Hollis Explorer User Manual - page 55
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CARBON DIOXIDE SENSING MODULE
Premise:
The EXPLORER comes with an option to fit a CO
2
sensor. The user can
elect to buy this from new or upgrade to the sensor later. The CO
2
sensor
gives many advantages as detailed below.
EXPLORERS not fitted with CO
2
sensors or that have had their CO
2
sensor
temporarily removed by the user, can still be dived but with no CO
2
sensor
fitted a 5 minute pretreated of the absorbent filter will be forced in stead of
the normal 1 minute.
DANGER: With no CO
2
sensor fitted careful monitoring of filter
duration is vital.
There is little confirmed data on actual absorbent durations typical for sport
diving rebreather use. Sports divers often push the absorbent duration be-
yond the published CE durations, because they assume that they will not
be creating as much CO
2
as the CE trials or operate at the same tempera-
ture or depths.
The problem can arise that if a diver has gone deep and works hard, per-
haps to rescue another diver; when the absorbent duration is near its limit,
the extra depth and work rate push the CO
2
to dangerously high levels very
quickly.
The CO
2
sensor will help by giving feedback in this scenario, and advise
the diver of the high CO
2
levels. The diver should then reduce their work
rate and reduce their depth and finish the dive as safely as possible or bail-
out to open circuit as indicated. The relatively fast rise in CO
2
readings is
also an indication that the absorbent cannot be pushed any harder without
causing even higher CO
2
levels.
A question asked already by many divers who have seen the system in
operation, is “Can the CO
2
reading be used to determine the duration
remaining in the filter?”
The answer in principle is ‘yes’. However with the current knowledge and
data available, there is no practical system to achieve this. The duration of
the absorbent changes with CO
2
generation, temperature, depth, and re-
3
.1
4
!