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64-413: Two basic functional variations of scuba are in general use: open-circuit-demand, and rebreather. In open-circuit demand scuba, the diver expels exhaled breathing gas to the environment, and each breath is delivered at ambient pressure, on demand, by a diving regulator which reduces the pressure from the storage cylinder. The breathing gas is supplied through a demand valve; when the diver inhales, they reduce

128-441: A demand regulator to control the supply of breathing gas, and most rebreathers have a constant-flow injector , or an electronically controlled injector to supply fresh gas, but also usually have an automatic diluent valve (ADV), which functions in the same way as a demand valve, to maintain the loop volume during descent. Open-circuit-demand scuba exhausts exhaled air to the environment, and requires each breath to be delivered to

192-416: A diving regulator consisting of a first-stage pressure-reducing valve connected to the diving cylinder 's output valve or manifold. This regulator reduces the pressure from the cylinder, which may be up to 300 bars (4,400 psi), to a lower pressure, generally between about 9 and 11 bar above the ambient pressure. A low-pressure hose links this with the second-stage regulator, or "demand valve", which

256-471: A fire department , paramedical service or lifeguard unit, and may be classed as public safety diving . There are also professional divers involved with the underwater environment , such as underwater photographers or underwater videographers, who document the underwater world, or scientific diving , including marine biology , geology, hydrology , oceanography and underwater archaeology . The choice between scuba and surface supplied diving equipment

320-411: A bite-controlled breathing gas supply valve, which could be considered a form of demand valve, and was successfully used for several years. This system consists of one or more diving cylinders containing breathing gas at high pressure, typically 200–300 bars (2,900–4,400 psi), connected to a diving regulator . The demand regulator automatically supplies the diver with as much gas as is needed at

384-404: A common compressor and connected to the same system. As with hose air lines, Fixed pipe air lines must be manufactured with anti-corrosion materials, such as non-ferrous metals or plastics, to prevent internal corrosion from air moisture content and condensate. Piped air lines are typically installed with a fall gradient away from the outlet point, this is to allow any build-up of moisture within

448-543: A firm called Submarine Products sold a sport air scuba set with three manifolded back-mounted cylinders. Cave and wreck penetration divers sometimes carry cylinders attached at their sides instead, allowing them to swim through more confined spaces. Constant flow scuba sets do not have a demand regulator; the breathing gas flows at a constant rate, unless the diver switches it on and off by hand. They use more air than demand regulated scuba. There were attempts at designing and using these for diving and for industrial use before

512-410: A gag reflex. Various styles of mouthpiece are available off the shelf or as customised items, and one of them may work better if either of these problems occur. The frequently quoted warning against holding one's breath on scuba is a gross oversimplification of the actual hazard. The purpose of the admonition is to ensure that inexperienced divers do not accidentally hold their breath while surfacing, as

576-504: A large industrial compressor , located remotely, in a plant room or dedicated space. The compressed air lines will be piped from the compressor to one or multiple point of use outlets. At the outlet of a fixed air line you will typically find a Pressure regulator installed upstream of the termination/outlet point, this allows the user to regulate the pressure and flow of air to suit the desired use. The regulator allows each outlet to be controlled independently, even though they are served by

640-493: A long history of military frogmen in various roles. Their roles include direct combat, infiltration behind enemy lines, placing mines or using a manned torpedo , bomb disposal or engineering operations. In civilian operations, many police forces operate police diving teams to perform "search and recovery" or "search and rescue" operations and to assist with the detection of crime which may involve bodies of water. In some cases search and rescue diving teams may also be part of

704-408: A loop of the hose into the shoulder strap cover of a jacket style BC, or suspended under the chin on a break-away bungee loop known as a necklace. These methods also keep the secondary from dangling below the diver and being contaminated by debris or snagging on the surroundings. Some divers store it in a BC pocket, but this reduces availability in an emergency. Occasionally, the secondary second-stage

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768-402: A loose bungee loop around the neck, supplied by a shorter hose, and is intended for backup use by the diver donating gas. The backup regulator is usually carried in the diver's chest area where it can be easily seen and accessed for emergency use. It may be worn secured by a breakaway clip on the buoyancy compensator , plugged into a soft friction socket attached to the harness, secured by sliding

832-413: A number of applications, including scientific, military and public safety roles, but most commercial diving uses surface-supplied diving equipment for the main gas supply when this is practicable. Surface supplied divers may be required to carry scuba as an emergency breathing gas supply to get them to safety in the event of a failure of surface gas supply. There are divers who work, full or part-time, in

896-597: A number of materials, meaning each type of hose can provide different characteristics to suit its use. Some important characteristics include flexibility, weight & manoeuvrability. A wide range of hose sizes & materials are available to accommodate the different pressures, flow rates & of its intended use. There are two types of air line hose which are most commonly used. The two types are known as Standard (straight) and Recoil (coiled) hose types. The outer diameter size of air line hoses are manufactured in both imperial and metric unit systems. The term air line

960-419: A range of corrosion-resistant materials. Typically air lines are made with flexible hose or rigid pipe. Air line hoses provide flexibility and mobility for use, whereas a piped air line is more permanent and resistant to damage. For a typical compressed air system, both types of air lines are used in conjunction. Air line hoses are flexible tubes used to convey pressurised air. They are commonly used for carrying

1024-504: A rebreather can be more economical when used with expensive gas mixes such as heliox and trimix , but this may require a lot of diving before the break-even point is reached, due to the high initial and running costs of most rebreathers, and this point will be reached sooner for deep dives where the gas saving is more pronounced. Gas cylinders used for scuba diving come in various sizes and materials and are typically designated by material – usually aluminium or steel , and size. In

1088-518: A reduced capacity to recover from a breathing gas supply emergency. The breathing apparatus will generally increase dead space by a small but significant amount, and cracking pressure and flow resistance in the demand valve will cause a net work of breathing increase, which will reduce the diver's capacity for other work. Work of breathing and the effect of dead space can be minimised by breathing relatively deeply and slowly. These effects increase with depth, as density and friction increase in proportion to

1152-422: A scuba in 1967, called "Mako", and made at least five prototypes . The Russian Kriolang (from Greek cryo- (= "frost" taken to mean "cold") + English "lung") was copied from Jordan Klein's "Mako" cryogenic open-circuit scuba. and were made until at least 1974. It would have to be filled a short time before use. A rebreather recirculates the breathing gas already used by the diver after replacing oxygen used by

1216-399: A separate hose, a configuration called a "secondary", or "octopus" demand valve, "alternate air source", "safe secondary" or "safe-second". This arrangement was intended to reduce the problems of buddy breathing from a single demand valve and has become the standard in recreational diving. By providing a second demand valve the need to alternately breathe off the same mouthpiece when sharing air

1280-414: A single demand valve as an obsolescent but still occasionally useful technique, learned in addition to the use of the backup DV, since availability of two second stages per diver is now assumed as standard in recreational scuba. There have been designs for a cryogenic open-circuit scuba which has liquid-air tanks instead of cylinders. Underwater cinematographer Jordan Klein, Sr. of Florida co-designed such

1344-594: A supply of compressed air to operate pneumatic powered systems, such as a road vehicle air brake system for large vehicles and a railway air brake system for railway carriages / locomotives . Due to the versatility of a flexible compressed air supply hoses are also used for pneumatic hand tools, pneumatic robotics and for connections to air powered equipment. Hose air lines are manufactured with anti-corrosion & abrasion resistant materials, to prevent internal corrosion from air moisture/condensate and from external abrasion when in use. Air line hoses are manufactured in

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1408-491: A yellow hose, for high visibility, and as an indication that it is an emergency or backup device. When a side-mount configuration is used, the usefulness of a secondary demand valve is greatly reduced, as each cylinder will have a regulator and the one not in use is available as a backup. This configuration also allows the entire cylinder to be handed off to the receiver, so a long hose is also less likely to be needed. Some diving instructors continue to teach buddy-breathing from

1472-414: Is a tube , or hose , that contains and carries a compressed air supply. In industrial usage, this may be used to inflate car or bicycle tyres or power tools worked by compressed air, for breathing apparatus in hazardous environments and to operate many other pneumatic systems. Air lines provide compressed air for a wide range of uses and to cater for a variety of uses air lines are manufactured in

1536-553: Is also used to describe fixed pipe compressed air systems. These systems are often found in laboratories, workshops, manufacturing facilities & on other sites for industrial processes. Fixed pipe air lines can also found onboard large shipping vessels, as compressed air is used to rotate the engines for starting up. Large diameter pipework systems are used for air lines that convey compressed air over great distances, these are typically found on large industrial sites & research facilities. Fixed pipe systems are typically connected to

1600-461: Is based on both legal and logistical constraints. Where the diver requires mobility and a large range of movement, scuba is usually the choice if safety and legal constraints allow. Higher risk work, particularly in commercial diving, may be restricted to surface supplied equipment by legislation and codes of practice. There are alternative methods that a person can use to survive and function while underwater, currently including: Breathing from scuba

1664-457: Is combined with the inflation and exhaust valve assembly of the buoyancy compensator device. This combination eliminates the need for a separate low pressure hose for the BC, though the low pressure hose connector for combined use must have a larger bore than for standard BC inflation hoses, because it will need to deliver a higher flow rate if it is used for breathing. This combination unit is carried in

1728-402: Is eliminated. This reduces the stress on divers who are already in a stressful situation, and this in turn reduces air consumption during the rescue and frees the donor's hand. Some diver training agencies recommend that a diver routinely offer their primary demand valve to a diver requesting to share air, and then switch to their own secondary demand valve. The idea behind this technique is that

1792-436: Is mostly a straightforward matter. Under most circumstances it differs very little from normal surface breathing. In the case of a full-face mask, the diver may usually breathe through the nose or mouth as preferred, and in the case of a mouth held demand valve, the diver will have to hold the mouthpiece between the teeth and maintain a seal around it with the lips. Over a long dive this can induce jaw fatigue, and for some people,

1856-640: Is mounted on the mouthpiece. Exhalation occurs through a rubber one-way mushroom valve in the chamber of the demand valve, directly into the water quite close to the diver's mouth. Some early single hose scuba sets used full-face masks instead of a mouthpiece, such as those made by Desco and Scott Aviation (who continue to make breathing units of this configuration for use by firefighters ). Modern regulators typically feature high-pressure ports for pressure sensors of dive-computers and submersible pressure gauges, and additional low-pressure ports for hoses for inflation of dry suits and BC devices. The primary demand valve

1920-399: Is necessary in an emergency. In technical diving donation of the primary demand valve is commonly the standard procedure, and the primary is connected to the first stage by a long hose, typically around 2 m, to allow gas sharing while swimming in single file in a narrow space as might be required in a cave or wreck. In this configuration the secondary is generally held under the chin by

1984-466: Is popular for tight cave penetrations; sling mount, used for stage-drop sets; decompression gas and bailout sets where the main gas supply is back-mounted; and various non-standard carry systems for special circumstances. The most immediate risk associated with scuba diving is drowning due to a failure of the breathing gas supply. This may be managed by diligent monitoring of remaining gas, adequate planning and provision of an emergency gas supply carried by

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2048-453: Is required to compensate for the higher risk involved. The rebreather's economic use of gas, typically 1.6 litres (0.06 cu ft) of oxygen per minute, allows dives of much longer duration for an equivalent gas supply than is possible with open-circuit equipment where gas consumption may be ten times higher. There are two main variants of rebreather – semi-closed circuit rebreathers, and fully closed circuit rebreathers, which include

2112-468: Is sufficient ventilation on average to prevent carbon dioxide buildup, and is done as a standard practice by underwater photographers to avoid startling their subjects. Holding the breath during descent can eventually cause lung squeeze, and may allow the diver to miss warning signs of a gas supply malfunction until it is too late to remedy. Skilled open circuit divers can and will make small adjustments to buoyancy by adjusting their average lung volume during

2176-406: Is the one the diver usually breathes from. There may be a secondary demand valve on the same regulator, or on a different first stage connected to the same scuba set. Additional scuba sets used for bailout, stages, decompression, or sidemount diving usually only have one second stage, which for that set is the primary by default. Most recreational scuba sets have a backup second-stage demand valve on

2240-602: The English language Lambertsen's acronym has become common usage and the name Aqua-Lung (often spelled "aqualung"), coined by Cousteau for use in English-speaking countries , has fallen into secondary use. As with radar , the acronym scuba has become so familiar that it is generally not capitalized and is treated as an ordinary noun. For example, it has been translated into the Welsh language as sgwba . Although

2304-617: The Cousteau-type aqualung became commonly available circa 1950. Examples were Charles Condert 's dress in the US (as of 1831), and Yves le Prieur 's hand-controlled supply valve in France (as of 1926); see Timeline of diving technology . These systems are obsolete as they waste most of the gas or require manual control of each breath, and more efficient demand regulators are available. " Ohgushi's Peerless Respirator " from Japan as of 1918 had

2368-427: The U.S. the size is designated by their nominal capacity , the volume of the gas they contain when expanded to normal atmospheric pressure. Common sizes include 80, 100, 120 cubic feet, etc., with the most common being the "Aluminum 80". In most of the rest of the world the size is given as the actual internal volume of the cylinder, sometimes referred to as water capacity, as that is how it is measured and marked (WC) on

2432-517: The ambient pressure. This type of breathing set is sometimes called an aqualung . The word Aqua-Lung , which first appeared in the Cousteau - Gagnan patent , is a trademark , currently owned by Aqua Lung/La Spirotechnique . This is the first type of diving demand valve to come into general use, and the one that can be seen in classic 1960s television scuba adventures, such as Sea Hunt . They were often use with manifolded twin cylinders. All

2496-409: The breathing circuit is at ambient pressure, and stored gas is provided through regulators or injectors , depending on the design. Within these systems, various mounting configurations may be used to carry the scuba set, depending on application and preference. These include: back mount, which is generally used for recreational scuba and for bailout sets for surface supplied diving; side-mount, which

2560-447: The breathing cycle. This adjustment is generally in the order of a kilogram (corresponding to a litre of gas), and can be maintained for a moderate period, but it is more comfortable to adjust the volume of the buoyancy compensator over the longer term. The practice of shallow breathing or skip breathing in an attempt to conserve breathing gas should be avoided as it tends to cause a carbon dioxide buildup, which can result in headaches and

2624-444: The cylinder (10 liter, 12 liter, etc.). Cylinder working pressure will vary according to the standard of manufacture, generally ranging from 200 bar (2,900 psi) up to 300 bar (4,400 psi). An aluminium cylinder is thicker and bulkier than a steel cylinder of the same capacity and working pressure, as suitable aluminium alloys have lower tensile strength than steel, and is more buoyant although actually heavier out of

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2688-509: The diver and removing the carbon dioxide metabolic product. Rebreather diving is used by recreational, military and scientific divers where it can have advantages over open-circuit scuba. Since 80% or more of the oxygen remains in normal exhaled gas, and is thus wasted, rebreathers use gas very economically, making longer dives possible and special mixes cheaper to use at the cost of more complicated technology and more possible failure points. More stringent and specific training and greater experience

2752-464: The diver in a bailout cylinder or supplied by the diver's buddy , and the skills required to manage the gas sources during the emergency. The word SCUBA was coined in 1952 by Major Christian Lambertsen who served in the U.S. Army Medical Corps from 1944 to 1946 as a physician. Lambertsen first called the closed-circuit rebreather apparatus he had invented "Laru", an ( acronym for Lambertsen Amphibious Respiratory Unit ) but, in 1952, rejected

2816-443: The diver on demand by a diving regulator, which reduces the pressure from the storage cylinder and supplies it through the demand valve when the diver reduces the pressure in the demand valve slightly during inhalation. The essential subsystems of an open-circuit scuba set are; Additional components which when present are considered part of the scuba set are; The buoyancy compensator is generally assembled as an integrated part of

2880-586: The diver with the advantages of mobility and horizontal range far beyond the reach of an umbilical hose attached to surface-supplied diving equipment (SSDE). Unlike other modes of diving, which rely either on breath-hold or on breathing gas supplied under pressure from the surface , scuba divers carry their own source of breathing gas , usually filtered compressed air , allowing them greater freedom of movement than with an air line or diver's umbilical and longer underwater endurance than breath-hold. Scuba diving may be done recreationally or professionally in

2944-435: The exhaust valve and final stage diaphragm , which would cause a free-flow of gas, or extra resistance to breathing, depending on the diver's orientation in the water. In modern single-hose sets this problem is avoided by moving the second-stage regulator to the diver's mouthpiece . The twin-hose regulators came with a mouthpiece as standard, but a full-face diving mask was an option. Most modern open-circuit scuba sets have

3008-410: The expansion of gas in the lungs could over-expand the lung air spaces and rupture the alveoli and their capillaries, allowing lung gases to get into the pulmonary return circulation, the pleura, or the interstitial areas near the injury, where it could cause dangerous medical conditions. Holding the breath at constant depth for short periods with a normal lung volume is generally harmless, providing there

3072-460: The increase in pressure, with the limiting case where all the diver's available energy may be expended on simply breathing, with none left for other purposes. This would be followed by a buildup in carbon dioxide, causing an urgent feeling of a need to breathe, and if this cycle is not broken, panic and drowning are likely to follow. The use of a low density inert gas, typically helium, in the breathing mixture can reduce this problem, as well as diluting

3136-568: The loop can greatly increase the resistance to gas flow through the scrubber. There is even less point in shallow or skip breathing on a rebreather as this does not even conserve gas, and the effect on buoyancy is negligible when the sum of loop volume and lung volume remains constant. Until Nitrox , which contains more oxygen than air, was widely accepted in the late 1990s, almost all recreational scuba used simple compressed and filtered air. Other gas mixtures, typically used for deeper dives by technical divers, may substitute helium for some or all of

3200-436: The narcotic effects of the other gases. Breathing from a rebreather is much the same, except that the work of breathing is affected mainly by flow resistance in the breathing loop. This is partly due to the carbon dioxide absorbent in the scrubber, and is related to the distance the gas passes through the absorbent material, and the size of the gaps between the grains, as well as the gas composition and ambient pressure. Water in

3264-473: The nitrogen (called Trimix , or Heliox if there is no nitrogen), or use lower proportions of oxygen than air. In these situations divers often carry additional scuba sets, called stages, with gas mixtures with higher levels of oxygen that are primarily used to reduce decompression time in staged decompression diving . These gas mixes allow longer dives, better management of the risks of decompression sickness , oxygen toxicity or lack of oxygen ( hypoxia ), and

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3328-409: The pipework (due to internal condensation) to drain via the automatic tank drain or via a drain leg installed on the system. Branch connections to serve outlets are typically taken vertically off the top of the main supply line and then loop down to the outlet point. This is done as a safety precaution and to avoid damaging pneumatic equipment. A connection into the top of a main air line greatly reduces

3392-435: The position where the inflator unit would normally hang on the left side of the chest. With integrated DV/BC inflator designs, the secondary demand valve is at the end of the shorter BC inflation hose, and the donor must retain access to it for buoyancy control, so donation of the primary regulator to help another diver is essential with this configuration. The secondary demand valve is often partially yellow in color, and may use

3456-416: The pressure in the demand valve housing, thus drawing in fresh gas. In rebreather scuba, the system recycles the exhaled gas, removes carbon dioxide, and compensates for the used oxygen before the diver is supplied with gas from the breathing circuit. The amount of gas lost from the circuit during each breathing cycle depends on the design of the rebreather and depth change during the breathing cycle. Gas in

3520-416: The primary demand valve is known to be working, and the diver donating the gas is less likely to be stressed or have a high carbon dioxide level, so has more time to sort out their own equipment after temporarily suspending the ability to breathe. In many instances, panicked divers have grabbed the primary regulators out of the mouths of other divers, so changing to the backup as a routine reduces stress when it

3584-436: The recreational diving community as instructors, assistant instructors, divemasters and dive guides. In some jurisdictions the professional nature, with particular reference to responsibility for health and safety of the clients, of recreational diver instruction, dive leadership for reward and dive guiding is recognised and regulated by national legislation. Other specialist areas of scuba diving include military diving , with

3648-429: The requirement to be able to safely bail out at any point of the dive. Rebreathers are generally used for scuba applications, but are also occasionally used for bailout systems or gas extenders for surface supplied diving. The possible endurance of a rebreather dive is longer than an open-circuit dive, for similar weight and bulk of the set, if the set is bigger than the practical lower limit for rebreather size, and

3712-413: The set, but is not technically part of the breathing apparatus. The cylinder is usually worn on the back. "Twin sets" with two low capacity back-mounted cylinders connected by a high pressure manifold were more common in the 1960s than now for recreational diving, although larger capacity twin cylinders ("doubles") are commonly used by technical divers for increased dive duration and redundancy. At one time

3776-418: The severity of nitrogen narcosis . Closed circuit scuba sets ( rebreathers ) provide a gas mix that is controlled to optimise the mix for the actual depth at the time. Scuba sets are of two types: Both types of scuba set include a means of supplying air or other breathing gas , nearly always from a high pressure diving cylinder , and a harness to attach it to the diver. Most open-circuit scuba sets have

3840-403: The stages of this type of regulator are in a large valve assembly mounted directly to the cylinder valve or manifold, behind the diver's neck. Two large bore corrugated rubber breathing hoses connect the regulator with the mouthpiece, one for supply and one for exhaust. The exhaust hose is used to return the exhaled air to the regulator, to avoid pressure differences due to depth variation between

3904-474: The subvariant of oxygen rebreathers. Oxygen rebreathers have a maximum safe operating depth of around 6 metres (20 ft), but several types of fully closed circuit rebreathers, when using a helium -based diluent, can be used deeper than 100 metres (330 ft). The main limiting factors on rebreathers are the duration of the carbon dioxide scrubber, which is generally at least 3 hours, increased work of breathing at depth, reliability of gas mixture control, and

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3968-484: The term "Laru" for "SCUBA" ("Self-Contained Underwater Breathing Apparatus"). Lambertsen's invention, for which he held several patents registered from 1940 to 1989, was a rebreather and is different from the open-circuit diving regulator and diving cylinder assemblies also commonly referred to as scuba. Open-circuit-demand scuba is a 1943 invention by the Frenchmen Émile Gagnan and Jacques-Yves Cousteau , but in

4032-471: The term was originally an acronym, "scuba" is currently used to refer to the apparatus or the practice of diving using the apparatus, either alone as a common noun, or as an adjective in scuba set and scuba diving respectively. It is also used as an adjective referring to equipment or activity relating to diving using self-contained breathing apparatus. A diver uses a self-contained underwater breathing apparatus (scuba) to breathe underwater . Scuba provides

4096-620: The water, which means the diver would need to carry more ballast weight. Steel is also more often used for high pressure cylinders, which carry more air for the same internal volume. Rebreather diving Too Many Requests If you report this error to the Wikimedia System Administrators, please include the details below. Request from 172.68.168.150 via cp1114 cp1114, Varnish XID 923341735 Upstream caches: cp1114 int Error: 429, Too Many Requests at Thu, 28 Nov 2024 07:52:50 GMT Air line An air line

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