Rebreathers – the biggest decision

If you have the latest phone with all the Apps and gadgets, you have already made your decision. What decision you ask? Well it certainly isn’t ‘whether to buy a re-breather or not’ as you have already decided to. Now it’s only a matter of when.

The real decision is quite simple really – whether to buy an mCCR or eCCR. Whether to be in conrol or controlled. OK, you are not sure what I am talking about? Well, all re-breathers are run by electronics to a degree and that degree differs between the eCCR and mCCR. Each has a control unit that constantly monitors the three or more oxygen sensors sampling your inhaled breathe. Your control unit (computer) reads the pressure of oxygen (PO2) in your unit and that is the point where the two CCRs differ.

The Electronic Closed Circuit Re-breather (eCCR) needs the diver to give it instructions as to what PO2 to maintain. These are entered into the control unit as commands for the solenoid. The solenoid then has responsibility for independently injecting oxygen into the unit to maintain that PO2. One of the positives for the eCCR is that once the PO2 is set, the diver is just responsible for monitoring it and ensuring the solenoid is behaving. If you are distracted, the solenoid should still do its job. This is like being a train driver, you set the speed and then sit back and hope the train stays on the tracks.

The mechanical Closed Circuit Re-breather (mCCR) control unit shows the diver the PO2 in the unit and the responsibility for adjusting and maintaining it rests with the diver. The diver decides the PO2 and is responsible for keeping the unit at that PO2. Most mCCRs have a unique feature and that is a constant flow of oxygen that will be just a bit less that the amount of oxygen the diver requires. All the diver has to do is decide when to top-up the PO2. These divers know they will have to press the button so are less likely to become complacent. Like a vehicle driver – they know the consequences of not paying attention while driving.

At first glance, the idea of a re-breather that will do everything for you sounds great. Full automation should equal absolute safety. Unfortunately though, some divers do become fatalities. When we study the CCR accident records we note all brands of CCR are represented and the overriding contributor to fatalities appears to be complacency. We should be taught on a CCR course a few commonsense rules such as: don’t dive alone, carry enough bail-out gas to get safely to the surface, don’t dive a CCR that has a malfunction, don’t exceed your training depth, don’t exceed your scrubber time, don’t dive deep without proper training. Despite these commonsense rules, divers don’t do pre-dive checks, do dive alone in caves, dive with oxygen sensors that don’t work, don’t turn cylinders on, have health issues, don’t carry bail-out and above all – become complacent.

When I qualified on an eCCR, it was an adrenaline pumping experience, I was told to listen for the second heart beat (solenoid injection) and I did. I was told to check my control unit every 1 to 4 minutes and I did. It was cool to set the PO2 and observe the machine take care of me. There were a couple of times though when the electronics failed and I was left in a bit of trouble. I managed safe ascents by following the simple bailout rule.

Having gone through the first CCR decision (to become a CCR diver) I didn’t want to stop but I began looking for a safer CCR alternative. Now at this stage let me calm the ruffled feathers of the eCCR divers. There are several thousand CCR divers happily and safely diving eCCR and mCCR units. The trick is “one size does NOT fit all”. There are divers who should never think of diving a CCR. Some mCCR divers upgrade to eCCR and some eCCR divers upgrade to mCCR – find the one that suits you.

Once I had decided my diving future lay with the KISS Classic mCCR, I did the course and took sound advice. What I found was that the control unit was me! My team of assistants consisted of my oxygen constant flow metre, my manual add valve and my Shearwater computers. I just love the fact that a bailout valve comes standard with the KISS. This is a wonderful safety device not fitted to all CCRs. I added a Shearwater wrist mounted and a Shearwater NERD computer (Google it) for additional peace of mind.

My NERD is a heads-up-display computer permanently in my vision peripheral. I am constantly aware of the PO2 in my unit and I can quickly change my PO2 if I want to. I found that the PO2 in the KISS mCCR is very stable and requires minimal O2 injection. The deeper I go, the more stable it is.

I am very happy now at every depth for which I am trained as I am in control. The reason I am comfortable with my mCCR is that I have found the one that ‘fits me’. Look beyond the bells, whistles and hype – select the best life support system for you, your life does depend on it.

A bit of advice on ‘depth’. Don’t be in a hurry to go deep. Get the best training you can afford, it is a long way ‘up’. You are learning to dive again remember! The real value of a re-breather is that it will take you to magic places that you can’t afford to go on scuba. That simply means longer or deeper or both. A CCR using trimix is cheap to operate. While I can dive to 100m – I don’t. My KISS mCCR and I do go for long dives on shipwrecks in the 40m to 70m range in Truk Lagoon, Scapa Flow, Solomon’s and elsewhere. A 22 dive trip costs me one 11 litre cylinder of trimix (and most of that isn’t used). Using a CCR is a cheap and wonderful way of diving.

So go ahead and buy your CCR; choose wisely, get the best training you can afford, obey the rules, stay alert, have fun and dive safely.

 

By Tony Howell

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