There are several categories of rebreathers, but let's start with the basics. A rebreather is a device which re-circulates the diver's breathing gas. A typical person consumes less than 10% of the Oxygen (O2) in the breathing gas in every breath. This means that the other 90+% is wasted if it is just exhaled, and not "rebreathed". There are three primary categories of rebreathers. They vary from Oxygen rebreathers to Semi-Closed Circuit (SCR) to state of the art Fully-Closed Circuit Rebreathers (CCR). These systems vary in the manner in which gas is added or replenished. All rebreathers must scrub out the CO2 from the breathing gas; otherwise the diver will become hypercapnic (which can cause blackout and other problems)

The Basic Rebreather Consists of:

1. Breathing loop:
2.
1. Mouthpiece. (Dive Surface Valve or DSV).
2. Counter-Lung(s). To contain the diver's exhaled gas for processing and rebreathing.
3. Scrubber. To remove carbon dioxide (CO2) from the breathing gas.
4. Check Valves. To keep gas flow directional.
5. Breathing Hoses. To connect the DSV, Counter-Lung(s), and Scrubber.
3. Gas Addition/Replenishment System.
4.
1. Compressed gas cylinder(s).
2. Regulators. To reduce the high pressure gas in the cylinders to ambient pressure.
3. Oxygen measuring device.
4. Gas addition controls.

Oxygen Rebreathers:

In this design, only pure O2 is injected into the breathing loop. This is done via a demand valve and manual override. These are Fully Closed Circuit systems which are extremely depth limited because the diver is breathing pure O2. The typical use is military. These are the only class of rebreathers which are totally "bubbleless". There is never a decompression obligation with these units, as there is no inert gas in the system to be absorbed by the diver's tissues.

Semi-Closed Rebreathers (SCR):

In this design, Nitrox (O2 enriched air) is injected into the breathing loop via a mass flow orifice valve, or a system which keys the injection to the divers breathing rate. Because gas is continually injected into the loop, it must also be expelled from the loop (hence the term semi-closed). These systems offer gas use economy over open circuit SCUBA, but there is no decompression advantage over nitrox open circuit diving.

Fully Closed Circuit Rebreathers (CCR):

In this design, there are two gases; pure O2 and a diluent gas (air, tri-mix or heliox, etc). Diluent is added either automatically or manually to the loop to make up the bulk of the loop volume during descent. In a CCR system, only O2 is consumed or burned by the diver. That consumption rate is based on the diver's metabolic rate. It is not affected by the depth of the dive, but by the diver's workload. This means that the diver will consume the same amount of O2 at 300 ft as at 30 ft or 3ft, provided he is performing the same task.

CCR's require the gas in the breathing loop to be monitored. This is done via oxygen sensors (typically 2 or 3). O2 is injected into the loop to maintain a set partial pressure of O2. There are two injection strategies within this topic. Electronically Controlled (automatic) and Manually Controlled. Some CCR's are designed to allow both strategies.

CCR's offer the maximum decompression advantage over open circuit SCUBA. CCR's are truly the best choice if your diving ranges from advanced recreational to heavy technical.

What are the advantages of using a CCR?

Frequently Asked Questions on Rebreathers

CCR Rebreathers ( Close-circuit )

SCR Rebreathers ( Semiclose )

To view a Molecular Products declaration of SOFNOLIME transport class as non-hazardous.

To view the material safety data sheet (MSDS) for SOFNOLIME.