Glossary of underwater diving terminology

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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.

Video Glossary of underwater diving terminology

A

AA6061

Aluminium alloy 6061 (not subject to sustained load cracking). Currently (2012) used for manufacture of new diving cylinders.

AA6351

Aluminium alloy 6351. This alloy is subject to sustained load cracking and requires periodical eddy current testing. No longer used for new cylinder manufacture, but many cylinders of this alloy are still in service.

ABLJ

see adjustable buoyancy life jacket

absolute pressure

Total static pressure at the reference point: Pressure relative to vacuum.

A-clamp fitting/valve

see yoke fitting/valve.

A-clamp adaptor

see yoke adaptor

active addition

see also Rebreather#Active addition semi-closed circuit

System for semi-closed circuit rebreather feed gas addition in which gas is added to the breathing circuit by a mechanism, regardless of current volume, and excess gas is vented to keep the loop volume within limits. Compare with passive addition

activated carbon

activated charcoal

A filter medium used to remove oil, water and odours from breathing air.

ADAS

Australian Diver Accreditation Scheme: An international commercial and occupational diver certification scheme.

adjustable buoyancy life jacket

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.

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.

A-frame

Part of Launch and Recovery System

Gantry or davit for launching and recovering bells, stages anchors or large ROVs. Usually deployed by hydraulic rams which swing the frame over the deck or overboard as required. The load is hoisted and lowered by cables from the top of the frame.

AGE

see arterial gas embolism

aggressive (decompression)

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.

air dome

A section of cave which traps air or other gas at the top. This gas is not directly connected to the surface.

airlift

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.

air top

1. Completing a planned breathing gas mix by topping up with compressed air.

2. Topping up a partly used breathing gas mix with compressed air, providing a different mixture which is analysed after the fill.

algal bloom

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.

alternative air source

A secondary supply of air or other breathing gas used by the diver in an emergency

alternobaric vertigo

Dizziness caused by a difference of pressure between the middle ears.

altitude diving

Diving at a location where the water surface is at an altitude which requires modification of decompression schedules. (more than about 300 m (980 ft) above sea level.

ambient pressure

Pressure of the surroundings.

anoxia

Completely lacking in oxygen.

AODC

Association of Offshore Diving Contractors, one of the predecessors to IMCA.

aphasia

An impairment of language ability which may range from having difficulty remembering words to being completely unable to speak, read, or write

apnea

1. Suspension of breathing, breath-hold.

2. Freediving.

Aqua-lung

Self contained open circuit underwater breathing equipment consisting of a diving cylinder and diving regulator.

arterial bubble model

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.

arterial gas embolism

Blockage of an artery by a gas bubble. A possible consequence of lung overpressure injury.

articulated loading platform

see ALP

AR vest

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.

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).

ascent rate

The rate at which depth is reduced at the end of a dive. An important component of decompression.

A.S.S.E.T.

Association of SCUBA Service Engineers and Technicians.

ATA

Also ata or atmospheres absolute

Unit of absolute pressure equivalent to standard atmospheric pressure.

atmospheric diving suit

Also ADS

A small one-man articulated submersible of anthropomorphic form which resembles a suit of armour, with elaborate pressure joints to allow articulation while maintaining an internal pressure of one atmosphere.

attack swimmer

see combat swimmer

attendant

see diver's attendant

Autonomous diver

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.

Maps Glossary of underwater diving terminology

B

back gas

Breathing gas carried by a scuba diver in back mounted cylinders. Generally the primary breathing gas for the bottom or longest sector of a dive.

back kick

backward kick

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

backmount

back mount

The practice of carrying a scuba set on the back of the diver, supported by a harness, backplate or stabilisor jacket BCD. Compare with sidemount

backplate

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.

backup regulator

also secondary, safe second or octopus

A second regulator connected to a cylinder or manifolded twin set.

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.

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.

bailout cylinder

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.

bailout set

bailout system

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.

balanced regulator

Regulator designed to provide a consistent demand effort not affected by cylinder gas pressure or depth.

band mask

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.

bands

see cylinder bands

bar

C

cage diving

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.

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.

canoe diving

Scuba diving from canoes, used when the dive site is beyond convenient swimming distances.

carbon dioxide poisoning

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.

carbon monoxide poisoning

The toxic effects of carbon monoxide, usually due to contaminated breathing gas supply.

cardio-pulmonary resuscitation

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

CAS

D

Dalton's law

Gas law describing the relation of component pressures of gases in a mixture to the total pressure.

DAN

see Divers Alert Network

dangly

Derogatory. Any part of a diver's equipment that dangles in a position that might impact the bottom or get caught on the surroundings.

DCAP

Decompression Analysis and Computation Program: Decompression planning software by Bill Hamilton.

DCIEM

Defence and Civil Institute of Environmental Medicine (Toronto, Canada).

DCIEM tables

Decompression tables based on the Kidd-Stubbs model, developed and published by the Defence and Civil Institute of Environmental Medicine.

DCI

see decompression illness

DDC

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.

DCS

see decompression sickness

dead man anchor

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.

decant

To transfer gas between cylinders by differential pressure. No energy is input, flow will stop when pressures are equalised.

decompression

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.

decompression algorithm

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.

decompression buoy

see DSMB

decompression chamber

Hyperbaric chamber used for decompressing divers and emergency therapeutic recompression.

decompression gas

Gas breathed during decompression with a composition designed to accelerate decompression, usually by an increased oxygen content.

decompression illness

Illness caused by decompression. Includes decompression sickness and arterial gas embolism due to lung overexpansion barotrauma.

decompression schedule

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.

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.

decompression stop

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.

decompression tables

Printed cards or booklets that allow divers to determine a decompression schedule for a particular dive profile and breathing gas.

decompression trapeze

also decompression bar

A horizontal bar or bars suspended at the depth of intended decompression stops by buoys used to make decompression stops more comfortable and more secure and provide the divers' surface cover with a visual reference for the divers' position.

deep stops

Decompression stops which are deeper than the deepest stops required by decompression algorithms using dissolved phase models.

deep water blackout

1. see also Freediving blackout. Freediving: Loss of consciousness caused by cerebral hypoxia on ascending from a deep breath-hold dive, when the swimmer does not necessarily experience an urgent need to breathe.

2. Scuba and surface-supplied diving: Loss of consciousness due to extreme nitrogen narcosis.

dehydration

A condition where the water content of the body is reduced.

demand helmet

Diving helmet which provides gas supply flow only when the diver inhales.

demand valve

Mechanism for providing the user with breathing gas flow only when required.

depth gauge

A pressure gauge calibrated to measure depth as a function of ambient pressure.

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.

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

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.

diffusion limited

Decompression hypothesis that the uptake and elimination of inert gas is limited by diffusion rates in the tissues

diluent

also sometimes dil

Gas mixture used to dilute the oxygen in the loop of a closed circuit rebreather to a partial pressure suited to the depth.

DIN fitting

also DIN valve, DIN regulator, DIN thread

Usually refers to G5/8" x 14 tpi parallel thread fittings used to connect a cylinder valve to a filling connection or regulator first stage. Available in 200 bar and 300 bar versions which should only be inter-connectable in safe combinations.

DIN plug

Screw in adaptor which can be used with many recent 200/240 bar DIN cylinder valves to allow connection of Yoke regulators or filling whips.

DIR

also Doing It Right

A holistic approach to scuba diving, which encompasses several essential elements, including fundamental diving skills, teamwork, physical fitness, and the use of streamlined and minimalistic equipment configurations.

distance line

also penetration line or guideline

A line used by scuba divers as a means of returning to a safe starting point in conditions of low visibility, water currents or where pilotage is difficult.

dive computer

also decompression computer

A device used by a scuba diver to measure the time and depth of a dive so that a safe ascent profile can be calculated and displayed so that the diver can avoid decompression sickness.

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.

dive flag

Flag used to indicate that there are divers in the water. There are two versions: the international code letter flag 'Alpha', , and the red flag with white diagonal bar, .

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.

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.

divemaster

A professional level recreational diver who leads a group of less experienced or visiting divers underwater.

dive profile

The variation of depth with elapsed time during a dive, often depicted as a graph.

dive tables

see decompression tables

dive time

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.

Divers Alert Network

also DAN

A non-profit organization for assisting divers in need and medical research on recreational scuba diving safety.

diver's attendant

also dive tender and line attendant

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.

diving bell

A rigid chamber suspended from a cable and used to transport divers to depth and back to the surface.

diving chamber

1. A simple form of submersible vessel to take divers underwater and to provide a temporary base and retrieval system in the depths (diving bell).

2. A land or ship-based hyperbaric chamber to artificially reproduce the hyperbaric conditions under the sea.

diving contractor

Legal persona responsible for commercial diving operations.

diving depth

Generally the maximum depth to which the diver is exposed during a dive.

diving heavy

E

EAD

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.

EAN

Enriched Air Nitrox, see Nitrox

ear beer

A mixture of alcohol and acetic acid in water used as a drying agent and disinfectant to rinse the ears after diving, to prevent ear infections.

ear clearing

Equalising the pressure in the middle and external ear by opening the Eustachian tubes. Several techniques are used.

ECCR

Electronic closed circuit rebreather. Sometime ECCCR for electronically controlled closed circuit rebreather.

eddy current test

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.

E-L algorithm

also Thalmann algorithm, (VVAL18)

Exponential-Linear algorithm of 2008 US Navy tables, assumes exponential ingassing and a combination of linear and exponential outgassing rates.

electro-galvanic oxygen sensor

An electro-chemical fuel cell which produces a voltage proportional to the partial pressure of oxygen.

emergency position indicating radio beacon

also emergency beacons or EPIRB,

Emergency position-indicating radio beacons are tracking transmitters which aid in the detection and location of boats and people in distress at sea.

emergency swimming ascent

also ESA, Controlled emergency swimming ascent, CESA

Emergency procedure where the diver makes an ascent from depth after a breathing gas supply failure.

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.

EPIRB

see emergency position indicating radio beacon

equalise

Balance pressure of a gas filled space with the ambient pressure, by adding or venting gas, to prevent barotrauma or pressure damage.

equivalent air depth

also EAD

A way of approximating the decompression requirements of nitrox mixtures at depth by comparison with the depth at which air would require the same decopression.

equivalent narcotic depth

also END

A way of expressing the narcotic effect of a breathing gas mixture at depth by comparison with the depth at which air would have a similar effect.

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.

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.

excursion umbilical

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.

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F

faceplate

Viewport of a full face mask or helmet

farmer john

Wet suit that covers the torso and legs only; it resembles a bib overall or salopettes.

fatigue cracking

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.

FFM

see full-face mask

ffw

FFW

Feet fresh water. Unit of pressure equal to 1/34 atm. Not a linear measure of depth.

filtration

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.

first stage

see Diving regulator#First stage

Diving regulator component which reduces gas pressure from stoage pressure in the cylinder to interstage pressure for supply to the second stage and for suit and BC inflation.

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.

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. Thrust is developed on both up and down strokes. See also modified flutter kick

fogging

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.

free air

G

gap

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.

gas blending

Mixing breathing gases for diving, filling diving cylinders with gas mixes such as nitrox or trimix.

gas embolism

Blockage of blood vessel by a bubble of gas.

gaseous impurities

Contaminants in the compressed breathing air or gas mixture which are in gaseous form. Compare with particulate and condensate impurities.

gas fraction

The fraction by molecular count, volume or pressure (they all come to the same thing) of a specific gas in a mixture of gases.

gas panel

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.

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.

gauge pressure

Gauge pressure is zero-referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure

gauge snubber

A needle valve or small bore orifice between the pressure supply and the gauge which damps pressure fluctuations.

Gay-Lussac's law

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.

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.

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.

gold line

The permanent main guideline in a cave system, that usually starts well inside the cave. Often yellow or gold in colour.

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.

GPS

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

gradient factor

A way of modifying the M-value of a decompression algorithm to a more conservative value. Often used to bias the algorithm towards deeper stops.

guideline

guide line

see distance line

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H

Haldanian

also Haldanean

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. This is a less conservative strategy for pressures greater than 1200psi.

half duplex

Voice communications system where users take turns to send and receive.

half mask

Diver's mask which covers the eyes and nose but not the mouth.

half times

see tissue half times

halocline

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.

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.

hard hat diving

Surface supplied diving, generally in professional diving, either wearing a modern diving helmet or the old-style standard diving dress and brass helmet.

hardwire communications

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.

hat

Commercial diver term for diving helmet.

HAZID

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.

hazmat diving

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.

heavy gear

see standard diving dress

heliox

Mixtures of helium and oxygen for use as a breathing gas.

heliair

Trimix blends made by topping up helium with air.

helicopter turn

Manoeuver in which a (usually horizontally trimmed) diver uses small fin movements to rotate on the spot on a vertical axis.

helium

An inert gas which is used as a component of breathing gas mixtures for deep diving.

helium analyzer

An instrument used to identify the presence and concentration of helium in a mixture of gases

helmet diving

see hard hat diving

Henry's law

Description of the relation between solubility of a given gas in a given liquid as pressure varies.

HID light

High intensity discharge light: Used in cave diving light heads (q.v.).

HIRA

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.

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.).

homebrew

Amateur blended mixed gas.

hood

Close-fitting thermal head protection, usually neoprene foam, but also latex on some dry suits.

hookah

also hooka and airline diving

Also known as airline diving; surface supplied diving where the breathing air is supplied to the diver by a simple hose. The diver usually breathes through a mouth held demand valve.

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.

hopcalite

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.

horse collar

see adjustable buoyancy lifejacket

hot mix

breathing gas mixture with a high percentage of oxygen for the depth at which it is used. Using a gas mixture with a high partial pressure of oxygen.

hot water suit

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.

HPNS

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.

HSE

Health and Safety Executive (UK), Government department responsible for occupational diver safety in UK.

H-valve

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.

hydro

Slang/abbreviation for hydrostatic test(q.v.)

hydrostatic pressure

Pressure due to the weight of the water column above a point at depth.

hydrostatic test

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.

hydreliox

Deep diving breathing gas mixture of hydrogen, helium and oxygen.

hydrox

Deep diving breathing gas mixture of hydrogen and oxygen.

hyperbaric evacuation system

System for evacuating divers under pressure from a saturation system in an emergency.

hyperbaric lifeboat

A lifeboat with a hyperbaric chamber and life support system built into it for evacuating saturation divers in an emergency.

hyperfilter

Additional filter to produce air of oxygen compatible quality. This may be built into the filling system or temporarily connected when required.

hypercapnia

Excessive level of carbon dioxide in the body.

hyperventilation

1. A deliberate deep breathing to reduce blood carbon dioxide level to extend the duration of a free dive.

2. Rapid breathing as the body's response to hypercapnia.

3. Rapid, often shallow breathing, associated with panic.

hyperventilation-induced blackout

see underwater blackout syndrome

hypocapnia

Abnormally low tissue and blood carbon dioxide concentration.

hypothermia

A lowering of deep body temperature due to heat loss.

hypoxia

Abnormally low tissue oxygen concentration: Insufficient oxygen in the body to support normal activities or consciousness.

hypoxic training

prolonged underwater distance swimming or extended breath-hold intervals.

src: upload.wikimedia.org

I

IDRF: 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.
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.
IMCA: International Marine Contractors Association.
inert gas: A gas which is not metabolically active, used to dilute the breathing gas.
ingassing: Inert gas uptake in body tissues during a dive or other hyperbaric exposure.
inherent unsaturation: 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.
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.
IP: 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 blackout: see constant depth blackout
isobaric counterdiffusion
ICD: 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.

src: www.hellionpowersystems.com

J

jackstay: A line secured at both ends to serve as a support or guide.
Jack-up rig: 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.
Jersey upline: see upline
JIC fitting: A type of pipe and hose fitting with a 37-degree flare seating surface. Commonly used in umbilical hose connections.
JIM suit: An atmospheric diving suit manufactured by Underwater Marine Equipment Limited.
jocking strap: webbing strap system used with diving helmets to hold the helmet assembly down on the diver to prevent buoyancy lifting it when underwater.
Jonline: 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.
job safety analysis
JSA: 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 is a harness with integral buoyancy jacket specifically designed for commercial diving work with helmets and bells.
jump line: 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.).
J-valve: Scuba cylinder valve with lever operated reserve mechanism.

src: upload.wikimedia.org

K

kayak diving: Diving from a special purpose kayak used to get to the site where the distance from a suitable entry and exit point is inconvenient for shore diving.
K-valve: Scuba cylinder valve without reserve mechanism.

Scuba Diving Glossary - The Scuba Doctor

src: www.scubadoctor.com.au

L

lanyard

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.

laryngospasm

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.

lazy shot

Shot line (q.v.) which does not reach the bottom

LDS

Local dive shop

LED

Light emitting diode, commonly used in dive lights.

lifeline

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.

life support technician

see LST

lifting bag

A robust and air-tight bag with straps, which is used to lift heavy objects underwater by means of the bag's buoyancy.

light head

The part of a canister light (q.v.) which emits light, and is held in the hand or mounted on the helmet.

lightweight helmet

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.

line tender

see diver's attendant

line trap

Narrow gap where the guide line passes but divers can not get through.

lipid pneumonia

A lung inflammation (pneumonia) that develops when lipids enter the bronchial tree

live-aboard

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.

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.

longshore current

Mass transport of water along a shoreline, generally due to wave action at an angle to the shoreline.

loop

also breathing loop

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.

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.

lung packing

see glossopharangeal insufflation

src: upload.wikimedia.org

M

mammalian diving reflex

also diving response

A reflex response to breathhold and chilling of the face diving response expressed by the cardiovascular system, which exhibits hypertension, bradycardia, oxygen conservation, arrhythmias, and contraction of the spleen.

manifold

see twin cylinder manifold

manufacturing standard

also manufacturing code

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.

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.

MCCR

Manual Closed Circuit Rebreather: A closed cirduit rebreather which relies on the diver to control the gas mixture in the loop.

microbubbles

Microscopic bubbles which are not detectable by ultrasound or Doppler ultrasound, yet can affect the likelihood of DCS by slowing off-gassing.

micronuclei

Microscopic cavities that function as bubble seeds by absorbing dissolved gas.

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.

mix

Short for trimix breathing gas

mixed gas

Breathing gas for diving other than air, but usually implies a helium based mixture.

MOD

Maximum operating depth: Limiting depth for safety based on partial pressure of oxygen of a breathing gas mixture.

modified flutter kick

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. 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.

monofin

A type of swimfin typically used in finswimming and free-diving. It consists of a single surface attached to footpockets for both of the diver's feet.

molecular sieve

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.

monkey diving

The use of sidemount configuration and procedures with a single cylinder.

moonpool

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.

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.

multiple stage compressor

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.

M-value

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.

File:OctopushTwoPlayers28092009.JPG - Wikimedia Commons

src: upload.wikimedia.org

N

NACD

National Association for Cave Diving

narcs

see nitrogen narcosis

Navy SEAL

A US Navy trained combat diver.

NDL

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.

NEDU

US Navy Experimental Diving Unit

negative buoyancy

also just negative in context

Buoyancy less than weight. Insufficient upward force due to buoyancy to keep afloat or remain at constant depth

negative buoyancy entry

negatively buoyant entry

negative entry

Entry into the water after reducing buoyancy of BC and, if applicable, dry suit by venting to ensure that the diver will not float back to the surface, but will continue to descend

neo-Haldanian

also neo-Haldanean

Decompression models based on later modifications of the principles described by John Scott Haldane.

neoprene

Synthetic elastomer used in the form of foamed sheets as the material for most wetsuits and some drysuits.

neutral buoyancy

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.

Newtsuit

An atmospheric diving suit designed and originally built by Phil Nuytten.

net cutter

A handle with a hooked blade used to cut netting or cordage to free the diver from entanglement

NFCI

Non-freezing cold injuries: Permanent tissue damage due to low temperature exposure without any freezing damage.

niggles

Minor symptoms characteristic of mild decompression sickness.

night diving

Diving during the hours of darkness.

NiMH

Nickel-metal hydride. A technology for rechargeable battery cells.

nitrile

A synthetic elastomer used for most standard O-ring seals.

nitrogen

The major component gas of air and many breathing gas mixtures used in diving. Important in diving as an active agent in nitrogen narcosis and decompression sickness.

nitrogen narcosis

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.

nitrox

also Enriched Air Nitrox (EAN)

Mixture of nitrogen and oxygen for use as breathing gas. Usually with oxygen percentage higher than air.

nitrox stick

A mixing tube used to blend oxygen with air before compressing to make nitrox breathing gas.

NOAA

National Oceanographic and Atmospheric Administration (US)

nominal capacity

Volume of free gas contained by a scuba cylinder when filled to charging pressure at constant temperature.

No-mount diving

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.

NSS

National Speleological Society

nystagmus

An oscillation of the eyes alternating a slow eye movement in one direction, and a fast eye movement in the other direction

src: upload.wikimedia.org

O

octopus breathing

Sharing air using an octopus regulator

octopus regulator

also octo reg

A secondary demand valve fitted to a first stage diving regulator for use as an alternative air source for another diver in case of an emergency.

off-gassing

see outgassing

offshore

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.

offshore diver

Colloquial term for a diver who works in the offshore oil and gas industry.

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.

on-gassing

see ingassing

onshore

see inshore

open circuit

Breathing apparatus which discharges exhaled gas into the environment, without any further use.

OOA

Out of air: An emergency situation where the supply of breathing gas to the diver has stopped.

open water

1. Water where there is no physical obstruction to a direct ascent to the surface.

2. Water which is open to influences by weather and climatic conditions.

OPV

Over-pressure valve. A pressure relief valve which automatically opens at a set pressure to allow excess gas to escape.

O-ring

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

outgassing

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.

overweighting

P

panic

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

parallel compartments

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

partial pressure

(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.

passive addition

see also Rebreather#Passive addition semi-closed circuit

Feed gas addition system for semi-closed circuit rebreathers which discharges a part of the gas in the breathing circuit. fresh gas is added when the volume of the circuit decreases during inhalation and triggers the addition valve. Compare with active addition

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

penetration

Entering a region with no direct vertical access to the surface, such as a cave or the interior of a wreck.

penetration line

see distance line

percolation

Cave diving: Bubbles making their way to the walls and the ceiling of the cave and dislodging silt.

perfusion

The process of delivery of blood to a capillary bed in the biological tissue.

perfusion limited

The assumption in a decompression model that perfusion has the dominant influence on gas uptake and release.

personal locator beacon

also PLB

Radio beacons for personal use which are intended to indicate a person in distress who is away from normal emergency services.

personal safety equipment

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.

photo quadrat

Q

quick link

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.

quadrat

R

rams head

Also cobra guard. Frame attached to the top of the cylinders to protect valves, manifold, and regulator first stages from impact with the surroundings.

rapture of the deep

see nitrogen narcosis

rash vest

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.

ratio decompression

also ratio deco

A technique for calculating decompression schedules for scuba divers engaged in deep diving without using dive tables, decompression software or a dive computer.

rebreather

Breathing apparatus which recycles most of the exhaled gas, removing carbon dioxide and topping up oxygen before the gas is breathed again.

reciprocating compressor

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.

reclaim helmet

Diving helmet with a reclaim gas regulator allowing exhaled gas to be safely returned to the surface through an additional hose on the umbilical.

reclaim system

System for recovering helium based breathing gas used by divers and recycling it.

recompression

Subjecting a diver to pressure after an ascent from a dive as treatment for decompression illness or to prevent decompression sickness. Preferably done in a recompression chamber, but occasionally done as in-water recompression.

recompression chamber

A hyperbaric chamber used to treat divers suffering from certain diving disorders such as decompression sickness.

recovery breathing

see hook breathing

recreational diving

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.

Recreational Dive Planner

also RDP

A no-stop decompression table developed by DSAT.

redundancy

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.

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.

red tide

see algal bloom

reel

Mechanism used to store, deploy and recover long lengths of line.

regulator

1. A mechanism for controlling the output pressure of a high pressure gas supply.

2. As 1, with a demand valve (q.v.) incorporated which provides the diver with breathing gas at ambient pressure.

regulator freeze

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.

repetitive dives

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.

reserve gas

Gas which is not intended to be used during the dive, and is reserved for contingencies.

reserve valve

Cylinder valve with a lever operated bypass valve to release the gas below reserve pressure

residual gas

Gas remaining in a cylinder from the previous fill.

residual nitrogen

Nitrogen in excess of normal atmospheric saturation remaining in the diver's tissues after a dive.

residual nitrogen time

also RNT

Time penalty in a repetitive dive equivalent to time at depth which would produce the residual nitrogen in the diver at the start of the dive.

residual pressure

Pressure of the gas remaining in a cylinder from the previous fill.

Pressure of gas remaining in a partly used cylinder.

respiratory quotient

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.

reverse profile

Repetitive dive which is deeper than the previous dive

Multilevel dive in which a later level is deeper than an earlier level.

RGBM

also reduced gradient bubble model

A bubble model decompression algorithm developed by Bruce Wienke.

Rimbach system

System of touch contact signalling. Push forward = go, pull back = back up, squeeze = stop.

ring bungee

S

SAC rate

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. SAC has a constant value for a given diver and represents gas used on the surface at rest. Surface Gas Consumption (SGC) is an alternative term referring to alternative breathing gas mixtures. Occasionally also termed Surface Consumption Rate (SCR)

safe air

Term used for nitrox by ANDI (American Nitrox Divers International)

safe second

Obsolete term for backup regulator.

safety reel

Reel for use in an emergency, usually for searches to find lost buddy or lost guideline or to jump a line break. Relatively short line.

safety stop

A voluntary (not required by the decompression schedule) additional decompression stop intended to reduce risk of decompression sickness.

salt water aspiration syndrome

A reaction of the lungs to inhalation of a mist of salt water

samba

Contractions experienced by breathhold divers when approaching hypoxic blackout.

saturation

Condition where the inert components of the breathing gas dissolved in a diver's tissues is in equilibrium with the gas in the lungs.

saturation diving

Diving procedure where the divers remain pressurised for periods of several days or weeks and decompress only at the end of the period.

saturation spread

Saturation diving system.

SCBA

Self-contained breathing apparatus (not for underwater use).

schrader valve

Valve using a standard automotive tyre valve insert, common in low pressure inflation hose female connectors and BC inflation valves.

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.

scooter

Diver propulsion vehicle used by scuba divers to increase range underwater.

scooter ring

D-ring on scuba harness used to attach to scooter tow line. Usually on front of the harness crotch strap.

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.

screw gate carabiner

A clip mechanism which can be locked in the closed position by turning a threaded barrel.

scrubber

Canister containing material (sorb) which chemically combines with carbon dioxide to remove it from the gas passed through the canister.

scuba

also SCUBA

Self-contained underwater breathing apparatus. May be open or closed circuit.

scuba orienteering

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.

search line

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.

search pattern

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.

secondary drowning

A complication of aspiration of water or other fluids into the lungs.

second stage

see demand valve

The part of a diving regulator which provides pressure reduction from intermediate pressure to ambient pressure on demand. Demand valve.

semi-dry suit

A wet suit with wrist and ankle seals, and usually a more watertight zipper than usual, to reduce flushing of water through the suit.

separator

Device which facilitates the separation of liquid particles from the compressed gas, usually with a drain to periodically remove accumulated liquid from the system.

serial compartments

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.

2. Character string, including number, marked on an item of equipment by the manufacturer to uniquely identify it.

SGC

seeSAC

Surface Gas Consumption

shallow water blackout

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.

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.

shock cord

see bungee cord

shore diving

Diving from a shore entry.

shot line

A rope between a float at the surface, and a sufficiently heavy weight holding the rope approximately vertical.

sidemount

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.

sidemount staging

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.

silica gel

A desiccant filter medium used to adsorb water.

silt out

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. Silt screws are generally stakes made from small bore plastic (PVC) pipe with a sharpened end.

single point mooring

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

sinkhole

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

sintered

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"

skandalopetra

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.

slate

Rigid plastic tablet used for writing messages or notes.

sling cylinder

Independent cylinders with their own regulators carried clipped to the harness at the side of the diver.

slingshot valve

see Y-valve

A cylinder valve with two valved outlets angled to left and right of the centreline

slob knob

Flexible extension used for operating valve knobs on a manifold

SMB

Surface marker buoy.

snag line

Line used for underwater search intended to snag on the target. May be dragged by boats or by divers. May be weighted if dragged over a smooth bottom.

snap shackle

A clip connector mechanism which locks when closed, can be operated without tools, and can usually be released under load.

snoopy loop

A heavy duty elastic band made from a slice of inner tube.

snorkel

Tube with a bend and mouthpiece used for breathing air from above the water surface when the wearer's mouth and nose are submerged.

snorkeling

also snorkelling

Swimming at the surface of the water while breathing through a snorkel. the snorkeller is almost always equipped with a diving mask or swim goggles, and usually swimfins.

snorkel keeper

Device to hold a snorkel in place at the side of a diving mask by fixing it to the mask strap

Snuba

Snuba is portmanteau of "snorkel" and "scuba" referring to a proprietary recreational surface supplied underwater breathing system supplied from a cylinder mounted on a small raft towed by the diver. see also Hookah.

solo diving

The practice of scuba diving alone, (without a "dive buddy/in-water standby diver").

sonic orifice

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.

speargun

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.

spearo

Slang term for breathhold spearfisher.

speleogen

Dissolution features in bedrock.

speleothem

Also known as a cave formation: A secondary mineral deposit formed in a cave.

SPG

submersible pressure gauge

SPHL

Self-propelled hyperbaric lifeboat

spider

Mask strap system for full-face masks with three or more straps. (commonly 5)

SPM

see single point mooring

spool

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.

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.

SPUMS

South Pacific Underwater Medicine Society

square profile

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.

squeeze

see barotrauma

Injury or discomfort caused by increase or decrease in volume of gas space in the diver's body or equipment due to a change in ambient pressure.

SSDE

Surface supply diving equipment.

stage

see diving stage

stage cylinder

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.).

staged decompression

The practice of making decompression stops.

stage-only diving

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

standard diving dress

also standard dress,copper helmet or heavy gear

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.

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.

static apnea

static apnoea

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.

{{term|1=stop]]

see decompression stop

storage depth

also living depth

Depth pressure in a saturation system at which divers live between compression and decompression

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.

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.

submersible compression chamber

see closed bell

submersible pressure gauge

also SPG

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.

sump

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.

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.

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.

supervisor

see diving supervisor

supply lock

Small lock on a saturation life support habitat for transfer of relatively small items.

SurD

see surface decompression

SURG

Southern Underwater Research Group. An organisation based in Cape Town, which publishes marine ecology field guides, dive travel guides and underwater maps.

surf

The mass or line of broken water formed by waves breaking on a shore or reef

surface compression chamber

A hyperbaric chamber for surface use for routine decompression or therapeutic recompression.

surface decompression

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

surface interval

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.

surface marker buoy

also SMB

A buoy towed by a diver to indicate location to people at the surface.

surface orientated diving

Any diving operation in which the diver is decompressed to surface pressure after the dive. Opposite to saturation diving.

surge

Reciprocating water movement parallel to the bottom surface caused by the passing of a wave overhead

sustained load cracking

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.

swell

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.

T

taravana

A form of decompression sickness found among Polynesian island natives who habitually do multiple repetitive deep breath-hold dives.

task loading

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.

technical diving

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.

tension leg rig

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.

tethered ascent

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.

tethered diving

Diving with a lifeline between the diver and a surface tender.

Thalmann algorithm

The Exponential/linear decompression algorithm used in the 2008 US Navy decompression tables

therapeutic recompression

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.

thermocline

A thin but distinct layer in a large body of fluid, in which temperature changes more rapidly with depth than it does in the layers above or below

thermodynamic decompression model

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.

thirds

see rule of thirds

three part shackle

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.

thunderflash

Friction initiated noisy but relatively harmless pyrotechnic device designed for military exercises, with civilian use for diver recall.

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.

tinnitus

The perception of sound within the human ear in the absence of corresponding external sound

tissue compartments

Imaginary tissues which are designated as fast and slow to describe the rate of saturation.

tissue half times

The time it takes for the tissue to take up or release 50% of the difference in dissolved gas capacity at a changed partial pressure.

TNT

1. Total Nitrogen Time: Equivalent time of hyperbaric exposure for a repetitive dive used with some decompression tables.

2. Trinitrotoluene, a high explosive

top up

To reconnect a partially filled cylinder and add gas until the pressure is within tolerance of the required charging pressure when corrected for temperature.

touch contact signals

see Rimbach system

Toynbee manouevre

Method of equalising the middle ears by pinching the nose and swallowing.

trait anxiety

A tendency to respond with anxiety in the anticipation of threatening situations.

transect

A path along which one counts and records occurrences of the phenomena of study.

transfill

also decant

Fill cylinder with gas by transfer from a cylinder with higher pressure.

transfill whip

High pressure hose and end fittings used to decant between cylinders. Usually includes purge valve and may include pressure gauge.

trauma shears

also bandage scissors or paramedic shears

Blunt tipped slightly serrated shears with angled blades sometimes used by divers as a safety cutting implement in place of a knife or line cutter.

travel gas

Gas mixture used for descent and ascent when the bottom gas is not suitable for breathing at shallower depths.

traverse

Pass through a cave by entering at one point and exiting at another.

tremie

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.

triglide

see belt slide

trilam

Material used for dry suit shells made of a layer of waterproof rubber laminated between two layers of woven textile.

trimix

Mixture of three gases for breathing. Oxygen, nitrogen and helium are the gases used. The gas fractions will usually be specified.

trim weight

Ballast weight placed to improve a diver's trim.

tube

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); Often mounted horizontally in manifolded groups on a trailer or intermodal container frame.

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

turbidity

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.

twilight zone

Deeper than 60m in the sea, or the part of a cave or cavern that has dim but discernible ambient light.

type 1 wet bell

Wet diving bell (q.v.) with no direct supply of gas and services to the bell. Diver umbilicals lead directly to the surface control point.

type 2 wet bell

Wet diving bell (q.v.) with umbilical supply of gas and other services to the bell, from which they are distributed to the divers umbilicals from a control panel in the bell.

U

UBA

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.

UHMS

Undersea and Hyperbaric Medical Society

umbilical

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.

undertow

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.

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.

upstream

Against the flow.

upstream valve

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.

upwelling

An oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water

V

Valsalva maneuver

Technique for equalising the middle ear by moderately forceful attempted exhalation against a closed mouth and blocked nose

valve cage

structure or frame fitted to scuba cylinder to protect the cylinder valve or manifold and regulator first stage from impact damage and roll-off.

valve drill

Safety exercise in which the diver shuts down, tests regulators and re-opens the manifold valves on a twin set in a specific order.

valve guard

protective structure or frame fitted to the top of a bulk storage cylinder to protect the cylinder valve from mechanical damage.

Van der Waals equation

Thermodynamic equation of state for a real (non-ideal) gas.

vasoconstriction

The narrowing of blood vessels resulting from contraction of the muscular wall of the vessels, particularly the large arteries and small arterioles.

vasodilation

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.

vertigo

A type of dizziness, where there is a feeling of motion when one is stationary.

VGE

see also Decompression (diving)#Bubble formation, growth and elimination

Venous gas emboli

viewport

1. Glass or plastic window on a diving helmet or full face mask.

2. Window on a hyperbaric chamber.

VIP

Visual Inspection Programme (US). Annual visual internal inspection of a scuba cylinder.

visual gap

Gap between guidelines which is small enough that each line can be seen from the other.

visual jump

The procedure of crossing a visual gap (q.v.) without the use of a jump line.

visual inspection

Internal and external inspection of a pressure vessel as part of revalidation procedure

Visual Plus

Eddy current test (q.v.) of parallel neck threads of aluminium cylinders

Viton

Synthetic elastomer suitable for oxygen service O-rings.

VPM

(also Variable permeability model). A decompression model and associated algorithms based on bubble dynamics.

VVAL18

The Exponential/linear decompression algorithm used in the 2008 US Navy decompression tables

W

wall diving

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)

water trap

Mechanism to trap liquid water carried by the compressed gas

weighting system

Weights, generally made of lead, to counteract the buoyancy of other diving equipment, and the belts, pockets or harnesses used to support them.

welding shield

Cover for the viewport area of a helmet or mask to filter excessive light and UV when welding or oxy-arc cutting.

wellhead

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.

wet bell

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.

wet pot

Water filled hyperbaric chamber.

wet notes

A small notebook of waterproof paper carried by some divers

wet suit

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.

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.

whip sock

also containment grip

Whip check device which contains a short section of the whip within a braided tube which reduces wear and point loading on the hose, and constrains motion of the hose end more than a standard whip check in case of disconnection under pressure

wing

Back inflation buoyancy compensator cell.

WKPP

Woodville Karst Plain Project

working pressure

Maximum filling pressure rating for the cylinder at standard temperature. (also Charging pressure)

work of breathing

also WOB

The effort expended in inhaling and exhaling the breathing gas.

wreck diving

Recreational or technical diving on and inside of shipwrecks.

wrist slate

A small plastic writing surface attached to the diver's wrist

X

Y

yoke adaptor: A fitting used to connect a regulator or filling whip with a DIN thread connection to an international connection cylinder valve.
yoke fitting/valve: A fitting or valve used to connect a regulator or filling whip to a diving cylinder using the "international" connection.
Y-valve: Cylinder valve body with two outlets and two valve mechanisms which can be independently controlled so that two regulator first stages can be fitted. Similar to H-valve but in Y configuration. Also known as Slingshot valve.

Z

ZHL-8
ZHL-16: Buhlmann decompression algorithms. Also ZHL-16a, b and c
zip tie: (also cable tie, tie wrap) Self-locking plastic strip used to connect objects together.
Z-knife: Line cutting tool with a replaceable blade in a slot.

References

External links

Schlumberger Oilfield Glossary

Source of article : Wikipedia

Wednesday, January 31, 2018