Cave CCR - On board gas management

[Laminappropria]

What are your thoughts are on onboard gas management for cave ccr diving. Do you follow thirds like you would for other gasses? Do you follow thirds for scrubber duration? During my course no mention was made of this and now I am getting very different and very strong opinions from different people. (I dive a sidewinder and in the standard configuration you can't monitor O2 pressure during the dive.)

 

[oya]

Apply the rule of thirds to all consumables. Your penetration is limited by whichever is shortest.

Oxygen. Scrubber. Diluent. Light burn time. Scooter burn time. Whatever it is that requires being refilled or recharged... divide it by three and you're only allowed to go as far as you will have AT LEAST two thirds of it avilable for your way home.

Onboard, offboard, whatever... if the plan is to use it, you are only allowed to use a third of however much of it you have before it's time to turn around.

 

[AJ]

Oxygen? Take a 40 cuft/7 liter plugable O2 tank with the team and you're good to go. I have never used all my oxygen by the way, not even 1/3 during a dive. The limiting factor for me is theoretical scrubber time. I plan on that time although I know it lasts much longer.

 

[oya]

Oxygen? Take a 40 cuft/7 liter plugable O2 tank with the team and you're good to go. I have never used all my oxygen by the way, not even 1/3 during a dive. The limiting factor for me is theoretical scrubber time. I plan on that time although I know it lasts much longer.

I have seen 2L O2 bottles run dry (it will happen somewhat predictably in a certain set of scenarios... predictably enough that I can say the most common response from random people who have never even met eachother, after I have said, "your oxygen bottle is going to run dry" and they insist that it isn't, when we surface, before I say a single word is, "I know, I know, I know."

I grant that I've only seen a 3L run dry a spare handful of times.

But I can't say that the solution, "Just bring more," is necessarily the right one.

 

[flymolo]

I don’t have a SPG of any sort on my O2 bottle, used to have a button SPG, but I don’t like the reliability of those things, took it off and procedure is the same, check pressure on assembly/predive, I just have to check it with a pressure checker or a different reg, a small inconvenience. Once in the water I don’t need to check it, consumption is based on metabolic rate and is depth independent, I’d have to over exert myself significantly to make a difference in that consumption, if that were to happen, other issues would arise before O2 reserves becomes the problem.

same here. just a button spg on the o2 reg that i check when turning on the o2 before donning the unit

 

[Capt Jim Wyatt]

I'd like to hear @kensuf and @Capt Jim Wyatt on this.

I think the OP needs to enroll in a CCR cave class with a competent instructor.

 

[Capt Jim Wyatt]

During my course no mention was made of this

This is why I opined that the OP needs to take a CCR cave class from a competent instructor. I am not quite sure exactly what @lostsheep disagrees with me about. I also do not think this is an appropriate venue to be teaching CCR cave gas management.

No disrespect to the OP intended.

 

[lostsheep]

This is why I opined that the OP needs to take a CCR cave class from a competent instructor. I am not quite sure exactly what @lostsheep disagrees with me about. I also do not think this is an appropriate venue to be teaching CCR cave gas management.

No disrespect to the OP intended.

I disagree with telling the OP to take the class again.

I concur this should have been covered but we do not know who the instructor was, we know very little about what was or wasn’t said in class, and we don’t know where the differing opinions are coming from.

 

[Capt Jim Wyatt]

I concur this should have been covered but we do not know who the instructor was, we know very little about what was or wasn’t said in class,

You are 100% correct. Maybe the CCR Cave instructor covered this material and the OP missed it.

 

[The Chairman]

Jim has his reasons. I think hearing HIS perspective would be invaluable. There is more than one approach used, and this is a great way to compare and contrast them.

 

[Laminappropria]

I disagree with telling the OP to take the class again.

I concur this should have been covered but we do not know who the instructor was, we know very little about what was or wasn’t said in class, and we don’t know where the differing opinions are coming from.

OP doesn’t want to name and shame here but I took my course with school run by the current head of training for Kiss. OP is also dives thirds on all consumables and has a transmitter for O2 however I receive a lot of pushback on the necessity of both these things from a lot of other rebreather divers. So I wanted to come to the community and hear some additional perspectives on what other people are doing.