Oxygen partial (ppO2) setting in dive comp

[jwc3]

A Nitrox course will make all of this clear to you.

Agreed. Don't change your computer's default settings unless you're absolutely sure you know what you're doing.

 

[giles45shop]

When the pO2>1.6 the risk of seizure is very high, although it is clear that many tech divers will expose themselves to these higher partial pressures. I think the record for an air dive is over 400 feet, which means pO2>13 if my math is correct. So clearly people can tolerate very high pO2 and survive but not without great risk.

QUOTE]

Actually that would be a pO2 of 2.75. 13 is the ATA (atmospheres of pressure). Multiply ATA x FO2 (0.21 for air) to get pO2.

I would echo everyone elses's comments:

1. O2 tox is a serious issue, but you can't always predict your individual response to high pO2's an it can change from day to day and dive to dive. In general, lower is less risky.

2. Take a nitrox class and ask lots of questions. My basic nitrox class gave a good overview for the Recreational diver, but Advanced Nitrox/Dec class was significantly better to help understand the implications for Technical diving. I didn't know what I didn't know

 

[DevonDiver]

I didn't know what I didn't know

This is very true with many aspects of scuba diving...especially as you enter the realms of technical diving and diving medicine.

 

[H2Andy]

If i am diving recreationally, and at a max depth of 40m, does it not mean that i should set the ppO2 to 1.05bar i.e. 5 ata times by 21%?

the partial pressure you select will dictate your max depth for that mixture. if you select a partial pressure of 1.2, you won't be able to go very deep. if you select a pressure of 1.8 you'll be able to go deeper.

1.4 is recommended for active diving, 1.6 for safety stops (these vary)

think about it this way: the partial pressure of a gas will dictate its MOD

and the less O2 you have in a mix, the greater the MOD

thus, less O2 in a mix = less partial pressure at any given depth = deeper MOD

and

more O2 in a mix = greater partial pressure at any given depth = shallower MOD

when you "set" a partial pressure on your computer, you are letting it know how much ppO2 you are willing to tolerate at any given depth. this increases your risk of ox tox but also increases your MOD