Home Innovations SEALED with a KISS

SEALED with a KISS

Over the past few years, there has been a noticeable increase in the number of divers jumping in the water without tanks on their backs, but instead carrying strange boxes, or weird looking configurations of pony cylinders, hoses and cables.  The Closed Circuit Rebreather is now an almost common sighting at most of the diving destinations around the world.  Still more commonly purchased by the members of the technical diving community, there are increasing numbers of recreational divers discovering the advantages of silent, bubble –free diving. 
In buying a unit for myself, I opted for the Classic KISS unit from Canadian company Jetsam Technologies Ltd. My decision was based on the fact that it is a manual CCR as opposed to an electronic CCR and so there are less parts to go wrong, and when things do go wrong, it is easier to get spares as they do not necessarily have to come only from the factory. Added to this was the fact that due to its lack of electronics, the price tag is far less than that of the electronic CCR.  Of course there are certain limitations to the KISS rebreather such as the maximum operating depth, but it was nevertheless more than suitable to the majority of my diving needs. 

In ‘normal’ scuba diving when a diver jumps in the water with a cylinder strapped to their back, they are diving what we call ‘Open Circuit’.  In other words, the diver breathes in from the tank via a regulator, and then exhales all of the waste gas into the water, hence the breathing cycle is ‘open’ to the surrounding water.  A Closed Circuit Rebreather, as the name suggests, has a closed breathing loop which recycles all of the diver’s exhaled gases back into the unit to be re-breathed by the diver.  The result of this is that the diver can make a dive with a much smaller gas supply (often just using two or three litre tanks) as they only require an oxygen supply to provide the oxygen which his or her body is using for metabolism. They also require a second tank containing air (or trimix), called the diluent gas, which maintains the volume of gas in the breathing loop so the diver can get a full breath even as they go deeper and the pressure causes the gas in the breathing loop to decrease in volume.

A Closed Circuit Rebreather keeps the gas a diver exhales, removing the carbon dioxide through a chemical scrubbing process, adds the tiny amount of oxygen the diver’s body requires, then feeds it back to the diver via the mouthpiece.  The diver is breathing into and out of bags, called counterlungs which enable the breathing loop to contain enough gas to give a full breath every time, with the scrubber canister usually located between the two counterlungs.  The counterlungs are connected to the diver through a breathing hose which is much wider than a normal regulator hose in order to minimise the breathing resistance to the diver.  Then finally, somewhere in the breathing loop will be located oxygen sensors, similar to a nitrox analyser, in order that the diver can monitor their partial pressure of oxygen at all times and maintain the optimum breathing mixture for the depth they are at.

While all this sounds complicated, the end result is a much longer gas supply all in relatively small package when compared to twinsets and stage tanks, and all this combined with the fact that the diver will be breathing the optimum gas mix at every depth so maximising their no decompression time, or should decompression stops be required, the rebreather will enable accelerated decompression profiles without the need for carrying several stage tanks containing different decompression mixtures.  In addition to this, because of the chemical reaction in the scrubber which removes the carbon dioxide, the diver is breathing warm, moist air rather than cold, dry air as in open circuit.

The two general types of Closed Circuit Rebreather on the market - manual and electronic - are both essentially doing the same thing, but with the electronic one monitoring the oxygen partial pressure and, through a computer, deciding when it needs to add oxygen automatically to maintain the diver’s breathing mixture. With a manual one, the diver still has the displays showing the partial pressure of oxygen, but it is up to the diver to decide when, and how much oxygen to add into the loop.  This has advantages and disadvantages. 

The advantage is that there are no computers, solenoids (which control oxygen injection) and other electronic components to fail, especially in the event of water getting into the loop.  Also the diver has full control over their oxygen partial pressure, being able to increase or decrease it at will without the need to reprogram computers under the water.  The disadvantage of this is that the diver must monitor the unit closely, knowing there is no help in ‘flying’ the unit from an onboard controller and so this may increase the task loading on an already stressful dive.  There is also a shallower maximum depth limit when compared to electronic units due to the oxygen injection method, although this is really only of great concern to those deeper trimix divers

So why doesn’t everybody use a Closed Circuit Rebreather if they are so good? Well obviously the price is a big factor for the more infrequent diver, with prices ranging from in the region of 5000 euros for a manual rebreather up to in excess of 15000 euros for the more expensive electronic units.  Costing aside, a rebreather diver also needs a different attitude towards their diving.  It is no longer possible to just put a regulator on a tank, check it’s full, then leap into the water in the space of a couple of minutes. Setting up a rebreather requires several steps and a number of pre-dive safety checks and tests.  All this takes time and dedication, so if you are not prepared to spend time setting up your unit and doing the checks while others on the boat are sunbathing or getting a cup of tea or stripping your unit completely after a days diving while others are watching TV, then rebreather diving is just not for you.

So I finally decided on the Classic KISS rebreather, a manual unit with a manufacturer’s depth rating of 75 metres.  It is a small unit, and has a price tag at the cheaper end of the rebreather market.  Obviously under no circumstances should a diver take a rebreather under the water without completing a proper course on the specific rebreather they are using.  The large warning on the top of my unit said it all – ‘This device is capable of killing you without warning.’

The theory sessions on the course, as would be expected for something as complicated as a rebreather, are quite in depth covering all manner of things from rebreather maintenance and check lists to diving on fixed partial pressures as opposed to open circuit diving on fixed gas fractions.  It’s a totally different concept and one which is covered at length. 

The diving started off with two confined water sessions lasting an hour each in which all the emergency procedures were covered, as with any diving course.  Most emergencies on a rebreather are to do with the oxygen partial pressure being too high or too low, resulting in oxygen toxicity problems or hypoxic situations.   In open circuit diving, the diver’s buoyancy changes with every breath as they inhale and exhale – a fact which is used in fine tuning that perfect hover.  On a rebreather, the diver is not changing the volume of gas in the breathing loop as they breathe - they are simply moving a fixed volume of gas around a loop of which the diver’s lungs have become a part.  This therefore means that the buoyancy control is done through the BCD alone, with a second consideration being the breathing loop volume which must be maintained on descent and ascent.

Following the confined water sessions, a further six hours of diving were required in open water at progressively deeper depths down to a maximum of 40 metres to practice the emergency skills and to get used to diving on a rebreather.  It was quite clear from the start that becoming proficient on a rebreather was going to take a lot more diving and practice than the course could offer in just five days.   It’s important to realise that you have to start shallow again and slowly build back up to your ‘regular’ diving depths. After over 130 dives and 110 hours on my unit, I am still finding improvements that need to be made to my diving.

I have become completely hooked on rebreather diving, finding that even a shallow nine metre dive is now far more enjoyable just because of the silence and the fact that the marine life now comes right up to me with no bubbles being produced to startle the fish.  Of course, on the deeper dives, the highly efficient gas consumption and reduced decompression times simply speak for themselves as a great advantage, especially when looking at the open circuit technical diver weighed down with a large twinset and two stage tanks. I do try not to laugh too much though – I used to be just like that!

 

 

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