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.
Contents
see adjustable buoyancy life jacket
Total static pressure at the reference point: Pressure relative to vacuum.
see yoke fitting/valve.
see yoke adaptor
see also Rebreather#Active addition semi-closed circuit
System for semi-closed circuit rebreather feed gas addition in which gas is added to the breathing circuit by a mechanism, regardless of current volume, and excess gas is vented to keep the loop volume within limits. Compare with passive addition
A filter medium used to remove oil, water and odours from breathing air.
Also known as ABLJ or horse collar buoyancy compensator
A combination of buoyancy compensator and inflatable life jacket worn on the chest and round the neck.
Part of Launch and Recovery System
Gantry or davit for launching and recovering bells, stages anchors or large ROVs. Usually deployed by hydraulic rams which swing the frame over the deck or overboard as required. The load is hoisted and lowered by cables from the top of the frame.
see arterial gas embolism
A device based on a pipe, used in by divers to suck small objects, sand and mud from the sea bed and to transport the resulting debris upwards and away from its source. Air is injected into the lower end of the pipe and the rising bubbles entrain water and cause an upward flow which draws the material from the bottom along.
A rapid increase or accumulation in the population of algae (typically microscopic) in an aquatic system. Some blooms may be recognized by discoloration of the water resulting from the high density of pigmented cells. Visibility can be severely impaired over a period of hours to days.
A secondary supply of air or other breathing gas used by the diver in an emergency
Dizziness caused by a difference of pressure between the middle ears.
Diving at a location where the water surface is at an altitude which requires modification of decompression schedules. (more than about 300 m (980 ft) above sea level.
Pressure of the surroundings.
Completely lacking in oxygen.
An impairment of language ability which may range from having difficulty remembering words to being completely unable to speak, read, or write
Decompression model in which the filtering capacity of the lung is assumed to have a threshold radius of the size of a red blood cell and sufficiently small decompression bubbles can pass to the arterial side, especially during the initial phase of ascent.
Blockage of an artery by a gas bubble. A possible consequence of lung overpressure injury.
The rate at which depth is reduced at the end of a dive. An important component of decompression.
Also ata or atmospheres absolute
Unit of absolute pressure equivalent to standard atmospheric pressure.
Also ADS
A small one-man articulated submersible of anthropomorphic form which resembles a suit of armour, with elaborate pressure joints to allow articulation while maintaining an internal pressure of one atmosphere.
see combat swimmer
A plate, normally made from metal, which rests against the diver’s back, and to which the primary scuba cylinders are attached. Held to the body by harness straps over the shoulders and round the waist. Sometimes also crotch straps and chest straps. Usually used with a back inflation buoyancy compensator.
also secondary, safe second or octopus
A second regulator connected to a cylinder or manifolded twin set.
also back roll entry
Water entry method in which the seated diver rolls backwards off the side of the boat, allowing the scuba cylinders to strike the water first.
see also gas block, or gas switching block
A gas switching block specifically intended for connection of a bailout set to the main gas supply (which may be scuba or surface supply) which allows the diver to switch from main gas supply to emergency gas supply while continuously using the same mouthpiece, regulator second stage, full face mask or helmet. A bailout block is generally used on open circuit breathing apparatus, the equivalent function on a rebreather is provided by a bailout valve (BOV). The bailout block may be mounted on the side of a diving helmet or full-face mask, or may be mounted in a convenient place on the diver's harness, and includes a bailout valve, used to select the gas source, and one or more non-return valves to ensure that the emergency gas supply is directed only to the diver.
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.
An independent breathing gas supply carried by a diver for use in case of failure of the main gas supply. Usually consists of a bailout cylinder with a first stage regulator, and either a second stage regulator or connected to a bailout block or bailout valve (q.v.) A submersible pressure gauge is also usually provided.
A heavy duty full-face mask with many of the characteristics of a lightweight demand helmet. In structure it is the front section of a lightweight helmet from above the faceplate to below the demand valve and exhaust ports, including the bailout block and communications connections on the sides. This rigid frame is attached to a neoprene hood by a metal clamping band, hence the name.
see cylinder bands
see also bar (unit)
Metric unit of pressure commonly used in diving, equal to 100 kiloPascal, and nearly equal to standard atmospheric pressure.
Tooth pain caused by pressure difference.
Injury caused by pressure difference.
see diving stage
see buoyancy compensator
see also dive marshal
A person on the beach who records when divers enter and exit the water. Typically used during recreational scuba training to keep track of the students, watch the gear, and provide assistance when required.
The combined supply and return hoses and cables for life-support, power and communications between a diving bell and the support platform
also belt slider, triglide, weight stop, weight slider
Hardware item with two parallel slots which is fitted to harness or weightbelt webbing to prevent other components such as D-rings and weights from sliding along the webbing.
also B.K. hook or BK safety hook
A type of safety lifting hook which is held closed when under load by a lever system where the weight of the load holds the bill of the hook against the safety latch.
Uncontrolled release of crude oil and/or natural gas from a well after pressure control systems have failed.
also BOP
A large, specialized valve used to seal, control and monitor oil and gas wells. Generally operated remotely by hydraulic ram.
A sink hole in a lake or the sea that is often the entrance to a cave. Blue holes in the sea are subject to tides so that their flows regularly reverse.
also piston bolt
A metal connecter comprising a hook with a spring-loaded axial sliding rod which must be manually retracted to allow the hook to be clipped onto something or removed. May be single- or double-ended, and if single-ended is usually fitted with a swivel ring opposite the jaws.
see bungee wing
Derogatory term for bungee wing based on fetishist terminology.
also booster pump
see also compressor
Machine used to increase pressure of a gas. Usually refers to the case where inlet pressure is above ambient pressure already.
see bailout valve
Knot used to form a secure, non-slipping loop at the end of a line.
Relationship between pressure and volume at constant temperature in an ideal gas.
Gas supplied to the diver to breathe, either directly to the diver or to the hyperbaric environment of the diving bell, dive chamber or saturation habitat.
Béance tubaire volontaire: Voluntary opening of the Eustachian tubes to equalise the middle ear.
Decompression models based on the assumption that bubbles will form during non-symptomatic decompression.
see glossopharangeal insufflation
A procedure carried out by scuba divers using the buddy system where each diver checks that the other's diving equipment is configured, fitted, and functioning correctly just before entering the water to dive.
A safety procedure where two or three divers monitor each other constantly during a dive and provide assistance or rescue when needed.
A procedure where two divers look out for the safety of each other, and give assistance if the other gets into difficulty.
Diving tables and decompression algorithm on which the tables are based, and some dive computers are programmed, based on the dissolved gas decompression model derived and tested by Dr A.A. Bühlmann.
see also ring bungee
Length of shock cord used to restrain the top end of side mount cylinders and keep them tucked in at the diver's shoulder while swimming. Usually clipped to the shoulder D-ring(s) of the harness and looped around the cylinder valve. May be attached to the back of the harness between the shoulder blades, or run continuous from one shoulder D-ring, around the back under the arms to the other shoulder D-ring.
also BC, BCD, buoyancy compensator device, ABLJ, horse collar, stabilisor jacket, stab jacket or wing
An airtight bladder worn by a diver which can be filled with air and vented to adjust and control the buoyancy of the diver.
A non-reclosing pressure relief device used to protect a diving cylinder from overpressurization.
Scuba diving from canoes, used when the dive site is beyond convenient swimming distances.
The toxic effects of carbon dioxide, due to incomplete elimination of carbon dioxide resulting from skip breathing, excessive work of breathing, scrubber failure in a rebreather system, or inadequate ventilation in a diving chamber or free flow helmet. Occasionally caused by contaminated gas supply.
The toxic effects of carbon monoxide, usually due to contaminated breathing gas supply.
An emergency procedure which is performed in an effort to manually preserve intact brain function until further measures are taken to restore spontaneous blood circulation and breathing in a person in cardiac arrest
see also critical pressure
Critical Air Supply, the amount of breathing air required to safely exit a penetration dive. When the air supply reaches this level the dive has reached a planned turning point.
Decanting from several storage cylinders in succession, generally using a procedure to maximise charge pressures. Often used in partial pressure gas blending.
Directional line markers which point the way to an exit.
A reel specifically made for cave diving, used to lay and recover large lengths of cave line which is used as a guide line to find the exit or a permanent guide line.
A sinkhole in Mexico. Generally with vertical overhanging walls or shafts with water that open into a cave system.
Relation of volume to temperature at constant pressure of an ideal gas.
A strap around the neck of a sidemount cylinder used to hold the bolt snap closer to the neck so that the head of the cylinder stays closer to the diver's armpit. The choker can be a small webbing strap with a sliding buckle for adjustment, so it can be tightened to bring the clip closer to the neck or slacked off while in use.
A symptom of decompression sickness manifested by shortness of breath, caused by a large number of venous gas bubbles in the lung capillaries which interfere with gas exchange.
also tree
An assembly of valves, spools, and fittings installed on top of the wellhead and used primarily to control the flow, usually oil or gas, out of the well.
see inshore diving
also dry bell
A closed or dry bell is a pressure vessel for human occupation which is lowered into the sea to the workplace, equalised in pressure to the environment, and opened to allow the divers in and out. Divers may be decompressed in the bell or transferred under pressure to a hyperbaric chamber at the surface.
Working under pressure: Occupational activity where gas is breathed at pressure in excess of atmospheric pressure, usually underwater.
Person trained in scuba diving or swimming underwater in a military capacity which can include combat
The process of making a well ready for production.
Pain in the joints caused by exposure to high ambient pressure at a relatively high rate of compression
Machine which pressurises gas. Generally intake gas is at ambient pressure, outlet gas at higher pressure. High pressure breathing air compressor output pressure is usually 200 to 330 bar.
Liquid resulting from phase change from gas due to cooling or pressure change.
also isobaric blackout
A Freediving blackout which occurs while the diver maintains a near constant shallow depth, where reduction of oxygen partial pressure due to ascent is not a factor. Usually induced by pre-dive hyperventilation. Also referred to as shallow water blackout, which is an ambiguous term
see restriction
see submersible pressure gauge
Decompression without stops. Instead of a fairly rapid ascent rate to the first stop, followed by a period at static depth during the stop, the ascent is slower, but without officially stopping. Ascent rate may vary with depth, usually slowing as the depth reduces.
A rescue technique used by scuba divers to raise an incapacitated diver to the surface from depth.
also CESA
An emergency technique for surfacing, usually when no breathable gas is available at depth. The diver fins upward while gently exhaling to keep expanding air in the lungs from causing lung expansion injuries.
Personal non-directional line markers that mark specific locations, or the direction of one's own exit at line intersections.
A diving helmet of traditional design and construction, usually made from spun or beaten copper, with brass or bronze fittings. There are usually two main sub-assemblies; the bonnet is the roughly spherical part which covers the head and is provided with viewports, valves and various other fittings, and the corselet, which rests on the upper torso of the diver, and to which the bonnet is connected when in use, and which may be sealed to the suit and ballasted to compensate for the buoyancy of the airspace inside the helmet.
Breastplate part of a copper helmet and some other heavy helmets, which clamps to the diving suit, and to which the helmet bonnet is clamped, screwed or bolted.
Flexible bag or bellows in a rebreather which compensates for the change in volume in the loop during breathing.
see cardio-pulmonary resuscitation
see CAS
Hypothesis that bubble formation during decompression will not occur if a critical pressure difference between tissue gas tension and inspired gas partial pressure is not exceeded.
Cylinder gas pressure which determines a safe limit to an underwater activity on scuba, such as start of ascent or turnaround during a penetration.
Hypothesis that bubble formation during decompression will not occur if a critical ratio of tissue gas tension and inspired gas partial pressure for a given gas is not exceeded.
Hypothesis that symptoms of decompression sickness will not be evident if a critical volume of tissue gas bubbles is not exceeded.
Trademark name Cyalume is a solid ester whose oxidation products are responsible for the chemiluminescence in a glowstick.
The appearance of a blue or purple coloration of the skin or mucous membranes due to the tissues near the skin surface being low on oxygen
Rubber or plastic cover for the base of a scuba cylinder to protect it from abrasion, and in the case of domed end cylinders, to allow it to stand upright.
Valve fitted to a compressed gas cylinder to control gas flow into and out of the cylinder. Also pillar valve.
see Divers Alert Network
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.
To transfer gas between cylinders by differential pressure. No energy is input, flow will stop when 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.
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.
see DSMB
Hyperbaric chamber used for decompressing divers and emergency therapeutic recompression.
Gas breathed during decompression with a composition designed to accelerate decompression, usually by an increased oxygen content.
Illness caused by decompression. Includes decompression sickness and arterial gas embolism due to lung overexpansion barotrauma.
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.
also DCS, divers' disease, the bends or caisson 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.
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.
Printed cards or booklets that allow divers to determine a decompression schedule for a particular dive profile and breathing gas.
also decompression bar
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.
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.
Mechanism for providing the user with breathing gas flow only when required.
Diamond Reef System is 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.
Decompression hypothesis that the uptake and elimination of inert gas is limited by diffusion rates in the tissues
also sometimes dil
Gas mixture used to dilute the oxygen in the loop of a closed circuit rebreather to a partial pressure suited to the depth.
also DIN valve, DIN regulator, DIN thread
Usually refers to G5/8" x 14 tpi 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.
Screw in adaptor which can be used with many recent 200/240 bar DIN cylinder valves to allow connection of Yoke regulators or filling whips.
also Doing It Right
A holistic approach to scuba diving, which encompasses several essential elements, including fundamental diving skills, teamwork, physical fitness, and the use of streamlined and minimalistic equipment configurations.
also penetration 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.
also decompression computer
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.
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 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.
see decompression tables
also DAN
A non-profit organization for assisting divers in need and medical research on recreational scuba diving safety.
also dive tender
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 underwater.
A rigid chamber suspended from a cable and used to transport divers to depth and back to the surface.
see also overweighting
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 cintact 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.
see regulator
The person who administers a United States university's research diving safety program.
Hand sign and light sign system used by scuba divers to communicate when underwater.
also known as the basket
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 him out of the water.
Person in charge of, and responsible for safety of a commercial diving operation.
Ultrasonic signals reflected from bubble surfaces to identify and quantify gas bubbles present in venous blood.
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.
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.
see closed bell
Filling scuba cylinders without the use of a water bath for cooling.
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
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
Method of keeping a diving support platform in position without anchoring, using thrusters and positional feedback.
Medical conditions resulting from changes in ambient pressure.
Equivalent Air Depth. 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 in decompression calculations.
Equalising the pressure in the middle and external ear by opening the Eustachian tubes. Several techniques are used.
also Thalmann algorithm, (VVAL18)
Exponential-Linear algorithm of 2008 US Navy tables, assumes exponential ingassing and a combination of linear and exponential outgassing rates.
also emergency beacons or EPIRB,
Emergency position-indicating radio beacons are tracking transmitters which aid in the detection and location of boats and people in distress at sea.
also ESA, Controlled emergency swimming ascent, CESA
Emergency procedure where the diver makes an ascent from depth after a breathing gas supply failure.
see emergency position indicating radio beacon
also EAD
A way of approximating the decompression requirements of nitrox mixtures at depth by comparison with the depth at which air would require the same decopression.
also END
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.
The combined supply and return hoses and cables for life-line, life-support, power and communications between a diving bell and the diver
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.
Cracking in a material resulting from multiple stress cycles below the ultimate or yield strength. Usually refers to large number of cycles.
see full-face mask
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 (Activated carbon, Molecular sieve, Silica gel), or may be chemically combined with the medium (Sodalime) or catalytically converted (Hopcalite) into a less objectionable substance.
see Diving regulator#First stage
Diving regulator component which reduces gas pressure from stoage pressure in the cylinder to interstage pressure for supply to the second stage and for suit and BC inflation.
Condensation of water vapour on the inside surface of a mask or helmet faceplate, reducing visibility.
see also free gas
Underwater diving that does not involve the use of external breathing apparatus, but relies on a diver's ability to hold his or her breath until resurfacing. also Breath-hold diving, and apnea (q.v.).
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.
Mixing breathing gases for diving, filling diving cylinders with gas mixes such as nitrox or trimix.
Blockage of blood vessel by a bubble of gas.
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 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 a low pressure compressor or high pressure storage cylinders.
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.
also buccal pumping, lung packing
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.
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-value of a decompression algorithm to a more conservative value. Often used to bias the algorithm towards deeper stops.
see distance line
also Haldanean
Decompression models based on the principles described by John Scott Haldane.
Voice communications system where users take turns to send and receive.
see tissue half times
A strong variation in salinity over a small depth range within a body of water. Often visible as a blurred or shimmering region due to uneven refractive index.
see standard diving dress
Mixtures of helium and oxygen for use as a breathing gas.
Trimix blends made by topping up helium with air.
An inert gas which is used as a component of breathing gas mixtures for deep diving.
An instrument used to identify the presence and concentration of helium in a mixture of gases
see hard hat diving
also hooka and airline diving
Also known as airline diving; surface supplied diving where the breathing air is supplied to the diver by a simple hose. The diver usually breathes through a mouth held demand valve.
also recovery breathing
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.
Catalyst sometimes used in air filters to oxidise carbon monoxide to carbon dioxide. Hopcalite is a mixture of manganese oxide, copper oxide and a small amount of silver oxide.
see adjustable buoyancy lifejacket
An insulated pipe in the umbilical line, which links the diver to the surface support, carries the hot water from a heater on the surface down to the suit. The diver controls the flow rate of the water allowing him to vary the warmth of the suit.
High-pressure nervous syndrome: A neurological and physiological diving disorder that results when a diver descends below about 500 feet (150 m) while breathing a helium–oxygen mixture.
Cylinder valve body with two outlets and two valve mechanisms which can be independently controlled so that two regulator first stages can be fitted. Similar to Y-valve but in configuration where the second valve is parallel to the primary, though the secondary valve can sometimes be swivelled.
Pressure due to the weight of the water column above a point at depth.
Non-destructive test to revalidate pressure vessels which uses water as a test medium. The vessel is pressurised to the test pressure (q.v.) and measured for permanent set.
Deep diving breathing gas mixture of hydrogen, helium and oxygen.
Deep diving breathing gas mixture of hydrogen and oxygen.
Excessive level of carbon dioxide in the body.
Abnormally low tissue and blood carbon dioxide concentration.
Abnormally low tissue oxygen concentration: Insufficient oxygen in the body to support normal activities or consciousness.
A gas which is not metabolically active, used to dilute the breathing gas.
Inert gas uptake in body tissues during a dive or other hyperbaric exposure.
Metabolic reduction of total gas pressure in the tissues.
A type of mobile platform that consists of a buoyant hull fitted with a number of movable legs, capable of raising its hull over the surface of sea. The buoyant hull enables transportation of the unit and all attached machinery to a desired location. Once on location the hull is raised to the required elevation above the sea surface on its legs supported by the sea bed.
see upline
A type of pipe and hose fitting with a 37-degree flare seating surface. Commonly used in umbilical hose connections.
An atmospheric diving suit manufactured by Underwater Marine Equipment Limited.
A short line used to connect to a shotline or anchor line, allowing the diver to move a short horizontal distance away to decompress. The line helps compensate for vertical movement in the anchor line or shot line due to waves.
A procedure to integrate health and safety principles and practices into a particular task or job. Each basic step of the job analysed to identify potential hazards and controls for each hazard.
A short cave line used to connect between two permanent lines that are not in contact. May also be used to search for the other end of a break in a cave line and repair the break
Scuba cylinder valve with lever operated reserve mechanism.
Diving from a special purpose kayak used to get to the site where the distance from a suitable entry and exit point is inconvenient for shore diving.
Scuba cylinder valve without reserve mechanism.
A piece of cordage used to secure or lower things, usually it is used where there is a risk of losing the object
An uncontrolled/involuntary muscular contraction (spasm) of the laryngeal cords which causes a partial blocking of breathing in, while breathing out remains easier.
also pipelay barge
Barge on which pipeline sections are assembled, welded and laid on the seabed as the barge is moved forward.
Shot line (q.v.) which does not reach the bottom
see LST
A robust and air-tight bag with straps, which is used to lift heavy objects underwater by means of the bag's buoyancy.
Low volume, close fitting diving helmet, usually with demand valve. Neutrally buoyant, and moves with the diver's head.
A lung inflammation (pneumonia) that develops when lipids enter the bronchial tree
A large boat which provides transport, accommodation and services for vacationing divers
Mass transport of water along a shoreline, generally due to wave action at an angle to the shoreline.
also breathing loop
The circuit in a rebreather through which the breathing gas passes during a breathing cycle.
see glossopharangeal insufflation
also diving response
A reflex response to breathhold and chilling of the face diving response expressed by the cardiovascular system, which exhibits hypertension, bradycardia, oxygen conservation, arrhythmias, and contraction of the spleen.
see twin cylinder manifold
also manufacturing code
Set of design and manufacturing rules intended to produce uniform and safe products by several manufacturers in an industry.
A type of swimfin typically used in finswimming and free-diving. It consists of a single surface attached to footpockets for both of the diver's feet.
Material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids. Molecules small enough to pass through the pores are absorbed while larger molecules are not. It is different from a common filter in that it operates on a molecular level.
The use of sidemount configuration and procedures with a single cylinder.
An opening in the floor or base of the hull, platform, or chamber giving access to the water below.
Compressor in which gases are compressed more than once, often with cooling between stages. Used to improve efficiency and reduce temperatures.
At a given ambient pressure, the M-value is the maximum theoretical value of absolute inert gas pressure that a tissue compartment can take without presenting symptoms of decompression sickness.
see nitrogen narcosis
A US Navy trained combat diver.
No decompression limit. The maximum time which a diver can remain at a specified depth without incurring a stage decompression obligation in terms of the specified decompression tables or algorithm.
also just negative in context
Buoyancy less than weight. Insufficient upward force due to buoyancy to keep afloat or remain at constant depth
Entry into the water after reducing buoyancy of BC and, if applicable, dry suit by venting to ensure that the diver will not float back to the surface, but will continue to descend
also neo-Haldanean
Decompression models based on later modifications of the principles described by John Scott Haldane.
Synthetic elastomer used in the form of foamed sheets as the material for most wetsuits and some drysuits.
Having a fully immersed buoyancy exactly equal to weight, so that the forces are balanced and the person or object statically remains at a constant depth. Effectively average density is equal to that of the surrounding fluid medium. The state of neutral buoyancy is typically metastable for a compressible system.
An atmospheric diving suit designed and originally built by Phil Nuytten.
Minor symptoms characteristic of mild decompression sickness.
Diving during the hours of darkness.
A synthetic elastomer used for most standard O-ring seals.
The major component gas of air and many breathing gas mixtures used in diving. Important in diving as an active agent in nitrogen narcosis and decompression sickness.
Also known as narcs, inert gas narcosis, raptures of the deep, Martini effect: A reversible alteration in consciousness that occurs while breathing gases containing nitrogen under elevated partial pressure similar to alcohol intoxication or nitrous oxide inhalation, and can occur during shallow dives, but usually does not become noticeable until greater depths, beyond 30 meters.
also Enriched Air Nitrox (EAN)
Mixture of nitrogen and oxygen for use as breathing gas. Usually with oxygen percentage higher than air.
A mixing tube used to blend oxygen with air before compressing to make nitrox breathing gas.
A specialized overhead-environment strategy for dealing with particularly tight restrictions which may involve divers wearing a very basic harness or simply hand-carrying cylinders.
An oscillation of the eyes alternating a slow eye movement in one direction, and a fast eye movement in the other direction
also octo reg
A secondary demand valve fitted to a first stage diving regulator for use as an alternative air source for another diver in case of an emergency.
see outgassing
see ingassing
A mechanical gasket in the shape of a torus; a loop of elastomer with a circular cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the contact surfaces.
Diffusion of gas out of the tissue into the blood, and transport to the lungs where it diffuses into the lung gas and is eliminated by exhalation.
see also diving heavy
Carrying more weight than is necessary to achieve neutral buoyancy at all times in a dive.
Important component gas of atmospheric air and essential component of any breathing gas. Required to sustain life.
Instrument for measuring the partial pressure of oxygen in a gas mixture
A notional alarm clock, which accumulates hyperbaric oxygen exposure at a rate which increases with higher ppO2 toward the maximum single exposure limit recommended
Fraction by volume or pressure of the gas mixture made up by oxygen
A condition resulting from the harmful effects of breathing molecular oxygen (O2) at elevated partial pressures.
Inherent unsaturation due to metabolic reduction of total gas pressure in the tissues.
A 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 animalistic 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.
see also Rebreather#Passive addition semi-closed circuit
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
Entering a region with no direct vertical access to the surface, such as a cave or the interior of a wreck.
see distance line
The process of delivery of blood to a capillary bed in the biological tissue.
The assumption in a decompression model that perfusion has the dominant influence on gas uptake and release.
also PLB
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.
see also jump camera
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.
Pipeline inspection gauge: A tool that is sent through a pipeline and propelled by the pressure of the product in the pipeline itself.
see cylinder valve
Standard connection type for portable medical oxygen cylinder valves and regulators.
see personal locator beacon
also pneumo
Instrument to measure depth of a diver using a gauge calibrated in msw, fsw, or often both, to measure the ambient pressure at the diver by measuring the pressure in a hose filled with air with an open end at the diver.
Air or other breathing gas in the chest cavity, often resulting in a collapsed lung.
Relatively small scuba set carried as an independent alternative breathing gas source by a scuba diver.
Diving which is done as part of the diver's employment or professional occupation.
Pulmonary barotrauma of ascent. Lung over-pressure injury.
see pendulum rebreather
also Pee-valve
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.
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.
see also photo quadrat
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.
see nitrogen narcosis
also ratio deco
A technique for calculating decompression schedules for scuba divers engaged in deep diving without using dive tables, decompression software or a dive computer.
Breathing apparatus which recycles most of the exhaled gas, removing carbon dioxide and topping up oxygen before the gas is breathed again.
Compressor in which the volume of the compression chamber/s is cyclically changed by reversing linear motion. E.g.: a piston moving back and forth in a cylinder.
Diving helmet with a reclaim gas regulator allowing exhaled gas to be safely returned to the surface through an additional hose on the umbilical.
System for recovering helium based breathing gas used by divers and recycling it.
A hyperbaric chamber used to treat divers suffering from certain diving disorders such as decompression sickness.
see hook breathing
Recreational diving or sport diving is a type of diving that uses scuba equipment for the purpose of leisure and enjoyment. In some diving circles, the term "recreational diving" is used in contradistinction to "technical diving", a more demanding aspect of the sport which requires greater levels of training, experience and equipment. In other circles, technical diving is considered a subset of recreational diving as opposed to professional diving, which is done as part of the diver's work.
also RDP
A no-stop decompression table developed by DSAT.
see algal bloom
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.
Any dive which is done while the tissues retain residual inert gas from a previous dive.
Gas which is not intended to be used during the dive, and is reserved for contingencies.
Nitrogen in excess of normal atmospheric saturation remaining in the diver's tissues after a dive.
also RNT
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.
The ratio of carbon dioxide produced as a metabolic product to the oxygen consumed.
also reduced gradient bubble model
A bubble model decompression algorithm developed by Bruce Wienke.
see also bungee (sidemount)
Length of shock cord with metal rings and a clip used to control the position of the top end of a sidemounted cylinder. Differs from a regular bungee in having the rings. 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
see residual nitrogen time
see also Scuba gas planning
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.
also: Positive reserve valve, automatic valve, or calibrated orifice
A cylinder valve which limits the outflow by a calibrated orifice when in the "on" position.
A voluntary (not required by the decompression schedule) additional decompression stop intended to reduce risk of decompression sickness.
A reaction of the lungs to inhalation of a mist of salt water
Diving procedure where the divers remain pressurised for periods of several days or weeks and decompress only at the end of the period.
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.
also SCUBA
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.
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. 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.
see demand valve
The part of a diving regulator which provides pressure reduction from intermediate pressure to ambient pressure on demand. Demand valve.
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,
seeSAC
Surface Gas Consumption
also: shark shield
Electrical device carried by a diver intended to repel sharks by electrical field pulses.
see bungee cord
A rope between a float at the surface, and a sufficiently heavy weight holding the rope approximately vertical.
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.
The practice of using sidemount configuration (bungee loops and/or buttplate rails) as a means for stowing stage/deco cylinders when otherwise diving in back-mounted scuba
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.
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
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
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.
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 a competitive sport.
also skins, or dive skins
A lycra suit worn by a diver in warm water or under a wet suit.
Independent cylinders with their own regulators carried clipped to the harness at the side of the diver.
see Y-valve
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.
Tube with a bend and mouthpiece used for breathing air from above the water surface when the wearer's mouth and nose are submerged.
also snorkelling
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.
Snuba is 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. see also Hookah.
The practice of scuba diving alone, (without a "dive buddy/in-water standby diver").
Metering device to provide constant mass flow of a gas.
also sodasorb, sodalime and sofnolime
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.
Dissolution features in bedrock.
Also known as a cave formation: A secondary mineral deposit formed in a cave.
see single point mooring
see barotrauma
Injury or discomfort caused by increase or decrease in volume of gas space in the diver's body or equipment due to a change in ambient pressure.
see diving stage
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. May be confused with sidemount
also Copper helmet or Heavy gear
Early free flow surface supplied diving equipment using a heavy canvas suit, copper helmet and corselet, and weighted boots.
Underwater breath-holding without changing location
also living depth
Depth pressure in a saturation system at which divers live between compression and decompression
also giant stride entry
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 bouyancy 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.
also SPG
Gauge attached to the first stage regulator and used to monitor pressure remaining in the diving cylinder.
A passage in a cave that is submerged under water.
see surface decompression
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.
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.
also SMB
A buoy towed by a diver to indicate location to people at the surface.
Reciprocating water movement parallel to the bottom surface caused by the passing of a wave overhead
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.
A series of surface gravity waves that is not generated by the local wind.
A form of decompression sickness found among Polynesian island natives who habitually do multiple repetitive deep breath-hold dives.
A multiplicity of responsibilities leading to an increased risk of failure on the part of the diver to undertake some key basic function which would normally be routine for safety
An extension of the scope of recreational scuba diving to applications with greater technical complexity and higher inherent risk. Definitions vary, but diving with multiple breathing gases, helium based gases, closed circuit rebreathers, or under extensive overheads are generally considered as technical diving. There is no sharp distinction from other forms of recreational diving.
A vertically moored floating structure normally used for the offshore production of oil or gas, particularly suited for water depths between 300 and 1500 meters. The platform is permanently moored by means of tethers at each of the structure's corners and virtually all vertical motion of the platform is eliminated.
The Exponential/linear decompression algorithm used in the 2008 US Navy decompression tables
A procedure for treating decompression sickness by recompressing the diver, thus reducing bubble size, and allowing the gas bubbles to re-dissolve, then decompressing slowly enough to avoid further formation or growth of bubbles, or eliminating the inert gases by breathing oxygen under pressure
A thin but distinct layer in a large body of fluid, in which temperature changes more rapidly with depth than it does in the layers above or below
Hypothesis that bubble formation during decompression will not occur provided absolute ambient pressure exceeds the total of the partial gas tensions in the tissue for each gas.
see rule of thirds
The perception of sound within the human ear in the absence of corresponding external sound
Imaginary tissues which are designated as fast and slow to describe the rate of saturation.
The time it takes for the tissue to take up or release 50% of the difference in dissolved gas capacity at a changed partial pressure.
see Rimbach system
Method of equalising the middle ears by pinching the nose and swallowing.
A tendency to respond with anxiety in the anticipation of threatening situations.
A path along which one counts and records occurrences of the phenomena of study.
also decant
Fill cylinder with gas by transfer from a cylinder with higher pressure.
also bandage scissors or paramedic shears
Blunt tipped slightly serrated shears with angled blades sometimes used by divers as a safety cutting implement in place of a knife or line cutter.
A pipe, through which concrete is placed below water level. The top of the tremie is above water and open, and the bottom end is kept below the surface of the poured concrete.
see belt slide
Mixture of three gases for breathing. Oxygen, nitrogen and helium are the gases used. The gas fractions will usually be specified.
Ballast weight placed to improve a diver's trim.
The cloudiness or haziness of a fluid caused by individual particles (suspended solids) that may be invisible to the naked eye, similar to smoke in air
Wet diving bell (q.v.) with no direct supply of gas and services to the bell. Diver umbilicals lead directly to the surface control point.
Wet diving bell (q.v.) with umbilical supply of gas and other services to the bell, from which they are distributed to the divers umbilicals from a control panel in the bell.
Life support connection to a surface supplied diver or diving bell. Comprises gas supply hoses, a strength member and communications cable, and may also include gas reclaim hose, hot water hose and hoses for hydraulic or pneumatic power, and electrical and optical cables for ancillary equipment. Also refers to the power, control and instrument cable for a ROV.
A subsurface flow of water returning seaward from shore as result of wave action
also hyperventilation-induced blackout
Loss of consciousness due to hypoxia during a breath-hold submersion preceded by hyperventilation where alternative causes of blackout have been excluded.
also Jersey upline
A fairly substantial natural fibre rope which is deployed from the bottom using a small lift bag to provide the equivalent of a shotline. The lower end is tied off to the bottom, usually on a wreck, and the diver ascends on the line to avoid being swept away from the site by currents. After reaching the surface, the last diver cuts the line and it sinks back down, Natural fibre is used so the line rots away over a few years.
Valve, (usually regulator first stage or demand valve), where the valve mechanism moves against the flow when opening, and the pressure difference over the valve tends to close it.
An oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water
Technique for equalising the middle ear by moderately forceful attempted exhalation against a closed mouth and blocked nose
Thermodynamic equation of state for a real (non-ideal) gas.
The narrowing of blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries and small arterioles.
The widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large veins, large arteries, and smaller arterioles.
A type of dizziness, where there is a feeling of motion when one is stationary.
see also Decompression (diving)#Bubble formation, growth and elimination
Venous gas emboli
Synthetic elastomer suitable for oxygen service O-rings.
(also Variable permeability model). A decompression model and associated algorithms based on bubble dynamics.
The Exponential/linear decompression algorithm used in the 2008 US Navy decompression tables
Diving along the face of a near vertical cliff wall, particularly if the bottom is below the range of the diver's equipment and certification. This requires good buoyancy control.
Weights, generally made of lead, to counteract the buoyancy of other diving equipment, and the belts, pockets or harnesses used to support them.
The component at the surface of an oil or gas well that provides the structural and pressure-containing interface for the drilling and production equipment.
A cable-suspended chamber, open at the bottom, that is lowered underwater to operate as a base or a means of transport for a small number of divers.
A close fitting, thermally-insulating, foam neoprene diving suit that allows a limited volume and movement of water inside the suit.
also containment grip
Back inflation buoyancy compensator cell.
also WOB
The effort expended in inhaling and exhaling the breathing gas.
Recreational or technical diving on and inside of shipwrecks.
Cylinder valve body with two outlets and two valve mechanisms which can be independently controlled so that two regulator first stages can be fitted. Similar to H-valve but in Y configuration. Also known as Slingshot valve.
(also cable tie, tie wrap) Self-locking plastic strip used to connect objects together.
A
see adjustable buoyancy life jacket
Total static pressure at the reference point: Pressure relative to vacuum.
see yoke fitting/valve.
see yoke adaptor
see also Rebreather#Active addition semi-closed circuit
System for semi-closed circuit rebreather feed gas addition in which gas is added to the breathing circuit by a mechanism, regardless of current volume, and excess gas is vented to keep the loop volume within limits. Compare with passive addition
A filter medium used to remove oil, water and odours from breathing air.
Also known as ABLJ or horse collar buoyancy compensator
A combination of buoyancy compensator and inflatable life jacket worn on the chest and round the neck.
Part of Launch and Recovery System
Gantry or davit for launching and recovering bells, stages anchors or large ROVs. Usually deployed by hydraulic rams which swing the frame over the deck or overboard as required. The load is hoisted and lowered by cables from the top of the frame.
see arterial gas embolism
A device based on a pipe, used in by divers to suck small objects, sand and mud from the sea bed and to transport the resulting debris upwards and away from its source. Air is injected into the lower end of the pipe and the rising bubbles entrain water and cause an upward flow which draws the material from the bottom along.
A rapid increase or accumulation in the population of algae (typically microscopic) in an aquatic system. Some blooms may be recognized by discoloration of the water resulting from the high density of pigmented cells. Visibility can be severely impaired over a period of hours to days.
A secondary supply of air or other breathing gas used by the diver in an emergency
Dizziness caused by a difference of pressure between the middle ears.
Diving at a location where the water surface is at an altitude which requires modification of decompression schedules. (more than about 300 m (980 ft) above sea level.
Pressure of the surroundings.
Completely lacking in oxygen.
An impairment of language ability which may range from having difficulty remembering words to being completely unable to speak, read, or write
Decompression model in which the filtering capacity of the lung is assumed to have a threshold radius of the size of a red blood cell and sufficiently small decompression bubbles can pass to the arterial side, especially during the initial phase of ascent.
Blockage of an artery by a gas bubble. A possible consequence of lung overpressure injury.
The rate at which depth is reduced at the end of a dive. An important component of decompression.
Also ata or atmospheres absolute
Unit of absolute pressure equivalent to standard atmospheric pressure.
Also ADS
A small one-man articulated submersible of anthropomorphic form which resembles a suit of armour, with elaborate pressure joints to allow articulation while maintaining an internal pressure of one atmosphere.
see combat swimmer
B
A plate, normally made from metal, which rests against the diver’s back, and to which the primary scuba cylinders are attached. Held to the body by harness straps over the shoulders and round the waist. Sometimes also crotch straps and chest straps. Usually used with a back inflation buoyancy compensator.
also secondary, safe second or octopus
A second regulator connected to a cylinder or manifolded twin set.
also back roll entry
Water entry method in which the seated diver rolls backwards off the side of the boat, allowing the scuba cylinders to strike the water first.
see also gas block, or gas switching block
A gas switching block specifically intended for connection of a bailout set to the main gas supply (which may be scuba or surface supply) which allows the diver to switch from main gas supply to emergency gas supply while continuously using the same mouthpiece, regulator second stage, full face mask or helmet. A bailout block is generally used on open circuit breathing apparatus, the equivalent function on a rebreather is provided by a bailout valve (BOV). The bailout block may be mounted on the side of a diving helmet or full-face mask, or may be mounted in a convenient place on the diver's harness, and includes a bailout valve, used to select the gas source, and one or more non-return valves to ensure that the emergency gas supply is directed only to the diver.
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.
An independent breathing gas supply carried by a diver for use in case of failure of the main gas supply. Usually consists of a bailout cylinder with a first stage regulator, and either a second stage regulator or connected to a bailout block or bailout valve (q.v.) A submersible pressure gauge is also usually provided.
A heavy duty full-face mask with many of the characteristics of a lightweight demand helmet. In structure it is the front section of a lightweight helmet from above the faceplate to below the demand valve and exhaust ports, including the bailout block and communications connections on the sides. This rigid frame is attached to a neoprene hood by a metal clamping band, hence the name.
see cylinder bands
see also bar (unit)
Metric unit of pressure commonly used in diving, equal to 100 kiloPascal, and nearly equal to standard atmospheric pressure.
Tooth pain caused by pressure difference.
Injury caused by pressure difference.
see diving stage
see buoyancy compensator
see also dive marshal
A person on the beach who records when divers enter and exit the water. Typically used during recreational scuba training to keep track of the students, watch the gear, and provide assistance when required.
The combined supply and return hoses and cables for life-support, power and communications between a diving bell and the support platform
also belt slider, triglide, weight stop, weight slider
Hardware item with two parallel slots which is fitted to harness or weightbelt webbing to prevent other components such as D-rings and weights from sliding along the webbing.
also B.K. hook or BK safety hook
A type of safety lifting hook which is held closed when under load by a lever system where the weight of the load holds the bill of the hook against the safety latch.
Uncontrolled release of crude oil and/or natural gas from a well after pressure control systems have failed.
also BOP
A large, specialized valve used to seal, control and monitor oil and gas wells. Generally operated remotely by hydraulic ram.
A sink hole in a lake or the sea that is often the entrance to a cave. Blue holes in the sea are subject to tides so that their flows regularly reverse.
also piston bolt
A metal connecter comprising a hook with a spring-loaded axial sliding rod which must be manually retracted to allow the hook to be clipped onto something or removed. May be single- or double-ended, and if single-ended is usually fitted with a swivel ring opposite the jaws.
see bungee wing
Derogatory term for bungee wing based on fetishist terminology.
also booster pump
see also compressor
Machine used to increase pressure of a gas. Usually refers to the case where inlet pressure is above ambient pressure already.
see bailout valve
Knot used to form a secure, non-slipping loop at the end of a line.
Relationship between pressure and volume at constant temperature in an ideal gas.
Gas supplied to the diver to breathe, either directly to the diver or to the hyperbaric environment of the diving bell, dive chamber or saturation habitat.
Béance tubaire volontaire: Voluntary opening of the Eustachian tubes to equalise the middle ear.
Decompression models based on the assumption that bubbles will form during non-symptomatic decompression.
see glossopharangeal insufflation
A procedure carried out by scuba divers using the buddy system where each diver checks that the other's diving equipment is configured, fitted, and functioning correctly just before entering the water to dive.
A safety procedure where two or three divers monitor each other constantly during a dive and provide assistance or rescue when needed.
A procedure where two divers look out for the safety of each other, and give assistance if the other gets into difficulty.
Diving tables and decompression algorithm on which the tables are based, and some dive computers are programmed, based on the dissolved gas decompression model derived and tested by Dr A.A. Bühlmann.
see also ring bungee
Length of shock cord used to restrain the top end of side mount cylinders and keep them tucked in at the diver's shoulder while swimming. Usually clipped to the shoulder D-ring(s) of the harness and looped around the cylinder valve. May be attached to the back of the harness between the shoulder blades, or run continuous from one shoulder D-ring, around the back under the arms to the other shoulder D-ring.
also BC, BCD, buoyancy compensator device, ABLJ, horse collar, stabilisor jacket, stab jacket or wing
An airtight bladder worn by a diver which can be filled with air and vented to adjust and control the buoyancy of the diver.
A non-reclosing pressure relief device used to protect a diving cylinder from overpressurization.
C
Scuba diving from canoes, used when the dive site is beyond convenient swimming distances.
The toxic effects of carbon dioxide, due to incomplete elimination of carbon dioxide resulting from skip breathing, excessive work of breathing, scrubber failure in a rebreather system, or inadequate ventilation in a diving chamber or free flow helmet. Occasionally caused by contaminated gas supply.
The toxic effects of carbon monoxide, usually due to contaminated breathing gas supply.
An emergency procedure which is performed in an effort to manually preserve intact brain function until further measures are taken to restore spontaneous blood circulation and breathing in a person in cardiac arrest
see also critical pressure
Critical Air Supply, the amount of breathing air required to safely exit a penetration dive. When the air supply reaches this level the dive has reached a planned turning point.
Decanting from several storage cylinders in succession, generally using a procedure to maximise charge pressures. Often used in partial pressure gas blending.
Directional line markers which point the way to an exit.
A reel specifically made for cave diving, used to lay and recover large lengths of cave line which is used as a guide line to find the exit or a permanent guide line.
A sinkhole in Mexico. Generally with vertical overhanging walls or shafts with water that open into a cave system.
Relation of volume to temperature at constant pressure of an ideal gas.
A strap around the neck of a sidemount cylinder used to hold the bolt snap closer to the neck so that the head of the cylinder stays closer to the diver's armpit. The choker can be a small webbing strap with a sliding buckle for adjustment, so it can be tightened to bring the clip closer to the neck or slacked off while in use.
A symptom of decompression sickness manifested by shortness of breath, caused by a large number of venous gas bubbles in the lung capillaries which interfere with gas exchange.
also tree
An assembly of valves, spools, and fittings installed on top of the wellhead and used primarily to control the flow, usually oil or gas, out of the well.
see inshore diving
also dry bell
A closed or dry bell is a pressure vessel for human occupation which is lowered into the sea to the workplace, equalised in pressure to the environment, and opened to allow the divers in and out. Divers may be decompressed in the bell or transferred under pressure to a hyperbaric chamber at the surface.
Working under pressure: Occupational activity where gas is breathed at pressure in excess of atmospheric pressure, usually underwater.
Person trained in scuba diving or swimming underwater in a military capacity which can include combat
The process of making a well ready for production.
Pain in the joints caused by exposure to high ambient pressure at a relatively high rate of compression
Machine which pressurises gas. Generally intake gas is at ambient pressure, outlet gas at higher pressure. High pressure breathing air compressor output pressure is usually 200 to 330 bar.
Liquid resulting from phase change from gas due to cooling or pressure change.
also isobaric blackout
A Freediving blackout which occurs while the diver maintains a near constant shallow depth, where reduction of oxygen partial pressure due to ascent is not a factor. Usually induced by pre-dive hyperventilation. Also referred to as shallow water blackout, which is an ambiguous term
see restriction
see submersible pressure gauge
Decompression without stops. Instead of a fairly rapid ascent rate to the first stop, followed by a period at static depth during the stop, the ascent is slower, but without officially stopping. Ascent rate may vary with depth, usually slowing as the depth reduces.
A rescue technique used by scuba divers to raise an incapacitated diver to the surface from depth.
also CESA
An emergency technique for surfacing, usually when no breathable gas is available at depth. The diver fins upward while gently exhaling to keep expanding air in the lungs from causing lung expansion injuries.
Personal non-directional line markers that mark specific locations, or the direction of one's own exit at line intersections.
A diving helmet of traditional design and construction, usually made from spun or beaten copper, with brass or bronze fittings. There are usually two main sub-assemblies; the bonnet is the roughly spherical part which covers the head and is provided with viewports, valves and various other fittings, and the corselet, which rests on the upper torso of the diver, and to which the bonnet is connected when in use, and which may be sealed to the suit and ballasted to compensate for the buoyancy of the airspace inside the helmet.
Breastplate part of a copper helmet and some other heavy helmets, which clamps to the diving suit, and to which the helmet bonnet is clamped, screwed or bolted.
Flexible bag or bellows in a rebreather which compensates for the change in volume in the loop during breathing.
see cardio-pulmonary resuscitation
see CAS
Hypothesis that bubble formation during decompression will not occur if a critical pressure difference between tissue gas tension and inspired gas partial pressure is not exceeded.
Cylinder gas pressure which determines a safe limit to an underwater activity on scuba, such as start of ascent or turnaround during a penetration.
Hypothesis that bubble formation during decompression will not occur if a critical ratio of tissue gas tension and inspired gas partial pressure for a given gas is not exceeded.
Hypothesis that symptoms of decompression sickness will not be evident if a critical volume of tissue gas bubbles is not exceeded.
Trademark name Cyalume is a solid ester whose oxidation products are responsible for the chemiluminescence in a glowstick.
The appearance of a blue or purple coloration of the skin or mucous membranes due to the tissues near the skin surface being low on oxygen
Rubber or plastic cover for the base of a scuba cylinder to protect it from abrasion, and in the case of domed end cylinders, to allow it to stand upright.
Valve fitted to a compressed gas cylinder to control gas flow into and out of the cylinder. Also pillar valve.
D
see Divers Alert Network
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.
To transfer gas between cylinders by differential pressure. No energy is input, flow will stop when 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.
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.
see DSMB
Hyperbaric chamber used for decompressing divers and emergency therapeutic recompression.
Gas breathed during decompression with a composition designed to accelerate decompression, usually by an increased oxygen content.
Illness caused by decompression. Includes decompression sickness and arterial gas embolism due to lung overexpansion barotrauma.
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.
also DCS, divers' disease, the bends or caisson 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.
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.
Printed cards or booklets that allow divers to determine a decompression schedule for a particular dive profile and breathing gas.
also decompression bar
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.
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.
Mechanism for providing the user with breathing gas flow only when required.
Diamond Reef System is 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.
Decompression hypothesis that the uptake and elimination of inert gas is limited by diffusion rates in the tissues
also sometimes dil
Gas mixture used to dilute the oxygen in the loop of a closed circuit rebreather to a partial pressure suited to the depth.
also DIN valve, DIN regulator, DIN thread
Usually refers to G5/8" x 14 tpi 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.
Screw in adaptor which can be used with many recent 200/240 bar DIN cylinder valves to allow connection of Yoke regulators or filling whips.
also Doing It Right
A holistic approach to scuba diving, which encompasses several essential elements, including fundamental diving skills, teamwork, physical fitness, and the use of streamlined and minimalistic equipment configurations.
also penetration 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.
also decompression computer
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.
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 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.
see decompression tables
also DAN
A non-profit organization for assisting divers in need and medical research on recreational scuba diving safety.
also dive tender
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 underwater.
A rigid chamber suspended from a cable and used to transport divers to depth and back to the surface.
see also overweighting
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 cintact 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.
see regulator
The person who administers a United States university's research diving safety program.
Hand sign and light sign system used by scuba divers to communicate when underwater.
also known as the basket
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 him out of the water.
Person in charge of, and responsible for safety of a commercial diving operation.
Ultrasonic signals reflected from bubble surfaces to identify and quantify gas bubbles present in venous blood.
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.
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.
see closed bell
Filling scuba cylinders without the use of a water bath for cooling.
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
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
Method of keeping a diving support platform in position without anchoring, using thrusters and positional feedback.
Medical conditions resulting from changes in ambient pressure.
E
Equivalent Air Depth. 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 in decompression calculations.
Equalising the pressure in the middle and external ear by opening the Eustachian tubes. Several techniques are used.
also Thalmann algorithm, (VVAL18)
Exponential-Linear algorithm of 2008 US Navy tables, assumes exponential ingassing and a combination of linear and exponential outgassing rates.
also emergency beacons or EPIRB,
Emergency position-indicating radio beacons are tracking transmitters which aid in the detection and location of boats and people in distress at sea.
also ESA, Controlled emergency swimming ascent, CESA
Emergency procedure where the diver makes an ascent from depth after a breathing gas supply failure.
see emergency position indicating radio beacon
also EAD
A way of approximating the decompression requirements of nitrox mixtures at depth by comparison with the depth at which air would require the same decopression.
also END
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.
The combined supply and return hoses and cables for life-line, life-support, power and communications between a diving bell and the diver
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.
F
Cracking in a material resulting from multiple stress cycles below the ultimate or yield strength. Usually refers to large number of cycles.
see full-face mask
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 (Activated carbon, Molecular sieve, Silica gel), or may be chemically combined with the medium (Sodalime) or catalytically converted (Hopcalite) into a less objectionable substance.
see Diving regulator#First stage
Diving regulator component which reduces gas pressure from stoage pressure in the cylinder to interstage pressure for supply to the second stage and for suit and BC inflation.
Condensation of water vapour on the inside surface of a mask or helmet faceplate, reducing visibility.
see also free gas
Air at normal atmospheric pressureUnderwater diving that does not involve the use of external breathing apparatus, but relies on a diver's ability to hold his or her breath until resurfacing. also Breath-hold diving, and apnea (q.v.).
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.
G
Mixing breathing gases for diving, filling diving cylinders with gas mixes such as nitrox or trimix.
Blockage of blood vessel by a bubble of gas.
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 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 a low pressure compressor or high pressure storage cylinders.
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.
also buccal pumping, lung packing
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.
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-value of a decompression algorithm to a more conservative value. Often used to bias the algorithm towards deeper stops.
see distance line
H
also Haldanean
Decompression models based on the principles described by John Scott Haldane.
Voice communications system where users take turns to send and receive.
see tissue half times
A strong variation in salinity over a small depth range within a body of water. Often visible as a blurred or shimmering region due to uneven refractive index.
see standard diving dress
Mixtures of helium and oxygen for use as a breathing gas.
Trimix blends made by topping up helium with air.
An inert gas which is used as a component of breathing gas mixtures for deep diving.
An instrument used to identify the presence and concentration of helium in a mixture of gases
see hard hat diving
also hooka and airline diving
Also known as airline diving; surface supplied diving where the breathing air is supplied to the diver by a simple hose. The diver usually breathes through a mouth held demand valve.
also recovery breathing
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.
Catalyst sometimes used in air filters to oxidise carbon monoxide to carbon dioxide. Hopcalite is a mixture of manganese oxide, copper oxide and a small amount of silver oxide.
see adjustable buoyancy lifejacket
An insulated pipe in the umbilical line, which links the diver to the surface support, carries the hot water from a heater on the surface down to the suit. The diver controls the flow rate of the water allowing him to vary the warmth of the suit.
High-pressure nervous syndrome: A neurological and physiological diving disorder that results when a diver descends below about 500 feet (150 m) while breathing a helium–oxygen mixture.
Cylinder valve body with two outlets and two valve mechanisms which can be independently controlled so that two regulator first stages can be fitted. Similar to Y-valve but in configuration where the second valve is parallel to the primary, though the secondary valve can sometimes be swivelled.
Pressure due to the weight of the water column above a point at depth.
Non-destructive test to revalidate pressure vessels which uses water as a test medium. The vessel is pressurised to the test pressure (q.v.) and measured for permanent set.
Deep diving breathing gas mixture of hydrogen, helium and oxygen.
Deep diving breathing gas mixture of hydrogen and oxygen.
Excessive level of carbon dioxide in the body.
Abnormally low tissue and blood carbon dioxide concentration.
Abnormally low tissue oxygen concentration: Insufficient oxygen in the body to support normal activities or consciousness.
I
A gas which is not metabolically active, used to dilute the breathing gas.
Inert gas uptake in body tissues during a dive or other hyperbaric exposure.
Metabolic reduction of total gas pressure in the tissues.
J
A type of mobile platform that consists of a buoyant hull fitted with a number of movable legs, capable of raising its hull over the surface of sea. The buoyant hull enables transportation of the unit and all attached machinery to a desired location. Once on location the hull is raised to the required elevation above the sea surface on its legs supported by the sea bed.
see upline
A type of pipe and hose fitting with a 37-degree flare seating surface. Commonly used in umbilical hose connections.
An atmospheric diving suit manufactured by Underwater Marine Equipment Limited.
A short line used to connect to a shotline or anchor line, allowing the diver to move a short horizontal distance away to decompress. The line helps compensate for vertical movement in the anchor line or shot line due to waves.
A procedure to integrate health and safety principles and practices into a particular task or job. Each basic step of the job analysed to identify potential hazards and controls for each hazard.
A short cave line used to connect between two permanent lines that are not in contact. May also be used to search for the other end of a break in a cave line and repair the break
Scuba cylinder valve with lever operated reserve mechanism.
K
Diving from a special purpose kayak used to get to the site where the distance from a suitable entry and exit point is inconvenient for shore diving.
Scuba cylinder valve without reserve mechanism.
L
A piece of cordage used to secure or lower things, usually it is used where there is a risk of losing the object
An uncontrolled/involuntary muscular contraction (spasm) of the laryngeal cords which causes a partial blocking of breathing in, while breathing out remains easier.
also pipelay barge
Barge on which pipeline sections are assembled, welded and laid on the seabed as the barge is moved forward.
Shot line (q.v.) which does not reach the bottom
see LST
A robust and air-tight bag with straps, which is used to lift heavy objects underwater by means of the bag's buoyancy.
Low volume, close fitting diving helmet, usually with demand valve. Neutrally buoyant, and moves with the diver's head.
A lung inflammation (pneumonia) that develops when lipids enter the bronchial tree
A large boat which provides transport, accommodation and services for vacationing divers
Mass transport of water along a shoreline, generally due to wave action at an angle to the shoreline.
also breathing loop
The circuit in a rebreather through which the breathing gas passes during a breathing cycle.
see glossopharangeal insufflation
M
also diving response
A reflex response to breathhold and chilling of the face diving response expressed by the cardiovascular system, which exhibits hypertension, bradycardia, oxygen conservation, arrhythmias, and contraction of the spleen.
see twin cylinder manifold
also manufacturing code
Set of design and manufacturing rules intended to produce uniform and safe products by several manufacturers in an industry.
A type of swimfin typically used in finswimming and free-diving. It consists of a single surface attached to footpockets for both of the diver's feet.
Material containing tiny pores of a precise and uniform size that is used as an adsorbent for gases and liquids. Molecules small enough to pass through the pores are absorbed while larger molecules are not. It is different from a common filter in that it operates on a molecular level.
The use of sidemount configuration and procedures with a single cylinder.
An opening in the floor or base of the hull, platform, or chamber giving access to the water below.
Compressor in which gases are compressed more than once, often with cooling between stages. Used to improve efficiency and reduce temperatures.
At a given ambient pressure, the M-value is the maximum theoretical value of absolute inert gas pressure that a tissue compartment can take without presenting symptoms of decompression sickness.
N
see nitrogen narcosis
A US Navy trained combat diver.
No decompression limit. The maximum time which a diver can remain at a specified depth without incurring a stage decompression obligation in terms of the specified decompression tables or algorithm.
also just negative in context
Buoyancy less than weight. Insufficient upward force due to buoyancy to keep afloat or remain at constant depth
Entry into the water after reducing buoyancy of BC and, if applicable, dry suit by venting to ensure that the diver will not float back to the surface, but will continue to descend
also neo-Haldanean
Decompression models based on later modifications of the principles described by John Scott Haldane.
Synthetic elastomer used in the form of foamed sheets as the material for most wetsuits and some drysuits.
Having a fully immersed buoyancy exactly equal to weight, so that the forces are balanced and the person or object statically remains at a constant depth. Effectively average density is equal to that of the surrounding fluid medium. The state of neutral buoyancy is typically metastable for a compressible system.
An atmospheric diving suit designed and originally built by Phil Nuytten.
Minor symptoms characteristic of mild decompression sickness.
Diving during the hours of darkness.
A synthetic elastomer used for most standard O-ring seals.
The major component gas of air and many breathing gas mixtures used in diving. Important in diving as an active agent in nitrogen narcosis and decompression sickness.
Also known as narcs, inert gas narcosis, raptures of the deep, Martini effect: A reversible alteration in consciousness that occurs while breathing gases containing nitrogen under elevated partial pressure similar to alcohol intoxication or nitrous oxide inhalation, and can occur during shallow dives, but usually does not become noticeable until greater depths, beyond 30 meters.
also Enriched Air Nitrox (EAN)
Mixture of nitrogen and oxygen for use as breathing gas. Usually with oxygen percentage higher than air.
A mixing tube used to blend oxygen with air before compressing to make nitrox breathing gas.
A specialized overhead-environment strategy for dealing with particularly tight restrictions which may involve divers wearing a very basic harness or simply hand-carrying cylinders.
An oscillation of the eyes alternating a slow eye movement in one direction, and a fast eye movement in the other direction
O
also octo reg
A secondary demand valve fitted to a first stage diving regulator for use as an alternative air source for another diver in case of an emergency.
see outgassing
see ingassing
A mechanical gasket in the shape of a torus; a loop of elastomer with a circular cross-section, designed to be seated in a groove and compressed during assembly between two or more parts, creating a seal at the contact surfaces.
Diffusion of gas out of the tissue into the blood, and transport to the lungs where it diffuses into the lung gas and is eliminated by exhalation.
see also diving heavy
Carrying more weight than is necessary to achieve neutral buoyancy at all times in a dive.
Important component gas of atmospheric air and essential component of any breathing gas. Required to sustain life.
Instrument for measuring the partial pressure of oxygen in a gas mixture
A notional alarm clock, which accumulates hyperbaric oxygen exposure at a rate which increases with higher ppO2 toward the maximum single exposure limit recommended
Fraction by volume or pressure of the gas mixture made up by oxygen
A condition resulting from the harmful effects of breathing molecular oxygen (O2) at elevated partial pressures.
Inherent unsaturation due to metabolic reduction of total gas pressure in the tissues.
P
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 animalistic 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.
see also Rebreather#Passive addition semi-closed circuit
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
Entering a region with no direct vertical access to the surface, such as a cave or the interior of a wreck.
see distance line
The process of delivery of blood to a capillary bed in the biological tissue.
The assumption in a decompression model that perfusion has the dominant influence on gas uptake and release.
also PLB
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.
see also jump camera
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.
Pipeline inspection gauge: A tool that is sent through a pipeline and propelled by the pressure of the product in the pipeline itself.
see cylinder valve
Standard connection type for portable medical oxygen cylinder valves and regulators.
see personal locator beacon
also pneumo
Instrument to measure depth of a diver using a gauge calibrated in msw, fsw, or often both, to measure the ambient pressure at the diver by measuring the pressure in a hose filled with air with an open end at the diver.
Air or other breathing gas in the chest cavity, often resulting in a collapsed lung.
Relatively small scuba set carried as an independent alternative breathing gas source by a scuba diver.
Diving which is done as part of the diver's employment or professional occupation.
Pulmonary barotrauma of ascent. Lung over-pressure injury.
see pendulum rebreather
also Pee-valve
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.
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.
Q
see also photo quadrat
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.
R
see nitrogen narcosis
also ratio deco
A technique for calculating decompression schedules for scuba divers engaged in deep diving without using dive tables, decompression software or a dive computer.
Breathing apparatus which recycles most of the exhaled gas, removing carbon dioxide and topping up oxygen before the gas is breathed again.
Compressor in which the volume of the compression chamber/s is cyclically changed by reversing linear motion. E.g.: a piston moving back and forth in a cylinder.
Diving helmet with a reclaim gas regulator allowing exhaled gas to be safely returned to the surface through an additional hose on the umbilical.
System for recovering helium based breathing gas used by divers and recycling it.
A hyperbaric chamber used to treat divers suffering from certain diving disorders such as decompression sickness.
see hook breathing
Recreational diving or sport diving is a type of diving that uses scuba equipment for the purpose of leisure and enjoyment. In some diving circles, the term "recreational diving" is used in contradistinction to "technical diving", a more demanding aspect of the sport which requires greater levels of training, experience and equipment. In other circles, technical diving is considered a subset of recreational diving as opposed to professional diving, which is done as part of the diver's work.
also RDP
A no-stop decompression table developed by DSAT.
see algal bloom
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.
Any dive which is done while the tissues retain residual inert gas from a previous dive.
Gas which is not intended to be used during the dive, and is reserved for contingencies.
Nitrogen in excess of normal atmospheric saturation remaining in the diver's tissues after a dive.
also RNT
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.
The ratio of carbon dioxide produced as a metabolic product to the oxygen consumed.
also reduced gradient bubble model
A bubble model decompression algorithm developed by Bruce Wienke.
see also bungee (sidemount)
Length of shock cord with metal rings and a clip used to control the position of the top end of a sidemounted cylinder. Differs from a regular bungee in having the rings. 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
see residual nitrogen time
see also Scuba gas planning
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.
also: Positive reserve valve, automatic valve, or calibrated orifice
A cylinder valve which limits the outflow by a calibrated orifice when in the "on" position.
S
A voluntary (not required by the decompression schedule) additional decompression stop intended to reduce risk of decompression sickness.
A reaction of the lungs to inhalation of a mist of salt water
Diving procedure where the divers remain pressurised for periods of several days or weeks and decompress only at the end of the period.
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.
also SCUBA
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.
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. 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.
see demand valve
The part of a diving regulator which provides pressure reduction from intermediate pressure to ambient pressure on demand. Demand valve.
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,
seeSAC
Surface Gas Consumption
Loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold dive in water typically shallower than five metres (16 feet), when the swimmer does not necessarily experience an urgent need to breathe and has no other obvious medical condition that might have caused it. 2. see also Freediving blackout#Terminology and latent hypoxia
Loss of consciousness caused by cerebral hypoxia at the end of a deep breath-hold dive during the latter part of the ascent or immediately after surfacing due to lowered pO2 caused by reduction in ambient pressure, see also latent hypoxia. 3. Loss of consciousness while ascending on a rebreather due to sudden drop of pO2 in the breathing loop, usually associated with manual CCR and SCR.
also: shark shield
Electrical device carried by a diver intended to repel sharks by electrical field pulses.
see bungee cord
A rope between a float at the surface, and a sufficiently heavy weight holding the rope approximately vertical.
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.
The practice of using sidemount configuration (bungee loops and/or buttplate rails) as a means for stowing stage/deco cylinders when otherwise diving in back-mounted scuba
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.
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
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
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.
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 a competitive sport.
also skins, or dive skins
A lycra suit worn by a diver in warm water or under a wet suit.
Independent cylinders with their own regulators carried clipped to the harness at the side of the diver.
see Y-valve
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.
Tube with a bend and mouthpiece used for breathing air from above the water surface when the wearer's mouth and nose are submerged.
also snorkelling
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.
Snuba is 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. see also Hookah.
The practice of scuba diving alone, (without a "dive buddy/in-water standby diver").
Metering device to provide constant mass flow of a gas.
also sodasorb, sodalime and sofnolime
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.
Dissolution features in bedrock.
Also known as a cave formation: A secondary mineral deposit formed in a cave.
see single point mooring
see barotrauma
Injury or discomfort caused by increase or decrease in volume of gas space in the diver's body or equipment due to a change in ambient pressure.
see diving stage
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. May be confused with sidemount
also Copper helmet or Heavy gear
Early free flow surface supplied diving equipment using a heavy canvas suit, copper helmet and corselet, and weighted boots.
Underwater breath-holding without changing location
also living depth
Depth pressure in a saturation system at which divers live between compression and decompression
also giant stride entry
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 bouyancy 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.
also SPG
Gauge attached to the first stage regulator and used to monitor pressure remaining in the diving cylinder.
A passage in a cave that is submerged under water.
see surface decompression
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.
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.
also SMB
A buoy towed by a diver to indicate location to people at the surface.
Reciprocating water movement parallel to the bottom surface caused by the passing of a wave overhead
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.
A series of surface gravity waves that is not generated by the local wind.
T
A form of decompression sickness found among Polynesian island natives who habitually do multiple repetitive deep breath-hold dives.
A multiplicity of responsibilities leading to an increased risk of failure on the part of the diver to undertake some key basic function which would normally be routine for safety
An extension of the scope of recreational scuba diving to applications with greater technical complexity and higher inherent risk. Definitions vary, but diving with multiple breathing gases, helium based gases, closed circuit rebreathers, or under extensive overheads are generally considered as technical diving. There is no sharp distinction from other forms of recreational diving.
A vertically moored floating structure normally used for the offshore production of oil or gas, particularly suited for water depths between 300 and 1500 meters. The platform is permanently moored by means of tethers at each of the structure's corners and virtually all vertical motion of the platform is eliminated.
The Exponential/linear decompression algorithm used in the 2008 US Navy decompression tables
A procedure for treating decompression sickness by recompressing the diver, thus reducing bubble size, and allowing the gas bubbles to re-dissolve, then decompressing slowly enough to avoid further formation or growth of bubbles, or eliminating the inert gases by breathing oxygen under pressure
A thin but distinct layer in a large body of fluid, in which temperature changes more rapidly with depth than it does in the layers above or below
Hypothesis that bubble formation during decompression will not occur provided absolute ambient pressure exceeds the total of the partial gas tensions in the tissue for each gas.
see rule of thirds
The perception of sound within the human ear in the absence of corresponding external sound
Imaginary tissues which are designated as fast and slow to describe the rate of saturation.
The time it takes for the tissue to take up or release 50% of the difference in dissolved gas capacity at a changed partial pressure.
see Rimbach system
Method of equalising the middle ears by pinching the nose and swallowing.
A tendency to respond with anxiety in the anticipation of threatening situations.
A path along which one counts and records occurrences of the phenomena of study.
also decant
Fill cylinder with gas by transfer from a cylinder with higher pressure.
also bandage scissors or paramedic shears
Blunt tipped slightly serrated shears with angled blades sometimes used by divers as a safety cutting implement in place of a knife or line cutter.
A pipe, through which concrete is placed below water level. The top of the tremie is above water and open, and the bottom end is kept below the surface of the poured concrete.
see belt slide
Mixture of three gases for breathing. Oxygen, nitrogen and helium are the gases used. The gas fractions will usually be specified.
Ballast weight placed to improve a diver's trim.
The cloudiness or haziness of a fluid caused by individual particles (suspended solids) that may be invisible to the naked eye, similar to smoke in air
Wet diving bell (q.v.) with no direct supply of gas and services to the bell. Diver umbilicals lead directly to the surface control point.
Wet diving bell (q.v.) with umbilical supply of gas and other services to the bell, from which they are distributed to the divers umbilicals from a control panel in the bell.
U
Life support connection to a surface supplied diver or diving bell. Comprises gas supply hoses, a strength member and communications cable, and may also include gas reclaim hose, hot water hose and hoses for hydraulic or pneumatic power, and electrical and optical cables for ancillary equipment. Also refers to the power, control and instrument cable for a ROV.
A subsurface flow of water returning seaward from shore as result of wave action
also hyperventilation-induced blackout
Loss of consciousness due to hypoxia during a breath-hold submersion preceded by hyperventilation where alternative causes of blackout have been excluded.
also Jersey upline
A fairly substantial natural fibre rope which is deployed from the bottom using a small lift bag to provide the equivalent of a shotline. The lower end is tied off to the bottom, usually on a wreck, and the diver ascends on the line to avoid being swept away from the site by currents. After reaching the surface, the last diver cuts the line and it sinks back down, Natural fibre is used so the line rots away over a few years.
Valve, (usually regulator first stage or demand valve), where the valve mechanism moves against the flow when opening, and the pressure difference over the valve tends to close it.
An oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water
V
Technique for equalising the middle ear by moderately forceful attempted exhalation against a closed mouth and blocked nose
Thermodynamic equation of state for a real (non-ideal) gas.
The narrowing of blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries and small arterioles.
The widening of blood vessels resulting from relaxation of smooth muscle cells within the vessel walls, particularly in the large veins, large arteries, and smaller arterioles.
A type of dizziness, where there is a feeling of motion when one is stationary.
see also Decompression (diving)#Bubble formation, growth and elimination
Venous gas emboli
Synthetic elastomer suitable for oxygen service O-rings.
(also Variable permeability model). A decompression model and associated algorithms based on bubble dynamics.
The Exponential/linear decompression algorithm used in the 2008 US Navy decompression tables
W
Diving along the face of a near vertical cliff wall, particularly if the bottom is below the range of the diver's equipment and certification. This requires good buoyancy control.
Weights, generally made of lead, to counteract the buoyancy of other diving equipment, and the belts, pockets or harnesses used to support them.
The component at the surface of an oil or gas well that provides the structural and pressure-containing interface for the drilling and production equipment.
A cable-suspended chamber, open at the bottom, that is lowered underwater to operate as a base or a means of transport for a small number of divers.
A close fitting, thermally-insulating, foam neoprene diving suit that allows a limited volume and movement of water inside the suit.
also containment grip
Whip check device which contains a short section of the whip within a braided tube which reduces wear and point loading on the hose, and constrains motion of the hose end more than a standard whip check in case of disconnection under pressureBack inflation buoyancy compensator cell.
also WOB
The effort expended in inhaling and exhaling the breathing gas.
Recreational or technical diving on and inside of shipwrecks.
Y
Cylinder valve body with two outlets and two valve mechanisms which can be independently controlled so that two regulator first stages can be fitted. Similar to H-valve but in Y configuration. Also known as Slingshot valve.
Z
(also cable tie, tie wrap) Self-locking plastic strip used to connect objects together.