56
GALILEO 2 TEK (G2TEK) USER MANUAL
3 .4
Diving with nitrox
Nitrox is the term used to describe
breathing gases made of oxygen-nitrogen
mixes with the oxygen percentage higher
than 21% (air). Because nitrox contains
less nitrogen than air, there is less nitrogen
loading on the diver’s body at the same
depth as compared to breathing air.
However, the increase in oxygen
concentration in nitrox implies an increase
in oxygen partial pressure in the breathing
mix at the same depth. At higher than
atmospheric partial pressures, oxygen
can have toxic effects on the human body.
These can be grouped into 2 categories:
1. Sudden effects due to oxygen
partial pressure over 1.4bar.
These are
not related to the length of the exposure
to high oxygen partial pressure. Sudden
effects can vary and depend on the exact
level of partial pressure they happen at. It is
commonly accepted that partial pressures
up to 1.4bar are tolerable during the active
part of the dive, and maximum oxygen
partial pressures up to 1.6bar during the
decompression.
2. Long exposure effects to oxygen
partial pressures over 0.5bar due to
repeated and/or long dives.
These can
affect the central nervous system and
cause damage to lungs or to other vital
organs. Long exposures can be divided
between more severe Central Nervous
System effects and less dangerous long-
term Pulmonary Toxicity effects.
The G2TEK treats high ppO
2
and long
exposure effects in the following ways:
• Against sudden effects.
The G2TEK
has an MOD alarm set for a user-defined
ppO
2
max. As you enter the oxygen
concentration for the dive, the G2TEK
shows you the corresponding MOD for
the defined ppO
2
max. The default value
of ppO
2
max from the factory is 1.4bar.
This can be adjusted to your preference
between 1.0 and 1.6bar. It can also be
turned off. Please refer to chapter:
ppO
2
max
for more information on how to
change this setting.
• Against long exposure effects.
The
G2TEK “tracks” the exposure by means
of the CNS O
2
clock. At levels of 100%
and higher there is risk of long exposure
effects, and consequently the G2TEK will
activate an alarm when this level of CNS
O
2
is reached. The G2TEK can also warn
you when the CNS O
2
level reaches 75%
(see chapter:
CNS=75%
). Note that the
CNS O
2
clock is independent of the value
of ppO
2
max set by the user.
CNS O
2
75%
warning and 100% alarm can
activate during a dive (see chapters:
CNS
O
2
= 75%
and
CNS O
2
= 100%)
, whereas
the remaining CNS O
2
value after a dive is
shown in the time-of-day display.
The CNS O
2
clock increases when the
oxygen partial pressure is higher than
0.5bar, and decreases when the oxygen
partial pressure is lower than 0.5bar.
Hence, while on the surface breathing air
you will always be decreasing the CNS O
2
clock. During the dive, the depth at which
0.5bar is reached for various mixes is as
follows:
Air: 13m/43ft
32%: 6m/20ft
36%: 4m/13ft
F
NOTE: For oxygen concentrations of
80% and higher, the ppO
2
max is fixed
at 1.6bar and cannot be changed.
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