Definitions of technical terms, jargon, diver slang and acronyms used in underwater diving
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.
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
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.[3]
ADV
Automatic Diluent Valve: A demand valve set into the breathing loop of a rebreather to inject diluent gas into the loop when the loop volume falls and there is not enough gas for inhalation.
Gantry or davit for launching and recovering bells, stages anchors or large ROVs.[4][5] 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.
Decompression profile tending to shorter overall decompression time for a given pre-ascent dive profile, accepting increased risk of decompression sickness to reduce the overall ascent time.[6]
air dome
A section of cave which traps air or other gas at the top. This gas is not directly connected to the surface.[7]
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.
ALP
Articulated Loading Platform, a type of single point mooring consisting of a buoyant upper structure with a lattice leg linked by an articulating joint to a mooring.[9]
Diving at a location where the water surface is at an altitude which requires modification of decompression schedules.[10] (more than about 300 m (980 ft) above sea level.
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.
A waistcoat (vest) style harness of heavy cloth with strong adjustable webbing straps so that the diver can not slide out under any predictable circumstance.[12]
ascent
Part of the dive profile where the diver is moving upwards towards the surface. An ascent may be interrupted by stops (q.v.), when the diver maintains a functionally constant depth for the purpose of decompression, and pulls (q.v.), during which periods there is consistently upwards movement (minor variations in the scale of a few seconds are generally ignored).
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.
EN 14153-2 / ISO 24801-2 standard competence for recreational scuba diver. The level 2 "Autonomous diver" has sufficient knowledge, skill and experience to make dives, in open water, which do not require in-water decompression stops, to a recommended maximum depth of 20 m with other scuba divers of the same level, only when appropriate support is available at the surface, and under conditions that are equal or better than the conditions where they were trained without supervision of a scuba instructor, unless they have additional training or are accompanied by a dive leader.[14]
A small plate with a slot for a webbing belt and two side by side holes for clipping on equipment, generally used similarly to a D-ring in combination with a belt slider as an alternative to a butterfly slider
A finning technique for moving backwards. Not an easy, powerful or elegant kick, but useful in many situations. The fins are angled outwards in opposite directions with the legs straight, then swept upwards and towards the diver by bending the knees in the power stroke. The knees may move downwards a bit at the same time by bending at the hips for stability. The return stroke feathers the fins by pointing them backwards in line with the body axis, to reduce forward thrust until the legs are straight again
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.
backpack
A rigid or semi-rigid structure similar in function to a backplate, usually made of moulded plastic, but sometimes of metal, used either as a stiffener and reinforcement for a jacket style buoyancy compensator, or as the basis of a scuba harness independent of a buoyancy compensator. The backpack supports and stabilises the scuba cylinder on the diver's back.
backup light
Dive light carried as a spare to be used in case of failure of the primary light.[7]
backup regulator
also secondary, safe second or octopus
A second regulator connected to a cylinder or manifolded twin set.[7]
backward roll entry
backward roll
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.[15]:125
bailout block
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.
bailout valve
1. An open circuit demand valve built into a rebreather mouthpiece, or other part of the breathing loop, which can be isolated while the diver is using the rebreather to recycle breathing gas, and opened at the same time as isolating the breathing loop when the diver bails out to open circuit.
2. A valve which opens the gas supply from the bailout cylinder of a surface supplied diver, used in case of surface gas failure, usually mounted on the side of a diving helmet or full-face mask, or on a manifold block on the diver's harness.
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.[16]
balanced regulator
Regulator designed to provide a consistent demand effort not affected by cylinder gas pressure or depth.[7]
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.
1. (also tank factor) Numeric value computed for a cylinder or manifolded set that relates volume and pressure in the imperial system of units. Computed by dividing nominal capacity (cubic feet) by cylinder working pressure (psi) to express cubic feet of volume per psi of fill pressure (sometimes multiplied by 100 to give cubic feet per 100 psi). Used to convert cylinder pressure to free gas volume.[7]
2. A line that is a base for measurement or for construction; see datum (calculations or comparisons)
3. A data set which is a point of reference (engineering or science) for later data.
Uncontrolled buoyant ascent caused by inability to release gas from the buoyancy compensator faster than it expands due to pressure reduction of ascent.
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.
Surface oriented diving operation in which the divers are transported in and deployed from a closed bell, and are either decompressed in the bell at the surface or transferred under pressure to a deck decompression chamber for decompression.
bell cursor
Mechanism or structure for guiding and constraining the motion of a bell when in the close vicinity of the deployment platform to improve handling in bad weather.[4]
bell diving
1. Any diving operation in which the divers travel in or work from a diving bell
2. Diving operations in which divers are transported in and deployed from a closed bell, either as a surface oriented (bell bounce) or saturation dive.[16]
bell harness
A safety harness made of strong webbing, which is fastened around a diver over the exposure suit, and allows the diver to be lifted without risk of falling out of the harness.[18]
The part of a bell dive operation from bell lock-off to bell lock-on (to and from the life support system)[4]
bell stage
A framework extending below a closed bell which keeps the base of the pressure vessel off the bottom sufficiently to provide clearance for the divers to use the bottom hatch when the bell is resting on the bottom or on the clump weight.
The combined supply and return hoses and cables for life-support, power and communications between a diving bell and the support platform
belt slider
also belt slide, 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.[7]
benign water
benign conditions
Sometimes also referred to as confined water. Environments of low risk, where it is extremely unlikely or impossible for the diver to get lost or entrapped, or be exposed to hazards other than the basic underwater environment.
bent D-ring
A D-ring which has been bent about 45° near the straight section on both sides, forcing it to project slightly from the harness when pushed to one side, allowing easier attachment of clips.
bends
Decompression sickness: Injury caused by bubble formation in the body tissues after hyperbaric exposure.
BIBS
Built in breathing system. A demand breathing gas supply system with external exhaust used to provide chamber occupants with breathing gases other than the gas used to pressurise the chamber. Used for treatment gases and emergency breathing gas if the chamber is contaminated.[10]
Billy ring
Three D rings welded together along their straight sides so that one is perpendicular to the other two. This uses the two flat rings to maintain the third in an upright position when mounted on harness webbing, allowing it to be more easily accessed to clip on stage cylinders. Named after Captain Billy Deans.[7]
BK hook
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.[19]
blending stick
Mixing tube in which gases are continuously mixed prior to intake by a compressor, usually at atmospheric pressure.[8] Usually refers to manufacture of nitrox from air with added oxygen, but also used for trimix. Gas mixture is usually continuously analysed at the exit of the blending stick to monitor composition.
blind traverse
Passing through a cave from one entrance to a different exit which the diver has not used before.[7]
block adaptor
Screw-in adaptor fitting which is fitted to a 200/240 bar DIN pillar valve to allow connection of a yoke regulator or filling whip.
blowdown
Procedure of pressurising a diving chamber or saturation habitat.
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.[7]
A metal connector 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.
bomb
Commercial diver slang for high pressure gas storage cylinder of around 50 litres water capacity, also known as a J.
Time used in calculating decompression obligation from decompression tables. For most tables this is defined as the elapsed time from starting the descent to starting the final ascent to the surface, excluding ascent and decompression time.[22]
bottom timer
Device used to measure and record the total time spent underwater during a dive. They do not generally only record bottom time {q.v.}.
bounce dive
1. also surface oriented dive: In commercial diving, bounce diving is the alternative to saturation diving. Any dive where the diver is decompressed directly after the dive.
2. In recreational diving, a bounce dive is a descent to maximum depth and then a direct ascent back to the surface with the minimal bottom time, in a dive profile resembling a spike.
Relationship between pressure and volume at constant temperature in an ideal gas.
breakdown room
An area in a cave where a large amount of material has fallen from the overhead.[7]
breakout
The point at which an object being lifted which is partly embedded in the bottom sediments overcomes the adhesion of the sediments and the force required to lift it drops rapidly to the apparent weight of the object.
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.[16][22] Colloquially just "gas" or "mix".
breathing loop
The gas flow path in a rebreather comprising the diver's lungs, the mouthpiece, valves, hoses, counterlungs and scrubber through which gas is rebreathed.
Broco cutter
A type of thermal lance initiated by an electric arc, in common use for underwater cutting work.
BRUV
Baited remote underwater video. A system for assessing fish populations using video cameras to record fish attracted to a bait canister.
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.
buddy line
A short line between two divers, used to maintain contact during a dive, generally in poor visibility, or other conditions where the divers might become separated and not be able to quickly locate each other.[22]
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.
bundle
A set of gas cylinders fastened together for transportation and manifolded for use as a unit,[23] also cylinder bundle.
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.[17] 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.
bungee wing
Back inflation buoyancy compensator with shock cord lacing or loops which exert a force on the bladder to oppose expansion during inflation.
buoyancy
1. (Main article: Buoyancy). Upward force on an object immersed in a fluid due to pressure exerted over the immersed surface.
2. Resultant upward force of buoyancy and weight of an object immersed in a fluid.
buoyancy check
Procedure to test and adjust weights carried by an underwater diver. The diver wears all the personal equipment to be used for the planned dive, with the scuba tank(s) nearly empty, and the buoyancy compensator empty, in shallow water of the same density as expected on the dive, and adds or removes weights until neutrally buoyant. After the buoyancy check it is usual to distribute the weights for safety, trim and convenience.
buoyancy compensator
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.
buoyancy control
The skill of maintaining the appropriate buoyancy at any time during a dive.
burn tester
Device for measuring the actual capacity of a battery relative to its nominal capacity, and the associated functional time for the device that the battery is powering.[7]
burn time
The effective use time of a battery powered device. Mainly used in reference to dive lights and scooters.[7]
A non-reclosing pressure relief device used to protect a diving cylinder from overpressurization.
butterfly clip
A type of bolt snap with a tapered guide gate opening formed by a protrusion on both the piston and the fixed sides of the gate.[7]
butterfly slider
butterfly D-ring
A plate with two D-shaped cutouts on opposite sides of two to four parallel longitudinal slots for webbing. Used at the top back of the crotch strap in place of a butt-plate (q.v.) on minimalist sidemount harnesses as a clip-on point for equipment.[17]
butt-plate
A rigid or fairly stiff flexible lower extension to a backplate or other scuba harness supporting butt-plate rails, used for clipping off the lower end of sidemount cylinders to the harness.[17]
Diving in a cage designed to protect the diver from potentially aggressive large marine animals, usually sharks
CALM
Catenary anchor leg mooring. Named for the catenary curve of the anchor cables that hold the buoy in position. Also referred to as single buoy mooring, monobuoy or loading buoy.[4]
cam band
A strap, usually of webbing, with a cam action tensioner buckle generally used to secure a diving cylinder to a backplate, stabilisor jacket BCD or other form of diving harness.
camel
A closed lifting bag, usually cylindrical in form.
canister light
Dive light comprising a light head connected to a battery canister by a cable.[21]
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.
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
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.[7]
Decanting from several storage cylinders in succession, generally using a procedure to maximise charge pressures. Often used in partial pressure gas blending.
caustic cocktail
A mixture of water and carbon dioxide absorbent caused by flooding the scrubber, and which may reach the diver's mouth through the breathing loop. The alkalinity depends on the absorbent used.
cave
A naturally occurring cavity in bedrock, or an underwater passage not illuminated by natural daylight, large enough to be entered by a human. Statute 810.13 of the Florida legislature defines a cave as: any void, cavity, recess, or system of interconnecting passages which naturally occurs beneath the surface of the earth or within a cliff or ledge, including natural subsurface water and drainage systems but not including any mine, tunnel, aqueduct, or other manmade excavation, and which is large enough to permit a person to enter. The word "cave" includes any cavern, natural pit, or sinkhole which is an extension of an entrance to a cave.[7]
Directional line markers which point the way to an exit.
cave fill
Filling a scuba cylinder to a pressure significantly above the rated safe working pressure (charging pressure).[7] Illegal in some jurisdictions, and increases risk of catastrophic failure.
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.
cavern
1. Two or more interconnected underground rooms or passages in bedrock, each large enough to be entered by a human.[7]
2. The initial room of an underwater cave system that is illuminated by natural daylight.[7]
3. A naturally occurring cavity in bedrock or an underwater passage, large enough to be entered by a human, which is illuminated by natural daylight, or in which it is possible from all points to see the exit by natural daylight.
cavern dive
Visibility greater than 40 feet, Maximum penetration of 130 feet, Maximum depth of 70 feet, and always within the ambient sunlight area. No passing through restrictions.[7]
C-card or certification card
Plastic card issued to a diver by a certification agency as evidence of completed diver training and experience required for the level of certification.
A sinkhole in Mexico. Generally with vertical overhanging walls or shafts with water that open into a cave system.[7]
CF
clusterfuck
charlie foxtrot
Occasion when the situation diverges notably and usually uncontrollably from the plan, sometimes involving immediate hazard to life and limb, and often involving poor judgement.[21]
CGA
The Compressed Gas Association is an American trade association for the industrial and medical gas supply industries.[24] The CGA publishes standards and practices that codify industry practices. In cases where government regulation is not specific, CGA documents are considered authoritative. CGA V-1 Standard for Compressed Gas Cylinder Valve Outlet and Inlet Connections covers diving cylinder valve outlets.[25] Safety devices like burst disk overpressure protection are specified by the CGA Standard S1.1.
Ring or hook shaped components used for installing and recovering conventional mooring systems. The chaser is hooked around the chain and pulled in the direction of the ancor until it slides onto the anchor shank and is stopped by the crown. The chaser is then used to break the anchor out by pulling directly upwards.[4]
chamber dive
Simulated dive in a hyperbaric chamber pressurised to equivalent pressure to the nominal depth of the dive.[22]
Pressure stamped on a container for a permanent gas to indicate the maximum gauge pressure (measured or corrected to 15°C) that may be applied at the time of filling.[27]
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.[21]
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.[4]
Christmas tree ladder
A boarding ladder which has a single central rail with rigid cantilevered rungs to each side, allowing use while wearing swimfins.[30]
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.
clump weight
A weight used to keep the guide wires of a diving bell aligned.
code of practice
A systematic set of professional standards or written guidelines and rules of procedures to be followed by members of a profession, trade, occupation or organization. A code of practice may be compiled and agreed on by members of a particular profession or written guidelines issued by an official body or a professional association to its members to help them comply with its ethical standards. A code of practice does not normally have the force of law, but is often required or compulsory practice for members of an organisation.
coded welder
Welder who is trained and qualified and assessed as competent for a specified type of welding under specified conditions.
The process of making a well ready for production.
competent person
Person who is able to perform a task or operation safely and according to required procedures. May require formal assessment or accreditation, or registration with government body.[27]
compressed air
Air at a pressure greater than ambient.
compressed neoprene
Foam neoprene that has been compressed to reduce volume. Used for dry suits which are less affected by depth induced buoyancy changes.
compression
The process of increasing the ambient pressure on a diver by descending into the water or pressurising the chamber.[16]
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. Machines which compress gas at higher intake pressures are called boosters
compressor log
Book or file containing records of compressor operation, filling of cylinders and maintenance records.
compressor operator
Person who operates a compressor, either to fill cylinders, or to provide breathing air to surface supplied divers.
confined water
Water that is enclosed and bounded sufficiently for safe training purposes. Generally implies that conditions are not affected by geographic or weather conditions, and that divers can not get lost.[31]
Decompression profile tending to minimise risk of decompression sickness at the cost of more decompression time for a given pre-ascent dive profile.[6]
constant depth blackout
constant pressure blackout
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
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.
contra-indications to diving
Conditions (usually medical) that indicate that a person should not dive.
control compartment
The tissue compartment that dictates the ascent profile of a given dive because it is theoretically the highest risk compartment for DCS.[6]
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.[32]
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.
Pressure required to open a valve. Often applied to the difference in pressure over the diaphragm of a demand valve required to open the valve to start flow. This may differ significantly from the pressure difference required to keep the valve open once flow has been initiated, and the pressure to keep the valve open may vary with flow rate.
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.
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.
crotch strap
Harness strap that passes from the lower part of the harness at the back, through between the diver's legs, to the front of the harness, effectively securing the harness from sliding up along the torso. In safety harness this is often in two parts and allows the diver to be lifted by the harness without risk of falling out.[7]
crushed neoprene
Proprietary material for dry suits manufactured by DUI in a process where the foam neoprene suit material is degassed by exposure to high hydrostatic pressure to reduce the volume after assembly. Less buoyancy variation with depth as the material is less compressible after the treatment.[33]
cuff dump
Dump valve mounted on a drysuit cuff, usually relatively small and non-adjustable.
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
cylinder
1. Diving cylinder: Refillable compressed gas container of water capacity between 0,5 L and 150 L.[27]
2. That part of a reciprocating compressor or booster in which the piston is moved to compress the air. The internal space is cylindrical with a circular section. The external surface is usually finned for air cooling.
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.
Deck decompression chamber: A twin-lock hyperbaric chamber suitable for surface decompression and emergency recompression. Large enough to hold at least two occupants, one of them lying down.
A heavy weight used to control the rise of a lift bag after breakout, or to capsize it to prevent a runaway lift
dead space or dead volume
1. The volume of a breathing apparatus which holds exhaled air, which is subsequently inhaled directly. without passing through a scrubber to remove carbon dioxide and without oxygen addition.
2. The volume of inhaled air, which does not take part in gas exchange either because it remains in the conducting airways or in alveoli that are poorly perfused.
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.[16]
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.
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.[10]
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.
deep water blackout
1. Freediving: An ambiguous alternative term for blackout of ascent following a deep breath-hold dive, in which loss of consciousness occurs as the surface is approached, or at the surface, caused by cerebral hypoxia arising from the rapid drop in the partial pressure of oxygen in the lungs during ascent as the ambient pressure drops and the gas in the lungs expands to surface volume.[34]
2. Scuba and surface-supplied diving: Loss of consciousness in deep air diving at depths below 50 m with no clear primary cause, associated with nitrogen narcosis, a neurological impairment with anaesthetic effects caused by high partial pressure of nitrogen dissolved in nerve tissue, and possibly acute oxygen toxicity. The term is not in widespread use at present.[35]
A condition where the water content of the body is reduced.
delta P
ΔP
δp
Environments where a pressure difference causes flow. Usually refers to cases where the flow is likely to entrain and pull the diver into an enclosed space.
demand helmet
Diving helmet which provides gas supply flow only when the diver inhales.
A substantial heavily weighted line attached to a secure point at the surface, such as a boat or buoy, which can be used by a diver to control position and depth during descent an ascent.[36]
developed pressure
The pressure of the compressed gas in a cylinder at a temperature other than the nominal temperature at which charging pressure is specified. Usually refers to pressure when fully charged at a variation in temperature.[27]
DGPS
Differential Global Positioning System
An enhancement to Global Positioning System that provides improved location accuracy. DGPS uses a network of fixed, ground-based reference stations to broadcast the difference between the positions indicated by the satellite systems and the known fixed positions.
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.
Gas mixture used to dilute the oxygen in the loop of a closed circuit rebreather to a partial pressure suited to the depth.
DIN fitting
also DIN valve, DIN regulator, DIN thread
Usually refers to G5/8" x 14 tpi[37] 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.
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.[21]
A line used by scuba divers as a means of returning to a safe starting point in conditions of low visibility, water currents or where pilotage is difficult.
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.[38]
dive factor
Factor used in gas consumption estimates which allows for increased breathing rate due to conditions other than depth. Range from 1.1 for relaxed, stress free conditions to >3.0 for heavy work.[39]
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, .
Dive Leader
EN 14153-3 / ISO 24801-3 standard competence for recreational scuba diver. A level 3 "Dive Leader" has sufficient knowledge, skill and experience to plan, organise and conduct their dives and lead other recreational scuba divers in open water, to conduct any specialised recreational scuba diving activities for which they have received appropriate training, plan and execute emergency procedures appropriate for the diving environment and activities.
If diving and environmental conditions are significantly different from those previously experienced, they require an appropriate orientation with regard to local environmental conditions, and must have appropriate specialised training and experience to lead on dives which have more demanding operational parameters.[40]
dive marshall
Recreational/club diving equivalent of a diving supervisor. Person who organizes and plans a group dive outing for recreational divers, assesses risk, logs divers into and out of the water and is available at the site to manage incident response.[41]
The total elapsed time spent underwater during a dive.
dive timer
An automatically operated electronic timer which records the elapsed time from the start of a dive.
diver training manual
A publication containing instructional material for diver training. This may relate to a specific certification or a range of certifications, and is usually published either by a certification agency or a diving school for their own use, but may also be published and sold for general consumption.
diver transfer chamber
Hyperbaric chamber connecting other component chambers of a saturation life support system which may be at different pressures.[10]
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.[22]
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.
The diving response exists in all air-breathing vertebrates. It is a series of autonomic responses to apnea which are strengthened by facial cooling and hypoxia. It consists of peripheral vasoconstriction and associated hypertension, vagally induced bradycardia and reduction of cardiac output. This appears to preferentially supply oxygen to the brain. Another aspect is splenic contraction which increases haemoglobin content of the blood.[43]
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. The diving stage is particularly effective for controlling rate of descent and ascent.[22]
diving superintendent
Person with overall responsibility for commercial diving operations at a large installation.[4]
Person in charge of, and responsible for safety of a commercial diving operation. Usually trained, assessed as competent, certified and formally appointed by the diving contractor.[16]
diving system
The complete set of equipment necessary to support a diving operation.[16]
DMAC
Diving Medical Advisory Committee: An independent body of diving medical specialists from Northern Europe which provides advice about medical and certain safety aspects of commercial diving.[45]
DMT
Diving medical technician: A paramedic specialising in diving related conditions.
dome port
A domed window of optical quality glass or plastic which covers the front of an underwater camera or video housing.
Rescue technique where the donor of breathing gas provides it via the primary 2nd stage –- the one from which the donor was breathing –- as it is known to be working and providing the correct gas. The donor then switches to their backup DV, often stowed under the chin by a bungee necklace with a breakaway connection.
donating the secondary
donate the secondary
Rescue technique where the donor of breathing gas provides it via the secondary, or octopus, 2nd stage, and continues to breathe off the primary.
donkey dick
Slang term for the corrugated buoyancy compensator inflation and deflation hose.[7]
Ultrasonic signals reflected from bubble surfaces to identify and quantify gas bubbles present in venous blood.
Dorf arrow
(also line arrow). Triangular plastic line marker with two slots used to indicate the direction of the exit.[7]
downline
down line
A rope leading from the surface down to the underwater workplace which allows a commercial diver to travel directly to and from the job site and to control rate of descent and ascent in the same way as using a shotline. Also sometimes called a jackstay.[46] A downline used for open ocean diving is much the same as a shotline (q.v.), but does not reach all the way to the bottom. An open-ocean downline is weighted at the bottom, and attached to a substantial float at the surface, which may be tethered to the boat. It may be marked at intervals by knots or loops, and may be attached to decompression trapeze system. In some cases a sea anchor may be used to limit wind drift, particularly if attached to a boat with significant windage.[47]
downstream
In the direction of flow. Displaced from the reference point in the direction of flow
Valve in which the closure is downstream of the orifice. Pressure in the line tends to assist in opening the valve. When spring-loaded a downstream valve may open automatically if the pressure difference is excessive, thus functioning as a pressure relief valve
down time
Period when planned activities can not be done due to unforeseen or uncontrollable circumstances.[4]
DP alert
Status of the dynamic positioning system regarding positional accuracy and reliability. Green indicates normal operation, yellow indicates degraded operation and red indicates emergency.[4]
DP footprint
Dynamic positioning footprint: The area around the nominal position to which a dynamically positioned vessel is constrained by the DP system.[4]
A ring shaped like a capital D, usually of stainless steel, stitched or buckled to a diver's harness and used as an attachment point for lifeline, cylinders or other equipment.[21]
Dräger tube
Draeger tube
Indicator tube used for testing breathing gas quality.
Any dive where the diver is transported significantly by drifting with currents during the dive.[21]
drillship
Ship built or converted for offshore well drilling, using dynamic positioning to maintain position in deep water.[4]
drop weight
Weight used during descent and ascent, but left on the bottom at the guideline during the deep part of the dive when it is not needed due to suit compression.[7]
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.
DSV
1. Dive/Surface valve: Valve on the mouthpiece of a rebreather which can be switched between the loop and ambient air at the surface.
2. Diving support vessel: A ship or boat used as a base for diving operations, particularly if designed or fitted out for that purpose.
DSMB
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
dump valve
Valve used to release excess air from a drysuit or buoyancy compensator.[7]
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.[10]
Method of non-destructive testing using electromagnetic induction to detect flaws in conductive materials. It is used to detect cracks in parallel neck threads of aluminium cylinders. Also called Visual Plus inspection. Required for cylinders of AA6351 alloy.
EDTC
European Diving Technology Committee. International committee of European representatives promoting good standards for diving and co-ordinating, where possible, differing standards with the aim of making European professional diving safer.[16][50]
Emergency procedure where the diver makes an ascent from depth after a breathing gas supply failure.
encapsulation
Using a diving suit which completely isolates the diver from direct contact with the environment.[51]
END
Equivalent Nitrogen Depth or Equivalent Narcotic Depth. The depth at which the narcotic effects of nitrogen in a given Trimix mixture at a given depth are equivalent to the effects of air. Used to choose nitrogen content of a Trimix breathing gas for a planned dive profile.
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.
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.
exceptional exposure
A dive in which the risk of decompresssion sickness, oxygen toxixity, and/or exposure to the elements is substantially greater than on a normal working dive.[52]
excursion
excursion dive
Saturation diving where the divers work at a depth deeper or shallower than the saturation depth, after which they are returned to the original saturation pressure.[16]
The combined supply and return hoses and cables for life-line, life-support, power and communications between a diving bell and the diver
extraction ratio
also: ventilation/oxygen extraction ratio
Ratio between minute ventilation and oxygen uptake, the volume rate of gas breathed to the amount of oxygen taken up in the bloodstream. A typical surface extraction ratio of 20 would mean that for every 20 litres of gas breathed, 1 litre of oxygen would be absorbed in the lungs.
Cracking in a material resulting from multiple stress cycles below the ultimate or yield strength. Usually refers to large number of cycles.
feather breathing
Technique for emergency breathing from a free-flowing demand valve where the diver manually controls air flow by opening and closing the cylinder valve.
Feet fresh water. Unit of pressure equal to 1/34 atm. Not a linear measure of depth.
filling ratio
ratio of the mass of gas in a cylinder to the internal volume of the cylinder (water capacity), usually expressed in kilograms per litre, or pounds per cubic foot.[23]
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.
fin keepers
Elastic rubber straps used to help prevent fins from falling off the diver's feet. Also known as fin retainers, fin holders, fin fasteners, fin grips, fin keeps, fin guards, flipper fixers, Y-straps, ankle straps, accessory safety straps, fix fins, grip fins and, in recognition of their French origin, as fixe-palmes. They are called Flossenhalter in German, fissapinne or reggipinne in Italian and sujeta aleta or sujetador de aletas in Spanish. See Swimfin#Attachment.
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.
flood-up valve
valve in a diving bell which allows air to escape and water level to rise
flow
Movement of water through a cave system. Similar in meaning to current in open water.[7]
fluorocarbon elastomers
Synthetic elastomers (rubber) with good performance in high partial pressures of oxygen. Preferred material for o-rings in diving regulators for oxygen service.
flutter kick
finning style where the fins are alternately moved up and down by movements of the full, usually fairly straight, leg.[7] Thrust is developed on both up and down strokes. See also modified flutter kick
Condensation of water vapour on the inside surface of a mask or helmet faceplate, reducing visibility.
forward roll entry
Water entry technique used by scuba divers from a boat or platform too high or unsuitable for backward roll entry. The diver bends forward at the hips and waist and falls forward into the water, making a partial somersault and breaking the water with the cylinder, back and shoulders. Not suitable for heights more than about 2 m.
four-wire system
Voice communications using separate wire pairs for each direction.
frame
Transportable assemblies of gas cylinders connected by a manifold and securely mounted to a structural framework.[4]
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.).
free-flow
1. Constant flow rate air supply
2. Malfunction of a demand regulator where the valve sticks in the open position, allowing a constant rate of flow.
free-flow helmet
A helmet where the breathing air supply is supplied at an approximately constant rate regardless of the diver's instantaneous breathing rate.
free-flow valve
Valve on the side of a demand helmet or full-face mask which opens a free flow of breathing gas into the helmet interior, usually directed over the interior of the viewport, hence alternative term defogging valve, as it is often used to blow condensation from the inside of the viewport.
free gas
Gas at normal atmospheric pressure. Usually refers to the volume of some amount of compressed gas when allowed to expand to atmospheric pressure at constant temperature
free gas volume
Equivalent volume of compressed gas if expanded to atmospheric pressure at constant temperature.[53]
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.
fsw
feet sea water: Unit of pressure equal to 1/33 atm. Not a linear measure of depth. Generally defined as the pressure exerted by a foot depth of seawater having a specific gravity of 1.027 and is approximately equal to 0.445 pounds per square inch.[54]
The space between two cave guidelines. Usually between a main guideline and a branch line.
gap spool
A relatively short length of cave line on a spool used to bridge a gap between lines when making an excursion from the main guideline to a branch guideline.
gaiter
(also gator (US)) Textile legging wrapped around the calf and ankle area over a dry suit to restrict the amount of air that can get into the lower leg area. Also can reduce drag of the suit in this area by smoothing over creases and folds.
gas blender
1. Person who mixes breathing gases for diving, filling diving cylinders with gas mixes such as nitrox or trimix.
2. Qualification to mix breathing gases for diving.[55]
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.
The procedure of changing from one breathing gas mixture to another during a dive. This may be done to avoid oxygen toxicity, hypoxia, or nitrogen narcosis, to accelerate decompression, or to avoid running out of breathing gas. Generally applied to open circuit breathing equipment, where a physical change-over of gas source is made. In closed circuit systems the gas composition is continuously controlled to follow the chosen set-point.
gas reversal point
The depth during an ascent or decompression when the intake of dissolved gas is exceeded by outgassing.
gauge mode
Operating mode for a personal dive computer where the decompression calculation is disabled, and the unit operated only as a timer and depth gauge. Typically used when diving with gas mixtures not supported by the algorithm, in which case decompression tables are used to monitor and control the decompression schedule.
Relation between temperature and pressure in an ideal gas for a constant volume.
general gas equation
general gas law
1. Relation between the variables pressure, volume and temperature for a given mass of a given mixture of an ideal gas.
2. Thermodynamic equation of state for gases for the variables volume, pressure, temperature and number and atomic weight of molecules.
glossopharangeal insufflation
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.[56]
glowstick
A single-use, translucent plastic tube containing isolated substances that, when combined, make light through chemiluminescence
gnarly
A general purpose adjective to denote particularly difficult section of cave, which may be low, tight, silty, etc. or a combination.[7]
go into decompression
Incur a decompression obligation. Generally refers to having a theoretical tissue inert gas concentration that requires the diver to make staged decompression stops during ascent to avoid an unacceptable risk of symptomatic decompression sickness according to the decompression model, algorithm, tables or dive computer in use.
Golden rule
The convention in cave diving that anyone can turn the dive at any time for any reason.[7]
gold line
The permanent main guideline in a cave system, that usually starts well inside the cave. Often yellow or gold in colour.[7]
Goodman handle
A handle used to carry the primary dive light head comprising a rigid slot through which the fingers and palm of the hand are extended, so that the light rests on the back of the hand, facing the direction of the extended fingers.
A satellite navigation system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites
Decompression models based on the principles described by John Scott Haldane.
half+200
An alternative reserve calculation strategy to the rule of thirds for breathing stage cylinders. The cylinder is breathed down to half of its starting pressure plus 200 psi, so that a stage cylinder filled to 3000 psi would be breathed down to 1700 psi before being dropped.[7] This is a less conservative strategy for pressures greater than 1200psi.
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.[21]
hand-off cylinder
A diving cylinder, complete with regulator, which can be handed off to another diver in an emergency, so that the two divers are not obliged to remain in close proximity during the exit and ascent. Transfer of a hand-off cylinder should not compromise either diver's buoyancy to the extent that they cannot make a normal, controlled ascent at neutral buoyancy.
hang
To remain stationary at a specific depth and location, particularly when decompressing.[7]
Voice communications using a cable for transmission.
harness
straps and webbing with associated buckles, D-rings and other accessories used to support the breathing apparatus and secure it to the diver. The harness often has other functions such as supporting weighting and buoyancy control systems and for recovery of the diver from the water.
Hazard identification study: A systematic qualitative assessment of potential hazards and threats to health, safety, equipment, property, environment production or reputation. May be followed by a risk assessment.
Diving in a known hazardous materials environment. The environment may be contaminated by hazardous materials, the diving medium may be inherently a hazardous material, or the environment in which the diving medium is situated may include hazardous materials with a significant risk of exposure to these materials to members of the diving team. Special precautions, equipment and procedures are associated with hazmat diving.
Hazard Identification and Risk Analysis: A risk management procedure for identifying hazards and assessing the risk associated with them and ways to reduce the risk to an acceptable level.
HP
High pressure, generally gas pressures in excess of 30 bar. In diving context gas working pressures do not frequently exceed 300bar, but pressures in hydraulic systems may be considerably higher.
Hogarthian configuration
A scuba combination of backplate, wing, one-piece harness with crotch-strap, regulator arrangement including long-hose primary with a necklaced secondary demand valve, and, if used with twin cylinders, an isolation manifold. Named after Willian Hogarth Main, a developer and proponent of the system.[21]
Hog looped
A scuba configuration where the primary demand valve has a long hose which is routed under the righr arm, usually tucked under a light battery canister on the waist belt of the harness, and around behind the neck to reach the mouth from the right hand side. Part of the Hogarthian configuration (q.v.).[21]
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.
hook breathing
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.
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.
HRC
Hyperbaric rescue capsule. A self contained buoyant hyperbaric chamber intended for emergency evacuation of saturation divers under pressure from a platform which has become so dangerous that it is considered safer to put the divers into the sea in the HRC to be picked up by a rescue vessel for transfer to another hyperbaric system for decompression.
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.
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.
International Diving Regulators and Certifiers Forum, previously International Diving Regulators Forum. A voluntary group of diving regulators and certifying agencies formed to work together toward mutual recognition and to identify and implement best practices in diver training with the object of harmonizing cross border diver training standards outside Europe. Members include Australia, Canada, France, Norway, South Africa and United Kingdom.[58]
IDSA
International Diving Schools Association: Formed with the primary purpose of developing common internationional diving standards for all occupational divers, Offshore, Inshore and Inland, and specialist related non-diving qualifications e.g. Supervisor, DMT and LST.[59]
Metabolic reduction of total gas pressure in the tissues.
inshore diver
Colloquial term for a diver who works on inland dive sites or coastal waters not associated with the oil and gas industry. Also referred to as "civils" as much of this work is connected with civil engineering works.[4]
integrated weight system
Any system for carrying dive weights on the buoyancy compensator or diving safety harness, avoiding the use of a separate weight harness or weightbelt.
internal condition of cylinder
The state of the internal surface of a cylinder regarding corrosion, contamination and cracking.
interstitial emphysema
Gas trapped in the spaces between organs after lung barotrauma.
Intermediate Pressure, or Interstage Pressure. The reduced pressure between the first and second stages of a diving regulator. Also referred to as LP (Low Pressure) in this context.
Isobaric counterdiffusion: The diffusion of gases in opposite directions caused by a change in the composition of the external ambient gas or breathing gas without change in the ambient pressure.
isolation manifold
Connection between two scuba cylinders which when open allows free flow of gas in both directions between the cylinders, but has an isolation valve to block this flow.
isolation valve
1. valve in an isolation manifold (q.v.) used to close the gas passage through the manifold and isolate the contents of the two cylinders. Used to prevent a leak on one cylinder from causing the other cylinder to also lose gas.
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.
J-cylinder
Bulk gas storage cylinder with internal volume 50 litres.
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.[61]
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.
jump
A path from a main guideline to another which is not in contact
jump camera
A camera mounted on a frame, which when lowered to the bottom of a body of water, takes a photograph, usually of the bottom under the camera. The frame constrains the camera to a fixed camera to subject distance, resulting in photographs of uniformly sized areas of bottom, equivalent to quadrats.
Jump jacket
The Jump Jacket[62] is a harness with integral buoyancy jacket specifically designed for commercial diving work with helmets and bells.
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
jump reel
jump spool
A reel or spool with a relatively short line intended to be used as a jump line (q.v.).
A piece of cordage used to secure or lower things; usually it is used where there is a risk of losing the object
LARS
Launch and Recovery System (q.v.)
launch and recovery system
Mechanised system for launching and recovery of a diving bell, diving stage, submersible or ROV from a vessel, offshore platform, dockside or other platform.
An uncontrolled or involuntary muscular contraction (spasm) of the laryngeal cords which causes a partial blocking of breathing in, while breathing out remains easier.
latent hypoxia
While freediving, an arterial pO2 which is sufficient to sustain consciousness at depth, but when ascending drops to hyoxic levels due to the reduction of ambient pressure, associated with ascent blackout.
lay barge
also pipelay barge
Barge on which pipeline sections are assembled, welded and laid on the seabed as the barge is moved forward.[4]
A line connected securely to the diver at one end and anchored at the other end at the diving control point, which is handled by a line tender, and is used to communicate with the diver and provide a means of finding the diver for a surface standby diver, and for assisting the diver to the surface and back to the control point if necessary.
life support
life support system
Equipment vital to the short term survival of the diver. Most notably the breathing gas supply, and for saturation diving, equipment for providing a correctly pressurised environment. In some cases thermoregulatory equipment is also considered life support, and in saturation diving, all of the peripheral systems essential to maintaining a habitable saturation system.
life support supervisor
A senior life support technician appointed by the diving contractor to supervise the operation of saturation life-support systems.[16]
Low volume, close fitting diving helmet, usually with demand valve. Neutrally buoyant, and moves with the diver's head.
line marker
Line arrows, cookies and sometimes clothes pegs. Used to indicate direction to exit, midway point between exits, jumps and personal markers to identify divers on a guide line.
A large boat which provides transport, accommodation and services for vacationing divers
live-boating
Diving from a boat which is under way (not moored). The major implication is that the engines will be running and propellers or thrusters may be engaged while divers are in the water, a significant hazard.
lockout
1. Working diver leaving the closed bell into the water.
2. (Lockout-tagout) Safety procedure when working on a hazardous energy source.[64]
lock
Compartment of a hyperbaric habitat or chamber which can be entered through two or more openings which can be closed and sealed, and the pressure adjusted relative to the adjacent chambers. Used to transfer personnel or equipment between areas of different pressure.
log book
Record of dives kept as proof of experience. Optional for recreational divers, but legally required for professional divers in many jurisdictions.
long hose
5 ft to 7 ft interstage hose used on one of the regulators used by cave and other technical divers, which allows gas sharing through narrow spaces.
The circuit in a rebreather through which the breathing gas passes during a breathing cycle.
loop volume
volume of the breathing loop of a rebreather.
lost buddy drill
standardised procedure followed when a diver realises that their buddy is not where they should be. Procedures may vary depending on the circumstances and training organisations.
lost line drill
Standardised procedure to be followed when the guideline to the surface is lost in a penetration dive, often in conditions of low visibility and darkness.
Diving with low environmental impact. Diving in a way that avoids contact with or disturbance of sensitive organisms and adversely affecting the environment.
LP
low pressure
LP compressor
Low-pressure compressor. Used for breathing air supply for surface supplied air diving.
LP cylinder
Low-pressure cylinder (US) with working pressure less than 2500 psi.
LP port
Opening on the first stage of a regulator through which regulated gas is supplied.
LST
Life support technician: A person who operates and maintains the life support systems of a saturation diving system.
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.[43]
Set of design and manufacturing rules intended to produce uniform and safe products by several manufacturers in an industry.
Marsh Marine connector
One of the popular underwater plug connector systems for diver communications cables.[65]
Martini's law
Rough rule of thumb for estimating nitrogen narcosis effects based on equivalence to consumption of dry martinis: Variously quoted as one martini per 10m or one martini per 50ft depth.
master link
(Rigging) The large heavy duty link to which the legs of a chain sling are attached, and which is the attachment point on the sling for the lifting hook or shackle
maze cave
Cave structure characterised by multiple branches and changes in direction.
Microscopic bubbles which are not detectable by ultrasound or Doppler ultrasound, yet can affect the likelihood of DCS by slowing off-gassing.[6]
micronuclei
Microscopic cavities that function as bubble seeds by absorbing dissolved gas.[6]
mid-water
Significantly distant from the both the bottom and the surface.
medical lock
Small lock on a decompression chamber used for transfer of medical equipment and other supplies into and out of the chamber while the chamber remains under pressure.
Version of the flutter kick finning style which reduces risk of silting by directing thrust more directly backwards. Two techniques exist: One version has the legs bent at the knees so that the fins are placed relatively high and on average are aligned more horizontally. The other version has one fin stationary below the moving fin to deflect downwash.[7] Leg movement is restrained, and ankle movement used for precision manoeuvring.
modified frog kick
Version of the frog kick finning style which reduces risk of silting by directing thrust more directly backwards. Performed with bent knees and fins raised above the line of the torso.
MODU
Mobile offshore drilling unit - a generic term for several classes of self-contained floatable or floating drilling rigs such as drilling vessels, semisubmersibles, submersibles, jack-ups, and similar facilities that can be moved without substantial effort. These facilities may have self-propulsion equipment on board and may require dynamic positioning equipment or mooring systems to maintain their position.[66]
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.
An opening in the floor or base of the hull, platform, or chamber giving access to the water below.
msw
metres sea water: Unit of pressure equal to 1/10 bar. Not a linear measure of depth.[67]
multilevel dive
A dive profile in which the diver remains in more than one distinct depth ranges for a significant period before beginning final ascent to the surface (excluding decompression stops).
mung
A brown organic deposit usually found on the ceilings of caves which is easily dislodged by diver's exhaust bubbles and then drifts down through the water.
Compressor in which gases are compressed more than once, often with cooling between stages. Used to improve efficiency and reduce temperatures.
mushroom valve
A rubber non-return valve flap which is circular or oval, with a stem in the middle to attach it to the holder in the centre of the grating over the orifice.
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.
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.
neck dam
The lower part of a lightweight diving helmet which includes a neoprene or latex neck seal to prevent ingress of water. The alternative is to clamp the helmet to the diver's drysuit.
necklace
Bungee loop attached to the secondary regulator second stage, worn around the neck to store the secondary close under the chin, where it is protected and the diver is immediately aware of a free-flow. With a little adjustment and practice it is possible to pick it up by head and mouth movement alone, not needing use of a hand. The bungee is attached to the second stage by a breakaway connection, often a close-fitting loop over the mouthpiece, so that it can be moved away from the diver's head in an emergency without disturbing the primary second stage or the mask.
Entry into the water in a buoyancy condition that will sink by default. When intentional, generally after reducing buoyancy of BC and, if applicable, dry suit by venting to ensure that the diver will not float back to the surface, but will continue to descend.
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.
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.
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.
normoxic
1. A breathing gas mixture with oxygen content approximating atmospheric air.
2. A breathing gas for diving which contains sufficient oxygen to minimise risk of hypoxia at atmospheric pressure.
1. A significant distance away from the shoreline.
2. Outside the national maritime border, in international waters, though generally still inside the exclusive economic zone.[68]
offshore diver
Colloquial term for a diver who works in the offshore oil and gas industry.[4]
O-lay
Method for installation of sub-sea pipeline for the oil and gas industry. The pipe is constructed in an onshore construction yard, moved into the water and bent into a spiral without causing plastic deformation of the material. When the pipeline is sufficiently long it is transported with the help of tugs to the installation area. At the installation area the pipeline is unwound and pulled over a simple lay barge with stinger and installed on the bottom.[69][self-published source?]
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.
oro-nasal mask
A breathing mask that covers the mouth and the nose only. It may occur independently, as an oxygen mask, or it may occur inside a full face diving mask or helmet to reduce the amount of dead space
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.
overhead
A physical or procedural obstruction to a direct ascent to the surface. Physical overheads include cave, cavern or culvery ceilings, fishing nets, ship hulls, and wreckage. Procedural overheads are generally a decompression obligation.
Instrument for measuring the partial pressure of oxygen in a gas mixture
oxygen clean
Cleaned for oxygen service by appropriate methods and materials and tested for contaminants.Verified that particulates, fibres, oils, greases and other contaminants are absent.[55]
A notional alarm clock, which accumulates hyperbaric oxygen exposure at a rate which increases with higher ppO2 toward the maximum single exposure limit recommended
oxygen compatible
Made from materials which are suitable for oxygen service. Capable of coexisting with elevated oxygen concentrations and a potential source of ignition without flashing, based on a system’s maximum operating pressure and temperature.[55]
oxygen compatible air
Air which has been filtered to reduce contaminants to a level suitable for blending with high pressure oxygen. Air with a reduced level of condensable hydrocarbon mist or vapour.[55]
oxygen design
Design that minimizes any tendency for heat generation, ignition of particulates, or the accumulation of contaminants for an intended partial pressure of oxygen and temperature.[55]
Fraction by volume or pressure of the gas mixture made up by oxygen
Oxygen Pete
Mythical monster associated with CNS oxygen toxicity, also CNS oxygen toxicity seizure.
oxygen service
Suitable for operating with significantly higher levels of oxygen than normal atmospheric air. Often implies special cleaning procedures, use of oxygen compatible materials, and design to reduce ignition risk. System or component that has been designed and tested for oxygen use, has been tested as oxygen clean and is oxygen compatible.[55]
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.
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
pendulum rebreather
Also push-pull rebreather. Rebreather with a single breathing hose from the mouthpiece to the scrubber and counterlung. Gas passes through it in both directions, unlike the one-way breathing loop configuration. The volume of the hose between the mouthpiece and scrubber is dead space
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.
PFO
patent foramen ovale: A form of congenital heart defect that enables blood flow between the left and right atria through a gap in the interatrial septum.
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 end manifold:. Point where flexible underwater hose string is attached to connect seabed pipeline with Single point mooring.[4]
pneumo breathing
Use of the pneumofathometer hose to supply breathing gas to a surface supplied diver in an emergency. Supply can be from the diver's own pneumo hose or from a standby diver's pneumo hose.
pneumofathometer
also pneumo
Instrument to measure depth of a diver using a gauge calibrated in msw, fsw, or often both, which measures the ambient pressure at the diver by measuring the pressure in a hose filled with air with an open end at the diver.
Air or other breathing gas in the chest cavity, often resulting in a collapsed lung.
positive displacement
(of compressor) Compresses gas by reducing volume of compression chamber (cylinder) by mechanical means (piston) to produce higher pressure of the contents.
Relatively small scuba set carried as an independent alternative breathing gas source by a scuba diver.
P-port
A large bore quick connector fitting designed and used by Draeger on diving and firefighting breathing apparatus, which has been used in rebreathers, particularly modifications.
pre-fill external inspection
Examination of the external condition of a pressure vessel and fittings to ensure that it complies with requirements before accepting for filling.[27]
pre-mix
Nitrox blend with high oxygen content used to mix nitrox by topping up the decanted premix with air.
pressure gradient
The rate of change of partial pressure of dissolved gas through a solvent, which is the driving mechanism for diffusion through the solvent. Also loosely used to refer to the difference between the dissolved gas pressure in a tissue and ambient pressure.[6]
primary light
The main light to be used on a dive. Usually the most powerful.
primary regulator
the regulator which the diver intends to breathe from for most of the dive. Particularly when diving with back-mounted manifolded twin cylinders.
primary tie-off
First tie off of the guideline in a penetration dive. This is usually made in a place with free vertical access to the surface.
Push to talk: Voice communication systems which require the user to press a button to transmit. Used with through water systems to conserve battery power.
The underwater work conducted by law enforcement, fire department rescue, and search & rescue/recovery dive teams.
pull
A relatively long pull on a lifeline when used for rope signals. (see "bell" for comparison).
Part of an ascent between the bottom and a decompression stop, between decompression stops, or to the surface. Possibly deriving from the practice of pulling a surface supplied diver up by the umbilical or lifeline.
Pulmonary barotrauma of ascent. Lung over-pressure injury.
purge
To press the purge button on a demand valve to induce a gas flow which is intended to clear the demand valve interior of water or other substances.
purge button
Button or flexible area on the front or side of a demand valve which allows the user to manually open the second stage valve to provide gas flow without inhalation.
purge valve
Valve in snorkel or mask which allows water to drain either under gravity or as a result of exhalation into the air space
push gradient
Tech diving jargon: Decompress at a high gradient factor, particularly when exceeding the baseline M-value.[72]
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.
Oval connector shaped like a chain link with a screw gate on one side.
quad
A group of high pressure gas storage cylinders mounted upright on a frame and manifolded together. Usually in 4, 6, 9, 12, or 16 cylinder arrangements.
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.
Also cobra guard. Frame attached to the top of the cylinders to protect valves, manifold, and regulator first stages from impact with the surroundings.
Also known as rash guard, or rashie, A shirt made of spandex and nylon or polyester to protect against rashes caused by abrasion. These shirts can be worn by themselves, in tropical water, or under a wetsuit.
Rat hat
Ratcliffe diving helmet, Designed by Bob Ratcliffe, later produced by Oceaneering International. No longer in production.[73]
A technique for calculating decompression schedules for scuba divers engaged in deep diving without using dive tables, decompression software or a dive computer.[74][75]
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.
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.
Technical diving philosophy of ensuring that a spare or backup is available for any item of life-support equipment that would immediately endanger the diver if it were to fail.[76]
redundant equipment
duplicated or spare equipment carried by the diver or team to substitute for vital primary equipment in case of a malfunction. In some cases, such as cave lights, multiple redundancy may be desirable. A redundant breathing gas supply is the most common example.
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.
reject criteria
Features, states or conditions which are not acceptable.[27]
Any dive which is done while the tissues retain residual inert gas from a previous dive.
Repex
Method of estimating tolerable repetitive exposure to high partial pressure oxygen.[77]
rescue tether
A short lanyard or strap carried by a surface supplied stand-by diver to be used to tether an unresponsive diver to the standby diver during a rescue. It is attached at one end to a D-ring on the stand-by diver's harness, and has a clip at the other end which may be secured to a D-ring on the casualty's harness to allow the rescuer the use of both hands during the return to the bell or surface.
The ratio of carbon dioxide produced as a metabolic product to the oxygen consumed.
restriction
Section of a cave which is difficult to pass through due to lack of space. A minor restriction is too small for two divers to swim through together, a major restriction requires the diver to remove equipment to fit through.
reverse jump
Procedure to cross a gap during an exit which allows the line to be retrieved without returning to the start point. In the event of a line break or removed primary reel, one diver holds the end of the search line at the break point, and the other searches for the other part of the broken line or the exit while laying line from the reel. When the original line or exit is found, the reel handler signals to the static diver with line pulls and the static diver swims in the direction of the line while the reel handler reels it in, recovering the line.[78]
reverse profile
Repetitive dive which is deeper than the previous dive
Multilevel dive in which a later level is deeper than an earlier level.
Length of shock cord with metal rings and a clip used to control the position of the top end of a sidemounted cylinder.[17] Differs from a regular bungee in having the rings.[17] 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 conduit that provides a temporary extension of a subsea oil well to a surface drilling facility
RMV
Respiratory minute volume: (or minute ventilation) The volume of gas inhaled (inhaled minute volume) or exhaled (exhaled minute volume) from a person's lungs in one minute.
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.
roll-off
Closing of a cylinder valve as a result of scraping contact between the valve knob and the overhead or other surroundings. The left hand knob is more likely to roll-off, closing the backup regulator in the standard twins configuration.[78]
Member of the drilling crew who works under the direction of the driller to make or break connections as drillpipe is tripped in or out of the hole.[4]
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.
run time
Time elapsed since the start of a dive.
running stop
A pause made during ascent to adjust the average ascent rate to the nominal value. For example a nominal ascent rate of 3 m per minute might use an actual ascent rate of about 5 m per minute and make a stop every 3m until the end of the current minute, resulting in a slightly stepped profile with an overall ascent rate corresponding to the nominal rate.[74]
run time schedule
Decompression schedule and dive plan based on elapsed time from the start of the dive, All waypoints and events are specified in terms of elapsed time with start of descent at zero.
R-valve
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.[63]
Surface Air Consumption rate: A measure of air consumption in units of pressure over time, usually psi/minute, adjusted to surface pressure, used to estimate air endurance of a cylinder of specific size. Useful for those who work in imperial units.[49] SAC has a constant value for a given diver and represents gas used on the surface at rest.[39] Surface Gas Consumption (SGC) is an alternative term referring to alternative breathing gas mixtures. Occasionally also termed Surface Consumption Rate (SCR)[79][80]
safe air
Term used for nitrox by ANDI (American Nitrox Divers International)
The combination of equipment and services to operate a saturation diving project. It would include the closed diving bell, the accommodation modules, decompression chamber, life-support systems, gas storage and supply systems, pressurisation equipment, underwater breathing apparatus, and launch and recovery systems. In may also include a hyperbaric evacuation system.
Valve using a standard automotive tyre valve insert, common in low pressure inflation hose female connectors and BC inflation valves.[78]
scientific diving
Diving for purposes of scientific research. The rules and constraints of scientific diving vary in different jurisdictions, but generally allow more options than mainstream commercial diving.
D-ring on scuba harness used to attach to scooter tow line. Usually on front of the harness crotch strap.[78]
SCR
Semi-closed circuit rebreather: A rebreather (q.v.) which either dumps part of each breath to the environment or continuously adds gas and dumps the excess. Compare with closed circuit rebreather (CCR) (q.v.).
Surface Consumption Rate - An alternative term with the same meaning as Surface Air Consumption (SAC) (q.v.). Not to be confused with Semi-closed Circuit Rebreather.
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.
scuba replacement
Surface-supplied diving equipment using portable gas storage cylinders for primary and reserve breathing gas supply. Preferred to scuba for commercial diving applications due to lower perceived risk compared to scuba, and because equipment and procedures are otherwise identical to surface supplied diving using compressors for air supply. Used when logistical constraints or air quality issues preclude use of a compressor.
S-drill
Safety drill. An air sharing exercise based on deploying the long hose primary regulator.
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.
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,
serial number
1. Number stamped on the cylinder by the manufacturer in the shoulder area which identifies the cylinder. In combination with the manufacturer’s identification this will be unique to the cylinder.[27]
2. Character string, including number, marked on an item of equipment by the manufacturer to uniquely identify it.
Reference value for oxygen partial pressure in an electronically controlled closed circuit rebreather. The control system monitors the real time value of oxygen partial pressure in the breathing loop and automatically adjusts the composition by adding gas to keep the concentration between the upper and lower set-points.
Loss of consciousness during a dive associated with occurrence at a shallow depth. Used for several different mechanisms, depending on context, therefore often leading to confusion.
1. see also Shallow-water blackout
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.[57]
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.
shark pod
also: shark shield
Electrical device carried by a diver intended to repel sharks by electrical field pulses.[82]
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
silent entry
An entry technique which minimises noise and splash, suitable for entry from a low platform. The diver sits with feet dangling over or into the water, turns the torso sideways, and takes his weight on his hands, then swings off the surface and drops feet first into the water, slowed by the arms, and lets go with the hands when in the water.[83]:251
A situation when underwater visibility is rapidly reduced to zero, usually when a diver disturbs silt deposits.
silt screw
Device which is inserted into silt or sand to provide an anchor point, such as for a tie-off on a cave line.[17] Silt screws are generally stakes made from small bore plastic (PVC) pipe with a sharpened end.
A loading buoy anchored offshore, that serves as a mooring point and interconnect for tankers loading or offloading gas or liquid products. SPMs are the link between geostatic subsea manifold connections and weathervaning tankers. They are capable of handling any size ship, even very large crude carriers (VLCC) where no alternative facility is available[4]
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.
siphon
Place where water from a stream flows into the ground. also "swallow hole"[7]
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.
skin
also skins, or dive skins
A lycra suit worn by a diver in warm water or under a wet suit.
skip breathing
Breathing pattern where the diver holds each breath a while to conserve breathing gas. Can cause CO2 buildup which can lead to headaches, and reduces physiological reserves in case of an emergency.
S-lay
Method of laying undersea pipelines by welding the sections together on the lay barge and deploying them from the stern horizontally guided by a "stinger" - a structure that supports the pipe string to control its bend radius.[84]
slate
Rigid plastic tablet used for writing messages or notes.
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.
snorkel keeper
Device to hold a snorkel in place at the side of a diving mask by fixing it to the mask strap. See Snorkel construction.
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 alsoHookah.
Metering device to provide constant mass flow of a gas.
sorb
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.
Hunting weapon for shooting fish underwater which propels a barbed steel spear a short distance forward using stored energy from stretched rubber strips or compressed air behind a captive piston.
Mask strap system for full-face masks with three or more straps. (commonly 5)
spitcock
A valve in the side of a copper diving helmet which could be used by the diver to suck in a mouthful of seawater to spit onto the inside face of a viewport to wash off condensation droplets to improve his view.
1. Circular device for storing line, comprising a short tubular section with a large flange at each end. No moving parts, small, compact, economical and reliable alternative to a reel for relatively short lines.
2. Short, straight section of pipe or tube with a flange at each end.
spread
The topside base for (usually) surface supplied commercial diving operations. Also "air spread", "saturation spread" (q.v.).[85]
spring
Place where a concentrated flow of water emerges from the ground.
spring strap
Fin strap using a stainless steel spring to secure the fin to the foot.
spring suit
A wetsuit that covers the torso and has short sleeves and long or short legs
spud can
The foot on a leg of a Jack-up type oil platform designed to spread the load so that the rig does not sink too deeply into the sea-bed.[4]
Dive profile where the diver descends continuously to the maximum depth and stays there for the duration of the dive before ascending directly at a stedy rate to the surface or first decompression stop. This profile provides worst case exposure for gas absorption by the body tissues for a given depth and time, and is assumed for decompression planning using decompression tables.
1. A cylinder used for a stage of a long penetration dive, also known as drop cylinder, which is placed on the distance line to be collected on the return.
2. Also generically used to refer to decompression gas cylinders carried as sling cylinders (q.v.).
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
Early free flow surface supplied diving equipment using a heavy canvas suit, copper helmet and corselet, and weighted boots. Still in use in some parts of the world.[16]
standard operating procedure
Procedure compiled by an organisation prescribing the processes to be followed when performing specified tasks.
stand-by diver
Diver functioning as a safety backup to the working diver. Often on the surface at the dive control point, but ready to enter the water at very short notice on the instruction of the supervisor.
Underwater breath-holding without changing location
steamer
A full one piece wetsuit that covers the torso and the full length of the arms and legs.
stinger
An overboard extension at the stern of an offshore pipe lay barge used to provide additional support at the over bend of an S-lay during offshore construction.[84]
Depth pressure in a saturation system at which divers live between compression and decompression[67]
stride entry
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 buoyancy compensator is held to prevent it riding up the torso on impact. The feet can be brought together after initial impact to limit depth of immersion in moderately shallow water, by applying fin thrust downwards.[15]
stroke
Derogatory term used by DIR zealots to describe divers who do not follow DIR procedures and use DIR approved equipment and configurations.
subcutaneous emphysema
Gas under the skin resulting from lung overpressure injury.[10]
Gauge attached to the first stage regulator and used to monitor pressure remaining in the diving cylinder.
suicide clip
Derogatory term for clip mechanisms which are capable of clipping onto a line or other object without the active and intentional intervention of a user.
suit blowup
excessive inflation of a dry suit leading to uncontrolled ascent.
A passage in a cave that is submerged under water.
sump pack
Tough waterproof bag with watertight seal used to carry dry equipment in caves, including through water filled passages.[17]
superoxide scrubber
Rebreather scrubber which not only removes carbon dioxide from the exhaled air, but also replenishes the oxygen by chemical reaction.
supersaturation
A temporary and thermodynamically unstable condition of a solvent containing more dissolved gas than it can hold in solution over the long term for the prevailing conditions.
supersaturation limit
The theoretical pressure ratio between tissue gas concentration and ambient pressure above which the probability of bubble formation is unacceptably high.[6]
Supervised Diver
EN 14153-1 / ISO 24801-1 standard competence for recreational scuba diver. The level 1 "Supervised Diver" has sufficient knowledge, skill and experience to dive, in open water, to a recommended maximum depth of 12 m, which do not require in-water decompression stops, under the direct supervision of a dive leader, in groups of up to four level 1 scuba divers per dive leader provided the dive leader is capable of establishing physical contact with all level 1 scuba divers at any point during the dive, only when appropriate support is available at the surface, and under conditions that are equal or better than the conditions where they were trained.[86]
Southern Underwater Research Group. An organisation based in Cape Town, which publishes marine ecology field guides, dive travel guides and underwater maps.[87]
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.
surface detection aids
Equipment, such as flags, surface marker buoys, flares, EPIRBs, mirrors, and whistles, carried by divers to maintain contact with dive boats or attract rescue when lost at sea.
surface equivalent volume
Gas volume adjusted to surface pressure. See also free gas volume
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.
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.[88]
A series of surface gravity waves that is not generated by the local wind.
swim line
Line used to space divers across the search area for a swim line search. Each diver holds the line at a distance from the previous diver of somewahat less than twuce the visibility distance. The line is used to keep the divers spaced evenly across the search area while swimming perpendicular to the line.
swimthrough
swim-through
A submerged arch or short tunnel that a diver can swim through without needing to remove equipment. It is usually possible to see natural light at the far end in good visibility and illumination. Usually refers to a natural formation. Technically an overhead environment, but usually with no risk of getting lost, though entrapment may be possible.
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
taut wire system
A constant tension wire from a vessel to a weight on the seabed used as a reference to detect movement of a dynamically positioned vessel from the reference point.[4]
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.
tech ring
D-ring welded to a belt slide so that it can not fold down against the webbing. Intended to make it easier to fit and remove snaps.[7]
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.
test pressure
Pressure at which the cylinder will be hydrostatically tested for revalidation. Usually 1.5 or 1.67 x working pressure.[27]
Ascent controlled by a line from the diver to a fixed point at the bottom. This may be used to control depth and rate of ascent when the diver has inadvertently lost complete control of buoyancy due to loss of ballast weight, so cannot attain neutral buoyancy at some point during the ascent, and needs to do decompression. CMAS require this skill for their Self-Rescue Diver certification.[89]
tethered diving
Diving with a lifeline between the diver and a surface tender.
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
therapeutic schedule
Procedure for hyperbaric treatment involving recompression to relieve symptoms, followed by decompression at a rate unlikely to cause a relapse. Use of special breathing gas, particularly oxygen, to increase the rate of elimination of inert gases is common.[16]
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.
also bolt and nut shackle, bolt shackle. A shackle which uses a bolt as the pin, secured with a nut. The nut may be locked with a split pin for greater security. The bolt may rotate in the shackle under load without great risk of unscrewing the pin
through-water communications
Wireless voice communications transmitted through the water
thumb the dive
Terminate the dive by signalling exit to surface at a time or place other than the planned turning point.[7]
thunderflash
Friction initiated noisy but relatively harmless pyrotechnic device designed for military exercises, with civilian use for diver recall.[90][91]
time to fly
The surface interval necessary after diving to reduce tissue gas concentrations to a level where the risk of decompression sickness due to the pressure reduction experienced in normal commercial airliners is acceptable.[10]
To reconnect a partially filled cylinder and add gas until the pressure is within tolerance of the required charging pressure when corrected for temperature.
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.
triangular profile
A triangular dive profile is one in which, after a descent at constant rate, and a short bottom time at maximum depth, the diver maintains a constant, slow ascent to the surface or first decompression stop. A plot of depth against elapsed time takes a triangular shape.
A seamless transportable compressed gas container, with a water capacity exceeding 150 litres (5.3 cu ft) but not more than 3,000 litres (110 cu ft);[27] Often mounted horizontally in manifolded groups on a trailer or intermodal container frame. Also known as "Kelly tubes" or "Kellys".[92]
TUP
Transfer Under Pressure: Transfer of personnel between hyperbaric environments, usually between a closed bell and a saturation system, or between a portable recompression chamber and a multi-occupant chamber
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
turn the dive
Start the return on a dive which has reached the planned turning point in terms of depth, time, gas supply or distance.[7]
twilight zone
Deeper than 60m in the sea, or the part of a cave or cavern that has dim but discernible ambient light.
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.
Underwater Breathing Apparatus: Equipment used to supply breathing gas to an underwater diver. Usually refers to the part of the system carried underwater by the diver.
UDT vest
Underwater Demolition Team vest, An inflatable surface life-jacket worn by underwater demolition teams. Similar in style and a precursor to the horse-collar style buoyancy compensator.
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.
umbilical cutter
mechanism fitted to a closed bell which allows the occupants to sever the bell umbilical from inside the sealed and pressurised bell in the event of an umbilical snag that prevents bell recovery. The device is typically hydraulically operated using a hand pump inside the bell, and can shear the umbilical at or just above the point where it is fastened to the top of the bell.[93]
A subsurface flow of water returning seaward from shore as result of wave action
underwater blackout syndrome
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.[94][95]
upline
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.[61]
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
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.
vertical entry
vertical drop entry
An entry technique for relatively high drops, up to and sometimes exceeding 3m. The feet are overlapped and the legs kept straight. The body is and head are kept vertical and the mask and DV held against the face with one or both hands, elbows tucked in. The intention is to hit the water vertically, with the least likelihood of knocking off or damaging vital equipment.[83]:249
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.
water capacity
Of a cylinder: The internal volume. The amount of water it would hold at ambient pressure at 20 °C (68 °F)[27]
water trap
Mechanism to trap liquid water carried by the compressed gas
Weightbelt
Ballasted waist belt worn by divers to compensate for excess buoyancy. For scuba and freediving, usually easily removed to establish positive buoyancy in an emergency.
weight harness
Webbing strap system to support diving weights, usually suspended from the shoulders and fastened around the waist. The harness may carry the weights directly, or they may be carried in pockets on the harness. For scuba diving the weights may be arranged for easy shedding.
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. Normally supplied with breathing gas from the surface.
wet filling
Filling scuba cylinders using a water bath for cooling the cylinders.[48]
wet pot
Water filled hyperbaric chamber.
wet notes
A small notebook of waterproof paper carried by some divers[96]
A close fitting, thermally-insulating, foam neoprene diving suit that allows a limited volume and movement of water inside the suit.
whip
Flexible high pressure gas hose with connector at the free end, used for temporary connections. e.g. Filling whip, for filling cylinders, Oxygen whip for oxygen transfer, Blending whip, for decanting gases when blending gas, etc.[8]
whip check
A cable or webbing strap connecting a hose end to the attachment point in addition to the hose end fitting, which restrains the movement of the hose if the connection is broken under pressure. Whip checks connecting two hose ends may also be attached to an anchor point to limit motion further if this is practicable.[97]
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 pressure[99]
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.
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^ abcdefghijklmSouth African National Standard SANS 10019:2008 Transportable containers for compressed, dissolved and liquefied gases - Basic design,manufacture, use and maintenance (6th ed.). Pretoria, South Africa: Standards South Africa. 2008. ISBN978-0-626-19228-0.
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