What is a rebreather>>>>

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When you use high helium percentages, there is great value in a rebreather. It will pay for itself against Open Circuit, if thats the diving you do.
 
Re-breather technology has been around longer than open-circuit scuba. You have several different types of commercially available re-breathers available to you today. One type is a manual control only. This unit you adjust during your training to automatically add oxygen to the breathing bags approximately equal to your metabolic rate. You may adjust the amount of oxygen in the breathing loop as its called on descent and ascent to maintain an appropriate partial pressure of oxygen. You don't want too little as it may cause you to pass out, and you don't want too much as this may trigger an oxygen toxicity event from which you may not recover. Either one is bad to have occur underwater. There are also electronic re-breathers which monitor the partial pressure of oxygen in the loop automatically and add oxygen to maintain a constant ppo2. These units are controlled by electronics and can have problems, again underwater, but all have the capacity to be operated manually if you need to in an electronic failure mode. Every re-breather requires that you carry open-circuit scuba cylinders with regulators for that "just in case" emergency evacuation back to the surface.
As for which is safer, unless you can breath water all systems can allow you to drown. Most all re-breathers require more extensive training in the operation and sanitary use of a closed breathing loop. The advantage is these units can extend the gas in the cylinders and make decompression from deeper dives more efficient. Others have commented on the process of there usage, but just remember with your open-circuit scuba you inhale gas from the cylinder, and exhale it into the water. You blow bubbles, when the pressure gauge reads low up you go. With a re-breather when you exhale you move gas from a breathing bag into your lungs where normal respiration and metabolism of gases take place. When you exhale the gas with the metabolic by product of co2 goes through a chemical that adsorbs the carbon dioxide and returns the rest of the gas to the breathing bag. While the process is a little more complicated than this, it is the basic concept behind a closed system.
 

I need to correct this...

For CCR's - Manual, Hybrid, Fully Electronic refer to how gas is added. Actual loop PPO2 levels are monitored using O2 sensors, units can have anywhere from 2-5 O2 sensors + redundant PPO02 monitoring.

Manual (mCCR) and Hybrid (hCCR) Units have a constant mass flow valve and non depth compensated O2 1st stage or variable valve with depth compensated 1st stage. O2 is added at a constant rate (you select with variable valve) - normally at resting metabolic rate. These units also have manual O2 and Diluant gas addition as when you exceed your resting metabolic rate, you consume more O2 than the unit.

Hybrid (hCCR) Fully Electronic CCR's (eCCR) also have active control of PPO2 - The same sensors that monitor PPO2 levels in the loop are connected to a computer which fires a solenoid to add O2 to the loop as PPO2 drops. Most hCCR's and eCCR's also have manual gas addition so unit can be run manually if solenoid and associated electronics fail.

In most cases, hybrid CCR's can be converted to eCCR's and you need to do this when deep diving as a non depth compensated O2 1st stage will stop delivering O2 when external pressure/depth reaches internal pressure/setting of the 1st stage. The Apeks 1st stage can be quickly converted from non depth compensating to depth compensating... Likewise, when this conversion is done, the CMF valve needs to be closed/sealed.

No matter what type of unit you dive you always know your PPO2 via redundant O2 cell monitoring electronics.
 
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I need to correct this...



Manual (mCCR) and Hybrid (hCCR) Units have a constant mass flow valve...

Nah, not all of them... I dive and teach on a couple of units.. One of them is fully manual and the oxygen flow is through a VARIABLE valve.

Just saying.
 
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I'm late to this party and not rebreather-trained. The idea that the concept itself is untrustworthy makes me laugh. At the moment, I am sitting near several operating rooms that have anesthetized patients. To the OP, think how many millions of general anesthetics are administered each year, in either semi or closed circuit recreating.

That said, it is certainly possible to kill someone with quickness by mishandling the machine or improperly addressing malfunctions. That's at 1 ATA with a person whose job is, among other things, to vigilantly mix the gasses while watching and reacting to the equipment and monitors. The potential for problems obviously increases at depth, in a water-filled environment, where the person monitoring the equipment is also concentrating on a multitude of tasks.
 
You could say a rebreather is a magical device that divers with high breathing rates desire... this being the Magic Carpet Ride side of rebreathers.
Unfortunately, unlike scuba, the rebreathers have a great many ways they can kill a diver, so you might say that is the "cost" of all this "magic".

Personally, I would use a rebreather only for very "mission specific" purposes, where scuba tanks just won't work....This is such a tiny percentage of all dives you could do, I see it as unlikely for most divers. Four miles back into a deep cave....a dive in open ocean with currents to an occulina reef at 450 feet deep for a 30 minute video session, with 4 mph drift current so no tanks can be used beyond what the diver carries.......there are a few scenarios I can imagine myself wanting the magic carpet ride, but not many. And these would be extremely dangerous, by recreational or technical use standards.

There are rebreathers such as the KISS GEM that are an outstanding alternative to OC, without as many risks as a full CCR. I dive mine with OC folks all the time, and I'm never the guy to call the dive on low air.

---------- Post Merged at 01:11 PM ---------- Previous Post was at 01:06 PM ----------

In addition, the training is 1/3 the cost for a CCR, and the KISS GEM is a very functionally simple design, not much to go wrong with it. And if it does, you flip to onboard OC.
 
https://www.shearwater.com/products/peregrine/

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