Many of us associate scuba diving with a tell-tale trail of bubbles burbling up the surface. The conventional open-circuit breathing set (aka aqua lung) most divers use, however, is not the only option available on today’s market.
A rebreather is a specialized underwater breathing apparatus that recycles exhaled gas, “scrubs” out the carbon dioxide, and mixes the remnants with oxygen to provide an appropriate mix for scuba divers. This method reduces the overall volume of gas, which means that a rebreather is both lighter and more compact than conventional scuba gear. The deeper the dive, the more efficient a rebreather is compared to conventional scuba gear. It also nearly completely eliminates escaped air, making for a delightfully smooth and quiet dive.
Rebreathers have been around for a while—Professor T. Schwann designed one in 1853. The first recorded practical use of the devise was in 1878, when another model (this one designed by Henry Fleuss) was used to rescue trapped mineworkers. The first mass-produced rebreather—designed for escape from sunken submarines—was introduced in Britain in 1900. A similar device was used in the 1907 filming of Twenty Thousand Leagues Under the Sea. Rebreathers were first used on a regular basis by divers beginning in the 1930s, as Italian spearfishers realized the advantages of quiet, bubble-free scuba capabilities. During World War II, rebreathers quickly gained popularity because of the obvious military advantages.
In addition to military use, rebreathers are prized by marine biologists and underwater photographers, who find them highly useful in getting close to marine life. Rebreathers also minimize decompression requirements by creating a constant, well oxygenated partial pressure at all depths. The gas in a rebreather is warmer and moister than an open circuit gas mix, creating a more comfortable environment for long dives and causing less dehydration.
One disadvantage to rebreathers is that it is difficult to detect scrubber failure until it is too late; it is also hard to catch insufficient oxygen until too late. Most modern rebreathers have electo-galvanic fuel cell sensors and onboard electronics to catch these errors if and when they occur. Rebreather divers are more susceptible that open-circuit divers to hypoxia, seizures due to oxygen toxicity, disorientations, panic, and hyperventilation due to too much carbon dioxide. The percentage of diver deaths involving rebreather use has risen from 1% to 5% in the period from 1998 to 2004, although to what extent this is due simply to expanded rebreather use is unclear.
Using a rebreather requires constant respiration, to keep exhaled gas flowing over the carbon dioxide absorber. Therefore, divers used to standard equipment generally need to reteach themselves underwater breathing habits. While they have the disadvantages of expense, complexity, and fewer failsafes, rebreathers have the advantages of being safer for deep dives or and environments in which additional length of dive time can be a life-saver, such as ice diving, cave diving, and wreck diving.
While rebreathing equipment is sleek and compact compared to conventional open-circuit equipment, the bailout requirement can necessitate extra bulk in the event of long decompression stops. Choosing to go without this additional failsafe equipment is called alpinist diving, and essentially means that you rely on your rebreather not to fail. Alpinism carries a small, but very severe, safety risk.
Common rebreathers on the market for sport divers include the KISS classic, the KISS sport, and the Draeger Dolphin. The cost of rebreathers ranges from slightly under $2,000 to $70,000. An electronically controlled closed-circuit rebreather costs around $6,000. In addition, rebreather-specific training is necessary in order to use the equipment—PADI offers specialty courses for this purpose. You must already be a PADI Open Water Diver with proof of at least ten post-qualification dives logged in order to be eligible for this training.
The costs for equipment and training are steep, and not likely to be worthwhile for the casual diver. If, however, you are a serious and frequent diver or simply passionate about getting close to marine life without a constant stream of bubbles disrupting them, then a rebreather might be your best friend. Many dive shops rent rebreathing equipment in addition to standard aqualungs—try one out in a pool and experience the difference!
