Pre-Newbie questions

[Lasse DK]

Hi,

Sorry if these questions have already been asked/answered by others, but I wasn’t able to find anything in the records.

I am hoping to buy a CCR (Inspiration) early next year and have therefore started to look a bit into the details of how it works.
I am currently doing OC wreck diving, and will therefore have to switch to Trimix on the CCR unit as soon as my experience is high/good enough in shallow water. (As far as I have gathered it is not a good idea to have a END of more than 25 meters on a CCR)..

I am sure that my question are answered in the normal curriculum of the Normixic CCR Trimix course, but I was hoping somebody could expedite my curiosity before I get to that level.


1.
If you dive the CCR with air as diluent, the only variables are ppo2 and preassure in the loop vs. ambient pressure. You have to handles : O2 injection and Air injection.
Hence when you get to a specific depth and the loop pressure vs. ambient pressure has been "equalised", then it is only a matter of keeping the ppo2 level steady and remove co2. By simply measuring the pp02, you know exactly what mix you are breathing.
But what happens if you are using Trimix as diluent ?
You reach a certain depth and stop supplying diluent to the loop. The CCR will then only supply o2 and not supply diluent any more. So how do you know what you are breathing ?? There are too many variables vs. number of handles...
The body will take up Helium from the loop, and release (perhaps, depending on ppn2) Nitrogen into the loop.
So how do you ensure that you keep breathing the correct trimix at depth ??? Do you keep flushing the loop manually at fixed intervals ? Or is the uptake of Helium in the body so small that it does not significantly change the mix in the loop?

2.
How many DCI incident has been recorded on xCR's ?
I have not been able to find any such records.
It looks to me as if the DCI incident rate on xCR is low..


This is my first posting on this board, so please forgive me if I am not following protocol.. I will learn eventually. I promise.

Thanks,
Lasse

 

[Hootis]

Welcome to the Rebreather forum.

You will really enjoy the benefits of closed circuit diving. You are asking good questions, ones that will be adressed in your training. You hit the nail on the head at the end of your first question...very little He is absorbed by the body....therefore the inert gas mix stays pretty constant. I do know some divers who flush the loop at depth...I think Padiscubapro is one of them. The thing to remember about closed circuit is that the Fraction of oxygen changes constantly (due to both metabolism, and addition of gases--o2 and dilluent) but the PPO2 (partial pressure of oxygen) stays relatively constant (within the systems ability to keep it constant--working against depth changes and metabolism) Therefore the fraction of the inert gas (or gasses) change through the dive, and so dive computers (or tables) specific to constant PPO2 diving must be used.

I don't know the answer to your second question, but the results will probably be slanted, due to the fact that statistically most rebreather divers are diving more agressive profiles than OC divers.

Good luck and enjoy your new rebreather (to be!)
Ryan

 

[Deputy821]

Hi,

Sorry if these questions have already been asked/answered by others, but I wasn’t able to find anything in the records.

I am hoping to buy a CCR (Inspiration) early next year and have therefore started to look a bit into the details of how it works.
I am currently doing OC wreck diving, and will therefore have to switch to Trimix on the CCR unit as soon as my experience is high/good enough in shallow water. (As far as I have gathered it is not a good idea to have a END of more than 25 meters on a CCR)..

I am sure that my question are answered in the normal curriculum of the Normixic CCR Trimix course, but I was hoping somebody could expedite my curiosity before I get to that level.


1.
If you dive the CCR with air as diluent, the only variables are ppo2 and preassure in the loop vs. ambient pressure. You have to handles : O2 injection and Air injection.
Hence when you get to a specific depth and the loop pressure vs. ambient pressure has been "equalised", then it is only a matter of keeping the ppo2 level steady and remove co2. By simply measuring the pp02, you know exactly what mix you are breathing.
But what happens if you are using Trimix as diluent ?
You reach a certain depth and stop supplying diluent to the loop. The CCR will then only supply o2 and not supply diluent any more. So how do you know what you are breathing ?? There are too many variables vs. number of handles...
The body will take up Helium from the loop, and release (perhaps, depending on ppn2) Nitrogen into the loop.
So how do you ensure that you keep breathing the correct trimix at depth ??? Do you keep flushing the loop manually at fixed intervals ? Or is the uptake of Helium in the body so small that it does not significantly change the mix in the loop?

2.
How many DCI incident has been recorded on xCR's ?
I have not been able to find any such records.
It looks to me as if the DCI incident rate on xCR is low..


This is my first posting on this board, so please forgive me if I am not following protocol.. I will learn eventually. I promise.

Thanks,
Lasse

Go to: www.therebreathersite.nl .There is also a good instructional DVD on ebay.com. search rebreather

 

[Deputy821]

Go to www.therebreathersite.nl and check ebay for an instuctional DVD

 

[caveseeker7]

The DVD is Rebreather FUNdamentals by Joe Dituri, Richard Pyle and I forgot the 3rd name, and available through e-bay and IANTD.

There is also a video by Mad Dog Expeditions (Andrew Driver) that showcases five different rigs. The Cis-Lunar MK-5p, the MK15, the Dräger Dolphin, Buddy Inspiration and Prism Topaz.
It's available through Mad Dog Expeditions, and they're are working on a new DVD featuring more rebreathers.

The IANTD DVD has more theorie, the Mad Dog video more footage of the different models both above and underwater.