Please dumb this down for me! PPO and ATA explain
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...I forgot a part to my story:
Jane struggles with the maths during the divemaster briefing, get lost, and dies because she screwed up a multiplication. (I like having my characters die, it's more dramatic).
Dick knows the theory, but wisely uses standard gas mixes and a chart to figure the max operating depth of what he breathes.
1.4 is not the depth but depending on the percent of oxygen (FO2) in your tank it is a number (PO2) used to calculate your maximum depth. (MOD)
ATM is pressure.
1.4 divided by .21 = 6.66ATM - 1ATM = 5.66ATM times 33 = 187 feet.
or
MOD = 33*((PO2/FO2)-1)
Anti-Hero
Contributor
P02 is easy to find.
At the surface, the pressure is 1 atmosphere absolute (ATA).
Every 33 ft. you gain an additional 1 ATA.
Air is 21% Oxygen and 79% nitrogen - so to find the PP02 for Air at 66ft (3 ATA) could be represented as: 0.21 * 3 which equals a partial pressure of: 0.63
Without going into formulas or more fractions, that is Partial Pressure in a very small nutshell.
At the surface, the pressure is 1 atmosphere absolute (ATA).
Every 33 ft. you gain an additional 1 ATA.
Air is 21% Oxygen and 79% nitrogen - so to find the PP02 for Air at 66ft (3 ATA) could be represented as: 0.21 * 3 which equals a partial pressure of: 0.63
Without going into formulas or more fractions, that is Partial Pressure in a very small nutshell.
Better illustration of ATA (pressure)
At sea level the air pressure that surrounds us is 14.7 psi (pounds per square inch). We call this 1 ATM or one atmosphere of pressure
At 33 feet, the pressure is double that of the surface or 2 ATA or 29.4psi.
At sea level the air pressure that surrounds us is 14.7 psi (pounds per square inch). We call this 1 ATM or one atmosphere of pressure
At 33 feet, the pressure is double that of the surface or 2 ATA or 29.4psi.
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There is a difference in atmospheres.
ATA = Atmospheres absolute. This takes into account the pressure that you are under just by standing on the surface of the Earth. It is the pressure placed upon you by the Earth itself. It is defined to be 14.7 psi (pounds per square inch). Meaning that just standing on the Earth you are under 1 ATA of pressure.
atm = (atmospheres) Is typically referred to as gauge pressure. It is the pressure that begins when you go under the water. Your pressure gauge (SPG) registers pressure in atm.
When calculating the TOTAL pressure you are under while diving, you have to account for the gauge pressure you are under, as well as the atmospheric pressure you are under.
To determine the amount of total pressure you are under (ATA) the formula is
P = D/33 + 1;
Where P = the total pressure in ATA;
D = your depth.
The 1 is the pressure you are under at the surface.
psi = is the pressure resulting from a force of one pound-force applied to an area of one square inch.
pp (partial pressure) = The pressure that a gas would exert on a cylinder if it were the only gas in the cylinder.
In air for example, you have oxygen and nitrogen (for the most part).
The ppO2 (partial pressure of oxygen) = The pressure oxygen would exert in a cylinder of air if the oxygen were in the cylinder by itself.
It's a way of looking at the pressure of each individual gas in a tank and determining how much pressure each gas would have in the tank. This becomes important when discussing Nitrox, but an understanding of these principles is important even to a new diver. Hope this helps.
The pp is determined by the equation : pp = Fg x ATA
Where the Fg is the fractional concentration of gas in the mix (in air, since it is 21% oxygen the Fg is 0.21)
And ATA is the Total pressure. Sorry for making this a but more complex. Without knowing how familiar you are with all of this, I don't want to make it so simple that it makes no sense.
ATA = Atmospheres absolute. This takes into account the pressure that you are under just by standing on the surface of the Earth. It is the pressure placed upon you by the Earth itself. It is defined to be 14.7 psi (pounds per square inch). Meaning that just standing on the Earth you are under 1 ATA of pressure.
atm = (atmospheres) Is typically referred to as gauge pressure. It is the pressure that begins when you go under the water. Your pressure gauge (SPG) registers pressure in atm.
When calculating the TOTAL pressure you are under while diving, you have to account for the gauge pressure you are under, as well as the atmospheric pressure you are under.
To determine the amount of total pressure you are under (ATA) the formula is
P = D/33 + 1;
Where P = the total pressure in ATA;
D = your depth.
The 1 is the pressure you are under at the surface.
psi = is the pressure resulting from a force of one pound-force applied to an area of one square inch.
pp (partial pressure) = The pressure that a gas would exert on a cylinder if it were the only gas in the cylinder.
In air for example, you have oxygen and nitrogen (for the most part).
The ppO2 (partial pressure of oxygen) = The pressure oxygen would exert in a cylinder of air if the oxygen were in the cylinder by itself.
It's a way of looking at the pressure of each individual gas in a tank and determining how much pressure each gas would have in the tank. This becomes important when discussing Nitrox, but an understanding of these principles is important even to a new diver. Hope this helps.
The pp is determined by the equation : pp = Fg x ATA
Where the Fg is the fractional concentration of gas in the mix (in air, since it is 21% oxygen the Fg is 0.21)
And ATA is the Total pressure. Sorry for making this a but more complex. Without knowing how familiar you are with all of this, I don't want to make it so simple that it makes no sense.
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Dsix36
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I will try to do this in "Dick and Jane" fashion, but first there are a couple of abbreviations that you need to know.
FO2 is the percent of O2 in your breasthing gas (air is 21%, nitrox is more, oxygen is 100%)
PO2 is the partial pressure of that gas at a given depth
ATA is the atmospheric pressure at a given depth (surface is 1ATA, every 33 foot of depth is 1 more ATA)
FO2 x ATA = PO2
air x 66ft= 0.63
.21 x 3 = 0.63
another example
32% nitrox at 132 foot = PO2 of 1.60
.32 x 5 = 1.60
very simple is: GAS x DEPTH = PO2
This is important because of the pressures upon our bodies. As we go underwater the weight of the water above us causes more and more pressure the deeper that we go. Our bodies will equalize and keep this pressure internally in many places to prevent crushing. This pressure (PO2 if you will apply it to the breathing gas) causes the breathing gas to be forced into our tissues and muscles at a much faster rate than if we were on the surface. Monitoring this pressure and gas loading is how we try to prevent the bends or DCS.
If I did or said anything wrong, please feel free to correct me.
FO2 is the percent of O2 in your breasthing gas (air is 21%, nitrox is more, oxygen is 100%)
PO2 is the partial pressure of that gas at a given depth
ATA is the atmospheric pressure at a given depth (surface is 1ATA, every 33 foot of depth is 1 more ATA)
FO2 x ATA = PO2
air x 66ft= 0.63
.21 x 3 = 0.63
another example
32% nitrox at 132 foot = PO2 of 1.60
.32 x 5 = 1.60
very simple is: GAS x DEPTH = PO2
This is important because of the pressures upon our bodies. As we go underwater the weight of the water above us causes more and more pressure the deeper that we go. Our bodies will equalize and keep this pressure internally in many places to prevent crushing. This pressure (PO2 if you will apply it to the breathing gas) causes the breathing gas to be forced into our tissues and muscles at a much faster rate than if we were on the surface. Monitoring this pressure and gas loading is how we try to prevent the bends or DCS.
If I did or said anything wrong, please feel free to correct me.
.....my effort at simplyfing this....
Picture 10 blocks in a horizontal row.
These blocks represent the air, or any other gas you breathe.
For simplicity sake and to make it easier to visualize, my example won't be 100% correct in the breakdown, let's assume you are breathing 2 blocks of Oxygen and 8 Blocks of Nitrogen - right now on the surface.
Surface = 1ATA/ATM = 2 blocks Oxy, 8 blocks Nitrogen
The term Partial Pressure is the blocks. It is PART of the pressure you are breathing. Partial pressure, or the block count, changes under pressure. Easy math, every 33' of salt water is one more atmosphere.
Gas can be compressed with pressure, because of this the Partial Pressure of each part of what you breath changes.
Surface = 1ATA/ATM = 2 blocks Oxy, 8 Blocks Nitrogen
33fsw = 2ATA/ATM = 4 blocks Oxy, 16 Blocks Nitrogen
The "mix" is the same, but now the air or gas your breathing is compressed because of the pressure you're now under. So with every breath now at 33' you're breathing 4 parts Oxygen and 16 parts nitrogen.
The Total pressure reflects the sum of each Partial Pressure you breath. The total pressure at the surface is 10 based on the example I gave. At 33 feet the total pressure is 20.
As divers we have to monitor what we breath and at what depth we breath a specific mix of gas. Even air can kill you if you go too deep; Oxygen becomes toxic to us at depth if we don't pay attention to the Partial Pressure of Oxygen (part of the total pressure).
The 1.4 and 1.6 people are talking about is the partial pressure of Oxygen, just part of what you are breathing.
Mixed Gases - Nitrox, EAN2....kind of all the same thing, just a different way of saying it. Diving is about managing our gas mix (partial pressure) to extend our dive times safely.
There are really only a few ways to manage our dive times.
1) Depth - Deeper - shorter times, Shallow - longer times
2) Time - Time in the water and time out of the water
3) Changing what we breathe (higher or lower levels of Oxygen, Nitrogen or even adding a gas, say Helium)
Most divers when they use that term or phrase are only talking about Oxygen. The truth is every 'part' or 'component' of what we breath has a Partial Pressure.
PP is Partial Pressure.
PPo2 is Partial Pressure of Oxygen.
PPN is Partial pressure of nitrogen.
etc...
PT is the total pressure. P1 + P2 + P3..etc..= PT
In diving we plan our dives. We have establish the maximum time we can be in the water before we go in...or at least we should. We plan for our dive and we plan for our contingency if we go a little too deep, or stay a little too long so we don't have mandatory decompression issues.
If we use #3, and change what we breathe, then we also need to plan on what we breath becoming toxic to our bodies. That's where all the partial pressure talk leads us.
1.4 in most cases is the Partial Pressure of Oxygen for our Dive plan
1.6 in most cases is the Partial Pressure of Oxygen if we screw up or run into a problem
This is the "magic" number that tells us to get out of the water so we don't push how our body uses oxygen and prevents it from being toxic.
Hope that made it simple for you.
Picture 10 blocks in a horizontal row.
These blocks represent the air, or any other gas you breathe.
For simplicity sake and to make it easier to visualize, my example won't be 100% correct in the breakdown, let's assume you are breathing 2 blocks of Oxygen and 8 Blocks of Nitrogen - right now on the surface.
Surface = 1ATA/ATM = 2 blocks Oxy, 8 blocks Nitrogen
The term Partial Pressure is the blocks. It is PART of the pressure you are breathing. Partial pressure, or the block count, changes under pressure. Easy math, every 33' of salt water is one more atmosphere.
Gas can be compressed with pressure, because of this the Partial Pressure of each part of what you breath changes.
Surface = 1ATA/ATM = 2 blocks Oxy, 8 Blocks Nitrogen
33fsw = 2ATA/ATM = 4 blocks Oxy, 16 Blocks Nitrogen
The "mix" is the same, but now the air or gas your breathing is compressed because of the pressure you're now under. So with every breath now at 33' you're breathing 4 parts Oxygen and 16 parts nitrogen.
The Total pressure reflects the sum of each Partial Pressure you breath. The total pressure at the surface is 10 based on the example I gave. At 33 feet the total pressure is 20.
As divers we have to monitor what we breath and at what depth we breath a specific mix of gas. Even air can kill you if you go too deep; Oxygen becomes toxic to us at depth if we don't pay attention to the Partial Pressure of Oxygen (part of the total pressure).
The 1.4 and 1.6 people are talking about is the partial pressure of Oxygen, just part of what you are breathing.
Mixed Gases - Nitrox, EAN2....kind of all the same thing, just a different way of saying it. Diving is about managing our gas mix (partial pressure) to extend our dive times safely.
There are really only a few ways to manage our dive times.
1) Depth - Deeper - shorter times, Shallow - longer times
2) Time - Time in the water and time out of the water
3) Changing what we breathe (higher or lower levels of Oxygen, Nitrogen or even adding a gas, say Helium)
Most divers when they use that term or phrase are only talking about Oxygen. The truth is every 'part' or 'component' of what we breath has a Partial Pressure.
PP is Partial Pressure.
PPo2 is Partial Pressure of Oxygen.
PPN is Partial pressure of nitrogen.
etc...
PT is the total pressure. P1 + P2 + P3..etc..= PT
In diving we plan our dives. We have establish the maximum time we can be in the water before we go in...or at least we should. We plan for our dive and we plan for our contingency if we go a little too deep, or stay a little too long so we don't have mandatory decompression issues.
If we use #3, and change what we breathe, then we also need to plan on what we breath becoming toxic to our bodies. That's where all the partial pressure talk leads us.
1.4 in most cases is the Partial Pressure of Oxygen for our Dive plan
1.6 in most cases is the Partial Pressure of Oxygen if we screw up or run into a problem
This is the "magic" number that tells us to get out of the water so we don't push how our body uses oxygen and prevents it from being toxic.
Hope that made it simple for you.
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