A rebreather is a breathing equipment which recycles the breathing gas, ensuring the rebreathed gas remains breathable. This will allow the user to breathe extended periods in environments where it is impossible to survive. In this way, and with this equipment, astronauts can breathe in space, and divers can breathe underwater.

Other environments where rebreather are used are mines, caves, hospitals, high altitude, planes and polluted or toxic environments. A few countries in the world still consider rebreathers as exclusively military equipment and therefore still ban the use of these equipments (like Jordan and Saudi Arabia).

It is the most advanced breathing life support technology available today.

So, how does it work ?

puredivingIn order to keep a breatheable gas, it will remove the carbon dioxide (CO2) from the exhaled breathing gas, which is a waste product produced by the metabolism of the body and which would become toxic if it accumulates in the inhaled gas. The removal of CO2 will typically be achieved by a filter cartridge filled with soda sorb which will absorb the CO2 thanks to a chemical reaction which will entrap the waste gas.

Also, the rebreather unit will replace the oxygen consumed by the body, ensuring an optimal level of oxygen for metabolism. This is generally achieved by the continuous addition of oxygen into the breathing mix, provided by a cylinder filled with pressurized pure oxygen.

The expired gas will so be directed through the filter and enriched with oxygen, before being redirected back to the lungs of the diver, creating a closed breathing loop, completely isolated from the external environment.

What types of rebreather units exist ?

Different rebreather systems are available, with the completely closed circuit rebreather (CCR) system being the most advanced system, allowing complete recycling of the breathing gas.

Two types of CCR units are available, being the eCCR and mCCR rebreather units.

  • The eCCR units, or electronic closed circuit rebreathers, will control all parameters of the breathing gas thanks to a computer system which will measure the concentrations of gases in the breathing loop, and which will inject the required gas to keep the breathing gas optimal. On the eCCR units, the role of the user will mainly be to double check if the computer systems function properly.
  • The mCCR units (mechanical or manual rebreather units) are more basic systems without electronics where the user is continuously controlling and mixing himself the required gases.

Another system of rebreather is the Semi-Closed rebreather system (SCR), which is less efficient, as it will only recycle a part of the gas, and thus releasing constantly gas, resulting in a waste of gas. Duration of a SCR unit is typically limited to one or two hours, while CCR units can be used for more extensive periods (depending on the filter used). Semi-closed rebreathers are generally qualified as gas-extending units, as the same gas will be rebreathed only a couple of times before being vented.

Here also, two types of SCR are available: the eSCR and mSCR units. 

  • The eSCR unit functions like an eCCR unit, except that it will not inject pure oxygen but a mix of oxgen and nitrogen (called nitrox), resulting in waste gas which has to be vented out of the system, as excess nitrogen has to be released on every addition of fresh gas.
  • The mSCR unit is very simple unit without any electronics. Two sub-types of mSCR units exist as well: the active SCR and the passive SCR (PSCR).
    • The active SCR has a continuous flow of gas (continuously active), assuming the user is breathing constantly, and thus ensuring a permanent refreshment of the gas. 
    • The PSCR unit will only give gas on demand of the user, so reducing a bit the waste of gas when the diver is not breathing. 




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