Cave Diving, Cave Exploration and Cave Mapping in Yucatan, Mexico
Chico at Cian Ka'an Park Mexico

When should I get a rebreather?

When should I get a rebreather?

Is it best to get some good caving experience before I go rebreather or is it preferred to get on RB as soon as you can? I know that I will definitely go RB one day, but I want to make sure I am not going too fast down that path.

I am Intro to Cave right now with 20 cave dives/ 250 total dives. — khacken, Cave Divers Forum

I saw this question on Cave Divers Forum today and started to write a short response that turned into a long response ad now it is a Blog post.

This is a pretty interesting question.  I learned to cave dive on OC back mount.  Then I learned how to dive CCR and did a bunch of CCR wreck dives.  Then I moved to Mexico and started CCR Cave diving.  Then I learned sidemount and found myself doing 80% of my dives, even in big cave in sidemount.  I have a couple of observations I would like to offer:

1. It is very easy to go beyond your limits with a CCR and not know it.  If you are only CCR diving, you have to calculate/guesstimate how long your bailout will last you in a very dynamic situation.  If you underestimate, you drown.  I think it is worth while to have dived many of those situations open circuit to see how the environment and situation will change your gas consumption.  This is in the same vein as swimming before scootering discussion.

2. Many many many situations in cave diving are not optimally handled on CCR.  Therefore, it is beneficial to have a broad set of options to solve your problem.  Is the cave small?  Go sidemount.  Is it unexplored?  Go with some 40’s to check it out.  Are tanks and sorb available?  Use double 80’s or go sidemount.  Is your CCR broken or too expensive for the dive?  Use OC.  Do you really want to spend your time setting up/breaking down your CCR for every dive?  NO!  Is the cave deep? Use CCR.There is one big caveat to this point, you need to analyze your diving and determine if you dive frequently enough to switch between OC and CCR and maintain two skill sets.  OC and CCR are different beasts and require different muscle memory.  If you dive sporadically, I suggest you dive only one system and you dive it in forgiving environments.  If you dive often, then you might be able to practice both often enough to be good at both, but this is very tough.  Sometimes when I am off the CCR for a month or more, I find it challenging for a dive or two.

3. Lets look at a side-by-side comparison of cost for diving.Typical shallow 3 hour cave dive cost the following for consumables.  The figures are USD.

Typical OC Cave Dive
Entrance: $10.00
Fuel: $10.00
Fills: $12.00 (3 Single 80’s with Fill)
Total: $32.00

Typical CCR Cave Dive
Entrance: $10.00
Fuel: $10.00
B/O Fills: $8.00 (2 Single 80’s with Fill)
O2: $12.00 (12cuft)
Dil: $3.00 (19cuft)
Sorb: $30.00
Total: $73.00

Add to the financial cost there is a time cost. First it takes me 30-40 minutes to setup the CCR and then it takes 20-40 minutes to break down the CCR. When I am on site, I need to check the unit and pre-breath it on top of my normal S drill. This doesn’t include the costs for O2 sensors or flying the CCR around or fixing it when you drop it. I also didn’t include the cost of servicing the regulators, because you need the same number or more with CCR. Remember with CCR, you need Dil, O2 and B/O regulators.

I am sure there are more reasons to choose one approach or another.  I can tell you that Patrick and I both own Megalodons and only dive them deep (>60ft).  Therefore, 80% of our diving is open circuit.

I think it is prudent to really consider where you are going to dive and the specific situations you will find yourself in.  If you cannot do that because of lack of experience, you need to seek the best possible training and gain the broadest experience possible.  Because you are already an Intro to Cave Diver, become a Cave Diver and make some dives.  Gain some experience.  Then start to layer on more technology, such as rebreather, scooter and stages.

So much of technical diving is about planning and choosing the right equipment and procedures.  Whether to dive OC or CCR, is one of those choices.

A great example is a dive I did with Santiago last week.  We dove the Lins/Walton line at The Pit.  I was diving CCR and Santi was diving OC.  We planned to make a 20 minute dive to 245ft.  When we got to 210ft at 6 minutes we found the end of the line.  I signaled to Santi asking him if I should tie in my reel?  He said yes and we went on.  We immediately found going cave and added 100+ft of line to the system and brought the end of the line to 238ft.  We tied off the newly laid line, installed our arrow and head up.  At 220ft, I found another lead with a nasty silty bottom pinching down.  After some inspection, I decided it was too nasty to attempt in CCR and I made the decision to return in sidemount to check out the lead.   I haven’t returned because I haven’t had the time.  However, because I know both systems, I have the option.

CCR was the perfect choice for the initial dive.  I used about $6 HE, $6 O2, $30 Sorb.  Santi used about $100 HE, $40 O2.  I did my initial exploration on the cheap.  Next time, I will go in sidemount and check out the lead.  It will cost more, but I will have a clear objective and the right tool for the job.  Fortunately, because I have a broad base of experience and more then just a hammer in my tool box, I don’t have to use a hammer on that screw.

I love my rebreather, I think it is an awesome tool that has enabled me to dive many places that few people will.  However, it is not always the right tool for the job and is not a panacea of safety.  Rebreathers fail and so you have to carry bailout.  If you bailout, you had better be sure of how much gas you need, because if you are not, fear will creep into your lizard brain and things will go to shit.  Therefore, if you are technical diving a rebreather and until we have truly fault-tolerate rebreathers or bailout rebreathers are standard issue, you need to have a foundation in open circuit.  The best way to develop that foundation is by diving open circuit.


1 John K { 04.02.09 at 5:39 am }


Nice thoughtful response. Now that I have gotten my sidemount cert I clearly understand the “tool for the job” and “easy cleanup” aspects.

So you love you Meg this week. Next week the honeymoon will be over. 😉


2 Hans { 04.02.09 at 8:30 am }

John, isn’t that the truth, my relationship with my Meg has been a bit rocky. Mostly I hate the machine when I haven’t been diving it much and I just come back to it. OC is just so much easier for me, I have about 4x the number of dives on OC then I do CC. However, since about February I have been diving the Meg at least once a week and I am in love with it again.

I am glad you enjoyed your sidemount course. Next time you come to MX, you can leave your CCR home and just go cave diving.

I was just thinking that most tourist’s CCR cave diving falls in the 1.5-2 hour range. They are not fit enough, practiced enough or have the desire to go past that time limit. And to be honest, they shouldn’t go much further then that. And at that level CCR is over kill for the job.

I think it is when the dives get up into the 3-4 hour range that the CCR really shines. You can use the hub and spoke method recalculating b/o requirements and really learn a cave. I know I did that at Little Rivers. I did a little more then 2.5 hours bottom time and about 1 hour of deco.

I swam past the well casing, and then checked just about every lead I could reasonably fit into all the way back to the Mud Tunnel Jump. It was an awesome dive that I wouldn’t have done on OC due to gas requirements. The CCR made it possible because I wasn’t drawing down on my gas volumes in a big way. Of course I was using my O2 and Dil, but that was nice and slow due to the nearly static depth at Little Rivers.

Who knows… maybe tomorrow I will hate my Meg again.

3 John K { 04.03.09 at 7:42 pm }

Yes I would like to come down and do some sidemount diving. I really liked it in Bahamas. I have not purchased a sidemount rig yet so your advise in that area would be great. I used a Armadillo on the course and it felt fine and I trimmed out easily with LP 85’s.