Rebreathers Simplified. A Complete Guide to Choosing,. Understanding and Diving a Closed. Circuit Rebreather. By Dr. Mel Clark. Rebreathers Simplified. Mel Clark. Mel is an active technical/rebreather diving instructor trainer and avid underwater photogra- pher. She has over four thousand dives with more than. 1 Rebreathers Simplified Rebreathers Simplified A Complete Guide to Choosing, Understanding and Diving a Closed Circuit Rebreather By Dr. Mel Clark.
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diving using rebreathers are: 1) the importance of knowing the oxygen partial .. method is a simple "clock" of how much dive time is spent using a particular. This manual is supplied with all Open Safety rebreathers to provide information .. has a manual inject to simplify purging or flushing the loop. 8. Manufacturer's minimum training standards and any additional course forms required by the manufacturer. Optional. Mel Clark- Rebreathers Simplified.
A rebreather is only a tool to be used on the rare occasions when the dive is beyond the capabilities of open circuit. Without consistent practice and training in benign environments, a rebreather diver can never be ready for that pinnacle dive that will require complete mastery of skills and protocols.
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Maintaining frequency and mastery of skills is also a critical component of emergency management. Rebreathers are a tool that should be reserved for divers that NEED them.
These are military, scientific, and commercial divers that require the technology to do a job. While rebreather diving does involve additional risks and considerations, it is fun. Many divers choose to dive a rebreather because they find it more enjoyable than diving open circuit, and there is nothing wrong with that. Your rebreather is trying to kill you.
While this is a funny concept, the reality is actually the exact opposite. Your rebreather is trying to keep you alive. Improper assembly, poor maintenance, complacency, and failure to conduct proper pre-dive checks are among the top reasons for rebreather accidents, not a machine with an affinity for murder. During a normal dive, I use about one liter of oxygen every minute.
It does not matter if I am at the surface, at 50 fsw 15 msw , fsw 30 msw , or fsw 90 msw. Thus, a given cylinder size will last me about the same amount of time, regardless of depth.
My primary rebreather uses a 13 cf 2L cylinder, smaller than a typical emergency gas supply cylinder used by OC divers. Yet that small cylinder will allow me to remain under water for over six hours! If I swap in a 21 cf 3L cylinder, that jumps to ten hours. Rebreathers eliminate time pressure associated with limited gas supplies.
Mind you, you cannot stay at deep depths indefinitely, even if you have an adequate breathing gas supply. Divers still need to consider inert gas loading to avoid decompression sickness at the end of the dive.
Yet, rebreathers provide benefits here as well. With the air diluent used by recreational divers, the inert gas is nitrogen. As with OC scuba, nitrogen dissolves into tissues when nitrogen pressures in the breathing mix exceed those in the body. The greater the differential, the faster nitrogen is dissolved, and the less time we can remain at depth before having to surface to avoid staged decompression. There are two ways to minimize nitrogen loading: Stay shallow, or reduce the amount of nitrogen in the breathing gas.
Often we do not have the ability to stay shallow.
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Many of the sights we desire to see simply cannot be found in shallow water. Coelacanths only live in deep water. Black corals are not found at the surface. We cannot move a wreck to shallower water to suit our desires.
But we can, to some degree, address the second option. In OC scuba, we reduce nitrogen uptake by filling our cylinders with nitrox. But OC nitrox is limited by having to select a particular mixture before the dive. Once the cylinder is filled, the diver cannot change it. And many dive operations only provide one or two standard nitrox mixtures, which may not be the best mix for a dive to a given depth.
They are capable of providing an optimal mix for whatever depth you are at. Suddenly, whole new possibilities open for divers. I get to spend LOTS more time under water, exploring, enjoying the scenery, and taking photographs of fish than I could otherwise. I love it! On a rebreather, our gas supply is used up at the same rate irrespective of depth and so the amount of gas we are carrying is no longer the limiting factor. This means that running out of gas on a rebreather is much less of a concern than for an open circuit diver.
Instead, the critical factors become the amount of decompression we are incurring, the duration of our carbon dioxide absorbent and our risk of oxygen toxicity. This has two aspects, the costs of the rebreather, including downloading and maintaining it, set against the cost of open circuit diving. One of the biggest disadvantages of open circuit trimix diving is the cost of the gas. This makes each trimix dive an expensive proposition.
On the other hand, a rebreather uses much smaller cylinders because the gas is reused rather than wasted, as a result we use much less and the gas costs are much lower. As a result there is a significant gas saving when compared to open circuit diving.
This can look very attractive when you are spending considerable amounts on each open circuit fill.
However this must be set against the costs of the rebreather. Depending on the model a rebreather is likely to cost between four and eight thousand pounds. If you go for an older second hand model then you might get one for less than this. In addition to the initial cost of the rebreather you will need to factor in training on the rebreather which is likely to add on another thousand pounds.
PADI Re-Breather Speciality
In addition there will undoubtedly be additional costs to add on extra equipment to the basic rebreather. As a result it is not uncommon for the initial start up costs on a rebreather to be between 6 and 10 thousand pounds. Obviously you will need to do a lot of trimix diving in order to save enough to justify this initial outlay.
The majority of divers do not do enough diving to clearly justify downloading a rebreather based on savings in gas costs. Unless you are doing 20 or more trimix dives a year then it is not cost effective. If you also do a significant amount of recreational diving then each dive may actually cost you more on a rebreather. On open circuit, you may only need to pay for an air fill but on even the shallowest dive you will still need to use pure oxygen in one of the cylinders and use carbon dioxide absorbent in the rebreather.
The annual replacement of the three oxygen sensors and handset batteries also needs to be taken into account. It is clear that unless you are doing significant numbers of deep trimix dives a year with little or no recreational diving then the gas savings from using a rebreather will not outweigh the initial start up costs. However, there are still a number of other reasons why a rebreather is an attractive option.
Open circuit divers may be using up twin 12L, 15L or even 18L cylinders on each trimix dive. In addition they may be using up to 4 stage cylinders for decompression gas for each dive.
This requires lots of additional helium and oxygen each day and filling these large back gas cylinders and decompression cylinders each day is expensive, time consuming and labourious.
Rebreathers and the Recreational Diver by Jeffrey Bozanic, Ph.D.
The fact that a rebreather uses smaller cylinders makes the logistics of filling much easier. The volumes of gas needed are much smaller when filling a 3L cylinder rather than twins 12s and so it becomes feasible to take enough gas with you for even a week's diving.
This contrasts with the situation when using open circuit where significant volumes of helium and oxygen will be required as the majority will be breathed out and wasted.
If you have to drive 50 miles there and back to drop off a twinset for a trimix fill and then do the same thing next day to pick it up, then the logistics of this can be significant. Similarly, if you are diving somewhere without easy access to a dive centre that can fill trimix, the ability to take your own gas simplifies the planning and logistics. Of course, this assumes that the rebreather will always work as intended. Just in case there are any problems with the rebreather, we also need to carry open circuit gas to get us safely to the surface.
In this case, we would need a bailout cylinder that we could start using at the maximum depth and would then need sufficient bailout to get to the surface completing all our decompression. Unlike the open circuit diver, the rebreather diver will not use their stages unless there is an emergency but will still need to carry them. However on open circuit the diver will use the decompression stages on each dive and so they will need to be filled each day.
For a diver using a twinset and a stage cylinder, they may plan their gas to have the optimum mix on the bottom, i. They will also make a choice of the decompression gas carried in the stage cylinder with a view to ensuring that they get rid of the inert gas as fast as possible during the decompression. However, the choice of each of these gasses will always be a compromise. The bottom gas will be chosen to be as rich as possible but with some margin for error in case the dive is a little deeper than expected.
If the diver ascends up from the planned maximum depth, then the mix is no longer the optimum mix. Equally, the decompression mix will only be the most effective mix at the depth at which the diver switches to it.
Prior to the switch, the diver could have switched to a leaner mix and at the later stops there will always be a richer mix that would have provided faster offgassing. A rebreather avoids these problems by constantly adjusting the gas being breathed to ensure the minimum amount of inert gas is being breathed.
The rebreather or the diver in the case of a manually operated rebreather adds oxygen to ensure that the minimum amount of inert gas is being breathed.Tec Sidemount Diver You are introduced to tec sidemount equipment and dive techniques, including up to six cylinders.
Coelacanths only live in deep water. There is a certain mindset that is required to ensure that the unit is assembled correctly each time and that all of the pre-dive checks are rigorously followed. Efficiency advantages[ edit ] The main advantage of the rebreather over open circuit breathing equipment is economical use of gas.
However, if there is any problem during the dive, the impact of the initial problem can be significantly increased by subsequent problems. Just in case there are any problems with the rebreather, we also need to carry open circuit gas to get us safely to the surface. Beyond 80m then rebreather technology becomes the more common tool and it is likely that for dives in excess of 80m rebreathers will continue to be viewed as the tool of choice.
Just great stuff! Open circuit divers may be using up twin 12L, 15L or even 18L cylinders on each trimix dive. We can see that rebreathers offer a number of significant advantages over open circuit diving.