The information in this post is what I remember from dive school as well as what I have gleaned from the internet…it is not 100% accurate and will be fixed\updated as I learn more. Oh and remember rebreathers kill!!
A Rebreather is a form of life support that is typically used either for Diving or in mines and the like. The type that I am interested in building is one for use underwater instead of traditional SCUBA gear. There are two basic types: CCR or OCR. CCR are Closed Circuit REbreathers and are called such sense the breathing loop (or circuit) is closed allowing now gas to escape. This type of rebreather is great for underwater photography and research as well as for sneaking into the enemy base and killing people (assuming of course that the enemies base has water around in ot even better if there base has some direct connection to the ocean.) Open Circuit rebreathers are just the oppisite, they let off bubbles and are basically a great way to conserve gas as well as dive deeper and safer.
The basic purpose of all rebreathers is to recycle the oxygen that you breathe since you use about 25% of the th oxygen that is inhaled. that other 75% is exhaled and wasted. This means that a typical tank of air (21% O2) will last about an hour at 50 feet of seawater. Whereas that same amount of air used in a rebreather might let you dive that same dive 3 or four times. In some cases you can dive even longer since a lot of rebreathers adjust the partial pressure of oxygen(PPO2). This is percentage of oxygen that is going into you blood. (MORE INFO). This means that as you move around in depth you are breathing a higher percentage of oxygen then normal air. This means you are breathing less dilutant gas(nitrogen, helium). this means that the chances of Nitrogen Narcosis and Decompression sickness(DCS) are less but not elimatnated, Also when you start messign with the PPO2 you increase your risk of CNS (central nervous system) Oxygen Toxicity. This is when the PPO2 increases to 1.6 or better, this causes certain parts of your nervous system to shut down and can ultimatly lead to death.
The type of rebreather that I am going to try to build first is a closed circuit oxygen rebreather. This is a rebreather that allow you to breathe 100% oxygen all fo the time. This set up while limeting the depth you can achieve it gets rid of the DCS and Narcosis risk. You maximum depth is around 20 feet, basically great for ponds or tropic diving, espseically if you are a photographer. FOr me the main reason I want to build one of these is for the fun of building my own life support equipment and the experiance so I can attack bigger rebreather projects in the future.