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.
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.