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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A sudden sensation of fear which is so strong as to dominate or prevent reason and logical thinking, replacing it with overwhelming feelings of anxiety and frantic agitation consistent with an irrational fight-or-flight reaction
A decompression model comprising a group of tissues with varied rates of perfusion, but supplied by blood of approximately equivalent gas concentration. It is assumed that there is no gas transfer between tissue compartments by diffusion. This results in a parallel set of independent tissues, each with its own rate of ingassing and outgassing dependent on the rate of blood flowing through the tissue
(Abbreviation PP or pp) The pressure that a component gas of a gas mixture would exert if it alone was present in the volume occupied by the gas mixture. [1]
The rate of change of partial pressure of dissolved gas through a solvent, which is the driving mechanism for diffusion through the solvent. Also loosely used to refer to the difference between the dissolved gas pressure in a tissue and ambient pressure. [2]
Feed gas addition system for semi-closed circuit rebreathers which discharges a part of the gas in the breathing circuit. fresh gas is added when the volume of the circuit decreases during inhalation and triggers the addition valve. Compare with active addition .
A common form of congenital heart defect that enables blood flow between the left and right atria through a gap in the interatrial septum. In some circumstances this may increase risk of decompression sickness if venous blood carrying gas bubbles is shunted into the arterial system, bypassing the pulmonary capillary network filter. [3]
Rebreather with a single breathing hose from the mouthpiece to the scrubber and counterlung. Gas passes through it in both directions, unlike the one-way breathing loop configuration. The volume of the hose between the mouthpiece and scrubber is dead space [4]
Entering a region with no direct vertical access to the surface, such as a cave or the interior of a wreck.
The passage of fluid through the circulatory system or lymphatic system to an organ or a tissue, usually referring to the delivery of blood to a capillary bed in tissue. [2]
The assumption in a decompression model that perfusion has the dominant influence on gas uptake and release. Compare with diffusion limited . [6]
Text and symbols stamped into the metal of the shoulder of a diving cylinder providing obligatory and optional information about the cylinder. [7]
Radio beacons for personal use which are intended to indicate a person in distress who is away from normal emergency services.
Equipment worn by personnel to reduce risk of injury at sites where it is not practicable to eliminate the hazard, including ear protectors, safety glasses, hard hats, gloves, overalls, respirators etc. Diving suits and underwater breathing apparatus are also personal protective equipment. [8]
A photograph of a quadrat taken for later analysis. Common in marine ecological research where in situ counting would be impractical. Quadrats may be identified by rigid frames or by a fixed camera to subject distance. [9]
Pipeline inspection gauge: A tool that is sent through a pipeline and propelled by the pressure of the product in the pipeline itself, for purposes such as cleaning, dewatering, inspecting, measuring, separation of contents, etc. [1]
Standard connection type for portable medical oxygen cylinder valves and regulators. [10]
The place where a flexible underwater hose string is attached to connect a seabed pipeline with a single point mooring. [11]
Use of the pneumofathometer hose to supply breathing gas to a surface supplied diver in an emergency. Supply can be from the diver's own pneumo hose or from a standby diver's pneumo hose. [13]
Instrument to measure the depth of a diver, which measures the ambient pressure at the diver by measuring the pressure in a hose filled with air with an open end at the diver and with the surface end connected to a gas supply, control valve and pressure gauge calibrated in msw, fsw, or often both. [1] [14]
Air or other breathing gas in the chest cavity, outside of the lung, particularly between the pulmonary pleurae, sometimes resulting in a collapsed lung.
Relatively small scuba set, usually carried as an independent alternative breathing gas source by a recreational scuba diver.
(of compressor) A configuration that compresses gas by reducing the volume of the compression chamber (eg. cylinder) by mechanical means (eg. piston) to produce higher pressure of the contents which flow out via the exhaust port, usually through a non-return valve. [16]
May also refer to a pump in which a fixed volume is transferred during each cycle, relatively independent of inlet and outlet pressures.Breathing against an external pressure slightly greater than the relaxed pressure in the lungs. More effort is needed to exhale, less to inhale. This can occur when using a positive pressure mask, front mounted counterlungs on a rebreather, or if in a steep head down position with a single-hose demand valve.
A full-face mask which maintains an internal pressure slightly higher than external ambient pressure, necessitating slight positive pressure breathing, and ensuring that if the mask skirt seal fails, gas will leak out, rather than water leaking in, which provides a more secure airway and provides some protection against contaminated water. [17]
Examination of the external condition of a pressure vessel and fittings to ensure that it complies with requirements before accepting for filling. [18]
Nitrox blend supplied in bulk containers for decanting or boosting for direct use, or with high oxygen content used to blend nitrox of lower oxygen content by topping up the decanted pre-mix with air.
A component that produces an output signal proportional to a pressure input, which can be processed to give an output indicating the pressure. Used in dive computers, electronic pressure gauges, and pressure transmitters, among other uses. [19]
Pressure transducer (q.v.) with a wireless transmitter that sends a coded signal to the diver's dive computer which uses the data to display remaining cylinder pressure, which can in some applications be used to provide other gas management information.
Diving which is done as part of the diver's employment or professional occupation. Definitions vary in different jurisdictions. [23]
An incremental approach to cave and wreck exploration. Each dive goes a bit further so that the divers develop a familiarity with the environment. [12]
Type of safety valve used to control or limit the pressure in a system.
Unit of pressure in the Imperial system.
Push to talk: Voice communication systems which require the user to press a button to transmit. Used with through water systems to conserve battery power.
The underwater work conducted by law enforcement, fire department rescue, and search & rescue/recovery dive teams.
Pulmonary barotrauma of ascent related diseases. Lung over-pressure injury which may manifest as arterial gas embolism, pneumothorax, tension pneumothorax, mediastinal emphysema, subcutaneous emphysema or occasionally pneumopericardium. [25]
Button or flexible area on the front or side of a demand valve which allows the user to manually open the second stage valve to provide gas flow without inhalation. [26]
Non-return valve in snorkel or mask which allows water to drain either under gravity or as a result of exhalation into the air space
A valved catheter fitted to a dry suit, which enables a diver to urinate at any time without having to get out of the water. [29]
Named after Richard Pyle, an early advocate of deep stops. An additional brief deep decompression stop, typically 2 minutes long and half way between the maximum depth and the first conventional decompression stop. [30]
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A small, typically rectangular plot used in ecology and geography to isolate a standard unit of area for study of the distribution of an item over a large area. The quadrat is suitable for sampling plants and slow-moving or sessile animals.
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Frame attached to the top of back-mounted scuba cylinders to protect valves, manifold, and regulator first stages from impact with the surroundings.
A shirt made of spandex and nylon or polyester, worn to protect against rashes caused by abrasion, and jellyfish stings. These shirts can be worn by themselves, in tropical water, or under a wetsuit.
A technique for calculating decompression schedules for scuba divers engaged in deep diving without using dive tables, decompression software or a dive computer. [32] [33]
Underwater breathing apparatus which recycles most of the exhaled gas, removing carbon dioxide and topping up oxygen before the gas is breathed again. [34]
Compressor in which the volume of the compression chamber/s is cyclically changed by reversing linear motion. Usually a positive-displacement compressor that uses pistons driven by a crankshaft to deliver gases a raised pressure. [35] [36]
Diving helmet with a reclaim gas regulator allowing exhaled gas to be safely returned to the surface through an additional hose on the umbilical. [37]
A diving regulator designed to safely return exhaled gas to a reclaim hose at lower than ambient pressure. Function is similar to a BIBS exhaust valve. [38]
System for recovering helium based breathing gas used by divers and recycling it. [39] [40]
A hyperbaric chamber used to treat divers suffering from certain diving disorders such as decompression sickness. [44]
A technique used by freedivers on surfacing to reduce the risk of surface blackout. A partial exhalation is made, followed by a quick inhalation, then the diver closes the airway and pressurises for a few seconds as if about to cough. This is repeated a few times over the first 30 seconds or so on the surface. The aim is to keep thoracic pressure slightly raised to artificially raise arterial oxygen partial pressure or prevent it from dropping in the critical seconds until newly oxygenated blood can reach the brain, and thereby prevent surface blackout. This is the same technique used by pilots during high-g maneuvers, and by mountaineers at high altitude. [45] [46]
A no-stop decompression table developed by DSAT. [50] [51]
A computationally intensive bubble model decompression algorithm developed by Bruce Wienke. [52] [53]
Technical diving philosophy of ensuring that a spare or backup is available for any item of life-support equipment that would immediately endanger the diver if it were to fail. [54]
A breathing gas supply, carried by the diver, which is both suitable for the depths at which it may be breathed, and sufficient to allow the diver to make a safe and controlled return to the surface or other place where more breathing gas is available, which is not used during the dive, and is stored in one or more cylinders which are mot the one the diver is breathing from at any given time. [55]
Locking of the regulator mechanism caused by freezing of the water due to expansion cooling of the regulated air. Often causes the mechanism to lock open, causing free flow and further cooling. [57]
Any dive which is done while the tissues retain residual inert gas from a previous dive. [43]
Gas which is not intended to be used during the dive, and is reserved for contingencies.
Cylinder valve with a lever operated bypass valve to release the gas below reserve pressure. [60]
Nitrogen in excess of normal atmospheric saturation remaining in the diver's tissues after a dive.
Time penalty in a repetitive dive equivalent to time at depth which would produce the residual nitrogen in the diver at the start of the dive.
Recreational dive by an uncertified person under the paid direct supervision of a recreational diving instructor, after a very basic training session to learn the essential safety skills in confined water. Resort dives are limited to shallow water free of significant additional hazards. No certification is gained, though the dive may count towards an entry level certification if it follows closely. Compare with try-diving and Supervised diver .
The volume of gas inhaled (inhaled minute volume) or exhaled (exhaled minute volume) from a person's lungs in one minute.
The ratio of carbon dioxide produced as a metabolic product to the oxygen consumed.
Barotrauma of the ear caused by a middle ear gas space pressure greater than ambient pressure, or greater than the pressure in the external autitory canal, causing the eardrum to bulge outwards. [61]
Length of shock cord with metal rings and a clip used to control the position of the top end of a sidemounted cylinder. [65] Differs from a regular bungee in having the rings. [65] A popular configuration is a bolt snap connected to a ring by a quick link, with a length of bungee from the ring to another quick link which is used to connect the assembly to a D-ring on the back of the harness. The bolt snap is clipped to the shoulder D-ring and the cylinder neck bolt snap is clipped to the ring.
A strong localised flow of water to seaward from near the shore, typically through the surf line
A conduit that provides a temporary extension of a subsea oil well to a surface drilling facility
Retention of a breathing gas reserve based on calculated values for the amount of gas required for a safe ascent from any point in the planned dive profile. Factors such as emergency supply of gas to a buddy, air consumption rates under stress and decompression gas requirements are considered in the calculations.
Cave and wreck penetration breathing gas management convention where no more than one third of the gas in a cylinder may be used on the inward part of the dive, and the other two thirds is kept for exit: One third for the planned exit, and one third in case of an emergency. [67]
A cylinder valve which limits the outflow by a calibrated orifice when in the "on" position. [68]
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A voluntary (not required by the decompression schedule) additional decompression stop intended to further reduce risk of decompression sickness. [69] [70]
A reaction of the lungs to inhalation of a mist of salt water. [71]
Condition where the inert components of the breathing gas dissolved in a diver's tissues are in equilibrium with the gas in the lungs. [41]
Diving mode where the divers remain pressurised for long enough for the slowest tissues to saturate with the inert components of the breathing gas, usually for periods of several days or weeks, and decompress only at the end of the period. Decompression from saturation is controlled only by the slowest tissue. [73] [74]
The combination of equipment and services to operate a saturation diving project. It would include the closed diving bell, the accommodation modules, decompression chamber, life-support systems, gas storage and supply systems, pressurisation equipment, underwater breathing apparatus, and launch and recovery systems. In may also include a hyperbaric evacuation system. [75]
Valve using a standard automotive tyre valve insert, common in low pressure inflation hose female connectors and BC inflation valves. [62]
Diving for purposes of scientific research. The rules and constraints of scientific diving vary in different jurisdictions, but generally allow different options to mainstream commercial diving.
A clip mechanism which can be locked in the closed position by turning a threaded barrel.
Canister containing material (sorb) which chemically combines with carbon dioxide to remove it from the gas passed through the canister.
Self-contained underwater breathing apparatus. May be open or closed circuit.
Competitive underwater sport in which scuba divers attempt to swim a circuit marked by buoys, without surfacing, using compass navigation and mechanical distance measurement. Points are awarded for time and accuracy according to the specific course definition and length.
Mobile surface-supplied diving equipment using portable gas storage cylinders for primary and reserve breathing gas supply. Preferred to scuba for commercial diving applications due to lower perceived risk compared to scuba, and because equipment and procedures are otherwise identical to surface supplied diving using compressors for air supply. Used when logistical constraints or air quality issues preclude use of a compressor. [1]
Cord used to indicate the transect for a search. The diver moves along the line, searching by sight or feel on one or both sides of the line. After the transect has been searched, the line is moved to the next transect. usually a short distance offset from the previous position, at a distance which depends on the visibility and the size of the target.
Systematic procedure for covering the search area sufficiently to be reasonably sure of finding a given target if it is there. Several patterns are in general use for underwater searches, depending on the target, the terrain, and available facilities.
A complication of aspiration of water or other fluids into the lungs.
The part of a diving regulator which provides pressure reduction from intermediate pressure to ambient pressure on demand. Demand valve. [76]
A pressure vessel adapted for use as a means of hyperbaric evacuation, and fitted to a conventional lifeboat hull. [1]
A wet suit with wrist and ankle seals, and usually a more watertight zipper than usual, to reduce flushing of water through the suit.
Device which facilitates the separation of liquid particles from the compressed gas, usually with a drain to periodically remove accumulated liquid from the system.
A decompression model based on the assumption that diffusion is the limiting mechanism of dissolved gas transport in the tissues, in which there is perfusion transport for one compartment, and diffusion between a series of compartments,
Reference value for oxygen partial pressure in an electronically controlled closed circuit rebreather. The control system monitors the real time value of oxygen partial pressure in the breathing loop and automatically adjusts the composition by adding gas to keep the concentration between the upper and lower set-points. [77] [78]
Surface Gas Consumption
Subsection: Top, Sa, Se, Si, So, Su
A rope between a float at the surface, and a sufficiently heavy weight holding the rope approximately vertical. [81]
A scuba diving equipment configuration which has diving cylinders mounted alongside the diver, below the shoulders and along the hips, instead of on the back of the diver. [82]
The practice of using sidemount configuration (bungee loops and/or butt-plate rails) as a means for stowing stage/deco cylinders when otherwise diving in back-mounted scuba. [83]
An entry technique which minimises noise and splash, suitable for entry from a low platform. The diver sits with feet dangling over or into the water, turns their torso sideways, takes their weight on their hands, then swings off the surface and drops feet first into the water, slowed by their arms, and lets go with the hands when in the water. [84] : 251
A desiccant filter medium used to adsorb water.
A situation when underwater visibility is rapidly reduced to zero, usually when a diver disturbs silt deposits. [85] [86]
Device which is inserted into silt or sand to provide an anchor point, such as for a tie-off on a cave line. [65] Silt screws are generally stakes made from small bore plastic (PVC) pipe with a sharpened end.
A loading buoy anchored offshore, that serves as a mooring point and interconnect for tankers loading or offloading gas or liquid products. SPMs are the link between geostatic subsea manifold connections and weathervaning tankers. They are capable of handling any size ship, even very large crude carriers (VLCC) where no alternative facility is available [11]
A natural depression or hole in the Earth's surface caused by karst processes — the chemical dissolution of carbonate rocks – or suffosion processes for example in sandstone [87] [88]
Particulate or granular material bonded together by the application of pressure and sufficient heat to partially melt the surface of the particles and weld them together. The product is usually porous. [89] [90]
A flat stone, usually of marble or granite, weighing between 8 and 14 kg, with rounded corners and edges, and tied to a rope, historically used by Greek sponge free-divers to assist descent. When the diver wishes to ascend the rope is used to signal the tender on the boat who then pulls in the rope. Currently skandalopetra diving is a competitive sport. [91] [92]
Breathing pattern where the diver holds each breath a while to conserve breathing gas, which can cause hypercapnia which can lead to headaches, aggravate nitrogen narcosis, increase risk of oxygen toxicity, and reduce physiological reserves in an emergency. [93]
Method of laying undersea pipelines by welding the sections together on the lay barge and deploying them from the stern horizontally guided by a "stinger" - a structure that supports the pipe string to control its bend radius. [96] The term refers to the shape of the bend in the pipe which transitions from roughly horizontal onboard where the sections are welded together, to angled downward over the stinger, to roughly horizontal again as it settles on the seabed.
Rigid hard plastic tablet used for writing messages or notes underwater. Compare with wet notes . Usually with a slightly roughened surface to accept pencil marks.
Independent cylinder with its own regulator carried clipped to the harness at the side of the diver. Compare with sidemount , and stage cylinder .
A cylinder valve with two valved outlets angled to left and right of the centreline
A clip connector mechanism which locks when closed, can be operated without tools, and can usually be released under load.
A heavy duty elastic band made from a slice of inner tube.
Accessory for a photographic strobe which limits illumination of the subject to a very small area, leaving the background datk, and virtually eliminating backscatter.
Tube with a bend and mouthpiece used for breathing air from above the water surface when the wearer's mouth and nose are submerged.
Swimming at the surface of the water while breathing through a snorkel. the snorkeller is almost always equipped with a diving mask or swim goggles, and usually swimfins.
Device to hold a snorkel in place at the side of a diving mask by fixing it to the mask strap.
Snuba is a portmanteau of "snorkel" and "scuba", referring to a proprietary recreational surface supplied underwater breathing system supplied from a cylinder mounted on a small raft towed by the diver.
The practice of scuba diving alone, without a dive buddy or in-water standby diver. [97]
Metering device to provide constant mass flow of a gas.
Carbon dioxide absorbent material used in rebreather or life support system scrubber to remove carbon dioxide from the breathing gas so it may be recycled. [98]
Hunting weapon for shooting fish underwater which propels a barbed steel spear a short distance forward using stored energy from stretched rubber strips or compressed air behind a captive piston. [99]
An electronic device to render words spoken in a hyperbaric helium environment intelligible. [1] [100]
Dissolution features in bedrock. [101]
Also known as a cave formation: A secondary mineral deposit formed in a cave. [102]
Mask strap system for full-face masks with three or more straps. (commonly 5)
A valve in the side of a copper diving helmet which could be used by the diver to suck in a mouthful of seawater to spit onto the inside face of a viewport to wash off condensation droplets to improve their view. [103]
Place where a concentrated flow of water emerges from the ground. [107]
Fin strap using a stainless steel spring to secure the fin to the foot.
Dive profile where the diver descends continuously to the maximum depth and stays there for the duration of the dive before ascending directly at a stedy rate to the surface or first decompression stop. This profile provides worst case exposure for gas absorption by the body tissues for a given depth and bottom time, and is assumed for most decompression planning using decompression tables. [112]
Injury or discomfort caused by increase of ambient pressure above the pressure in a gas space in contact with the diver's body, causing a pressure difference tending to squeeze body tissues into the lower pressure volume of the gas space. A cause of several kinds of barotrauma.
The practice of making decompression stops .
Placing a stage cylinder at the distance line for planned later use.
The use of standard deco/stage cylinder configuration, without back-mounted cylinders, on an otherwise standard, or partially modified tec/rec BCD. The cylinders are attached to waist and shoulder D-Rings by direct bolt-snap, and no bungee cord is used in the upper attachment. Similar to, and may be confused with sidemount [114]
The clips, straps and cords fastened to a scuba cylinder which are used to mount it as a stage cylinder.
A scuba set to be used during a specific stage of a dive. Often rigged and carried as a sling mount or sidemount set. Sometimes dropped at the end of the outward leg of the stage, and retrieved on the return to complete the return leg of the same stage.
Early free flow surface supplied diving equipment using a heavy rubberised canvas suit, copper helmet and corselet , and weighted boots. Still in use in some parts of the world. [41]
The copper and brass free-flow diving diving helmet used with standard diving dress.
Procedure compiled by an organisation prescribing the processes to be followed when performing specified tasks. [115] [116]
(Professional) diver functioning as a safety backup to the working diver. Often on the surface at the dive control point, but ready to enter the water at very short notice on the instruction of the supervisor. In bell diving the stand-by diver would be the bellman. [1]
Underwater breath-holding without changing location [117]
The pressure difference between gas inside the lungs and the gas inside the mouthpiece of the breathing apparatus or inside the helmet. In most rebreathers this is the hydrostatic pressure at depth of the counterlung. In ballasted bellows counterlungs the pressure is modified by the force exerted by the ballast weight. [118]
Depth pressure in a saturation system at which divers live between compression and decompression when not locked out on a dive. [119]
Entry technique from a platform a small to moderate distance above the water surface, which is suitable to stand on before entry. The diver faces the water and steps out with the leading foot, pushing away from the platform with the back foot, and drops into the water while maintaining a vertical posture until fully submerged. It is usually advisable to hold loose equipment against the body, particularly the mask and DV, and if there is no crotch strap, the buoyancy compensator is held to prevent it riding up the torso on impact. The feet can be brought together after initial impact to limit depth of immersion in moderately shallow water, by applying fin thrust downwards. [120]
Gas under the skin resulting from lung overpressure injury. [27]
A closed diving bell, used for transferring divers under pressure to and from the worksite. Particularly if used for decompression. [41] [1]
Gauge attached to the first stage regulator and used to monitor pressure remaining in the diving cylinder. [76]
Excessive inflation of a dry suit leading to uncontrolled ascent. [29]
A passage in a cave that is submerged under water. [121]
Rebreather scrubber which not only removes carbon dioxide from the exhaled air, but also replenishes the oxygen by chemical reaction with potassium superoxide. [122]
A temporary and thermodynamically unstable condition of a solvent containing more dissolved gas than it can hold in solution over the long term for the prevailing conditions. A necessary condition for bubble growth in decompression sickness.
EN 14153-1 / ISO 24801-1 standard competence for recreational scuba diver. The level 1 "Supervised Diver" has sufficient knowledge, skill and experience to dive, in open water, to a recommended maximum depth of 12 m, which do not require in-water decompression stops, under the direct supervision of a dive leader, in groups of up to four level 1 scuba divers per dive leader provided the dive leader is capable of establishing physical contact with all level 1 scuba divers at any point during the dive, only when appropriate support is available at the surface, and under conditions that are equal or better than the conditions where they were trained. [123]
Small lock on a saturation life support habitat for transfer of relatively small items.
A voluntary member of a technical diving team who acts as a stand-by diver to the primary dive team, or provides in-water logistical support for a dive.
The mass or line of broken water formed by waves breaking on a shore or reef
A procedure in which some or all of the staged decompression obligation is done in a decompression chamber immediately after surfacing instead of in the water.
Gas volume calculated as expanded to surface pressure.
The time spent by a diver at surface pressure after a dive during which inert gas which was still present at the end of the dive is further eliminated from the tissues.
A buoy towed by a diver to indicate the diver's position to people at the surface.
Reciprocating water movement parallel to the bottom surface caused by the passing of a wave overhead, by analogy with the transient linear motion of a ship in the direction of travel also called surge.
The development of cracks in a material subjected over long term to static stress significantly less than the yield stress. There is a low but significant risk of this mode of failure in pressure vessels of AA6351 aluminium alloy. [130]
A series of surface gravity waves that is not generated by the local wind.
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.
Technical diving is scuba diving that exceeds the agency-specified limits of recreational diving for non-professional purposes. Technical diving may expose the diver to hazards beyond those normally associated with recreational diving, and to a greater risk of serious injury or death. Risk may be reduced via appropriate skills, knowledge, and experience. Risk can also be managed by using suitable equipment and procedures. The skills may be developed through specialized training and experience. The equipment involves breathing gases other than air or standard nitrox mixtures, and multiple gas sources.
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 pony bottle or pony cylinder is a small diving cylinder which is fitted with an independent regulator, and is usually carried by a scuba diver as an auxiliary scuba set. In an emergency, such as depletion of the diver's main air supply, it can be used as an alternative air source or bailout bottle to allow a normal ascent in place of a controlled emergency swimming ascent. The key attribute of a pony bottle is that it is a totally independent source of breathing gas for the diver.
In underwater diving, an alternative air source, or more generally alternative breathing gas source, is a secondary supply of air or other breathing gas for use by the diver in an emergency. Examples include an auxiliary demand valve, a pony bottle and bailout bottle.
Diving equipment, or underwater diving equipment, is equipment used by underwater divers to make diving activities possible, easier, safer and/or more comfortable. This may be equipment primarily intended for this purpose, or equipment intended for other purposes which is found to be suitable for diving use.
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 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.
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:
Investigation of diving accidents includes investigations into the causes of reportable incidents in professional diving and recreational diving accidents, usually when there is a fatality or litigation for gross negligence.
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.
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