A rebreather is a breathing apparatus that absorbs the
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
of a user's
exhaled breath to permit the rebreathing (recycling) of the substantially unused
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
content, and unused inert content when present, of each breath. Oxygen is added to replenish the amount metabolised by the user. This differs from open-circuit breathing apparatus, where the exhaled gas is discharged directly into the environment. The purpose is to extend the breathing endurance of a limited gas supply, and, for covert military use by
frogmen
A frogman is someone who is trained in scuba diving or swimming underwater in a tactical capacity that includes military, and in some European countries, police work. Such personnel are also known by the more formal names of combat diver, comb ...
or observation of underwater life, eliminating the bubbles produced by an open circuit system and in turn not scaring wildlife being filmed. A rebreather is generally understood to be a portable unit carried by the user. The same technology on a vehicle or non-mobile installation is more likely to be referred to as a
life-support system
A life-support system is the combination of equipment that allows survival in an environment or situation that would not support that life in its absence. It is generally applied to systems supporting human life in situations where the outsid ...
.
Rebreather technology may be used where
breathing gas
A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed h ...
supply is limited, such as underwater or in space, where the environment is toxic or
hypoxic
Hypoxia means a lower than normal level of oxygen, and may refer to:
Reduced or insufficient oxygen
* Hypoxia (environmental), abnormally low oxygen content of the specific environment
* Hypoxia (medical), abnormally low level of oxygen in the tis ...
, as in firefighting, mine rescue and high-altitude operations, or where the breathing gas is specially enriched or contains expensive components, such as helium diluent or anaesthetic gases.
Rebreathers are used in many environments: Underwater, diving rebreathers are a type of
self-contained underwater breathing apparatus
A scuba set, originally just scuba, is any breathing apparatus that is entirely carried by an underwater diver and provides the diver with breathing gas at the ambient pressure. ''Scuba'' is an anacronym for self-contained underwater breathing ...
which have provisions for both a primary and emergency gas supply. On land they are used in
industrial applications where poisonous gases may be present or oxygen may be absent,
firefighting
Firefighting is the act of extinguishing or preventing the spread of unwanted fires from threatening human lives and destroying property and the environment. A person who engages in firefighting is known as a firefighter.
Firefighters typically ...
, where firefighters may be required to operate in an atmosphere immediately dangerous to life and health for extended periods, in hospital
anaesthesia breathing systems to supply controlled concentrations of anaesthetic gases to patients without contaminating the air that the staff breathe, and at high altitude, where the
partial pressure
In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas ...
of oxygen is low, for high altitude mountaineering. In aerospace there are applications in unpressurised aircraft and for high altitude parachute drops, and above the earth's atmosphere, in
space suit
A space suit or spacesuit is a garment worn to keep a human alive in the harsh environment of outer space, vacuum and temperature extremes. Space suits are often worn inside spacecraft as a safety precaution in case of loss of cabin pressure, ...
s for
extra-vehicular activity
Extravehicular activity (EVA) is any activity done by an astronaut in outer space outside a spacecraft. In the absence of a breathable Earthlike atmosphere, the astronaut is completely reliant on a space suit for environmental support. EVA inc ...
. Similar technology is used in
life-support system
A life-support system is the combination of equipment that allows survival in an environment or situation that would not support that life in its absence. It is generally applied to systems supporting human life in situations where the outsid ...
s in submarines, submersibles,
atmospheric diving suits
An atmospheric diving suit (ADS) is a small one-person articulated submersible which resembles a suit of armour, with elaborate pressure joints to allow articulation while maintaining an internal pressure of one atmosphere. An ADS can enable di ...
, underwater and surface
saturation
Saturation, saturated, unsaturation or unsaturated may refer to:
Chemistry
* Saturation, a property of organic compounds referring to carbon-carbon bonds
**Saturated and unsaturated compounds
** Degree of unsaturation
**Saturated fat or fatty aci ...
habitats, spacecraft, and space stations, and in
gas reclaim system
Saturation diving is diving for periods long enough to bring all tissues into equilibrium with the partial pressures of the inert components of the breathing gas used. It is a diving mode that reduces the number of decompressions divers working ...
s used to recover the large volumes of helium used in
saturation diving
Saturation diving is diving for periods long enough to bring all tissues into equilibrium with the partial pressures of the inert components of the breathing gas used. It is a diving mode that reduces the number of decompressions divers working ...
.
The recycling of breathing gas comes at the cost of technological complexity and specific hazards, some of which depend on the application and type of rebreather used. Mass and bulk may be greater or less than open circuit depending on circumstances. Electronically controlled diving rebreathers may
automatically maintain a
partial pressure
In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas ...
of oxygen between programmable upper and lower limits, or set points, and be integrated with
decompression computer
A dive computer, personal decompression computer or decompression meter is a device used by an underwater diver to measure the elapsed time and depth during a dive and use this data to calculate and display an ascent profile which according to t ...
s to monitor the
decompression status
The practice of decompression by divers comprises the planning and monitoring of the profile indicated by the algorithms or tables of the chosen decompression model, to allow asymptomatic and harmless release of excess inert gases dissolved in ...
of the diver and record the
dive profile
A dive profile is a description of a diver's pressure exposure over time. It may be as simple as just a depth and time pair, as in: "sixty for twenty," (a bottom time of 20 minutes at a depth of 60 feet) or as complex as a second by second grap ...
.
General concept
As a person breathes, the body consumes
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
and produces
carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
.
Base metabolism requires about 0.25 L/min of oxygen from a
breathing rate
The respiratory rate is the rate at which breathing occurs; it is set and controlled by the respiratory center of the brain. A person's respiratory rate is usually measured in breaths per minute.
Measurement
The respiratory rate in humans is mea ...
of about 6 L/min, and a fit person working hard may ventilate at a rate of 95 L/min but will only metabolise about 4 L/min of oxygen
The oxygen metabolised is generally about 4% to 5% of the inspired volume at normal
atmospheric pressure
Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, 7 ...
, or about 20% of the available oxygen in the
air
The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...
at
sea level
Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardised g ...
. Exhaled air at sea level contains roughly 13.5% to 16% oxygen.
The situation is even more wasteful of oxygen when the
oxygen fraction
Fraction of inspired oxygen (''FI''O2), corrected denoted with a capital "I", is the molar or volumetric fraction of oxygen in the inhaled gas. Medical patients experiencing difficulty breathing are provided with oxygen-enriched air, which means a ...
of the
breathing gas
A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed h ...
is higher, and in underwater diving, the
compression
Compression may refer to:
Physical science
*Compression (physics), size reduction due to forces
*Compression member, a structural element such as a column
*Compressibility, susceptibility to compression
*Gas compression
*Compression ratio, of a c ...
of breathing gas due to depth makes the recirculation of exhaled gas even more desirable, as an even larger proportion of open circuit gas is wasted. Continued rebreathing of the same gas will deplete the oxygen to a level which will no longer support consciousness, and eventually life, so gas containing oxygen must be added to the breathing gas to maintain the required concentration of oxygen.
However, if this is done without removing the carbon dioxide, it will rapidly build up in the recycled gas, resulting almost immediately in mild respiratory distress, and rapidly developing into further stages of
hypercapnia
Hypercapnia (from the Greek ''hyper'' = "above" or "too much" and ''kapnos'' = "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous pro ...
, or carbon dioxide toxicity.
A high ventilation rate is usually necessary to eliminate the metabolic product carbon dioxide (CO
2). The
breathing reflex is triggered by CO
2 concentration in the blood, not by the oxygen concentration, so even a small buildup of CO
2 in the inhaled gas quickly becomes intolerable; if a person tries to directly rebreathe their exhaled breathing gas, they will soon feel an acute sense of
suffocation
Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects primarily the tissues and organs. There are many circumstances that can i ...
, so rebreathers must remove the CO
2 in a component known as a
carbon dioxide scrubber
A carbon dioxide scrubber is a piece of equipment that absorbs carbon dioxide (CO2). It is used to treat exhaust gases from industrial plants or from exhaled air in life support systems such as rebreathers or in spacecraft, submersible craft or a ...
.
By adding sufficient oxygen to compensate for the metabolic usage, removing the carbon dioxide, and rebreathing the gas, most of the volume is conserved.
Architecture
![Rebreather architecture](https://upload.wikimedia.org/wikipedia/commons/6/6f/Rebreather_architecture.png)
There are two basic arrangements controlling the flow of breathing gas inside the rebreather, known as the pendulum and loop systems.
Pendulum
In the pendulum configuration, the user inhales gas from the counterlung through a breathing hose, and exhaled gas returns to the counter lung by flowing back through the same hose. The scrubber is usually between the breathing hose and the counterlung bag, and gas flow is bi-directional. All of the flow passages between the user and the active absorbent in the scrubber are
dead space
''Dead Space'' is a science fiction/horror fiction, horror media franchise created by Glen Schofield and Michael Condrey, developed by Visceral Games, and published and owned by Electronic Arts. The franchise's chronology is not presented in a lin ...
– volume containing gas which is rebreathed without modification by the rebreather. The dead space increases as the absorbent is depleted. Breathing hose volume must be minimised to limit dead space.
Loop
In the loop configuration, the user inhales gas through one hose, and exhales through a second hose. Exhaled gas flows into the scrubber from one side, and exits at the other side. There may be one large counterlung, on either side of the scrubber, or two smaller counterlungs, one on each side of the scrubber. Flow is in one direction, enforced by non-return valves, which are usually in the breathing hoses where they join the mouthpiece. Only the flow passage in the mouthpiece before the split between inhalation and exhalation hoses is dead space, and this is not affected by hose volume.
Components
![2009](https://upload.wikimedia.org/wikipedia/commons/2/2d/2009._%D0%94%D0%BE%D0%BD%D0%B5%D1%86%D0%BA_012.jpg)
There are some components that are common to almost all personal portable rebreathers. These include the ambient pressure breathing volume components, usually called the breathing loop in a circulating flow rebreather, and the make-up gas supply and control system.
Counterlung
The counterlung is an airtight bag of strong flexible material that holds the volume of the exhaled gas until it is inhaled again. There may be a single counterlung, or one on each side of the scrubber, which allows a more even flow rate of gas through the scrubber, which can reduce
work of breathing
Work of breathing (WOB) is the energy expended to inhale and exhale a breathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not partic ...
and improve scrubber efficiency by a more consistent .
Scrubber
The scrubber is a container that has an inlet on one side and an outlet on the other side, filled with carbon dioxide absorbent material, mostly
strong bases, through which the exhaled gas passes to remove the carbon dioxide. The absorbent may be granular or in the form of a moulded cartridge.
Granular sorb may be manufactured by breaking up lumps of lime and sorting the granules by size, or by moulding granules at a consistent size and shape.
Gas flow through the scrubber may be in one direction in a loop rebreather, or both ways in a pendulum rebreather.
A typical absorbent is Sodalime, which is made up of calcium hydroxide Ca(OH)
2, potassium hydroxide KOH, and/or sodium hydroxide NaOH. (Either or both of these may be present). The main component of soda lime is calcium hydroxide, which is relatively cheap and easily available. Other components may be present in the absorbent. Sodium hydroxide is added to accelerate the reaction with carbon dioxide. Other chemicals may be added to prevent unwanted decomposition products when used with standard halogenated inhalation anaesthetics. An
indicator
Indicator may refer to:
Biology
* Environmental indicator of environmental health (pressures, conditions and responses)
* Ecological indicator of ecosystem health (ecological processes)
* Health indicator, which is used to describe the health o ...
may be included to show when carbon dioxide has dissolved in the water of the soda lime and formed carbonic acid, changing the pH from basic to acid, as the change of colour shows that the absorbent has reached saturation with carbon dioxide and must be changed.
The carbon dioxide combines with water or water vapor to produce a weak carbonic acid: CO
2 + H
2O –> H2CO
3. This reacts with the hydroxides to produce carbonates and water in an exothermic reaction:
In the intermediate reaction, the carbonic acid reacts exothermically with sodium hydroxide to form sodium carbonate and water: H
2CO
3 + 2NaOH –> Na
2CO
3 + 2H
2O + heat. In the final reaction, the sodium carbonate reacts with the slaked lime (calcium hydroxide) to form calcium carbonate and sodium hydroxide:: H
2CO
3 + Ca(OH)
2 –> CaCO
3 + 2H
2O. The sodium hydroxide is then available again to react with more carbonic acid.
of this absorbent can remove about of carbon dioxide at standard atmospheric pressure
This process also heats and humidifies the air, which is desirable for diving in cold water, or climbing at high altitudes, but not for working in hot environments.
Other reactions may be used in special circumstances.
Lithium hydroxide
Lithium hydroxide is an inorganic compound with the formula LiOH. It can exist as anhydrous or hydrated, and both forms are white hygroscopic solids. They are soluble in water and slightly soluble in ethanol. Both are available commercially. While ...
and particularly
lithium peroxide
Lithium peroxide is the inorganic compound with the formula Li2 O2. It is a white, nonhygroscopic solid. Because of its high oxygen:mass and oxygen:volume ratios, the solid has been used to remove CO2 from the atmosphere in spacecraft.
Preparat ...
may be used where low mass is important, such as in space stations and space suits. Lithium peroxide also replenishes the oxygen during the scrubbing reaction.
Another method of carbon dioxide removal occasionally used in portable rebreathers is to freeze it out, which is possible in a cryogenic rebreather which uses liquid oxygen. The liquid oxygen absorbs heat from the carbon dioxide in a heat exchanger to convert the oxygen to gas, which is sufficient to freeze the carbon dioxide. This process also chills the gas, which is sometimes, but not always, desirable.
Breathing hoses
![Draeger Ray DSV and breathing hoses P5167633](https://upload.wikimedia.org/wikipedia/commons/1/15/Draeger_Ray_DSV_and_breathing_hoses_P5167633.JPG)
A breathing hose or sometimes ''breathing tube'' on a rebreather is a flexible tube for breathing gas to pass through at ambient pressure. They are distinguished from the low-, intermediate-, and high-pressure hoses which may also be parts of rebreather apparatus. They have a wide enough bore to minimise flow resistance at the ambient pressure in the operational range for the equipment, are usually circular in cross section, and may be corrugated to let the user's head move about without the tube collapsing at kinks.
Each end has an airtight connection to the adjacent component, and they may contain a
one-way valve
A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid ( liquid or gas) to flow through it in only one direction.
Check valves are two-port valves, meaning they have ...
to keep the gas circulating the right way in a loop system. Depending on the service, they may be made of a flexible polymer, an
elastomer
An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic p ...
, a fibre or cloth reinforced elastomer, or elastomer covered with a woven fabric for reinforcement or abrasion resistance. If the woven layer is bonded to the outside surface it protects the rubber from damage from scrapes but makes it more difficult to wash off contaminants.
Breathing hoses are usually long enough to connect the apparatus to the user's head in all attitudes of their head, but should not be unnecessarily long, which will cause additional weight,
hydrodynamic drag
In fluid dynamics, drag (sometimes called air resistance, a type of friction, or fluid resistance, another type of friction or fluid friction) is a force acting opposite to the relative motion of any object moving with respect to a surrounding flu ...
, risk snagging on things, or contain excess
dead space
''Dead Space'' is a science fiction/horror fiction, horror media franchise created by Glen Schofield and Michael Condrey, developed by Visceral Games, and published and owned by Electronic Arts. The franchise's chronology is not presented in a lin ...
in a pendulum rebreather. Breathing hoses can be tethered down to a diver's shoulders or ballasted for neutral buoyancy to minimise loads on the mouthpiece.
Mouthpiece or facemask
A
mouthpiece with bite-grip, an
oro-nasal mask
An orinasal mask, oro-nasal mask or oral-nasal mask is a Breathing mask (disambiguation), breathing mask that covers the mouth and the nose only. It may be a complete independent item, as an oxygen mask, or on some anaesthetic apparatuses, or it ...
, a
full-face mask
A full-face diving mask is a type of diving mask that seals the whole of the diver's face from the water and contains a mouthpiece, demand valve or constant flow gas supply that provides the diver with breathing gas. The full face mask ha ...
, or a sealed helmet is provided so that the user can breath from the unit hands-free.
Oxygen supply
A store of oxygen, usually in a high pressure cylinder, but sometimes as liquid oxygen, that feeds gaseous oxygen into the ambient pressure breathing volume, either continuously, or when the user operates the oxygen addition valve, or via a demand valve in an oxygen rebreather, when the volume of gas in the breathing circuit becomes low and the pressure drops, or in an electronically controlled mixed gas rebreather, after a sensor has detected insufficient oxygen partial pressure, and activates a solenoid valve.
Valves
Valves are needed to control gas flow in the breathing volume, and gas feed from the storage container. They include:
* Non-return valves in the breathing loop of loop rebreathers, which enforce one-directional flow to minimise dead space,
* Dive/surface valves on diving rebreathers, which prevent water from entering the breathing volume when the mouthpiece is removed, or the user elects to breathe ambient air at the surface.
* Gas supply valves, including a cylinder valve, to allow high pressure gas to flow from the cylinder. This may be manually operated by the user to directly supply make-up gas, or may provide the gas to a pressure regulator which reduces the pressure to a few bar above ambient pressure, and supplies this intermediate pressure gas to the gas feed system, which may contain one or more of:
** Manually operated feed valve,
** Constant mass flow orifice or needle valve, to provide a continuous feed,
** Demand valve which automatically adds gas when the volume of the counterlung(s) is too low, and pressure in the breathing volume drops below ambient pressure.
* Overpressure valve, to release excess gas. This is mainly used in diving rebreathers to compensate for expansion during ascent. Excess gas may also be vented past the skirt seal of a full-face mask, or through the nose when a mouthpiece is used.
Oxygen sensors
Oxygen sensors may be used to monitor partial pressure of oxygen in mixed gas rebreathers to ensure that it does not fall outside the safe limits, but are generally not used on oxygen rebreathers, as the oxygen content is fixed at 100%, and its partial pressure varies only with the ambient pressure.
System variants
Rebreathers can be primarily categorised as diving rebreathers, intended for hyperbaric use, and other rebreathers used at pressures from slightly more than normal atmospheric pressure at sea level to significantly lower ambient pressure at high altitudes and in space. Diving rebreathers must often deal with the complications of avoiding hyperbaric oxygen toxicity, while normobaric and hypobaric applications can use the relatively trivially simple oxygen rebreather technology, where there is no requirement to monitor oxygen partial pressure during use providing the ambient pressure is sufficient.
Oxygen rebreathers
![Aa proto1](https://upload.wikimedia.org/wikipedia/commons/c/c9/Aa_proto1.jpg)
This is the earliest type of rebreather and was commonly used by
navies
A navy, naval force, or maritime force is the branch of a nation's armed forces principally designated for naval and amphibious warfare; namely, lake-borne, riverine, littoral, or ocean-borne combat operations and related functions. It includ ...
for submarine escape and shallow water diving work, for mine rescue, high altitude mountaineering and flight, and in industrial applications from the early twentieth century. Oxygen rebreathers can be remarkably simple and mechanically reliable, and they were invented before open-circuit scuba. They only supply oxygen, so there is no requirement to control the gas composition other than removing the carbon dioxide.
Oxygen feed options
In some rebreathers the oxygen cylinder has oxygen supply mechanisms in parallel. One is
constant flow; the other is a manual on-off valve called a bypass valve; both feed into the same hose which feeds the
counterlung
A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. Oxygen is ...
.
Others are supplied via a demand valve on the counterlung. This will add gas at any time that the counterlung is emptied and the diver continues to inhale. Oxygen can also be added manually by a button which activates the demand valve.
Some simple oxygen rebreathers had no automatic supply system, but only the manual feed valve, and the diver had to operate the valve at intervals to refill the breathing bag as the volume of oxygen decreased below a comfortable level.
Mixed gas rebreathers
![Agnes Milowka by J Axford](https://upload.wikimedia.org/wikipedia/commons/8/83/Agnes_Milowka_by_J_Axford.jpg)
All rebreathers other than oxygen rebreathers may be considered mixed gas rebreathers, as the breathing gas is a mixture of oxygen and metabolically inactive diluent gas. These can be divided into semi-closed circuit, where the supply gas is a breathable mixture containing oxygen and inert diluents, usually nitrogen and helium, and which is replenished by adding more of the mixture as the oxygen is used up, sufficient to maintain a breathable partial pressure of oxygen in the loop, and closed circuit rebreathers, where two parallel gas supplies are used: the diluent, to provide the bulk of the gas, and which is recycled, and oxygen, which is metabolically expended. Carbon dioxide is considered a waste product, and in a correctly functioning rebreather, is effectively removed when the gas passes through the scrubber.
Rebreathers using an absorbent that releases oxygen
![IDA-71 with lid of casing opened showing interior P5167777](https://upload.wikimedia.org/wikipedia/commons/2/23/IDA-71_with_lid_of_casing_opened_showing_interior_P5167777.JPG)
There have been a few rebreather designs (e.g. the Oxylite) which use
potassium superoxide
Potassium superoxide is an inorganic compound with the formula KO2. It is a yellow paramagnetic solid that decomposes in moist air. It is a rare example of a stable salt of the superoxide anion. It is used as a scrubber, dehumidifier, and gen ...
, which gives off oxygen as it absorbs carbon dioxide, as the carbon dioxide absorbent: 4KO
2 + 2CO
2 = 2K
2CO
3 + 3O
2. A small volume oxygen cylinder is needed to fill and purge the loop at the start of the dive.
This technology may be applied to both oxygen and mixed gas rebreathers, and can be used for diving and other applications.
Rebreathers which use liquid oxygen
![Aa aerorlox1](https://upload.wikimedia.org/wikipedia/commons/8/88/Aa_aerorlox1.jpg)
A liquid oxygen supply can be used for oxygen or mixed gas rebreathers. If used underwater, the liquid-oxygen container must be well insulated against heat transfer from the water. 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 due to conflicting heat transfer requirements. The set's liquid oxygen tank must be filled immediately before use. Examples of the type include:
*
Blackett's Aerophor
*
Aerorlox
Cryogenic rebreather
A cryogenic rebreather removes the carbon dioxide by freezing it out in a "snow box" by the low temperature produced as liquid oxygen evaporates to replace the oxygen used.
Fields of application
*
Underwater – as a
self-contained breathing apparatus
A self-contained breathing apparatus (SCBA), sometimes referred to as a compressed air breathing apparatus (CABA) or simply breathing apparatus (BA), is a device worn to provide breathable air in an atmosphere that is immediately dangerous to ...
, where it is sometimes known as "closed circuit
scuba
Scuba may refer to:
* Scuba diving
** Scuba set, the equipment used for scuba (Self-Contained Underwater Breathing Apparatus) diving
* Scuba, an in-memory database developed by Facebook
* Submillimetre Common-User Bolometer Array, either of two in ...
" as opposed to "open circuit scuba" where the diver exhales breathing gas into the surrounding water.
Surface-supplied diving
Surface-supplied diving is diving using equipment supplied with breathing gas using a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell. This is different from scub ...
equipment may incorporate rebreather technology either as a
gas reclaim system
Saturation diving is diving for periods long enough to bring all tissues into equilibrium with the partial pressures of the inert components of the breathing gas used. It is a diving mode that reduces the number of decompressions divers working ...
, where the
surface-supplied breathing gas is returned and scrubbed at the surface, or as a carried by the diver.
Rebreathers may also be used as self-contained
diver bailout systems for either scuba or surface-supplied diving.
*
Mine rescue
Mine rescue or mines rescue is the specialised job of rescuing miners and others who have become trapped or injured in underground mines because of mining accidents, roof falls or floods and disasters such as explosions.
Background
Mining law ...
and other
industrial applications – where poisonous gases may be present or oxygen may be absent.
*
Fire fighting
Firefighting is the act of extinguishing or preventing the spread of unwanted fires from threatening human lives and destroying property and the environment. A person who engages in firefighting is known as a firefighter.
Firefighters typicall ...
, where personnel may be required to operate in an atmosphere immediately dangerous to life and health for longer periods than open-circuit
Self-contained breathing apparatus
A self-contained breathing apparatus (SCBA), sometimes referred to as a compressed air breathing apparatus (CABA) or simply breathing apparatus (BA), is a device worn to provide breathable air in an atmosphere that is immediately dangerous to ...
(SCBA) can provide air.
*Crewed
spacecraft
A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...
and
space suit
A space suit or spacesuit is a garment worn to keep a human alive in the harsh environment of outer space, vacuum and temperature extremes. Space suits are often worn inside spacecraft as a safety precaution in case of loss of cabin pressure, ...
s –
outer space
Outer space, commonly shortened to space, is the expanse that exists beyond Earth and its atmosphere and between celestial bodies. Outer space is not completely empty—it is a near-perfect vacuum containing a low density of particles, pred ...
is, effectively, a
vacuum
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...
without oxygen to support life.
*
Himalayan or high-altitude mountaineering. High altitude reduces the partial pressure of oxygen in the ambient air, which reduces the ability of the climber to function effectively. Mountaineering rebreathers are closed-circuit oxygen sets that provide a higher partial pressure of oxygen to the climber than the ambient air.
*Medical
anaesthesia
Anesthesia is a state of controlled, temporary loss of sensation or awareness that is induced for medical or veterinary purposes. It may include some or all of analgesia (relief from or prevention of pain), paralysis (muscle relaxation), am ...
breathing systems – to supply controlled concentrations of anaesthetic gases to patients without contaminating the air that the staff breathe, and to conserve anaesthetic gas.
*
Life-support system
A life-support system is the combination of equipment that allows survival in an environment or situation that would not support that life in its absence. It is generally applied to systems supporting human life in situations where the outsid ...
s of
submarine
A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
s,
underwater habitat
Underwater habitats are underwater structures in which people can live for extended periods and carry out most of the basic human functions of a 24-hour day, such as working, resting, eating, attending to personal hygiene, and sleeping. In thi ...
s, and
saturation diving
Saturation diving is diving for periods long enough to bring all tissues into equilibrium with the partial pressures of the inert components of the breathing gas used. It is a diving mode that reduces the number of decompressions divers working ...
systems use a
scrubber
Scrubber systems (e.g. chemical scrubbers, gas scrubbers) are a diverse group of air pollution control devices that can be used to remove some particulates and/or gases from industrial exhaust streams. An early application of a carbon dioxide scr ...
system working on the same principles as a rebreather.
This may be compared with some applications of open-circuit breathing apparatus:
*The oxygen enrichment systems primarily used by medical patients, high altitude mountaineers and commercial aircraft emergency systems, in which the user breathes ambient air which is enriched by the addition of pure oxygen,
*Open circuit breathing apparatus used by firefighters, underwater divers and some mountaineers, which supplies fresh gas for each breath, which is then discharged into the environment.
*Gas masks and respirators which filter contaminants from ambient air which is then breathed.
Diving rebreathers
The widest variety of rebreather types is used in diving, as the consequences of breathing under pressure complicate the requirements, and a large range of options are available depending on the specific application and available budget. A diving rebreather is
safety-critical
A safety-critical system (SCS) or life-critical system is a system whose failure or malfunction may result in one (or more) of the following outcomes:
* death or serious injury to people
* loss or severe damage to equipment/property
* environme ...
life-support equipment
A life-support system is the combination of equipment that allows survival in an environment or situation that would not support that life in its absence. It is generally applied to systems supporting human life in situations where the outsid ...
– some
modes of failure can kill the diver without warning, others can require immediate appropriate response for survival.
Surface supplied diving gas reclaim systems
A helium reclaim system (or push-pull system) is used to recover helium based breathing gas after use by the diver when this is more economical than losing it to the environment in open circuit systems. The recovered gas is passed through a scrubber system to remove carbon dioxide, filtered to remove odours, and pressurised into storage containers, where it may be mixed with oxygen to the required composition for re-use, either immediately, or at a later date.
Saturation diving life-support systems
The life support system provides breathing gas and other services to support life for the personnel under pressure in the accommodation chambers and closed diving bell. It includes the following components:
*Breathing gas supply, distribution and recycling equipment: scrubbers, filters, boosters, compressors, mixing, monitoring, and storage facilities
*Chamber climate control system - control of temperature and humidity, and filtration of gas
*Instrumentation, control, monitoring and communications equipment
*Fire suppression systems
*Sanitation systems
The life support system for the bell provides and monitors the main supply of breathing gas, and the control station monitors the deployment and communications with the divers. Primary gas supply, power and communications to the bell are through a bell umbilical, made up from a number of hoses and electrical cables twisted together and deployed as a unit.
This is extended to the divers through the diver umbilicals.
The accommodation life support system maintains the chamber environment within the acceptable range for health and comfort of the occupants. Temperature, humidity, breathing gas quality, sanitation systems, and equipment function are monitored and controlled.
Atmospheric diving suits
![Navy Diver4](https://upload.wikimedia.org/wikipedia/commons/4/42/Navy_Diver4.jpg)
An atmospheric diving suit is a small one-man articulated submersible of roughly anthropomorphic form, with limb joints which allow articulation under external pressure while maintaining an internal pressure of one atmosphere.
Breathing gas supply may be surface supplied by umbilical, or from a rebreather carried on the suit. An emergency gas supply rebreather may also be fitted to a suit with either surface supply or rebreather for primary breathing gas.
As the internal pressure is maintained at one atmosphere, there is no risk of acute oxygen toxicity. This is an underwater diving application, but has more in common with industrial applications than with ambient pressure scuba rebreathers.
Industrial and rescue self-contained rebreathers
Different design criteria apply to
SCBA
A self-contained breathing apparatus (SCBA), sometimes referred to as a compressed air breathing apparatus (CABA) or simply breathing apparatus (BA), is a device worn to provide breathable air in an atmosphere that is immediately dangerous to ...
rebreathers for use only out of the water:
*There is no variation in ambient pressure on the components. The counterlung may be placed for comfort and convenience.
*Cooling of the gas in the breathing loop may be desirable, as the absorbent produces heat as it reacts with carbon dioxide, and the warming of the gas is not welcome in hot industrial situations such as firefighting and deep mines.
*Absorbent containers may in some cases rely on gravity for preventing channeling.
*If a full-face mask is used, it may have viewports designed for convenience or improved field of vision, and they do not need to be flat and parallel to prevent visual distortion as when underwater.
*In
firefighting
Firefighting is the act of extinguishing or preventing the spread of unwanted fires from threatening human lives and destroying property and the environment. A person who engages in firefighting is known as a firefighter.
Firefighters typically ...
rebreathers, consideration must be given to making the set reasonably flame-proof and protecting it from heat and debris impacts.
*The need to ditch the set quickly may not arise, and harness straps may not need a quick-release.
*Buoyancy is not a consideration, but weight may be critical. Good ergonomic design for ease of carrying, comfort, and balance are important where the unit may be worn in confined spaces, while climbing and crawling through small gaps.
*A spring loaded counterlung pressurisation system may be used to provide slight positive pressure in the breathing loop, to prevent noxious gas entry if the mask seal is not perfect.
*There are no constraints due to the physiological effects of breathing under pressure. Complex gas mixtures are unnecessary. Oxygen rebreathers can usually be used, which makes the design considerably simpler, and the mechanism more reliable.
*A system allowing the user to access drinking water from a bag may be fitted, A bite operated valve van be used to control flow.
*Radio voice communications may be fitted.
*A constant mass flow systen may be used to ensure a minimum fresh gas supply, with a demand valve to add gas if the loop is emptied.
*Gas supply and absorbent duratio would usually be matched for efficiency
*Insulation may be needed for the breathing loop for use in sub-zero temperatures where freezing of the absorbent would reduce its effectiveness.
*A water trap may be provided to collect condensed water from the absorbent reaction and from metabolic product.
*Monitoring functions may include:
**Cylinder pressure (analog and digital)
**Estimated remaining duration of use until residual low pressure warning is activated
**Temperature indication
**Automatic recording of warning signals
*Optical and/or acoustic warning signals may be provided for:
**Low gas pressure in the cylinder
**Alarm triggered by lack of user movement
**Manually triggered alarm.
Mountaineering rebreathers
Mountaineering rebreathers provide
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
at a higher concentration than available from atmospheric air in a naturally hypoxic environment. They need to be lightweight and to be reliable in severe cold including not getting choked with deposited frost.
A high rate of system failures due to extreme cold has not been solved. Breathing pure oxygen results in an elevated partial pressure of oxygen in the blood: a climber breathing pure oxygen at the summit of Mt. Everest has a greater oxygen partial pressure than breathing air at sea level. This results in being able to exert greater physical effort at altitude. The exothermic reaction helps keep the scrubber contents from freezing, and helps reduce heat loss from the user.
Both chemical and compressed gas oxygen have been used in experimental closed-circuit oxygen systems – the first on
Mount Everest
Mount Everest (; Tibetan: ''Chomolungma'' ; ) is Earth's highest mountain above sea level, located in the Mahalangur Himal sub-range of the Himalayas. The China–Nepal border runs across its summit point. Its elevation (snow heig ...
in
1938
Events
January
* January 1
** The Constitution of Estonia#Third Constitution (de facto 1938–1940, de jure 1938–1992), new constitution of Estonia enters into force, which many consider to be the ending of the Era of Silence and the a ...
. The
1953 expedition used closed-circuit
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
equipment developed by
Tom Bourdillon
Thomas Duncan Bourdillon ( ; 16 March 1924 – 29 July 1956) was an English mountaineer and member of the 1953 British Mount Everest Expedition which made the first ascent of Mount Everest. He died in the Valais, Switzerland, on 29 July 1956 aged ...
and his father for the first assault team of Bourdillon and
Evans
Evans may refer to:
People
*Evans (surname)
*List of people with surname Evans
Places United States
*Evans Island, an island of Alaska
*Evans, Colorado
*Evans, Georgia
*Evans County, Georgia
*Evans, New York
*Evans Mills, New York
*Evans City, ...
; with one "dural" 800l compressed oxygen cylinder and soda lime canister (the second (successful) assault team of Hillary and Tenzing used open-circuit equipment).
Rebreathers for unpressurised aircraft and high altitude parachuting
Similar requirement and working environment to mountaineering, but weight is less of a problem. The Soviet
IDA71
The Soviet, later Russian IDA71 military and naval rebreather is an oxygen rebreather intended for use by naval and military divers including Russian commando frogmen. As supplied it is in a plain backpack harness with no buoyancy aid. The casin ...
rebreather was also manufactured in a high altitude version, which was operated as an oxygen rebreather.
Anaesthesia systems
Anaesthetic machine
An anaesthetic machine (British English) or anesthesia machine (American English) is a medical device used to generate and mix a fresh gas flow of medical gases and inhalational anaesthetic agents for the purpose of inducing and maintaining an ...
s can be configured as rebreathers to provide oxygen and
anaesthetic gases to a patient during surgery or other procedures that require sedation. An absorbent is present in the machine to remove the carbon dioxide from the loop.
[
Both semi-closed and fully closed circuit systems may be used for anaesthetic machines, and both push-pull (pendulum) two directional flow and one directional loop systems are used.] The breathing circuit A breathing system or breathing circuit is a medical device used to deliver oxygen, remove carbon dioxide, and deliver inhalational anaesthetic agents to a patient. Originally developed for use in anaesthesiology, many variants of breathing system ...
of a loop configured machine has two unidirectional valves so that only scrubbed gas flows to the patient while expired gas goes back to the machine.
The anaesthetic machine can also provide gas to ventilated patients who cannot breathe on their own. A waste gas scavenging system removes any gasses from the operating room to avoid environmental contamination.
Space suits
One of the functions of a space suit is to provide the wearer with breathing gas. This can be done via an umbilical from the life-support systems of the spacecraft or habitat, or from a primary life support system
A primary (or portable or personal) life support system (or subsystem) (PLSS), is a device connected to an astronaut or cosmonaut's spacesuit, which allows extra-vehicular activity with maximum freedom, independent of a spacecraft's life support ...
carried on the suit. Both of these systems involve rebreather technology as they both remove carbon dioxide from the breathing gas and add oxygen to compensate for oxygen used by the wearer.
Space suits usually use oxygen rebreathers as this allows a lower pressure in the suit which gives the wearer better freedom of movement.
Habitat life-support systems
Submarine
A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
s, underwater habitat
Underwater habitats are underwater structures in which people can live for extended periods and carry out most of the basic human functions of a 24-hour day, such as working, resting, eating, attending to personal hygiene, and sleeping. In thi ...
s, bomb shelters, space station
A space station is a spacecraft capable of supporting a human crew in orbit for an extended period of time, and is therefore a type of space habitat. It lacks major propulsion or landing systems. An orbital station or an orbital space station i ...
s, and other living spaces occupied by several people over medium to long periods on a limited gas supply, are equivalent to closed circuit rebreathers in principle, but generally rely on mechanical circulation of breathing gas through the scrubbers.
Safety
There are several safety issues with rebreather equipment, and these tend to be more severe in diving rebreathers.
Hazards
Some of the hazards are due to the way the equipment works, while others are related to the environment in which the equipment is used, as rebreathers are usually used where no breathable ambient atmosphere is available.
Hypoxia
Hypoxia can occur in any rebreather which contains enough inert gas to allow breathing without triggering automatic gas addition.
In an oxygen rebreather this can occur if the loop is not sufficiently purged at the start of use. Purging is the replacement of the original gas content by fresh gas, and may have to be repeated to completely remove inert gas. Purging should be done while breathing off the unit so that the inert gas in the user's lungs and body tissues that finds its way into the loop is also removed from the system.
Carbon dioxide buildup
Carbon dioxide buildup will occur if the scrubber medium is absent, badly packed, inadequate or exhausted. The normal human body is fairly sensitive to carbon dioxide partial pressure, and a buildup will be noticed by the user. However, there is not often much that can be done to rectify the problem except changing to another breathing gas supply until the scrubber can be repacked. Continued use of a rebreather with an ineffective scrubber is not possible for very long, as the levels will become toxic and the user will experience extreme respiratory distress, followed by loss of consciousness and death. The rate at which these problems develop depends on the volume of the circuit and the metabolic rate of the user at the time.
Carbon dioxide buildup can also occur when a combination of exertion and work of breathing
Work of breathing (WOB) is the energy expended to inhale and exhale a breathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not partic ...
exceeds the capacity of the user. If this occurs where the user cannot reduce exertion sufficiently, it may be impossible to correct. This problem is more likely to occur with diving rebreathers at depths where the density of the breathing gas is severely elevated.
Leakage of toxic gases into the breathing loop
Industrial rebreathers are often used where the ambient air is contaminated, and may be toxic. Parts of the loop will be at a slightly lower than external ambient pressure during inhalation, and if the circuit is not airtight external gases may leak in. This is a particular issue around the edge of a full-face mask, where the rubber mask skirt must seal against the user's face.
Fire hazards of high concentration of oxygen
High partial pressures of oxygen greatly increase fire hazard, and many materials which are self-extinguishing in atmospheric air will burn continuously in a high oxygen concentration. This is more of a hazard for terrestrial applications such as rescue and firefighting than for diving, where the ignition risk is relatively low.
Caustic cocktail
Caused by a loop flood reaching the absorbent canister, so only applicable in immersed applications.
Failure modes
Scrubber failure
The term "break-through" means the failure of the scrubber to continue removing sufficient carbon dioxide from the gas circulating in the loop. This will inevitably happen if the scrubber is used too long, but can happen prematurely in some circumstances.
There are several ways that the scrubber may fail or become less efficient:
*Complete consumption of the active ingredient in a "general break through". Depending on scrubber design and user workload, this may be gradual, allowing the user to become aware of the problem in time to make a controlled exit or bailout to open circuit, or relatively sudden, triggering an urgent or emergency response.
*Bypassing the absorbent. The absorbent granules must be packed closely so that all exhaled gas comes into contact with the surface of soda lime and the canister is designed to avoid any large spaces or gaps between the absorbent granules or between the granules and the canister walls that would let gas bypass contact with the absorbent. If any of the seals, such as O-ring
An O-ring, also known as a packing or a toric joint, is a mechanical gasket in the shape of a torus; it is a loop of elastomer with a round cross-section, designed to be seated in a groove and compressed during assembly between two or more par ...
s, or spacers that prevent bypassing of the scrubber, are not present or not fitted properly, or if the scrubber canister has been incorrectly packed or fitted, it may allow the exhaled gas to bypass the absorbent, and the scrubber will be less effective. This failure mode is also called "tunneling" when absorbent settles to form void spaces inside the canister. Bypass will cause an unexpected early break-through.
*When the gas mix is under pressure at depth, the gas molecules are more densely packed, and the carbon dioxide molecules' mean path between collisions is shorter, so they are not so free to move around to reach the absorbent surface, and require a longer dwell time. Because of this effect, the scrubber must be bigger for deep diving than is needed for a shallow-water, industrial or high altitude rebreather.
*Carbon dioxide absorbent can be caustic
Caustic most commonly refers to:
* Causticity, a property of various corrosive substances
** Sodium hydroxide, sometimes called ''caustic soda''
** Potassium hydroxide, sometimes called ''caustic potash''
** Calcium oxide, sometimes called ''caus ...
and can cause burns to the eyes, mucous membranes and skin. A mixture of water and absorbent occurs when the scrubber floods and depending on the chemicals used, can produce a chalky taste or a burning sensation if the contaminated water reaches the mouthpiece, which should prompt the diver to switch to an alternative source of breathing gas
A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed h ...
and rinse their mouth out with water. This is known to rebreather divers as a ''caustic cocktail''. The excessive wetting of the absorbent also reduces the rate of carbon dioxide removal and can cause premature break-through even if no caustic liquid reaches the diver. Work of breathing may also increase. Many modern diving rebreather absorbents are designed not to produce this caustic fluid if they get wet.
*In below-freezing operation (primarily mountain climbing), wet scrubber chemicals can freeze when oxygen bottles are changed, while there is a pause in the exothermic reaction of taking up the carbon dioxide, thus preventing carbon dioxide from reaching the scrubber material, and slowing the reaction when used again.
Other failure modes
*Flooding of the ambient pressure volume can occur in diving rebreathers.
*Gas leakage to or from the ambient pressure volume can occur. Since the volume of gas lost or gained is likely to be very small, it is most relevant when the surroundings contain toxic gases or fumes.
*Oxygen monitoring failure can lead to incorrect partial pressure of oxygen in the breathing gas. This is only relevant in mixed gas rebreathers used for diving.
*Gas injection system failure is also mainly a problem of mixed gas diving rebreathrs. Oxygen rebreathers gas injection systems are generally robust and reliable and can be manually overridden if they fail, and this form of failure is identifiable by an inappropriate volume of gas in the ambient pressure volume of the rebreather.
History
Early history
Around 1620, Cornelius Drebbel
Cornelis Jacobszoon Drebbel ( ) (1572 – 7 November 1633) was a Dutch engineer and inventor. He was the builder of the first operational submarine in 1620 and an innovator who contributed to the development of measurement and control systems, op ...
discovered that heating saltpetre (potassium nitrate
Potassium nitrate is a chemical compound with the chemical formula . This alkali metal nitrate salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ions K+ and nitrat ...
) would generate oxygen.
The first basic rebreather based on carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
absorption was patented in France
France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
in 1808 by Pierre-Marie Touboulic
Pierre-Marie Touboulic (17 June 1783, Brest, France - 8 June 1859 Paris) was a naval engineer, inventor and writer.
Biography
Pierre-Marie Touboulic was born in Brest on 17 June 1783. He was the fifth of six children of master locksmith Jean-Lou ...
from Brest
Brest may refer to:
Places
*Brest, Belarus
**Brest Region
**Brest Airport
**Brest Fortress
*Brest, Kyustendil Province, Bulgaria
*Břest, Czech Republic
*Brest, France
**Arrondissement of Brest
**Brest Bretagne Airport
** Château de Brest
*Brest, ...
, a mechanic in Napoleon
Napoleon Bonaparte ; it, Napoleone Bonaparte, ; co, Napulione Buonaparte. (born Napoleone Buonaparte; 15 August 1769 – 5 May 1821), later known by his regnal name Napoleon I, was a French military commander and political leader who ...
's Imperial Navy. This early rebreather design worked with an oxygen reservoir, the oxygen being delivered progressively by the diver and circulating in a closed circuit through a sponge
Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...
soaked in limewater
Limewater is the common name for a saturated aqueous solution of calcium hydroxide. Calcium hydroxide, Ca(OH)2, is sparsely soluble at room temperature in water (1.5 g/L at 25 °C). "Pure" (i.e. less than or fully saturated) limewater i ...
, a solution of calcium hydroxide in water. Touboulic called his invention ''Ichtioandre'' (Greek for 'fish-man'). There is no evidence of a prototype having been manufactured.
A prototype rebreather was built in 1849 by Pierre Aimable De Saint Simon Sicard
Pierre is a masculine given name. It is a French form of the name Peter. Pierre originally meant "rock" or "stone" in French (derived from the Greek word πέτρος (''petros'') meaning "stone, rock", via Latin "petra"). It is a translation ...
,
In 1853 Professor T. Schwann presented a rebreather at the Belgian Academy of Science
Belgian may refer to:
* Something of, or related to, Belgium
* Belgians, people from Belgium or of Belgian descent
* Languages of Belgium, languages spoken in Belgium, such as Dutch, French, and German
*Ancient Belgian language, an extinct language ...
. It had a large back mounted oxygen tank with working pressure of about 13.3 bar, and two scrubbers containing sponges
Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through ...
soaked in a caustic soda
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions .
Sodium hydroxide is a highly caustic base and alka ...
solution.
Working rebreathers
The first commercially practical closed-circuit scuba was designed and built by the diving engineer Henry Fleuss
Henry Albert Fleuss (13 June 1851 – 6 January 1933) was a pioneering diving engineer, and Master Diver for Siebe, Gorman & Co. of London.
Fleuss was born in Marlborough, Wiltshire in 1851.
In 1878 he was granted a patent which improved rebr ...
in 1878, while working for Siebe Gorman
Siebe Gorman & Company Ltd was a British company that developed diving equipment and breathing equipment and worked on commercial diving and marine salvage projects. The company advertised itself as 'Submarine Engineers'. It was founded by Aug ...
in London. His self-contained breathing apparatus
A self-contained breathing apparatus (SCBA), sometimes referred to as a compressed air breathing apparatus (CABA) or simply breathing apparatus (BA), is a device worn to provide breathable air in an atmosphere that is immediately dangerous to ...
consisted of a rubber mask connected to a breathing bag, with (estimated) 50–60% O2 supplied from a copper tank and CO2 scrubbed by rope yarn soaked in a solution of caustic potash; the system giving a duration of about three hours. Fleuss tested his device in 1879 by spending an hour submerged in a water tank, then one week later by diving to a depth of 5.5 m in open water, upon which occasion he was slightly injured when his assistants abruptly pulled him to the surface.
His apparatus was first used under operational conditions in 1880 by Alexander Lambert, the lead diver on the Severn Tunnel
The Severn Tunnel ( cy, Twnnel Hafren) is a railway tunnel in the United Kingdom, linking South Gloucestershire in the west of England to Monmouthshire in south Wales under the estuary of the River Severn. It was constructed by the Great Western ...
construction project, who was able to travel 1000 feet in the darkness to close several submerged sluice
Sluice ( ) is a word for a channel controlled at its head by a movable gate which is called a sluice gate. A sluice gate is traditionally a wood or metal barrier sliding in grooves that are set in the sides of the waterway and can be considered ...
doors in the tunnel; this had defeated his best efforts with standard diving dress
Standard diving dress, also known as hard-hat or copper hat equipment, deep sea diving suit or heavy gear, is a type of diving suit that was formerly used for all relatively deep underwater work that required more than breath-hold duration, which ...
due to the danger of the air supply hose becoming fouled on submerged debris, and the strong water currents in the workings.[
In 1880 Fleuss, used a rebreather to inspect Seaham Colliery in the UK after a gas explosion.]
Fleuss and Siebe Gorban developed the Proto breathing apparatus
The Proto is a type of rebreather that was made by Siebe Gorman. It was an industrial breathing set and not suitable for diving. It was made from 1914 or earlier to the 1960s or later. (Distinguish from "Proton", which is another sort of Siebe Go ...
for mine rescue in 1911.
Fleuss continually improved his apparatus, adding a demand regulator and tanks capable of holding greater amounts of oxygen at higher pressure. Sir Robert Davis, head of Siebe Gorman
Siebe Gorman & Company Ltd was a British company that developed diving equipment and breathing equipment and worked on commercial diving and marine salvage projects. The company advertised itself as 'Submarine Engineers'. It was founded by Aug ...
, improved the oxygen rebreather in 1910 with his invention of the Davis Submerged Escape Apparatus
The Davis Submerged Escape Apparatus (also referred to as DSEA), was an early type of oxygen rebreather invented in 1910 by Sir Robert Davis, head of Siebe Gorman and Co. Ltd., inspired by the earlier Fleuss system, and adopted by the Royal Na ...
, the first practical rebreather to be made in quantity. While intended primarily as an emergency escape apparatus for submarine
A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
crews, it was soon also used for diving
Diving most often refers to:
* Diving (sport), the sport of jumping into deep water
* Underwater diving, human activity underwater for recreational or occupational purposes
Diving or Dive may also refer to:
Sports
* Dive (American football), a ...
, being a handy shallow water diving apparatus with a thirty-minute endurance, and as an industrial breathing set
A self-contained breathing apparatus (SCBA), sometimes referred to as a compressed air breathing apparatus (CABA) or simply breathing apparatus (BA), is a device worn to provide breathable air in an atmosphere that is immediately dangerous to ...
.
The rig comprised a rubber breathing/buoyancy bag containing a canister of barium hydroxide
Barium hydroxide is a chemical compound with the chemical formula Ba(OH)2. The monohydrate (''x'' = 1), known as baryta or baryta-water, is one of the principal compounds of barium. This white granular monohydrate is the usual commercial form.
P ...
to scrub exhaled CO2 and, in a pocket at the lower end of the bag, a steel pressure cylinder holding approximately 56 litres of oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
at a pressure of 120 bar. The cylinder was equipped with a control valve and was connected to the breathing bag
A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. Oxygen is ...
. Opening the cylinder's valve admitted oxygen to the bag and charged it to the pressure of the surrounding water. The rig also included an emergency buoyancy bag on the front of to help keep the wearer afloat. The DSEA was adopted by the Royal Navy
The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...
after further development by Davis in 1927. Various industrial oxygen rebreathers such as the Siebe Gorman Salvus
The Siebe Gorman Salvus is a light oxygen rebreather for industrial use (including by firemen and in coalmine rescue) or in shallow diving. Its duration on a filling is 30 to 40 minutes. It was very common in Britain during World War II and for ...
and the Siebe Gorman Proto
The Proto is a type of rebreather that was made by Siebe Gorman. It was an industrial breathing set and not suitable for diving. It was made from 1914 or earlier to the 1960s or later. (Distinguish from "Proton", which is another sort of Siebe Go ...
, both invented in the early 1900s, were derived from it.
Professor Georges Jaubert invented the chemical compound Oxylithe in 1907. It was a form of sodium peroxide
Sodium peroxide is an inorganic compound with the formula Na2O2. This yellowish solid is the product of sodium ignited in excess oxygen. It is a strong base. This metal peroxide exists in several hydrates and peroxyhydrates including Na2O2·2H2O ...
(Na2O2) or sodium superoxide
Sodium superoxide is the inorganic compound with the formula Na O2. This yellow-orange solid is a salt of the superoxide anion. It is an intermediate in the oxidation of sodium by oxygen.
Preparation
NaO2 is prepared by treating sodium peroxide ...
(NaO2). As it absorbs carbon dioxide
Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
in a rebreather's scrubber it emits oxygen. This compound was first incorporated into a rebreather design by Captain S.S. Hall and Dr. O. Rees of the Royal Navy
The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...
in 1909. Although intended for use as a submarine escape apparatus, it was never accepted by the Royal Navy and was instead used for shallow water diving.[
In 1912 the German firm Dräger began mass production of their own version of standard diving dress with the air supply from a rebreather. The apparatus had been invented some years earlier by Hermann Stelzner, an engineer at the Dräger company,] for mine rescue
Mine rescue or mines rescue is the specialised job of rescuing miners and others who have become trapped or injured in underground mines because of mining accidents, roof falls or floods and disasters such as explosions.
Background
Mining law ...
.[
]
Rebreathers during World War II
In the 1930s, Italian
Italian(s) may refer to:
* Anything of, from, or related to the people of Italy over the centuries
** Italians, an ethnic group or simply a citizen of the Italian Republic or Italian Kingdom
** Italian language, a Romance language
*** Regional Ita ...
sport spearfishers began to use the Davis rebreather; Italian manufacturers received a licence from the English patent holders to produce it. This practice soon came to the attention of the Italian Navy
"Fatherland and Honour"
, patron =
, colors =
, colors_label =
, march = ( is the return of soldiers to their barrack, or sailors to their ship after a ...
, which developed an extensively upgraded model designed by Teseo Tesei
Teseo Tesei (3 January 1909 – 26 July 1941) was an Italian naval officer, who invented the human torpedo (called ''Maiale'', Italian for "pig") used by the '' Regia Marina'' during World War II.
Life
Teseo Tesei was born in Marina de Ca ...
and that was used by its frogman unit Decima Flottiglia MAS
The ''Decima Flottiglia MAS'' (''Decima Flottiglia Motoscafi Armati Siluranti'', also known as ''La Decima'' or Xª MAS) (Italian for "10th Assault Vehicle Flotilla") was an Italian flotilla, with commando frogman unit, of the ''Regia Marina'' ...
with good results during World War II.
During the Second World War
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, captured Italian frogmen's rebreathers influenced improved designs for British rebreathers.[ Many British frogmen's breathing sets used aircrew breathing oxygen cylinders salvaged from shot-down German ]Luftwaffe
The ''Luftwaffe'' () was the aerial-warfare branch of the German ''Wehrmacht'' before and during World War II. Germany's military air arms during World War I, the ''Luftstreitkräfte'' of the Imperial Army and the '' Marine-Fliegerabtei ...
aircraft. The earliest of these breathing sets may have been modified Davis Submerged Escape Apparatus
The Davis Submerged Escape Apparatus (also referred to as DSEA), was an early type of oxygen rebreather invented in 1910 by Sir Robert Davis, head of Siebe Gorman and Co. Ltd., inspired by the earlier Fleuss system, and adopted by the Royal Na ...
; their fullface masks were the type intended for the Siebe Gorman Salvus
The Siebe Gorman Salvus is a light oxygen rebreather for industrial use (including by firemen and in coalmine rescue) or in shallow diving. Its duration on a filling is 30 to 40 minutes. It was very common in Britain during World War II and for ...
, but in later operations different designs were used, leading to a fullface mask
A full-face diving mask is a type of diving mask that seals the whole of the diver's face from the water and contains a mouthpiece, demand valve or constant flow gas supply that provides the diver with breathing gas. The full face mask ha ...
with one big face window, at first circular or oval and later rectangular (mostly flat, but the sides curved back to allow better vision sideways). Early British frogman's rebreathers had rectangular counterlung
A rebreather is a breathing apparatus that absorbs the carbon dioxide of a user's exhaled breath to permit the rebreathing (recycling) of the substantially unused oxygen content, and unused inert content when present, of each breath. Oxygen is ...
s on the chest like Italian frogman's rebreathers, but later designs had a square recess in the top of the counterlung so it could extend further up toward the shoulders. In front they had a rubber collar that was clamped around the absorbent canister.[ Some British armed forces divers used bulky thick diving suits called ]Sladen suit
The Sladen Suit was a heavy type of British divers' drysuit made by Siebe Gorman. It is entered by a wide rubber tube at the umbilicus: this tube is folded and tied off before the diver dives. It was used by British manned torpedo
Human to ...
s; one version of it had a flip-up single faceplate for both eyes to let the user get binoculars
Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...
to his eyes when on the surface.
The Dräger rebreathers, especially the DM20 and DM40 model series, were used by the German helmet divers and German frogmen
A frogman is someone who is trained in scuba diving or swimming underwater in a tactical capacity that includes military, and in some European countries, police work. Such personnel are also known by the more formal names of combat diver, comb ...
during World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
. Rebreathers for the US Navy
The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage of ...
were developed by Dr. Christian J. Lambertsen for underwater warfare. Lambertsen held the first closed-circuit oxygen rebreather course in the United States for the Office of Strategic Services
The Office of Strategic Services (OSS) was the intelligence agency of the United States during World War II. The OSS was formed as an agency of the Joint Chiefs of Staff (JCS) to coordinate espionage activities behind enemy lines for all branc ...
maritime unit at the Naval Academy
A naval academy provides education for prospective naval officers.
See also
* Military academy
A military academy or service academy is an educational institution which prepares candidates for service in the officer corps. It normally pro ...
on 17 May 1943.
During and after WWII
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, needs arose in the armed forces to dive deeper than allowed by pure oxygen. That prompted, at least in Britain, design of simple constant-flow "mixture rebreather" variants of some of their diving oxygen rebreathers (= what is now called "nitrox
Nitrox refers to any gas mixture composed (excepting trace gases) of nitrogen and oxygen. This includes atmospheric air, which is approximately 78% nitrogen, 21% oxygen, and 1% other gases, primarily argon. In the usual application, underwater ...
"): SCMBA from the SCBA (Swimmer Canoeist's Breathing Apparatus
The Clearance Divers Breathing Apparatus (CDBA) is a type of rebreather made by Siebe Gorman in England.
The British Royal Navy used it for many years. It was for underwater work rather than for combat diving. The main oxygen diving cylinder, cy ...
), and CDMBA from the Siebe Gorman CDBA
The Clearance Divers Breathing Apparatus (CDBA) is a type of rebreather made by Siebe Gorman in England.
The British Royal Navy used it for many years. It was for underwater work rather than for combat diving. The main oxygen diving cylinder, cy ...
, by adding an extra gas supply cylinder. Before a dive with such a set, the diver had to know the maximum or working depth of his dive, and how fast his body used his oxygen supply, and from those to calculate what to set his rebreather's gas flow rate to.
Post-WWII
The diving pioneer Hans Hass
Hans Hass (23 January 1919 – 16 June 2013) was an Austrian biologist and underwater diving pioneer. He was known mainly for being among the first scientists to popularise coral reefs, stingrays, octopuses and sharks. He pioneered the making of ...
used Dräger oxygen rebreathers in the early 1940s for underwater cinematography.
Due to the military importance of the rebreather, amply demonstrated during the naval campaigns of the Second World War
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, most governments were reluctant to issue the technology into the public domain. In Britain rebreather use for civilians was negligible, and the BSAC formally prohibited rebreather use by its members. The Italian firms Pirelli
Pirelli & C. S.p.A. is a multinational tyre manufacturer based in Milan, Italy. The company, which has been listed on the Milan Stock Exchange since 1922, is the 6th-largest tyre manufacturer and is focused on the consumer production of tyre ...
and Cressi-Sub
Cressi is one of the largest manufacturers of water sports equipment in the world serving the scuba dive, Snorkeling, snorkel and Human swimming, swim industries. The company's five divisions cover four markets—scuba diving, snorkeling, spearfi ...
at first each sold a model of sport diving rebreather, but after a while discontinued those models. Some home made rebreathers were used by cave diver
Cave-diving is underwater diving in water-filled caves. It may be done as an extreme sport, a way of exploring flooded caves for scientific investigation, or for the search for and recovery of divers or, as in the 2018 Thai cave rescue, other ...
s to penetrate cave sumps.
Most high-altitude mountaineers use open-circuit oxygen equipment; the 1953 Everest expedition used both closed-circuit and open-circuit oxygen equipment: see bottled oxygen
Bottled oxygen is oxygen in small, portable, high pressure storage cylinders, as used for high-altitude climbing. Bottled oxygen may also be for a breathing gas, especially for scuba diving or during surgery. (see also diving cylinder and oxygen ...
.
Eventually the Cold War
The Cold War is a term commonly used to refer to a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term '' cold war'' is used because the ...
ended, and in 1989 the Communist Bloc
The Eastern Bloc, also known as the Communist Bloc and the Soviet Bloc, was the group of socialist states of Central and Eastern Europe, East Asia, Southeast Asia, Africa, and Latin America under the influence of the Soviet Union that existed du ...
collapsed, and as a result the perceived risk of sabotage attacks by combat divers dwindled, and Western armed forces had less reason to requisition civilian rebreather patent
A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A p ...
s, and automatic and semi-automatic recreational diving rebreathers with oxygen partial pressure sensors started to appear.
Manufacturers and models
Industrial/rescue:
* made in England from 1910 onwards for use in mine
Mine, mines, miners or mining may refer to:
Extraction or digging
* Miner, a person engaged in mining or digging
*Mining, extraction of mineral resources from the ground through a mine
Grammar
*Mine, a first-person English possessive pronoun
...
rescue and other industrial uses.
*
**SEFA
The SEFA is a make of backpack industrial breathing set formerly made by Sabre Safety. It is an oxygen rebreather. "SEFA" is an acronym for "selected elevated flow apparatus".
Description
It is in a shiny backpack stainless steel sheet casing w ...
(Selected Elevated Flow Apparatus) – an industrial oxygen rebreather formerly made by Sabre Safety with 2 hours duration on a filling.
*
**The Savox was an oxygen rebreather with a use duration of 45 minutes. It had no hard casing and was worn in front of the body.
**
*
Others:
See also
*
*
*
* (surface-only (industrial) breathing sets including rebreathers)
References
External links
*
Anesthesia breathing systems
* NIOSH
The National Institute for Occupational Safety and Health (NIOSH, ) is the United States federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness. NIOSH is part of the C ...
Docket # 123, titled "Reevaluation of NIOSH limitations on and precaution for safe use of positive-pressure closed-circuit SCBA" is available a
web.archive.org
{{UnderwaterDiving, divequ
Industrial breathing sets
Spaceflight technology
Breathing gases