Everything about Rebreather totally explained
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 can't safely breathe from the atmosphere. In the
armed forces it's sometimes called "CCUBA" (Closed Circuit Underwater Breathing Apparatus).
Basics
Rebreather technology is used in many environments:
- Underwater - where it's sometimes known as CCR = "closed circuit rebreather", "closed circuit scuba" or "semi closed scuba", 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.
- Space suits - outer space is, for all intents and purposes, a vacuum where there's 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.
- Submarines and hyperbaric oxygen therapy chambers - where the gas in the habitat must remain safe. Here the rebreather is big and is connected to the air in the habitat.
This article is mainly about diving rebreathers.
As a person breathes, the body consumes
oxygen and makes
carbon dioxide. A person with an
open-circuit breathing set typically only uses about a quarter of the oxygen in the air that's breathed in. The rest is breathed out along with
nitrogen and carbon dioxide.
The rebreather recirculates the exhaled gas for re-use and doesn't 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.
Nearly always, the oxygen comes from a
gas cylinder, and the carbon dioxide is absorbed in a canister full of some suitable absorbent such as a form of
soda lime. Some absorbent chemical designed for diving applications are
Sofnolime,
Dragersorb, or Sodasorb. Some systems use a prepackaged
Reactive Plastic Curtain
(RPC) based cartridge: one brand of these RPC cartridges is
ExtendAir.
Pure oxygen isn't considered to be safe for recreational diving below 6 meters, so recreational rebreathers and many professional diving rebreathers also have a cylinder of
diluent gas. This reduces the percentage of oxygen breathed and enables the unit to be used at greater depths. This diluent cylinder may be filled with compressed air or another diving gas mix such as
nitrox or
trimix.
History of rebreathers
Around
1620 in
England,
Cornelius Drebbel made an early oar-powered
submarine. Records show that, to re-oxygenate the air inside it, he likely generated oxygen by heating
saltpetre (
sodium or
potassium nitrate) in a metal pan to make it emit oxygen. That would turn the saltpetre into sodium or potassium
oxide or
hydroxide, which would tend to absorb carbon dioxide from the air around. That may explain how 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 nearly three centuries before Fluess and Davis.
In 1853 Professor T. Schwann designed a rebreather in
Belgium; he exhibited it in Paris in 1878.
In 1878
Henry Fleuss invented the first certainly known rebreather using stored oxygen and absorption of carbon dioxide by an absorbent (here rope yard soaked in
caustic potash solution), to rescue
mineworkers who were trapped by water.
(External Link)
The
Davis Escape Set was the first rebreather which was practical for use and produced in quantity. It was designed about
1900 in
Britain for escape from sunken submarines. Various industrial oxygen rebreathers (for example the
Siebe Gorman Salvus and the
Siebe Gorman Proto, both invented in the early 1900's) were descended from it;
this link shows a
Draeger rebreather used for
mines rescue in 1907.
In 1903 to 1907 Professor Georges
Jaubert, invented Oxylithe, which is a form of
sodium peroxide (Na
2O
2) or
sodium dioxide (NaO
2). As it absorbs
carbon dioxide it emits oxygen. 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
(External Link); it was used in the first filming (1907) of
Twenty Thousand Leagues Under the Sea.
The first known systematic use of rebreathers for diving was by
Italian sport spearfishers in the
1930s. This practice came to the attention of the
Italian Navy, which developed
its frogman unit, which affected
World War II.
In
World War II captured Italian frogmen's rebreathers influenced design of British frogman's rebreathers.
Sport diving rebreather technology innovations
Over the past ten or fifteen years rebreather technology has advanced considerably, often driven by the growing market in recreational diving equipment. Innovations include:
The electronic, fully closed circuit rebreather itself - use of electronics and electro-galvanic fuel cells to monitor oxygen concentration within the loop and maintain a certain partial pressure of oxygen
Automatic diluent valves - these inject diluent gas into the loop when the loop pressure falls below the limit at which the diver can comfortably breathe.
Dive/surface valves or bailout valves - a device in the mouthpiece on the loop which connects to a bailout demand valve and can be switched to provide gas from either the loop or the demand valve without the diver taking the mouthpiece from his or her mouth. An important safety device when carbon dioxide poisoning occurs.
Integrated decompression computers - these allow divers to take advantage of the decompression benefits provided by the ideal mix in the loop of a fully closed circuit rebreather. By monitoring the oxygen content of the mix they can work out the inert gas content and generate a schedule of decompression stops.
Carbon dioxide scrubber life monitoring systems - temperature sensors monitor the progress of the reaction of the soda lime and provide an indication of when the scrubber will be exhausted.
Advantages of rebreather diving
Efficiency advantages
The main advantage of the rebreather over other breathing equipment is the rebreather's economical use of gas. With "open circuit" scuba, the entire breath is expelled into the surrounding water when the diver exhales. A breath inhaled from an open circuit scuba system whose cylinder(s) are filled with ordinary air is about 21% oxygen. When that breath is exhaled back into the surrounding environment, it has an oxygen level in the range of 15 to 16% when the diver is at atmospheric pressure.; Google search for information
Siebe Gorman Salvus
The Savox was made by Siebe Gorman. See this link and . It was an oxygen rebreather with a use duration of 45 minutes. It was worn in front of the body. It had no hard casing.
The Blackett's Aerophor is a nitrox semi-closed-circuit rebreather with liquid gas storage made in England from 1910 onwards for use in mine rescue and other industrial uses.
SEFA is a make of industrial oxygen rebreather with 2 hours duration on a filling.
SDBA is a type of frogman's oxygen rebreather. It has a nitrox variant called ONBA.
FROGS (= Full Range Oxygen Gas System) is the make of frogman's oxygen rebreather which has been used in France since 15 October 2002: see this link (in French): image at this link: it's made by the diving gear makers Aqualung: see this link for more information.
Some military rebreathers (for example the US Navy MK-25 and the MK-16 mixed-gas rebreather), and the Phibian CCS50 and CCS100 rebreathers, were developed by Oceanic. (Stuart Clough of Undersea Technologies developed the Phibian's electronics package (External Link).)
The current US Navy Mark 16 Mod 2 (Explosive Ordinance Disposal) and Mark 16 Mod 3 (Naval Special Warfare) units utilize the Juergensen Defense Corporation Mark V Control System.
The KISS line of manually operated closed circuit rebreathers designed by Gordon Smith of Jetsam Technologies
Oceanic developed the Phibian CCS50 and CCS100 rebreathers; Stuart Clough of Undersea Technologies developed the Phibian's electronics package. (External Link). They have developed military rebreathers, for example the US Navy MK-25 and the MK-16 mixed-gas rebreather. There were unconfirmed reports that Oceanic was going to bring out a new rebreather around October 2006. (External Link).Further Information
Get more info on 'Rebreather'.
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