It’s strange to think that man’s first attempt at creating scuba began with thoughts of breathing his own expired air from an inflated animal skin as many times as possible. But in 1878, Henry Floss’s design for a self-mixing re-breathing system based on this simple technique provided the first means to carry out work underwater independent of surface supplied air.

The development of both re-breathers (closed-circuit scuba) and the modern demand valve regulator (open circuit scuba) progressed rapidly after WWII. However until just recently, the complexity of re-breathers, there reliance on caustic chemical scrubbers and the ever present risk of Oxygen Toxicity lead to their decline in use for all but ‘high end’ military & commercial applications.

In 1995 though, the German Draeger company took the brave step of deciding that the time was right to introduce the first purpose designed recreational re-breather unit to the scuba industry. The ‘Draeger Atlantis’ re-breather (now known as the Draeger Dolphin) was eagerly received by divers.

How do rebreathers work?

For simple ‘open circuit’ demand valve scuba, when you breathe in, your air is supplied directly from the scuba tank. When you breathe out, all your expired air is released as bubbles. Open circuit scuba is wasteful of the scuba tank air, since the air we breathe out still contains approx 75% of the Oxygen present in the air we breathed in. In a re-breather, the air we breathe out is not released after only one breath. Our expired air is cleaned (‘scrubbed’) to remove the excess Carbon Dioxide produced by our bodies metabolism, Oxygen is added to replace that which we used, and then we breathe the same air again. Miraculously, as long as the Oxygen content, Carbon dioxide levels, and inert gas levels are within an acceptable range, we can breathe the same breath indefinitely.

The Draeger Dolphin (featured in the PADI Rebreather Diver Specialty Course) is a ‘semi closed’ re-breather. This means that it releases a small amount of its gas to the surface during operation. The ‘Dolphin’ uses Nitrox as a breathing gas, so on top of the benefit of efficient gas usage and longer bottom times, its user also benefits from increased no-decompression limits too.

Advantages of re-breathers

• More efficient Gas use

• Longer bottom time

• Increased no decompression limits

• Reduced inert gas in the breathing mix

• More efficient decompression

• Bubble free operation

• Warm breathing gas

Disadvantages of re-breathers

• Oxygen toxicity. The maximum operating depth of the Nitrox must be respected

• Nitrogen management. The NDL of the breathing mix must be calculated.

• Carbon Dioxide removal. The scrubber chemicals must be changed every few hours.

With proper training and scrupulous maintenance the rebreather has distinct benefits to all divers requiring longer bottom times or bubble free operation. Additional benefits include the ability to approach normally shy fish extremely close for underwater video and photo shoots. I can personally report being accepted into a large shoal of barracuda as a ‘shoal member’ when using one. Although I kind of got the feeling they were really eyeing me up for lunch!

Steve Burton is a PADI MI & Technical Diving Instructor for Mermaids Dive School , Pattaya.