The rebreather, another way to dive and a real philosophy
Diving with a rebreather is very different from diving with an open circuit.
Whether you have got 200 dives behing your back ( eventhought you need to be at ease underwater ), or 10000, it won’t matter at all.
In both cases, you will have to start from the beginning again.
Good to know :
The stabilisation :
The lost of a ballast lung requires a big stabilisation effort. In an open circuit, the diver can compensate the stabilisation problems of his vest using the ballast lung, most of the time, he does it without even realising it.
Using a rebreather, it’s not possible due to the volume that constant.
Indeed, the expired air goes to the fake expiratory lungs, and the inspired air comes from the fake inspiratory long. The volume being always simlir, we can’t manage our buoyancy using our lungs
The lost of the ballast lung is therefore an handicap for young divers in close circuit, so much that a perfectly aquired stabilisation isn’t so any more.
Personally, it took me 6 months, diving once a week to perfectly master the recycler’s stabilisation, ( especially as a photographer, where it needs to be perfect .
On top of that, you have 2 volumes to take care of :
- The stabiliser vest
- The volume of the fake lungs
- AND even 3 volumes if your suit is waterproof
If evolve at a constant depth, you won’t need to play witht he injectors or the purges in order to maintain yourself in a stable position.
On the other hand, the depth changes will have an impact of the loop’s volume.
The deeper you go, the higher the pressure, and you will be obliged to inject more diluant into the loop.
Conversely if you go back up, the rise of gaz volume present in the loop will have to be evacuated by the nose.
More over the PPO2 will drop, which will cause the soleinoide to activate and poor out some O2.
You guessed it, it will take some time before being able to master each and every of these volumes
Managing the dive :
This is where the diving philosophy radically changes ! In fact, the reasoning isn’t the same at all !
In an open circuit, here is the question we ask ourself : How much air have I got in the block ?
In a rebreather diving : What am I breathing ?
The autonomy countdown is not longer felt, eventhought it still exists.
We have got time !! Even in median space, between 30 and 40 M we have got time.
Without getting into TEK dives, which, at this depth, gives all the meaning to the rebreather
The fact that we have got that much time allows us to rediscover the sites we thought we already knew by hear.
Why does the rebreather optimises the decompression ?
It’s a question that I often get asked. In order to reply, we need to talk about oxygene toxicity, and to understand the notion of partial pressure.
Oxygene is toxical !
I often hear in TV reportages, the speaker talking about oxygene bottles when divers are on the screen.
This is totally wrong.
In most of the cases, it’s bottles of air like the one you are currently breathing.
They are NOT filled with oxygene
Here is why :
The oxygene, essential element of life, is paradoxally very toxical at certain pressures.
The human body is perfectly adapted to our natural envirronement.
Good to know :
a pressure at sea level of 1030 HECTOPASCAL
and an atomosphere ( air ) composed of 79% of nitrogene, 20.9 % of oxygene ( and a few rare gazes ).
The rest of this, we will simply it by saying the air is composed of 79% of nitrogene and 21% of oxygene.
Nitrogene:1bar x 0,80 = 0,8 bar PPN2
Oxygène :1bar x 0,20 = 0,2 bar PPO2
It’s called the DALTON law
These conditions change while diving !
At 10 meters deep, the ambiante pressure is of 2 bar (1 bar of atmospherical pressure + 1 bar of water collumn pressure).
At 20M, it’s 3 bars, at 30m it’s at 4 bars, and goes on and on…..
The partial pressures therefore evolve according to the depth
At 10 m we get :
Nitrogene :2bar x 0,80 = 1,6 bar PPN2
Oxygene :2bar x 0,20 = 0,4 bar PPO2
At 20m :
Nitrogene :3bar x 0,80 = 2,4 bar PPN2
Oxygene :3bar x 0,20 = 0,6 bar PPO2
It’s good to know that the partial pressures of azote (PPN2) and of the oxygene ( PPO2), have some critical steps that shouldn’t be trepassed.
The PPO2 is fixed at 1.6 bar ( the lenght of exposition is also limited ) and the PPN2, is at 5 bars.
By breathing at a 10m depth, we breat air at a pressure of 2 bars.
Our metabolism consumes oxygene.
Azote is diffused in our organism so that it is balanced ( equi-pressure ) with the ambiant pressure.
When coming back to the surface, the extra azote in our body has to escape in order to keep the balance. This is the reason we do compression bearings.
In a recycler, the PPO2 is managed by the machine.
Generally, it’s set to 1,3 Bar, and that no matter the depth of evolution. There is a composition modification of the gaz according to the depth we are at.
Here is a comparative board of a gaz breathed in with a rebreather at a fixed 1.3 bar PPO2, compared to the air that would have otherwise been breathed in with an open circuit :
We notice that when using an open curcuit, the gaz proportion stays the same, no matter the depth. This phenomenum is normal as the composition doesn’t change.
Only the pressure varies
On the other hand, when using a recycler the gaz mixture varies according to the depth.
We have an evolutive Nitrox.
The gaz breathed is optimised according to the depth. We notice that there is less nitrogene with the recycler’s mixture. Our organism satures less, and therefore the decompression bearing time are reduced.
At 50M deep, the expired mixture has almost the same composition as the air. Tis induces maximum rebreather diving depth with an air diluentr. This limit is due to 2 phenomenums :
The air viscosity : the deeper we dive, the more the air density rises and the harder it is to breath.
The narcose : below 60m, the recyler will keep the PP02 level at 1.3 Bar, but the PPN2 will keep rising.
The breathed mixture is very narcotic, as there is a lot of nitrogene.
Is diving with a rebreather more dangerous than diving with an open circuit ?
At this question, I feel like I need to say : Yes…. but no !
Sure there is more technology in a recycler. More electronics, more joings, a waterproof circuit…. so potentially more breakdownds that Open Circuits.
But we have a couple of safety bottles !
Haha, we aren’t that crazy after all !
On the other hand, the breathed in gaz is optimised for decompression, therefore, we greatly minimise the decompression risks.
Therefore, it’s very hard to balance to assets and the drawbacks.
According to me, the risks comes more from the way we dive. And that being true for both OC and CC.
Keep a critical mindset towards your rebreather !
The rebreather is the machine that’s keeping you alive , but , it can also kill you.
It’s particularly true , and the Murphy law won’t disagree with that : “Anything that can go wrong will go wrong”.
In other words, make sure the dive goes fine !
And in order for it to go fine, you need to respect a few important things.
The danger with the rebreather is to be too trustworthy towards the machine. It is therefore primordial to have a good initial course to know what to do in case some breakdown happen. ( The famous ” what ifs ” )
The machine’s assembly : the different tests and checks that have to be systematically done before each and every dive. Therefore, the planification of this dive should never be done too fast. These are automatisms that are to be acquired , plannification and preparation towards the dive. Indeed the importance of often diving with a rebreather. The error would be to buy a course without buying a rebreather, and never diving with a rebreather after that.
To be very cautious with your gear is a key rule : this is also true with an Open Circuit, but even more with a Close circuit. If a breakdown happens before the dive, it has to be fixed immediatly, or you have to cancel the dive.
Never dive with a failing machine : the entire tests have to be done before the dive, in a calm place, without any disruption.
Beware of any distractions in those key moments.
Always be aware of the PPO2 : : This seems pretty obvious, but in fact, it’s not always that easy ! Especially for photographers like myself who always draw their attention towards the camera’s viewfinder. You always have to keep in mind that at any moment the PPO2 can rise or drop and reach critical steps. Becareful to the lifetime of the ceculles that analyse the PPO2, it’s the HUGE drawback of recyclers.
Take care our your bail out, verify gazes, regulators, and make sure to have enough quantity to get to the surface while doing your safety bearings. You have to prepare and planify your dive !
When should you step up to the CCR ?
In France, the legislation requires you to be at least level 3 and Nitrox confirmed, to start a course.
It’s the strict minimum to my mind !
To start thinking about getting into recycler diving you have to :
be perfectly at ease underwater
be passionate about diving, and technique i am not talking about TEK dives, but of techniques at the proper meaning of this term)
Love your gear, and take care of it
Be disciplined and methodical. If the simple fact of preparing your block is a hastle, don’t even think about the rebreather.
Diving using a rebreather isn’t done randomly
You got it ! To dive with a rebreather, you need to be passionate, a very self-aware passionate.
If you are a young underwater photographer, don’t even think about going towards the recycler before perfectly mastering your technique.
The management of a CCR requires more attention and pratice than an open circuit one.
Conclusion : I am a rebreather diver
It has now been 4 years since I started diving in closed circuit, and there is NO WAY I am going back to an open circuit.
Beside the advantages these kind of machines offer, I have always been attracted to this technology and this technical part of diving.
I enjoy it, and I am very enthousiatic, even at the thought of preparing my machine for a dive !
It’s a true passion and I think this is the main motivation of diving with a rebreather.
Of course, as a photographer, I have other points of interests while diving in closed circuit.
The approach towards animals is totally different.
Some fish are still very fearful at the sight of divers, but most of the time, they don’t mind, or they are curious and come have a look at you.
I managed to see behaviors at I never saw in open circuit, and that I would have never been the witness otherwise .
Settle at the bottom of the sandy ground, between two reefs, and in less than 5 minutes you will feel invinsible.
The real reef life will open to you !
The exploration of the 40/50M zone also takes another dimension.
The pressure of time being less strong, we can take more time to sit, watch and enjoy.
Think about sharing this article if you found it useful, or if it helped you !