Technically Speaking

By Bill Nadeau

When people see a rebreather or hear the term closed circuit underwater breathing apparatus they think of the future or something relatively new in the dive industry. It has been suggested that the rebreather concept has been around for thousands of years. In 885 BC an illustration was discovered in an Assyrian Bas-Relief which showed a diver breathing from an air filled leather bag strapped to his chest suggesting that perhaps this individual was breathing in and out of the same source. Since that time, a huge evolution in rebreather technology has occurred and is continuing at an ever-increasing rate. Today there are over a dozen rebreather models available on the market, at a fraction of their original cost. The reliability and benefits of these units are quickly being discovered and there is no question that the rebreather will soon become as accepted as a dive computer or BCD. But just exactly where did these gizmos come from and how do they work? Is the rebreather just a fad?

As I have said, rebreathers have been around for a very long time. Some of the earliest rebreather designs date back as far as the late 1800s, with units that used highly caustic potash to scrub out the carbon dioxide. In fact, it was during this era when the first dives on scuba were made and they were conducted using a semi-closed Rebreather. Later, at the turn of the century, a German company called Dräger, designed a unit for a fire department that used pure oxygen. This allowed rescue crews and firefighters to carry large amounts of breathing gas in relatively small kits. Soon, similar units were produced for miners and before long the first underwater oxygen rebreather was developed and tested. In 1941, Dräger manufactured a light, compact, pure oxygen rebreather as an escape mechanism from submarines in World War II. This was the primitive version of what would become the chest mounted LAR V pure oxygen rebreather that has been a military standard for shallow water clandestine operations since 1981. The LAR V and another shallow water oxygen rebreather used by the military since its development in the early 1970s, the CCR (closed circuit rebreather) 25, showed the world that divers could stay down for incredible lengths of time with a very small gas supply. The needs of the military were a powerful driving influence in the research and development of rebreather designs, eventually giving birth to true, free-swimming (non-depth limited) CCR units such as the Biomarine MK15 and the CCR155, manufactured by Carlton Technologies, which has mixed capabilities of over 300fsw. We are now seeing units with depth capabilities of over 1500fsw and six-hour bottom times. Even DAN (Divers Alert Network) has employed rebreather applications to their oxygen first aid kits. It is this kind of technological maturing that makes you wonder how long open circuit will last.

Despite its complex appearance, the concept of a rebreather is actually quite simplein fact you can build one right now! Grab a paper bag and seal it around your mouth. Congratulations! You have just passed CCR 101: 'Building your own Rebreather'! Warning though don't actually try to breathe on your new unit quite yet. You see there are a couple of problems with your specific model. It is true that with each breath of fresh air we take, we only metabolize a very small portion of the oxygen in our lungs, the rest is exhaled and wasted. If we re-circulate that air in and out of a bag we will gradually use up all of the oxygen. We therefore need to add a little O2 every now and then in order to maintain a healthy level of oxygen. Another problem is that our breathing bag will begin to accumulate an excess of carbon dioxide and if it reaches dangerous levels then we will eventually suffer from hypercapnia (too much CO2). This is not a good thing, as it will eventually lead to unconsciousness. So in addition to installing a system that supplies our breathing bag with a small amount of oxygen or nitrox, we need to pass our exhaust through a system that will scrub out the CO2 before we 're-breath' the gas supply. That's it, those are the basics to every rebreather model on the market. Other features of today's rebreathers include oxygen monitoring systems, electronics that control oxygen, nitrox and mixed gas flow rates and some even have bailout switches that allow you to go to open circuit. What makes each of the rebreathers so different is their ability to budget the gas flow and the means with which they can determine the best mix during any particular point or depth in the dive.

Like any new enterprise there is a bit of pioneering that has to be donea trial and error process involving risks. Yet the rebreather evolution has progressed through its dark ages and has emerged as a viable and safe tool to conduct sport diving activities. Those incidents that seem to black-mark its reputation are more often user error due to improper instruction or equip ment abuse or unfamiliarity. It is true that even a basic semi-closed rebreather, such as the Dräger Dolphin or Atlantis 1, does require some additional training, preparation and dive planning but the benefits far outweigh the disadvantages. Rebreathers breath easier, are much quieter, less disturbing to marine life, supply warm moist gas enriched with optimum nitrox blends and weigh far less than bulky steel or aluminum tanks.

Rebreathers are not the future they are today. Training is now available from large international training organizations including PADI, IANTD, NAUI, TDI and ANDI. I just try to imagine a new diver finishing his open water course in ten or fifteen years from now looking back through an old magazine. What will his response be when his instructor tells him that divers used to strap so much metal on their backs for such a small gas supply? Just imagine.

The insides of BMR500 and CCR155 closed Circuit Rebreathers.

Ryan cicansky testing a BMR500 Closed Circuit Rebreather.

Drager rebreather.