Why Closed Circuit Rebreathers Are Transforming Cave Diving
No bubbles in this photo! Cave diving photoshoot on rebreather (Photo by Alvaro Herero)
Cave diving represents the pinnacle of technical diving - the most demanding and rewarding pursuits in the underwater world. As divers, to have near unlimited time to stay and enjoy the underground world is pretty amazing. As explorers, wanting to push deeper into submerged passages and discover new cave sections, the technical diving equipment we choose becomes increasingly critical. Over the past two decades, Closed Circuit Rebreathers (CCRs) have revolutionized cave diving, offering advantages that open circuit scuba simply cannot match.
Deep cave diving with rebreathers and scooters (Photo by Mekan)
Extended Bottom Time and Range
The most compelling benefit of CCR technology is the dramatic extension of underwater time. Unlike open circuit systems that exhaust every breath into the water, rebreathers recycle your exhaled gas, removing carbon dioxide and replenishing the oxygen your body uses. This efficiency means that a cave dive limited to 90 minutes on an open circuit system might extend to 3-4 hours (or longer) on a CCR with the same gas volume. Planning for a CCR cave dive we are often able to cover the same distance as 2 or 3 open circuit dives, planning for multiple navigations that would not be possible on open circuit.
For cave explorers, this translates directly into range. Those tantalizing leads that lie just beyond the limits of open circuit suddenly become accessible. Also, the possibility to stay and check for leads in the area under exploration without needing to turn on gas pressure means an exploration dive can be much more productive. The ability to spend more time at depth without the need to bring an increasing amount of tanks opens new frontiers in cave exploration and surveying.
Ready for a rebreather exploration dive, logistics to get to the water were difficult enough with just 2 tanks! (Photo by Mekan)
Reduced Gas Logistics
Jungle exploration used to require a team of porters to get enough tanks, docs and dive gear to the Cenote. At the end of the day all the tanks had to come back for filling. Now, unless lots of gas is used from the sidemount tanks as diluent or in case of bailing out, the tanks can stay in the water ready for the next day of diving. This was really a massive advantage when diving in the Nullabor Desert in Western Australia diving Panikin Plains cave where the water was a long way from the surface. For deep diving projects like the Blue Abyss we could leave our decompression bailout tanks staged in the water as we didn’t use them.
Sidemount rebreathers have some advantages over backmount units when the cave gets small! (Photo by Mekan)
Optimal Breathing Gas at Every Depth
CCRs maintain a constant partial pressure of oxygen throughout the dive, adjusting the gas mix as you ascend or descend. This means you can be breathing an optimal mix for your current depth, maximizing decompression efficiency and minimizing stop times. Longer no decompression limit dives, or reduced decompression times can be a real advantage especially in cold water - and I experienced this deep cave diving in Romania when I had to exit on open circuit.
On open circuit, divers breathe progressively richer mixes as they ascend, switching tanks at predetermined depths. With a CCR, these transitions happen seamlessly and continuously, resulting in more efficient decompression and better physiological performance throughout the dive.
Surveying out after a exploration dive, on a rebreather there is better visibility! (Photo by Mekan)
Reduced Bubbles, Better Visibility
The near bubbless nature of rebreathers offers unexpected advantages in cave environments. The reduced bubbles also minimize silt percolating down from the ceiling in delicate cave environments, helping preserve visibility for you and following teams. Less percolation means the visibility in the cave stays great longer! This was of great help during the exploration of Cenote Santa Maria. In marine environments, less bubbles also means more interactions with marine life that would otherwise be scared off by bubbles of Open Circuit SCUBA.
For cave photographers and videographers, the absence of bubbles creates cleaner shots and allows closer approaches to cave life without startling fish or disturbing delicate formations.
Warmth and Comfort
Breathing warm, humid gas instead of cold, dry tank air significantly improves comfort on long cave dives. The reduced heat loss through breathing can be the difference between completing a dive comfortably and fighting hypothermia. This becomes especially important in the cooler cave systems in Europe, and other regions where water temperatures hover at 8 degrees or below. The moist breath should not be overlooked either, on a CCR you can say goodbye to that parched, dry mouth feeling during the dive!
This section of cave would have been logistically challenging to explore without rebreather!
Enhanced Safety Through Redundancy
With a rebreather, and particularly a KISS Sidewinder, you have the exact same open circuit tank and regulator configuration. Any rebreather issue and you can bailout to your sidemount regulator. Modern CCRs incorporate multiple oxygen sensors, some have redundant electronics, and sophisticated monitoring systems that provide real-time feedback on your breathing gas. With the Petrel 3 incorporating a vibration function, this has further made diving rebreathers safer. When properly maintained and operated within training limits, this redundancy can enhance safety. Knowing how your rebreather works, there also may be troubleshooting options for some CCR failures. As cave divers facing problems like broken lines or confusion at a navigational decision, the time a rebreather gives us can be critical in calmly dealing with the situation.
Rebreather divers training during a MOD 1 course
The Path Forward
Closed circuit rebreathers are not without their challenges. They require extensive training, meticulous maintenance, and unwavering attention to detail. The learning curve is steep, and the consequences of complacency can be severe. However, for committed cave divers willing to invest in proper training and disciplined procedures, CCRs open many possibilities.
As exploration continues to push into deeper, longer, and more remote cave systems, rebreather technology will undoubtedly continue to play an increasingly central role. The underwater passages we explore today on CCRs may well become the main lines of tomorrow, inspiring new generations of cave divers to venture even further into the unknown.
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