Hollis Explorer User Manual - page 56
50 |
breather design. People have achieved over 8 hours duration with relatively
small absorbent loads, but this has been in warm water, with low breathing
rates and shallow depths. It is currently not known what the effects are
when an absorbent filter working at a CO
2
level of say 2mBar that has been
used in a shallow scenario is taken deeper and the work rate is increased.
We know that the CO
2
would increase, but do not know how fast. In field
tests, we have seen the CO
2
jump quickly from 3mBar to 6mBar just by the
diver going deeper near the end of absorbent duration. This same rise will
not occur if the filter is at the start of its life. Forecasting potential duration
with the CO
2
sensor will be possible in the future after more development
but this is not currently the main function of the CO
2
sensor. Its’ current
functionality is as an active warning device for CO
2
absorbent system
issues.
It can detect for bad absorbent, no absorbent, high work rates
and general CO
2
seal issues.
WARNING: Currently the CO
2
sensor reading should not be
used as a duration meter for the rebreather. It is vital that it
is used to report and alarm for a high CO
2
reading that could
occur with a faulty seal or exhausted absorbent.
Our bodies produce the same CO
2
quantities independently of depth. So
just staying shallow does not reduce CO
2
. It can however; help the CO
2
absorbent perform more efficiently. Therefore a low CO
2
reading on a filter
that has been used in shallow water for some time may rapidly increase if
(towards the end of its’ life) it is taken deeper or the work rate increases.
Be aware that the CO
2
reading can rise dramatically for higher work rates
and deeper depths, especially when an absorbent has been used for over
50% of its recommended duration.
Therefore, in order of priority, the EXPLORER is fitted with a gaseous CO
2
sensor, a metabolism ‘click’ counter (providing an estimate of oxygen con-
sumed, hence CO
2
generated) and a TPM giving an indication of thermal
activity within the filter. These three features give a more accurate indica-
tion of absorbent life remaining.
The use of the CO
2
readings is four fold:
1. To ensure active absorbent has been fitted
2. To ensure the absorbent sealing systems are operative
3. To warn of reducing absorbent efficiency in order to give the diver time
to respond by reducing depth, temperature or work rate to avoid an inci-
dent occurring.
!