Rebreather Question from a non-rebreather user

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sea2summit

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O2 rebreathers where touched on so I wont hit that again. What I will add is that a CCR, especially when running trimix with low O2 content, is much more labor intensive when shallow and not maintaining a consistant depth. Deeper is better but it helps if you can maintain a depth. Also I don't think they're the best method for extreem depth (in excess of ~ 650') because you have to suck the gas through the scrubber.

So long answer short, they're safe shallow but require extra management and really have a sweet spot between ~60' and <650' IMHO.
 
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tflaris

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Is a rebreather safe at any depth or just deep depths? I thought I read somewhere that rebreather can be dangerous at shallow depths but my fiance said that you can use them at any depth. He said that military uses them at shallow depths and that is how he knows you can use a rebreather at shallow depths. So can you SAFELY use a rebreather at say, 40' and above or is it only for deep diving?

ECCR Rebreathers can be used at any depth they are rated for. As long as the diluent is correct for the planned depth.

The oxygen content in the diluent would determine the depth of the dive (ppO2 1.4 max). Refer to to your nitrox manual.

Bailout mixtures recommended to a 1.0 ppO2 to allow flushing of the breathing loop.

mCCR Rebreathers without modification are rated for 300-350' depending upon the IP of the first stage.

At the surface if you are working hard i.e. a lot of current, swimming back to boat, etc they can be very dangerous. But the diver can manually add oxygen to the loop to prevent this from happening.

There are O2 Rebreathers that can only be used at shallow depths.

A great book is Mastering Rebreathers by Jeff Bonzanic

Safe Diving

Tony Flaris
Meg CCR Diver
Evolution CCR Diver


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rob.laurie

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For me, diving to 300 feet on open circuit scuba is worth it. Doing the same dive on a rebreather is not.

Hey Frank,

I am curious as to your reasoning here.

I feel the opposite, I would much rather be on CCR on a 300' dive than than OC.

Cheers,
Rob
 

rob.laurie

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ECCR Rebreathers can be used at any depth they are rated for. As long as the diluent is correct for the planned depth.

The oxygen content in the diluent would determine the depth of the dive (ppO2 1.4 max). Refer to to your nitrox manual.

Bailout mixtures recommended to a 1.0 ppO2 to allow flushing of the breathing loop.

mCCR Rebreathers without modification are rated for 300-350' depending upon the IP of the first stage.

At the surface if you are working hard i.e. a lot of current, swimming back to boat, etc they can be very dangerous. But the diver can manually add oxygen to the loop to prevent this from happening.

There are O2 Rebreathers that can only be used at shallow depths.

A great book is Mastering Rebreathers by Jeff Bonzanic

Safe Diving

Tony Flaris
Meg CCR Diver
Evolution CCR Diver


Sent from my iPad using Tapatalk

Hey Tony,

I think you meant the other way around as far as Diluent & bailout PPO2.

Would be better to plan for a Diluent flush using gas that gives you a max PPO2 of 1.0 at depth & a max PPO2 for bailout of 1.4.

Jeffs book is a great primer for anyone interested in learning more about rebreathers for sure.

Cheers,
Rob
 

padiscubapro

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Hey Tony,

I think you meant the other way around as far as Diluent & bailout PPO2.

Would be better to plan for a Diluent flush using gas that gives you a max PPO2 of 1.0 at depth & a max PPO2 for bailout of 1.4.

Jeffs book is a great primer for anyone interested in learning more about rebreathers for sure.

Cheers,
Rob

ANDI teaches when possible the on board Diluent should be able to flush the loop at the deepest planned point to the target PO2 for the setpoint.. The bailout should be safely breatheable at the deepest planned depth...
 

rob.laurie

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ANDI teaches when possible the on board Diluent should be able to flush the loop at the deepest planned point to the target PO2 for the setpoint.. The bailout should be safely breatheable at the deepest planned depth...

Hi Joe,

I wasn't aware ANDI taught that way. I use dil thats leaner than setpoint to be able to flush down a hyperoxic loop quicker with less gas, wouldn't ever plan for 1.4.

Of course bailout should be safe at deepest planned depth, but again I wouldn't plan for PPO2 of 1.0, when possible it would be closer to the 1.4 mentioned for dil.

A dil of 1.4 and planned bailout of 1.0 is just backwards to me. I have never dived with anyone that would plan that way. But thats just my training & experiance, YMMV.

Your thoughts ?

Cheers,
Rob
 

tflaris

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Hey Tony,

I think you meant the other way around as far as Diluent & bailout PPO2.

Would be better to plan for a Diluent flush using gas that gives you a max PPO2 of 1.0 at depth & a max PPO2 for bailout of 1.4.

Jeffs book is a great primer for anyone interested in learning more about rebreathers for sure.

Cheers,
Rob

I was using 1.4 as a planning ppO2 in order to determine the max O2 of my dil. My setpoint for deep dives would be 1.0. Shallow dives 1.2 setpoint.

When diving deep I tend to use pretty standard mixtures.

10/50
15/45
20/30


Hope this clarifies.


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padiscubapro

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Hi Joe,

I wasn't aware ANDI taught that way. I use dil thats leaner than setpoint to be able to flush down a hyperoxic loop quicker with less gas, wouldn't ever plan for 1.4.

Of course bailout should be safe at deepest planned depth, but again I wouldn't plan for PPO2 of 1.0, when possible it would be closer to the 1.4 mentioned for dil.

A dil of 1.4 and planned bailout of 1.0 is just backwards to me. I have never dived with anyone that would plan that way. But thats just my training & experiance, YMMV.

Your thoughts ?

Cheers,
Rob


no need to flush below the setpoint.. if done correctly a diluent flsuh only takes seconds.. useing a leaner mix doesnt make it any faster..


I usually try and have my primary bailout and my diluent be the same gas..

The one thing you must take into account when using a diluent that is lower than the expected sp is that your END is deeper than what the mix normally would be so you have to plan oin this and use more helium in the diluent to make up for the additional o2 that will be added..
AFAIK the only agency that was teaching a 1.0 for the diluent was IANTD so that they could get around the contradiction of a normoxic mix and a 60m max depthom their noxmic classes sicne their earlier standards actually forced the instructor to break standards (max po2) to achieve a 60m depth... but now you are not using a normic mix... so another contradiction.. nomoxic means 20.95% +/- 1% (for meter error).. if you want to do a 60m dive and have a 1.0 you now need a hypoxic mix.. definately a higher risk than using a normix mix for the same depth (even a 1.1 leaves you a mix that is borderline breathable at the surface)... if there is a training accident a good lawyer will have a field day with the instructor..
 

Gill Envy

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mCCR Rebreathers...at the surface if you are working hard i.e. a lot of current, swimming back to boat, etc they can be very dangerous. ...
Tony Flaris
Meg CCR Diver
Evolution CCR Diver

Tony, have you put substantial hours on an mCCR? Where do you get your conclusion that they are more dangerous at the surface in current, swimming back to a boat, etc. than an eCCR?

I think it's fair to say that both eCCR's and mCCR's are potentially "very dangerous", but I don't see how you can support that eCCR's are safer. I suspect the tendency to think an eCCR is more safe may be at the crux of the higher number of fatal mistakes associated with them. So far, there is no data that supports that eCCR's are safer than mCCR's, the body count even seems to suggest the contrary, and even that is debatable.

G
 

down4fun

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no need to flush below the setpoint.. if done correctly a diluent flsuh only takes seconds.. useing a leaner mix doesnt make it any faster...

maybe not for a complete dil flush but if you pp02 is creeping up a leaner dil will bring it down quicker with less gas used no?
 
https://www.shearwater.com/products/perdix-ai/

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