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134-400: The invention revolutionised autonomous underwater diving by providing a compact, reliable system capable of a greater depth range and endurance than its precursors, and was a major factor influencing the development of recreational scuba diving after WWII. The twin-hose Aqua-Lung demand regulator is the foundation of all modern scuba regulators. A diaphragm is used to control a valve to deliver

268-480: A National Geographical Society Magazine article about Cousteau's underwater archaeological expedition to Grand Congloué  [ fr ] . In France, aqualung diving was popularized by Cousteau's movie Épaves , while his book The Silent World also helped significantly. As with some other registered trademarks , the term "aqualung" became a genericized trademark in English-speaking countries as

402-524: A diving regulator (the Aqua-Lung ) that supplied the diver with breathing gas at ambient pressure via a demand valve. For more than ten years, seen in the films Épaves ( Shipwrecks , 1943) and Le Monde du silence ( The Silent World , 1956) the main scuba equipment used by Cousteau and his divers was an Aqua-Lung mounted on three diving cylinders, one being used as a reserve. The Aqua-Lung allowed divers to spend more time underwater, and, along with

536-414: A full-face diving mask with a shut-off valve, the dive/surface valve, which is closed when the diver is not breathing from the unit to prevent flooding if the set is in the water. This is connected to one or two breathing hoses ducting inhaled and exhaled gas between the diver and a counterlung or breathing bag, which expands to accommodate gas when it is not in the diver's lungs. The reservoir also includes

670-661: A partial pressure of oxygen between programmable upper and lower limits, or set points, and be integrated with decompression computers to monitor the decompression status of the diver and record the dive profile . Diving rebreathers are generally used for scuba applications , where the amount of breathing gas carried by the diver is limited, but are also occasionally used as gas extenders for surface-supplied diving and as bailout systems for scuba or surface-supplied diving. Gas reclaim systems used for deep heliox diving use similar technology to rebreathers, as do saturation diving life support systems , but in these applications

804-415: A rebreather has two main components: Resistive work of breathing is due to the flow restriction of the gas passages causing resistance to flow of the breathing gas, and exists in all applications where there is no externally powered ventilation. Hydrostatic work of breathing is only applicable to diving applications, and is due to difference in pressure between the lungs of the diver and the counterlungs of

938-421: A breathing pattern that is slower and deeper than normal rather than fast and shallow, as this gives maximum gas exchange per unit effort by minimising turbulence, friction, and dead space effects. Carbon dioxide is a product of cell metabolism which is eliminated by gas exchange in the lungs while breathing. The rate of production is variable with exertion, but there is a basic minimum. If the rate of elimination

1072-460: A deep open-circuit dive, as breathing pure oxygen helps the nitrogen diffuse out of the body tissues more rapidly, and the use of a rebreather may be more convenient for long decompression stops. US Navy restrictions on oxygen rebreather use: Oxygen rebreathers are no longer commonly used in recreational diving because of the depth limit imposed by oxygen toxicity, but are extensively used for military attack swimmer applications where greater depth

1206-482: A device to help assist in escaping from flooded mines. The Rouquayrol regulator was adapted to diving in 1864, when Rouquayrol met the lieutenant de vaisseau Auguste Denayrouze . The Rouquayrol-Denayrouze apparatus went into mass production and commercialization on 28 August 1865, when the French Navy Minister ordered the first units. After 1884, several companies and entrepreneurs bought or inherited

1340-421: A dive to extend the available depth range of some SCRs. Operational scope and restrictions of SCRs: Closed circuit diving rebreathers may be manually or electronically controlled, and use both pure oxygen and a breathable mixed gas diluent. Operational scope and restrictions of CCRs: Closed circuit rebreathers are mainly restricted by physiological limitations on the diver, such as maximum operating depth of

1474-718: A division of Air Liquide in order to mass-produce and sell their invention, this time under a new 1945 patent, and known as CG45 ("C" for Cousteau, "G" for Gagnan and "45" for 1945). This same CG45 regulator, produced for more than ten years and commercialized in France as of 1946, was the first to actually be called the "Aqua-Lung". In France, the terms scaphandre autonome ("autonomous diving set"), scaphandre Cousteau-Gagnan ("Cousteau-Gagnan diving set"), or CG45 were meaningful enough for commercialization, but to sell his invention in English-speaking countries, Cousteau needed an appealing name following English language standards. He then coined

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1608-437: A given breathing gas mixture, the density will increase with an increase in depth. A higher gas density requires more effort to accelerate the gas in the transitions between inhalation and exhalation. To minimise the work of breathing the flow velocity can be reduced, but this will reduce RMV unless the depth of breathing is increased to compensate. Slow deep breathing improves efficiency of respiration by increasing gas turnover in

1742-489: A larger range than for back or chest mount, and the resisistive work of breathing is also relatively large due to the long breathing hoses and multiple bends necessary to fit the components into a long narrow format. As of 2019, no sidemount rebreather had passed the CE test for work of breathing. Sidemount rebreathers may also be more susceptible to major loop flooding due to lack of a convenient exhalation counterlung position to form

1876-449: A low profile to penetrate tight restrictions in cave and wreck diving, and is convenient for carrying a bailout rebreather. A sidemount rebreather as the main breathing apparatus can be mounted on one side of the diver's body and can be balanced weight-wise and hydrodynamically by a large bailout cylinder side mounted on the other side. Sidemount rebreathers are sensitive to diver orientation, which can change hydrostatic work of breathing over

2010-404: A mouthpiece and counterlung to form a closed loop. Although there are several design variations of diving rebreather, all types have a gas-tight reservoir to contain the breathing gas at ambient pressure that the diver inhales from and exhales into. The breathing gas reservoir consists of several components connected together by water- and airtight joints. The diver breathes through a mouthpiece or

2144-412: A person breathes, the body consumes oxygen and produces carbon dioxide . Base metabolism requires about 0.25 L/min of oxygen from a breathing rate 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 , or about 20% of

2278-407: A rebreather. Gas density at ambient pressure is a limiting factor on the ability of a diver to effectively eliminate carbon dioxide at depth for a given work of breathing. At increased ambient pressure the increased breathing gas density causes greater airway resistance. Maximum exercise ventilation and maximum voluntary ventilation are reduced as a function of density, which for a given gas mixture

2412-496: A reference to volume or time. It can be calculated in terms of the pulmonary pressure multiplied by the change in pulmonary volume, or in terms of the oxygen consumption attributable to breathing. In a normal resting state the work of breathing constitutes about 5% of the total body oxygen consumption. It can increase considerably due to illness or constraints on gas flow imposed by breathing apparatus , ambient pressure , or breathing gas composition. The normal relaxed state of

2546-626: A result of common use by the public and in publications, including the BSAC 's official diving manuals. Presumably, lawyers for Cousteau or Air Liquide could have slowed or stopped this genericization by taking prompt action, but this seems not to have been done in Britain, where Siebe Gorman held the British rights to both the trade name and the patent. In the United States, the term aqualung

2680-421: A roll to the right side made breathing easier. Raising the mouthpiece above the regulator increases the delivered pressure of gas at the mouth and increases exhaust resistance, and lowering the mouthpiece reduces delivered pressure and increases inhalation resistance. An earlier underwater breathing regulator, known as the régulateur , was invented in France in 1860 by Benoît Rouquayrol . He first conceived it as

2814-539: A scrubber containing absorbent material to remove the carbon dioxide exhaled by the diver. There will also be at least one valve allowing addition of gas, such as oxygen, and often a diluent gas, from a gas storage container, into the reservoir. There may be valves allowing venting of gas, sensors to measure partial pressure of oxygen and possibly carbon dioxide, and a monitoring and control system. Critical components may be duplicated for engineering redundancy. There are two basic gas passage configurations: The loop and

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2948-406: A sharp exhalation. By rolling in the right direction in a horizontal position, the trapped water will flow by gravity into the exhaust hose, and when the mouthpiece is shallower than the diaphragm, the regulator will tend to free-flow when out of the mouth, which can also be used to purge the inhalation hose. Ideally the delivered pressure is equal to the resting pressure in the diver's lungs as this

3082-477: A single breath and is described in hertz. Because measuring the work of breathing requires complex instrumentation, measuring it in patients with acute serious illness is difficult and risky. Instead, physicians determine if the work of breathing is increased by gestalt or by examining the patient looking for signs of increased breathing effort. These signs include nasal flaring, the contraction of sternomastoid , and thoraco-abdominal paradox . Work of breathing

3216-518: A slower rate than if there were only one counterlung. This decreases work of breathing, and also increases dwell time of the gas in the scrubber, as it flows through the scrubber during both exhalation and inhalation. Most mixed gas diving rebreathers use this arrangement. Many rebreathers have their main components in a hard casing for support, protection and/or streamlining. This casing must be sufficiently vented and drained to let surrounding water or air in and out freely to allow for volume changes as

3350-414: A strong counterlung to hold the components together. The parts of a diving rebreather (counterlung, absorbent canister, gas cylinder(s), tubes and hoses linking them), can be arranged on the wearer's body in four basic ways, with the position of the counterlung having a major effect on work of breathing. Back mount is common on the more bulky and heavier units. This is good for support of the weight out of

3484-469: A term for an open-circuit, demand valve-controlled breathing apparatus (even after Air Liquide's patent expired and other manufacturers started making identical equipment), occasionally also for rebreathers , and in figurative uses (such as "the water spider 's aqualung of air bubbles"). The word entered the Russian language as the generic noun акваланг ("akvalang"). That word was taken into Lithuanian as

3618-515: A two stage single hose regulator which he marketed in Australia as the Porpoise . Virtually all modern open-circuit scuba regulators use the single-hose two-stage design, though Aqualung did market a modernised twin-hose Mistral model in 2005 and 2006. Aqualung , Aqua-Lung , and Aqua Lung are registered trademarks for scuba diving breathing equipment. That trade name was originally owned in

3752-438: A water trap. Sidemount rebreathers usually use a form factor equivalent to a single sidemount open circuit cylinder, which mimics the streamlining of a sidemount cylinder, but has hydrostatic work of breathing variability issues if the unit isn't perfectly rigged and mounted. The work of breathing is only optimised when the diver is trimmed correctly. The KISS Sidewinder is a sidemount MCCR that reduces this problem by mounting

3886-410: Is "gas extender". Semi-closed circuit equipment generally supplies one breathing gas such as air, nitrox or trimix at a time. The gas is injected into the loop at a constant rate to replenish oxygen consumed from the loop by the diver. Excess gas must be constantly vented from the loop in small volumes to make space for fresh, oxygen-rich gas. As the oxygen in the vented gas cannot be separated from

4020-432: Is a function of flow velocity, density and viscosity. As density increases, the amount of pressure difference required to drive a given flow rate increases. When the density exceeds about 6g/litre the exercise tolerance of the diver becomes significantly reduced, and by 10 g/litre it is marginal. At this stage even moderate exertion may cause a carbon dioxide buildup that cannot be reversed by increased ventilation, as

4154-409: Is affected by several factors in underwater diving at ambient pressure. There are physiological effects of immersion, physical effects of ambient pressure and breathing gas mixture, and mechanical effects of the gas supply system. The properties of the lung can vary if a pressure differential exists between the breathing gas supply and the ambient pressure on the chest. The relaxed internal pressure in

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4288-409: Is an underwater breathing apparatus that absorbs the carbon dioxide of a diver'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 added to replenish the amount metabolised by the diver. This differs from open-circuit breathing apparatus, where the exhaled gas is discharged directly into

4422-404: Is an exhalation counterlung it is inflated on exhalation, but no gas flows through the scrubber until inhalation starts, at which point the diver sucks the gas through at a rate forced by inhalation rate. If it is an inhalation counterlung, the diver must blow gas through the scrubber during exhalation, but inhales from the full inhalation counterlung, with no further flow through the scrubber. If it

4556-411: Is between split scrubbers the diver must blow the gas through the exhalation scrubber during exhalation, and suck it through the inhalation scrubber. In all these cases there is no buffer, and peak flow rates are relatively high, which means peak flow resistance is relatively high and may be in one half of the breathing cycle or split between both halves, analogous to the pendulum configuration, but without

4690-461: Is blocked by the demand valve. When the diver consumes ambient pressure gas, the pressure falls in the low pressure chamber and the diaphragm deforms inwards pushing against the valve lifter. This opens the high pressure valve permitting gas to flow past the valve seat into the low pressure chamber. When the diver stops inhaling, pressure in the low pressure chambers quickly rises until the diaphragm returns to its neutral position and no longer presses on

4824-411: Is consumed and carbon dioxide produced in the same quantities underwater as at the surface for the same amount of work, but breathing requires work, and work of breathing can be much greater underwater, and work of breathing is similar to other forms of work in the production of carbon dioxide. The ability of a diver to respond to increases in work of breathing is limited. As work of breathing increases,

4958-565: Is flushed out, and the greater the pressure gradient between the venous blood and alveolar gas that drives carbon dioxide diffusion from the blood. Maintenance of the correct carbon dioxide levels is critically dependent on adequate lung ventilation, and there are multiple aspects of diving that can interfere with adequate ventilation of the lungs. Carbon dioxide retention as a consequence of excessively high work of breathing may cause direct symptoms of carbon dioxide toxicity, and synergistic effects with nitrogen narcosis and CNS oxygen toxicity which

5092-422: Is greater than atmospheric pressure (positive barometric values), and not during passive expiration when intrapleural pressure remains at subatmospheric pressures (negative barometric values). Clinically, dynamic compression is most commonly associated to the wheezing sound during forced expiration such as in individuals with chronic obstructive pulmonary disorder (COPD). The density of the gas also influences

5226-419: Is inevitable. Work of breathing is affected by gas density, so use of a low density helium rich diluent can increase depth range at acceptable work of breathing for a given configuration. WoB is also increased by turbulent flow , which is affected by flow velocity ( Reynolds number ). To some extent work of breathing can be reduced or limited by breathing circuit design, but there are physiological limits too, and

5360-417: Is less than the rate of production, the levels will increase, and produce symptoms of toxicity such as headache, shortness of breath and mental impairment, eventually loss of consciousness, which can lead to drowning. In diving there are factors which increase carbon dioxide production (exertion), and factors which can impair elimination, making divers particularly vulnerable to carbon dioxide toxicity. Oxygen

5494-575: Is metabolically expended. These are almost exclusively used for underwater diving, as they are bulkier, heavier, and more complex than closed circuit oxygen rebreathers. Military and recreational divers use these because they provide better underwater duration than open circuit, have a deeper maximum operating depth than oxygen rebreathers and can be fairly simple and cheap. They do not rely on electronics for control of gas composition, but may use electronic monitoring for improved safety and more efficient decompression. An alternative term for this technology

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5628-416: Is not clear who invented the first single hose regulator. The invention was motivated by an effort to bypass Aqua-Lung's patent on the twin-hose regulator, which involved the return of exhaust gas to the regulator to reduce the differential pressure and therefore reduce the amount and variation of over- or under-pressure of the breathing gas in the lungs. The single hose regulator accomplishes this by relocating

5762-409: Is not required, due to their simplicity, light weight and compact size. Semi-closed circuit rebreathers (SCRs) used for diving may use active or passive gas addition, and the gas addition systems may be depth compensated. They use a mixed supply gas with a higher oxygen fraction than the steady state loop gas mixture. Usually only one gas mixture is used, but it is possible to switch gas mixtures during

5896-538: Is now called " nitrox "): SCMBA from the SCBA ( Swimmer Canoeist's Breathing Apparatus ), and CDMBA from the Siebe Gorman CDBA , 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. During this long period before

6030-464: Is proportional to pressure. Maximum voluntary ventilation is approximated by a square root function of gas density. Exhalation flow rate is limited by effort independent turbulent flow. Once this occurs further attempts to increase flow rate are actively counterproductive and contribute to further accumulation of carbon dioxide. The effects of negative static lung load are amplified by increased gas density. To reduce risk of hypercapnia, divers may adopt

6164-442: Is provided by the stored elastic energy. When there is increased gas flow resistance, the optimal respiratory rate decreases. This work (generally during the inhalation phase) is stored as potential energy which is recovered during exhalation. A pressure difference is required to overcome the frictional resistance to gas flow due to viscosity, inertial resistance due to density, and to provide non-elastic components of movement of

6298-462: Is the Joule, equivalent to a force of 1 Newton exerted along a distance of 1 metre. In gas flow across a constant section this equates to a volume flowing against a pressure: Work = Pressure x Volume and Power = Work / time with SI units for Power: Watts = Joules per second The term "work of breathing" should be more accurately referred to as the "power of breathing," unless it is in reference to

6432-422: Is toxic when inhaled at pressure, recreational diver certification agencies limit oxygen decompression to a maximum depth of 6 metres (20 ft) and this restriction has been extended to oxygen rebreathers; In the past they have been used deeper (up to 20 metres (66 ft)) but such dives were more risky than what is now considered acceptable. Oxygen rebreathers are also sometimes used when decompressing from

6566-555: Is used in life-support systems in submarines, submersibles, underwater and surface saturation habitats, and in gas reclaim systems used to recover the large volumes of helium used in saturation diving . The recycling of breathing gas comes at the cost of technological complexity and additional hazards, which depend on the specific application and type of rebreather used. Mass and bulk may be greater or less than equivalent open circuit scuba depending on circumstances. Electronically controlled diving rebreathers may automatically maintain

6700-532: Is used in diving, as the physical and physiological consequences of breathing under pressure complicate the requirements, and a large range of engineering options are available depending on the specific application and available budget. A diving rebreather is safety-critical life-support equipment – some modes of failure can kill the diver without warning, others can require immediate appropriate response for survival. General operational requirements include: Special applications may also require: As pure oxygen

6834-446: Is usually necessary to eliminate the metabolic product carbon dioxide (CO 2 ). The breathing reflex is triggered by carbon dioxide concentration in the blood, not by the oxygen concentration, so even a small buildup of carbon dioxide 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 , so rebreathers must chemically remove

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6968-552: 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 recycled 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 , or carbon dioxide toxicity. A high ventilation rate

7102-406: Is what human lungs are adapted to breathe. With a twin hose regulator behind the diver at shoulder level, the delivered pressure changes with diver orientation. if the diver rolls on his or her back the released air pressure is higher than in the lungs. Divers learned to restrict flow by using their tongue to close the mouthpiece. When the cylinder pressure was running low and air demand effort rising,

7236-408: The counterlung and will increase the work of breathing and in extreme cases lead to dynamic airway compression. The effects of positive static lung load in these circumstances have not been clearly demonstrated, but may delay this effect. Density of a given gas mixture is proportional to absolute pressure at a constant temperature throughout the range of respirable pressures, and resistance to flow

7370-468: The 1930s for deep diving, circulated the breathing gas through the helmet and scrubber by using an injector system where the added gas entrained the loop gas and produced a stream of scrubbed gas past the diver inside the helmet, which eliminated external dead space and resistive work of breathing, but was not suitable for high breathing rates. Factors which influence the work of breathing of an underwater breathing apparatus include density and viscosity of

7504-471: The French Navy during the first few years of World War II. It was an open circuit system supplied from two 200 bar cylinders, and used a single stage regulator to supply gas to a bag between the two back-mounted cylinders at slightly above ambient pressure. The gas was then supplied to the left side of a full-face mask by a corrugated rubber hose, and exhausted directly from the right side of the mask. It

7638-532: The United States by a company known as U.S. Divers (now Aqua Lung America ). The term was in use before the trademark was registered by René Bussoz, who owned a sporting goods store called René Sports in Los Angeles. He obtained a contract with Air Liquide , the parent company of Aqua Lung/La Spirotechnique , to import the new scuba equipment into the United States for sale on the Pacific coast (SPACO Inc. had

7772-453: The additional carbon dioxide produce in doing this work pushes up the need for higher elimination rate, which is proportional to ventilation, in the case of negligible carbon dioxide in the inspired air. Carbon dioxide production by the tissues is a simple function of tissue metabolism and oxygen consumption. The more work done in a tissue, the more oxygen will be consumed and the more carbon dioxide will be produced. Carbon dioxide removal in

7906-413: The air passages induces blood engorgement of the distensible lung blood vessels, reducing the compliance of the lung tissue and making the lung stiffer than normal, therefore requiring more muscular effort to move a given volume of gas through the airways. This effect can occur in an upright open-circuit diver, where the chest is deeper than the regulator, and in a rebreather diver if the chest is deeper than

8040-489: The airway tissues to accommodate pulmonary volume change. Dynamic airway compression occurs when intrapleural pressure equals or exceeds alveolar pressure , which causes dynamic collapsing of the lung airways. It is termed dynamic given the transpulmonary pressure (alveolar pressure − intrapleural pressure) varies based on factors including lung volume , compliance , resistance , existing pathologies, etc. It occurs during forced expiration when intrapleural pressure

8174-400: The alveoli depends on the partial pressure gradient for carbon dioxide diffusion between blood and the alveolar gas. This gradient is maintained by flushing carbon dioxide out of the alveoli during breathing, which depends on replacing air in the alveoli with more carbon dioxide by air with less carbon dioxide. The more air moved in and out of the alveoli during breathing, the more carbon dioxide

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8308-565: The alveoli, and exertion must be limited to match the gas transfer possible from the RMV which can be comfortably maintained over long periods. Exceeding this maximum continuous exertion may lead to carbon dioxide buildup, which can cause accelerated breathing rate, with increased turbulence, leading to lower efficiency, reduced RMV and higher work of breathing in a positive feedback loop. At extreme depths this can occur even at relatively low levels of exertion, and it may be difficult or impossible to break

8442-407: The ambient pressure, set by an adjustable spring preloading the diaphragm, The interstage breathing gas is then reduced to ambient pressure by the second stage. The first stage diaphragm is a spring-loaded flexible cover to the interstage pressure chamber. When the diver consumes gas from the second stage, the pressure falls in the interstage chamber and the diaphragm deforms inwards pushing against

8576-434: The amount of equipment that the diver needs to carry. PADI criteria for "R" class rebreathers include electronic prompts for pre-dive checks, automatic setpoint control, status warnings, a heads up display for warnings, a bailout valve, pre-packed scrubber canisters and a system for estimating scrubber duration. While these constraints do make the recreational class of rebreather inherently less hazardous, they do not reduce

8710-405: The available oxygen in the air at sea level . Exhaled air at sea level contains roughly 13.5% to 16% oxygen. The situation is even more wasteful of oxygen when the oxygen fraction of the breathing gas is higher, and in underwater diving, the compression of breathing gas due to depth makes the recirculation of exhaled gas even more desirable, as an even larger proportion of open circuit gas

8844-627: The back of the helmet and an inlet gas injection system which recirculates the breathing gas through the scrubber to remove carbon dioxide and thereby conserve helium. The injector nozzle would blow 11 times the volume of the injected gas through the scrubber. The first attempts at making practical rebreathers were simple oxygen rebreathers, when advances in industrial metalworking made high-pressure gas storage cylinders possible. From 1878 on they were used for work in unbreathable atmospheres in industry and firefighting, at high altitude, for escape from submarines; and occasionally for swimming underwater; but

8978-431: The breathing gas to the diver on demand, at ambient water pressure. However, the layout has changed to a single hose system, where the second stage is split from the first stage along with the exhaust valve, as they must be kept at the same depth, and repositioned at the diver's mouth, eliminating the need for the exhaust hose, and allowing the use of a more rugged, smaller bore hose for the intermediate pressure gas supply to

9112-435: The breathing hoses where they connect to the mouthpiece prevent any water that gets into the mouthpiece from going into the inhalation hose, and ensures that once it is blown into the exhalation hose that it cannot flow back. This slightly increases the flow resistance of air and the work of breathing , but makes the regulator easier to clear, particularly when the diver does not have enough air in their lungs to blast clear with

9246-450: The carbon dioxide in a component known as a carbon dioxide scrubber . By adding sufficient oxygen to compensate for the metabolic usage, removing the carbon dioxide, and rebreathing the gas, most of the volume is conserved. There will still be minor losses when gas must be vented as it expands during ascent, and additional gas will be needed to make up volume as the gas is compressed during descent. The widest variety of rebreather types

9380-435: 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. All rebreathers other than oxygen rebreathers may be considered mixed gas rebreathers. These can be divided into semi-closed circuit, where

9514-402: The components underwater, and leaves the back free for other equipment for amphibious operations. The rebreather can be unclipped from a common harness without disturbing the load on the back. Front mounted counterlungs have a centroid which is generally slightly below the lung centroid, and result in slight positive pressure breathing for most common orientations of the diver. Sidemount allows

9648-604: The contract for the Atlantic coast). Bussoz changed the name of his company to U.S. Divers and registered the name Aqua-Lung. This turned out to be a wise move, because when the French company decided not to renew his five-year contract, no one had even heard of their product, but everyone was familiar with the names he had registered. Bussoz sold the company and the trade names for a handsome profit, returning to France. The name U.S. Divers sounded very official and very American, but it

9782-422: The counterlung inflates and deflates, and to prevent trapping large volumes of buoyant air as the diver submerges, and of water as the diver emerges into air. The components may be mounted on a frame or inside a casing to hold them together. Sometimes the structure of the scrubber canister forms part of the framework, particularly in side-mount configuration. Position of most parts is not critical to function, but

9916-409: The counterlungs must be positioned so that their centroid of volume is at a similar depth to the centroid of the diver's lungs at most times while underwater, and the breathing tubes to the mouthpiece should not encumber the diver more than necessary, and allow free movement of the head as much as possible. Early oxygen rebreathers were often built without frame or casing, and relied on the harness and

10050-400: The cycle. The resulting stress can be a cause of panic as the perception is of an insufficient gas supply due to carbon dioxide buildup though oxygenation may be adequate. Negative static lung load increases work of breathing and can vary depending on the relative depth of the regulator diaphragm to the lungs in open circuit equipment, and the relative depth of the counterlung to the lungs in

10184-403: The diluent mix while remaining breathable up to the surface, though this can be worked around by switching diluent. Work of breathing at depth can be a constraint, as there is a point where the breathing effort required to counter metabolic carbon dioxide production rate exceeds the work capacity of the diver, after which hypercapnia increases and distress followed by loss of consciousness and death

10318-422: The dive, both desirable features. Both the first and second stage valve mechanisms of the regulator are packaged in the circular brass housing mounted on the cylinder valve behind the diver's neck. High pressure gas flows into the regulator from the cylinder valve outlet, and is blocked by the first stage valve. The first stage reduces cylinder pressure to an interstage pressure, a fairly constant few bars higher than

10452-422: The diver again in a closed loop. In open circuit free-flow systems, the air is supplied at an approximately constant rate, and the diver uses only a relatively small part of the passing gas. The original Aqua-Lung regulator was a single stage unit, packaged in a circular brass housing mounted on the cylinder valve behind the diver's neck. High pressure gas flows into the regulator from the cylinder valve outlet, and

10586-416: The diver due to hypoxia . A higher gas addition rate reduces the likelihood of hypoxia but wastes more gas. 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 particularly useful without

10720-459: The diver may also be known as a gas extender . The same technology on a submersible or surface installation is more likely to be referred to as a life-support system . Diving rebreather technology may be used where breathing gas supply is limited, or where the breathing gas is specially enriched or contains expensive components, such as helium diluent. Diving rebreathers have applications for primary and emergency gas supply. Similar technology

10854-477: The duration of the Flyaway Mixed Gas System diving operations by five times while retaining the original mixed-gas storage footprint on the support ship. The Soviet IDA-72 semi-closed rebreather has a scrubber endurance of 4 hours on surface supply, and bailout endurance at 200m of 40 minutes on on-board gas . The US Navy Mark V Mod 1 heliox mixed gas helmet has a scrubber canister mounted on

10988-412: The effort of breathing could vary considerably during a dive, even without taking diver attitude into account. Later models included a first stage regulator to provide air to the demand valve at a lower pressure, compensated for depth, which allowed finer control and greater sensitivity to small pressure differences over the second stage diaphragm, but less sensitivity to cylinder pressure variation during

11122-435: The environment. The purpose is to extend the breathing endurance of a limited gas supply, and, for covert military use by frogmen or observation of underwater life, to eliminate the bubbles produced by an open circuit system. A diving rebreather is generally understood to be a portable unit carried by the user, and is therefore a type of self-contained underwater breathing apparatus (scuba). A semi-closed rebreather carried by

11256-467: The exhaled gas is vented to the surroundings. Scuba systems invented before the Aqua-Lung were mostly closed circuit rebreather equipment, in which breathing gas flows through an ambient pressure hose to the diver, and exhaled gas is returned through a scrubber which removes carbon dioxide, to a counter-lung reservoir. Some fresh gas is added to maintain the oxygen content and is then circulated back to

11390-412: The external work of an average single breath taken through the specified apparatus for given conditions of ambient pressure, underwater environment, flow rate during the breathing cycle, and gas mixture - underwater divers may breathe oxygen-rich breathing gas to reduce the risk of decompression sickness , or gases containing helium to reduce narcotic effects . Helium also has the effect of reducing

11524-415: The flow continues only until the pressure in the low pressure chamber balances the ambient water pressure on the outside of the low pressure diaphragm. To prevent free-flow or excessive exhaust back-pressure, the exhaust valve must be at the same depth as the diaphragm, and the only reliable place to do this is in the same housing. The air flows through a pair of large bore corrugated rubber hoses to and from

11658-415: The gas in the interstage chamber until it is opened by a reduction in pressure in the low-pressure chamber. It reduces the pressure of the interstage air supply to very nearly ambient pressure when the diver inhales the air in the low pressure chamber and the larger, more sensitive, low pressure diaphragm deflects inwards to push against the lever operating the second stage valve. When the diver stops inhaling,

11792-434: The gas recycling equipment is not carried by the diver. Atmospheric diving suits also carry rebreather technology to recycle breathing gas as part of the life-support system. Rebreathers are usually more complex to use than open circuit scuba, and have more potential points of failure , so acceptably safe use requires a greater level of skill, attention and situational awareness, which is usually derived from understanding

11926-406: The gas, flow rates, cracking pressure (the pressure differential required to open the demand valve), and back pressure over exhaust valves. Diver orientation affects the relative depths of lungs and regulator or breathing loop, which can cause variation between positive and negative pressure breathing. Work of breathing of a diver has a physiological component as well as the equipment component. for

12060-483: The generic noun "akvalangas"; "langas" happens to be Lithuanian for "window", giving a literal meaning "aqua-window". In the United States, U.S. Divers managed to keep "Aqualung" as a trademark. The acronym "SCUBA", or "Self Contained Underwater Breathing Apparatus", originated in the United States Navy , where it referred to a frogman 's oxygen rebreather designed by Christian J. Lambertsen . SCUBA became

12194-420: The generic term for any type of self-contained breathing set for diving, and soon the acronym SCUBA became a common noun – " scuba " – all in lower-case. "Scuba" was a trademark for a time – used by Healthways , now known as Scubapro  – one of the competitors of U.S. Divers. In Britain, Siebe Gorman (who held the rights to the tradename "Aqualung") made no serious attempt to control use of

12328-424: The inert gas component, which simply recirculates. In effect, a simple closed circuit oxygen rebreather arrangement used as a life-support system . Since there is usually an adequate power supply for other services, powered circulation through the scrubber should not normally be an issue for normal service, and is more comfortable for the operator, as it keeps the face area clear and facilitates voice communication. As

12462-489: The inert gas, semi-closed circuit is wasteful of both oxygen and inert components. A gas mix which has a maximum operating depth that is safe for the depth of the dive being planned, and which will provide a breathable mixture at the surface must be used, or it will be necessary to change mixtures during the dive. As the amount of oxygen required by the diver increases with work rate, the gas injection rate must be carefully chosen and controlled to prevent unconsciousness in

12596-412: The internal pressure is maintained at one atmosphere, there is no risk of acute oxygen toxicity. Endurance depends on the scrubber capacity and oxygen supply. Circulation through the scrubber could be powered by the diver's breathing, and this is an option for an emergency backup rebreather, which may also be fitted to the suit. A breathing driven system requires reduction of mechanical dead space by using

12730-457: The invention of several underwater cameras, to film and explore more freely. The Aqua-Lung was not the first self contained underwater breathing apparatus, but it was the first to be widely popular. In 1934, René Commeinhes developed a firefighter 's breathing apparatus which was adapted for diving as the G.C. - 42, and patented in April, 1942 (no.976,590) by his son Georges in 1937. It was used by

12864-430: The large dead space. A twin counterlung rebreather has two breathing bags, so the exhaled gas inflates the exhalation counterlung while starting to pass through the scrubber and starting to inflate the inhalation counterlung. By the time the diver starts to inhale, the inhalation counterlung has built up a volume buffer, so there is less flow resistance as the gas continues to flow through the scrubber during inhalation at

12998-452: The lung and chest is partially empty. Further exhalation requires muscular work. Inhalation is an active process requiring work. Some of this work is to overcome frictional resistance to flow, and part is used to deform elastic tissues, and is stored as potential energy, which is recovered during the passive process of exhalation, Tidal breathing is breathing that does not require active muscle contraction during exhalation. The required energy

13132-485: The lungs is equal to the pressure at the mouth, and in the immersed diver, the pressure on the chest may vary from the pressure at the mouth depending on the attitude of the diver in the water. This pressure difference is the static lung load or hydrostatic imbalance. A negative static lung load occurs when the gas supply pressure is lower than the ambient pressure at the chest, and the diver needs to apply more effort to inhale. The small negative pressure differential inside

13266-645: The modern age of automatic sport nitrox rebreathers, there were some sport oxygen diving clubs, mostly in the USA. Eventually the Cold War ended and in 1989 the Communist Bloc 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 patents , and automatic and semi-automatic recreational diving rebreathers with ppO2 sensors started to appear. As

13400-406: The mouthpiece through a single hose to the scrubber, into the counterlung, and on inhalation the gas is drawn back through the scrubber and the same hose back to the mouthpiece. The pendulum system is structurally simpler, but inherently contains a larger dead space of unscrubbed gas in the combined exhalation and inhalation tube, which is rebreathed. There are conflicting requirements for minimising

13534-410: The mouthpiece. The supply hose is connected to one side of the regulator body and supplies air to the mouthpiece through a non-return valve, and the exhaled air is returned to the regulator housing on the outside of the diaphragm, also through a non-return valve on the other side of the mouthpiece and through another non-return exhaust valve in the regulator housing. The non-return valves fitted to each of

13668-465: The narcotic effects, but also the density and thereby the work of breathing. To be non-combustible, there must be less than 4% by volume of oxygen n a hydrogen rich mixture. The presence and concentration of other diluents such as nitrogen or helium does not affect the flammability limit in a hydrogen rich mixture. In the diving industry the performance of breathing apparatus is often referred to as work of breathing. In this context it generally means

13802-667: The patent and produced it until 1965. In 1942, during the German occupation of France, the patent was held by the Bernard Piel Company ( Établissements Bernard Piel ). One of their apparatuses went to Émile Gagnan , an engineer employed by the Air Liquide company. Gagnan miniaturized and adapted it to gas generators in response to a fuel shortage, which was a consequence of German requisitioning. Gagnan's boss, Henri Melchior, knew that his son-in-law Jacques-Yves Cousteau

13936-435: The pendulum. The loop configuration uses a one directional circulation of the breathing gas which on exhalation leaves the mouthpiece, passes through a non-return valve into the exhalation hose, and then through the counterlung and scrubber, to return to the mouthpiece through the inhalation hose and another non-return valve when the diver inhales. The pendulum configuration uses a two-directional flow. Exhaled gas flows from

14070-404: The planned dive without undue risk of developing symptomatic decompression sickness. This limitation reduces the necessity to carry offboard bailout gas, and the need for the skills to bail out with a staged decompression obligation. This class of rebreather diving provides an opportunity to sell training and certification which omits a large part of the more complex and difficult skills, and reduces

14204-465: The pressure reduction in the airways, and a higher density causes a greater drop in pressure for a given volumetric flow rate, which has consequences in ambient pressure diving, and can limit ventilation at densities over 6g/litre. It can be exacerbated by a negative static lung load. The effect is modeled by the Starling resistor Work is defined as a force applied over a distance. The SI unit of work

14338-431: The rebreather. This pressure difference is generally due to a difference in hydrostatic pressure caused by a difference in depth between lung and counterlung, but can be modified by ballasting the moving side of a bellows counterlung . Resistive work of breathing is the sum of all the restrictions to flow due to bends, corrugations, changes of flow direction, valve cracking pressures, flow through scrubber media, etc., and

14472-418: The recommended recreational diving depth limit of 40 m, air and nitrox density reaches 6.5 g/litre The maximum voluntary ventilation and breathing capacity are approximately inversely proportional to the square root of gas density, which for a given gas is proportional to absolute pressure. Use of a low density gas like helium or hydrogen to replace nitrogen in the mixture helps not only to reduce

14606-567: The resistance to flow of the gas, due to inertia and viscosity, which are influenced by density, which is a function of molecular weight and pressure. Rebreather design can limit the mechanical aspects of flow resistance, particularly by the design of the scrubber , counterlungs and breathing hoses. Diving rebreathers are influenced by the variations of work of breathing due to gas mixture choice and depth. Helium content reduces work of breathing, and increased depth increases work of breathing. Work of breathing can also be increased by excessive wetness of

14740-414: The risk to the same level as open circuit equipment for the same dive profile. 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 could be surface supplied by umbilical, but would then have to be exhausted back to

14874-465: The scrubber media, usually a consequence of a leak in the breathing loop, or by using a grain size of absorbent that is too small. Both of these factors cause restrictions to the gas flow. The semi-closed rebreather systems developed by Drägerwerk in the early 20th century as a scuba gas supply for Standard diving dress , using oxygen or nitrox, and the US Navy Mark V Heliox helmet developed in

15008-610: The second stage pressure sensing diaphragm to the point of exhaust at the mouthpiece, rather than routing the exhaust back to the regulator diaphragm at the cylinder. An advertisement in Popular Mechanics of October 1950 offered a single hose regulator for sale by Divers Supply in Wilmington, California. At about the same time as Divers Supply began selling the Sport Diver regulator, Australian Ted Eldred designed

15142-441: The second stage valve at the mouthpiece, but increasing the load on the diver's jaw and releasing bubbles nearer the eyes and ears. The Aqua-Lung is a self-contained open-circuit demand system, which means that breathing gas is provided from high-pressure storage carried by to the diver on demand, when the diver inhales and reduces the pressure in the supply hose, subsequently the flow is shut off when not required. Once breathed,

15276-422: 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

15410-538: The supply is adequate, exhaled gas is flushed away by fresh gas flow, and only fresh gas is inhaled – there is no dead space. Work of breathing is affected by gas density due to pressure and gas composition, and there may be positive or negative static lung loading, but there is no additional external work of breathing due to airflow through the breathing apparatus. Surface-supplied divers who will be working hard underwater often use free-flow systems for this reason. Demand systems: Recirculating systems: Work of breathing of

15544-401: The surface to maintain internal pressure below the external ambient pressure, which is possible but presents pressure-hull breach hazards if the umbilical hoses are damaged, or from a rebreather system built into the suit. As there is a similar problem in venting excess gas, the simple and efficient solution is to make up oxygen as it is consumed and scrub out the carbon dioxide, with no change to

15678-566: The systems, diligent maintenance and overlearning the practical skills of operation and fault recovery . Fault tolerant design can make a rebreather less likely to fail in a way that immediately endangers the user, and reduces the task loading on the diver which in turn may lower the risk of operator error. Semi-closed rebreather technology is also used in diver carried surface supplied gas extenders, mainly to reduce helium use. Some units also function as an emergency gas supply using on-board bailout cylinders: The US Navy MK29 rebreather can extend

15812-514: The time needed for decompression stops . The first Cousteau-Gagnan Aqua-Lungs (like the CG45 of 1945 or the Mistral of 1955) were twin-hose open-circuit scuba . Similar configurations have since been made by various manufacturers with varying design details and numbers of cylinders. Like open-circuit scuba with single-hose regulators, they consisted of one or more high pressure diving cylinders and

15946-656: The trade name Aqua-Lung . In the late 1940s and early 1950s, La Spirotechnique started exporting the Aqua-Lung and leasing its patent to foreign companies like the British Siebe Gorman . The equipment was a great success compared to the Rouquayrol-Denayrouze apparatus, which was limited because the technology of its time could only produce compressed-air tanks that could hold 30 atmospheres , which allowed dives of only 30 minutes at no more than ten meters depth. Before 1945, French divers preferred

16080-622: The traditional standard diving dress with copper helmet and surface supplied breathing air. When the Aqua-Lung became available for commercial use, divers around the world found the Cousteau-Gagnan equipment smaller and easier to use than either the Le Prieur or Rouquayrol-Denayrouze apparatus. The Aqua-Lung could be also be mounted on stronger and more reliable air tanks holding up to 200 atmospheres, allowing extension of diving duration to more than an hour at significant depths, including

16214-710: The two relatively small scrubber canisters on both sides of the diver, connected by a single 8-litre counterlung across the diver's back, and worn with a regular sidemount harness. This configuration is claimed to provide good work of breathing in most diver orientations. A small butt-mounted transverse oxygen cylinder and standard sidemount diluent/bailout cylinders (usually two) are carried. 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

16348-594: The usual way to work underwater was in standard diving dress , breathing open circuit surface-supplied air. (Draeger and Mark V Helium helmet) The Italian Decima Flottiglia MAS , the first unit of combat frogmen, was founded in 1938 and went into action in 1940. WWII saw a great expansion of military-related use of rebreather diving. During and after WWII , 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

16482-465: The valve lifter, shutting off the flow until the next breath is taken. On a single stage regulator, the flow rate through the demand valve orifice will vary depending on cylinder pressure for the same opening size, and the opening force required will vary depending on the inlet pressure and orifice area, together making the delivery rate vary as the pressure in the cylinder changes. Flow rate is also affected by downstream pressure, which varies with depth, so

16616-400: The valve lifter. This opens the high pressure valve permitting gas to flow past the valve seat into the interstage chamber. When the diver stops inhaling, pressure in the low pressure chambers quickly rises until the diaphragm returns to its neutral position and no longer presses on the valve lifter, shutting off the flow until the next breath is taken. The second, or demand valve stage, keeps

16750-514: The volume of dead space while minimising the flow resistance of the breathing passages. A pendulum rebreather only has one counterlung, on the far side of the scrubber from the single breathing hose. The diver blows exhaled gas through the scrubber, then sucks it back during inhalation. Gas flow rate through the scrubber is forced by the breathing rate of the diver. A single counterlung in a loop rebreather can be an exhalation or inhalation counterlung, or fitted between split scrubber canisters. If it

16884-403: The water, and keeps the front of the diver clear for working underwater. Back mount usually uses back or over the shoulder counterlungs, which have a centroid above the lung in most common orientations of the diver, resulting in slight negative pressure breathing . Chest mount is fairly common for military oxygen rebreathers, which are usually relatively compact and light. It allows easy reach of

17018-578: The word, and "aqualung" remained a common public generic word for that sort of apparatus – including in the British Sub-Aqua Club 's official publications – for many years. Aqua Lung America , the current name of the U.S. Divers Company, now makes rebreathers whose tradenames or catalog descriptions include the word "Aqualung". The name U.S. Divers is now used as a trademark by Aqua Lung America for its line of snorkeling equipment. Diving rebreather A Diving rebreather

17152-405: The work associated with a specific number of breaths or a given interval of time. It is important to differentiate between the terms "breathing rate" and "breathing frequency." Although the two are frequently used interchangeably, "breathing rate" refers to the respiratory rate and is described in breaths per minute (BPM). On the other hand, "breathing frequency" refers to the frequency composition of

17286-406: The work of breathing by reducing density of the mixture, though helium's viscosity is fractionally greater than nitrogen's. Standards for these conditions exist and to make useful comparisons between breathing apparatus they must be tested to the same standard. Free-flow systems; In a free-flow breathing apparatus , the user breathes from the volume of ambient pressure gas in front of the face. If

17420-474: The work of circulating the gas through the breathing loop and scrubber can be a large part of the total work of breathing. Some recreational diver certification agencies distinguish a class of rebreather which they deem suitable for recreational diving. These rebreathers are unsuitable for decompression diving, and when electronically controlled, will not allow the diver to do dives with obligatory decompression, thereby allowing an immediate ascent at any point of

17554-635: The work required to increase ventilation produces more carbon dioxide than is eliminated by the increased ventilation, and flow may be choked by the effects of dynamic airway compression. In some cases the person may resort to coughing exhalation to try to increase flow. This effect can be delayed by using lower density gas such as helium in the breathing mix to keep the combined density below 6 g/litre. On air or nitrox, maximum ventilation drops to about half at 30 m, equivalent to 4 bar absolute and gas density of about 5.2 g/litre. The 6 g/litre recommended soft limit occurs at about 36 m and by

17688-531: Was looking for an automatic demand regulator to increase the useful endurance of the underwater breathing apparatus invented by Commander Yves le Prieur , so he introduced Cousteau to Gagnan in December 1942. On Cousteau's initiative, the Gagnan regulator was modified for use in diving. Cousteau and Gagnan were issued a patent some weeks later in 1943. After the war, in 1946, both men founded La Spirotechnique as

17822-560: Was owned by a Frenchman and sold to a French company. Air Liquide held the patent on the original "Aqualung" (also written as "Aqua-Lung" or "Aqua Lung") until the patent expired sometime around 1960 to 1963. The term "Aqualung", as far as is known, first appeared in print on page 3 of Jacques-Yves Cousteau 's first book, The Silent World , in 1953. Public use of the word "aqualung", and public interest in Aqualungs and scuba diving, were started around 1953 in English-speaking counties by

17956-509: Was popularized by the popular television series Sea Hunt (1958), in which actual Aqua-Lungs appeared in early episodes. This series never said that a scuba regulator could be called anything else, or made by anyone else, but the Voit Rubber Corporation provided most of the diving equipment used in the series, and supplied Mike Nelson, the lead character. The word "aqualung" was commonly used in speech and in publications as

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