Glossary of underwater diving terminology | Wikipedia audio article

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. == 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 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. airline
air line see Surface-supplied diving#Airline
Simple low pressure hose carrying breathing air to a diver. 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. == B ==
B-ring A small plate with a slot for a webbing belt
and two side by side holes for clipping on equipment, generally used similarly to a D-ring
in combination with a belt slider as an alternative to a butterfly slider 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
see also bar (unit) Metric unit of pressure commonly used in diving,
equal to 100 kiloPascal, and nearly equal to standard atmospheric pressure. barodontalgia Tooth pain caused by pressure difference. barotrauma Injury caused by pressure difference. baseline
1. (also tank factor) Numeric value computed for a cylinder or manifolded set that relates
volume and pressure in the imperial system of units.

Computed by dividing nominal capacity
(cubic feet) by cylinder working pressure (psi) to express cubic feet of volume per
psi of fill pressure (sometimes multiplied by 100 to give cubic feet per 100 psi). Used
to convert cylinder pressure to free gas volume. 2. A line that is a base for measurement or
for construction; see datum (calculations or comparisons)
3. A data set which is a point of reference (engineering or science) for later data. basket
see diving stage BAT wing
Buoyancy And Trim wing. A back mounted buoyancy compensator cell used with sidemount harness.
The buoyancy volume is mostly over the lower back. BC
BCD see buoyancy compensator
BCD blowup Uncontrolled buoyant ascent caused by inability
to release gas from the buoyancy compensator faster than it expands due to pressure reduction
of ascent. beach master
see also dive marshal A person on the beach who records when divers
enter and exit the water. Typically used during recreational scuba training to keep track
of the students, watch the gear, and provide assistance when required.

Bell
1. diving bell (q.v.) 2. Short tug on a lifeline, used in pairs,
for signalling purposes. bell bounce dive
Surface oriented diving operation in which the divers are transported in and deployed
from a closed bell, and are either decompressed in the bell at the surface or transferred
under pressure to a deck decompression chamber for decompression. bell cursor
Mechanism or structure for guiding and constraining the motion of a bell when in the close vicinity
of the deployment platform to improve handling in bad weather. bell diving
1. Any diving operation in which the divers travel in or work from a diving bell
2.

Diving operations in which divers are transported in and deployed from a closed bell, either
as a surface oriented (bell bounce) or saturation dive. bell harness
A safety harness made of strong webbing, which is fastened around a diver over the exposure
suit, and allows the diver to be lifted without risk of falling out of the harness. bellman Standby diver deployed in the diving bell bell run
The part of a bell dive operation from bell lock-off to bell lock-on (to and from the
life support system) bell stage
A framework extending below a closed bell which keeps the base of the pressure vessel
off the bottom sufficiently to provide clearance for the divers to use the bottom hatch when
the bell is resting on the bottom or on the clump weight.

Bell umbilical The combined supply and return hoses and cables
for life-support, power and communications between a diving bell and the support platform belt slider
also belt slide, triglide, weight stop, weight slider
Hardware item with two parallel slots which is fitted to harness or weightbelt webbing
to prevent other components such as D-rings and weights from sliding along the webbing. benign water
benign conditions Sometimes also referred to as confined water.
Environments of low risk, where it is extremely unlikely or impossible for the diver to get
lost or entrapped, or be exposed to hazards other than the basic underwater environment. bent D-ring
A D-ring which has been bent about 45° near the straight section on both sides, forcing
it to project slightly from the harness when pushed to one side, allowing easier attachment
of clips.

Bends
Decompression sickness: Injury caused by bubble formation in the body tissues after hyperbaric
exposure. BIBS
Built in breathing system. A demand breathing gas supply system with external exhaust used
to provide chamber occupants with breathing gases other than the gas used to pressurise
the chamber. Used for treatment gases and emergency breathing gas if the chamber is
contaminated. Billy ring
Three D rings welded together along their straight sides so that one is perpendicular
to the other two. This uses the two flat rings to maintain the third in an upright position
when mounted on harness webbing, allowing it to be more easily accessed to clip on stage
cylinders. Named after Captain Billy Deans. BK hook
also B.K. hook or BK safety hook A type of safety lifting hook which is held
closed when under load by a lever system where the weight of the load holds the bill of the
hook against the safety latch. blending stick
Mixing tube in which gases are continuously mixed prior to intake by a compressor, usually
at atmospheric pressure.

Usually refers to manufacture of nitrox from air with added
oxygen, but also used for trimix. Gas mixture is usually continuously analysed at the exit
of the blending stick to monitor composition. blind traverse
Passing through a cave from one entrance to a different exit which the diver has not used
before. block adaptor
Screw-in adaptor fitting which is fitted to a 200/240 bar DIN pillar valve to allow connection
of a yoke regulator or filling whip. blowdown
Procedure of pressurising a diving chamber or saturation habitat. blowout Uncontrolled release of crude oil and/or natural
gas from a well after pressure control systems have failed. blowout preventer
also BOP A large, specialized valve used to seal, control
and monitor oil and gas wells. Generally operated remotely by hydraulic ram. blue hole A sink hole in a lake or the sea that is often
the entrance to a cave.

Blue holes in the sea are subject to tides so that their flows
regularly reverse. blue-water diving Underwater diving in mid-water where the bottom
is not visible and is out of diving range. bolt snap
also piston bolt A metal connecter comprising a hook with a
spring-loaded axial sliding rod which must be manually retracted to allow the hook to
be clipped onto something or removed. May be single- or double-ended, and if single-ended
is usually fitted with a swivel ring opposite the jaws. bomb
Commercial diver slang for high pressure gas storage cylinder of around 50 litres water
capacity, also known as a J. bondage wing
see bungee wing Derogatory term for bungee wing based on fetishist
terminology.

Bonnet
The upper part of a copper helmet which encloses the diver's head and is sealed to the lower
part or corselet (q.v.) booster booster pump
see also compressor Machine used to increase pressure of a gas.
Usually refers to the case where inlet pressure is above ambient pressure already. BOP stack
Blowout preventer stack: An assembly of several blowout preventer rams which may be used to
shut off a well. bottom gas
The gas breathed by the diver at the deepest part of the dive. Compare with travel gas
and decompression gas. bottom time
Time used in calculating decompression obligation from decompression tables. For most tables
this is defined as the elapsed time from starting the descent to starting the final ascent to
the surface, excluding ascent and decompression time.

Bottom timer
Device used to measure and record the total time spent underwater during a dive. They
do not generally only record bottom time {q.v.}. bounce dive
1. also surface oriented dive: In commercial diving, bounce diving is the alternative to
saturation diving. Any dive where the diver is decompressed directly after the dive.
2. In recreational diving, a bounce dive is a descent to maximum depth and then a direct
ascent back to the surface with the minimal bottom time, in a dive profile resembling
a spike. BOV
see bailout valve bowline Knot used to form a secure, non-slipping loop
at the end of a line. Boyle's law Relationship between pressure and volume at
constant temperature in an ideal gas. breakdown room
An area in a cave where a large amount of material has fallen from the overhead.

Breakout
The point at which an object being lifted which is partly embedded in the bottom sediments
overcomes the adhesion of the sediments and the force required to lift it drops rapidly
to the apparent weight of the object. breathing gas
also breathing mixture Gas supplied to the diver to breathe, either
directly to the diver or to the hyperbaric environment of the diving bell, dive chamber
or saturation habitat. Colloquially just "gas" or "mix". breathing loop
The gas flow path in a rebreather comprising the diver's lungs, the mouthpiece, valves,
hoses, counterlungs and scrubber through which gas is rebreathed. Broco cutter
A type of thermal lance initiated by an electric arc, in common use for underwater cutting
work.

BRUV
Baited remote underwater video. A system for assessing fish populations using video cameras
to record fish attracted to a bait canister. BTV Béance tubaire volontaire: Voluntary opening
of the Eustachian tubes to equalise the middle ear. bubble models Decompression models based on the assumption
that bubbles will form during non-symptomatic decompression. buccal pumping
see glossopharangeal insufflation buddy bottle
Bailout cylinder carried by a scuba diver, particularly when diving solo. buddy breathing
Sharing breathing gas from one demand valve by two or more divers, generally after an
out-of-gas emergency. buddy check A procedure carried out by scuba divers using
the buddy system where each diver checks that the other's diving equipment is configured,
fitted, and functioning correctly just before entering the water to dive.

Buddy diving A safety procedure where two or three divers
monitor each other constantly during a dive and provide assistance or rescue when needed. buddy line
A short line between two divers, used to maintain contact during a dive, generally in poor visibility,
or other conditions where the divers might become separated and not be able to quickly
locate each other. buddy system A procedure where two divers look out for
the safety of each other, and give assistance if the other gets into difficulty. Bühlmann tables
Bühlmann algorithm Diving tables and decompression algorithm
on which the tables are based, and some dive computers are programmed, based on the dissolved
gas decompression model derived and tested by Dr A.A. Bühlmann. bundle
A set of gas cylinders fastened together for transportation and manifolded for use as a
unit, also cylinder bundle. bungee (sidemount)
see also ring bungee Length of shock cord used to restrain the
top end of side mount cylinders and keep them tucked in at the diver's shoulder while swimming.
Usually clipped to the shoulder D-ring(s) of the harness and looped around the cylinder
valve.

May be attached to the back of the harness between the shoulder blades, or run
continuous from one shoulder D-ring, around the back under the arms to the other shoulder
D-ring. bungee wing
Back inflation buoyancy compensator with shock cord lacing or loops which exert a force on
the bladder to oppose expansion during inflation. buoyancy
1. (Main article: Buoyancy). Upward force on an object immersed in a fluid due to pressure
exerted over the immersed surface. 2. Resultant upward force of buoyancy and
weight of an object immersed in a fluid. buoyancy check
Procedure to test and adjust weights carried by an underwater diver. The diver wears all
the personal equipment to be used for the planned dive, with the scuba tank(s) nearly
empty, and the buoyancy compensator empty, in shallow water of the same density as expected
on the dive, and adds or removes weights until neutrally buoyant.

After the buoyancy check
it is usual to distribute the weights for safety, trim and convenience. buoyancy compensator
also BC, BCD, buoyancy compensator device, ABLJ, horse collar, stabilisor jacket, stab
jacket or wing An airtight bladder worn by a diver which
can be filled with air and vented to adjust and control the buoyancy of the diver. buoyancy control
The skill of maintaining the appropriate buoyancy at any time during a dive. burn tester
Device for measuring the actual capacity of a battery relative to its nominal capacity,
and the associated functional time for the device that the battery is powering. burn time
The effective use time of a battery powered device. Mainly used in reference to dive lights
and scooters. burst disk A non-reclosing pressure relief device used
to protect a diving cylinder from overpressurization. butterfly clip
A type of bolt snap with a tapered guide gate opening formed by a protrusion on both the
piston and the fixed sides of the gate.

Butterfly slider
butterfly D-ring A plate with two D-shaped cutouts on opposite
sides of two to four parallel longitudinal slots for webbing. Used at the top back of
the crotch strap in place of a butt-plate (q.v.) on minimalist sidemount harnesses as
a clip-on point for equipment. butt-plate
A rigid or fairly stiff flexible lower extension to a backplate or other scuba harness supporting
butt-plate rails, used for clipping off the lower end of sidemount cylinders to the harness.

== 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
see also critical pressure Critical Air Supply, the amount of breathing
air required to safely exit a penetration dive. When the air supply reaches this level
the dive has reached a planned turning point.

Cascade filling Decanting from several storage cylinders in
succession, generally using a procedure to maximise charge pressures. Often used in partial
pressure gas blending. caustic cocktail
A mixture of water and carbon dioxide absorbent caused by flooding the scrubber, and which
may reach the diver's mouth through the breathing loop. The alkalinity depends on the absorbent
used. cave
A naturally occurring cavity in bedrock, or an underwater passage not illuminated by natural
daylight, large enough to be entered by a human. Statute 810.13 of the Florida legislature
defines a cave as: any void, cavity, recess, or system of interconnecting passages which
naturally occurs beneath the surface of the earth or within a cliff or ledge, including
natural subsurface water and drainage systems but not including any mine, tunnel, aqueduct,
or other manmade excavation, and which is large enough to permit a person to enter.
The word "cave" includes any cavern, natural pit, or sinkhole which is an extension of
an entrance to a cave.

Cave arrow Directional line markers which point the way
to an exit. cave fill
Filling a scuba cylinder to a pressure significantly above the rated safe working pressure (charging
pressure). Illegal in some jurisdictions, and increases risk of catastrophic failure. cave line
1. see distance line 2. Small diameter braided synthetic cordage
used for this purpose. cave reel A reel specifically made for cave diving,
used to lay and recover large lengths of cave line which is used as a guide line to find
the exit or a permanent guide line. cavern
1. Two or more interconnected underground rooms or passages in bedrock, each large enough
to be entered by a human. 2. The initial room of an underwater cave
system that is illuminated by natural daylight. 3. A naturally occurring cavity in bedrock
or an underwater passage, large enough to be entered by a human, which is illuminated
by natural daylight, or in which it is possible from all points to see the exit by natural
daylight. cavern dive
Visibility greater than 40 feet, Maximum penetration of 130 feet, Maximum depth of 70 feet, and
always within the ambient sunlight area.

No passing through restrictions. C-card or certification card
Plastic card issued to a diver by a certification agency as evidence of completed diver training
and experience required for the level of certification. CCR
Closed Circuit Rebreather: see also ECCR, MCCR. CCUBA
Closed Circuit Underwater Breathing Apparatus. Military alternative term for CCR ceiling
Solid overhead or decompression restriction to a safe direct vertical ascent to the surface cenote A sinkhole in Mexico. Generally with vertical
overhanging walls or shafts with water that open into a cave system. CF
clusterfuck charlie foxtrot
Occasion when the situation diverges notably and usually uncontrollably from the plan,
sometimes involving immediate hazard to life and limb, and often involving poor judgement. CGA
The Compressed Gas Association is an American trade association for the industrial and medical
gas supply industries. The CGA publishes standards and practices that codify industry practices.
In cases where government regulation is not specific, CGA documents are considered authoritative.
CGA V-1 Standard for Compressed Gas Cylinder Valve Outlet and Inlet Connections covers
diving cylinder valve outlets.

Safety devices like burst disk overpressure protection are
specified by the CGA Standard S1.1. CGA 850
Compressed Gas Association valve standard CGA 850 is the standard for the scuba cylinder
valve outlet for yoke connector chain chaser
Ring or hook shaped components used for installing and recovering conventional mooring systems.
The chaser is hooked around the chain and pulled in the direction of the ancor until
it slides onto the anchor shank and is stopped by the crown. The chaser is then used to break
the anchor out by pulling directly upwards. chamber dive
Simulated dive in a hyperbaric chamber pressurised to equivalent pressure to the nominal depth
of the dive. chamber operator
Person competent to operate a diving chamber charging pressure
Pressure stamped on a container for a permanent gas to indicate the maximum gauge pressure
(measured or corrected to 15°C) that may be applied at the time of filling.

Charles's law Relation of volume to temperature at constant
pressure of an ideal gas. chicken vest
Sleeveless neoprene wetsuit vest with attached hood. chimney
A section of a cave that is vertical or near vertical and like a shaft. Chinese lantern
Connection between pipeline end manifold (PLEM) and single point mooring buoy (SPM) using
two to four separate flexible underwater hose strings. choker (sidemount) A strap around the neck of a sidemount cylinder
used to hold the bolt snap closer to the neck so that the head of the cylinder stays closer
to the diver's armpit.

The choker can be a small webbing strap with a sliding buckle
for adjustment, so it can be tightened to bring the clip closer to the neck or slacked
off while in use. chokes A symptom of decompression sickness manifested
by shortness of breath, caused by a large number of venous gas bubbles in the lung capillaries
which interfere with gas exchange. Christmas tree
also tree An assembly of valves, spools, and fittings
installed on top of the wellhead and used primarily to control the flow, usually oil
or gas, out of the well. Christmas tree ladder
A boarding ladder which has a single central rail with rigid cantilevered rungs to each
side, allowing use while wearing swimfins. Christo-lube
Usually Christo-lube MCG111, an oxygen compatible lubricant suitable for use in breathing apparatus
in oxygen service.

Circuit
Cave dive route in which there is a one-way segment. The circuit can be simple or complex
depending on the number of jumps involved. civils
see inshore diving closed bell
also dry bell A closed or dry bell is a pressure vessel
for human occupation which is lowered into the sea to the workplace, equalised in pressure
to the environment, and opened to allow the divers in and out. Divers may be decompressed
in the bell or transferred under pressure to a hyperbaric chamber at the surface. clump weight
A weight used to keep the guide wires of a diving bell aligned. code of practice
A systematic set of professional standards or written guidelines and rules of procedures
to be followed by members of a profession, trade, occupation or organization.

A code
of practice may be compiled and agreed on by members of a particular profession or written
guidelines issued by an official body or a professional association to its members to
help them comply with its ethical standards. A code of practice does not normally have
the force of law, but is often required or compulsory practice for members of an organisation. coded welder
Welder who is trained and qualified and assessed as competent for a specified type of welding
under specified conditions. combat swimmer Person trained in scuba diving or swimming
underwater in a military capacity which can include combat command signal
A signal from a diver in a team that requires a response from another diver. There are three:
Are you OK, Hold, and Surface. commercial diving Working under pressure: Occupational activity
where gas is breathed at pressure in excess of atmospheric pressure, usually underwater. completion The process of making a well ready for production. competent person
Person who is able to perform a task or operation safely and according to required procedures.
May require formal assessment or accreditation, or registration with government body.

Compressed air
Air at a pressure greater than ambient. compressed neoprene
Foam neoprene that has been compressed to reduce volume. Used for dry suits which are
less affected by depth induced buoyancy changes. compression
The process of increasing the ambient pressure on a diver by descending into the water or
pressurising the chamber. compression arthralgia Pain in the joints caused by exposure to high
ambient pressure at a relatively high rate of compression compressor Machine which pressurises gas. Generally intake
gas is at ambient pressure, outlet gas at higher pressure. High pressure breathing air
compressor output pressure is usually 200 to 330 bar. compressor log
Book or file containing records of compressor operation, filling of cylinders and maintenance
records. compressor operator
Person who operates a compressor, either to fill cylinders, or to provide breathing air
to surface supplied divers. confined water
Water that is enclosed and bounded sufficiently for safe training purposes. Generally implies
that conditions are not affected by geographic or weather conditions, and that divers can
not get lost.

Condensate Liquid resulting from phase change from gas
due to cooling or pressure change. conduit
Tunnel or passage in a cave system. conservative (decompression)
Decompression profile tending to minimise risk of decompression sickness at the cost
of more decompression time for a given pre-ascent dive profile. constant depth blackout
constant pressure blackout also isobaric blackout
A Freediving blackout which occurs while the diver maintains a near constant shallow depth,
where reduction of oxygen partial pressure due to ascent is not a factor. Usually induced
by pre-dive hyperventilation. Also referred to as shallow water blackout, which is an
ambiguous term constriction
see restriction contents gauge
see submersible pressure gauge continuous decompression Decompression without stops. Instead of a
fairly rapid ascent rate to the first stop, followed by a period at static depth during
the stop, the ascent is slower, but without officially stopping. Ascent rate may vary
with depth, usually slowing as the depth reduces. contra-indications to diving
Conditions (usually medical) that indicate that a person should not dive. control compartment
The tissue compartment that dictates the ascent profile of a given dive because it is theoretically
the highest risk compartment for DCS.

Controlled buoyant lift A rescue technique used by scuba divers to
raise an incapacitated diver to the surface from depth. controlled emergency swimming ascent
also CESA An emergency technique for surfacing, usually
when no breathable gas is available at depth. The diver fins upward while gently exhaling
to keep expanding air in the lungs from causing lung expansion injuries. cookie Personal non-directional line markers that
mark specific locations, or the direction of one's own exit at line intersections. copper hat
copper helmet A diving helmet of traditional design and
construction, usually made from spun or beaten copper, with brass or bronze fittings. There
are usually two main sub-assemblies; the bonnet is the roughly spherical part which covers
the head and is provided with viewports, valves and various other fittings, and the corselet,
which rests on the upper torso of the diver, and to which the bonnet is connected when
in use, and which may be sealed to the suit and ballasted to compensate for the buoyancy
of the airspace inside the helmet.

Corselet Breastplate part of a copper helmet and some
other heavy helmets, which clamps to the diving suit, and to which the helmet bonnet is clamped,
screwed or bolted. counterlung Flexible bag or bellows in a rebreather which
compensates for the change in volume in the loop during breathing. CPR
see cardio-pulmonary resuscitation cracking pressure
Pressure required to open a valve. Often applied to the difference in pressure over the diaphragm
of a demand valve required to open the valve to start flow. This may differ significantly
from the pressure difference required to keep the valve open once flow has been initiated,
and the pressure to keep the valve open may vary with flow rate. critical air supply
see CAS critical difference hypothesis Hypothesis that bubble formation during decompression
will not occur if a critical pressure difference between tissue gas tension and inspired gas
partial pressure is not exceeded. critical pressure Cylinder gas pressure which determines a safe
limit to an underwater activity on scuba, such as start of ascent or turnaround during
a penetration.

Critical ratio hypothesis Hypothesis that bubble formation during decompression
will not occur if a critical ratio of tissue gas tension and inspired gas partial pressure
for a given gas is not exceeded. critical volume hypothesis Hypothesis that symptoms of decompression
sickness will not be evident if a critical volume of tissue gas bubbles is not exceeded. crotch strap
Harness strap that passes from the lower part of the harness at the back, through between
the diver's legs, to the front of the harness, effectively securing the harness from sliding
up along the torso. In safety harness this is often in two parts and allows the diver
to be lifted by the harness without risk of falling out. crushed neoprene
Proprietary material for dry suits manufactured by DUI in a process where the foam neoprene
suit material is degassed by exposure to high hydrostatic pressure to reduce the volume
after assembly. Less buoyancy variation with depth as the material is less compressible
after the treatment. cuff dump
Dump valve mounted on a drysuit cuff, usually relatively small and non-adjustable.

Cyalume Trademark name Cyalume is a solid ester whose
oxidation products are responsible for the chemiluminescence in a glowstick. cyanosis The appearance of a blue or purple coloration
of the skin or mucous membranes due to the tissues near the skin surface being low on
oxygen cylinder
1. Diving cylinder: Refillable compressed gas container of water capacity between 0,5
L and 150 L. 2. That part of a reciprocating compressor
or booster in which the piston is moved to compress the air.

The internal space is cylindrical
with a circular section. The external surface is usually finned for air cooling. cylinder boot Rubber or plastic cover for the base of a
scuba cylinder to protect it from abrasion, and in the case of domed end cylinders, to
allow it to stand upright. cylinder bundle
see bundle cylinder valve Valve fitted to a compressed gas cylinder
to control gas flow into and out of the cylinder.

Also pillar valve. == 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 obligation Theoretical requirement to make decompression
stops during ascent based on the dive profile and the decompression model in use. 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. Freediving: An ambiguous alternative term for blackout of ascent following a deep breath-hold
dive, in which loss of consciousness occurs as the surface is approached, or at the surface,
caused by cerebral hypoxia arising from the rapid drop in the partial pressure of oxygen
in the lungs during ascent as the ambient pressure drops and the gas in the lungs expands
to surface volume.

2. Scuba and surface-supplied diving: Loss
of consciousness in deep air diving at depths below 50 m with no clear primary cause, associated
with nitrogen narcosis, a neurological impairment with anaesthetic effects caused by high partial
pressure of nitrogen dissolved in nerve tissue, and possibly acute oxygen toxicity. The term
is not in widespread use at present. dehydration A condition where the water content of the
body is reduced. delta P
ΔP δp
Environments where a pressure difference causes flow. Usually refers to cases where the flow
is likely to entrain and pull the diver into an enclosed space. demand helmet
Diving helmet which provides gas supply flow only when the diver inhales. 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. descending line
see also jackstay, downline and shotline A substantial heavily weighted line attached
to a secure point at the surface, such as a boat or buoy, which can be used by a diver
to control position and depth during descent an ascent. 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
see also overweighting Practice of carrying significantly more ballast
weight than necessary to neutralise buoyancy. Common in professional diving operations where
the diver needs to remain in firm cintact with the bottom to work effectively, and is
tethered by a lifeline or umbilical to a control point at a place of safety, which is managed
by a tender. diving manual
1. see operations manual 2. see diver training manual diving regulator
see regulator diving response
The diving response exists in all air-breathing vertebrates. It is a series of autonomic responses
to apnea which are strengthened by facial cooling and hypoxia.

It consists of peripheral
vasoconstriction and associated hypertension, vagally induced bradycardia and reduction
of cardiac output. This appears to preferentially supply oxygen to the brain. Another aspect
is splenic contraction which increases haemoglobin content of the blood. diving safety officer The person who administers a United States
university's research diving safety program. diving signals Hand sign and light sign system used by scuba
divers to communicate when underwater. diving stage
also known as the basket A platform on which a diver stands which is
hoisted into the water, lowered to the workplace at the bottom, and then hoisted up again to
return the diver to the surface and lift him out of the water. The diving stage is particularly
effective for controlling rate of descent and ascent. diving superintendent
Person with overall responsibility for commercial diving operations at a large installation. diving supervisor Person in charge of, and responsible for safety
of a commercial diving operation. Usually trained, assessed as competent, certified
and formally appointed by the diving contractor. diving system
The complete set of equipment necessary to support a diving operation. DMAC
Diving Medical Advisory Committee: An independent body of diving medical specialists from Northern
Europe which provides advice about medical and certain safety aspects of commercial diving.

DMT
Diving medical technician: A paramedic specialising in diving related conditions. dome port
A domed window of optical quality glass or plastic which covers the front of an underwater
camera or video housing. donating the octopus donating the primary
donate the primary Rescue technique where the donor of breathing
gas provides it via the primary 2nd stage –- the one from which the donor was breathing
–- as it is known to be working and providing the correct gas. The donor then switches to
their backup DV, often stowed under the chin by a bungee necklace with a breakaway connection.

Donating the secondary
donate the secondary Rescue technique where the donor of breathing
gas provides it via the secondary, or octopus, 2nd stage, and continues to breathe off the
primary. donkey dick
Slang term for the corrugated buoyancy compensator inflation and deflation hose. Doppler bubble detection Ultrasonic signals reflected from bubble surfaces
to identify and quantify gas bubbles present in venous blood. Dorf arrow
(also line arrow). Triangular plastic line marker with two slots used to indicate the
direction of the exit. downline
down line A rope leading from the surface down to the
underwater workplace which allows a commercial diver to travel directly to and from the job
site and to control rate of descent and ascent in the same way as using a shotline. Also
sometimes called a jackstay. A downline used for open ocean diving is much the same as
a shotline (q.v.), but does not reach all the way to the bottom. An open-ocean downline
is weighted at the bottom, and attached to a substantial float at the surface, which
may be tethered to the boat. It may be marked at intervals by knots or loops, and may be
attached to decompression trapeze system.

In some cases a sea anchor may be used to
limit wind drift, particularly if attached to a boat with significant windage. downstream
In the direction of flow. Displaced from the reference point in the direction of flow downstream valve Valve in which the closure is downstream of
the orifice. Pressure in the line tends to assist in opening the valve. When spring-loaded
a downstream valve may open automatically if the pressure difference is excessive, thus
functioning as a pressure relief valve down time
Period when planned activities can not be done due to unforeseen or uncontrollable circumstances. DP alert
Status of the dynamic positioning system regarding positional accuracy and reliability. Green
indicates normal operation, yellow indicates degraded operation and red indicates emergency. DP footprint
Dynamic positioning footprint: The area around the nominal position to which a dynamically
positioned vessel is constrained by the DP system. DPV
1. Diver propulsion vehicle. 2. Dynamically positioned vessel. D-ring
A ring shaped like a capital D, usually of stainless steel, stitched or buckled to a
diver's harness and used as an attachment point for lifeline, cylinders or other equipment.

Dräger tube
Draeger tube Indicator tube used for testing breathing
gas quality. drift diving Any dive where the diver is transported significantly
by drifting with currents during the dive. drillship
Ship built or converted for offshore well drilling, using dynamic positioning to maintain
position in deep water. drop weight
Weight used during descent and ascent, but left on the bottom at the guideline during
the deep part of the dive when it is not needed due to suit compression.

Drowning The process of experiencing respiratory impairment
from submersion/immersion in liquid. dry bag Bag which seals in a watertight manner. Used
for keeping clothes and other equipment dry in a wet environment. dry bell
see closed bell dry filling Filling scuba cylinders without the use of
a water bath for cooling. dry suit A watertight suit worn to keep the diver dry
and to provide protection from the environment. Thermal insulation may be provided by the
suit or garments worn under the suit. DSV
1. Dive/Surface valve: Valve on the mouthpiece of a rebreather which can be switched between
the loop and ambient air at the surface. 2. Diving support vessel: A ship or boat used
as a base for diving operations, particularly if designed or fitted out for that purpose. DSMB
also delayed surface marker buoy An inflatable marker buoy deployed from underwater
to indicate the position of a diver and to control ascent rate. Can also be used to mark
a position or signal an emergency.

Duckbill valve A non-return valve, manufactured from rubber
or synthetic elastomer, and shaped somewhat like the beak of a duck. Used as exhaust valve
in some twin-hose diving regulators dump valve
Valve used to release excess air from a drysuit or buoyancy compensator. dynamic positioning Method of keeping a diving support platform
in position without anchoring, using thrusters and positional feedback. dysbarism Medical conditions resulting from changes
in ambient pressure. == 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. encapsulation
Using a diving suit which completely isolates the diver from direct contact with the environment. 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. == 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. filling ratio
ratio of the mass of gas in a cylinder to the internal volume of the cylinder (water
capacity), usually expressed in kilograms per litre, or pounds per cubic foot. 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.

Also
known as fin retainers, fin holders, fin fasteners, fin grips, fin keeps, fin guards, flipper
fixers, Y-straps, ankle straps, accessory safety straps, fix fins, grip fins and, in
recognition of their French origin, as fixe-palmes. They are called Flossenhalter in German, fissapinne
or reggipinne in Italian and sujeta aleta or sujetador de aletas in Spanish. See Swimfin#Attachment. 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
see also free gas Air at normal atmospheric pressure
free-diving Underwater diving that does not involve the
use of external breathing apparatus, but relies on a diver's ability to hold his or her breath
until resurfacing. also Breath-hold diving, and apnea (q.v.). free-flow
1. Constant flow rate air supply 2. Malfunction of a demand regulator where
the valve sticks in the open position, allowing a constant rate of flow.

Free-flow helmet
A helmet where the breathing air supply is supplied at an approximately constant rate
regardless of the diver's instantaneous breathing rate. free-flow valve
Valve on the side of a demand helmet or full-face mask which opens a free flow of breathing
gas into the helmet interior, usually directed over the interior of the viewport, hence alternative
term defogging valve, as it is often used to blow condensation from the inside of the
viewport. free gas
Gas at normal atmospheric pressure. Usually refers to the volume of some amount of compressed
gas when allowed to expand to atmospheric pressure at constant temperature free gas volume
Equivalent volume of compressed gas if expanded to atmospheric pressure at constant temperature. Frenzel maneuver Technique for equalising the middle ear by
pinching the nose closed and moving the back of the tongue upwards.

Frog kick Finning technique where thrust is developed
by sweeping the fins horizontally toward each other with the fins twisted into a nearly
vertical plane, with the soles facing each other, followed by a recovery stroke which
develops negligible thrust where the fin blades are feathered. The legs are fairly straight
during the power stroke. See also modified frog kick frogman A scuba diver, particularly a military diver
on an undercover mission. fsw
feet sea water: Unit of pressure equal to 1/33 atm.

Not a linear measure of depth. Generally
defined as the pressure exerted by a foot depth of seawater having a specific gravity
of 1.027 and is approximately equal to 0.445 pounds per square inch. full duplex Voice communication system where both users
can transmit and receive at the same time. Compare with half duplex full-face mask
Diving mask covering the eyes, nose and mouth, and provides the diver with breathing gas == 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 == 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.

== 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. integrated weight system
Any system for carrying dive weights on the buoyancy compensator or diving safety harness,
avoiding the use of a separate weight harness or weightbelt. internal condition of cylinder
The state of the internal surface of a cylinder regarding corrosion, contamination and cracking. interstitial emphysema
Gas trapped in the spaces between organs after lung barotrauma. 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. == 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. == 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-cylinder
Bulk high pressure gas storage cylinder size designation (approximately 50 litres internal
volume) Kelly
Kelly tube see tube
K-valve Scuba cylinder valve without reserve mechanism.

== 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.

LID
see low impact diving 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
Alternative term for a viewport of a standard diving helmet. 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. low impact diving Diving with low environmental impact. Diving
in a way that avoids contact with or disturbance of sensitive organisms and adversely affecting
the environment. LP
low pressure LP compressor
Low-pressure compressor. Used for breathing air supply for surface supplied air diving. LP cylinder
Low-pressure cylinder (US) with working pressure less than 2500 psi. LP port
Opening on the first stage of a regulator through which regulated gas is supplied. LST
Life support technician: A person who operates and maintains the life support systems of
a saturation diving system. lung packing
see glossopharangeal insufflation == 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. == 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 in a buoyancy condition
that will sink by default. When intentional, generally after reducing buoyancy of BC and,
if applicable, dry suit by venting to ensure that the diver will not float back to the
surface, but will continue to descend. 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 == 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
see also diving heavy Carrying more weight than is necessary to
achieve neutral buoyancy at all times in a dive. oxygen Important component gas of atmospheric air
and essential component of any breathing gas. Required to sustain life. oxygen analyzer Instrument for measuring the partial pressure
of oxygen in a gas mixture oxygen clean
Cleaned for oxygen service by appropriate methods and materials and tested for contaminants.Verified
that particulates, fibres, oils, greases and other contaminants are absent. oxygen clock A notional alarm clock, which accumulates
hyperbaric oxygen exposure at a rate which increases with higher ppO2 toward the maximum
single exposure limit recommended oxygen compatible
Made from materials which are suitable for oxygen service. Capable of coexisting with
elevated oxygen concentrations and a potential source of ignition without flashing, based
on a system’s maximum operating pressure and temperature. oxygen compatible air
Air which has been filtered to reduce contaminants to a level suitable for blending with high
pressure oxygen. Air with a reduced level of condensable hydrocarbon mist or vapour. oxygen design
Design that minimizes any tendency for heat generation, ignition of particulates, or the
accumulation of contaminants for an intended partial pressure of oxygen and temperature.

Oxygen fraction Fraction by volume or pressure of the gas
mixture made up by oxygen Oxygen Pete
Mythical monster associated with CNS oxygen toxicity, also CNS oxygen toxicity seizure. oxygen service
Suitable for operating with significantly higher levels of oxygen than normal atmospheric
air. Often implies special cleaning procedures, use of oxygen compatible materials, and design
to reduce ignition risk.

System or component that has been designed and tested for oxygen
use, has been tested as oxygen clean and is oxygen compatible. oxygen toxicity A condition resulting from the harmful effects
of breathing molecular oxygen (O2) at elevated partial pressures. oxygen window Inherent unsaturation due to metabolic reduction
of total gas pressure in the tissues. == 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
see also jump camera A photograph of a quadrat taken for later
analysis. Common in marine ecological research where in situ counting would be impractical.
Quadrats may be identified by rigid frames or by a fixed camera to subject distance. pig Pipeline inspection gauge: A tool that is
sent through a pipeline and propelled by the pressure of the product in the pipeline itself. pigtail
Coiled section of pipe to provide greater flexibility.

Pillar valve
see cylinder valve pin index connection Standard connection type for portable medical
oxygen cylinder valves and regulators. placements
Securing the guideline as it is being run and the choice of primary and secondary tie
offs. PLB
see personal locator beacon PLEM
Pipeline end manifold:. Point where flexible underwater hose string is attached to connect
seabed pipeline with Single point mooring. pneumo breathing
Use of the pneumofathometer hose to supply breathing gas to a surface supplied diver
in an emergency.

Supply can be from the diver's own pneumo hose or from a standby diver's
pneumo hose. pneumofathometer
also pneumo Instrument to measure depth of a diver using
a gauge calibrated in msw, fsw, or often both, which measures the ambient pressure at the
diver by measuring the pressure in a hose filled with air with an open end at the diver. pneumothorax Air or other breathing gas in the chest cavity,
often resulting in a collapsed lung. positive displacement
(of compressor) Compresses gas by reducing volume of compression chamber (cylinder) by
mechanical means (piston) to produce higher pressure of the contents. pony cylinder Relatively small scuba set carried as an independent
alternative breathing gas source by a scuba diver. P-port
A large bore quick connector fitting designed and used by Draeger on diving and firefighting
breathing apparatus, which has been used in rebreathers, particularly modifications.

Pre-fill external inspection
Examination of the external condition of a pressure vessel and fittings to ensure that
it complies with requirements before accepting for filling. pre-mix
Nitrox blend with high oxygen content used to mix nitrox by topping up the decanted premix
with air. pressure gradient
The rate of change of partial pressure of dissolved gas through a solvent, which is
the driving mechanism for diffusion through the solvent. Also loosely used to refer to
the difference between the dissolved gas pressure in a tissue and ambient pressure.

Primary light
The main light to be used on a dive. Usually the most powerful. primary regulator
the regulator which the diver intends to breathe from for most of the dive. Particularly when
diving with back-mounted manifolded twin cylinders. primary tie-off
First tie off of the guideline in a penetration dive. This is usually made in a place with
free vertical access to the surface. professional diving Diving which is done as part of the diver's
employment or professional occupation. progressive penetration
An incremental approach to cave and wreck exploration. Each dive goes a bit further
so that the divers develop a familiarity with the environment. PRV
Pressure relief valve psi
Pounds per square inch. Unit of pressure in the Imperial system. PTT
Push to talk: Voice communication systems which require the user to press a button to
transmit.

Used with through water systems to conserve battery power. public safety diving
The underwater work conducted by law enforcement, fire department rescue, and search & rescue/recovery
dive teams. pull
A relatively long pull on a lifeline when used for rope signals. (see "bell" for comparison).
Part of an ascent between the bottom and a decompression stop, between decompression
stops, or to the surface. Possibly deriving from the practice of pulling a surface supplied
diver up by the umbilical or lifeline. pulmonary over-inflation syndrome Pulmonary barotrauma of ascent. Lung over-pressure
injury. purge
To press the purge button on a demand valve to induce a gas flow which is intended to
clear the demand valve interior of water or other substances. purge button
Button or flexible area on the front or side of a demand valve which allows the user to
manually open the second stage valve to provide gas flow without inhalation. purge valve
Valve in snorkel or mask which allows water to drain either under gravity or as a result
of exhalation into the air space push gradient
Tech diving jargon: Decompress at a high gradient factor, particularly when exceeding the baseline
M-value.

Push-pull rebreather
see pendulum rebreather P-valve
also Pee-valve A valved catheter fitted to a dry suit, which
enables a diver to urinate at any time without having to get out of the water. Pyle stops Named after Richard Pyle, an early advocate
of deep stops. An additional brief deep decompression stop, typically 2 minutes long and half way
between the maximum depth and the first conventional decompression stop. == Q ==
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
see also photo quadrat A small, typically rectangular plot used in
ecology and geography to isolate a standard unit of area for study of the distribution
of an item over a large area. The quadrat is suitable for sampling plants and slow-moving
or sessile animals. == R ==
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. rescue tether
A short lanyard or strap carried by a surface supplied stand-by diver to be used to tether
an unresponsive diver to the standby diver during a rescue.

It is attached at one end
to a D-ring on the stand-by diver's harness, and has a clip at the other end which may
be secured to a D-ring on the casualty's harness to allow the rescuer the use of both hands
during the return to the bell or surface. 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
see also bungee (sidemount) Length of shock cord with metal rings and
a clip used to control the position of the top end of a sidemounted cylinder. Differs
from a regular bungee in having the rings. A popular configuration is a bolt snap connected
to a ring by a quick link, with a length of bungee from the ring to another quick link
which is used to connect the assembly to a D-ring on the back of the harness. The bolt
snap is clipped to the shoulder D-ring and the cylinder neck bolt snap is clipped to
the ring.

Rip current A strong localised flow of water to seaward
from near the shore, typically through the surf line riser A conduit that provides a temporary extension
of a subsea oil well to a surface drilling facility RMV
Respiratory minute volume: (or minute ventilation) The volume of gas inhaled (inhaled minute
volume) or exhaled (exhaled minute volume) from a person's lungs in one minute. RNPL
Royal Navy Physiological Laboratory RNT
see residual nitrogen time rock bottom gas management
see also Scuba gas planning Retention of a breathing gas reserve based
on calculated values for the amount of gas required for a safe ascent from any point
in the planned dive profile. Factors such as emergency supply of gas to a buddy, air
consumption rates under stress and decompression gas requirements are considered in the calculations.

Roll-off
Closing of a cylinder valve as a result of scraping contact between the valve knob and
the overhead or other surroundings. The left hand knob is more likely to roll-off, closing
the backup regulator in the standard twins configuration. ROV
ROUV Remotely operated underwater vehicle – A
tethered underwater mobile device operated by a remote crew. roughneck
Member of the drilling crew who works under the direction of the driller to make or break
connections as drillpipe is tripped in or out of the hole. roustabout
Any unskilled manual laborer on the rigsite. rule of thirds Cave and wreck penetration breathing gas management
convention where no more than one third of the gas in a cylinder may be used on the inward
part of the dive, and the other two thirds is kept for exit: One third for the planned
exit, and one third in case of an emergency.

Run time
Time elapsed since the start of a dive. running stop
A pause made during ascent to adjust the average ascent rate to the nominal value. For example
a nominal ascent rate of 3 m per minute might use an actual ascent rate of about 5 m per
minute and make a stop every 3m until the end of the current minute, resulting in a
slightly stepped profile with an overall ascent rate corresponding to the nominal rate. run time schedule
Decompression schedule and dive plan based on elapsed time from the start of the dive,
All waypoints and events are specified in terms of elapsed time with start of descent
at zero. R-valve
also: Positive reserve valve, automatic valve, or calibrated orifice
A cylinder valve which limits the outflow by a calibrated orifice when in the "on" position. == 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. Sasuba
A shallow water airline diving system using a scuba cylinder on a float towed by the diver. 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. See Snorkel construction.

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) spitcock
A valve in the side of a copper diving helmet which could be used by the diver to suck in
a mouthful of seawater to spit onto the inside face of a viewport to wash off condensation
droplets to improve his view. 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. 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. swimthrough
swim-through A submerged arch or short tunnel that a diver
can swim through without needing to remove equipment.

It is usually possible to see natural
light at the far end in good visibility and illumination. Usually refers to a natural
formation. Technically an overhead environment, but usually with no risk of getting lost,
though entrapment may be possible. == 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 manoeuvre 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. Also known as "Kelly tubes"
or "Kellys". 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. umbilical cutter
mechanism fitted to a closed bell which allows the occupants to sever the bell umbilical
from inside the sealed and pressurised bell in the event of an umbilical snag that prevents
bell recovery.

The device is typically hydraulically operated using a hand pump inside the bell,
and can shear the umbilical at or just above the point where it is fastened to the top
of the bell. 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 Weightbelt
Ballasted waist belt worn by divers to compensate for excess buoyancy. For scuba and freediving,
usually easily removed to establish positive buoyancy in an emergency. weight harness
Webbing strap system to support diving weights, usually suspended from the shoulders and fastened
around the waist. The harness may carry the weights directly, or they may be carried in
pockets on the harness. For scuba diving the weights may be arranged for easy shedding. 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 gripWhip 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 woolly bear
A wool or synthetic pile thermal under-suit worn under a diving dry suit, particularly
with standard diving dress, often one-piece. 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.

== See also.

Read more