Rebreather Sidemount Bailout for Cave Divers

Lamar writes about how sidemount bailout is a benefit for rebreather divers and gives advice on how it's done.by Lamar Hires

There are minimum standards for rebreather bailout set by training agencies, and there is the comfort zone. I think people confuse the two. Training should teach you to evaluate the risk and draw conclusions based on your personal physical ability and personal perception of risk. Sometimes I think divers take the easy way of doing the math. There are many variables for determining bailout needs and reality is never as simple as classroom practice. The experienced cave diver can rationalize anything and practice it to get a memorized response based on repetition. What he can’t control is his breathing rate or the catalyst that triggers the bailout procedure.


To truly determine bailout needs one should consider the circumstances and the factors which lead up to getting off the loop and going to bailout. I understand this from experimenting and building a rebreather. You never truly know how you will respond when you take your last breath or can’t take one at all. This is sure to elevate your breathing rate and response to the problem.
All this leads to the question “how much bailout is enough?” The open circuit cave community believes that rebreather cave divers don’t take enough bailout because they cannot relate. I try to relate closed circuit needs to open circuit disciplines learned from years of cave diving. I guess after years of starting a dive with about 270 cu ft of compressed gas I can’t get past the need to have at least 80 cu ft of bailout gas. Even if practice gets you out on 30 cu ft of gas having at least 80 cu ft gives you the extra gas to deal with the catalyst that got you off the loop. I think this is the one point training cannot emulate. During training you always know it’s a drill. You wait for the queue and respond. There aren’t any flashing lights or taste of a caustic cocktail. In the real world there are no “abort the drill” signals.


One can argue minimum bailout needs and justify it. On expeditions bailout needs for closed circuit are rationalized just like the open circuit one-third rule. Anyone can rationalize their needs verses what’s available. I see it all the time. A dive at home utilizes oxygen for decompression, but on expedition oxygen is not available so now it is ok to do a deep dive on air because it’s a remote area. I am more concerned about what people rationalize when they have all the resources needed available.


Now the cave diver comes out in me. Redundancy is the key to safety and returning home. For cave diving closed circuit bailout needs should be treated like sidemount, two cylinders for balance, safety and buddy team. Closed circuit minimum bailout should start with 80 cu ft just like open circuit and this should be two aluminum 40 cu ft cylinders for redundancy. Two cylinders provide multiple advantages:


1) If you have to go off the loop two cylinders provide the peace of mind that you still have full cave redundancy for the exit. Worn sidemount, these bottles tuck in under the arms for streamlining. A friend of mine wore a single 80 bailout on a dive and at 3000-foot penetration, 25 minutes away from the entrance his electronics signaled he needed to get off the loop. The diver turned on the bailout bottle to have a HP hose blow. Now he is faced with the dilemma of going back on the loop with indicated failures or to breathe his bailout in single breaths by opening and closing the valve. Not much of a choice. He was able to get back on the loop, but had a major scare.


2) It is much easier to go from two small cylinders for shallow dives to two large cylinders for deeper dives. No extra rigging is needed when making this transition so the transition is much easier.


3) The buddy element is the biggest argument: that is whether to be self-sufficient systems verses the buddy system. I don’t like the idea of single bottle sharing for bailout. I personally will not give up my only full bailout bottle in exchange for a half empty bottle (yes, now the glass is half empty) in hopes that the diver in stress, (yes, he is in stress since he had to get off the loop) has only breathed the bottle down 50-percent before passing it off.


There are three bailout configurations for CCR cave divers: buddy system, self-sufficient and stage. I find myself using at least two of them on any given dive. I agree every diver should be self-sufficient, but you should always be ready to help your buddy. CCR divers have more options to them for bailout since their dive is determined by scrubber duration and how much time he wishes to spend based on more physical aspects of the dive. How much decompression are you willing to do? Are you dressed to do the decompression and stay hydrated? Gas supply is usually not a consideration, but bailout is.


Since I subscribe to at least 80 cu ft of gas for bailout let me share with you several dive scenarios that called for different approaches.


1) Devil’s Ear – 4000 foot penetration at 100 feet in depth. Since my buddy and I were going to explore some of the side passages beyond the 3000 foot restriction called the Henkel , we opted for a single 80 cu ft stage each and two aluminum 40 cu ft sidemount bottles. My buddy dropped his 80 stage at 1500 feet, while I dropped mine at 3000 feet where we dropped our DPVs. We went on to explore the smaller side passages with 80 cu ft of bailout apiece configured in two aluminum 40 cu ft cylinders. So the bailout plan was buddy combined with staggered, staged bailouts for the swimming portion of the dive in the smaller, remote passages where we went to self sufficient mode with small sidemount cylinders. This allowed us to explore with less drag and maximize our exploration.


2) Devil’s Ear – 4200 foot penetration at 100 feet in depth. This dive we had the same penetration as above, yet this was a working dive; a body recovery of a solo cave diver at 4200 feet. The passage was small in places and we knew we would be in zero visibility. Even though my team mate and I were together, we were very busy so we opted to go with two aluminum 80’s each so that if either of us had a problem we could deal with our own bailout needs and still complete the task. Same dive, but different approach due to conditions of the dive.


3) Rose Sink – 4500 foot exploration at 140 feet in depth. This dive required the use of all three bailout methods. The dive is a multi-level siphon and the flow increases the farther back you get as in feeders add to the total volume. We staged one 80 each. My buddy dropped his bottle at 1300 feet with a richer mix for the final exit leg and I dropped a bottom mix bottle at 2500 feet. We dropped DPVs at 3000 feet, keeping two aluminum 40’s each for self sufficient bailout, and then continued the final portion of the dive in a low crawl trying to stay ahead of our silt while we picked up the last of the survey on the last 900 feet of passage.

Evaluate every dive mission based on its needs for bailout planning. If you have the opportunity, talk to local divers to see what kind of planning the open circuit divers’ use for the site to be sure you use the proper bailout for the dive. Look at the mission, and the team, and then plan according to ability, experience and familiarity with the system. You can’t make every dive fit the same bailout planning unless you use this as a tool to limit your penetration. Proper planning of bailout is just as important as planning your decompression or mission. Make sure all team members are up to it and do their part in any team effort of staging gas. Practice various methods and see what works for you.

Lamar Hires