PpO2: oxygen partial pressure
Pick your mix and your depth: you instantly see the oxygen partial pressure you breathe, on the bottom and at the stops.
Your mix
The oxygen % from your analysis, not the one you asked for.
Your depth
The maximum depth planned for the bottom.
Settings
Limit 1.4 bar · Sea
Your bottom limit
1.4 bar is the usual limit. 1.6 bar remains the absolute maximum, kept for stops.
Where you dive
PpO2 at 30 m · Nx32
1.28bar
Within your limit
PpO2 ≤ 1.4 bar: fine for the bottom phase.
Nx35
On the bottom and at the stops
The PpO2 drops as you ascend.
With your Nx32
If you switch to pure O2 at the stops
How it is calculated
The partial pressure of a gas is its share of the mix multiplied by the ambient pressure (Dalton’s law).
Absolute P = surface P + depth ÷ k
PpO2 = O2 % ÷ 100 × absolute P
Max depth = (max PpO2 ÷ FO2 − surface P) × k
Best mix = max PpO2 ÷ absolute P
- k = 10 m per bar at sea, 10.2 m per bar in fresh water (less dense).
- Surface P = 1 bar at sea level, as in dive courses. At altitude it drops according to the standard atmosphere (about 0.89 bar at 1,000 m, 0.79 bar at 2,000 m).
- Always rounded on the cautious side: PpO2 up (down below 0.5 bar, so as not to hide hypoxia), max depth and best mix down, min depth up.
- Benchmarks: 1.4 bar on the bottom, 1.6 bar at most, at rest at the stops. Below 0.16 bar the mix is hypoxic: risk of blacking out without warning.
- Stops are read on the depth gauge: real 3, 6 and 9 m, even at altitude.
Examples: EAN32 at 30 m → 0.32 × 4 = 1.28 bar. Pure O2 at 6 m → 1 × 1.6 = 1.60 bar. EAN32 in a lake at 1,000 m, 30 m → 0.32 × (0.887 + 30 ÷ 10.2) = 1.23 bar. A helper tool: it replaces neither your training nor your computer.
Understanding ppO2
What is ppO2?
The oxygen partial pressure (ppO2) is the share of the ambient pressure due to oxygen. It follows Dalton’s law: O2 fraction × absolute pressure. At the surface, air gives 0.21 bar. At 30 m the pressure is 4 bar, so EAN32 gives 0.32 × 4 = 1.28 bar. The deeper you go or the richer your mix, the higher the ppO2.
The limits: 1.4 bar on the bottom, 1.6 bar at most
Above 1.4 bar during exertion, the risk of an oxygen seizure rises: convulsions without warning, and therefore a risk of drowning. 1.6 bar is the absolute maximum, kept for stops, at rest. Conversely, below 0.16 bar the mix no longer holds enough oxygen: that is hypoxia. The depth where your mix reaches your limit is its MOD: the MOD tool details it, with a table for every mix.
At the stops and with a deco cylinder
The ppO2 falls as you ascend. Switching to pure oxygen at the 6 m and 3 m stops gives 1.6 and 1.3 bar: that is what speeds up off-gassing. The tool shows your mix’s ppO2 on the bottom and at 9, 6 and 3 m, then pure O2 at the stops. To pick the ideal mix for a depth, use the best mix tool; for nitrogen, the EAD tool.
Lakes and altitude
In fresh water it takes 10.2 m to gain 1 bar. At altitude, surface pressure drops (about 0.89 bar at 1,000 m), so the ppO2 is slightly lower at the same depth. Open the settings to choose Lake and the altitude. Stops are still read on the depth gauge: real 3, 6 and 9 m.
Frequently asked questions
How do you calculate ppO2?
ppO2 = oxygen fraction × absolute pressure. At sea, absolute pressure is depth ÷ 10 + 1. Example: EAN32 at 30 m → 0.32 × 4 = 1.28 bar.
What is the maximum ppO2 in diving?
1.4 bar for the bottom phase is the most common limit. 1.6 bar is the absolute maximum, kept for stops, at rest.
What is the ppO2 of pure oxygen at 6 m?
1.6 bar: absolute pressure at 6 m is 1.6 bar and pure oxygen makes up all of it. That is why pure O2 is not used below 6 m.
What is hypoxia in diving?
A lack of oxygen: below a ppO2 of 0.16 bar you can black out with no warning signs. It concerns mixes with less than 16 % O2, used for deep trimix diving.