No matter where your life has taken you, or what your current love is now, you will always remember your First...
My First Closed Circuit Oxygen Rebreather is not pretty. In fact, it is probably the most hideous item of diving equipment I own. But, oh what love I have for this unit. How can I not love something which I have created (read: assembled) and more importantly, which gives me the sweet Carbon Dioxide-scrubbed Breath of Life, without the bubbles (read: which works). I use the word "assembled" because as you know, this is no new invention. Closed Circuit Oxygen (CC02) Rebreathers have been around for quite some time. In 1876 Henry Fleuss (ref. #1) began development of an oxygen rebreathing device which was successfully tested in 1879. In 1936 the Italian Navy used a descendant of this unit in their Chariot Torpedo system. Rebreather technology for underwater use got a push during WWII, as a military need for operations involving clandestine combat swimming became a driving force in their development.
It was soon discovered (ref. #2), using 100% Oxygen as a breathing gas was limited to very shallow depth's due to a toxic effect 02 has on the Central Nervous System (CNS) when breathed under pressure. This is termed CNS 02 Toxicity, and can produce convulsions without a warning. If a diver is not using a helmet or full face mask these convulsions can result in death from drowning. The very shallow depth limitation, and catastrophic consequences of improperly using pure oxygen as a breathing gas has resulted in very limited practical applications of this technology. Other than in clandestine governmental operations, a quiet breathing system does have some practical uses in the fields of marine science research and photography.
The need of the military to extend the depth range of their clandestine operations resulted in the development of mixed-gas rebreather diving equipment, both as semi--closed circuit, and fully closed circuit systems. The active control of the partial pressure of oxygen (PO2) in a mixed-gas diving system can involve a complex inter-action of various gas sensors, electronic/computer logic, electronic-pneumatic controls, operator displays and means for manual over-ride. A single gas, pure oxygen rebreather on the other hand is a much simpler technology. A CCO2 Rebreather can contain technology that is so low-technology intensive that I am surprised that we have not heard of more divers making them, particularly underwater photographers. An CCO2 rebreather basically is a breathing loop composed of a breathing bag, a canister containing a carbon dioxide (CO2) scrubber, a gas source (100 percent oxygen), and associated plumbing. (ref. #3)
I shall not deny that it was Michael Mendunos' ‘94 TEK Conference which got my closed circuit juices flowing again. I have been aware of the existence of CCO2 rebreathers since I started diving in the 1960's. Things were different back then, oxygen rebreathers were not commercially available, they were dangerous, and only the US Navy held technical diving conferences. A lot has happened since then. Rebreathers are still not readily available to the diving public, we understand more about the physiological limitations of diving them, Michael Menduno also hosts technical diving conferences, and now I finally built and used an oxygen rebreather. The building of this rebreather followed the premise of Form Following Function. Concepts such as Streamlining, Ergonomics, Comfort, Ease of Use and Esthetics never even got a hint of being addressed in this project.
My first unit was built around the Scrubber Canister which holds the C02 Absorbent. I sandwiched the granular absorbent between an open cell foam to filter out dusting, and compacted it slightly with a closed cell foam ‘gasket' to prevent settling/channeling of the absorbent. The counterlung was made out of a UDT Swim Vest, a standard double hose mouthpiece was used, and the remaining fittings was obtained from various aisles of my local Home Builders Supply. High pressure systems consisted of items designed for oxygen use (pressure vessel), or oxygen cleaned and converted (regulator). My Rebreather can be best classified as one Hideous-Looking Working-Prototype in Research-And-Development. But it does work. I add at this point that I have one heck of an appreciation for RESEARCH AND DEVELOPMENT.
The first open water dive, (after pool testing for system integrity), revealed a major design error; that of excess buoyancy. My problem was literally too much plumbing, and too large of a counterlung. This problem was temporarily over-come by two extra weight belts, and my boats spare anchor. Other problems encountered included inadequate harness design (O.K., no harness design). The free floating counterlung acted like a lift bag attached to my Adam's apple. Though uncomfortable, this first dive was nevertheless considered successful: Dive time 45 minutes, Maximum depth 25 fsw, Gas Consumption 1.5 cubic feet, and no bubbles! With some modification of the original unit to reduce circulating gas volume, and the addition of a crotch strap, the unit became user friendly enough to allow my safety divers to take photos.
My First Oxygen Rebreather is not a replacement for my open circuit SCUBA, and it is not competition for the Drager LAR V. It is a working exercise in design, development and production of dive gear. It could even be called a new art form in recapitulating the evolution of a part of diving history. This Rebreather is many things to me, an Art, a Science, a Hobby, and of course a Love. What is Your rebreather?
References:
(ref. #1 US Navy Dive Manual. Volume II, Chapter Nine)
(ref. #2 Oxygen and the Diver, K. Donald)
(ref. #3 Mixed Gas Diving, T. Mount, B. Gilliam, Chapter 20)
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The above was submitted in 1994. The article based upon this manuscript
can be seen in AquaCorps Dec/Jan 95, Vol 12, p35, Build Your Own Rebreather.
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Robert R. Iannello, DDS
23940 Ironwood Ave., Ste C
Moreno Valley, California 92557
909 242-4000 (day)