Being an open circuit cave diver and enjoying the challenge of the deep caves of Thailand I have for a long time wondered about the benefits of closed circuit rebreather technology in relation to caves. As CCR divers will tell you the units work best in a classic diving profile (max depth work shallower) and when a diving colleague Bruce Konefe took me on a course, ANDI CCR cave, I was intrigued to learn about the gas management rules for cave profiles as caves tend to follow their own profile without regard for the divers.
The cave where we were to complete our training, Song Hong, is a huge sink hole slap bang in the middle of Thailand. Song Hong is well known with local cave divers and stands out for its’ enormous size and depth with exceptionally clear water below the hydrogen sulphide layer. Part of the sink hole which allows for direct access to the surface is used by technical divers wishing to complete wishing to complete deep trimix diver training, avoiding the problems associated with currents and elevating respiration in the sea.
As any rebreather diver will tell you you, rebreathers, due to the design do not lend themselves to achieving good trim, a skill that is essential for cave diving. A lot of time was spent moving weights and adjusting the height of the wing to counter the lift at the shoulders caused by the counter lung. The rebreathers I had with me, Evolution and Inspiration, due to the box they are protected by make it hard to move weights and tanks, to assist in this and I found it easier to remove the can and head and put them in a customized box. This has helped a lot and now it isn’t so much effort to maintain a horizontal position acceptable for cave diving.
Thankfully the gas management rules were a lot easier to master although I was surprised to see many applications of this. It depends on the amount of divers in a team and the amount of confidence in the individual team members, running from the bare minimum, carried around team members with a variation calculated at the largest RMV of this with a third reserve on top again. This is shared around the team to the old third in third out thirds developed by Sheck Exley with each team member carrying their own reserve. It can be quite unsettling when at depth and on the way in to a cave if you start to have doubts about your buddy’s ability to keep his shit together when the said shit hits the fan and you’re relying on your buddy to carry part of the emergency gas you need to get to the surface! At this point you begin to choose your buddies more carefully bearing in mind it’s the team gas rule that that has helped cave divers push back the curtain and explore deeper and longer cave systems.
Overall though CCRs greatly enhance the divers ability to explore caves and with careful adherence to the gas rules (whichever one you adopt) and choosing your your buddies with as much attention to detail there is no doubt CCRs take cave diving to another level. Happily, I had good diving buddies and the shared enjoyment of achieving a goal of completing the 60 metre circuit added to the pleasure.