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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Gas law describing the relation of component pressures of gases in a mixture to the total pressure. [1]
Diver-controlled closed-circuit rebreather. A closed circuit rebreather which requires the diver to monitor oxygen levels and manually inject oxygen or diluent as needed to maintain an appropriate partial pressure in the loop.
Defence and Civil Institute of Environmental Medicine (Toronto, Canada).
Decompression tables based on the Kidd-Stubbs model, developed and published by the Defence and Civil Institute of Environmental Medicine.
A heavy weight used to control the rise of a lifting bag after breakout , or to capsize it to prevent a runaway lift. Sometimes just called a deadweight. More generally, an anchor that relies on its weight to provide resistance to drag or lift loads. Deadman anchor more generally refers to a buried log, and may be misused in this context, but it is a common term in commercial diving.
To transfer gas between cylinders by differential pressure. No energy is input, flow will stop when valve is closed on reaching target pressure, or pressures are equalised.
A twin-lock hyperbaric chamber suitable for surface decompression and emergency recompression. Large enough to hold at least two occupants, one of them lying down. [3]
Reduction in ambient pressure experienced by the diver during the ascent at the end of a dive or hyperbaric exposure, and the process of allowing dissolved inert gases to be eliminated from the body tissues during this reduction in pressure. [4]
Specified step-by step procedures used to calculate the decompression stops needed for a given dive profile. The algorithm can be used to generate decompression schedules for a particular dive profile, decompression tables for more general use, or be implemented in dive computer software to perform real-time analysis of decompression status of the diver. [5]
Hyperbaric chamber used for decompressing divers and emergency therapeutic recompression. [6]
Gas breathed during decompression. Commonly implies a composition chosen to accelerate decompression by using an increased oxygen content. [6]
Illness caused by decompression. Includes decompression sickness and arterial gas embolism due to lung overexpansion injury. [7]
A conceptual explanation for the physiological effects of decompression and an associated mathematical approximation, usually expressed as an algorithm or formula, which describes and predicts those physiological effects. Some are more reliable than others. None are a true description of the physiological processes, but they may be sufficiently reliable to be useful.
Calculated theoretical requirement to make decompression stops during ascent based on the dive profile, breathing gases, and the decompression model in use.
A specific ascent rate and series of increasingly shallower decompression stops that a diver uses to allow inert gases to be eliminated from the body tissues during ascent after a specific hyperbaric exposure, to reduce the risk of decompression sickness. [6]
A condition arising from dissolved inert gases coming out of solution during decompression as bubbles in the tissues, organs and blood vessels of the body causing symptoms ranging from rashes to death. [6]
A pause during the ascent phase of a dive that a diver spends at a constant relatively shallow depth to allow safe release of inert gases from the body tissues to avoid decompression sickness. [6]
An indicator of risk for decompression sickness associated with the excess (supersaturation) of inert gas dissolved in the various tissues throughout the body, driving bubble formation and growth. Decompression stress can occur without symptomatic decompression sickness, but decompression sickness is a consequence of a high decompression stress. [8] [9]
Printed cards or booklets that allow divers to determine a decompression schedule for a particular dive profile and breathing gas. [6]
A horizontal bar or bars suspended at the depth of intended decompression stops by buoys, used to make decompression stops more comfortable and more secure and provide the divers' surface cover with a visual reference for the divers' position. [10]
Decompression stops which are deeper than the deepest stops required by decompression algorithms using dissolved phase models.
A condition where the water content of the body is reduced.
Diving helmet which provides breathing gas supply flow only when the diver inhales, triggered by the pressure drop.
Mechanism for providing the user with breathing gas flow only when required. The valve may be triggered by a reduction of pressure across the actuator diaphragm to below ambient due to inhalation, or by pressing a manual override (Purge button). [14]
A pressure gauge calibrated to measure depth as a function of ambient pressure.
A substantial heavily weighted line attached to a secure point at the surface, such as a boat or buoy, which can be used by a diver to control position and depth during descent an ascent. [16]
The pressure of the compressed gas in a cylinder at a temperature other than the nominal temperature at which charging pressure is specified. Usually refers to pressure when fully charged at a variation from the reference temperature. [17]
An enhancement to Global Positioning System that provides improved location accuracy. DGPS uses a network of fixed, ground-based reference stations to broadcast the difference between the positions indicated by the satellite systems and the known fixed positions. [18]
A diving skills program that uses a set of standardized portable obstacles to train and evaluate buoyancy skills and educate scuba divers on how to interact with coral reefs. [19]
Situation where water flows from a region of higher pressure to one of lower pressure, and where obstructing the flow will induce a large force on the obstruction. A type of diving hazard. [20]
Decompression hypothesis that the uptake and elimination of inert gas is limited by diffusion rates in the tissues. Compare with perfusion limited .
Gas mixture used to dilute the oxygen in the loop of a closed circuit rebreather to a partial pressure suited to the depth.
Replacing the gas within the breathing loop of a rebreather by injecting diluent gas while venting the previous gas mix. Usually done to get a breathable mixture of known composition in the loop to check calibration of the oxygen cells. [21]
Usually refers to G5/8" x 14 tpi [22] parallel thread fittings used to connect a cylinder valve to a filling connection or regulator first stage. Available in 200 bar and 300 bar versions which should only be inter-connectable in safe combinations. 232 bar DIN (5-thread, G5/8) Outlet/Connector #13 to DIN 477 part 1, and 300 bar DIN (7-thread, G5/8) Outlet/Connector #56 to DIN 477 part 5 - these are similar to 5-thread DIN fitting but are rated to 300 bar working pressures. The 300 bar pressures are common in European diving and in US cave diving. [23]
Screw in adapter which can be used with many recent 200/240 bar DIN cylinder valves to allow connection of Yoke regulators or filling whips.
A short tube screwed into the hole in the bottom of the cylinder valve body, which projects into the cylinder internal space. Its function is to prevent any loose debris inside the cylinder from getting into the outlet passages if the cylinder is inverted in use. [14] [25]
Display integrated vibrating alarm – A head-up display module which produces a warning vibration to draw the attention of the diver, generally mounted on the diver's mask or the rebreather mouthpiece. [21]
A line used by scuba divers as a means of returning to a safe starting point in conditions of low visibility, water currents or where pilotage is difficult. They are often used in cave diving and wreck diving where the diver must return to open water after a penetration when it may be difficult to discern the return route. [26] [27] Guide lines are also useful in the event of silt out. [28]
Disconnect and drop, unceremoniously or hastily abandon.
A device used by a scuba diver to measure the time and depth of a dive so that a safe ascent profile can be calculated and displayed so that the diver can avoid decompression sickness. [30]
Factor used in gas consumption estimates which allows for increased breathing rate due to conditions other than depth. Values range from 1.1 for relaxed, stress free conditions to more than 3.0 for heavy work. [31]
A ladder suitable for divers dressed for the specific dive to climb up and down between the surface deployment area and the water.
A professional level recreational diver who leads a group of less experienced or visiting divers underwater.
The variation of depth with elapsed time during a dive, often depicted as a graph.
The place at which the dive occurs. Also, more broadly, a place at which diving occurs, has occurred, or is planned to occur, and the general locality, with extent depending on context. Professional divers may also refer to a work site, or search area if relevant.
An automatically operated electronic timer which records the elapsed time from the start of a dive.
A mechanism used to lower one or more divers into the water to a shallow depth, and to lift them out again.
A publication containing instructional material for diver training. This may relate to a specific certification or a range of certifications, and is usually published either by a certification agency or a diving school for their own use, but may also be published and sold for general consumption.
Bundle of life-support hoses, communication cable, pneumofathomer hose and strength member between the surface control point and a surface-supplied diver.
A non-profit organization for assisting divers in medical and travel emergencies, advising divers on medical matters, and medical research on recreational diving safety.
A person who assists the working diver to prepare for a dive, get in and out of the water, and to undress from the diving equipment, and who tends the lifeline or umbilical while the diver is in the water. [35]
Piece of opaque white or pale coloured rigid plastic sheet with matte finish that is easily marked with a graphite pencil, used for taking notes, making sketches and written communication underwater.
Valve on the mouthpiece of a rebreather which can be switched between the loop and ambient air at the surface. It seals the breathing loop on the surface setting to prevent flooding the loop and is used for this purpose if the mouthpiece is removed from the mouth in the water. Compare with bailout valve (BOV).
A rigid chamber suspended from a cable and used to transport divers to depth and back to the surface.
Practice of carrying significantly more ballast weight than necessary to neutralise buoyancy. Common in professional diving operations where the diver needs to remain in firm contact with the bottom to work effectively, and is tethered by a lifeline or umbilical to a control point at a place of safety, which is managed by a tender.
An independent body of diving medical specialists from Northern Europe which provides advice about medical and certain safety aspects of commercial diving. [36]
A paramedic specialising in diving related conditions, and medically fit to dive in a hyperbaric chamber.
The combination of diving equipment, breathing medium and compression/decompression used for a diving operation, e.g. breathhold, open circuit scuba, nitrox rebreather, surface-supplied air, heliox saturation, etc. [20]
A portion of a diving project that can be safely supervised by one person, which can be a single dive or a number of dives. [20]
The involuntary physiological response to immersion which exists in all air-breathing vertebrates. It is a series of autonomic responses to apnea which are strengthened by facial cooling and hypoxia. It consists of peripheral vasoconstriction and associated hypertension, vagally induced bradycardia and reduction of cardiac output. This appears to preferentially supply oxygen to the brain. Another aspect is splenic contraction which increases haemoglobin content of the blood. [37]
The person who administers a United States university's research diving safety program. [38]
Hand sign and light sign system used by scuba divers to communicate when underwater.
A platform on which a diver stands which is hoisted into the water, lowered to the workplace at the bottom, and then hoisted up again to return the diver to the surface and lift them out of the water. The diving stage is particularly effective for controlling rate of descent and ascent. [35]
Person in charge of, and responsible for safety of a commercial diving operation. Usually trained, assessed as competent, certified and registered. Formally appointed by the diving contractor. [4]
A ship or boat used as a base for diving operations, particularly if designed or fitted out for that purpose.
A holistic philosophy of scuba diving, which encompasses several essential elements, including fundamental diving skills, teamwork, physical fitness, strictly defined standard procedures, and the use of standardised, streamlined and minimalistic equipment configurations. [40]
Ultrasonic signals reflected from bubble surfaces to identify and quantify gas bubbles present in venous blood.
Triangular plastic line marker with two slots which is mounted on a cave guide line to indicate the direction of the exit. [1]
Valve in which the closure is downstream of the orifice. Pressure in the line tends to assist in opening the valve. When spring-loaded a downstream valve may open automatically if the pressure difference is excessive, thus functioning as a pressure relief valve
Any dive where the diver is transported significantly by drifting with currents during the dive. [40]
The process of experiencing respiratory impairment from submersion/immersion in liquid.
Bag which seals in a watertight manner. Used for keeping clothes and other equipment dry in a wet environment.
Filling scuba cylinders without the use of a water bath for cooling. [43]
A watertight suit worn to keep the diver dry and to provide protection from the environment. Thermal insulation may be provided by the suit or garments worn under the suit.
Uncontrolled ascent due to over-inflation of a dry suit.
An inflatable marker buoy deployed from underwater to indicate the position of a diver and to control ascent rate. Can also be used to mark a position or signal an emergency.
A non-return valve, manufactured from rubber or synthetic elastomer, and shaped somewhat like the beak of a duck. Used as exhaust valve in some twin-hose diving regulators
Time that the breathing gas passing through a filter stack or absorbent canister remains in contact with the active filtration medium where the absorption of impurities can occur. [44]
Vessel which maintains position and heading using thrusters and positional feedback [40]
Method of keeping a floating platform in position without anchoring, using thrusters and positional feedback.
A target value for oxygen partial pressure in a rebreather loop which varies as a function of depth. Generally a setpoint that changes to optimize gas use, no stop time and other dive variables. [21]
Medical conditions resulting from changes in ambient pressure.
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Equalising the pressure in the middle and external ear by opening the Eustachian tubes. Several techniques are used. [45]
Electronic closed circuit rebreather. Sometimes ECCCR for electronically controlled closed circuit rebreather, which is the same thing.
Method of non-destructive testing using electromagnetic induction to detect flaws in conductive materials. It is used to detect cracks in parallel neck threads of aluminium cylinders. Also called Visual Plus inspection . Required for cylinders of AA6351 alloy.
An Electro-chemical fuel cell which produces a voltage proportional to the partial pressure of oxygen.
Breathing gas supply to a diver that is intended for use in a failure of primary, and where applicable, secondary, breathing gas supply systems. More than one emergency gas supply may be available, of which at least one is usually carried by the diver (scuba).
Tracking transmitters which aid in the detection and location of boats and people in distress at sea.
Emergency procedure where the diver makes an ascent at approximately neutral buoyancy from depth after a breathing gas supply failure.
Depth at which partial pressure of nitrogen in a nitrox mixture at a given depth is equal to the partial pressure of nitrogen in air. Used for approximating the decompression requirements of nitrox mixtures by finding the depth at which air would require the same decompression. Based on exposure to equal partial pressures of nitrogen at maximum depth. [6]
A way of expressing the narcotic effect of a breathing gas mixture at depth by comparison with the depth at which air would have a similar effect. Used to choose nitrogen content of a Trimix breathing gas for a planned dive profile to limit nitrogen narcosis. Based on limiting the partial pressure of nitrogen during the dive by diluting the breathing gas with helium.
International committee of European representatives promoting good standards for diving and co-ordinating, where possible, differing standards with the aim of making European professional diving safer. [4] [47]
In Saturation diving an excursion is a lockout dive in which the diver is exposed to a depth pressure significantly more or less than the saturation storage depth, usually within limits that allow excursion and return to the storage depth without decompression being required before, during, or after the excursion. It can also mean a significant stepwise reduction of pressure at the start of decompression from saturation to a depth pressure which will maximise the utility of the oxygen window of the breathing gas, to reduce the total duration of decompression. This is not allowed by some decompression schedules. [49]
The combined supply and return hoses and cables for life-line, life-support, heating, power and communications between a diving bell and the diver
Ratio between minute ventilation and oxygen uptake, the volume rate of gas breathed to the amount of oxygen taken up in the bloodstream. A typical surface extraction ratio of 20 would mean that for every 20 litres of gas breathed, 1 litre of oxygen would be absorbed in the lungs.
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A methodology used to identify potential failure modes, determine their effects and identify actions to mitigate the potential failures. [20]
An extension to FMEA of a criticality analysis, which combines the probability of failure modes with the severity of their consequences to identify relative risk of each mode, allowing remedial effort to be directed where it is likely to produce the greatest effect. [20]
Cracking in a material resulting from multiple stress cycles below the ultimate or yield strength. Usually refers to large number of cycles.
Technique for emergency breathing from a free-flowing demand valve or leaking first stage where the diver manually controls air flow by opening and closing the cylinder valve. [50]
Unit of pressure equal to 1/33 atm. Not a linear measure of depth. Generally defined as the pressure exerted by a foot depth of seawater having a specific gravity of 1.027 and is approximately equal to 0.445 pounds per square inch. [20]
Feet fresh water. Unit of pressure equal to 1/34 atm. Not a linear measure of depth.
High pressure flexible hose used to connect a cylinder to the storage cylinder, filling panel, booster or compressor, through which high pressure gas flows to fill the cylinder.
Process for removing impurities from a fluid. Particulates are commonly removed by passing the fluid through porous material with pore size small enough to trap the particles (e.g. micron filters). Liquids and gases are commonly absorbed or adsorbed by the surface of the filter medium (e.g. activated carbon, molecular sieve, silica gel), or may be chemically combined with the medium (e.g. Sodalime) or catalytically converted (e.g. Hopcalite) into a less objectionable substance.
Y-shaped elastic rubber straps worn over the arch, the heel and the instep of each foot to help prevent swim-fins from falling off the diver's feet. Mainly used with full-foot-pocket fins.
Diving regulator component which reduces gas pressure from storage pressure in the cylinder to interstage pressure for supply to the second stage and for suit and buoyancy compensator inflation.
A valve in a diving bell which allows air to escape and internal water level to rise. This can be useful to assist the bellman in recovering an incapacitated diver through the bottom hatch. [53] [54]
Synthetic elastomers (rubber) with good performance in high partial pressures of oxygen. Preferred material for o-rings in diving regulators for oxygen service.
finning style where the fins are alternately moved up and down by movements of the full leg. [1] Thrust is developed on both up and down strokes. Vortices shed move both upwards and downwards. See also modified flutter kick .
Condensation of water vapour on the inside surface of a mask or helmet faceplate, reducing visibility.
Water entry technique used by scuba divers from a boat or platform too high or unsuitable for backward roll entry . The diver bends forward at the hips and waist and falls forward into the water, making a partial somersault and breaking the water with the cylinder, back and shoulders. Not suitable for heights more than about 2 m, and can be problematic if the diver is carrying several heavy items like stage cylinders or large cameras.
Air at normal atmospheric pressure.
Underwater diving that does not involve the use of external breathing apparatus, but relies on a diver's ability to hold their breath until resurfacing. See also breath-hold diving , and apnea (q.v.)
A helmet where the breathing air supply is supplied at an adjustable, but approximately constant rate regardless of the diver's instantaneous breathing rate.
Technique for equalising the middle ear by pinching the nose closed and moving the back of the tongue upwards.
Finning technique where thrust is developed by sweeping the fins horizontally toward each other with the fins twisted into a nearly vertical plane, with the soles facing each other, followed by a recovery stroke which develops negligible thrust where the fin blades are feathered. The legs are fairly straight during the power stroke. See also: modified frog kick .
A scuba diver, particularly a military diver on an undercover mission.
Voice communication system where both users can transmit and receive at the same time. Compare with half duplex
Diving mask covering the eyes, nose and mouth, and which provides the diver with breathing gas
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The space between two cave guidelines. Usually between a main guideline and the start tie-off of a branch line.
A relatively short length of cave line on a spool used to bridge a gap between lines when making an excursion from the main guideline to a branch guideline. The line is left in place during the excursion, and usually retrieved on the way out
Textile legging wrapped around the calf and ankle area over a dry suit to restrict the amount of air that can get into the lower leg area. Also can reduce drag of the suit in this area by smoothing over creases and folds.
Mixing breathing gases for diving, filling diving cylinders with gas mixes such as nitrox or trimix.
Blockage of a blood vessel by a bubble of gas.
Technology to display gas pressure in a scuba cylinder on a dive computer, and in some cases make further use of the information for gas management.
The fraction by molecular count, volume or pressure (they all come to the same thing) of a specific gas in a mixture of gases.
The calculation of reserve and turn pressures for divers using different cylinder volumes on the same dive, allowing each diver to ensure that sufficient gas is retained at all times to allow for foreseeable contingencies based on each diver's cylinder volumes, and both divers' individual gas consumption rates. [58]
The control equipment for providing breathing gas to surface supplied divers via umbilicals. Primary and reserve gas is supplied to the panel through shutoff valves from low pressure compressors or high pressure storage cylinders.
The procedure of changing from one breathing gas mixture to another during a dive. This may be done to avoid oxygen toxicity, hypoxia, or nitrogen narcosis, to accelerate decompression, or to avoid running out of breathing gas. Generally applied to open circuit breathing equipment, where a physical change-over of gas source is made. In closed circuit systems the gas composition is continuously controlled to follow the chosen set-point .
Operating mode for a personal dive computer where the decompression calculation is disabled, and the unit operated only as a timer and depth gauge. Typically used when diving with gas mixtures not supported by the algorithm, in which case decompression tables are used to monitor and control the decompression schedule. Some dive computers will automatically switch to gauge mode if the diver violates a depth limit, leaving the diver without decompression information.
Gauge pressure is zero-referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure
Relation between temperature and pressure in an ideal gas for a constant volume.
A method used by freedivers for filling the lungs with more air than maximal inspiration to normal total lung capacity (TLC). After a full inhalation, the diver fills the mouth with air, while the glottis remains closed, then opens the glottis and forces this air into the lung using the cheeks and tongue to reduce the mouth volume. This may be repeated several times. [59]
A satellite navigation system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites
A way of modifying the M-values of a decompression algorithm to more conservative values in proportion to depth. Often used to bias the algorithm towards deeper stops by using a smaller value for the deeper value.
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.
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).
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.
An emergency ascent is an ascent to the surface by a diver in an emergency. More specifically, it refers to any of several procedures for reaching the surface in the event of an out-of-gas emergency, generally while scuba diving.
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 underwater diving starts with freediving as a widespread means of hunting and gathering, both for food and other valuable resources such as pearls and coral. By classical Greek and Roman times commercial applications such as sponge diving and marine salvage were established. Military diving also has a long history, going back at least as far as the Peloponnesian War, with recreational and sporting applications being a recent development. Technological development in ambient pressure diving started with stone weights (skandalopetra) for fast descent. In the 16th and 17th centuries diving bells became functionally useful when a renewable supply of air could be provided to the diver at depth, and progressed to surface-supplied diving helmets—in effect miniature diving bells covering the diver's head and supplied with compressed air by manually operated pumps—which were improved by attaching a waterproof suit to the helmet and in the early 19th century became the standard diving dress.
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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