Conventional SCUBA diving uses an open circuit breathing apparatus, which means that the air we inhale into our lungs from the tank is dispelled through the regulator in our mouth into the water as we exhale. The problem with open circuit breathing is that it wastes precious gas. Out of the air we fill into our scuba tanks, 80% of it is Nitrogen and other gases, and only 20% of the air is Oxygen. Out of that 20% of Oxygen in our dive tanks, our lungs only absorb a quarter of the Oxygen contained in the air for each lungful we take, which means divers exhale 3/4ths of the total oxygen available to them each dive. This means despite carrying all that air in our tanks, we are only really consuming a tiny fraction approximately 5% of the total air (oxygen) and exhaling everything else.
A Rebreather also known as a Closed Circuit Breathing Apparatus or CCUBA or a CCR (Closed Circuit Rebreather), allows a diver to breathe the exhaled air, again and again while constantly removing the CO2 while replenishing Oxygen into the system as necessary. Oxygen or a Gas Mix, is fed electronically or using a demand valve into a closed circuit system. The air goes into the Diver’s lungs and the Carbon Dioxide rich air is breathed out into a separate one -way-valve path into a counter lung which is a bag that expands and contracts like a lung 
that stores exhaled air, allowing the air in the loop to remain the same. The air from the counterlung is then pulled into a Carbon Dioxide Scrubber, which is a container filled with a CO2 absorbing Chemical usually sodium hydroxide (Sofnolime). The carbon dioxide (gas) reacts with sodium hydroxide and calcium hydroxide to form calcium carbonate (solid). The Oxygen or Gas mix that is released from the tank into the loop is controlled by oxygen sensors that monitor the partial pressure of oxygen in the breathing loop and send this information to a microprocessor that controls the oxygen-delivery system.
Advantages of a Rebreather
- A Longer Bottom Time A Closed Circuit diver doesn’t need to worry about running out of gas they are is limited only by decompression. This too can be minimized by selecting a partial pressure of oxygen which virtually gives the diver limitless bottom times in 60 feet or less of water.
- No Bubbles A Fully closed circuit breathing apparatus, discharges no bubbles, making it ideal for underwater photographers/videographers who would otherwise scare away marine life with the constant stream of bubbles. Rebreathers are also used by the Military because of this; they can stealthy move underwater without fear of detection at the surface by the giveaway stream of bubbles.
- Gas Efficiency As the oxygen in the system is re-circulated in the loop, a diver may utilize up to 99% of the Oxygen in the system as opposed to an open circuit system where 20% of the Oxygen is absorbed by the Divers lungs. This creates gas efficiency, with a tank the size of a regular air tank of oxygen lasting ages longer before needing to be changed, limited only by the scrubber.
- Deep Diving A closed circuit rebreather helps in deep diving as a helium system could be easily added to the circuit to eliminate narcosis. The tanks needed for a deep dive are not as many with a rebreather as needed for an open circuit system, allowing the diver greater mobility.
Are you ready to switch yet? Do keep in mind that everything isn’t all perfect with a rebreather. They are extremely expensive pieces of Scuba diving equipment, and require chemical cartridges changes, and proper maintenance. There is more that can go wrong with the complexity of the rebreather, and the diver must be aware of scrubbers failing or reaching absorption capacity, or Oxygen toxicity if the controllers fail.
*Photo credits: photos by tiswango, amell, on flickr.
Related posts:
