Skipping open circuit and going straight to CCR

[takez0]

This is my first post here. I've learned a ton on this board and I'm grateful for the insights you all provide.

I'm getting into technical diving and I'd like to jump straight into a CCR. Does the group see any benefit or hindrance in skipping open circuit tech training costs and equipment costs and going straight into a CCR? CCR's are obviously an investment. I'd rather not spend money on a new BCD, manifold, tanks, etc., that would only be used specifically for dual-tank open circuit, considering I know where I want to end up already. Let me know your thoughts or if you think this is missed training opportunity.

 

[lostsheep]

An agency doing something does not make it the right thing to do.

There was that one agency that used to claim they were doing the right thing directly in the title of their text book

 

[happy-diver]

Here's some real stuff really worth learning

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Another smart dude

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The 'Rebreather Day 1' (RD1) 'kit' provides open-architecture components to allow a very easy build-out for those already RB-savvy. Our recommendation is to first configure the unit as a simple oxygen only system which is depth limited to 20 feet/6 meters depth. Once proficiency is attained, the...

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[Angelo Farina]

I admit that I don't know very much about the ARO, so correct me if I'm wrong, but it's an Oxygen rebreather, right? So at 15m the loop PO2 is 2.5 ATA? Were there seizures?

Yes, there were seizures. But the "trick" was to start with the loop partially or completely full of air, instead of "washing" it properly for ensuring to start with pure oxygen.
There was no mean for estimating ppO2 in the loop, so even with the trick of incomplete loop washing, there were still seizures.
The max accepted depth for short periods was 18m. The max depth for 2h exposure was 10m. This was usually enough for a previous free diver who wanted to extend his time on the bottom.
The main safety measure against seizures was to use a full face mask, which avoids drowning in case of seizure. Then your buddy can bring you to the surface.

 

[Wibble]

Another smart dude

RD1 Rebreather - Kit System (Back Mount)

The 'Rebreather Day 1' (RD1) 'kit' provides open-architecture components to allow a very easy build-out for those already RB-savvy. Our recommendation is to first configure the unit as a simple oxygen only system which is depth limited to 20 feet/6 meters depth. Once proficiency is attained, the...

www.underseatools.com

RD1 Rebreather - Kit System (Back Mount)​

Regular price$1,758.93

CHEEP!!!

If it's an oxygen rebreather, no need for cells, computers, monitoring, even diluent isn't required so when the loop volume drops, you just inject oxygen.

The 6m/20ft limitation makes it utterly pointless. Except maybe as a decompression rebreather?!?

 

[formernuke]

If it's an oxygen rebreather, no need for cells, computers, monitoring, even diluent isn't required so when the loop volume drops, you just inject oxygen.

The 6m/20ft limitation makes it utterly pointless. Except maybe as a decompression rebreather?!?

It can be turned into a regular rebreather. He is like 30 minutes from me. I'm trying to set a time to go check it out.

 

[MyBuddy]

Yes, there were seizures. But the "trick" was to start with the loop partially or completely full of air, instead of "washing" it properly for ensuring to start with pure oxygen.
There was no mean for estimating ppO2 in the loop, so even with the trick of incomplete loop washing, there were still seizures.
The max accepted depth for short periods was 18m. The max depth for 2h exposure was 10m. This was usually enough for a previous free diver who wanted to extend his time on the bottom.
The main safety measure against seizures was to use a full face mask, which avoids drowning in case of seizure. Then your buddy can bring you to the surface.

Sounds like the ARO rebreather is “dead” simple. Considering that the OP’s goal for getting in to a rebreather was to go “deeper, farther, longer” an oxygen rebreather wouldn’t get him there. It might get him longer, might, but if the max exposure at 10m is 2hours, I know a fair number of people that could just about do that on an AL80. Unless the OP is only going to shallow dives or has the need to do long shallow clandestine swims to place limpet mines on the hulls of ships I don’t think the ARO is what the OP should be considering. So offering it up as A rebreather that one can jump in to without a health OC base is a bit disingenuous.

 

[PfcAJ]

There was that one agency that used to claim they were doing the right thing directly in the title of their text book

They weren’t wrong in that particular instance

 

[Wibble]

It can be turned into a regular rebreather. He is like 30 minutes from me. I'm trying to set a time to go check it out.

Point was that the oxygen rebreather is easy as there's effectively no monitoring required; fully manual with no electronics or special valves.

When moving to use diluent in a CLOSED circuit rebreather (CCR), you must be able to monitor the loop oxygen as too much or too little = death. That's the hard bit and needs lots of mechanics and electronics = complexity = cost.

It's possible to build a SEMI-closed rebreather (SCR) that's manually run that uses diluent for gas and has a gas exhaust, be that overpressure or leaky. These are often called gas extenders. There's a couple of commercial SCRs available which also monitor oxygen.


However, it's lovely to see that someone's got the bits required to DIY your own CCR.

 

[Wibble]

...but if the max exposure at 10m is 2hours...

It's much less than that.

10m/33ft is 2ATA. At 100% that's a PPO2 of 2.0; way above the amount you should be breathing.

The NOAA level for PPO2 of 1.6, i.e. 6m/20ft, is 45mins for a single exposure and 150mins/2h30 total in 24h.

 

[Angelo Farina]

Sounds like the ARO rebreather is “dead” simple. Considering that the OP’s goal for getting in to a rebreather was to go “deeper, farther, longer” an oxygen rebreather wouldn’t get him there. It might get him longer, might, but if the max exposure at 10m is 2hours, I know a fair number of people that could just about do that on an AL80. Unless the OP is only going to shallow dives or has the need to do long shallow clandestine swims to place limpet mines on the hulls of ships I don’t think the ARO is what the OP should be considering. So offering it up as A rebreather that one can jump in to without a health OC base is a bit disingenuous.

The ARO was the simple, cheap, basic CCR employed for training new divers.
After the first certification with it, most divers proceeded with twin tanks full of air (the standard OC system at the time) or, in rare cases, with mixed-gas rebreathers (the most natural progression after an ARO).
The typical mixed gas rebreather, at the time, was simply an ARO with an additional air tank on the back, carrying a standard two-stages regulator as bailout and an hose with a manual valve allowing to inject air in the loop.
In the seventies these systems were fully manual, and the very early ppO2 monitoring systems were employed for providing the diver with knowledge if they needed to manually inject oxygen or air.
Using these manual mixed-gas CC rebreathers the max depth was around 60 m, and it was possible to perform accelerated deco in almost-pure oxygen.
Nowadays such a progression can be done with the RB1 rebreather, as posted above.
As said, indeed, this was the less common path, most divers (me included), after being trained with the ARO, preferred switching to twin tanks full of air and never considered coming back to CCR.