BACK

Rebreather Project

Us divers are a funny breed, we spend fortunes on equipment and spend hours travelling to the most obscure parts of Britain and the World in order to fulfil our desire to explore and sample the undersea world.

At the very pinnacle of the species of diver is the underwater photographer, they can spend even more obscene sums of money on cameras and housings, and can spend a whole dive working on few square metres of reef, whilst the rest of the boat have covered several hundred metres.

It is from this background that I come, so while on a liveaboard in the Deep South of the Red Sea at the end of January, I found myself pondering a re-breather try-dive. During the previous summer I had evaluated the possibility of training for and owning an Inspiration, a fully closed circuit rebreather (CCR). This I had dismissed due to initial cost, £6K, on-going costs and lack of diving opportunities to justify the costs.

The dive guide on the boat had an Inspiration, and I felt smug in the fact that for me at least I had made the right decision. The Inspiration is very much a machine that has to be ‘flown’ and will add considerably to the task loading during a dive, not something a photographer wants. The dive guide also offered a try dive using a Drager Dolphin semi-closed rebreather (SCR).

Time for a quick lesson. CCR’s, are as the name suggests a closed circuit, the expired gas the diver breaths out is re-circulated around the loop, scrubbed of CO2 and passed back to the diver for breathing again. The diver sets a PPO2 and the O2 cells in the unit monitor and maintains that PPO2, regardless of depth and if required adds either a dilutent or O2. This has advantages for both oxygen toxicity and decompression if managed correctly, if not you stand a very good chance of dying. An SCR, in the case of a Dolphin, is a loop in much of the same way as a CCR, but the loop is constantly fed with breathing gas, normally a nitrox mix, through a controlled ‘leak’, so over a given period of time the gas will be exhausted, normally 2 – 3 hours. The PPO2 will vary in much the same way as it does for open circuit scuba and the decompression requirements will be those for the open circuit nitrox equivalent. Any excess gas from the controlled leak will be vented from the loop, irrespective, whether it still has usable O2 in it.

So I hear you say :- what are the advantages over a huge 15L dustbin of nitrox ?

So with the technical and science part over I decided to take the plunge. The try dive took the form of a kind of show and tell session initially, a very quick tour of the anatomy of a Dolphin, followed by a very important list of do’s and don’ts, critical if you are to stay alive. If the gas in the loop was to become hypoxic (levels of O2 that will not support life) you normally pass out without warning and find yourself in a very sticky situation.

A major attraction for me was the extended dive time for a given amount of air, and not having to use large cylinders and stage cylinders etc. (It is important to stress that dive planning needs to be meticulous and you need to carry or have available sufficient bailout gas to complete your decompression requirements). The other major benefit is the lack of bubbles, its not only Moses that can part the Red Sea, any open circuit diver holding a camera, can part and send running for cover, any fish he comes into contact with.

After the briefing and my head spinning from the potential disasters that can befall me, I leapt from the back of the boat, and had the most surreal experience. I started diving some 20 years ago and this was the nearest thing to that initial experience of weightlessness and exhilaration I have ever experienced since. The feeling of freedom and silence and being at one with the alien underwater world was extreme.

The important technique with a rebreather is not to skip breath but to breath as normally as possible, as the volume of air going around the loop remains constant, you can’t fine tune your buoyancy by breathing in or out, so your buoyancy control needs to be spot on. This again is a tremendous asset for the photographer as you can hang motionless on a wall waiting for that perfect moment to press the shutter.

All of a sudden, with 10 or so divers in the water you realise just how noisy open circuit scuba is, it must terrify fish. The air to control the buoyancy in your jacket comes from your bail out and on some dives, if not managed properly can exhaust quicker that the air feeding the breathing loop. So a different approach to diving is required, you find yourself going around things rather than over or under, as the only way to change buoyancy to fill or empty your jacket.

In what seemed like no time at all, in fact it was over an hour, and Helen had already left the water, my dive was over. I had chosen not to take my camera, as I didn’t want to increase my task load, in hindsight, the Dolphin was so easy and intuitive to use, I could have taken the camera.

From looking at the course notes, we skipped a lot of technical material and practical skills that need to be covered in order to be certified to safely use a Dolphin. You are required to have a nitrox qualification before progressing on to a SCR, so much of the material will be familiar. It was a good sign to me of the inherent safety of a Dolphin, that so quickly, a try diver could be let lose in the sea with one, even if under the very watchful eye of an instructor.

I now very much have the bug, I’m mid-way through a PADI/TDI Dolphin Course, most liveaboards and foreign dive schools have rental units for use or can arrange same. Any piece of kit that if used correctly and at the right depths can double the time to get images can only be a good thing. After all, the cost of diving abroad is calculated by dividing holiday costs by total holiday dive time. A dolphin can halve those costs for the same outlay.