# Genesis Resource Pro computer...which PO2 setting?



## polar21 (Nov 5, 2007)

Which PO2 setting should I use? I am diving air and the range is 1.0 to 1.6 I believe.


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## jamesw21 (Feb 26, 2011)

Personally I use 1.6 and have never had a problem.


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## flappininthebreeze (Jul 13, 2009)

1.4 - 1.6 is fine.


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## WhackUmStackUm (Jan 31, 2010)

polar21 said:


> Which PO2 setting should I use? I am diving air and the range is 1.0 to 1.6 I believe.


A bit more detail, for anyone who is interested...

Like the other guys, I'll assume you are diving open circuit (regular scuba) gear, and you are setting up your max PPO2 warning level. Open circuit divers hit their maximum PPO2 at the maximum depth of their dive. Closed circuit rebreather divers (or anyone with a O2 bottle) can encounter high PPO2 levels (above 1.6) at any depth below 20 feet.

Let's calculate the max depths represented by diving air with assorted PPO2 settings.

The fraction of O2 in air at the surface (1 atmosphere) is about 0.21. This can also be written as 21%. The partial pressure of O2 at the surface is also 0.21.

At a depth of 33 feet, we experience a pressure of 2 atmospheres, one at the surface, and one due to the 33 feet of water. So the partial pressure of O2 (PPO2) at 33 feet is 0.21 x 2 = 0.42.

At a depth of 66 feet, we experience a pressure of 3 atmospheres, one at the surface, and 2 due to the 66 feet of water. So the partial pressure of O2 (PPO2) at 66 feet is 0.21 x 3 = 0.63. ...and so on for deeper depths.


So, if you were diving on air, the maximum depth you could dive without causing your computer to sound a warning is:

124 feet (max PPO2 set to 1.0)
140 feet (1.1)
155 feet (1.2)
171 feet (1.3)
187 feet (1.4)
203 feet (1.5)
218 feet (1.6)
When/if you start diving nitrox, you can run the calculation again with a higher percentage of oxygen to determine your max depth for a particular max PPO2 setting.

So you would not reach a PPO2 level of 1.6 when diving air until you got down to 218 feet. A common guideline is that most people can tolerate a PPO2 level of 1.6 for 45 minutes per day. If you are only diving a single tank, it is unlikely that you would be down at 218 feet for anywhere near 45 minutes. However, some of the hardcore skip-breathers like flappininthebreeze and sealark may be able to come close! :notworthy:

Now, aren't you sorry you asked?! :yes:


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## polar21 (Nov 5, 2007)

Dang, thanks for the explanation whackum. I read the manual and it didnt go into detail at all as to what the setting actually indicates.


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