CCR Rebreathers
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Koh Tao, Thailand |
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[CCR Rebreather Training]
At DJL Diving we offer closed circuit rebreather diving courses.
Training is run by ex-naval engineer Leon Webber, teaching IANTD rebreather courses on Buddy Evolution & Inspiration units.
For 2008, we're offering 2 courses.
 1 day introduction to rebreather diving
IANTD CCR Rebreather Course
First, here's some background info on rebreathers, written by Leon:
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Lets start with what you already know, Open circuit diving, normal everyday first and second stage regulators. The first stage drops, or regulates, the high pressure 200 bar tank air down to about or 10 bar above the ambient pressure (the pressure of the air or water around you). You take a breath, inhaling 21% oxygen and 79% nitrogen (if using air), you exhale a breath that contains 16% oxygen, nitrogen and carbon dioxide (the body’s waste product from combustion), metabolizing only about 5% of the gas you inhaled, the rest is wasted, sent up as bubbles to break, noisily, on the surface, scaring the fish and marking your position. You have also given away some of your body’s heat and hydration, which exist in finite amounts, more on that later.
OK, you know what you are giving away, how do we fix that? Simple, by recirculating that exhaled breath back to you, removing the CO2 (carbon dioxide), adding back the O2 (oxygen) you used, now you can breathe that air again. That’s it in a nutshell, however the mechanics and electronics of it are what the science of rebreathers is all about.
Lets look at the loop, what we call the parts of the rebreather that contain the air we breathe. First the mouth piece, it is fitted with hoses on both sides, that lead back to the scrubber housing unit. Following the air flow as the diver exhales gas low in oxygen, high in CO2 the gas travels out the mouth piece through a one way valve into a counter lung, which is just a bag with some fittings on it. and over the divers RIGHT shoulder into the rebreather housing. This bag is designed to trap moisture, should any get in from loose lips, or excess water vapor that has condensed from your breath. It also has an over pressure relief valve on it, that is the black valve you see in the center, on top of an inspiration or evolution, this valve is designed to vent excess pressure that has built up in the loop and works just like a dry suit exhaust valve, spring loaded and adjustable. With either dive or pre dive setting.
The gas we exhaled then travels into the scrubber canister, which has another water trap, the reason for the water traps is inside the scrubber canister. We have packed our scrubber canister with soda lime (divesorb, sofnolime etc) which doesn’t like water in large quantities, see the paragraph on caustic cocktails. The soda lime is a chemical that absorbs CO2 and in the process produces heat and a bit of water vapor and slowly changes itself into chalk, not something you can take to school, but chemically it is the same stuff.
So now we have scrubbed out the waste product and are ready to add fresh gas.
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In a fully closed rebreather,(CCR) you have two gas feed systems, one is only to provide volume to the loop, we call the gas the diluent and it should have enough oxygen to breathe it directly at the maximum depth you plan to be at, it is either added via pushbutton valve, or added automatically via an ADV (automatic diluent valve), when you bottom out the loop. The other gas system is an oxygen injection system and there are several ways to get O2 into your loop. Some RB’s, like the KISS, add O2 continually via a small orifice, plumbed between a tank full of pure O2 and the breathing loop. The flow rate is controlled by the intermediate pressure of the regulator on the O2 tank combined with the size of the orifice. The flow rate is set by the diver to match his/her metabolic oxygen use rate.
Other more sophisticated CCR’s such as the buddy inspiration and buddy evolution, use a system of oxygen analyzers, voting logic, and a solenoid to inject the oxygen into the loop, these systems can also be controlled manually if the electronics fail. Rebreathers of this type are the Megaladon, Inspiration, CCR 2000 and the Cis-Lunar, just to name a few. All types of CCR’s must have some form of Oxygen Partial Pressure monitoring, if for example, the O2 flow was to fail, the diver must be made aware of it to be able to either fix the problem or end the dive. Hypoxia can sneak up on a diver with absolutely no warning.
Now about that caustic cocktail. Soda lime, when exposed to copious amounts of water, especially sea water, tends to become slightly corrosive and has a metallic taste that is not at all pleasant to have sloshing around in your mouth. It is important to keep your breathing loop as dry as possible, small amounts of water that get in are trapped by the design of the system and are kept on the exhale side of the scrubber, water vapor that is part of your breath make it through the scrubber with no problem and the soda lime’s reaction to the CO2 produce small amounts of water too, this is no problem. If you get a major flood, its time to switch to your open circuit bailout and end the dive.
OK, so now you may have a clue as to what rebreathers are all about, so why would you want one, and is it right for you?
GAS EFFICIENT One of the main advantages of rebreathers is Efficiency, a SCR is at least 5 times more efficient than open circuit, and a CCR is at least 10 times, and even more efficient as you dive deeper because your need for oxygen doesn’t change as you go deeper, the CCR only provides the O2 that you metabolize. I can dive for an hour, at any depth, and only use 2-3 cubic feet of oxygen, compare that to your conventional scuba equipment.
This makes diving the unit on a DJL wreck finding trip almost essential. Giving you longer bottom times on the wrecks.
WARMER You also stay warmer diving a rebreather. Open circuit sucks heat out of you with every breath, you breathe in cold air, warm it with you lungs and then blow it out into the ocean, with a rebreather your warm breath comes back around again and again, and the chemical reactions in the scrubber canister are providing more heat too.
DRY MOUTH OC divers come back from a dive with dry mouths, along with the heat you exhale goes moisture, not so with rebreather, warm moist breaths are the rule here.
NOISE, NOISE and more noise. You can never appreciate just how nice a quiet dive is until all you hear are the light pops of the one way valves in your mouth piece working until you try rebreather diving. I can hear open circuit divers from hundreds of feet away, imagine what the fish hear. There is nothing like having a school of fish completely surrounds you, not even noticing your presence. Seals blow air bubbles as a sign of aggression, do you think they will hang around a group of aggressive bubble blowing divers, usually not. At a place called the farne islands, England, I have had closer encounters with more seals whilst diving my rebreather than ever before on OC. If you are into underwater photography or video, consider a rebreather, you will get shots you never thought.
Now for the down side.
Expensive: Rebreathers are EXPENSIVE. The entry level is around $3500usd for a basic SCR with no Oxygen monitoring, your not going to dive a rebreather without O2 monitoring are you??? An A full spec Buddy Inspiration is around $10000.
Here at DJL we can offer the latest inspiration and evolution rebreather units for hire. Either per day or of you would like to come along on one of our wreck hunting expeditions, We can arrange a unit to suit your needs.
Training Did we mention training? This is not the place to go bargain hunting, you are playing with your life here and you need to do your homework. What if you need more dive time than the average person? Are books included? Don’t be afraid to ask questions Training should include, theory, math, physics, operation, assembly, cleaning, maintenance, safety, bailout techniques, and actual diving in open water and maybe pool time.
Here at DJL we can offer the only training available on Koh Tao, Thailand and after completing your introductory dive, if you wish to continue your training your intro dive will be taken into account and you will have made the first steps towards certification.
More down side:
Rebreathers are not for every diver. If you are the kind of diver who runs out of air frequently, or doesn’t pay close attention to your diving, forgets equipment, gets distracted easily, doesn’t maintain your gear after every dive or weekend, leaves things lying about to get stepped on, makes every purchase with only price in mind and is just generally absent minded or careless, DON’T EVEN THINK ABOUT IT!!!!! You can kill yourself easier on a rebreather than by putting a plastic bag on your head, probably faster too. This is not a hobby that you can't dabble at, it is not for the twice a year diver. If you are a serious diver, that wants to extend your bottom time, play with the fishies closer and more intimately than ever before, and don’t mind the extra attention, training, cost and maintenance issues that come with diving a rebreather, then come on in, the water is quiet.
So that gives you some background info about rebreather function.
The rebreather training that we currently offer is:
Introduction to rebreather diving [4000 baht]
1 day theory and shallow water rebreather diver, giving you an idea of what it's all about!
IANTD CCR Rebreather Course [from 50,000 baht]
Leon offers full rebreather training - the course is split into modules whixh run right through to CCR Trimix Rebreather.
For full details please contact us. |
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info@techdivethailand.com |
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