Modern, closed-circuit rebreathers have without a doubt had a major impact on SCUBA industry as we know it today. Whilst largely shrouded in myth and urban legend, the reality about the potential benefits offered by rebreathers is rarely disputed.

Diving with a rebreather requires commitment and diligence. In addition, the training you receive and who you receive it from is vitally important.

Types of Rebreathers:

Closed-Circuit Rebreathers (CCR)

Fully closed circuit rebreathers are what most people refer to when they use the term rebreather. Military, photographic, and recreational divers use these because they allow long dives and produce no bubbles. Closed circuit rebreathers generally supply two breathing gases to the loop: one is pure oxygen and the other is a diluent or diluting gas such as air or trimix.

The major task of the fully closed circuit rebreather is to control the oxygen concentration, known as the oxygen partial pressure, in the loop and to warn the diver if it is becoming dangerously low or high. The concentration of oxygen in th

e loop depends on two factors: depth and the proportion of oxygen in the mix. Too low a concentration of oxygen results in hypoxia leading to sudden unconsciousness and ultimately death.Too high a concentration of oxygen results in hyperoxia, leading to oxygen toxicity, a condition causing convulsions which can make the diver lose the mouthpiece when they occur underwater, and can lead to drowning.

In fully electronic closed-circuit systems (eCCR), a mechanism injects oxygen into the loop when it detects that the partial pressure of oxygen in the loop has fallen below the required level. The AP Diving Inspiration and Evolution family of rebreathers are prime examples of fully electronic closed-circuit units.

Manually controlled rebreathers (mCCR) operate on the same principles as fully electronic ones, however the oxygen addition system is very different. These units use a valve (often referred to as a KISS or leaky valve) which continually leaks oxygen into the loop at a constant rate just under the divers metabolic rate. In addition to this, the dive must manually add oxygen to adjust for depth changes (particularly the ascent) or periods of higher exertion. Manually controlled units are often referred to as KISS units, as the Jetsam KISS rebreathers were amongst the first to that the leaky valve concept mainstream.

Closed-circuit units have traditionally been used by technical divers due to their ability to execute long and/or deep divers with relatively simple gas management logistics. Photographers also use them for similar reasons to extend bottom time and reduce decompression obligations.

Semi Closed Ciruit Rebreathers (sCCR)

Military and recreational divers use these because they provide better underwater duration than open circuit, have a deeper maximum operating depth than oxygen rebreathers and are fairly simple and cheap.

Semi-closed circuit equipment generally supplies one breathing gas such as air or nitrox or trimix. The gas is injected into the loop at a constant rate to replenish oxygen consumed from the loop by the diver. Excess gas must be constantly vented from the loop in small volumes to make space for fresh, oxygen-rich gas. As the oxygen in the vented gas cannot be separated from the inert gas, semi-closed circuit is wasteful of oxygen compared with fully closed units. The diver must fill the cylinders with gas mix that has a maximum operating depth that is safe for the depth of the dive being planned.

The Draeger Dolphin is one of the most popular semi closed units due to its small size and relatively cheap cost. The dolphin is also often modified using aftermarket components to retrofit it into a fully closed unit.

Passive addition semi closed units are an evolution of the semi closed concept, however are seen by many as simply and open circuit gas extended. The Halcyon RB80 is an example of a passive unit, which is dived mainly by GUE divers.

Ambient Pressure Diving Rebreathers

Inspiration

The Inspiration was the first CE approved closed-circuit rebreather and is the most commonly used unit today. The “Inspo” as it is affectionately called by many has dual microprocessor oxygen controllers that automatically maintain a constant partial pressure of oxygen giving outstanding gas duration and an optimum breathing mix at all depths.

The unit comes in two primary configurations, which are with and without Vision electronics.
The original incarnation, the Inspiration Classic is the basic Inspiration rebreather. It has dual microprocessor oxygen controllers and respective handsets, however does not include a HUD or decompression software. In this configuration, the Inspiration requires use of an external dive computer, tables or both to calculate decompression information.

The newer version is the Inspiration with Vision electronics, which incorporates the HUD, full decompression software and other Vision features.Regardless of which version you choose, both are rated to 40m with air diluent and 100-150m with heliox diluent (with and without CE approval).

Evolution/Evolution+

As its name suggests, the Evolution was developed after the Inspiration and only comes configured with Vision electronics. The unit is smaller and lighter than the Inspiration, however this does come at the expense of scrubber and cylinder size. The later Evolution+ model sports the same scrubber however as the Inspiration, which extends its capability for minimal weight gain.

Ultimately, the Evolution’s size and weight make it ideal for those wanting a smaller unit, however one should understand the limitations of the smaller scrubber and cylinders before purchasing.

Like its big brother, the “Evo” is rated to 40m with air diluent and 100-150m with heliox diluent. The 2 litre size of the Evolution’s cylinders should however be a consideration for anyone wanting to do longer decompression diving.