79 comes from the N content of ordinary air, around 21% O2, 79% N
>
> The Depth + 10 =MUST= be in metres, the +10 (then / 10) gives you the
> additional 1 BAR pressure of the atmosphere to give you the absolute
> pressure at depth. e.g. 10m of water gives you (10 + 10) / 10 = 2 BAR
> absolute.
>
> HTH, do the course
>
> Keith L
>
>

"Pete Melbourne" <psmvsl@yahoo.co.uk> wrote in message
news:o1jeh0p21k28g93kqt4fga2kot5nd55r07@4ax.com...
> On 9 Aug 2004 02:13:55 -0700, marmagi@hotmail.com (Mario) wrote:
>
> >Hello,
> >
> >Can some one explain me or tell me a web link in which is explained
> >the origin or source of the formulas for calculating:
> >
> >EAD= (((1-O2%) x (Depth+10) )/ 0.79)-10
> >
> >0.79 comes from where?
> >
> >PO2=(((Depth+10))/10)x 02%
> >
> >this formula comes from where?
> >
> >I would like to understand where these formulas come from.
> >
>
> It is all Dalton's Law which you should have been taught in your basic
> scuba and Nitrox courses

I didn't know that peanuts were involved! Where'se Percy?

--
> Pete
>
> news 'at' melbourne 'dot' me 'dot' uk

On Tue, 10 Aug 2004 15:37:07 +0000 (UTC), "TonyH"
<tony@samesamediving.com> wrote:

>> It is all Dalton's Law which you should have been taught in your basic
>> scuba and Nitrox courses
>
>I didn't know that peanuts were involved! Where'se Percy?

OK you've lost me
--
Pete

news 'at' melbourne 'dot' me 'dot' uk