This is a glossary of technical terms, jargon, diver slang and acronyms used in underwater diving. The definitions listed are in the context of underwater diving. There may be other meanings in other contexts.
Underwater diving can be described as a human activity – intentional, purposive, conscious and subjectively meaningful sequence of actions. Underwater diving is practiced as part of an occupation, or for recreation, where the practitioner submerges below the surface of the water or other liquid for a period which may range between seconds to the order of a day at a time, either exposed to the ambient pressure or isolated by a pressure resistant suit, to interact with the underwater environment for pleasure, competitive sport, or as a means to reach a work site for profit, as a public service, or in the pursuit of knowledge, and may use no equipment at all, or a wide range of equipment which may include breathing apparatus, environmental protective clothing, aids to vision, communication, propulsion, maneuverability, buoyancy and safety equipment, and tools for the task at hand.
Many of the terms are in general use by English speaking divers from many parts of the world, both amateur and professional, and using any of the modes of diving. Others are more specialised, variable by location, mode, or professional environment. There are instances where a term may have more than one meaning depending on context, and others where several terms refer to the same concept, or there are variations in spelling. A few are loan-words from other languages.
There are five sub-glossaries, listed here. The tables of content should link between them automatically:
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An underwater structure inside which divers can carry out dry welding or which is fitted out with life support facilities. [1]
Decompression models based on the principles described by John Scott Haldane.
An alternative scuba reserve gas management strategy to the rule of thirds for breathing stage cylinders. The cylinder is breathed down to half of its starting pressure plus 200 psi (or 15 bar), so that a stage cylinder filled to 3000 psi would be breathed down to 1700 psi before being dropped. [2] Primary cylinder gas (usually back gas) is retained for use in contingencies. [3]
Voice communications system where users take turns to send and receive. [4]
Diver's mask which covers the eyes and nose but not the mouth.
A strong variation in salinity over a small depth range within a body of water. Often visible as a blurred or shimmering region due to uneven refractive index. [5]
Commercial diving procedure where the diver ascends to a shallower depth to minimise in-gassing during periods of waiting for surface support. The diver generally ascends to 30 ft waiting depth, and bottom time at that depth is not counted towards decompression obligation. When the support is ready, the diver returns to working depth and time elapsed from leaving hang-off depth accumulates towards decompression obligation. The profile appearance approximates a square wave form, or yo-yo profile. [6]
Diving in a known hazardous materials environment. The environment may be contaminated by hazardous materials, the diving medium may be inherently a hazardous material, or the environment in which the diving medium is situated may include hazardous materials with a significant risk of exposure to these materials to members of the diving team. Special precautions, equipment and procedures are associated with hazmat diving.
A visual display mounted where it is normally in the diver's field of vision. [7]
UK government department responsible for occupational diver safety in UK.
Trimix blends made by topping up helium with air. [8]
Mixtures of helium and oxygen for use as a breathing gas. [9] [8]
An inert gas which is used as a component of breathing gas mixtures for deep diving.
An instrument used to identify the presence and concentration of helium in a mixture of gases
Description of the changes in solubility of a given gas in a given liquid as pressure varies.
A scuba configuration where the primary demand valve has a long hose which is routed under the right arm, usually tucked under a light battery canister on the waist belt of the harness, and around behind the neck to reach the mouth from the right hand side. Part of the Hogarthian configuration (q.v.). [5]
Valve on the US Navy MK V helium helmet. The gas supply at the diver was controlled by two valves. The "Hoke valve" controlled flow through the injector to the "aspirator" which circulated gas from the helmet through the scrubber, and the main control valve used for bailout to open circuit, flushing the helmet, and for extra gas when working hard or descending. [10]
Catalyst sometimes used in breathing air compressor filters to oxidise carbon monoxide to carbon dioxide. Hopcalite is a mixture of manganese oxide, copper oxide and a small amount of silver oxide.
Equipment to position and stabilise a hose, particularly in the context of sidemount or sling mounted scuba cylinders, where the regulator air hoses are stored against the cylinder when not in use.
Quick connection coupling that can be connected by an ROV underwater, often to provide hydraulic power. The hot stab is the connector unit supplying the utilities, and it is usually inserted into a port after pulling out the plug stab, which is used to protect the port when it is not in use. Typically the alignment is not critical and the port will guide the stab in as it has concentric flow channels and o-ring seals. It may lock into place when fully inserted, or may require an external force to hold it in place while in use. [12] [13] [14]
A loose fitting wetsuit supplied with heated water through a hose in the diver's umbilical, which links the diver to the surface support. The diver controls the flow rate of the water, allowing them to vary the warmth of the suit. [15] [16]
A neurological and physiological diving disorder that occurs when a diver descends below about 500 feet (150 m) while breathing a helium–oxygen mixture. [17]
Cylinder valve body with two outlets and two valve mechanisms which can be independently controlled so that two regulator first stages can be fitted. Similar to Y-valve but in configuration where the second valve is parallel to the primary, though the secondary valve can sometimes be swivelled.
Pressure due to the weight of the water column above a point at depth. [18]
Non-destructive test to revalidate pressure vessels which uses water as a test medium. The vessel is pressurised to the test pressure (q.v.) and measured for permanent set. [19]
Deep diving breathing gas mixture of hydrogen, helium and oxygen. [20]
Deep diving breathing gas mixture of hydrogen and oxygen. [20]
Evacuation of divers under pressure from a saturation chamber to a hyperbaric rescue craft via a pressurised transfer system. [1]
System for evacuating divers under pressure from a saturation system in an emergency. [21] The whole system set up to provide hyperbaric evacuation, including planning, procedures, equipment used for evacuation, reception facility, contingency plans, possible safe havens and anything else requited for a successful hyperbaric evacuation. [1]
A lifeboat with a hyperbaric chamber and life support system built into it for evacuating saturation divers in an emergency. [22]
A unit which allows for connection of hyperbaric lifeboats and hyperbaric rescue capsules. Usually modular and portable so they can be moved to a suitable venue for standby with the hyperbaric rescue vessel. [24]
Generic term for the unit provided to evacuate divers from a saturation system. It may be an HRC or a SPHL or some other suitable pressure vessel. [1]
A ship provided with equipment to handle the recovery of hyperbaric lifeboats and hyperbaric rescue capsules. [25]
Excessive level of carbon dioxide in the body, to a partial pressure of above 45 mmHg. [26]
Additional filter to produce air of oxygen compatible quality, usually for partial pressure gas blending. This may be built into the filling system or temporarily connected when required.
Property of an oxygen sensor to produce linear output at partial pressures above the highest calibration point. [7] [27]
Abnormally low tissue and blood carbon dioxide concentration. [28]
A lowering of core body temperature, usually due to heat loss. [29]
Abnormally low tissue oxygen concentration. [30] Insufficient oxygen in the body to support normal activities or consciousness.
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International trade association for the marine contracting industry.
A gas which is not metabolically active, used to dilute the breathing gas.
Inert gas uptake in body tissues during a dive or other hyperbaric exposure.
Metabolic reduction of total gas pressure in the tissues . [34]
Any system for carrying dive weights on the buoyancy compensator or diving safety harness, avoiding the use of a separate weight harness or weightbelt.
The international forum of the oil and gas producing industry.
Recompression of a diver by returning to a specified depth in the water, followed by decompression on a specified gas, commonly oxygen, as treatment for decompression sickness or as prophylaxis for incomplete or missed decompression after a dive.
The diffusion of gases in opposite directions caused by a change in the composition of the external ambient gas or breathing gas without change in the ambient pressure. [37]
Connection between two scuba cylinders which when open allows free flow of gas in both directions between the cylinders, but has an isolation valve which can be used to block this flow.
Valve in an isolation manifold (q.v.) used to close the gas passage through the manifold and isolate the contents of the two cylinders. Used to prevent a leak on one cylinder from causing the other cylinder to also lose gas.
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A line secured at both ends to serve as a support [38] or guide. [39]
Underwater search techniques using one or more jackstays to guide the searcher. [39]
A type of mobile platform that consists of a buoyant hull fitted with three or more movable legs, capable of raising its hull over the surface of sea. The buoyant hull enables transportation of the unit and all attached machinery to a desired location. Once on location the hull is raised to the required elevation above the sea surface on its legs supported by the sea bed. [40] [41]
A type of pipe and hose fitting with a 37-degree flare seating surface. Commonly used in umbilical hose connections. [42]
An atmospheric diving suit manufactured by Underwater Marine Equipment Limited. [43]
A short line used to connect to a shotline or anchor line, allowing the diver to move a short horizontal distance away to decompress. The line helps compensate for vertical movement in the anchor line or shot line due to waves. [46]
A procedure to integrate health and safety principles and practices into a particular task or job. Each basic step of the job is analysed to identify potential hazards and controls for each hazard. [47]
A variation on the movable jackstay search suitable for a single diver.
A path from a main guideline to another which is not in contact [48]
A short cave line , usually stored on a spool, used to connect between two permanent lines that are not in contact. May also be used to search for the other end of a break in a cave line and repair the break [48]
Scuba cylinder valve with lever operated reserve mechanism. [51]
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Diving from a special purpose kayak used to get to the site where the distance from a suitable entry and exit point is inconvenient for shore diving. [52]
Scuba cylinder valve without reserve mechanism. [51]
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A piece of cordage used to secure or lower things; usually it is used where there is a risk of losing the object. [53]
An uncontrolled or involuntary muscular contraction (spasm) of the laryngeal cords which causes a partial blocking of breathing in, while breathing out remains easier. [54]
Mechanised system for lowering a diving bell, diving stage, hyperbaric evacuation unit, [55] submersible or ROV from a vessel, offshore platform, dockside or other platform, and lifting it back on board. [56] [57]
Barge on which pipeline sections are assembled, welded and laid on the seabed as the barge is moved forward. [36]
To run line (unreel under light tension while advancing) and place it
A shot line (q.v.) which does not reach the bottom
A semiconductor device for producing light from an electrical current commonly used in dive lights.
A line connected securely to the diver at one end and anchored at the other end at the diving control point, which is handled by a line tender, and is used to communicate with the diver and provide a means of finding the diver for a surface standby diver, and for assisting the diver to the surface and back to the control point if necessary. [58]
Equipment vital to the short term survival of the diver. Most notably the breathing gas supply, and for saturation diving, equipment for providing a correctly pressurised environment. In some cases thermoregulatory equipment is also considered life support, and in saturation diving, all of the peripheral systems essential to maintaining a habitable saturation system.
A collection of equipment and supplies kept in a suitable location such that when a hyperbaric rescue chamber or self-propelled hyperbaric lifeboat arrives at the safe haven it is available to support or complete decompression by using the LSP components to maintain the decompression environment by way of power, gas mixtures, heating and cooling. [1]
A person who operates and maintains the life support systems of a saturation diving system. [59]
A robust and air-tight bag with straps, which is used to lift heavy objects underwater by means of the bag's buoyancy when filled with air. [60]
The part of a canister light (q.v.) which emits light, and is held in the hand or mounted on the helmet. [61]
Low volume, close fitting diving helmet, usually with demand valve. Neutrally buoyant, and moves with the diver's head.
Line arrows, cookies and sometimes clothes pegs. Tags used to indicate the direction to an exit, midway point between exits, jumps and personal markers to identify divers on a guide line in an overhead environment. [62]
A lung inflammation (pneumonia) that develops when lipids enter the bronchial tree [63]
A large boat which provides transport, accommodation and services for vacationing recreational divers. [64]
Compartment of a hyperbaric habitat or chamber which can be entered through two or more openings which can be closed and sealed, and the pressure adjusted relative to the adjacent chambers. Used to transfer personnel or equipment between areas of different pressure, and for transfer under pressure between hyperbaric chambers. [66]
Safety procedure when working on a hazardous energy source. [67]
Factory set function of some dive computers which disables the computer from decompression calculation after a violation of a factory set limit for depth, decompression ceiling or other violation of approved operating range for a period sufficient for tissues to fully desaturate if the diver survives uninjured (48 hours in some models). Some models will lockout immediately, usually to gauge mode which provides depth and time data but no decompression information, leaving the diver without some safety-critical information, others will continue to provide the diver with best estimate decompression information until the end of the dive. [68]
5 to 7 feet (1.5 to 2.1 m) interstage hose used on one of the regulators used by cave and other technical divers, which allows gas sharing through narrow spaces where the divers must pass through in single file. [69]
Mass transport of water along a shoreline, often due to wave action at an angle to the shoreline. [70]
The ambient pressure circuit in a rebreather through which the breathing gas passes during a breathing cycle.
standardised procedure followed when a diver realises that their buddy is not where they should be. Procedures may vary depending on the circumstances and training organisations. [72]
Standardised procedure to be followed when the guideline to open water is lost in a penetration dive, often in conditions of low visibility and darkness. [72]
Diving with low environmental impact. Diving in a way that avoids contact with or disturbance of sensitive organisms and adversely affecting the environment. Usually applied to recreational diving. [73]
Water where, regardless of illumination, the distance over which objects can be seen is small. It is a term with highly variable and often relative meaning, but it would be almost universally accepted that less than 0.5 metres (1.6 ft) visibility would be considered low visibility. For operational purposes NOAA define it as "When visual contact with the dive buddy can no longer be maintained", and DAN Southern Africa suggest less than 3 metres (9.8 ft). [74] [75]
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A reflex response to breathhold and chilling of the face diving response expressed by the cardiovascular system, which exhibits hypertension, bradycardia, oxygen conservation, arrhythmias, and contraction of the spleen. [76]
Panel for the distribution of diver breathing gas. [1]
A person such as a life support technician (LST), diving supervisor, or mixed-gas diver, who is designated to perform the duties of gas distribution on a surface-supplied mixed gas (HeO2) diving operation, who is competent in the operation of the manifold and whose primary responsibility is to operate the manifold. [1]
A closed circuit rebreather which relies on the diver to monitor and control the gas mixture in the loop.
Set of design and manufacturing rules intended to produce uniform and safe products by several manufacturers in an industry.
Small lock on a decompression chamber used for transfer of medical equipment and other supplies into and out of the chamber while the chamber remains under pressure. [78]
Unit of pressure equal to 1/10 bar. Not a linear measure of depth. [79]
A diving system (q.v.) which is installed on a vessel or installation on a temporary basis and that is not fixed, i.e. can be demobilised, transported and re-sited. Includes surface supplied air, nitrox, heliox and saturation diving systems. [1]
A generic term for several classes of self-contained floatable or floating drilling rigs such as drilling vessels, semisubmersibles, submersibles, jack-ups, and similar facilities that can be moved without substantial effort. These facilities may have self-propulsion equipment on board and may require dynamic positioning equipment or mooring systems to maintain their position. [84]
A type of swimfin typically used in finswimming and free-diving. It consists of a single surface attached to footpockets for both of the diver's feet. [87]
Material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids. Molecules small enough to pass through the pores are absorbed while larger molecules are not. It is different from a common filter in that it operates on a molecular level. [88]
The use of sidemount configuration and procedures with a single cylinder. [89]
An opening in the floor or base of the hull, platform, underwater habitat, or chamber, giving access to the water below. [90]
Recreational diving in low visibility, generally because there are some organisms of interest which live in that habitat. [91]
A dive profile in which the diver remains in more than one distinct depth ranges (excluding decompression stops) for a significant period before beginning final ascent to the surface. [92]
Compressor in which gases are compressed more than once, usually with cooling between stages. Used to improve efficiency and reduce temperatures. [93]
At a given ambient pressure, the M-value is the maximum theoretical value of absolute inert gas pressure that a tissue compartment can take without presenting symptoms of decompression sickness. [96] [97]
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The United States Navy Experimental Diving Unit, the primary source of diving and hyperbaric operational guidance for the US Navy, located in Florida. [98]
A US Navy trained combat diver.
The lower part of a lightweight diving helmet which includes a neoprene or latex neck seal similar to the neck seal on a dry suit, to prevent ingress of water. [99]
Internal screw thread in the bore of the cylinder neck to fit a cylinder valve, which controls flow of gas into and out of the cylinder. [100]
Buoyancy less than weight. Insufficient upward force due to buoyancy to keep afloat or remain at constant depth
Entry into the water in a buoyancy condition that will sink by default. When intentional, generally after reducing buoyancy of BC and, if applicable, dry suit by venting to ensure that the diver will not float back to the surface, but will continue to descend.
Breathing against an external pressure slightly less than the relaxed pressure in the lungs. More effort is needed to inhale, less to exhale. This can occur when using back mounted counterlungs on a rebreather, in a steep head up position with a single-hose demand valve, or when snorkelling.
Decompression models based on later modifications of the principles described by John Scott Haldane.
Synthetic elastomer used in the form of foamed sheets as the material for most wetsuits and some drysuits.
Having a fully immersed buoyancy exactly equal to weight, so that the forces are balanced and the person or object statically remains at a constant depth. Effectively average density is equal to that of the surrounding fluid medium. The state of neutral buoyancy is typically metastable for a compressible system.
An atmospheric diving suit designed and originally built by Phil Nuytten.
Minor symptoms characteristic of mild decompression sickness.
Diving during the hours of darkness.
A synthetic elastomer used for most standard O-ring seals.
The major component gas of air and many breathing gas mixtures used in diving. Important in diving as an active agent in nitrogen narcosis and decompression sickness.
Also known as narcs, inert gas narcosis, raptures of the deep, Martini effect: A reversible alteration in consciousness that occurs while breathing gases containing nitrogen under elevated partial pressure similar to alcohol intoxication or nitrous oxide inhalation, and can occur during shallow dives, but usually does not become noticeable until greater depths, beyond 30 meters. [101]
Mixture of nitrogen and oxygen for use as breathing gas. Usually with oxygen percentage higher than air.
A mixing tube used to blend oxygen with air before compressing to make nitrox breathing gas.
No decompression limit. The maximum time which a diver can remain at a specified depth without incurring a stage decompression obligation in terms of the specified decompression tables or algorithm.
A specialized overhead-environment strategy for dealing with particularly tight restrictions which may involve divers wearing a very basic harness or simply hand-carrying cylinders. [89]
An oscillation of the eyes alternating a slow eye movement in one direction, and a fast eye movement in the other direction.
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A secondary demand valve fitted to a diving first stage for use as an alternative air source for another diver in case of an emergency. Also occasionally useful as a backup in case of some kinds of malfunction of the primary
Colloquial term for a diver who works in the offshore oil and gas industry. [36] A professional diver who works in regions outside the jurisdiction of national occupational health and safety and labour laws.
Organic light-emitting diode: A low energy high contrast light source commonly used on instrument displays such as later generation dive computers. [104]
Procedure for managing a diver who surfaces without completing required decompression. If a chamber is available, the diver is recompressed in it, otherwise if no symptoms have presented, the diver may be recompressed as soon as practicable in the water. Various schedules for further decompression depend on the dive history. [105]
Breathing apparatus which discharges exhaled gas into the environment, without any further use.
Optical sensor device to measure a specific substance, usually with the aid of a chemical transducer.
A mechanical gasket in the shape of a torus; a loop of elastomer with a circular cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the contact surfaces.
Diffusion of gas out of the tissue into the blood, and transport to the lungs where it diffuses into the lung gas and is eliminated by exhalation.
Underwater diving emergency in which the breathing gas supply to the diver is interrupted.
Carrying more ballast weight than is necessary to achieve neutral buoyancy at all times during a dive. In scuba diving usually a dangerous error, but used in surface-supplied diving to stabilise the diver when working on the bottom.
Important component gas of atmospheric air and essential component of any breathing gas. Required to sustain life.
Instrument for measuring the partial pressure of oxygen in a gas mixture
Cleaned for oxygen service by appropriate methods and materials and tested for contaminants. Verified that particulates, fibres, oils, greases and other contaminants are absent. [9]
A notional alarm clock, which accumulates hyperbaric oxygen exposure at a rate which increases with higher oxygen partial pressure toward the maximum single exposure limit recommended. This function is implemented as cumulative oxygen exposure for acute (CNS) oxygen toxicity in some dive computers.
Made from materials which are suitable for oxygen service. Capable of coexisting with elevated oxygen concentrations and a potential source of ignition without flashing, based on a system’s maximum operating pressure and temperature. [9]
Design that minimizes any tendency for heat generation, ignition of particulates, or the accumulation of contaminants for an intended partial pressure of oxygen and temperature. [9]
Fraction by volume or pressure of the gas mixture made up by oxygen
A closed circuit rebreather that uses only oxygen as a gas supply. [7]
Suitable for operating with significantly higher levels of oxygen than normal atmospheric air. Often implies special cleaning procedures, use of oxygen compatible materials, and design to reduce ignition risk. System or component that has been designed and tested for oxygen use, has been tested as oxygen clean and is oxygen compatible. [9]
A condition resulting from the harmful effects of breathing molecular oxygen (O2) at elevated partial pressures.
Inherent unsaturation due to metabolic reduction of total gas pressure in the tissues.
A scuba set, originally just scuba, is any breathing apparatus that is entirely carried by an underwater diver and provides the diver with breathing gas at the ambient pressure. Scuba is an anacronym for self-contained underwater breathing apparatus. Although strictly speaking the scuba set is only the diving equipment that is required for providing breathing gas to the diver, general usage includes the harness or rigging by which it is carried and those accessories which are integral parts of the harness and breathing apparatus assembly, such as a jacket or wing style buoyancy compensator and instruments mounted in a combined housing with the pressure gauge. In the looser sense, scuba set has been used to refer to all the diving equipment used by the scuba diver, though this would more commonly and accurately be termed scuba equipment or scuba gear. Scuba is overwhelmingly the most common underwater breathing system used by recreational divers and is also used in professional diving when it provides advantages, usually of mobility and range, over surface-supplied diving systems and is allowed by the relevant legislation and code of practice.
A diving regulator or underwater diving regulator is a pressure regulator that controls the pressure of breathing gas for underwater diving. The most commonly recognised application is to reduce pressurized breathing gas to ambient pressure and deliver it to the diver, but there are also other types of gas pressure regulator used for diving applications. The gas may be air or one of a variety of specially blended breathing gases. The gas may be supplied from a scuba cylinder carried by the diver, in which case it is called a scuba regulator, or via a hose from a compressor or high-pressure storage cylinders at the surface in surface-supplied diving. A gas pressure regulator has one or more valves in series which reduce pressure from the source, and use the downstream pressure as feedback to control the delivered pressure, or the upstream pressure as feedback to prevent excessive flow rates, lowering the pressure at each stage.
Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The name scuba is an anacronym for "Self-Contained Underwater Breathing Apparatus" and was coined by Christian J. Lambertsen in a patent submitted in 1952. Scuba divers carry their own source of breathing gas, usually compressed air, affording them greater independence and movement than surface-supplied divers, and more time underwater than free divers. Although the use of compressed air is common, a gas blend with a higher oxygen content, known as enriched air or nitrox, has become popular due to the reduced nitrogen intake during long or repetitive dives. Also, breathing gas diluted with helium may be used to reduce the effects of nitrogen narcosis during deeper dives.
Diver rescue, usually following an accident, is the process of avoiding or limiting further exposure to diving hazards and bringing a diver to a place of safety. A safe place generally means a place where the diver cannot drown, such as a boat or dry land, where first aid can be administered and from which professional medical treatment can be sought. In the context of surface supplied diving, the place of safety for a diver with a decompression obligation is often the diving bell.
A bailout bottle (BoB) or, more formally, bailout cylinder is a scuba cylinder carried by an underwater diver for use as an emergency supply of breathing gas in the event of a primary gas supply failure. A bailout cylinder may be carried by a scuba diver in addition to the primary scuba set, or by a surface supplied diver using either free-flow or demand systems. The bailout gas is not intended for use during the dive except in an emergency, and would be considered a fully redundant breathing gas supply if used correctly. The term may refer to just the cylinder, or the bailout set or emergency gas supply (EGS), which is the cylinder with the gas delivery system attached. The bailout set or bailout system is the combination of the emergency gas cylinder with the gas delivery system to the diver, which includes a diving regulator with either a demand valve, a bailout block, or a bailout valve (BOV).
Underwater breathing apparatus is equipment which allows the user to breathe underwater. The three major categories of ambient pressure underwater breathing apparatus are:
Scuba gas planning is the aspect of dive planning and of gas management which deals with the calculation or estimation of the amounts and mixtures of gases to be used for a planned dive. It may assume that the dive profile, including decompression, is known, but the process may be iterative, involving changes to the dive profile as a consequence of the gas requirement calculation, or changes to the gas mixtures chosen. Use of calculated reserves based on planned dive profile and estimated gas consumption rates rather than an arbitrary pressure is sometimes referred to as rock bottom gas management. The purpose of gas planning is to ensure that for all reasonably foreseeable contingencies, the divers of a team have sufficient breathing gas to safely return to a place where more breathing gas is available. In almost all cases this will be the surface.
Scuba gas management is the aspect of scuba diving which includes the gas planning, blending, filling, analysing, marking, storage, and transportation of gas cylinders for a dive, the monitoring and switching of breathing gases during a dive, efficient and correct use of the gas, and the provision of emergency gas to another member of the dive team. The primary aim is to ensure that everyone has enough to breathe of a gas suitable for the current depth at all times, and is aware of the gas mixture in use and its effect on decompression obligations, nitrogen narcosis, and oxygen toxicity risk. Some of these functions may be delegated to others, such as the filling of cylinders, or transportation to the dive site, but others are the direct responsibility of the diver using the gas.
Rebreather diving is underwater diving using diving rebreathers, a class of underwater breathing apparatus which recirculate the breathing gas exhaled by the diver after replacing the oxygen used and removing the carbon dioxide metabolic product. Rebreather diving is practiced by recreational, military and scientific divers in applications where it has advantages over open circuit scuba, and surface supply of breathing gas is impracticable. The main advantages of rebreather diving are extended gas endurance, low noise levels, and lack of bubbles.
The Halcyon RB80 is a non-depth-compensated passive addition semi-closed circuit rebreather of similar external dimensions to a standard AL80 scuba cylinder. It was originally developed by Reinhard Buchaly (RB) in 1996 for the cave exploration dives conducted by the European Karst Plain Project (EKPP).
Scuba skills are skills required to dive safely using self-contained underwater breathing apparatus, known as a scuba set. Most of these skills are relevant to both open-circuit scuba and rebreather scuba, and many also apply to surface-supplied diving. Some scuba skills, which are critical to divers' safety, may require more practice than standard recreational training provides to achieve reliable competence.
The history of scuba diving is closely linked with the history of the equipment. By the turn of the twentieth century, two basic architectures for underwater breathing apparatus had been pioneered; open-circuit surface supplied equipment where the diver's exhaled gas is vented directly into the water, and closed-circuit breathing apparatus where the diver's carbon dioxide is filtered from the exhaled breathing gas, which is then recirculated, and more gas added to replenish the oxygen content. Closed circuit equipment was more easily adapted to scuba in the absence of reliable, portable, and economical high pressure gas storage vessels. By the mid-twentieth century, high pressure cylinders were available and two systems for scuba had emerged: open-circuit scuba where the diver's exhaled breath is vented directly into the water, and closed-circuit scuba where the carbon dioxide is removed from the diver's exhaled breath which has oxygen added and is recirculated. Oxygen rebreathers are severely depth limited due to oxygen toxicity risk, which increases with depth, and the available systems for mixed gas rebreathers were fairly bulky and designed for use with diving helmets. The first commercially practical scuba rebreather was designed and built by the diving engineer Henry Fleuss in 1878, while working for Siebe Gorman in London. His self contained breathing apparatus consisted of a rubber mask connected to a breathing bag, with an estimated 50–60% oxygen supplied from a copper tank and carbon dioxide scrubbed by passing it through a bundle of rope yarn soaked in a solution of caustic potash. During the 1930s and all through World War II, the British, Italians and Germans developed and extensively used oxygen rebreathers to equip the first frogmen. In the U.S. Major Christian J. Lambertsen invented a free-swimming oxygen rebreather. In 1952 he patented a modification of his apparatus, this time named SCUBA, an acronym for "self-contained underwater breathing apparatus," which became the generic English word for autonomous breathing equipment for diving, and later for the activity using the equipment. After World War II, military frogmen continued to use rebreathers since they do not make bubbles which would give away the presence of the divers. The high percentage of oxygen used by these early rebreather systems limited the depth at which they could be used due to the risk of convulsions caused by acute oxygen toxicity.
The following outline is provided as an overview of and topical guide to underwater diving:
The following index is provided as an overview of and topical guide to underwater diving:
Diving procedures are standardised methods of doing things that are commonly useful while diving that are known to work effectively and acceptably safely. Due to the inherent risks of the environment and the necessity to operate the equipment correctly, both under normal conditions and during incidents where failure to respond appropriately and quickly can have fatal consequences, a set of standard procedures are used in preparation of the equipment, preparation to dive, during the dive if all goes according to plan, after the dive, and in the event of a reasonably foreseeable contingency. Standard procedures are not necessarily the only courses of action that produce a satisfactory outcome, but they are generally those procedures that experiment and experience show to work well and reliably in response to given circumstances. All formal diver training is based on the learning of standard skills and procedures, and in many cases the over-learning of the skills until the procedures can be performed without hesitation even when distracting circumstances exist. Where reasonably practicable, checklists may be used to ensure that preparatory and maintenance procedures are carried out in the correct sequence and that no steps are inadvertently omitted.
A Diving rebreather 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 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 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.
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