20
4.1.3
Nitrox information (O
2
information)
For dives with compressed air in normal recreational diving, nitrogen is the decisive gas for the
decompression calculations. When diving with Nitrox, the risk of oxygen toxicity rises with the increase
of the fraction of oxygen and the increase of depth and can limit dive time and the maximum depth.
Subgear XP-3H includes this in the calculations and displays the necessary information:
O
2
% mix
Fraction of oxygen: The fraction of oxygen in the Nitrox mixture can be set between
21% (normal compressed air) and 50% in 1% increments. Your selected mix will be
the basis for all calculations.
ppO
2
max
Maximum allowed partial pressure of oxygen: the higher the fraction of oxygen in
the mixture, the shallower the dive depth at which this value of the partial pressure
of oxygen is reached. The depth at which ppO
2
max is reached is called Maximum
Operating Depth (MOD).
When you enter the settings for the gas mixture, Subgear XP-3H will display the
ppO
2
max limit setting and the corresponding MOD. Subgear XP-3H warns you audibly
and visually once the depth is reached at which the ppO
2
reaches the maximum
allowed value ->26.
• Default setting of ppO
2
max is 1.4bar.
The value of ppO
2
max can be set by means of Dive.Log or with "set 1" between
1.2 and 1.6bar (->69). It can also be changed at the time of setting the gas
mixture (->26).
• The CNS O
2
% value/alarm is not influenced by the selected ppO
2
max setting.
CNS O
2
%
Oxygen toxicity: With the increased percentage of oxygen, the oxygen in the tissues,
especially in the central nervous system (CNS), becomes important. If the partial
pressure of oxygen rises above 0.5bar, the CNS O
2
value increases, if the partial pressure
of oxygen is below 0.5bar, the CNS O
2
value decreases. The closer the CNS O
2
value is
to 100%, the closer the limit where symptoms of oxygen toxicity can occur.
Depth
at which ppO
2
reaches 0.5bar
for three
commonly
used mixes
CNS O
2
%
decreases
CNS O
2
%
increases
21% 13m (43ft)
32% 6m (20ft)
36% 4m (13ft)
ppO
2
0.21bar
0.5bar
WARNING
Nitrox diving may only be attempted by experienced divers after proper training from an
internationally recognized agency.
Preparation for the dive
