Please dumb this down for me! PPO and ATA explain

[Ladyvalea]

Ok, I'm still new and I would like someone to explain in examples ...Analogies help learners make these interconnections by linking new information ... easy text.

Partial Pressure of oxygen ...is it the Pressure in a tank with Partial Oxygen??
ATA 1.2 to 1.6 Atomospheres?? Like is this the depth pressure??
this is in reference to Nixtrox? I know I need to go back and read somemore! Thanks so much

 

[battles2a5]

Yep, in reference to nitrox and/or mixed gas.

Dalton's Law states that the sum of the partial pressures of a gas is equal to the total pressure of the gas. So at sea level, there is 1 ATA of pressure. Since oxygen makes up 21% of air, the partial pressure of O2 at sea level is .21 ATA and the partial pressure of nitrogen (+ trace gases) is .79 ATA. Partial pressures increase with depth in a linear fasion. So at 2 ATM (33fsw) there is .42 ATA of O2, at 3ATA (66fsw) there is .63 ATA of O2.

Max PO2 for diving is general accepted as 1.4ATA for the working portion of the dive and 1.6ATA for deco. Since air does not hit a PO2 of 1.4 within recreational limits these concepts are generally not covered in a basic course. But since nitrox uses elevated levels of O2, you need to understand the depth limits of the gas you plan to breathe to keep yourself safe.

Hope this helps!

 

[Ladyvalea]

what! this sounds like a science class! so what is 1.4 recreational limit? is that a depth?

 

[ptyx]

Partial pressure of a gas in a blend of gases (such as air) is the pressure the gas would have if it was alone in the container (i.e. if you 'removed' all the others from the tank).

For example, in a soda bottle full of air (not compressed, so at 1 bar/ata), partial pressure of oxygen is 0.21 ATA.

The math is simple: (total pressure) = sum of (partial pressures for each gas), and (partial pressure of a gas) = (% of that gas / 100) * (total pressure).

The reason people worry about partial pressures is because some effect of gases on the body depends of their partial pressure. What you do when you dive nitrox or trimix is that you change the mix of gases in your tank in order to change the partial pressure of oxygen and nitrogen you're breathing during the dive so you don't get hurt.

1.4-1.6 ATA is the range of partial pressure where oxygen becomes harmful.

 

[Ladyvalea]

I do need it explain to me in a Dick and Jane fashion! See Dick run!! thanks...

 

[battles2a5]

what! this sounds like a science class! so what is 1.4 recreational limit? is that a depth?

The depth at which a gas reaches 1.4ATA depends on the gas mixture. There are some simple calculations to figure out max depth for a gas but essentially divide the desired PO2 (1.4) by the fraction of O2 (FO2) to get the depth in ATA's. Then convert ATA to depth.

So for instance, 32% at 1.4 would be .32/1.4 = 4.375ATA. Subtract 1 ATA for sea level, then the max depth is 3.375 * 33 = 111fsw max depth for 32% at a PO2 of 1.4 ATA.

 

[gcbryan]

Air = 79% nitrogen and 21% oxygen (roughly). So the fraction of oxygen in air will remain 21% regardless of depth. The partial pressure at the surface of oxygen is 21% but increases with depth. At 189 feet the partial pressure of oxygen would be 1.4 ATA. At that point you are at 6.72 ATA

ATA...atmospheres absolute so this is the atmosphere at the surface and the depth expressed in atmospheres...each 33 feet is another atmosphere...189 feet divided by 33 = 5.72 add 1 for the surface atmosphere and you get 6.72 ATA.

This doesn't have to be in reference to nitrox but you do have to know it to use nitrox. It's good for you to know it even if you don't use nitrox. Hopefully this helps and I haven't made any mistakes!

Edit=wow, we have some who are fast at typing!

 

[pafindr]

ATA is the shortened version of Atmosphere
So 1 ATA= 1 Atsmophere.
When we are at land we are at 1 ATA and every 33ft down is another ATA.
So at 33ft you are at 2 ATA at 66ft you are at 3ATA

With PPO if you are using a standard air fill (21% O2) on land your O2 is .21 ATA
So 33ft is .42 ATA (2ATA X .21 = .42)
As you keep doing the math it will get you to about 187ft or 6.6666 ATA
(6.6666 ATA X .21= 1.3999ATA)



Edit: Yeah you guys type way to fast LOL

 

[ptyx]

I do need it explain to me in a Dick and Jane fashion! See Dick run!! thanks...

Let me give it a try...

Oxygen and Nitrogen comes through a regulator - it's EANx 40 (Nitrox 40% oxygen) so there is 40% oxygen.
Jane is breathing from this regulator.
The total pressure of Oxygen and Nitrogen coming from the regulator is also the water pressure (otherwise Jane wouldn't be able to breathe).

As Jane go deeper, the water pressure increases.
Therefore, the total pressure of Oxygen and Nitrogen she is breathing increases.
Therefore, the partial pressure of Oxygen she is breathing increases.

If Jane goes deep enough so the partial pressure of oxygen reaches 1.6 ATA, Jane dies (to simplify).
Therefore, Jane wants to stop when it is 1.4 to be on the safe side.
Therefore, Jane wants to stop when total pressure is 1.4 / (40% / 100) = 3.5 ATA.
Therefore, Jane wants to stop before she is (3.5 - 1) * 10 = 25 meters deep. (Yes, the math is LOTs easier in metric).

Here you go, Jane's depth limit for EANx 40 is 25 meters (about 80 feet).

 

[mudhole]

See Jane dive with beginning divers on a tour boat. . . See Jane pick up an air tank with 21% Oxygen, makes one non decompression dive, see Jane happy!

See Jane dive on a boat with very advanced divers. . . See Jane pick up the wrong tank, not with air but mixed gas for decompression with 100% Oxygen, See Jane at shallow depth happy, See Jane go down to 20 feet, 30 feet. . . See Jane go into convulsions. . . see Jane sick on the bottom of the boat, after someone else pulls her out of the water.

For simple, non complicated diving, breathe compressed air, and follow the time and depths listed on the diving tables. When you hear of advanced divers "mixing gasses" to go very deep or to stay very long. . . they are mixing their breathing gasses to gain some advantage. Mixing gasses is very advanced technique, not for simple answers. You'll have a lot of fun with plain 21% oxygen above and below the surface. Probably less than 10 percent of dives for beginners involve anything than simple air. . . when you want to make multiple dives a day, or go to great depths. . . take the advanced training one step at a time.