A SCUBA device that allows you to recycle what you breathe over and over again is called a rebreather. Your body burns the oxygen you inhale then you exhale the carbon dioxide waste, so a rebreather does the following:

• Captures and recirculates the gas you are breathing with a breathing loop.
• Purifies the gas to remove carbon dioxide with a process called scrubbing.
• Refreshes the breathing gas by adding replacement oxygen gas.
• Compensates for reducing loop volume during descent by adding inert diluent gas.

There are a variety of designs for rebreathers and their components. For recreational diving the most popular type of rebreather has become the fully closed-circuit breathing loop and is often referred to as a CCR. The loop uses counterlungs to store the gas when you exhale and to supply the gas when you inhale. Also part of the loop is a scrubber canister, which contains chemicals to act as a carbon dioxide absorbent. As the oxygen in the loop is consumed by the diver, the CCR replaces it to maintain a constant level of oxygen known as the set point.

The rebreather set point can be controlled using either manual or automatic systems. There are lower cost manual only rebreathers (mCCR) where the diver is responsible for monitoring the breathing loop via oxygen sensors and operating a valve to manually adjust the oxygen level. The most popular closed-circuit rebreather design today is capable of both manual and/or electronic (eCCR) operation. The eCCR uses a small battery powered computer to continuously monitor the oxygen sensors and automatically control a solenoid valve to adjust the amount of oxygen.

Key Advantages of Rebreathers

Key Disadvantages

• Silence - The closed-circuit rebreather produces almost no bubbles and the resulting silence enhances the dive in part because the marine life are not alarmed by the diver.
  
  
• Extended Ranges for Depth and Time - The CCR carries hours of breathing gas regardless of depth, so diving time is no longer limited by the size of the tank. A rebreather can also greatly extend the no decompression time limits (NDL's) for sport divers.

• High Cost - There is a wide price range, but a typical investment in rebreather equipment and training is about $10,000.
  
  
• Complexity - The rebreather being somewhat more complex means additional time spent on equipment maintenance and greater risk of accident if the diver is careless or poorly trained.

The recreational divers most active in using a rebreather have been photographers because of the benefits in marine life interactions. Technical divers are now very rapidly moving toward widespread use of the rebreather because their efficiency and safety is enabling extended range dives that were previously too logistically difficult or too dangerous. So much so, divers interested in extended range diving should consider switching to closed-circuit rebreather before entering technical training. The new generation of CCR designs have dropped significantly in price, are much easier to use and require only slightly more maintenance than most open-circuit dive equipment. These technological improvements are making the rebreather more common among sport divers.