Category — Rebreather bailout

CCR (Closed Circuit Rebreather) cave cross over

I recently conducted a ccr cave cross over with Bill from Hawaii. The reason and purpose of the ccr cave cross over program is to combine ccr rebreather diving with cave diving. The term cross over is coming from the fact that a diver who had a cave diving education in open circuit as well as a ccr rebreather diving education who wishes to combine his cave diving experience with his rebreather experience.

The ccr cave cross over program to my knowledge (and I could be wrong) is only offered by two training agencies, IANTD and NSS-CDS. The prerequisites to participate in the ccr cave cross over is to be a trained cave diver with cave diving experience (75 cave dives with Bill) and to be a ccr rebreather diver with at least 20 dives and 35 hours on his unit (30 dives and 35 hours on his Classic Inspiration for Bill) to ensure that the skills of cave diving and rebreather diving a well rehearsed before bringing the two together.

The ccr cave cross over training program starts with a long discussion about bailout techniques and concepts as well as the advantages of diving a rebreather in water filled caves in terms of time we can spend and complex navigation we can do. Bailout is the alternative path to the surface in case your rebreather is non operational for whatever reason allowing us to return safely to the cave exit and surface. Bailout can be organized in three ways: open circuit (o/c), scr rebreather or ccr rebreather depending on a diver’s preference and recourses. Most divers opt for o/c as it is the easiest to obtain and simple. Team bailout concept versus individual bailout concept is a question about how much gas is carried by each individual, if the needed bailout volume to bring at least 1 ½ divers to the surface will be split in-between the divers or carried by each individual diver.

The complex and task loading training for the ccr cave cross over is coming from the fact that all cave diving related skills such as touch contact in zero viz, backup light exit, sharing gas in zero viz, lost line in zero viz plus the line protocol, team diving awareness and cave conservation have to be done using the rebreather doing them in the cave. The rebreather related skills such as partial and complete flood recovery, hypercapnia, hyperoxia, hypoxia, flying the unit manual as well as long horizontal o/c bailout swims have to be done in the cave.

All drills and skills are not new to the cross over student as he has done them many times before, only in separate environments and different breathing sources. The ccr cave cross over program is to bring the two together by first discussing the drills, then practice in openwater and then to practice them in the cave environment with safety and cave conservation in mind.

What will help the student is to have done as many cave dives as possible before the cross over as well as have done as many as possible rebreather dives on his unit. The basic operation of the rebreather should be second nature as we move from basic rebreather training and diving into a more advanced form of rebreather diving where we have two choices after an event on the rebreather which is either to stay o/c or go back onto the loop if we have figured out what is wrong with the unit, and go back onto the loop after a diluent flush to do a full or at least partial exit out of the cave using the rebreather.

Ccr rebreather cave diving is one of the most complex forms of diving due to the complex and task loading skills that need to be mastered by the ccr cave diver. To dive a rebreather in a water filled cave takes time to learn but can open new doors into the art of cave diving as we are not just going in and out of the cave anymore but are freed to stay much longer, as long as we stay within our bailout range and within save diving parameters including our consumables such as oxygen, diluent and Co2 absorbent duration and time limitations.

Save diving and greetings

Matt

Bailout is the alternate path to the surface if our rebreather does not work anymore for any given reason such as a full flood, not trusting the unit anymore, flooded handsets, malfunctioning mushroom vales or electronics failure. The CCR Cave Diver has a variety of options, scenarios and approaches that will get him back to the surface safely.

In an open circuit ( O/C ) bailout scenario the minimum breathing gas that is needed and to be carried by the team is the breathing gas volume needed to get 1 ½ divers back to the surface. In a rebreather bailout such as a SCR or CCR bailout rebreather a second rebreather can be used as bailout to bring us back to the surface in case of our primary unit malfunction. If we think in overhead environment terms gas planning , in particular the rule of 1/3′s a second rebreather might not be the end of the scenario but a third rebreather might be considered.

In the 1 1/2 diver to the surface scenario, diving in a team of 3 we calculate the gas volume needed for 1 1/2 diver and can separate the needed gas into 3 tanks, carried by three divers. The needed bailout volume is seen as a total carried by 3 divers. The team-bailout approach may work in most cases but it does not factor in a team separation, particular for the diver who is on its own who does not have sufficient bailout gas to come all the way back to the surface.

I believe that having and major rebreather problem that forces me to take drastic actions or even may force me off the loop, and due to that major problem in the cave environment we may create bad or zero visibility that could result in a team separation is not something I personally would like to leave out of the equation and my dive planning.

CCR cave diver with bailout tank

As the individual bailout approach is allowing to have for each CCR diver sufficient bailout gas to bring every diver separate to the surface, plus a margin of reserve the CCR cave diver has a larger bailout gas reserve. During later dives this can be practiced and then expanded upon to further penetration and team bailout approach as larger bailout gas volumes are needed if depth or penetration is expanded.

The whole bailout concept needs to be understood by the CCR cave diver in terms of not having all the time in the world anymore when on open circuit bailout as we are breathing our life support away, a breath at a time. Potentially we need to deal with some 25 – 30 % more decompression due to falling Po2´s on the way up and or poor bailout gas choices, depending on dive profile. Teaching a CCR cave course or diving with a rebreather in a cave without proper bailout planning capability to the student or diver is nothing else then giving the student or diver a loaded gun.

On open circuit bailout tanks a long 5 or 7 foot / 1.5 or 2 meter hose is a must and the deployment of the long hose from the always open and turned on bailout tank must be well practiced during predive safety drills. That will be a life saver and in some environments the only way to deal with a failed CCR while diving in a cave. Handing over the bailout tank in a fluid motion while sharing gas now on o/c and being under time and mental pressure will only lead to further problems, delays and stress. The hand over and sharing of the 7 foot hose, and not the handover of a stage tank will be the key to some real emergencies. However, the hand over and exchange of bailout tanks in-between divers must be well rehearsed to enable proper execution in case the skill is needed in earnest.

The choice between team or individual bailout, the balancing of bailout gas volume within the team, within all present bailout tanks must be discussed and rehearsed within the team prior diving and followed in either 1) team approach because the needed volume is split up in-between the team members and the out of CCR diver need their gas to make it back to the surface alternating between bailout tanks when the gas pressure reached 50 % of the initial starting pressure or 2) individual approach to have enough gas for oneself but not breathe the bailout tank totally empty and loose all redundancy when still with other team members, alternating here as well on the 50% rule. Larger bailout gas supplies are present with the individual approach, even when diving as a team allowing for delays exits such as restrictions, zero visibility, potential team separation and increased RMV due to stress.

When talking about the furthest point of penetration o/c bailout versus right before deco or close to exit bailout it is the furthest penetration that would be most problematic, as the divers still have to do the exit out of the overhead environment and then potentially have to deal with decompression. As we are talking about cave diving and not ocean drift diving we are able to stage the deco gas bailout if needed at the cave entrance. Having planned and carried sufficient bailout gas traveling horizontally through the cave will be the trick. Potential air hogs that go CCR to have more time in the cave still need to sling them large bailout tanks or they going to be running out of bailout gas fast. Taking a bailout tank without proper volume planning and reserves is like Russian roulette, and must not be done.

Besides opting for O/C bailout different options have been developed as Jochen Hasenmaier, Olivier Isler and the Wakulla II team went to SCR or CCR bailout for at least two reasons. First the bailout gas volume and the ability to carry it, drag and streamlining, second is time pressure of diminishing gas supplies and associated stress levels translating in potential errors and elevated RMV. If diving in deep caves the decompression obligation and related gas volume requirements are a factor too.

The bailout gas and volume planning will bring with it a change of breathing gas and Po2 at the bottom, changing decompression schedules and breathing gases needed to finish the warranted decompression. A dive computer capable of switching from O/C mode to CCR mode will help to control inert gas loading either wired into the loop with a separate sensor, or separate from the rebreather. Breathing gases as well as CCR and O/C operation of the rebreather can and must be changed when going from CCR to O/C in a bailout scenario in order for the dive computer to give us the correct inert gas load information. Diving with only one of such dive computers has no redundancy, that is where submersible tables or dive plans come in. Bailout gas volume calculations are a must and are done prior diving and separate to insure sufficient breathing gas bailout volumes.

In my opinion we need to take submersible bailout tables with us underwater in order to recalculate potential changes in dive plans as long we stay on our CCR. Submersible tables need to be designed for the breathing gases used during proper function of our CCR as well as the O/C bailout gases we may use. Planning dives with deco planning software including the calculation bailout scenarios with to deep and to long profiles as well as having them on a slate works well when diving known caves and profiles.