Your Questions about Closed Circuit Rebreather (CCR) diving answered.

[Gary_Ward]

We asked some of our friends, associates, and followers on social media to ask us questions about rebreathers we could include in an upcoming video. Here is Jon and my take on the 'Dark Art' for both recreational and technical divers

 

[emoreira]

Hi, I'm not a rebreather diving.
I've seen the video, and though much of the things said I already knew, it was very informative and clear.
I have some questions I still don't know.
I asume that if diving with a rebreather and drysuit, the diver has to carry a drysuit inflation tank with, I guess, argon.
The second question is about BCDs and rebreather. Does a diver with a rebreather has to use a BCD ? What type of BCD and which is the inflation method used ? The same as with the drysuit ?

 

[davehicks]

Both BCD and Drysuit typically connect to the air diluent tank. If you are using something other than Air Diluent (pricey trimix) then you could use a separate 6 or 13 cf tank for inflation only.

 

[Gary_Ward]

Hi, I'm not a rebreather diving.
I've seen the video, and though much of the things said I already knew, it was very informative and clear.
I have some questions I still don't know.
I asume that if diving with a rebreather and drysuit, the diver has to carry a drysuit inflation tank with, I guess, argon.
The second question is about BCDs and rebreather. Does a diver with a rebreather has to use a BCD ? What type of BCD and which is the inflation method used ? The same as with the drysuit ?

Thanks for responding and asking some very sensible questions. I'll try to cover those below.

Lets first talk about gas supply and redundancy. On a typical CCR unit your diluent gas (and your O2) are typically very small tanks (<20 cuft). This means we're typically diving with an off-board bail out tank - just in case something were to go wrong with the unit, the bail out would be sufficient that we could safely make it to the surface. We use 6 liter, of 40cuft bailout tank for this purpose for most dives. Therefore when you're diving on a CCR you'll either have you drysuit connected to your diluent tank, as too will you bcd, or you can connect it to your off-board bailout via a separate low pressure inflator hose. If you're diving using trimix, you probably don't want to use that in your drysuit (too expensive), or if you're diving in extreme cold, you might want to consider Argon - but for most air from an off-board tank is perfect.

Rebreather technology has come more into the mainstream from the technical diving side of the sport, and as such the majority of units will come equipped with some form of backplate and wing or harness and wing set up. The main reason for this is because you want the unit to be well fitted to your back and not able to roll around. You'll also want to minimise clutter too, so we all tend to dive a lot more minimalist rigs. I know that Hollis was offering their rebreathers with a jacket style BCD for a short while, but it proved to be very unpopular and was dropped very quickly. The advantages of the harness/wing setup is that you can adjust your harness so that it perfectly fits you. The wing is also a great design to hold you in near perfect trim too.

In terms of inflation, the CCR has a low pressure inflator hose coming from the regulator on the diluent (air) tank which you run over your shoulder and it connects to a very standard looking BCD inflator, which inflates the wing. You can add a second hose for a drysuit, or as mentioned above, add an inflator hose from your bailout.

Let me know if you've got any more questions

Gary

 

[broncobowsher]

Hi, I'm not a rebreather diving.
I've seen the video, and though much of the things said I already knew, it was very informative and clear.
I have some questions I still don't know.
I asume that if diving with a rebreather and drysuit, the diver has to carry a drysuit inflation tank with, I guess, argon.
The second question is about BCDs and rebreather. Does a diver with a rebreather has to use a BCD ? What type of BCD and which is the inflation method used ? The same as with the drysuit ?

Maybe and probably not.

If diving recreationally (no trimix) and the bailout is just air it is pretty easy to just plug the drysuit into the bailout.
The whole Argon for insulation thing, that can go down a whole other rabbit hole. Check in the exposure protection section about the use of Argon. In general it has been found to not do anything and everyone just uses air.

Now if you are going to have a trimix in the bailout bottle (normal for anything tech/deep) you don't want that in the drysuit. Since you generally won't have any other gas with you that is appropriate for inside a drysuit, that is when you add a drysuit specific bottle. Helium is too thermally conductive and you get cold, oxygen in a bag full of synthetic materials (and sometimes an electric heater) is just too risky. There are a few stories about combustion inside a drysuit with oxygen. All the gasses you take for a deep/tech dive are high helium and/or oxygen. Thus a drysuit bottle of air.

Most of us are also taught to run the wing and drysuit on separate gas sources. That is if you have a failure in one system, you still have the other. Since the wing doesn't care about helium content (it doesn't get cold like a person in a drysuit) the wing generally gets it's gas off the diluent bottle. Helium in a wing doesn't matter.

As mentioned in the video there are a lot of little differences between rebreathers. Thus the crossover class when going to a different brand (sometimes model). Part of that will involve the different ways they are configured. As much as things are standard, there is almost always one version that has one feature different/backwards from the norm. Most of the backmount stuff is pretty close to each other, but sidemount rebreathers have not standardized as much as backmount has. So none of this is a one size fits all answer.

 

[1c3d1v3r]

The whole Argon for insulation thing, that can go down a whole other rabbit hole. Check in the exposure protection section about the use of Argon. In general it has been found to not do anything and everyone just uses air.

Argon got real proven benefits. You need to use it right. 2-3 flushes with argon on surface.

For short dives you won't notice a difference. Where it matters is long and cold dives. With argon you can dive longer before feeling as chilly as with air. It's equivalent of having a thicker under garment or an extra microfleece layer.

 

[wedivebc]

Using diluent as a drysuit inflation gas is a bad idea as it leaves you without redundancy. Using bailout to inflate is best. If you are using trimix for bottom bailout you can inflate your suit from your deco bailout. Offboard inflation gas is good too but adds another system to an already bulky rebreather/bailout system.

 

[grantctobin]

Using diluent as a drysuit inflation gas is a bad idea as it leaves you without redundancy. Using bailout to inflate is best. If you are using trimix for bottom bailout you can inflate your suit from your deco bailout. Offboard inflation gas is good too but adds another system to an already bulky rebreather/bailout system.

Running 50% or greater O2 for suit gas with heat is asking for injury.

 

[Gary_Ward]

Using diluent as a drysuit inflation gas is a bad idea as it leaves you without redundancy. Using bailout to inflate is best. If you are using trimix for bottom bailout you can inflate your suit from your deco bailout. Offboard inflation gas is good too but adds another system to an already bulky rebreather/bailout system.

That's kinda one of the reasons why I like the simplicity of the KISS rebreathers which use an off-board dil. Working on the premise that you're carrying an external tank (bailout) anyway, why not use it? I typically dive with a 6 or 8L external tank, which means I'm carrying typically 4-6L (x 200bar) of redundant gas (assuming I might use 2L through my CCR or through inflation). Whilst I may not want to use this for deep exploration diving.... it makes for a very simple setup

 

[wedivebc]

Running 50% or greater O2 for suit gas with heat is asking for injury.

Can you recall one example of when there was a drysuit fire due to oxygen rich inflation gas? I've never heard of one and I've been doing it dor 20+ years without incident.