Rebreather

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A rebreather is a breathing apparatus that absorbs carbon dioxide from a user-breathed breath to allow rebreathing of substantially unused oxygen content, and inert content that is not used when present, from every breath. Oxygen is added to fill the amount metabolized by the user. This differs from the open circuit breathing apparatus, in which the exhaled gas is discharged directly into the environment.

The rebreather technology may be used where the supply of gas is limited, such as under water or in space, where the environment is toxic or hypoxic, such as in firefighting operations, mine rescue and high altitude operations, or where the respiratory gas is enriched or contained expensive. components, such as helium diluent or anesthetic gas.

The rebreather technology is used in many environments:

• Underwater - as a self-contained breathing apparatus, sometimes known as a "scuba-covered circuit" as opposed to "open circuit scuba" in which divers breathe respiratory gas into the surrounding water. Surface-supplied submersible equipment may incorporate both rebreather technology as a gas retrieval system, in which the respiratory gas provided by surfaces is returned and polished on the surface, or as a self-resident diver system.
• Rescue of mines and other industrial applications - where toxic gases may be present or oxygen may be absent.
• Crewed spacecraft and space suit - outer space, effectively, vacuum without oxygen to support life.
• Respiratory system of anesthesia of the hospital - to supply controlled concentrations of anesthetic gases to patients without polluting the air inhaled by staff.
• climbing Himalayas. The high altitude reduces the partial pressure of oxygen in the ambient air, which reduces the ability of the climber to function effectively. Rebreathers mounts provide a higher oxygen partial pressure to climber.
• Submarines, underwater habitats, and saturated dive systems use scrubbers that work on the same principles as rebreather.

This can be compared to some open circuit apparatus:

• Oxygen enrichment systems are primarily used by medical patients, high altitude hikers and commercial aircraft emergency systems, where users breathe ambient air enriched with the addition of pure oxygen,
• The open circuit breathing device used by firefighters and underwater divers, which supplies fresh gas for each breath, which is then discharged into the environment.
• Gas masks that filter contaminants from ambient air which is then inhaled.

Respiratory gas recycling comes at the expense of mass, mass, technological complexity and special hazards, which depend on the specific application and type of rebreather used.

Video Rebreather

General concepts

When a person breathes, the body consumes oxygen and produces carbon dioxide. Basic metabolism requires about 0.25 L/min of oxygen from the respiratory rate of about 6 L/min, and a healthy person working hard can provide ventilation at a rate of 95 L/min but will only metabolize about 4 L/min Oxygen Metabolised Oxygen is generally about 4 % to 5% of the inspiration volume at normal atmospheric pressure, or about 20% of the oxygen available in the air at sea level. The air exhaled at sea level contains about 13.5% to 16% oxygen.

This situation is even more wasteful of oxygen when the oxygen fraction of the respiratory gas is higher, and in underwater diving, the compression of respiratory gas due to the depth makes the recirculation of exhaled gas even more desirable, as a larger proportion of open circuits. gas wasted. Beaming back from the same gas will deplete oxygen to a level that will no longer support consciousness, and ultimately life, so that the oxygen-containing gas must be added to the respiratory gas to maintain the necessary oxygen concentration.

However, if this is done without removing carbon dioxide, it will rapidly build up in recycled gas, which is produced almost immediately in mild respiratory distress, and progresses rapidly to a further stage of hypercapnia, or toxicity of carbon dioxide. A high level of ventilation is usually required to remove carbon dioxide metabolic products (CO ₂ ). The respiratory reflex is triggered by the concentration of CO ₂ in the blood, not by the oxygen concentration, therefore even the small buildup of CO ₂ in the gas being inhaled quickly becomes unbearable; if one tries to immediately revive the respiratory gas they breathe, they will soon sense acute suffocation, therefore rebreathers must chemically remove CO ₂ in a component known as carbon dioxide scrubbers.

By adding enough oxygen to compensate for metabolic usage, eliminating carbon dioxide, and rebreathing gas, most of the volume is preserved.

Maps Rebreather

History

Initial history

Around 1620, in the UK, Cornelius Drebbel made the first paddle powered submarine. To re-oxygenate the air in it, it may produce oxygen by heating the saltpetre (potassium nitrate) in the metal pan to emit oxygen. Heating turns the saltpetre into potassium oxide or hydroxide, which absorbs carbon dioxide from the air. That may explain why Drebbel people are not affected by the expected carbon dioxide formation. If so, he accidentally made a raw rebreather more than two centuries before the patent of Saint Simon Sicard.

The first basic rebreather based on carbon dioxide absorption was patented in France in 1808 by Pierre Sieur Pierre-Marie Touboulic of Brest, a mechanic in the Royal Napoleon Navy. This early rebreather design works with an oxygen reservoir, oxygen that is progressively transmitted by divers and circulated in a closed circuit through a sponge soaked in lime water. Touboulic called his invention Ichtioandre (Greek for 'fish-man'). No evidence of a prototype has been produced.

A rebreather prototype was built in 1849 by Pierre Aimable De Saint Simon Sicard, and in 1853 by Professor T. Schwann in Belgium. It has a large rigid oxygen tank with a working pressure of about 13.3 bar, and two scrubbers containing a sponge soaked in a caustic soda solution.

Modern Rebreathers

Scuba closed commercial circuits were first designed and built by engineer Henry Fleuss in 1878, while working for Siebe Gorman in London. The respirator consists of a rubber mask connected to the respiratory bag, with (estimated) 50-60% O ₂ supplied from copper tank and CO ₂ rubbed with rope yarn soaked in potash caustic solution; the system provides a duration of about three hours. Fleuss tested his device in 1879 by spending an hour immersed in a water tank, then a week later by diving to a depth of 5.5 m in open water, where on occasion he was slightly injured when his assistant suddenly pulled him to the surface.

The apparatus was first used in operational conditions in 1880 by Alexander Lambert, the main diver of the Severn Tunnel construction project, capable of traveling 1,000 feet in the dark to seal several submerged gates in the tunnel; it has defeated its best efforts with standard wetsuits because of the danger of air supply hoses being dirty in the drowning ruins, and strong water currents in the workplace.

Fleuss continues to improve its apparatus, adding demand regulators and tanks capable of holding larger amounts of oxygen at higher pressures. Sir Robert Davis, head of Siebe Gorman, perfected rebreather oxygen in 1910 with his discovery of the Davis Submerged Escape Apparatus, the first practical rebreather to be made in quantity. While intended primarily as an emergency escape tool for submariners, it was soon also used for diving, becoming a useful shallower dive tool with a thirty-minute durability, and as an industrial breathing set.

The rig consists of a rubber-breathing bag/buoyancy containing a tube of barium hydroxide to rub the CO exhaled ₂ and, in a pocket at the lower end of the bag, the steel pressure cylinder holds about 56 liters of oxygen at a pressure of 120 bar. The cylinder is equipped with a control valve and connected to the respiratory bag. Opening the cylinder valve recognizes oxygen into the bag and puts it to the surrounding water pressure. The rig also includes an emergency floating bag on the front to help keep the wearer afloat. DSEA was adopted by the Royal Navy after further development by Davis in 1927. Various industrial oxygen rebreathers such as Siebe Gorman Salvus and Siebe Gorman Proto, both found in the early 1900s, derived from it.

Professor Georges Jaubert invented the Oxylithe chemical compound in 1907. It is a form of sodium peroxide (Na ₂ O ₂ ) or superoxide sodium (NaO ₂ ). When absorbing carbon dioxide in a rebreather scrubber, it emits oxygen. This compound was first incorporated into the rebreather design by Captain SS Hall and Dr. O. Rees of the Royal Navy in 1909. Although intended to be used as a submarine breakout device, it was never accepted by the Royal Navy and instead used to be shallow. water diving.

In 1912, the German company DrÃÆ'¤ger started mass production of their own standard wetsuits with an air supply from a rebreather. The equipment was invented years earlier by Hermann Stelzner to save the mine, an engineer at DrÃÆ'¤ger's company.

Rebreathers during World War II

In the 1930s, Italian sports spearfishers started using a Davis rebreather; Italian manufacturers receive licenses from UK patent holders to produce them. This practice soon became the concern of the Italian Navy, which developed its Decima Flottiglia MAS frog unit and was used effectively in World War II.

During the Second World War, the people who caught the Italian rebrogernist influenced the enhanced design for the English rebreathers. Many respiratory British breaths use the air oxygen tubes that were rescued from the German Luftwaffe plane that was shot down. The earliest of these breathing sets may have been modified. Davis Submerged Escape Apparatus; Their fullface mask is the type devoted to Siebe Gorman Salvus, but in the later operations are used different designs, leading to a fullface mask with one large face window, on the first circle or oval and then rectangle (mostly flat, but curved side to back ). to allow for better vision to the side). The early English rebana had a rectangular adventurer on the chest like an Italian breeder rebrowathers, but then the design had a square recess at the top of the counterlung so it could extend farther toward the shoulder. In front they have a rubber collar clamped around an absorbent tube. Some British armed smugglers wore thick thick submarine clothing called the Sladen suits; one version of it has a single flip-up faceplate for both eyes to let the user get binoculars to his eyes when on the surface.

The DrÃÆ'¤ger rebreathers, especially the DM20 and DM40 model series, were used by German helmet divers and German frogmen during World War II. Rebreathers for the US Navy was developed by Dr. Christian J. Lambertsen for the underwater war. Lambertsen held the first closed circuit rebreather course in the United States for the Office's Strategic Unit of maritime service at the Naval Academy on May 17, 1943.

Post World War II

Hans Hassve pioneer used the Drebro's oxygen rebreathers in the early 1940s for underwater cinematography.

Because of the military importance of the rebreather, simply demonstrated during the Second World War naval campaign, most governments were reluctant to issue technology into the public domain. In the UK, the use of rebreather for civilians is negligible - BSAC even officially prohibits the use of rebreather by its members. The Italian company Pirelli and Cressi-Sub initially each sold the diving rebreather sport model, but after a while stopped the model. Some home rebreathers are used by cave divers to penetrate cave sumps.

With the end of the Cold War and the collapse of the Communist Bloc, the risk of attack by combat divers diminished. Western armed forces have less reason to ask for a civil rebreather patent, and automatic and semi-automatic recreational rebreathers begin to appear.

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System variant

The oxygen bucket

This is the earliest type of rebreather and is usually used by the navy and to help the early twentieth century. Oxygen rebreathers can be a very simple design, and they were created before the open scuba circuit. They only supply oxygen, so there is no requirement to control the gas mixture other than removing carbon dioxide.

Oxygen feed options

In some rebreathers, eg Siebe Gorman Salvus, oxygen canisters have an oxygen supply mechanism in parallel. One is a constant stream; the other is a manual on-off valve called a bypass valve; both feed into the same hose that feeds the counterlung. In Salvus there is no second stage and the gas is turned on and off on the cylinder.

Others such as USN Mk25 UBA are supplied through the demand valve at the counterlung. This will add gas anytime when counterlung is emptied and the diver continues to inhale. Oxygen can also be added manually with a button that activates the request valve.

Some simple oxygen rebertathers do not have an automatic supply system, but only manual feed valves, and divers should operate the valves at intervals to refill the respiratory bag when the oxygen volume decreases below a comfortable level.

Rebreathers semi-closed circuit

These are generally used for underwater diving, as they are bigger and heavier than the closed-circuit oxygen rebreathers. Military and recreational divers use this because they provide better underwater duration than open circuits, have a deeper depth of deeper operation than oxygen rebreathers and can be quite simple and inexpensive. They do not rely on electronics to control gas composition, but can use electronic monitoring to improve security and decompress more efficiently.

Semi-closed circuit equipment generally supplies a respiratory gas such as air, nitrox or trimix at a time. The gas is injected into the loop at a constant rate to fill the oxygen consumed from the loop by the diver. Excess gases must be constantly removed from loops in small volumes to allow room for fresh, oxygen-rich gases. Since the oxygen in the released gas can not be separated from the inert gas, the semi-closed circuit is an oxygen wastage.

A gas mixture having maximum safe operating depth for the planned dive depth, and which will provide a surface-breathing mixture should be used, or will be required to replace the mixture during the dive.

Since the amount of oxygen required by the diver increases with the rate of action, the rate of gas injection must be carefully selected and controlled to prevent the unconscious of the diver due to hypoxia. Higher levels of gas addition reduce the chances of hypoxia but remove more gas.

Semi-closed passive addition

This type of rebreather works with the principle of adding fresh gas to offset the reduced volume in the breathing circuit. Some of the smoothed gases are discarded which in some ways is proportional to the use. Generally this is a fixed volumetric fraction of the respiratory flow, but more complex systems have been developed that drain close estimates of the ratio to surface respiratory flow rates. This is described as a depth compensation system or some in-depth compensation. The addition of gas is triggered by low count volume.

The simple case of fixed ratio discharge can be achieved by concentric belligerent counterlungs, in which the exhaled gas extends both countend, and while the larger outer volume bellies pass back into the loop when the diver breathes in the next breath, the inner bellows release the contents around it, using a non-valve -back to ensure one-way flow. The amount that is processed during each breath depends on the tidal volume of the breath.

Towards the end of the inhalation, the bottom of the vessel exits and activates the supplemental valve, in many ways the regulator diaphragm activates the demand valve, to form the gas issued by the inner bellows. This type of rebreather tends to operate at a minimal volume.

The fixed ratio system usually discharges between 10% (1/10) and 25% (1/4) of the volume of each breath to the ocean. Consequently, gas endurance is from 10 to four times that of open circuits, and depends on the level and depth of breathing in the same way as open circuits. The oxygen fraction in the loop depends on the discharge ratio, and to a lesser extent on the respiratory rate and work rate of the diver. Because some gases are recycled after inhaling, the oxygen fraction will always be lower than the make-up gas, but it can approach closely the make-up gas after the flush loop, so the gas is generally selected to breathe at maximum depth. , which allows it to be used for open circuit bailouts. The oxygen fraction of the loop gas will increase with depth, since the rate of metabolically used oxygen mass remains almost constant with the change in depth. This is the opposite trend of what is done in a closed circuit rebreather, where the oxygen partial pressure is controlled to be more or less the same within the boundary throughout the dive. Fixed ratio system has been used in rebreathers DC55 and Halcyon RB80. In addition to passive rebreathers with small discharge ratios can be hypoxic near the surface when gas supply moderate oxygen fraction is used.

The depth compensation system delivers a portion of the volume of the diver spear which varies in inverse proportion to absolute pressure. On the surface they generally release between 20% (1/5) and 33% (1/3) of each breath, but it decreases with depth, to keep the oxygen fraction in the circle approximately constant and reduce gas consumption. The full compensation system will release the gas volume, inversely proportional to the pressure, so that the volume released at a depth of 90m (absolute pressure of 10 bar) will be 10% of the surface discharge. This system will give approximately the fraction of oxygen remains without depth, when used with the same make-up gas, because effective mass release remains constant.

Partial partial compensation system is part of the road between fixed ratio and depth compensation system. They provide a high discharge ratio near the surface, but the discharge ratio is not fixed either as a proportion of volume or mass of respiration. The oxygen gas fraction is more difficult to calculate, but will be between the limiting value for fixed ratio and full compensation system. The Halcyon PVR-BASC uses a variable volume inner bellows system to compensate for depth.

An additional semi-closed circuit is active

The active addition system adds feed gas to the respiratory circuit and excess gas is discharged into the environment. These rebreathers tend to operate close to the maximum volume.

Constant flow gas flow constant

The most common system of the addition of active make-up gases to semi-closed rebreathers is by using a constant mass flow injector, also known as faltered flow. This is easily achieved by using an orifice, such as that given the pressure drop above the hole enough to ensure a sonic flow, the mass flow for a given gas will be released from downstream pressure. The mass flow through the sonic hole is a function of upstream pressure and gas mixture, so the upstream pressure must remain constant for the rebreather working depth range to provide reliably predictable mixtures in the respiratory circuit, and modified regulator is used unaffected by pressure changes ambient. The addition of the gas does not depend on the use of oxygen, and the gas fraction in the loop is highly dependent on diverting - it is possible to exhaust oxygen very dangerously by excessive physical activity.

Request for controlled gas addition

Only one model using this gas mix control principle has been marketed. This is DCSC Interspiro. The principle of operation is to add a mass of oxygen that is proportional to the volume of each breath. This approach is based on the assumption that the volumetric breathing rate of a diver is directly proportional to the consumption of metabolic oxygen, which the experimental evidence suggests is close enough to work.

The addition of fresh gas is carried out by controlling the pressure in the dose space proportional to the volume of the counterlung bellows. The dose chamber is filled with fresh gas until the pressure is proportional to the volume of the bellows, with the highest pressure when the bellows are in an empty position. When the bellows fill up when exhaling, the gas is released from the dose chamber into the breathing circuit, proportional to the volume in the bellows when exhaling, and is released completely when the bellows are full. Excess gas is discharged into the environment via overpressure valve after full bellows.

The result is an increase in gas mass proportional to the volume of ventilation, and the oxygen fraction stabilizes above the normal range of exertion.

The dose space volume is matched with a specific gas supply mixture, and changes when gas is changed. DCSC uses two nitrox standard mixtures: 28% and 46%.

The closed circuit gas rebreathers

Military, photographic, and recreational diversists use closed-circuit rebreathers because they allow long dives and do not produce bubbles. Rebreathers closed circuits supply two respiratory gas to the loop: one is pure oxygen and the other is a dilution or dilution gas such as air, nitrox, heliox or trimix.

The main function of rebreather closed circuit is to control the partial pressure of oxygen in the loop and to warn the diver if it becomes very low or high. Too low the concentration of oxygen produces hypoxia that causes unconsciousness and ultimately death. Oxygen concentrations that are too high cause hypoxoxia, causing oxygen toxicity, a condition that causes seizures that can make the divers lose the funnel when they occur underwater, and can cause drowning. The monitoring system uses oxygen-sensitive electro-galvanic fuel cells to measure the partial pressure of oxygen in the loop. The partial pressure of oxygen in the loop can generally be controlled with a reasonable tolerance of a fixed value. This set point is selected to provide an acceptable risk of long-acting and acute oxygen toxicity, while minimizing decompression requirements for planned dive profiles.

The gas mixture is controlled by divers in manually controlled closed-circuit rebreathers. Divers can control the mixture manually by adding dilution gas or oxygen. Adding a diluent can prevent the mixture of the gas loop becoming too oxygen rich, and adding oxygen is done to increase the oxygen concentration.

In a fully automatic closed circuit system, an electronically controlled solenoid valve injected oxygen into the loop when the control system detected that the partial oxygen pressure in the loop had dropped below the required level. The electronically controlled CCRs can be routed to manual controls in case of a control system failure.

The addition of gas to compensate for the compression during descent is usually done by an automatic fastening valve.

Rebreathers using oxygen-releasing absorbents

There are several rebreather designs (eg Oxylite) that have an absorbent tube filled with potassium superoxide, which releases oxygen by absorbing carbon dioxide: 4KO ₂ 2CO ₂ = 2K ₂ CO ₃ 3O ₂ ; it's a very small oxygen cylinder to fill the loop at the beginning of the dive. This system is dangerous because of the explosive heat reaction that occurs when water gets a potassium superoxide. Russian IDA71 military and rebreather navy are designed to run in this mode or as a regular rebreather.

Tests at IDA71 in the United States Navy Experimental Diving Unit in Panama City, Florida show that IDA71 can provide significantly longer dive times with superoxide in one tube than without.

Rebreathers that store liquid oxygen

If used under water, the oxygen-liquid tank must be well insulated against the incoming heat of water. As a result, industrial devices of this type may not be suitable for diving, and this type of dive may not be suitable for outdoor use. The liquid oxygen tank sets must be filled immediately before use. They include these types:

• Aerophor Blackett
• Aerorlox

Cryogenic Rebreather

A cryogenic rebreather removes carbon dioxide by freezing it in a "snow case" by the resulting low temperature when liquid oxygen evaporates to replace the oxygen used.

A cryogenic rebreat called S-1000 was built around or soon after 1960 by Sub-Marine Systems Corporation. It has a duration of 6 hours and a maximum diving depth of 200 meters (660 ft). PpO ₂ can be set to anything from 0.2 to 2 bar (3 to 30 psi) without electronics, by controlling the temperature of the liquid oxygen, thus controlling the oxygen gas equilibrium pressure above the liquid. The diluent can be either liquid or helium nitrogen depending on the depth of the dive. The set can freeze 230 grams of carbon dioxide per hour from the loop, corresponding to 2 liters of oxygen consumption per minute. If oxygen is consumed more quickly (high workload), regular cleaning is required.

Cryogenic rebreathers were widely used in Soviet oceanography in the 1980-1990 period.

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Application field

Diving rebreathers

The widest variety of the rebreather type is used in diving, because the consequences of breathing under pressure complicate the requirements, and the wide range of options available depends on the specific application and budget available.

Design criteria for scuba rebreathers

Operational requirements for diving rebreathers include

• waterproof construction and corrosion resistant
• almost close neutral after ballasting
• is quite efficient, to minimize additional pool resistance
• low breathing work in all diver's attitudes and full operating range
• the unit should not adversely affect trim and balance divers
• easy and fast harness release and unaided units from divers
• accessibility control components and settings
• unambiguous feedback to important information divers
• no important one-point failure mode - Users must be able to handle any suspected failures without outside help

Custom apps may also require

• low noise signal
• low bubbles/small bubbles
• low electromagnetic signature
• rough construction
• light in the air
• minimal additional tasks for normal operation

Rebreathers oxygen for diving

Because pure oxygen is toxic when inhaled at pressure, recreational divers certification bodies restrict oxygen decompression to a maximum depth of 6 meters (20 feet) and this restriction has been extended to oxygen rebreathers; In the past they have been used deeper (up to 20 meters (66 feet)) but such dives are more risky than what is now considered acceptable. Oxygen rebreathers are also sometimes used when decompressed from a deep-circuit dive, because inhaling pure oxygen helps nitrogen diffuse out of body tissue faster, and the use of rebreather may be more convenient to stop long decompression.

US Navy restrictions on the use of oxygen rebreather

• The normal working limit is 25 feet (7.6 m) for 240 minutes.
• Maximum working limit is 50 feet (15 m) for 10 minutes.

Oxygen boobers are no longer commonly used in recreational dives due to depth limits determined by oxygen toxicity, but are extensively used for military attack swimmers applications where greater depth is not required, due to their simplicity, lightness and compact size.

Rebreathers mixed gas for diving

Rebreathers semi-enclosed circuits used for diving may use additional active or passive gas, and the gas addition system can be compensated in depth. They use supply gas mixtures with higher oxygen fractions than steady state loop gas mixtures. Usually only one gas mixture is used, but it is possible to replace the gas mixture during the dive to extend the depth coverage available from some SCR.

Operational scope and SCR restrictions

• The passive passive addition of non-depth compensation reduces the safe range of operating depth in inverse proportion for the extension of gas resistance. This can be compensated by gas exchange, at the expense of complexity and increasing the number of potential failure points.
• The constant mass flow of SCRs gives an inconsistent gas mixture of variations in power diver. It also limits the range of safe depth of operation unless the gas composition is monitored, also at the expense of increased complexity and possible additional failure points.
• The demand for controlled active gas addition provides a reliable gas mixture across all potential operating depth ranges, and requires no oxygen monitoring, but at the expense of mechanical complexity.
• The higher passive addition of compensation provides a reliable gas mixture over the potential operating depth range, which is only slightly reduced from the open circuit operating range for the gas used at the cost of higher mechanical complexity.

Rebreathers closed circuits can be controlled manually or electronically, and use both pure oxygen and a breathable mixed gas diluent.

Operational scope and CCR restrictions

Surface gas escape system provided

The helium reclamation system (or pull-pull system) used to restore helium-based breathing gas after use by divers is now more economical than its loss to the environment in open circuit systems. The recovered gas passes through the scrubber system to remove carbon dioxide, filtered to remove odor, and is pressed into a storage container, where it can be mixed with oxygen to the composition needed for reuse.

Rebecathers standalone industry

Different design criteria apply for SCBA rebreathers for use only outside water:

• There is no variation of ambient pressure on the component. Counterlung can be placed for comfort and convenience.
• Gas cooling in the respiratory circle may be desirable, because the absorbent produces heat because it reacts with carbon dioxide, and the heating of the gas is not acceptable in hot industrial situations such as deep mine.
• Absorbent containers may in some cases rely on gravity to prevent drainage.
• If a full-face mask is used, it may have viewports designed for comfort or improve the field of vision, and does not need to be flat and parallel to prevent visual distortion as if under water.
• In firefighting rebreathers, consideration should be given to making the set quite refractory and protecting it from the effects of heat and debris.
• The need to get rid of sets quickly, may not show up, and straps may not require a quick release.
• Buoyancy is not a consideration, but weight may be very important.
• There are no constraints because of the physiological effects of breathing under stress. A complex gas mixture is not required. The oxygen boiler can usually be used.

Mountaineering rebreathers

Mountain rebreathers provide oxygen at higher concentrations than are available from atmospheric air in a naturally hypoxic environment. They should be light and reliable in severe cold including not stuck with frost. Chemical oxygen and compressed gases have been used in experimental closed-circuit oxygen systems - the first at Mt. Everest in 1938. The high system failure rate due to extreme cold weather has not been solved. Inhaling pure oxygen produces an increase in the partial pressure of oxygen in the blood: the climber breathes pure oxygen at the top of Mt. Everest has a greater oxygen partial pressure than breathing air at sea level. These results are capable of doing greater physical effort at altitude.

Atmosphere submarine

The atmospheric submarine setting is a one-person submarine articulated from an anthropomorphic form, with a leg joint that allows articulation under external pressure while maintaining the internal pressure of one atmosphere. Respiratory gas supplies may be supplied by umbilical surfaces, or from rebreather carried by the lawsuit. Emergency gas supply restorers may also be installed for suit with surface supplies or rebreather for primary respiratory gas.

Rebreathers for unstressed aircraft and high parachute

Similar requirements and working environment for mountain climbing, but less weight than the problem. The Soviet IDA-71 rebreather is also produced in high altitude versions, which are operated as an oxygen rebreather.

Anesthesia System

Anesthesia machines can be configured as rebreathers to provide oxygen and anesthetic gases to patients during surgery or other procedures requiring sedation. The absorber is present in the engine to remove carbon dioxide from the loop.

Both semi closed and fully enclosed circuit systems can be used for anesthesia machines, and both push-pull (pendulum) two directional flow and one directional loop system are used. The respirator circuit of the rotary control machine has two direct valves so that only the gas flow is delivered to the patient while the out-of-date gas returns to the engine.

The anesthesia machine can also provide gas for the ventilated patient who can not breathe on his own. Exhaust system removes any gas from the operating room to avoid environmental contamination.

Train anesthesia personnel for equipment failure using medical simulation techniques.

Space settings

One of the space suit functions is to provide the wearer with respiratory gas. This can be done through umbilicals from life support systems of spacecraft or habitat, or from the main life support systems brought by the lawsuit. Both of these systems involve rebreather technology because they both emit carbon dioxide from the respiratory gas and add oxygen to compensate for the oxygen used by the wearer. Spaceship usually uses oxygen rebreathers because it allows lower pressure in a setting that gives the wearer better freedom of movement.

Habitat life support system

(Submarine, submarine habitat, bomb shelter, space station, etc.) Living room occupied by several people in the medium to long term with limited gas supply. This is equivalent to rebreathers of closed circuits in principle, but generally depends on the mechanical circulation of respiratory gas through scrubbers.

Other designs

• This link describes experimental dry clothing (with a built-in hood and fullface mask) and a rebreather combination in which dry clothing acts as a breathing pouch, as in the old Draeger standard wet suit that has an installed rebreather package.

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rebreather architecture

Although there are several variations of diving rebreather designs, all types have a gas-tight bob-loop that dives breathe in and exhale into it. The loop consists of several components that are unified. Divers breathe through funnel or full mask. It is connected to one or more tubes that drain the inhaled and exhaling gas between the diver and the counterbalance bag or respiration b/b. It holds gas when not in the lungs of divers. This loop also includes scrubber containing carbon dioxide absorbent to remove carbon dioxide exhaled by a diver. Attached to the loop there will be at least one valve that allows the addition of gas, such as oxygen and possibly dilution gas, from gas storage into the loop. There may be a valve that allows gas ventilation from the loop.

Respiratory configuration

There are two basic configurations of gas flow: Loop and pendulum.

The loop configuration uses a one-way circulation of respiratory gas which breaths out of the funnel, passes the non-return valve to the respiratory tube, and then through the counterlung and scrubber, to return to the funnel through the inhalation hose and other non-return valves when the diver inhales.

The pendulum configuration uses a two-way flow. The exhaled gas flows from the funnel through a single hose to the scrubber, into the counterlung, and when inhaled the gas is pulled back through the scrubber and the same hose back into the funnel. The pendulum system is structurally simpler, but inherently contains a larger die space than gas released in the combined rehydration and inhalation tubes, which are rejuvenated. There are conflicting requirements to minimize the volume of dead space while minimizing breath flow resistance.

Spokesman

The diver breathes from the rebreather circuit through a mouthpiece or an oro-nasal mask that may be part of a full face mask or a diving helmet. The funnel is connected to the rest of the rebreather by inhaling the hose. The funnel from the diving refreather will usually include the closing valve, and may incorporate a dive/surface valve or a bailout valve or both. In a configurable loop rebreathers the funnel is usually the place where the non-return valve for the loop is installed.

Diving/Surface Valves

The Dive/Surface valve (DSV) is a valve on a funnel that can switch between the loop and the surrounding environment. This is used to close the loop at the surface to allow the diver to breathe the atmospheric air, and may also be used underwater to isolate the loop so that it will not flood if the funnel is taken out of the mouth.

Bailout valve

An adjustable valve/surface to close the loop and simultaneously open the connection to the open circuit demand valve is known as the bailout valve, since its function is to switch to open circuit bailout without having to remove the funnel. Safety devices are important when carbon dioxide poisoning occurs.

Respiratory Hose

A flexible corrugated rubber hose is used to connect the funnel to other breathing circuits, as this allows the head free movement of the diver. These hoses are surging to allow for greater flexibility while maintaining high resistance to collapse. Hose is designed to provide low resistance to respiratory gas flow. A single breathing tube is used for pendulum configuration (push-pull), and two hoses for one-way loop configuration.

Counterlungs

The counterlung is part of the loop that is designed to change the volume by an amount equal to the tidal volume of the user when breathing. This allows the loop to expand and contract as the user breathes, allowing the total gas volume in the lungs and the loop to remain constant throughout the respiratory cycle. Counter volume should allow for maximum possible breath volume from users, but generally it is not necessary to match the vital capacity of all possible users.

Underwater, the position of counterlung - in the chest, above the shoulder, or behind - has an effect on the hydrostatic breathing work. This is due to the difference in pressure between the counterlung and the diver's lungs caused by the vertical distance between the two.

Recreational, technical and professional divers will spend most of the time swimming under their water facing down and being trimmed horizontally. Counterlungs should work well with low breathing work in this position, and with the diver standing upright.

• Front mounting: When horizontal, they are under greater hydrostatic pressure than the diver's lungs. Easier to breathe, more difficult to exhale.
• Back mounted: When they are horizontal they are under less hydrostatic pressure than the diver's lungs. The numbers vary, as some are closer to the rear than others. More difficult to breathe, easier to exhale.
• Over the shoulder: Hydrostatic pressure will vary depending on how much gas is in the counterlung, and increases as the volume increases and the lower part of the gas chamber moves down. The work of holding the breath often negates the advantages of a good position near the center of the lung.

The design of the counterlung can also affect the downsizing of swimming divers because of the location and form of the counterlung itself.

For use outside the water, the position of the counterlung does not affect the work of breathing and can be positioned wherever comfortable. For example, in the industrial version of Siebe Gorman Salvus, the breathing bag hangs on the left hip.

A rebreather using rubber counterlung not in a closed casing should be protected from sunlight when not in use, to prevent rubber from dying from ultraviolet light.

Concentric bellows counterlungs

Most sealed semi-closed passive steam controls the gas mixture by removing the fixed volumetric proportion of the exhaled gas, and replacing it with fresh feed gas from the demand valve, triggered by low volume of the counterlung.

This is done by using a concentent belligerent counterlungs - the counterlung is configured as a bellows with rigid top and bottom, and has a flexible wavy membrane that forms a side wall. There are bellows, both smaller on the inside, also connected to the upper and rigid upper surfaces of the counterlung, so that as rigid surfaces move in the direction and away from each other, the inner and outer bellows volumes change in equal proportions.

The exhaled gas expands into the counterlung, and partly flows into the inner bellows. In inhalation, the diver only breathes from the outside counterlung - the reverse flow of the inner bellows is blocked by the non-return valve. The inner bellows are also connected to the non-returning valve openings to the outer environment, and thus the gas from the inner bellows is removed from the circuit in a fixed proportion of the breath volume inhaled. If the volume of counterlung is reduced sufficiently for a rigid cover to activate the feed gas demand valve, the gas will be added until the diver finishes inhaling it.

Scrubber carbon dioxide

The exhaled gas is directed through a chemical scrubber, the corresponding absorbent tube of carbon dioxide such as a lime soda form, which removes the carbon dioxide from the gas mixture and leaves the oxygen and other gas available for breathing again.

Some absorbent chemicals are produced in granular formats for dive applications, such as Sofnolime, Dragersorb, or Sodasorb. Other systems use Reactive Plastic Curtain (RPC) based cartridges: The term Reactive Plastics The curtains were originally used to describe Micropore absorbing curtains for emergency submarine use by the US Navy, and recently RPCs have been used to refer to their Reactive Plastic Cartridges.

The carbon dioxide passing through the absorbent scrubber is removed when reacting with the absorbent in the canister; This chemical reaction is exothermic. This reaction occurs along the "front" which is the area across the gas stream through the lime-soda in the tube. The front moves through a scouring tube, from the gas input end to the gas output end, when the reaction consumes the active ingredient. The front of this will be a zone of thickness depending on the grain size, reactivity, and speed of the gas flow because the carbon dioxide in the gas through the tube takes time to reach the absorbent granular surface, and then time to penetrate to the center of each absorbent grain when the outside of the seed- the grains become tired. Eventually the gas with the remaining carbon dioxide will reach the end of the tube and the "breakthrough" will occur. After this, the carbon dioxide content of the released gas will tend to increase because the effectiveness of the scouring drops until it becomes apparent to the user, then can not be cured.

In larger systems, such as the recompression chamber, the fan is used to pass gas through the tube.

Effectiveness of scrubber

In rebreather diving, the effective effective duration of the scrubber will be half an hour to several hours of respiration, depending on the granularity and composition of soda lime, ambient temperature, rebreather design, and canister size. In some dry open environments, such as a recompression room or hospital, it is possible to place fresh absorber in the tube when damage occurs.

Gas ventilation

Overpressure valve

During the ascent, the gas in the respiratory circuit will expand, and should have some way out before the pressure difference causes injury to the diver or damage to the loop. The simplest way to do this is to diver to allow excess gas to escape around the funnel or through the nose, but a simple overpressure valve is reliable and can be adjusted to control the allowed overpressure. Overpressure valves are usually installed on counterlung and military dive rebreathers may be equipped with a diffuser.

Diffuser

Some military dive rebreathers have a diffuser on top of the blowoff valve, which helps to hide the presence of divers by covering the release of bubbles, by breaking it down to a size less easily detected. Diffuser also reduces bubble noise.

Loop drainage

Many rebreathers have a "water trap" in the counterlung or scrubber casing, to stop large volumes of water entering the scrubber media if the diver issues an underwater funnel without closing the valve, or if the diver's lips become saggy and let the water leak in.

Some rebels have manual pumps to remove water from water traps, and some passive SCR additives automatically pump water along with the gas during the exhaust exhaust count.

Work breathe

The work of breathing is the effort needed to breathe. Part of the respiratory work is due to inherent physiological factors, in part due to the mechanisms of the external breathing apparatus, and partly due to the characteristics of respiratory gas. High breathing work can cause carbon dioxide buildup in divers, and reduce the ability of divers to generate useful physical effort

The breathing work of the rebreather has two main components: The work of respiratory resistance is due to the limitation of gas line flow causing resistance to respiratory gas flow, and is present in all applications where there is no external powered ventilation. Hydrostatic breathing work is only applicable to dive applications, and because of the pressure difference between the diver's lungs and counter rebreather counter. This pressure difference is generally caused by differences in hydrostatic pressure caused by the difference in depth between the lung and the counterlung, but can be modified by ballasting the moving side of the counterlung bellows.

Respiratory resistance work is the sum of all flowing restrictions due to bends, wrinkles, changes in flow direction, valve cracking pressure, flow through the scrubber medium, etc., and resistance to gas flow, due to inertia and viscosity, which is affected by density, which is a function of weight and molecular pressure. The rebreather design can limit the mechanical aspects of flow resistance, especially by the scrubber design, counterlung and respiratory hose. Diving rebreathers are affected by the variation of breathing work due to the choice and depth of the gas mixture. Helium content reduces respiratory work, and increased depth increases respiratory work.

Gas source

Rebels must have a source of oxygen to fill that is consumed by divers. Depending on the variant of the rebreather design, the source of oxygen will be a pure or mixed respiratory gas that is almost always stored in a gas cylinder. In some cases, oxygen is given as liquid oxygen or from chemical reactions.

Pure oxygen is not considered safe for diving over 6 meters, so recreational rebreathers and many professional diving rebreathers also have gas cylinders. This diluent cylinder can be filled with compressed air or other dive gas mixtures such as nitrox or trimix. The diluent reduces the percentage of oxygen being inhaled and increases the maximum operating depth of the rebreather. The diluent is not an oxygen-free gas, such as nitrogen or pure helium, and may breathe as it will be used in an emergency to either flush the loop with a breathable gas of a known composition or as a bailout.

Gas enhancer valve

Automatic release valve (ADV)

It has a function similar to the open-circuit demand valve. That adds gas to the circuit if the volume in the circuit is too low. The mechanism is operated either by a special diaphragm as in the second stage of scuba, or it can be operated by the top of the counterlung bellows type that reaches the bottom of its journey.

Manual addition

Rebreathers closed circuits usually allow divers to add gas manually. On oxygen rebreathers, these are only oxygen, but mixed gas rebreathers usually have manual sperate summation valves for oxygen and diluents, as they may be needed to improve the composition of the loop mix, either as a standard operating method for manually controlled CCRs, or as a backup system on CCRs which are electronically controlled. Added manual diluents sometimes by cleaning button on ADV.

Mass flow constant

The constant mass flow separation is used in the addition of active semi-closed rebreathers, where it is a normal method of addition at a constant depth, and in many closed-circuit rebreathers, where it is the primary method of oxygen addition, at a rate less than metabolically required by the diver at rest , and the remainder is made by the control system through the solenoid valve, or manually by the diver.

The constant mass flow is achieved by the sonic flow through the hole. The flow of the compressible liquid through the hole is limited to the flow at the sonic velocity in the orifice. It can be controlled by upstream pressure and size and shape of the hole, but once the flow reaches the speed of sound in the hole, further decrease of downstream pressure has no effect on the flow rate. This requires a gas source at a fixed pressure, and only works at a depth that has ambient pressure low enough to provide a sonic flow in the hole.

Regulators that have their control components isolated from ambient pressure are used to supply gas at pressure independent from depth.

Passive addition

In the passive addition of semi-closed bamboo shoots, the gas is usually added by a demand-type valve that is driven by the counter-opponent when the bellows are empty. This is the same actuation condition as the automatic fastening valve of each rebreather, but the actual trigger mechanism is slightly different. A passive rebreather of this type does not require a separate ADV because the passive additional valve already serves this function.

Electronically controlled (solenoid valve)

An electronically controlled closed circuit with mixed gas rebreathers may have a portion of the oxygen feed provided by a constant mass flow orifice, but subtle control of the partial pressure is performed by solenoid-operated valves driven by the control circuitry. The timely opening of the solenoid valve will be triggered when the oxygen partial pressure in the loop mix falls below the lower set-point.

If the constant mass flow orifice is compromised and does not provide the correct flow, the control circuit will compensate by firing the solenoid valve more often.

Control of respiratory gas mixture

The fundamental requirement for controlling gas mixtures in respiratory circuits for rebreather applications is that carbon dioxide is removed, and stored at a tolerable level, and that the partial pressure of oxygen is stored within safe limits. For rebreathers used at normobaric or hypobaric pressures, this only requires adequate oxygen, which is easily achieved in an oxygen rebreather. Hyperbaric applications, such as in diving, also require that the maximum oxygen partial pressure is limited, to avoid oxygen toxicity, which is technically a more complex process, and may require oxygen dilution with inert metabolically.

If not enough oxygen is added, the oxygen concentration in the circle may be too low to support life. In humans, the drive for breathing is usually caused by the buildup of carbon dioxide in the blood, rather than the lack of oxygen. Hypoxia can cause blackouts with little or no warning, followed by death.

The method used to control the oxygen partial pressure range in the respiratory loop depends on the type of rebreather.

• In an oxygen rebreator, once the loop is completely flushed, this mixture is effectively static at 100% oxygen, and the partial pressure only serves as ambient pressure.
• In a semi-closed rebreather, the loop mix depends on a combination of factors:

• type of gas addition system and its arrangement, combined with the gas mixture used, which controls the rate of added oxygen.
• work rate, and therefore the level of oxygen consumption, which controls the rate of oxygen depletion, and therefore the resulting oxygen fraction.
• ambient pressure, as a partial pressure proportional to ambient pressure and oxygen fraction.

• In closed controlled manually controlled rebreathers, the user controls the gas and volume mixtures in the loop by injecting each of the available gases into the loop and by releasing the loop.
• Most closed rebreathers-electronically controlled circuits have electro-galvanic oxygen sensors and electronic control circuits, which monitor ppO ₂ , inject more oxygen if necessary and emit sound, visual and/or vibration warning to divers if ppO ₂ reaches a dangerous high or low level.

The volume in the loop is usually controlled by a pressure-controlled automatic fastening valve, which works on the same principle as the demand valve. This adds to dilution when the pressure in the loop decreases under ambient pressure, such as during down or if gas is lost from the loop. The set may also have an additional manual valve, sometimes called cut off . In some early oxygen rebreathers the user has to manually open and close the valve to the oxygen cylinder to recharge the counterlung every time the volume becomes low.

Configuration

Settings

The rebreather sections (bag, absorbent tube, cylinder) can be set on the wearer's body in many ways, rather than with open air air scuba. As an example:

• In early Russian Epron-1 rebreather, the scrubber tube, counterlung and oxygen tube are parallel to the chest, from left to right, with a breathing tube loop from the end of the canister to the bag.
• In this old German industrial rebreather, the functioning section is at the user's left waist and has one long tube of breathing.
• Some are reinstalled. Some are worn on the chest. Some have hard casing. If used underwater, the counterlung should be near the lungs of the user. The length of use on the fill varies greatly with make.

Casing

Many rebreathers have their main components in hard backpacks for support, protection and/or downsizing. This casing should be released to allow water or air around it in and out to allow volume changes as the respiratory bag expands and deflates. The diving rebreather requires a large hole, including a hole in the bottom to drain the water when the diver out of the water. SEFA, used for mine rescue, to keep sand and stones from working, completely sealed, except for large venting panels lined with metal mesh, and holes for oxygen cylinder on/off valves and cylinder pressure gauges. Underwater casing also functions for downsizing, eg. in IDA71 and Cis-Lunar.

src: www.jonasdive.com

Security

Dangers

Hypoxia

Hypoxia can occur in rebreather containing enough inert gas to allow breathing without triggering the addition of automatic gas.

In an oxygen rebreather, this can occur if the loop is not adequately cleaned at the start of use. Cleaning should be done while breathing from the unit so that the inert gas in the user's lungs is also removed from the system.

Carbon dioxide buildup

Carbon dioxide buildup will occur if the scrubber media does not exist, is very dense, inadequate or exhausted. The normal human body is quite sensitive to the partial pressure of carbon dioxide, and the buildup will be noticed by the user. However, there is not much that can be done to remedy this problem unless replacing it to another gas supply of breathing until the scrubber can be repackaged. Continuing to use rebreather with an ineffective scrubber is not possible for a very long time, because the level will be toxic and the user will experience distress

Source of the article : Wikipedia