Closed-circuit rebreathers offer many benefits for divers, yet for the uninitiated they remain objects of myth, suspicion, even fear. Our training correspondent Chris Boardman set out to dispel the mystery by doing a TDI rebreather course - and becoming a complete novice again

DO YOU KNOW HOW TO CLEAR A MASK Can you make yourself neutrally buoyant Are you able to use an alternative air source and make a controlled ascent from 20m
     Whether you are an advanced trimix diver or only a few dives on from your initial open-water course, if you want to try closed-circuit rebreather (CCR) diving, throw away your rule book and get ready to start all over again.
     Clouds of speculation have surrounded rebreathers in recent years - surprising in a way, considering that they have been around for 120 years, long before open-circuit (OC) scuba, and commercially available since 1954!
     It is true that an unaccountably high number of deaths have occurred among the small CCR community. Most seem to be unexplained or caused by proven user error - the cause of most diving accidents. Whatever the facts, people have come either to love or hate closed-circuit rebreathers.
     Having followed the various debates about them, I was unable to decide whether the fears of the anti- camp were justified or born of fear of the unknown.
     A rebreather course was next on my list of training evaluations for Diver, and I hoped that learning more about this growing branch of diving might help to dispel some of the mythology around it.
     The most popular CCR unit in the UK is Ambient Pressures Inspiration, and most technical agencies run an Inspiration course. I decided to check out TDIs five-day version with Dive Action, based in the beautiful village of St Keverne on the South Cornish coast. The owner, instructor and pretty much everything else was Gary Fox.
     Yorkshireman Gary has taught diving for more than 20 years (half his life) and seems to hold qualifications with every organisation under the sun. He moved to Cornwall eight years ago but his mannerisms remain those of his birthplace - he is plain-speaking and never misses the chance for a friendly go at his colleagues.
     If you are of a delicate disposition, this might take some getting used to!
     Gary got into CCRs two years ago, at a time when he considered them death traps. He had to be persuaded to try an Inspiration, but the experience turned him 180Â and he now believes they are Gods gift to divers. He trained up to teach CCR diving, and where most schools will teach you only after you have bought a unit, his school maintains five of its own.
     There have been several modifications to the Inspiration since its launch in 1997, though none you could call fundamental.
     It is now so popular both in Europe and the USA that you have to wait at least three months to get a unit, and only then if you have undertaken the mandatory training.

Day One
I had arrived at the Parc-an-Grouse guesthouse at 1 in the morning, so had yet to meet fellow-student John Cobb. We introduced ourselves over breakfast while Sadie, the resident horse, poked her head through the window in search of Fruit and Fibre.
     A lively and clearly well-educated man, John had already committed to buying an Inspiration. He had been diving since 1978, though he had done fewer than 300 dives due to work commitments, but now he was running a small consulting business and had more spare time.
     All my equipment was due for replacement and I wanted a new challenge, so I decided to look into rebreathers and became fascinated by them and what they offer, he told me. John had no technical training beyond the required nitrox certification. I was curious to see whether he would be at a disadvantage to someone with open-circuit tekkie experience.
     Gary and Kevin Rainford, our safety diver, joined us for breakfast and I soon realised that the course structure was going to be pretty fluid, I guessed to accommodate the weather. With the wind blowing quite hard, a tour of AP Valves/Ambient Pressure Diving had been arranged.
     Dive Action is fewer than 12 miles from its factory, and Gary tries to organise a visit for all his students. It proved fascinating, and allowed John and I to see how Inspirations are built from the ground up, and to quiz the people who design, test and build them.
     John asked Terry Fisher, APs chief engineer, to respond to the negative comments made about the Inspiration. Terrys replies didnt smack of toeing the company line and served to suggest that many rumours had been born of ignorance.
     Considering the 16-week backlog in production, I was amazed at everyones willingness to stand around chewing the fat. In the end I had to drag Gary and John away!
     I had assumed that we would head back to the classroom for the theory but, no, we were off to one of Garys haunts for a long lunch! We didnt start on the theory until gone 3pm - I would have to adjust my watch to Cornish time.
     We started with the history of rebreathers and their basic features, followed by maintenance procedures (part 1) and some of the basic bail-out options we would be practising. Our coffee break lasted 75 minutes because of customers turning up downstairs. Afterwards we went over unit assembly/disassembly and pre-dive checks.
     To demonstrate that these checks do not, as rumoured, take hours, Gary ran through them in just under three minutes.
     I suspected that it would take a little longer when rolling around on a RIB, but it would not be a million miles from the open-circuit equivalent.

Day Two
It was becoming apparent that Gary was trying to keep about 10 balls in the air at the same time. It was a familiar-enough scene in an expanding dive business, but today we were putting together the Inspirations ourselves for the first time, and having seen it demonstrated only once the night before, I would have appreciated his undivided attention.
     As it was, I had to wait for Gary to come and go between phone calls for advice. He struggled with this problem for the next two days until his weekend help arrived.
     Units prepped and stowed in the van, Gary decided to give us another hour of theory. We took in physiology, highlighting the differences between OC and CCR, and the various forms of gas toxicity rebreather style and what to do about them.
The three main killers are:

  • Hypoxia, or too little oxygen, caused by a leak, power failure or having the O2 cylinder turned off by mistake;
  • Hyperoxia, or too much O2, likely to be caused by the solenoid sticking open and continuously injecting oxygen, or misprogramming the handset;
  • Carbon dioxide build-up, caused by exhausted or poorly packed CO2 absorbent (soda lime), which can lead to the diver losing consciousness.
     Apart from a totally flooded loop (which, it became clear, was difficult to achieve), and providing you fully understand how the rebreather works, all these problems can be dealt with under water, we were told. However, the fixes involve various degrees of diagnostic thinking while under water and under stress. Thats why progression with rebreathers must be slow and methodical.
     The next two hours at the pool proved that the rumours about having to learn all over again were true. From the moment I dropped into the water, I regressed from trimix diver to novice.
     I timed our pre-dive checks and they did take only five minutes, but I had to concentrate hard. Drysuited and in the pool, we were taken through the in-water pre-descent checks.
     As I descended the 3m to the pool bottom, I was struck by two big differences between CCR and open-circuit scuba.
     With CCR the air in the counter-lungs collapses on descent, like all your other air spaces. Unless you push a button and put it back, as you would with your drysuit or BC, you cant breathe in. So its helpful to know where the button is to inject diluent into the counter-lung.
     With OC, compressed gas is sucked out of the cylinder to expand in your lungs, increasing buoyancy as it does so until you breathe it away into the water. By contrast, the breathing gas in a rebreather stays in the loop, simply moving from one bag (your lungs) to another (the counter-lungs) and back again.
     This means that your buoyancy cannot be adjusted by breathing in and out, so all adjustments have to be made manually. I realised this as I slowly approached the pool bottom, instinctively took a deep breath to slow myself and collided with it!
     This is both a plus and a minus. Controlling buoyancy can be finicky to start with, but once set, it is possible to lie motionless in the water. It is a marvellous feeling and would be a real plus for photography or on long deco-stops.
     For a few minutes we swam around, getting used to the silence and the strange sensation. Then it was time to start the drills.
     First up was mouthpiece removal and replacement. This is not as simple as it sounds, because the mouthpiece must be closed whenever it is not in your mouth to keep water out of the breathing loop.
     This is one of the few CCR situations where you are really up the Swannee with only the tiniest of paddles, in the form of a 3 litre diluent cylinder.
     The exercise was combined with switching to and from the open-circuit option. With all new Inspirations, this is in the form of a combined low-pressure inflator and regulator, the Buddy Auto Air.
     Next came diluent-flushing, the first line of defence for most problems. It involves manually flooding the counter-lungs with fresh gas while venting off the former contents. By doing this you know exactly what you are breathing - the key to safe CCR diving - and this step buys you time to sort out a problem.
     It was time for mask-clearing. Dont forget that with this closed-loop system, as soon as you breathe out through the nose, you cant breathe in without manually replacing the gas in the loop.
     We learnt how to clear water from the mouthpiece and twin hoses by closing and removing the mouthpiece, stretching the hose vertically to straighten the ridges and allowing the moisture to flow into the water traps. This looks dodgy (imagine pulling one of the hoses off) but the joints and hoses, I am assured, are strong enough to be able to lift the 32kg unit off the ground without damage.
     Contrary to popular belief, an Inspiration will keep working with litres of water in the water traps and even if the absorbent material gets partially wet.
     Next, we examined one of the most serious problems that can occur with a rebreather - a high O2 warning, such as might occur if the solenoid that injects the oxygen sticks open.
     The O2 drill is one of the few situations in which it may be necessary to get off the loop to prevent an oxygen toxicity attack, which usually results in spasm, then spitting the mouthpiece out and drowning.
     If the partial pressure of oxygen in the breathing loop reaches 1.6 bar, a warning will show on the handsets - if, that is, you cant already hear the alarm screaming. You must close the mouthpiece and switch to open-circuit, usually fed by the Inspirations diluent cylinder (in our case, air).
     At the same time, the O2 cylinder needs to be switched off and the breathing loop flushed with diluent until the handset indicates that the pressure of O2 is back at a safe level to breathe.
     Then its back onto the loop to preserve that precious gas you have been blowing away into the water, and slowly crack open the O2 cylinder to see if the switch-off/on has cured the sticking solenoid.
     If not, you must either bail out (if you have enough gas) or leave the oxygen cylinder turned off and use the Inspiration as a semi-closed unit to return to the surface. Imagine trying to work all that out in mid-water.
     For obvious reasons, this is one of the few exercises that must be performed quickly. It was therefore the one that Gary would spring on us throughout every dive until it became second nature.
     Next, Gary showed us how to fly the system manually as a semi-closed circuit rebreather, something you might do if you lost all electronics or had a sticking solenoid. The loop is emptied by breathing in through the mouth and out through the nose, then fresh diluent (air) is injected manually while breathing in until one full breath can be taken. This is then breathed about four times before the process is repeated. Its less tricky than it sounds and allows a 3 litre cylinder to last as long as a 12 litre.
     The final two exercises involved manually holding a higher set-point (ppO2) than the computer was set to (again, not too difficult) and running the unit as a fully closed-circuit O2 rebreather, something you might want to do for the final stage of decompression from 6m.
     If you got into trouble and needed to hold your 6m stop for as long as possible, a full 3 litre cylinder could last you up to 10 hours. This would far outstrip the recommended life of your CO2 absorbent and score you about 1400% Oxygen Toxicity Units, but you get the idea!
     With gas now expanding in the counter-lungs too, even making a simple ascent was very different to OC. If you use solely the drysuit or wing for buoyancy, rather than both, this is not as complicated as it sounds, as the drysuit dumps on its own and the extra loop volume is simply disposed of through the nose. Using this method, I found going up was smoother than with OC, because my breathing caused no variations in ascent rate.
     It was a very instructive two hours. In the water, where Garys phone wouldnt work, his teaching was very good and well-paced. Most frustrating for me was the feeling of being a novice again. There is no place for egos on a CCR course.
     All that let us down in this session was the Buddy Auto Air. Two of the three units in the water were leaking air through the system, and would do so again before the course was over. With CCRs, the 600 litres in the diluent cylinder is ample as long as you are not losing any through leaky kit.
     I like the Auto Air idea, because incorporating the alternative air source in the low-pressure inflator helps to reduce clutter, but on a £4000 piece of kit leakage is not acceptable.
     A quick trip to Ambient Pressure on the way back to Garys proved that such leakage was not unusual. When Big Mike kindly brought out a pail of water to help fix the offending items on the spot, Auto Air Bucket was written on the side!
     Gary decided this was enough for today, so we finished at a sociable 5:30. I had enjoyed the session and learned masses. I had a lot to think about before our first session in the sea.

Day Three
We awoke to bright sunshine and gale-force winds. I was unhopeful about getting in the water, but in this part of Cornwall its always possible to find shelter. Porthoustock beach was just a mile from our B&B and two from Garys base.
     After re-assembling our Inspirations, a process that was already starting to become a lot easier, we headed off. We had not changed the soda lime in the scrubber canister since the pool session as we could get another hours diving out of it - the recommended limit is three hours.
     From the steep pebble beach we could see white caps 500m out to sea, but the water in the bay was flat calm. Gary briefed us, we did our checks and wandered to the waters edge.
     First up was a weight check. I discovered that an Inspiration required me to carry more than 4kg more than I would with a single 12 litre cylinder to achieve neutral buoyancy.
     We were reminded of the in-water checks: make sure cylinder valves have not been switched off or rolled themselves off, as they might aboard a bouncing RIB (the knobs are at the bottom) and that handsets are reading properly. We then descended, pausing briefly at 3m to check each other for bubbles. You can do your own bubble-check simply by looking up - you should be unable to see any!
     At the bottom at 10m, we rechecked the handsets to confirm that they were reading properly and that our gas supply was sufficient for the dive before switching to the high set-point (1.3 bar O2). The unit would now ensure electronically that we were breathing the ideal nitrox mix, no matter what the depth, thus keeping nitrogen absorption and deco time to a minimum.
     We swam around while Gary made us repeat all the skills we had learnt in the pool and sprang O2 drills on us.
     After an hour, we started to make our way back to the exit point. I checked the gauges on my two 3 litre cylinders. Even with the repeated drills, where we vented gas into the water, I had still used only 40 bar of gas.
     As we approached 4m, Gary reminded us to switch back to the low set-point of 0.70 for the final ascent. No rocket science, just simple procedures - but a lot of them!
     Back at Garys, it was time to replace the soda lime for the next three hours of diving. When you remove the canister, the first thing that hits you is the warmth, a by-product of the CO2-removing process. This means that you breathe moist, warmed gas, a very pleasant upside to CCRs, particularly in Britain. The other surprise is the amount of condensation, resulting from both the heat and the chemical reaction.
     Packing the canisters is a bit of an art form, as the quantity has to be precise. Too loose and gas can channel and flow unscrubbed through the soda lime; too tight and sucking the gas is like drinking a McDonalds milkshake.
     Again, it takes an awful lot of simple steps, none of which you want to forget.
     I was getting an inkling of why there might have been so many deaths among CCR divers - there are so many opportunities for the user to make errors. CCRs demand a very disciplined approach.
     We repeated all the drills on dive two. A large chunk of a CCR course consists of simply diving the unit.
     For the required minimum of six hours you have to go through the steps repeatedly, so after the pool no more skills came into play.
     As John was being subjected to another surprise high-O2 drill, I discovered another advantage of rebreathers - the ability to talk under water, albeit sounding like a ventriloquist. As John listened to Garys coaching Im not sure he saw it as an advantage, but from where I was floating, it was great!
     It was then back to base for unit-cleaning, undoubtedly the biggest downside to rebreathers. Have you ever wondered how much drool you produce while under water for two hours Try draining a CCR counter-lung which, being the perfect environment for micro-organism growth, has to be regularly cleaned and disinfected. Worst of all, we had to clean Garys unit too!
     We went through this process every day. Including topping-off cylinders, it took 45-60 minutes to prep a unit for a days diving and 30 minutes to clean it down.

Day Four
The wind had not abated, but by tucking into the coast we were able to get out on Garys Predator RIB. He had two full charters on this weekend and we would be going out between them to dive the wreck of the Volnay.
     Our skipper today was Haggis, an ex-military man of few words who remained soaking wet on the RIB from 10am to 5pm without a whimper.
     Haggis was a serious asset. I saw him lift a female client one-handed out of the water and deposit her in the boat without touching the sides!
     He was also invaluable when heaving 32kg rebreathers into the RIB.
     At 20m the Volnay (Wreck Tour 24, February 2001) would give us a chance to practise our ascents and descents more thoroughly. As I rolled off the RIB I had to remind myself to keep the mouthpiece in at all costs. It would have been so easy to whip it out to share a joke, only to hear my counter-lungs empty through the mouthpiece as I sank out of sight.
     Bubble-checks done, I descended the shot, replenishing the gas in the counter-lungs every time I needed to breathe.
     Having to do this every few seconds meant that buoyancy was only ever just negative, so descent speed was very steady. Eight metres from the bottom, the Volnay came into sight. Despite the storm-force winds we enjoyed a consistent 5m-plus visibility throughout the course.
     After 45 minutes of skills and exploration, even with skimpy 3mm gloves I was toasty-warm. I felt sorry for Dickie Kirsopp, our photographer, diving twin 12s and making a hell of a racket breathing as he got cold towards the end of each dive.
     We used the Volnay for all our course dives. There was lots to see and it was virtually current-free at all states of tide, and only three minutes from shore.
     At the end of our second dive, I saw that Johns Aladdin computer showed nine minutes of stops. I compared this with Garys Buddy Nexus, which can be set to follow a continuous partial pressure and had been set to track that of the Inspiration. It indicated 144 minutes of no-stop time remaining! Now thats what I call an advantage.

Day Five
Our final day of diving started with a dip at 8.30am before the charter crowd arrived. The dives on the Volnay were pretty much identical to the previous days. We then headed back to Garys for the final exam and cleaning session (yuck).
     The exam was comprehensive, not the usual multiple-choice affair. As we headed for the showers, I asked John what he had made of the course.
     Im glad I bought an Inspiration but I can see that if you go this route itll take a lot of diving to stay dive fit, he said. This isnt a piece of kit you can use every now and again. It must be your primary diving equipment, but after this week I cant see me ever wanting to go back to OC anyway!
     I was happy with the training Gary gave us. I feel as if Ive had a good grounding in the basics of CCR diving, which is what Module One is for. The factory tour was a real bonus. It was one of the reasons I wanted to do the course here.
     What was his next step I certainly wont be doing anything deeper than this for a while, and Im not yet contemplating deco dives with it. I think its important to progress slowly with this piece of kit. It needs the appropriate respect, as its quite capable of killing you.
     I really want to become comfortable with all the drills first, especially doing them midwater as opposed to on the bottom, as weve done here. Thats where things are going to happen in the real world.

My own views largely mirror Johns. The Inspiration is a fantastic piece of kit that has been thoroughly thought through, offering incredible advantages to the diver. It is totally different to open circuit and requires a substantial relearning phase, though it is not complicated or even difficult to dive.
     There are, however a lot of simple elements, any one of which give the user an opportunity to make a mistake - such as leaving out the O-ring on the scrubber canister during assembly (which I nearly did) or not monitoring gauges carefully. CCRs are very unforgiving.
     Stick rigidly to all the assembly steps, pre-dive checks, diving techniques taught and maintenance recommendations, and you are unlikely to have a problem, but then, that also goes for OC diving!
     If something does go wrong with the unit, the problem will require varying degrees of diagnostic thinking to rectify under pressure.
     For that reason it should be used only by divers who have a very disciplined, methodical approach and are perfectly comfortable under water. Most people think this describes them, but I suggest it covers only about a fifth of divers.
     A cool £4230 for the course and unit is quite an investment. John jumped straight from single cylinder and pony to CCR but had no more difficulties with the course than I did, despite his lack of technical training. His computing background did mean that the physics posed no problem for him. By going this route, he will have spent a similar amount on his equipment to an OC technical diver
     With Dive Action it is possible to pay the £500 course fee before committing to purchase an Inspiration. Should you decide within a month or so to buy one through the school, it will deduct the course fee from the unit cost.
     Garys struggle to stay focused on the course for the first few days has since been alleviated by a new recruit, allowing him to spread the workload and concentrate on teaching.
     TDIs supporting material for this course consisted solely of Power Point slides and the final exam. Surprisingly for a subject as complex and unlike OC diving as this, it has no course manual, choosing to rely on classroom-teaching and the manufacturers user manual, which can be downloaded free from Ambient Pressures website.
     This manual is comprehensive, nicely laid out and easy to understand, with sufficient diagrams to illustrate the various points. It also has a self-check Q&A section. However, I still feel a manual to accompany TDIs other materials would provide the student with something for future reference - perhaps concentrating on emergency procedures.
     Module One certifies the diver to make no-stop dives to 40m with the Inspiration and is in line with most technical agencies. Module Two covers more advanced trimix options to a maximum 90m and can be taken after 100 logged hours on the unit.
     I was fascinated by CCR technology and would have no qualms about using an Inspiration in the future. The benefits are immense, but as I cant be sure how much I would use a unit, I wont be rushing out to buy one just yet.

Dive Action Diving Services, 01326 280719/ 07831 820820, www.divecornwall.co.uk;
Parc-An-Grouse Guest House, St Keverne 01326 280259, www.parcangrouse.com;
Ambient Pressure Diving, 01326 563 834, Ambientpressurediving.com

Chris and John receive a pre-dive briefing from Gary Fox
Removing moisture build-up after the first dive
Packing the soda lime in the canister
calibrating the handsets on Porthoustock beach
turning on the O2 and checking the Auto Air
Pre-breathing the unit to check that everything is working
The gauge shows 40 bar used after an hour of drills
Once oxygen is returned to within safe limits, the O2 cylinder is turned back on while monitoring the gauges
Leaning to one side and flushing the loop with diluent, the step that buys a diver time
Clearing water and drool out of the mouthpiece and hoses into the water traps
Safely on the bottom and switching to the higher set-point
mask removal step one - no breathing out through the nose
Mask replacement
mask-clearing while injecting gas back into the loop