See the Outline of underwater diving for a hierararchical listing of underwater diving related articles grouped by topical relevance
Surface-supplied divers riding a stage to the underwater workplace
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:
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.
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.
1. The volume of a breathing apparatus which holds exhaled air, which is subsequently inhaled directly. without passing through a scrubber to remove carbon dioxide and without oxygen addition. there can be dead space in both open and closed circuit breathing apparatus
2. The volume of inhaled air, which does not take part in gas exchange either because it remains in the conducting airways or in alveoli that are poorly perfused.[2]
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.
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]
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]
Also: "the bends", "caisson disease", "DCS", or "divers' disease"
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]
decompression status
Theoretical tissue inert gas loading after a given dive history according to the chosen decompression model. It is a measure of whether, and how much, decompression is recommended by the algorithm.
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]
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]
deep-sea diving
deep sea diving
1. A term originally referring to diving with standard diving dress, where the helmet is sealed to the watertight diving suit, as contrasted with a shallow-water diving helmet, which is open at the bottom and was used for work in shallow water where the diver could ditch the helmet and make a free ascent in an emergency. Several incompatible definitions or usages have been published, including diving in the deeper parts of the ocean, but the only technology that can withstand those pressures is specialised submersibles.
1. Diving in special submersibles capable of withstanding the pressures of deeper parts of the ocean. The first dive of Otis Barton and William Beebe in their Bathysphere on June 11, 1930, to below 1400ft off Bermuda has been cited as the first deep-sea dive.[11]
Decompression stops which are deeper than the deepest stops required by decompression algorithms using dissolved phase models.
deep water blackout
1. Freediving: An ambiguous alternative term for blackout of ascent following a deep breath-hold dive, in which loss of consciousness occurs as the surface is approached, or at the surface, caused by cerebral hypoxia arising from the rapid drop in the partial pressure of oxygen in the lungs during ascent as the ambient pressure drops and the gas in the lungs expands to surface volume.[12]
2. Scuba and surface-supplied diving: Loss of consciousness in deep air diving at depths below 50 m with no clear primary cause, associated with nitrogen narcosis, a neurological impairment with anaesthetic effects caused by high partial pressure of nitrogen dissolved in nerve tissue, and possibly acute oxygen toxicity. The term is not in widespread use at present.[13]
A condition where the water content of the body is reduced.
delta P
ΔP
δp
Environments where a pressure difference causes flow. Usually refers to cases where the flow is likely to entrain and pull the diver into an enclosed space or through an opening.
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]
demobilisation
demobilization
Stage of a contract in which the contractor's equipment on site is dismantled, packed up, transported back to the storage area and prepared for storage. Compare with mobilisation.[15]
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]
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]
DIN fitting
Also: "DIN valve", "DIN regulator", "DIN thread"
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]
DIN plug
Screw in plug to seal the outlet of a DIN valve.[24]
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]
Uninterrupted approximately vertical ascent to the water's surface without decompression stops, usually also without a safety stop
display integrated vibratory alarm
Also: "DIVA"
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]
distance line
Also: "penetration line" "cave line", or "guideline"
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]
ditch
Also: shed
Disconnect and drop, unceremoniously or hastily abandon.
ditchable weight
Ballast weight that is carried in a way that it can be released to fall free of the diver to increase buoyancy in an emergency. The classic example is a weightbelt with a quick-release buckle.
(legal) A human activity in which a person enters water or any other liquid, or a chamber in which they are subject to a pressure greater than 100 millibars above atmospheric pressure and, while in such an environment, they breathe air or other gas at a pressure greater than atmospheric pressure.[20][29]
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]
dive flag
Flag used to indicate that there are divers in the water. There are two versions: the international code letter flag 'Alpha', , and the red flag with white diagonal bar, .
A ladder suitable for divers dressed for the specific dive to climb up and down between the surface deployment area and the water.
Dive Leader
EN 14153-3 / ISO 24801-3 standard competence for recreational scuba diver. A level 3 "Dive Leader" has sufficient knowledge, skill and experience to plan, organise and conduct their dives and lead other recreational scuba divers in open water, to conduct any specialised recreational scuba diving activities for which they have received appropriate training, plan and execute emergency procedures appropriate for the diving environment and activities. If diving and environmental conditions are significantly different from those previously experienced, they require an appropriate orientation with regard to local environmental conditions, and must have appropriate specialised training and experience to lead on dives which have more demanding operational parameters.[32]
dive location
(Professional) The vessel, structure, or base from which occupational dives are conducted and supported. More specifically, the point from which the actual dive is controlled.[20]
dive marshall
Recreational and club diving equivalent of a diving supervisor. The person who organizes and plans a group dive outing for recreational divers, assesses risk, logs divers into and out of the water and is available at the site to manage incident response.[33]
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.
dive skins
A lycra suit worn by a diver in warm water or under a wet suit.
dive spread
diving spread
The on-site topside infrastructure for commercial diving, particularly the diving support equipment. The spread may be assembled from modular components, often mounted in intermodal container frames for easy transport, assembly, and secure fixing down on site. [34]
dive station
The site from which a professional diving operation is directly controlled.[20]
An automatically operated electronic timer which records the elapsed time from the start of a dive.
diver deployment system
Equipment and procedures to get professional divers into the water, to the underwater work site, and back.
diver excursion
Movement of a diver away from a reference point, such as the diving bell or stage, the workplace, or the working depth. For example, an excursion by a saturation diver from a closed bell to the underwater workplace may involve an excursion upwards or downwards to a different ambient pressure, or a combat swimmer with an operating depth of 6m may make a short term excursion to a maximum depth of 15m on an oxygen rebreather. [35]
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.
diver transfer chamber
Hyperbaric chamber connecting other component chambers of a saturation life support system which may be at different pressures.[6]
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.[36]
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).
diving
Underwater activity and related recompression facility operations where personnel are subjected to elevated ambient pressure.[20]
diving basket
A diver deployment device similar to a diving stage, normally designed with an open cage.[20]
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.[37]
diving medical technician
Also: "DMT"
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]
diving procedure
Sequence of actions used to achieve a specific outcome during a diving operation. Often standardised, and based on experience of the procedure being safe and efficient. May be specified, recommended, or authorised by a training manual, operations manual or code of practice, and may have to be adapted to suit circumstances, while remaining essentially similar. See Standard operating procedure.
diving project
The overall diving job by a diving contractor under a specific contract or plan, regardless of duration.[20][29]
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.[38]
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.[36]
diving superintendent
Person with overall responsibility for commercial diving operations at a large installation.[40]
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.
diving system
The complete set of equipment necessary to support a diving operation.[4] The equipment and facilities required to execute the planned diving activity, including compression, decompression, rescue and recovery.[20]
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.[41]
dome port
A domed window of optical quality glass or plastic which covers the front of an underwater camera or video housing.
Rescue technique where the donor of breathing gas provides it via the primary second stage – the one from which the donor was breathing – as it is known to be working and providing the correct gas. The donor then switches to their backup DV, often stowed under the chin by a bungee necklace with a breakaway connection.
donating the secondary
Rescue technique where the donor of breathing gas provides it via the secondary, or octopus, second stage, and continues to breathe off the primary.
donkey dick
Slang term for the corrugated buoyancy compensator inflation and deflation hose.[1]
Ultrasonic signals reflected from bubble surfaces to identify and quantify gas bubbles present in venous blood.
Dorf arrow
Also: "line arrow"
Triangular plastic line marker with two slots which is mounted on a cave guide line to indicate the direction of the exit.[1]
downline
down line
A rope leading from the surface down to the underwater workplace which allows a commercial diver to travel directly to and from the job site and to control rate of descent and ascent in the same way as using a shotline. Also sometimes called a jackstay.[42] A downline used for open ocean diving is much the same as a shotline (q.v.), but does not reach all the way to the bottom. An open-ocean downline is weighted at the bottom, and attached to a substantial float at the surface, which may be tethered to the boat. It may be marked at intervals by knots or loops, and may be attached to decompression trapeze system. In some cases a sea anchor may be used to limit wind drift, particularly if attached to a boat with significant windage.[43]
downstream
In the direction of flow. Displaced from the reference point in the direction of flow
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
down time
Period when planned activities can not be done due to unforeseen or uncontrollable circumstances.[40]
DP alert
Status of the dynamic positioning system regarding positional accuracy and reliability. Green indicates normal operation, yellow indicates degraded operation and red indicates emergency.[40]
DP footprint
Dynamic positioning footprint: The area around the nominal position to which a dynamically positioned vessel is constrained by the DP system.[40]
A ring shaped like a capital D, usually of stainless steel or plastic, stitched or buckled to a diver's harness and used as an attachment point for lifeline, cylinders or other equipment.[41]
Dräger tube
Draeger tube
Indicator tube used for testing breathing gas quality.
Weight used during descent and ascent, but left on the bottom at the guideline during the deep part of the dive when it is not needed due to suit compression.[1]
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.
Also: "delayed surface marker buoy" and "decompression buoy"
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. Also known as a spear valve or flutter valve, this automatic device serves as a gas exhaust valve on the inside of some twin-hose diving regulators and as an excess gas release valve on the outside of certain mid-twentieth-century dry suits.
dump line
A rope attached to the dump valve on a lift bag which is used by a diver to operate the dump valve to release air for control and adjustment of the bag buoyancy.[20]
dump valve
Valve used to release excess gas from a dry suit, buoyancy compensator, rebreather, or lift bag. Usually manually operated in buoyancy compensators and lift bags, and automatic in dry suits and rebreathers. May also function as an overpressure valve.[1]
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.[45]
Method of keeping a floating platform in position without anchoring, using thrusters and positional feedback.
dynamic setpoint
Also: "floating setpoint"
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]
A home made mixture of alcohol and acetic acid in water used as a drying agent and disinfectant to rinse the ears after diving, to prevent ear infections.
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.
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).
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.
eSCR
Electronic semi-closed circuit rebreather, where an electronic control system monitors the partial pressure of oxygen and adds gas to maintain a floating setpoint to optimise gas use and compensate for variations in diver exertion.[21]
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][48]
exceptional exposure
A dive in which the risk of decompression sickness, oxygen toxicity, and/or exposure to the elements is substantially greater than on a normal working dive.[49]
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.[50]
excursion dive
Saturation diving where the divers work at a depth deeper or shallower than the saturation depth, after which they are returned to the original saturation pressure.[4]
excursion tables
Tables for use in saturation diving that specify the limit upward and downward of excursions from the nominal depth, and provide a zone in which the diver can move freely without regard to the number of excursions or their duration without incurring a decompression penalty.[20]
The combined supply and return hoses and cables for life-line, life-support, heating, power and communications between a diving bell and the diver
exhaust valve
A valve controlling the venting of gas from any higher pressure source such as a diving chamber, diver’s helmet, dry suit, buoyancy system, volume tank, lift bag etc. For some of these applications, also known as a dump valve.[20]
extraction ratio
Also: "ventilation/oxygen extraction ratio"
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.
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]
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.[51]
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]
Ratio of the mass of gas in a cylinder to the internal volume of the cylinder (water capacity), usually expressed in kilograms per litre, or pounds per cubic foot.[52]
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.
fin keepers
fin retainers
Also: "fin holders", "fin fasteners", "fin grips", "fin keeps", "fin guards", "flipper fixers", "Y-straps", "ankle straps", "accessory safety straps", "fix fins", "grip fins" and, in recognition of their French origin, "fixe-palmes".
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.
fin strike
Fin impact
Impact of a swimfin on the solid environment, usually unintentional, sometimes causing environmental damage
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.
five nines
five nines purity
99.999% pure gas. Usually referring to breathing grade oxygen or helium for blending.[1]
fixed diving system
A diving system (q.v.) installed permanently on a vessel or structure.[20]
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.[54][55]
flow
Movement of water through a cave or ducting system. Similar in meaning to current in open water.[1]
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.
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.
four-wire system
Voice communications using separate wire pairs for each direction.
frame
Transportable assemblies of gas cylinders connected by a manifold and securely mounted to a structural framework.[40] See also quad and kelly.
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.
free-flow valve
Valve on the side of a demand helmet or full-face mask which opens a continuous flow of breathing gas into the helmet interior, usually directed over the interior of the viewport, hence alternative term defogging valve, as it is often used to blow condensation from the inside of the viewport.
free gas
Gas at normal atmospheric pressure. Usually refers to the volume of some amount of compressed gas when allowed to expand to atmospheric pressure at constant temperature
free gas volume
Equivalent volume of a compressed gas if expanded to standard atmospheric pressure at constant temperature.[57]
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.
Diving mask with one or more shut-off valve fitted breathing tubes, covering the eyes, nose and mouth and supplying the user with atmospheric air while face down on, or slightly below, the surface of the water
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
gaiter
Also: "gator" (US)
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.
gas blender
1. Person who mixes breathing gases for diving, filling diving cylinders with gas mixes such as nitrox or trimix.
2. Certification of competence to mix breathing gases for diving.[58]
Carbon dioxide scrubber used to allow partial recirculation of surface-supplied or scuba breathing gas to reduce waste. A form of semi-closed circuit rebreather.
gaseous impurities
Contaminants in the compressed breathing air or gas mixture which are in gaseous form. Compare with particulate and condensate impurities.
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.[59]
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.
gas reversal point
The depth during an ascent or decompression when the intake of dissolved gas is exceeded by outgassing.
gas sensor
A component that produces a signal in the presence of a specific gas, often in proportion to the concentration of the gas.
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.
gas switching block
A valve set used for switching from one breathing gas to another during a dive. The most common application is a bailout block, but also used to switch gases for decompression on a full face mask, and to switch between deep and shallow gases on a semi-closed rebreather.
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.
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.[60]
glowstick
A single-use, translucent plastic tube containing isolated substances that, when combined, make light through chemiluminescence
gnarly
A general purpose adjective to denote a particularly difficult section of a cave, which may be low, tight, silty, etc. or a combination.[1]
Incur a decompression obligation. Generally refers to having a theoretical tissue inert gas concentration that requires the diver to make staged decompression stops during ascent to avoid an unacceptable risk of symptomatic decompression sickness according to the decompression model, algorithm, tables or dive computer in use.
golden rule
The convention in cave diving that anyone can turn the dive at any time for any reason.[1]
gold line
The permanent main guideline in a cave system, that usually starts well inside the cave. Often yellow or gold in colour.[1]
Goodman handle
A handle used to carry the primary dive light head comprising a rigid slot through which the fingers and palm of the hand are extended, so that the light rests on the back of the hand, facing the direction of the extended fingers.
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.
^Intagliata, S.; Rizzo, A; Gossman, W. (5 July 2022). "Physiology, Lung Dead Space". StatPearls [Internet]. Treasure Island, FL: StatPearls Publishing. PMID29494107. Retrieved 8 July 2023.
^Eliott, David (September 1996). "Deep water blackout"(PDF). SPUMS Journal. 26 (3): 205–208. Archived from the original on 26 September 2012. Retrieved 31 July 2019.{{cite journal}}: CS1 maint: unfit URL (link)
^ abHarlow, Vance (1999). Scuba regulator maintenance and repair. Warner, New Hampshire: Airspeed Press. ISBN0-9678873-0-5.
^South African National Standard SANS 10019:2008 Transportable containers for compressed, dissolved and liquefied gases - Basic design, manufacture, use and maintenance (6th ed.). Pretoria, South Africa: Standards South Africa. 2008. ISBN978-0-626-19228-0.
^ abc"Diving Regulations 2009". Occupational Health and Safety Act 85 of 1993 – Regulations and Notices – Government Notice R41. Pretoria: Government Printer. Archived from the original on 4 November 2016. Retrieved 3 November 2016 – via Southern African Legal Information Institute.
^Lang, M.A.; Hamilton, Jr, R.W. (1989). Proceedings of the AAUS Dive Computer Workshop. United States: USC Catalina Marine Science Center. p. 231. Archived from the original on 7 July 2012. Retrieved 14 December 2011.{{cite book}}: CS1 maint: unfit URL (link)
^SDI Solo Instructor guide (v1.3 ed.). Scuba Diving International.
^ abcDepartment of Labour (11 January 2002). Diving regulations 2001. Government Gazette, Republic of South Africa, Regulation Gazette No. 7243. Vol. 438. Pretoria: Government Printer. {{cite book}}: |work= ignored (help)
^"Homepage". www.dmac-diving.org/. Diving Medical Advisory Council. Retrieved 19 October 2017.
^Lindholm, Peter; Lundgren, Claes E.G. (1 January 2009). "The physiology and pathophysiology of human breath-hold diving". Journal of Applied Physiology. 106 (1): 284–292. doi:10.1152/japplphysiol.90991.2008. PMID18974367.
^Barsky, Steven M.; Christensen, Robert W. (2004). The Simple Guide to Commercial Diving (Illustrated ed.). Hammerhead Press. p. 92. ISBN9780967430546.
^James W. Miller, ed. (1979). "12.6 Decompression after an air or nitrogen-oxygen saturation dive". NOAA Diving Manual (2nd ed.). United States Department of Commerce.
^NOAA Diving Program (U.S.) (28 February 2001). "8.5". In Joiner, James T. (ed.). NOAA Diving Manual, Diving for Science and Technology (4th ed.). Silver Spring, Maryland: National Oceanic and Atmospheric Administration, Office of Oceanic and Atmospheric Research, National Undersea Research Program. ISBN978-0-941332-70-5. CD-ROM prepared and distributed by the National Technical Information Service (NTIS) in partnership with NOAA and Best Publishing Company
^"Valve Feather". www.youtube.com. SDI TDI ERDI PFI FRTI. Retrieved 19 March 2024.
^SANS 10019:2019 South African National Standard: Transportable pressure receptacles for compressed, dissolved and liquefied gases — Basic design, manufacture, use and maintenance (8th ed.). Pretoria: South African Bureau of Standards. 2019. ISBN978-0-626-37092-3.
^ abEdmonds, C.; McInnes, Sophie; Bennett, Michael (2005). "Reverse dive profiles: The making of a myth". South Pacific Underwater Medicine Society Journal. 35: 139–143.
^Potkin, Ralph; Cheng, Victor; Siege, Robert (1 September 2007). "Effects of glossopharyngeal insufflation on cardiac function: an echocardiographic study in elite breath-hold divers". Journal of Applied Physiology. 103 (3): 823–827. CiteSeerX10.1.1.550.5487. doi:10.1152/japplphysiol.00125.2007. PMID17556497.
