A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycles exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather a lighter and more compact than an open-circuit breathing set for long durations in environments where humans cannot safely breathe from the atmosphere. For breathing apparatus used underwater, see scuba sets and rebreather and surface supplied diving. ... Air is the most common and only natural breathing gas. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance transparent (gas) very pale blue (liquid) Atomic mass 15. ... Open circuit can mean: In electronics, where there is nothing connected to a load and no current can flow. ... For breathing apparatus used underwater, see scuba sets and rebreather and surface supplied diving. ...

Inspiration closed circuit diving rebreather

Download high resolution version (500x667, 30 KB)rebreather inspiration front This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... Download high resolution version (500x667, 30 KB)rebreather inspiration front This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ...

Basics

Rebreather technology is used in many environments:

• Underwater - where it is sometimes known as "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 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.
• 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. SCUBA is an acronym for Self-Contained Underwater Breathing Apparatus. ... SCUBA is an acronym for Self-Contained Underwater Breathing Apparatus. ... ... Mine rescue teams are specialized groups of people who are familiar with procedures used to rescue persons trapped in mines by hazards. ... Apollo 15 space suit A spacesuit is a complex system of garments, equipment, and environmental systems designed to keep a person alive and comfortable in the harsh environment of outer space. ... This article or section seems not to be written in the formal tone expected of an encyclopedia entry. ... Look up Vacuum in Wiktionary, the free dictionary. ... Anesthesia (AE), also anaesthesia (BE), is the process of blocking the perception of pain and other sensations. ... German UC-1 class World War I submarine A model of Gunter Priens Unterseeboot 47 (U-47), German WWII Type VII diesel-electric hunter-killer (SSK) submarine Inside of the Argonaute, showing the typical obstructed, tiny space of a post-WWII diesel attack submarine. ... Hyperbaric oxygen therapy (HBOT) is the medical use of oxygen at a higher than atmospheric pressure. ...

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 is breathed in. The rest is breathed out along with nitrogen and carbon dioxide. General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance transparent (gas) very pale blue (liquid) Atomic mass 15. ... Carbon dioxide is an atmospheric gas comprised of one carbon and two oxygen atoms. ... Open circuit can mean: In electronics, where there is nothing connected to a load and no current can flow. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ...

With a rebreather, the exhaled gas is not discharged to waste. The rebreather recovers the exhaled oxygen for re-use. It absorbs the carbon dioxide, which otherwise would accumulate and cause carbon dioxide poisoning. It adds oxygen to replace what was consumed. Thus, the gas in the rebreather's circuit remains breathable and supports life processes. Nearly always, the oxygen comes from a gas cylinder, and the carbon dioxide is absorbed in a canister full of some absorbent chemical such as soda lime. Hypercapnia is a condition where there is too much carbon dioxide (CO2) in the body. ... Industrial compressed gas cylinders used for oxy-fuel welding and cutting of steel. ... Soda lime is a mixture of chemicals, used in granular form in closed breathing environments, such as general anaesthesia, submarines, rebreathers and recompression chambers, to remove carbon dioxide from breathing gases to prevent CO2 retention and carbon dioxide poisoning. ...

History of rebreathers

British navy frogman in 1945

Also see Timeline of underwater technology. Timeline of underwater technology // Pre-industrial Several centuries BC: (Relief carvings made at this time show Assyrian soldiers crossing rivers using inflated goatskin floats. ...

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: see this link. Events September 6 - English emigrants on the Mayflower depart from Plymouth, England for the future New England and arrive at the end of the year. ... Motto: (French for God and my right) Anthem: Multiple unofficial anthems Capital London Largest city London Official language(s) English Government Constitutional monarchy  - Queen Queen Elizabeth II  - Prime Minister Tony Blair MP Unification    - by Athelstan AD927  Area    - Total 130,395 km² (1st in UK)   50,346 sq mi   - Water (%) Population... Cornelius Jacobszoon Drebbel (Alkmaar, 1572 - London, November 7, 1633) was the Dutch inventor of the first navigable submarine in 1620. ... German UC-1 class World War I submarine A model of Gunter Priens Unterseeboot 47 (U-47), German WWII Type VII diesel-electric hunter-killer (SSK) submarine Inside of the Argonaute, showing the typical obstructed, tiny space of a post-WWII diesel attack submarine. ... Saltpeter is variously: potassium nitrate (niter); or sodium nitrate (soda niter) ... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Atomic mass 22. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Atomic mass 39. ... An electrostatic potential map of the nitrate ion. ... An oxide is a chemical compound of oxygen with other chemical elements. ... Hydroxide is a polyatomic ion consisting of oxygen and hydrogen: OH− It has a charge of −1. ... Hypercapnia (from the Greek hyper = above and kapnos = smoke) is a condition where there is too much carbon dioxide (CO2) in the body. ...

The first certainly known closed circuit breathing device using stored oxygen and absorption of carbon dioxide by an absorbent (here caustic soda), was invented by Henry Fluess in 1879 to rescue mineworkers who were trapped by water. Sodium hydroxide (NaOH), also known as caustic soda or lye in North America, is a caustic metallic base used in industry (mostly as a strong chemical base) in the manufacture of paper, textiles, and detergents. ... Henry Fluess, a british inventor. ... 1879 (MDCCCLXXIX) was a common year starting on Wednesday (see link for calendar). ... Chuquicamata, the largest open pit copper mine in the world, Chile. ...

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 (e.g. the Siebe Gorman Salvus and the Siebe Gorman Proto) were descended from it. The Davis Submerged Escape Apparatus (also referred to as DSEA), is an early make of oxygen rebreather invented in 1910 by Sir Robert Davis, head of Messrs. ... 1900 (MCM) was an exceptional common year starting on Monday. ... CGI image: 2 views of a diver wearing a Siebe Gorman Salvus rebreather The Salvus is a light oxygen rebreather for industrial use (including by firemen and in coalmine rescue) or in shallow diving. ... The Proto is a type of rebreather that was made by Siebe Gorman. ...

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 had a big effect in World War II. This article or section is missing references or citation of sources. ... Pre-unitarian navies of the Italian states Regia Marina - Royal Navy of the Kingdom of Italy (1861 - 1946) Marina Militare - Navy of the Italian Republic (1946 - today) This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... The Decima Flottiglia MAS (Decima Flottiglia Mezzi dAssalto, also known as La Decima or Xª MAS) (Italian for 10th Assault Vehicle Flotilla) was an Italian commando frogman unit created during the Fascist government. ... To meet Wikipedias quality standards, the use of images on this page may require cleanup, involving adjustment of image placement, formatting, size, or other adjustments. ...

US Navy rebreathers were developed by Dr. Christian J. Lambertsen in the early 1940s for underwater warfare. Dr. Lambertsen, who currently works at the University of Pennsylvania, is considered by the US Navy as "the father of the Frogmen." The United States Navy (USN) is the branch of the United States armed forces responsible for naval operations. ... // Events and trends World War II was a truly global conflict with many facets: immense human suffering, fierce indoctrination, and the use of new, extremely devastating weapons such as the atomic bomb. ... The University of Pennsylvania (Penn is the moniker used by the university itself [2]) is a private, nonsectarian research university located in Philadelphia, Pennsylvania. ... For the Wizard of Oz series character, see Frogman (Oz character). ...

Advantages of rebreather diving

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. Long or deep dives using open circuit equipment may not be feasible as there are limits to the number and weight of diving cylinders the diver can carry. SCUBA is an acronym for Self-Contained Underwater Breathing Apparatus. ... 12 litre and 3 litre steel diving cylinders A diving cylinder or SCUBA tank is used to store and transport high pressure breathing gas as a component of an Aqua-Lung. ...

The economy of gas consumption is also useful when the gas mix being breathed contains expensive gases, such as helium. In normal use only oxygen is consumed: small volumes of expensive inert gases can be reused for many dives. General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ...

Rebreathers produce far fewer bubbles and make less noise than Aqua-Lungs; this can conceal military divers and allow divers engaged in marine biology and underwater photography to avoid alarming marine animals and thereby get closer to them. Soap bubbles Bubble may refer to: Soap bubble, spherical liquid film, also possibly of bubble gum Cavitation, pocket of air caught in a liquid Bubble (economics), where speculation causes prices to rise to unsustainable levels a (normally) transparent dome Light bulb, in theater lighting terminology [1] in poker tournaments, the... ... Military diving is a branch of professional diving carried out by world armed forces. ... Marine life can be very abundant. ... car wreck in a lake A NikonosV underwater camera with flash and lanyard Underwater photography is the process of taking photographs while underwater. ...

One type of rebreather, the electronic fully-closed circuit rebreather, is able to minimise the proportion of inert gases in the breathing mix, and therefore minimise the decompression requirements of the diver, by maintaining a specific and relatively high oxygen partial pressure at all depths. A Decompression Stop is a period of time a diver must spend at a constant depth in shallow water at the end of a dive in order safely to eliminate inert gases from the divers body to avoid decompression sickness. ... In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. ...

The breathing gas in a rebreather is warmer and more moist than the dry and cold gas from open circuit equipment making it more comfortable to breathe on long dives and causing less dehydration in the diver.

Parts of a rebreather

A simple naval-type diving oxygen rebreather with the parts labelled

Back of an Inspiration Diving Rebreather, with its casing opened

A simple naval-type diving oxygen rebreather with the parts labelled I made the image with CGI. File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... A simple naval-type diving oxygen rebreather with the parts labelled I made the image with CGI. File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Download high resolution version (500x667, 31 KB)rebreather inspiration back I photographed thi myself This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ... Download high resolution version (500x667, 31 KB)rebreather inspiration back I photographed thi myself This image has been released into the public domain by the copyright holder, its copyright has expired, or it is ineligible for copyright. ...

The loop

Although there are several design variations of diving rebreather, all types have a gas-tight loop that the diver inhales from and exhales into. The loop consists of components sealed together. The diver breathes through a mouthpiece or a fullface mask (or with industrial breathing sets, sometimes a mouth-and-nose mask). This is connected to one or more tubes bringing inhaled gas and exhaled gas between the diver and a counterlung or breathing bag. This holds gas when it is not in the diver's lungs. The loop also includes a scrubber containing carbon dioxide absorbent to remove from the loop the carbon dioxide exhaled by the diver. Attached to the loop there will be at least one valve allowing injection of gases, such as oxygen and perhaps a diluting gas, into the loop. There may be valves allowing venting of gas from the loop. A diver in a pool wearing an AGA full face mask A diver wearing an Ocean Reef full face mask A full-face diving mask is a type of diving mask worn by SCUBA divers so that they can talk with the surface or other divers. ... Carbon dioxide is an atmospheric gas comprised of one carbon and two oxygen atoms. ...

Most modern rebreathers have a twin hose mouthpiece or breathing mask where the direction of flow of gas through the loop is controlled by one-way valves. Some have a single pendulum hose, where the inhaled and exhaled gas passes through the same tube in opposite directions. The mouthpiece often has a valve letting the diver take the mouthpiece from the mouth while underwater or floating on the surface without water getting into the loop. Many rebreathers have "water traps" in the counterlungs, to stop large volumes of water from entering the loop if the diver removes the mouthpiece underwater without closing the valve, or if the diver's lips get slack letting water leak in.

Carbon dioxide scrubber

The scrubber is often called a "canister".

The term "break through" means the failure of the "scrubber" to continue removing carbon dioxide from the exhaled gas mix.

The active ingredient of the scrubber is often soda lime. All gas moving through the loop must pass through the absorbent so its carbon dioxide is removed by reacting with the absorbent in the canister; this chemical reaction is exothermic. Soda lime is a mixture of chemicals, used in granular form in closed breathing environments, such as general anaesthesia, submarines, rebreathers and recompression chambers, to remove carbon dioxide from breathing gases to prevent CO2 retention and carbon dioxide poisoning. ... Carbon dioxide is an atmospheric gas comprised of one carbon and two oxygen atoms. ... A chemical reaction is a process that results in the interconversion of chemical substances [1]. The substance or substances initially involved in a chemical reaction are called reactants. ... Exothermic means to release energy in the form of heat. ...

In larger environments, such as recompression chambers, a fan is used to pass gas through the canister.

Some say that the reaction occurs along a "front", which is a cross section of the canister, of the unreacted soda lime that is exposed to carbon dioxide-laden gas. This front moves through the canister, from the gas input end to the gas output end, as the reaction consumes the active ingredients. But this front would be a wide zone, because the carbon dioxide in the gas going through the canister needs time to reach the surface of a grain of absorbent, and then time to penetrate to the middle of each grain of absorbent as the outside of the grain becomes exhausted.

There are at least three ways that the scrubber may fail or become less efficient:-

• Complete consumption of the active ingredient ("break through").
• The scrubber canister has been incorrectly packed or configured. This allows the exhaled gas to bypass the absorbent. In a rebreather, the soda lime must be packed tightly so that all exhaled gas comes into close contact with the granules of soda lime and the loop is designed to avoid any spaces or gaps between the soda lime and the loop walls that would let gas avoid contact with the adsorbent. If any of the seals, such as o rings, or spacers that prevent bypassing of the scrubber, are not cleaned or lubricated or fitted properly, the scrubber will be less efficient, or outside water or gas may get in circuit.
• When the gas mix is under pressure caused by depth, the inside of the canister is more crowded by other gas molecules (oxygen or diluent) and the carbon dioxide molecules are not so free to move around to reach the absorbent. In deep diving with a nitrox or other gas-mixture rebreather, the scrubber needs to be bigger than is needed for a shallow-water or industrial oxygen rebreather, because of this effect.

In rebreather diving, the typical effective duration of the scrubber will be half an hour to several hours of breathing, depending on the granularity and composition of the soda lime, the ambient temperature, the design of the rebreather, and the size of the canister. In some dry open environments, such as a recompression chamber or a hospital, it may be possible to put fresh absorbent in the canister when break through occurs. Typical O-ring and application An O-ring is a loop of elastomer with a round (o-shaped) cross-section used as a mechanical seal. ... Typical decal used on scuba cylinders containing Nitrox Nitrox is a breathing gas consisting of oxygen and nitrogen (similar to air), but with a higher proportion of oxygen than the normal 20. ...

There are several approaches to avoiding or detecting breakthrough:

• An indicating dye in the soda lime. It changes the colour of the soda lime after the active ingredient is consumed. For example, a rebreather absorbent called "Protosorb" supplied by Siebe Gorman had a red dye, which was said to go white when the absorbent was exhausted. With a transparent canister, this may be able to show the position of the reaction "front". This is useful in dry open environments, but is not useful on diving equipment, where:-
  • A transparent canister would likely be brittle and easily cracked by knocks.
  • Opening the canister to look inside would flood it with water or get unbreathable outside gas in circuit.
  • The canister is usually out of sight of the user, e.g. inside the breathing bag or inside a backpack box.
• Temperature monitoring. As the reaction between carbon dioxide and soda lime is exothermic, temperature sensors, such as thermocouples along the length of the scrubber can be used to measure the position of the front and therefore the life of the scrubber. [1]
• Diver training. Divers are trained to monitor and plan the exposure time of the soda lime in the scrubber and replace it within the recommended time limit. At present, there is no effective technology for detecting the end of the life of the scrubber or a dangerous increase in the concentration of carbon dioxide causing carbon dioxide poisoning. The diver must monitor the exposure of the scrubber and replace it when necessary.
• Carbon dioxide gas sensors exist, but they are not sensitive enough to be used in a rebreather - the scrubber "break through" occurs quite suddenly and the diver shows symptoms before the sensor indicates a dangerous build-up of carbon dioxide. Even if a sensitive carbon dioxide sensor is developed, it may not be useful as the primary tool for monitoring scrubber life when underwater, because mixed gas rebreathers allow very long dives where long decompression stops may be needed: knowing that the rebreather will begin to deliver a poisonous breathing gas in five minutes may not be useful to a diver needing to carry out an hour or more of decompression stops.

Among British naval rebreather divers, this type of carbon dioxide poisoning was called shallow water blackout. Yarn drying after being dyed in the early American tradition, at Conner Prairie living history museum. ... Siebe Gorman Ltd was a British company which developed diving equipment and breathing equipment and worked on commercial diving and underwater salvage projects. ... In electronics, thermocouples are a widely used type of temperature sensor and can also be used as a means to convert thermal potential difference into electric potential difference. ... Hypercapnia is a condition where there is too much carbon dioxide (CO2) in the body. ... A Decompression Stop is a period of time a diver must spend at a constant depth in shallow water at the end of a dive in order safely to eliminate inert gases from the divers body to avoid decompression sickness. ... Air is the most common and only natural breathing gas. ... Hypercapnia is a condition where there is too much carbon dioxide (CO2) in the body. ... Victims go quietly, often unnoticed. ...

Caustic cocktail

Soda lime is caustic and can cause burns to the eyes and skin. A "caustic cocktail" is a mixture of water and soda lime that occurs when the "scrubber" floods. It gives rise to a chalky taste, which should prompt the diver to switch to an alternative source of breathing gas and rinse his or her mouth out with water. Many modern diving rebreather absorbents are designed not to produce "cocktail" if they get wet. The word caustics has several meanings depending upon the context in which it is used: In Greek language, from which this word originates, caustics means to burn or burning. In optics, a caustic is a bundle of light rays. ... Air is the most common and only natural breathing gas. ...

Controlling the mix

A basic need with a rebreather is to keep the amount of oxygen in the mix, or more technically known as the partial pressure of oxygen or ppO₂, from getting too low (causing anoxia or hypoxia) or too high (causing oxygen toxicity). In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. ... Asphyxia is a condition of severely deficient supply of oxygen to the body. ... Hypoxia is a pathological condition in which the body as a whole (generalised hypoxia) or region of the body (tissue hypoxia) is deprived of adequate oxygen supply. ... Oxygen toxicity or oxygen toxicity syndrome is severe hyperoxia caused by breathing oxygen at elevated partial pressures. ...

With humans, the urge to breathe is caused by a build-up of carbon dioxide rather than lack of oxygen. When using a rebreather, carbon dioxide is removed from the breathing gas by the scrubber, suppressing this natural warning. The resulting serious hypoxia causes sudden blackout with little or no warning. This makes hypoxia a deadly problem for rebreather divers. Hypoxia is a pathological condition in which the body as a whole (generalised hypoxia) or region of the body (tissue hypoxia) is deprived of adequate oxygen supply. ...

In many rebreathers the diver can control the gas mix and volume in the loop manually by injecting each of the different available gases to the loop and by venting the loop. The loop often has a pressure relief valve preventing the "hamster cheek" effect on the diver caused by over-pressure of the loop. This article could benefit from improvement in writing style to reach the quality described in the guide to writing the perfect article. ...

In some early rebreathers the diver had to manually open and close the valve to the oxygen cylinder to refill the counter-lung each time. In others the oxygen flow is kept constant by a pressure-reducing flow valve like the valves on blowtorch cylinders; the set also has a manual on/off valve called a bypass. In some modern rebreathers, the pressure in the breathing bag controls the oxygen flow like the demand valve in open-circuit scuba; for example, trying to breathe in from an empty bag makes the cylinder release more gas. Most modern closed-circuit rebreathers have electro-galvanic fuel cell sensors and onboard electronics, which monitor the ppO₂, injecting more oxygen if necessary or issuing an audible warning to the diver if the ppO₂ reaches dangerously high or low levels. The top torch is a welding torch and the bottom is a cutting torch, or blowtorch A blowtorch is a torch used to cut metal. ... SCUBA is an acronym for Self-Contained Underwater Breathing Apparatus. ... An electro-galvanic fuel cell is an electrical device used to measure the concentration of oxygen gas in SCUBA diving and medical equipment. ...

Counterlung

Underwater, the position of the breathing bag, on the chest, over the shoulders, or on the back, has an effect on the ease of breathing. The design of the rebreather also affects the swimming diver's streamlining and thus ease of swimming. In fluid dynamics, a streamline is the path that an imaginary massless particle would make if it followed the flow of a fluid in which it was embedded. ...

For use out of water, this does not matter so much: for example, in an industrial version of the Siebe Gorman Salvus the breathing bag hangs down by the left hip. CGI image: 2 views of a diver wearing a Siebe Gorman Salvus rebreather The Salvus is a light oxygen rebreather for industrial use (including by firemen and in coalmine rescue) or in shallow diving. ...

A rebreather whose counterlung is rubber and not in an enclosed casing, should be sheltered from sunlight when not in use, to prevent the rubber from perishing. Rubber is an elastic hydrocarbon polymer which occurs as a milky emulsion (known as latex) in the sap of several varieties of plants. ... Prism splitting light Sunlight in the broad sense is the total spectrum of electromagnetic radiation given off by the Sun. ... Vulcanization, or curing, of rubber, is a chemical process in which individual polymer molecules are linked to other polymer molecules by atomic bridges. ...

Bailout

Some diving rebreather sets include a bailout regulator allowing the user to bail onto open-circuit using his diluent tank. This lets the diver ascend on a separate gas supply. The majority of rebreather trainers teach students to also carry an open-circuit scuba cylinder and regulator as a separate bailout source. Bailout is a key area of discussion for rebreather diving, as when the depth starts to increase the bailout strategy becomes a crucial part of planning particularly for technical diving. Open circuit can mean: In electronics, where there is nothing connected to a load and no current can flow. ... Technical diving is a form of SCUBA diving that exceeds the scope of recreational diving. ...

Casing

Many rebreathers have their main parts in a hard backpack casing. This casing needs venting to let surrounding water or air in and out to allow for volume changes as the breathing bag inflates and deflates. In a diving rebreather this needs fairly large holes, including a hole at the bottom to drain the water out when the diver comes out of water. The SEFA, which is used for mine rescue, to keep grit and stones out of its working, is completely sealed, except for a large vent panel covered with metal mesh, and holes for the oxygen cylinder's on/off valve and the cylinder pressure gauge. Underwater the casing also serves for streamlining, e.g. in the IDA71 and Cis-Lunar. Mine rescue teams are specialized groups of people who are familiar with procedures used to rescue persons trapped in mines by hazards. ... A mesh is similar to fabric or a web in that it has many connected or weaved pieces. ... In fluid dynamics, a streamline is the path that an imaginary massless particle would make if it followed the flow of a fluid in which it was embedded. ... 3 views of a frogman with IDA rebreather The Russian IDA71 military and naval rebreather is an oxygen rebreather intended for use by naval and military divers. ... The word cis-lunar is Latin for on this side of the moon, not beyond the moon, and may refer to the scuba sets described here, or it may refer generically to space travel. ...

Main rebreather design variants

Oxygen rebreather

This is the oldest type of rebreather and was commonly used by navies from the early twentieth century. The only gas that it supplies is oxygen. As pure oxygen is toxic when inhaled at pressure, oxygen rebreathers are limited to a depth of 6 meters (20 feet); some say 9 meters (30 feet). Oxygen rebreathers are also sometimes used when decompressing from a deep open-circuit dive, as breathing pure oxygen makes the nitrogen diffuse out of the blood more rapidly. The multinational Combined Task Force One Five Zero (CTF-150) The British Grand Fleet, the supreme naval force of World War I A rare occurrence of a 5-country multinational fleet, during Operation Enduring Freedom in the Oman Sea. ... Oxygen toxicity or oxygen toxicity syndrome is severe hyperoxia caused by breathing oxygen at elevated partial pressures. ... A Decompression Stop is a period of time a diver must spend at a constant depth in shallow water at the end of a dive in order safely to eliminate inert gases from the divers body to avoid decompression sickness. ...

In some rebreathers, e.g. the Siebe Gorman Salvus, the oxygen cylinder has two first stages in parallel. One is constant flow; the other is a plain on-off valve called a bypass; both feed into the same exit pipe which feeds the breathing bag. In the Salvus there is no second stage and the gas is turned on and off at the cylinder. Some simple oxygen rebreathers had no constant-flow valve, but only the bypass, and the diver had to operate the valve at intervals to refill the breathing bag as he used the oxygen. CGI image: 2 views of a diver wearing a Siebe Gorman Salvus rebreather The Salvus is a light oxygen rebreather for industrial use (including by firemen and in coalmine rescue) or in shallow diving. ... A gas pressure regulator has one or more valves in series, which let the gas out of a gas cylinder in a controlled way, lowering its pressure at each stage. ... In rebreather breathing sets, a bypass is a hand-operated valve that can be used to let more oxygen (or other breathing gas) into the breathing system, by-passing the cylinders flow rate control valve. ... Inspiration Closed Circuit Diving Rebreather Description A rebreather is a type of breathing equipment that provides a breathing gas containing oxygen and recycles exhaled gas. ...

Semi-closed circuit rebreather

Military and recreational divers use these because they provide good underwater duration with fairly simple and cheap equipment. Semi-closed circuit equipment generally supplies one breathing gas such as air, nitrox or trimix. The gas is injected at a constant rate. Excess gas is constantly vented from the loop in small volumes.

The diver must fill the cylinders with gas mix that has a maximum operating depth that is safe for the depth of the dive being planned. As the amount of oxygen required by the diver increases with work rate, the oxygen injection rate must be carefully chosen and controlled to prevent either oxygen toxicity or unconsciousness in the diver due to hypoxia. In technical diving, the maximum operating depth (MOD) of a breathing gas is the depth at which the partial pressure of oxygen (ppO2) of the gas mix exceeds a safe limit. ... Unconsciousness is the absence of consciousness. ...

Fully closed circuit rebreather

Military, photographic and recreational divers use these because they allow long dives and produce no bubbles. Closed circuit rebreathers generally supply two breathing gases to the loop: one is pure oxygen and the other is a diluent or diluting gas such as air, nitrox or trimix.

The major task of the fully closed circuit rebreather is to control the oxygen concentration, known as the oxygen partial pressure, in the loop and to warn the diver if it is becoming dangerously low or high. The concentration of oxygen in the loop depends on two factors: depth and the proportion of oxygen in the mix. Too low a concentration of oxygen results in hypoxia leading to sudden unconsciousness and ultimately death when the oxygen is exhausted. Too high a concentration of oxygen results in oxygen toxicity, a condition causing convulsions, which when they occur underwater can lead to drowning. In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. ... Death is the full cessation of vital functions in the biological life. ...

In fully automatic closed-circuit systems, a mechanism injects oxygen into the loop when it detects that the partial pressure of oxygen in the loop has fallen below the required level. Often this mechanism is electrical and relies on oxygen sensitive electro-galvanic fuel cells called ppO₂ meters to measure the concentration of oxygen in the loop. The article on electrical energy is located elsewhere. ... An electro-galvanic fuel cell is an electrical device used to measure the concentration of oxygen gas in SCUBA diving and medical equipment. ... A diving breathing gas oxygen analyser consisting of the cylindrical fuel cell connected to the display and calibration box An electro-galvanic fuel cell is an electrical device used to measure the concentration of oxygen gas in scuba diving and medical equipment. ...

The diver may be able to manually control the mixture by adding diluent gas or oxygen. Adding diluent can prevent the loop's gas mixture becoming too oxygen rich. Manually adding oxygen is risky as additional small volumes of oxygen in the loop can easily raise the partial pressure of oxygen to dangerous levels.

Rebreathers whose absorbent releases oxygen

There have been a few rebreather designs (e.g. the Oxylite) which had an absorbent canister filled with potassium superoxide, which gives off oxygen as it absorbs carbon dioxide: 4KO₂ + 2CO₂ = 2K₂CO₃ + 3O₂; it had a very small oxygen cylinder to fill the loop at the start of the dive. This system is dangerous because of the explosively hot reaction that happens if water gets on the potassium superoxide. The Russian IDA71 military and naval rebreather was designed to be run in this mode or as an ordinary rebreather. 3 views of a frogman with IDA rebreather The Russian IDA71 military and naval rebreather is an oxygen rebreather intended for use by naval and military divers. ...

Rebreathers which store their oxygen as liquid oxygen

Aerorlox rebreather in a coalmining museum

If used underwater, the liquid-oxygen tank must be well insulated against heat coming in from the water. As a result, industrial sets of this type may not be suitable for diving, and diving sets of this type may not be suitable for use out of water. They include these types:-

• Aerophor.
• Aerorlox. See http://www.healeyhero.co.uk/rescue/glossary/aerorlox.htm .
• Cryogenic rebreather: see below.

Cryogenic rebreather

There have been plans for a "cryogenic rebreather". It has a tank of liquid oxygen and no absorbent canister. The carbon dioxide is frozen out in a "snow box" by the cold produced as the liquid oxygen expands to gas as the oxygen is used and is replaced from the oxygen tank.

Such a rebreather called the S-1000 was built around or soon after 1960 by Sub-Marine Systems Corporation. It had a duration of 6 hours and a maximum dive depth of 200 meters of salt water. Its ppO₂ could be set to anything from 0.2 bar to 2 bar without electronics, by controlling the temperature of the liquid oxygen, thus controlling the equilibrium pressure of oxygen gas above the liquid. The diluent could be either liquid nitrogen or helium depending on the depth of the dive. The set could freeze out 230 grams of carbon dioxide per hour from the loop, corresponding to an oxygen consumption of 2 liters per minute. If oxygen was consumed faster (high workload), a regular scrubber was needed. See Fischel H., Closed circuit cryogenic SCUBA, "Equipment for the working diver" 1970 symposium, Washington, DC, USA. Marine Technology Society 1970:229-244. Carbon dioxide is an atmospheric gas comprised of one carbon and two oxygen atoms. ...

See also Cushman, L., Cryogenic Rebreather, Skin Diver magazine, June 1969, and reprinted in Aqua Corps magazine, N7, 28, 79.

There are articles on the web about a cryogenic rebreather called Titanic II. These articles are a hoax; some of them include unrealistic technology. A hoax is an attempt to trick an audience into believing that something false is real. ... Unobtainium is a term frequently used to describe any material with properties that are unlikely or impossible for any real material to possess and is hence unobtainable. ...

Other designs

In the Siebe Gorman Proto the absorbent was in a flexible-walled compartment in the bottom of the breathing bag and not in a canister. The Proto is a type of rebreather that was made by Siebe Gorman. ...

Risks and precautions with rebreather diving

Many diver training organizations teach the "diluent flush" technique as a safe way to restore the mix in the loop to a level of oxygen that is neither too high nor too low. It only works when partial pressure of oxygen in the diluent alone would not cause hypoxia or hyperoxia, such as when using a normoxic diluent and observing the diluent's maximum operating depth. The technique involves simultaneously venting the loop and injecting diluent. This flushes out the old mix and replaces it with a known proportion of oxygen from the diluent. This page lists SCUBA diver training organizations. ... In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. ... Hypoxia is a pathological condition in which the body as a whole (generalised hypoxia) or region of the body (tissue hypoxia) is deprived of adequate oxygen supply. ... Wikipedia does not have an article with this exact name. ... Trimix is a breathing gas, consisting of oxygen, helium and nitrogen, and is often used during the deep phase of dives carried out using Technical diving techniques. ... In technical diving, the maximum operating depth (MOD) of a breathing gas is the depth at which the partial pressure of oxygen (ppO2) of the gas mix exceeds a safe limit. ...

Divers using oxygen rebreathers are advised to flush the system when they start the dive, to get surplus nitrogen out of the system.

In addition to the other diving disorders suffered by divers, rebreather divers are also more susceptible to: Divers face specific physical and health risks when they go underwater (e. ...

• Sudden blackout due to hypoxia caused by too low a partial pressure of oxygen in the loop. A particular problem when using a closed circuit rebreather is the drop in ambient pressure caused by the ascent phase of the dive, which reduces the partial pressure of oxygen to hypoxic levels leading to what is sometimes called deep water blackout.
• Seizures due to oxygen toxicity caused by too high a partial pressure of oxygen in the loop. This can be caused by the rise in ambient pressure caused by the descent phase of the dive, which raises the partial pressure of oxygen to hyperoxic levels. In fully closed circuit equipment, aging oxygen sensors may become "current limited" and fail to measure high partial pressures of oxygen resulting in dangerously high oxygen levels.
• Disorientation, panic, headache, and hyperventilation due to excess of carbon dioxide caused by incorrect configuration, failure or inefficiency of the scrubber. The scrubber must be configured so that no exhaled gas can bypass it; it must be packed and sealed correctly. Another problem is the diver producing carbon dioxide faster than the absorbent can handle, for example, during hard work or fast swimming. The solution to this is to slow down and let the absorbent catch up. The scrubber efficiency may be reduced at depth where the increased concentration of other gas molecules, due to pressure, stops all the carbon dioxide molecules reaching the active ingredient of the scrubber.
• The rebreather diver must keep breathing in and out all the time, to keep the exhaled gas flowing over the carbon dioxide absorbent, so the absorbent can work all the time. Divers need to lose any air conservation habits that may have been developed while diving with open-circuit scuba. In closed circuit rebreathers, this also has the advantage of mixing the gases preventing oxygen-rich and oxygen-lean spaces developing within the loop, which may give inaccurate readings to the oxygen control system.
• "Caustic cocktail" in the loop if water comes into contact with the soda lime used in the carbon dioxide scrubber. The diver is normally alerted to this by a chalky taste in the mouth. A safe response is to bail out to "open circuit" and rinse the mouth out.

When compared with Aqua-Lungs, rebreathers have some disadvantages including expense, complexity of operation and maintenance and fewer failsafes. A malfunctioning rebreather can supply a gas mixture which cannot sustain life. Various rebreathers try to solve these problems by montoring the system with electronics, sensors and alarm systems. Many very competent divers have died using rebreathers in accidents, which are often put down to operator error. Rebreathers are generally considered safer in extreme conditions such as deep dives (75m = 246 feet or more) or overhead environments, as they reduce the risk of running out of breathable gas. In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. ... Latent hypoxia hits on ascent A deep water blackout is a loss of consciousness caused by cerebral hypoxia on ascending from a deep freedive or breath-hold dive, typically of ten metres or more when the swimmer does not necessarily experience an urgent need to breathe and has no other... This article is about the medical term, epileptic seizure, as distinct from psychogenic non-epileptic seizure. ... Oxygen toxicity or oxygen toxicity syndrome is severe hyperoxia caused by breathing oxygen at elevated partial pressures. ... An electro-galvanic fuel cell is an electrical device used to measure the concentration of oxygen gas in SCUBA diving and medical equipment. ... Panic is a sudden fear which dominates thinking and often affects groups of people or animals. ... A headache (medically known as cephalalgia) is a condition of pain in the head; sometimes neck or upper back pain may also be interpreted as a headache. ... In medicine, hyperventilation (or hyperpnea) is the state of breathing faster or deeper (hyper) than necessary, and thereby reducing the carbon dioxide concentration of the blood below normal. ... Hypercapnia (from the Greek hyper = above and kapnos = smoke) is a condition where there is too much carbon dioxide (CO2) in the body. ... Soda lime is a mixture of chemicals, used in granular form in closed breathing environments, such as general anaesthesia, submarines, rebreathers and recompression chambers, to remove carbon dioxide from breathing gases to prevent CO2 retention and carbon dioxide poisoning. ... Open circuit can mean: In electronics, where there is nothing connected to a load and no current can flow. ... SCUBA is an acronym for Self-Contained Underwater Breathing Apparatus. ... Soda lime is a mixture of chemicals, used in granular form in closed breathing environments, such as general anaesthesia, submarines, rebreathers and recompression chambers, to remove carbon dioxide from breathing gases to prevent CO2 retention and carbon dioxide poisoning. ... Carbon dioxide is an atmospheric gas comprised of one carbon and two oxygen atoms. ... ... The term Fail-safe is used to describe: A device which, if (or when) it fails, fails in a way that will cause no harm or at least a minimum of harm to other devices or danger to personnel. ... In scuba diving, an Overhead environment is a situation where there is not open water overhead, and thus the diver in an emergency cannot escape upwards to atmosphere if his breathing set malfunctions. ...

The bailout requirement of rebreather diving can sometimes also require a rebreather diver to carry almost as much bulk of cylinders as an open-circuit diver so the diver can complete the necessary decompression stops if the rebreather fails completely. Some rebreather divers prefer not to carry enough bailout for a safe ascent breathing open circuit, but instead rely on the rebreather, believing that an irrecoverable rebreather failure is very unlikely. This practice is known as alpinism or alpinist diving and is generally maligned due to the perceived extremely high risk of death if the rebreather fails. Inspiration closed circuit diving rebreather A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycles exhaled gas. ... 12 litre and 3 litre steel diving cylinders A diving cylinder or SCUBA tank is used to store and transport high pressure breathing gas as a component of an Aqua-Lung. ... A Decompression Stop is a period of time a diver must spend at a constant depth in shallow water at the end of a dive in order safely to eliminate inert gases from the divers body to avoid decompression sickness. ...

Innovations in recreational diving rebreather technology

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 elecronics 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. [2]
• 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. [3]
• 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. [4]
• 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. [5]

An electro-galvanic fuel cell is an electrical device used to measure the concentration of oxygen gas in SCUBA diving and medical equipment. ... In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. ... Hypercapnia is a condition where there is too much carbon dioxide (CO2) in the body. ... A Decompression Stop is a period of time a diver must spend at a constant depth in shallow water at the end of a dive in order safely to eliminate inert gases from the divers body to avoid decompression sickness. ... Soda lime is a mixture of chemicals, used in granular form in closed breathing environments, such as general anaesthesia, submarines, rebreathers and recompression chambers, to remove carbon dioxide from breathing gases to prevent CO2 retention and carbon dioxide poisoning. ...

Some makes of rebreather

• The Davis Submerged Escape Apparatus was the first or nearly the first rebreather to be made in quantity.
• The "Universal" rebreather was a long-dive derivative of the Davis Submerged Escape Apparatus, intended to be used with the Sladen Suit, which see for more information about it.
• Russian IDA71 military and naval rebreather
• Siebe Gorman CDBA: see there also for CDMBA, SCBA, SCMBA, UBA
• Siebe Gorman Salvus
• The Savox was made by Siebe Gorman. See this link and the image at this link. 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 is made by the diving gear makers Aqualung: see this link for more information.
• Sport diving mixture rebreathers made by Ambient Pressure Diving:-
  • Inspiration: also see http://www.therebreathersite.nl/menu_inspiration_info.htm
  • Evolution

The Davis Submerged Escape Apparatus (also referred to as DSEA), is an early make of oxygen rebreather invented in 1910 by Sir Robert Davis, head of Messrs. ... The Davis Submerged Escape Apparatus (also referred to as DSEA), is an early make of oxygen rebreather invented in 1910 by Sir Robert Davis, head of Messrs. ... The Sladen Suit was a heavy type of British divers drysuit made by Siebe Gorman. ... 3 views of a frogman with IDA rebreather The Russian IDA71 military and naval rebreather is an oxygen rebreather intended for use by naval and military divers. ... The Siebe Gorman CDBA from three angles The Clearance Divers Breathing Apparatus (CDBA) is a type of rebreather made by Siebe Gorman in England. ... CGI image: 2 views of a diver wearing a Siebe Gorman Salvus rebreather The Salvus is a light oxygen rebreather for industrial use (including by firemen and in coalmine rescue) or in shallow diving. ... Siebe Gorman Ltd was a British company which developed diving equipment and breathing equipment and worked on commercial diving and underwater salvage projects. ... The Blacketts 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. ... Typical decal used on scuba cylinders containing Nitrox Nitrox is a breathing gas consisting of oxygen and nitrogen (similar to air), but with a higher proportion of oxygen than the normal 20. ... Chuquicamata, the largest open pit copper mine in the world, Chile. ... The SDBA is a type of frogmans rebreather breathing set. ... Typical decal used on scuba cylinders containing Nitrox Nitrox is a breathing gas consisting of oxygen and nitrogen (similar to air), but with a higher proportion of oxygen than the normal 20. ... // This page describes a type of scuba diver. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance transparent (gas) very pale blue (liquid) Atomic mass 15. ...

External links

Diving rebreather manufacturers

• Ambient Pressure Diving - maker of the Inspiration and Evolution rebreathers
• Cis-Lunar - made closed-circuit automatic rebreathers, now operated by Juergensen Marine.
• Divematics - maker of the Shadow Pac II rebreather
• Divex Ltd - manufacturer of several military semi-closed and closed circuit rebreathers.
• Drager - maker of various semi-closed circuit rebreathers
• Halcyon - maker of a semi-closed circuit rebreather
• Jetsam - maker of the KISS rebreather
• Megalodon & Mini Meg - The Megalodon Expedition class rebreather
• Rebreather US - The Juergensen Marine Hammerhead Electronic System
• Rebreathers Australia - maker of the Abyss and Stingray closed circuit rebreathers
• Siebe Gorman, see also Siebe Gorman. Important in diving history, but now closed down.
• Steam Machines - Prism rebreathers
• Submatix Rebreather - manufacturer of the Submatix SCR 100 ST
• O.M.G. Italy - manufacturer of the AZIMUTH and many military rebreathers.

The word cis-lunar is Latin for on this side of the moon, not beyond the moon, and may refer to the scuba sets described here, or it may refer generically to space travel. ... Siebe Gorman Ltd was a British company which developed diving equipment and breathing equipment and worked on commercial diving and underwater salvage projects. ...

Other information sources

• Rebreather Scuba Diving Rebreather world contains further information on rebreathers. The site includes a Rebreather library and Rebreather Forums, and Rebreather Trips, Vacations, and Holidays.
• Richard Pyle's rebreather page
• Rebreather Forums Largest Rebreather Forums on the net
• The Rebreather Site Long list of types of rebreathers (including nitrox) at "database on oxygen rebreathers".
• Diver Dave's site. It has many detailed photographs of rebreathers and their components.
• Karl Kramer's site (more history)
• British Sub-Aqua Club - BSAC Technical Diving Resource Centre
• Shallow Water Blackout
• Some photos of various Soviet-Russian rebreathers (text in Russian)
• 100 Dollar Rebreather - Rebreather built from a hot water bottle
• Teknosofen homepage - General rebreather theory and rebreather tear-downs
• Links to images of old and modern Russian rebreathers
• Page in Russian describing the images at the previous link. (Click each thumbnail to get a fullsized image).