ISSUE 16 ARCHIVE - TECH DIVING: TOOLS IN BIKINIS

Paulo Vincenzo Toomer

I’m back.

What a wild few months I’ve had. What with my little guy being born and me jetting off to Bikini Atoll, it’s been all systems go.

Now, I’m not going to write an article on Bikini as that will probably lead to more suicides than there normally are after reading my column. But, Bikini did prompt me to write the article you are about to read. No, I’m not going to discuss me wearing a bikini, or how the bikini is the in accessory for hairy- arsed tech divers. I am going to discuss rebreathers, because our two week trip to Bikini was only open to rebreather divers. I have several trips and expeditions planned over the next two years and they are all CCR only. Can you believe that? A year ago us CCR divers were all searching for CCR friendly facilities, now the poor open circuit techies have to look for OC friendly trips. Wild!

For the last two years we have been in
what has been termed the“Rebreather Revolution”. I love the sound of that because I am NUTS about rebreathers. I don’t just like my rebreather. I have a deep, meaningful relationship with my rebreather.

I love everything about CCR, the quiet, the warmth, the ease of breathing, the seemingly unlimited gas supply and the incredible no decompression times. CCR however, has been eternally viewed as a machine used either in clandestine operations for blowing the crap out of some poor b*****d waiting at anchor, or for deep, dark, scary technical dives conducted by hard core divers that never get cold and eat bats for lunch.

But, things are a changing. There are a few people out there, very forward thinking people that think rebreathers should be used by everyday recreational divers. Hell, one training agency thinks you should be allowed to learn how to dive on a rebreather and bypass open circuit entirely. I can hear the hard-core element out there groaning as they read these words, but please, allow me to explain.

Here is a (very) brief explanation of a rebreather. A rebreather takes used gas from a diver, moves it through a carbon dioxide removal system and then after an analysis, tops up the used oxygen to the pre-set level approved by the diver. There is an oxygen cylinder that is used to top up used oxygen. And because we can’t breath oxygen deeper than 6 metres without serious consequences, there is a diluent cylinder, which is filled with a breathable (at depth) gas, that makes up the balance of the gas breathed by the diver. It effectively“dilutes (diluent)”the oxygen. Easy.

Up until very recently, most rebreathers have been aimed at the technical market only, hence the units being reasonably complicated. These units have huge diver input and when they fail the diver is trained to try and keep the rebreather running manually. They are also capable of use at extreme (100 metres plus) depths.

This all changed a few years back when Poseidon released their MKvI recreational closed circuit rebreather. This unit is a fully electronic unit that has virtually no diver interaction at all. On a technical unit the partial pressure of oxygen that the diver breathes is selected by the diver, on a recreational CCR this is set by the manufacturer to optimise no decompression diving. If a technical CCR suffers from low oxygen (injection solenoid stuck closed) the diver will add oxygen, and the converse for a high oxygen situation. On a recreational CCR, the unit will electronically try to fix the situation with redundant oxygen and diluent solenoids, adding the relevant gas to make the diver safe. Recreational rebreathers are used to a maximum of 40 metres, much like most recreational divers worldwide.

There are very few events that would lead a technical CCR diver to bailout. The reason we want this is that carrying the open circuit bailout gas that would be required for a BIG technical dive where the CCR fails is difficult to say the least. As you can imagine, swimming from 40 metres to the surface with no decompression schedule to complete is quite easy to plan. Therefore carrying the gas for this ascent is relatively simple. So recreational rebreathers rely on open circuit bailout in the event of almost any failure. This makes recreational CCR diving easy.

So should we skip the open water diver open circuit course or go straight to rebreather? It’s actually not a difficult answer. When a diver learns to dive open circuit they realize quite quickly that their lungs have a massive effect on buoyancy. Basically, breathe in,
go up, breathe out, go down. But on CCR when you breathe in or out, you are taking the gas from a simple bag design called a counterlung. The reason CCRs have these
 is simple. If there was no bag it would be
like trying to breathe out of a milk bottle,
the bottle has no flex, therefore you cannot draw breath or breath out. So if the diver is trading gas with a counterlung, the buoyancy of the diver will stay the same, no matter where on the breathing cycle the diver is.

Most of the skills learned to master CCR diving are similar to their OC cousins but not the same. The setup of CCR versus OC is vastly different as well. So adding all these little things together means that an OC diver will have to“unlearn what they have already learned”when they move to CCR. So, why not start with CCR?

The training agencies and manufacturers have obviously addressed the fact that if you are already a diver you understand OC, therefore you understand the CCR bailout system. With this in mind, the CCR open water course will credit divers with diving experience and will ask divers with no experience to take a little more time with training.

I could go on and on about rebreathers, especially recreational units so I am going to continue this discussion next month.

Now get your ass down to your local centre and get some info on the“Rebreather Revolution”.

Paul is Director of Technical Training
for SSI (Scuba Schools International).
 He owns Diving Matrix Tec Lab with facilities in London, Manchester, Red Sea and Malta.