rebreather and closed circuit diving?

closed circuit and open circuit whats what

2 Answers

  • 1 decade ago
    Favorite Answer

    Closed circuit and semi closed circuit are rebreathers. Yup..two different types there and they operate just a tad differently in how they deal with breathing gas.

    Rebreathers are a diving rig that utilize a sort of gas recycling system. Not unlike what you'll find on modern submarines or on space craft. They use a scrubber material to take CO2 out of the breathing loop and most of that gas you get to breathe again with possible injections of O2 or a diluent( a gas like nitrogen or helium) or both are injected.

    Open circuit is regular old scuba gear.You inhale the gas from your tank via a first and second stage reg set and when you breathe out..that gas goes out into the water column never to be used by you again. That entire lungfull that actually had some usable oxygen in it.

    Here's a link you might find helpful since it goes more in depth than the simple explanations I have given you about rebreathers :

  • 1 decade ago

    Just to add to Scubabob's explanation.

    Semi-Closed Circuit Rebreathers (SCCR) are usually used with a mixed gas, called NITROX but can be used with air. They have one gas mixture that is injected. Its continually added in a small amount to maintain the pressure in the breathing loop and O2 level thus, it needs to be "burped" from the system occasionally so you get some bubbles. SCCRs are not as expensive as Closed Circuit Rebreathers because they don't require the amount of sensors and electronics and are, by design, simpler.

    Closed-Circuit Rebreathers (CCR) have one gas and a dilutent mixture of gases that are injected into the system and none exhausted, no bubbles. The Dilutent is the "inert" gas mixture and could be air, NITROX, TRIMIX, or HELIOX. (NOTE: All of these dilutent mixtures contain O2, although it may be a small percentage based on maximum depth. Its very rare that a Dilutent tank would be filled with straight Nitrogen or Helium.) Then you have the the Oxygen side. CCR's work by maintaining the optimal PPO2 or partial pressure of oxygen and "scrubbing" the mix of exhaled carbon dioxide. Think of it this way, as you descend oxygen becomes "concentrated" and as you ascend, it becomes "unconcentrated". Since too much or too little O2 in diving can be dangerous, the system constantly adjusts the mix to maintain the right amount of oxygen or PPO2 for the depth, also taking into account the metabolic rate of O2 consumption . (Note: The PPO2 target is usually around 1.4 but, the military may go as low as .70 and SAT Divers bailout systems are around .50. The max recommended is 1.6 and the lowest to support life is .18. Just for reference) The system adjusts via a network of depth sensors, Oxygen sensors(usually 2 to 3 for redundency), solinoids, and valves that are controlled by a central computer, you can also add O2 manually to bring up the "concentration" for decompression but, the computer will not allow that until you are at a safe depth for the PPO2 you are trying to reach..

    Both systems use a scrubbing medium to remove Carbon Dioxide and both systems have come a very long way in their development. Costs can be as low as $1500 for some SCCR's too as high as $35000 for some of the latest CCR's I have also heard that Homeland Security maintains a list of all CCR certified divers but, I don't know if it's true.

    Hope this helps,


    ACDE/IMCA Saturation Diver

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