2
Chapter 2 Gases and Gas Mixtures 33
The two separate calculations could also be
combined into a single formula:
or
It is straightforward to calculate oxygen or nitrogen
partial pressures at depth for enriched air nitrox. Of
course, to save the effort of calculating, one can employ
an oxygen partial pressure table, which can quickly show
the partial pressure of oxygen for various mixes over a
range of depths.
Determining Oxygen Partial Pressure
by Table
Using Figure 2-9, to find the oxygen partial pressure for
a nitrox mixture, move along the top row to the oxygen
fraction of the mix. Then move down that column to the
row of the desired depth. If the exact mix or the exact
depth is not shown, round up to the next higher value.
The NAUI MobileTM Application
The NAUI Mobile Application is another dive tool that
can be used to determine oxygen partial pressures, as
well as several other useful values, such as equivalent air
Pgas = Fgas ×( D msw
+ 1 bar
) = 10 msw / bar
× (D msw + 10 msw)
10 msw / bar
Fgas
Pgas = Fgas × ( D fsw
+ 1 atm
) = 33 fsw / atm
× (D fsw + 33 fsw)
33 fsw / atm
Fgas
Oxygen Partial Pressure (in atmospheres absolute) at Depth
FO2 Air 0.24 0.26 0.28 0.30 0.32 0.34 0.36 0.38 0.40
Figure 2-9 Oxygen partial pressure at depth for various nitrox blends–moderate shading indicates an oxygen
partial pressure between 1.4 and 1.6 ata. Dark shading indicates oxygen partial pressure in excess
of 1.6 ata. (Calculations derived using feet sea water fsw.)
Depth
(msw)
Depth
(fsw)
12 40 0.46 0.53 0.58 0.62 0.66 0.71 0.75 0.80 0.84 0.88
15 50 0.53 0.60 0.65 0.70 0.75 0.80 0.86 0.91 0.96 1.01
18 60 0.59 0.68 0.73 0.79 0.85 0.90 0.96 1.01 1.07 1.13
21 70 0.66 0.75 0.81 0.87 0.94 1.00 1.06 1.12 1.19 1.25
24 80 0.72 0.82 0.89 0.96 1.03 1.10 1.16 1.23 1.30 1.37
27 90 0.78 0.89 0.97 1.04 1.12 1.19 1.27 1.34 1.42 1.49
30 100 0.85 0.97 1.05 1.13 1.21 1.29 1.37 1.45 1.53 1.61
33 110 0.91 1.04 1.13 1.21 1.30 1.39 1.47 1.56 1.64 1.73
36 120 0.97 1.11 1.21 1.30 1.39 1.48 1.58 1.66 1.76 1.85
40 130 1.04 1.19 1.28 1.38 1.48 1.58 1.68 1.77 1.88 1.98