BEING LET DOWN BY A LOVED ONE is a very hurtful experience. It's impossible not to take it personally. As I climbed the ladder back onto the boat I was feeling shocked, bewildered and heartbroken. My Inspiration had just tried to kill me.
At least, that was how it felt. In the amount of time it had taken me to leap from the boat, a closed-circuit rebreather (CCR) that had tested and functioned perfectly had silently transformed itself into the perfect killing machine.
The tide was still running and I had been anxious to swim to the shot as soon as I hit the water. No alarm sounded, but I glanced down at the handsets while I was swimming through the heavy chop.
One was dead, while the other, designed to take over and run things if this happened, was reading nonsense.
I had no idea how much oxygen was in the small volume of gas that I was breathing, but I knew I was using it up rapidly and none was being added by the rebreather. Yikes!
I hit the oxygen inflate button, filling my breathing loop with 100% oxygen, and made some unmistakable hand signals to indicate that I had binned the dive and was heading back to the boat.
As I slumped onto the bench in full kit, the guys on board examined my handsets with interest and discussed what had gone wrong.
Bouncing batteries caused by the jump off the boat was the commonly agreed diagnosis.
The skipper said nothing, but handed me a bottle of Navy Rum and chuckled at my expression when I took a large swig. I had been off the boat for barely five minutes, and if I hadn't been paying attention, I would have killed myself.
I love my rebreather, but I don't trust it to work faultlessly. It has a remarkably varied repertoire of potentially life-threatening habits, and my job is to keep myself alive.
Pay attention or die, that's the deal.
ARE MORE PEOPLE DYING ON CCR THAN ON NORMAL SCUBA GEAR?
On a straight "number of people using the equipment v number of deaths" comparison, the answer appears to be a resounding yes.
In the UK, there are, say, 100,000 active open-circuit divers and about 15 deaths per year - about one death per 7000 users.
For Ambient Pressure Inspirations, the most popular closed-circuit rebreathers. there are an average of three deaths per year for more than 3000 users; that's roughly one death for every 1000.
A number of factors make this kind of like-for-like comparison problematic.
Inspiration users are likely to be carrying out more dives than the average diver. You have to be serious about diving to justify the financial outlay for the equipment and training.
Inspiration divers are also likely to spend longer on their dives because there are fewer gas limitations. A more useful comparison would be number of deaths against hours spent under water.
People diving Inspirations are often experienced technical divers, and they are more likely to be doing deeper, more challenging diving that is inherently more risky.
If all that sounds like an excuse to explain away the number of deaths on rebreathers, consider the following:
No women have died on the Inspiration, but several women have died on open-circuit scuba gear. Does this mean that the rebreather is 100% safe for women?
Statistics alone have little meaning. We need to interpret them; and people have an unnerving habit of using the same statistics to support completely different arguments.
ARE REBREATHERS DANGEROUS?
If a scuba-diver jumps off a boat without turning his cylinder on, and drowns because he had no buoyancy and sank, is that the fault of the equipment or the diver? Most people would agree that the diver is to blame for not carrying out his pre-dive checks.
If a rebreather diver jumps off a boat without turning the rebreather on, passes out from lack of oxygen and drowns, do most people blame the diver for not carrying out pre-dive checks, or are we more willing to believe that it was somehow the fault of the rebreather?
Divers are familiar with scuba gear, and this leads us to view it as safe, a known quantity.
Our relative lack of familiarity with rebreathers predisposes us to view them as suspect and possibly dangerous. But that doesn't mean that they aren't.
The Inspiration is the only rebreather to have CE safety approval, yet many good, experienced divers have lost their lives on the unit.
A rebreather is no respecter of reputation. Fail to heed a warning or make a mistake in dealing with it, and it can easily kill you.
If the problem you are experiencing is with CO2 in the loop, or a partial pressure of oxygen less than 0.16, your ability to think clearly is likely to be impaired by the very problem you're trying to solve.
Dave Thompson, who designed the Inspiration, compares the introduction of the unit to that of other diving technologies.
"Some people warned that ABLJs, BCs and drysuits were dangerous when they first appeared, and they were right," he says. "Divers did have an increase in problems and incidents until diving techniques adjusted to the change.
"Many of the first Inspiration divers were very experienced open-circuit divers and they didn't appreciate that they had effectively become novices again.
"Are rebreathers dangerous? That's like asking whether guns are dangerous. It's down to the user."
COMPLACENCY CAN KILL
Rebreathers solve one of the biggest dangers facing scuba-divers - running out of something to breathe. On the vast majority of dives, an Inspiration will function perfectly.
These two factors can make divers feel very safe on the unit, perhaps even lull them into a false sense of security.
"I've been diving for 28 years now, the last seven being on closed-circuit, and I feel much safer using the rebreather. The immense gas duration is an incredible luxury, particularly on dives at 30m and deeper," commented Martin Parker, Managing Director of Ambient Pressure Diving, which makes the Inspiration.
"There are maintenance and set-up procedures for the rebreather that need to be carried out correctly by the user, but probably the most important aspect of rebreather diving is simply to pay attention to the handsets.
"If people did this adequately, there would be a lot fewer incidents."
Richard Pyle explained how his attitude to rebreather diving had altered over time. "After 20 hours' diving, I felt I knew everything about rebreathers. After 100 hours' diving, I was beginning to appreciate how much I still had to learn."
The KISS closed-circuit rebreather is a recent addition to the market. Manufactured at home in Canada by its designer and shipped out in self-assembly kit form, the rebreather has a warning engraved in red letters on the back. It says: "This device is capable of killing you without warning."
Perhaps all rebreathers should carry this warning, because unless you are prepared to accept responsibility for that harsh reality, you should not be diving on a rebreather.
Martin Parker agrees with the sentiment. "I'd like people to be wary of the unit, because hopefully that way they'll treat it with respect and avoid becoming complacent."
Above and below: These AP Inspiration and KISS rebreathers both carry health warnings. The Inspiration sticker says "Danger of death", the KISS: "This device is capable of killing you without warning".
|CCR - THE PLUSES
- Gas volume is not an issue, regardless of depth
- Constant buoyancy
- Warm gas
- Optimal gas mix = minimum deco
- Low gas costs for trimix divers
- Smooth ascents and descents
- Verbal communication possible
- No gas switches required on deep dives
|CCR - THE MINUSES
- Big investment
- Must be used as primary kit
- Bail-out options need regular practice and considerable thought
- If you bail out (as the unit is supplied) the remainder of a 3 litre cylinder won't last long!
- Auto Air regulators need regular tweaking
|Unit + course (mandatory before purchase) ||£4230.00|
|O2 cells, (three per rebreather, annual replacement recommended) ||£165.00|
|20kg drum of soda lime (18 hours' diving) plus carriage ||£67.00|
|Cost of soda lime per hour of diving ||£3.70|
|Annual (recommended) electronics service ||£176.00|
|Annual O2 cleaning of oxygen cylinder ||£15.00|
|Annual cleaning of O2 cylinder first stage || £20.00|
|Buddy clean/Trygene (lasts forever) ||£10.00|
|Buddy Nexus Computer (recommended) ||£300.00|
|3 litre O2 fill (150 bar top-up) ||£3.00|
|3 litre air fill ||£1.50|
|HOW A CLOSED-CIRCUIT REBREATHER WORKS
Breath exhaled by the diver (denoted by the red arrows) is recirculated from the mouthpiece to the exhalation bag (where any water present is trapped) and then through a scrubber-unit filled with soda lime.
This chemically removes any carbon dioxide present, producing calcium carbonate, some water and heat. The scrubber unit also has a water trap.
The remaining gas mixture is then analysed by a group of sensors and oxygen (denoted by the green arrows) is added (by the automatic operation of a solenoid-driven valve) in the mixing chamber above the scrubber unit until it is at the required and predetermined partial pressure.
The enriched breathing gas (blue arrows) is then drawn into the inhalation bag, up through the mouthpiece and back to the lungs of the diver, where some oxygen is metabolised and the diver exhales again. The whole cycle is driven by the diaphragm muscles of the diver.
A diluent gas is used to dilute the oxygen and provide enough volume to fill the lungs of the diver and the counter-lung of the rebreather unit, so that the diver can breathe at the ambient pressure of the depth of water he is at.
This diluent has to be added to as he goes deeper, and some is off-gassed as he comes more shallow.
When air is used as a diluent, the diver effectively breathes a nitrox mix that is varied by percentage but with an oxygen content of constant pressure. Trimix (oxygen, helium, nitrogen) is used as a diluent when depths are considered to exceed those safe for use with nitrox.
Back to Primary School - Chris Boardman takes a TDI Rebreather Course.
WHAT DIVERS THINK
I asked a range of divers for their opinions on whether the Inspiration is a dangerous piece of kit.
Janine Gould, owner of Old Harbour Dive Shop, Weymouth: "I wouldn't dive with one myself, and I don't see a place for them in normal sport diving.
"Do I think they're dangerous? Yes. I've seen experienced divers die on the Inspiration, and I believe that if they'd been diving on open circuit they'd still be here.
"I think you're more likely to survive a problem on open circuit than on a rebreather, and while I know that people will disagree with that, you only have to look at the statistics."
Ian Potten, Inspiration user: "I think the unit is safe, and the deaths on rebreathers are caused by users. A major problem seems to be over-determination to dive. People can see that there's a problem with the rebreather before the dive, but they're out on a boat at the dive site and they're determined to dive regardless.
"You can understand the frustration if you're out in Jutland or somewhere, and you've spent a lot of time and money to get there. If you dive on a rebreather you have to be prepared to miss a dive if your unit isn't working properly."
Keith Forward, commercial diver, owner of Forward Diving Poole: "I don't think the Inspiration is dangerous but personally I'm not enamoured of the unit and I wouldn't dive one. When I dive, I'm working and must concentrate on what I'm doing. Inspirations need to be checked continuously and they appear to go wrong a lot. But the deaths do seem to be down to user error. The key thing with a rebreather is being able to interpret what it is telling you.
"A lot of experienced divers have died using them, but they didn't always have that many hours of experience on the unit. Open circuit is a lot more forgiving of user error than closed-circuit diving.
"In my opinion, most people don't need an Inspiration for the type of diving they're doing."
Bill Reid, technical diver, open circuit: "I think the Inspiration is a good idea, but it's not for me. I don't want to give up a season's diving to train on one and I don't feel it would give me anything extra. I've been diving since the late '70s and you know what they say about old dogs and new tricks! But if I was starting out now, I would want to dive a rebreather."
Fiona Watson, Inspiration user: "Carbon dioxide could be contributing to a lot of the incidents - people may be using their scrubber material for too long. Inspiration divers can be in the water for a long time, so it's relatively easy to overrun the three hours and exhaust the chemicals if you don't plan properly or can't be bothered. At present there is no alarm or warning system for a CO2 breakthrough. The big problem with breathing too much carbon dioxide is that it stops you from thinking straight; like being very narked.
By the time you've realised there's a CO2 problem you'll be feeling confused. Any kind of problem on the rebreather requires quick thinking and a clear head, so CO2 build-up is extremely dangerous."
Martin Parker agrees: "I want to stress the importance of changing the scrubber regularly. If people are diving deep, they should definitely change their soda lime beforehand. Ambient Pressure is developing CO2 duration warnings for the unit."
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
Back to Primary School - Chris Boardman takes a TDI Rebreather Course.