Rebreathers

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A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where humans cannot safely breathe from the atmosphere. In the armed forces it is sometimes called "CCUBA" (Closed Circuit Underwater Breathing Apparatus).

Rebreather technology is used in many environments:

• Underwater – where it is sometimes known as CCR = "closed circuit rebreather", "closed circuit scuba", "semi closed scuba", SCR = "semi closed rebreather", or CCUBA = "closed circuit underwater breathing apparatus", as opposed to Aqua-Lung-type equipment, which is known as "open circuit scuba".
• Mine rescue and in industry – where poisonous gases may be present or oxygen may be absent.
• Crewed spacecraft and space suits – outer space is, for all intents and purposes, a vacuum where there is no oxygen to support life.
• Hospital anaesthesia breathing systems – to supply controlled proportions of gases to patients without letting anaesthetic gas get into the atmosphere that the staff breathe.
• Himalayan mountaineering. Both chemical and compressed oxygen has been used in experimental closed-circuit oxygen systems—the first on Mt. Everest in 1938. A high rate of system failures due to extreme cold has not been solved.

Theory

As a person breathes, the body consumes oxygen and makes carbon dioxide. At shallow depths, a person with an open-circuit breathing set typically only uses about a quarter of the oxygen in the air that is breathed in (4%–5% of the inspired volume). The remaining oxygen is exhaled along with nitrogen and carbon dioxide. As the diver goes deeper, roughly the same quantity of oxygen is used, which represents an increasingly smaller fraction of the compressed air breathed in. Because exhaled air can contain as much as 79% nitrogen (which is not utilized in the body) and 16% (or more) unused oxygen, every exhaled breath from an open-circuit scuba set represents at least 95% wasted, potentially useful gas volume, which has to be replaced from the air supply.

The rebreather recirculates the exhaled gas for re-use and does not discharge it to the atmosphere or water. It absorbs the carbon dioxide, which otherwise would accumulate and cause carbon dioxide poisoning. It removes the carbon dioxide by a process called scrubbing. The rebreather adds oxygen, to replace the oxygen that was consumed. Thus, the gas in the rebreather's circuit remains breathable and supports life and the diver needs only a fraction of the gas that would be required for an open-circuit system.

History of rebreathers

Around 1620: In England, Cornelius Drebbel made an early oar-powered submarine. To re-oxygenate the air inside it, he likely generated oxygen by heating saltpetre (potassium nitrate) in a metal pan to emit oxygen. Heating turns the saltpetre into potassium oxide or hydroxide, which absorbs carbon dioxide from the air. That may explain why Drebbel's men were not affected by carbon dioxide build-up as much as would be expected. If so, he accidentally made a crude rebreather more than two centuries before Saint Simon Sicard's patent.

1808: The oldest known rebreather based on carbon dioxide absorption was patented in France by Sieur (old French for "sir" or "Mister") Touboulic from Brest, mechanic in the Napoleon's Imperial Navy. This early rebreather design worked with an oxygen reservoir, the oxygen being delivered progressively by the diver himself and circulating in a closed circuit through a sponge soaked in lime water. Touboulic called his invention Ichtioandre (Greek for 'fish-man').There's no evidence of a prototype having been manufactured.
1849: Patent for the oldest known prototype of a rebreather also used an oxygen reservoir, granted to the Frenchman Pierre Aimable De Saint Simon Sicard.

1853: Professor T. Schwann designed a rebreather in Belgium; he exhibited it in Paris in 1878. It had a big backpack oxygen tank at pressure about 13.333 bars, and two scrubbers containing sponges soaked in caustic soda.
1878: Henry Fleuss invented a rebreather using stored oxygen and absorption of carbon dioxide by an absorbent (here rope yarn soaked in caustic potash solution), to rescue mineworkers who were trapped by water.

About 1900: The Davis Escape Set was designed in Britain for escape from sunken submarines. It was the first rebreather which was practical for use and produced in quantity. Various industrial oxygen rebreathers (e.g. the Siebe Gorman Salvus and the Siebe Gorman Proto, both invented in the early 1900s) were derived from it.

1903 to 1907: Professor Georges Jaubert invented Oxylithe, which is a form of sodium peroxide (Na2O2) or sodium dioxide (NaO2). As it absorbs carbon dioxide (e.g. in a rebreather's scubber) it emits oxygen.

1907: Oxylithe was used in the first filming of Twenty Thousand Leagues Under the Sea.

1907: This link shows a Draeger rebreather used for mines rescue.
In 1909 Captain S.S. Hall, R.N., and Dr. O. Rees, R.N., developed a submarine escape apparatus using Oxylithe; the Royal Navy accepted it. It was used for shallow water diving but never in a submarine escape;

1912: The first recorded mass production of rebreathers started with the Drager rebreathers, invented some years earlier by an engineer of the Drager company, Hermann Stelzner. The Drager rebreathers, especially the DM20 and DM40 model series, were those used by the German helmet divers and German frogmen during World War II.

1930's: Italian sport spearfishers used rebreathers systematically. This practice came to the attention of the Italian Navy, which developed its frogman unit Decima Flottiglia MAS, which was used effectively in World War II.

World War II: Captured Italian frogmen's rebreathers influenced design of British rebreathers. Many British frogmen's breathing sets' oxygen cylinders were German pilot's oxygen cylinders recovered from shot-down German Luftwaffe planes. Those first breathing sets may have been modified Davis Submarine Escape Sets; their fullface masks were the type intended for the Siebe Gorman Salvus. But in later operations different designs were used, leading to a fullface mask with one big face window, at first oval like in this image, and later rectangular (mostly flat, but the ends curved back to allow more vision sideways). Early British frogman's rebreathers had rectangular breathing bags on the chest like Italian frogman's rebreathers; later British frogman's rebreathers had a square recess in the top so they could extend further up onto his shoulders; in front they had a rubber collar that was clamped around the absorbent canister, as in the illustration below.

Some British armed forces divers used bulky thick diving suits called Sladen suits; one version of it had a flip-up single window for both eyes to let the user get binoculars to his eyes when on the surface.

Early 1940s: US Navy rebreathers were developed by Dr. Christian J. Lambertsen for underwater warfare and is considered by the US Navy as "the father of the frogmen". Lambertsen held the first closed-circuit oxygen rebreather course in the United States for the Office of Strategic Services maritime unit at the Naval Academy on 17 May 1943.