3. Diving with Galileo
42
3. Diving with Galileo
3.
DIVING WITH GALILEO
3.1 Nitrox
Nitrox is the term used to describe
breathing gases made of oxygen-nitrogen
mixes with 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 lumped into two categories:
- Sudden effects due to oxygen partial
pressure over 1.4bar. These are not
related to the length of the exposure to
high partial pressure oxygen, and can
vary in terms of the exact level of partial
pressure they happen at. It is commonly
accepted that partial pressures up to
1.4bar are tolerable, and several training
agencies advocate maximum oxygen
partial pressures up to 1.6bar.
- Long-exposure effects to oxygen
partial pressures over 0.5bar due to
repeated and/or long dives. These can
affect the
C
entral
N
ervous
S
ystem,
cause damage to lungs or to other vital
organs.
Galileo keeps you safe with respect to
these two effects in the following ways:
1) Against sudden effects: Galileo has
an MOD alarm set for a user-defined
ppO
2
max. As you enter the oxygen
concentration for the dive, Galileo
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
1.2
and
1.6bar.
It
can also be turned
OFF
. Please refer to
section 2.3.4 for more information on
how to change this setting.
2) Against long exposure effects: Galileo
“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 Galileo will
activate an alarm when this level of
CNS O
2
is reached. Galileo can also
warn you when the CNS O
2
level
reaches 75% (see section 2.6.2). Note
that the CNS O
2
clock is independent
of the value of ppO
2
max set by the
user.
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
ppO
2
0.21bar
0.5bar
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)
3.2 Alarms
Galileo can alert you of potentially
dangerous situations via warnings and
alarms.
Warnings represent situations that require
the diver’s attention, but ignoring them
does not represent an immediate risk. The
detailed description of each warning and
how it appears on the screen is presented
in section 2.6.
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