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Diving With More Than One Gas Mixture; Setting More Than One Gas; Switching Gas - Mares SMART AIR Instruction Manual

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model in the computer. Any dive started
while there is remaining desaturation on
your computer is considered a repetitive
dive, meaning that Smart Air accounts
for the pre-existing nitrogen load in your
body. The bar graph shows the calculated
nitrogen load in the leading tissue. You can
use this to gauge your progress in getting
rid of nitrogen as the surface interval
grows. Smart Air continues to perform
decompression-related calculations
(nitrogen release), for as long as there is
desaturation time left.
- The no-fly time (NO FLY): this is the time
during which an exposure to the reduced
pressure inside the cabin of an airplane
could cause decompression sickness. Smart
Air employs, as recommended by NOAA,
DAN and other agencies, a standard 12-hour
(no-deco non-repetitive dives) or 24-hour
(deco and/or repetitive dives) countdown.
Hence you may find a situation in which
the desaturation time is shorter than the
no-fly time. This is simply the consequence
of the desaturation time being calculated
by the algorithm based on the actual dive
profile, while the no-fly time is an accepted
standard in the diving industry. Since the
real effect of flying after diving has never
been fully investigated, this approach fits
with our philosophy.
Flying while Smart Air displays NO FLY can
result in serious injury or death.
- The surface interval (S.I.): this is displayed
from the moment the dive is closed (3
minutes after surfacing) for as long as there
is remaining desaturation or no-fly time on
the computer.
- In case of a dive violation, the corresponding
symbol (
) is shown.
The post-dive display is the default display for
as long as either the no-fly or the desaturation
is greater than 0 minutes. By pressing the
DOWN button you can go to all other screens
but Smart Air will revert automatically to the
post-dive display after an 8-second time out.
For as long as there is desaturation, Smart Air
also features a condensed log of the last dive:
maximum and average depth in the top row,
dive time and set O
% in the bottom row.

- Diving with more than one gas mixture

represents a much higher risk than
diving with a single gas mixture, and
mistakes by the diver may lead to
serious injury or death.
- During dives with more than one gas
mixture, always make sure you are
breathing from the tank that you intend
to breathe from. Breathing from a high
oxygen concentration mix at the wrong
depth can kill you instantly.
- Mark all your regulators and tanks so
that you cannot confuse them under any
- Before each dive and after changing
a tank, ensure that each gas mixture
is set to the correct value for the
corresponding tank.
Smart Air enables you to use up to three
gas mixtures during the dive (air and Nitrox
only). The three mixtures are labeled G1, G2
and G3 and must be in ascending order of
oxygen content, i.e. G1 has the lowest oxygen
concentration, G2 an intermediate value, and
G3 has the highest oxygen concentration of the
three. If you are diving with only two mixtures,
you will be utilizing tanks G1 and G2.
It is not possible to switch to a gas at a
depth at which the oxygen partial pressure
for that gas is greater than the set
maximum value.
- If you dive using just one gas, select G1
and deselect the other two.
- For dives with two gases, select G1 and
G2 and deselect the third.
- When enabling G2 and G3, you must first
define G2 and then G3.
- You cannot activate G3 without first
having activated G2.
- G2 cannot have an oxygen percentage
higher than G3.
- If you set G2 to OFF, G3 will
automatically be set to OFF also.
- The MOD for G2 and G3 is the switch
depth for the corresponding gas. This is
what Smart Air uses for its calculation,
alarms and suggested switch points.


The characteristics of the gases must be
entered in the computer before the dive. It will
then be your responsibility to tell Smart Air
which gas is currently being used during the
various phases of the dive.
To use multiple gases, you will need to enable
the gases and set the oxygen percentage and
the ppO
max for each one. This is done in the
same way as for G1, with the difference that
for G2 and G3 you can turn a gas ON or OFF.
Keep in mind that the MOD for G2 and G3 is
the depth at which Smart Air will prompt you
to perform the gas switch (see section 3.5.2
below). To enable G2 press the UP button from
the G2 OFF display. You will now see G2 ON, a
value of oxygen concentration, ppO
Proceed as you would for G1 until you get
to the G3 OFF screen. Either press and hold
the DOWN button if you have finished setting
gases, or press the UP button to advance to the
G3 ON display and setting of G3.


Smart Air always begins the dive with G1,
which has the lowest percentage of oxygen.
When during the ascent you reach the depth
corresponding to the MOD of G2, Smart Air
sounds an audible signal and the oxygen
concentration of G1 starts to blink in the lower
right corner.
Press the DOWN button while this indication is
blinking to initiate the gas switch: the oxygen
percentage of G2 starts to blink in lieu of that
of G1, and in the top right corner the MOD of
G2 is displayed, also blinking.
Press and hold the DOWN button to confirm
the switch to G2: the set oxygen concentration
will be displayed steadily in the lower right
corner of the screen, and within 20 seconds
the ascent time is updated to reflect the higher
oxygen concentration in the breathing gas.
and MOD.


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