TAKE YOUR BREATH
In preparation for the much awaited retail launch of the Phibian
rebreather, Oceanic has launched training and familiarisation courses
at its Honiton, Devon, headquaters. The course is presented by Stuart
Clough of Undersea Technologies who developed the electronics package
for the Phibian for Oceanic and uses pre-production protypes.
Most divers have heard of the benefits of rebreathers - longer
bottom times and shorter decompression penalties. But many are put
off by the perceived complexities and the cost.
The seminar explains the history and the concept of rebreather
technology and describes the benefits of reclaiming and recycling
the oxygen in the gas mix and adding fresh oxygen as required. It
is at this stage that the course participants really begin to sit
up and take notice, whether their interest in technical diving,
cave diving, or marine biology, as the comparative bottom times,
gas consumption and decompression requirements are unravelled before
For example a standard air dive to 40m for a theoretical 60 minutes
would mean 118 minutes of decompression. The same dive using the
Phibian rebreather would mean 46mins decompression time.
The Phibian system can be specified for use up to 50m depth in
which the diluent gas will be compressed air, or for deeper 'technical'
diving in which the diluent gas will be Heliox or another suitable
inert gas mixture. In both specifications none of the expired gas
mixture is lost from the system but is recycled, scrubbed and enriched
with oxygen as necessary.
There follows a detailed description of the way that the hardware
and electronics software functions. This is all displayed using
computer generated graphics and animated diagrams which are very
easy to follow no matter how rusty your recollection of diving physics
There were two pre-production prototype units available for trial
at the time of my visit - a closed circuit, pure oxygen re-breather
and the Phibian CCS50 designed for air range diving using oxygen
at a constant partial pressure with compressed air as the diluent
gas. Monitoring, mixing and delivery of the breathing gas in the
CCS50 is controlled by the electronics package which has an integral
dive computer, while the oxygen rebreather is an entirely manual
unit which provided an interesting contrast.
The mixed gas model, the CCS100, is similar to the CCS50 with the
exception of breathing gas and computation requirements. All of
the Phibian's hardware is contained in a moulded casing with a waistcoat
BC attached. Buoyancy compensation and bale out are provided by
the diluent gas cylinder using a standard demand valve and low pressure
The first step is to accustom yourself to the breathing characteristics
of the unit on the surface and to be reminded that the mouthpiece
valve must be closed if it is removed from your mouth for any reason.
Initially you are required to trim the counter-lungs to your breathing
rate and lung volume on the surface. This is achieved by bleeding
off or injecting diluent gas into the system until the inhalation
and exhalation effort is comfortable. This is followed by a slow
descent down a shot line in the centre of the tank to its maximum
depth of 10m. As you descend the increase in water pressure progressively
collapses the counter-lung and you must manually increase the volume
of diluent gas in the lung until breathing is comfortable.
The first impression is, of course, the total lack of bubbles and
almost silent operation, except for the reassuring click of the
solenoid on the oxygen injection valve. Unlike a conventional demand
system there is no positive pressure delivery as you are breathing
the gas at ambient pressure. Breathing in and out has no effect
on your buoyancy, for the same reasons ,and it is not until you
begin to ascend that your buoyancy changes as the volume of the
gas in the counter-lung expands. On the current prototypes this
expanding gas is vented either by breathing out through your nose
or the corner of your mouth , however production models will be
fitted with pressure relief valves to eliminate this requirement.
Ascending and descending a few times soon makes you comfortable
with the basic operation of the system and lets you concentrate
more on this strange and exciting experience.
One or two drawbacks of the current prototypes were apparent. The
bulk of the enclosed unit would make swimming difficult in current
or a shallow swell and similarly the size and buoyancy of the hoses
restrict head movement (although we were informed that production
units will be trimmed down in both these areas). Also, because the
counter lung is on your back, if you roll over you find a noticeable
increase in breathing resistance due to the increase in hydrostatic
pressure. The Phibian will cost between £5-10,000 dependant
Oceanic suggests that interested technical divers should start
with the familiarisation day and then perhaps take a more comprehensive
course, tailored to their intended use, with further extended and
open water practical sessions. Course Fee: Mon-Fri £65, Sat/Sun
£75. Contact Oceanic on 01404 891819