A A A

A FLAG Flag in the International Code of Signals which indicates 'I have a diver down, keep well clear and at a slow speed. commonly called flag Alpha it has been adopted by most of the world's diving organisations, including the world Underwater Federation, as the diving flag

A.B.L.J. Adjustable Buoyancy Life Jacket

ABSOLUTE PRESSURE The true or total pressure being exerted at any point.Thus the absolute pressure at sea level is 14-7 psi or one atmosphere and at 33ft or 10m it is 29-4 psi or two atmospheres

ABSOLUTE ZERO The lowest temperature attainable is minus 459 for minus 273C.This figure is necessary for calculations involving gas pressures

ACCESSORY Any piece of equipment that is not essential to underwater use, but makes diving easier or safer, eg, depth gauge, watch, knife

ACETYLENE Inflammable gas used in welding above water. It becomes unstable (explosive) at pressures above two atmospheres and so should never be used under water

A-CLAMP Device for clamping charging hoses,regulators or manifolds to an air cylinder pillar valve

ACTIVATED Treated in such a way that their powers of adsorption are considerably increased. Used as a filter medium in compressores to remove traces of oil, water and solid particles from compressed air.

ACTIVATED ALUMINA Special form of aluminium oxide

ACTIVATED CHARCOAL Carbon made from coconut husk, wood, bone, etc

ADSORPTION Process of concentrating molecules upon the surface of a solid.

AERODON TALGIA Pain in a tooth caused by compressed air expanding. Also caused by compression of a gas (air) space beneath a filling causing that filling to move

AFT Towards the Stern, in the rear part of a boat.

AFTER DROP When a person suffering hypothermia is placed in a warm environment, the core temperature may actually drop before rising again.

AHEAD Forward, or ahead of a boat

AIR COMPOSITION Approximate Nitrogen 78%, Oxygen 21%, inert gases 1%, Carbon Dioxide 0.03%, variable amounts of water vapour.

AIR CONSUMPTION There are many standard of air consumtpion.As a very rough guide it can be assumed that a person walking steadily consumes 1cu ft or 25 ltrs of air per minute.

AIR DENSITY Dry air at 0C (32F) and 760mm mercury.1-293gm/1 or 0-0807 lbs/ft3

AIR EMBOLISM Air in the Bloodstream. Blockage of one or more blood vessels by a bubble of air. Usually a result of barotrauma

AIR ENDURANCE This relates directly to air consumption and depends on individual metabolism, fitness and degree of exertion. air cylinder capacity, depth, degree of experience and emotional state, ill

AIR FILTER Filter, Air

AIR LIFT A device for raising small objects or silt, etc from the bottom of a body of water. It forces a stream of air bubbles into the bottom of a hose or tube. Bubbles float up the hose or tube. Bubbles float up the hose and cause it to function rather like a vacuum cleaner

AIR PURITY Pure air is that which is found in nature uncontaminated by man or by processes of decay, etc. It is frequently diffult to set a suitable standard of purity and then to get air of that standard

AIR PURITY STANDARDS There are many, all slightly different, eg, United States Navy, Canadian Standards Association, British Standards Association (BS4001) BSAC, etc

AIR RESERVOIR A large static air cylinder used in conjunction with a compressor. It permits more rapid filling of air cylinders than the compressor alone can achieve, decanting

AIR TESTING A means of discovering whether a given sample of air is within a stated standard of purity. Accurate analysis is carried out by drawing known quantities of air over chemical reagents and noting any colour change

AIR WEIGHT Air, at normal atmospheric pressure, has a specific weight. This may be taken as 1.25 gm/1 or 0.08 lbs/cu.ft air density

AIRWAY The air passage of nose, mouth, pharynx, larynx and trachea by which air passes to the lungs. A tube introduced into the above to keep them open during unconsciousness.

ALCOHOL Ethyl alcohol is the active ingredient of nitrogen nacosis. Diving should not take place within four hours of consuming alcohol, or while hung over.

ALGAE The group of non-flowering plants called the seaweeds (there are freshwater varieties). The three most important groups are Chlorohyta - green algae, phaeophyta - brown algae, rhodophyta - red algae.

ALLOY A mixture of two or more metals. With such a mixture the properties of both metals might be improved.

ALPHA Phonetic for letter A

ALTERNOBARIC VERTIGO Vertigo, giddyness and/or loss of orientation or balance resulting from pressure changes in the ear, due to changes in depth and/or ear clearing.

ALTITUDE Height above sea level. Whether on land or in an aircraft, this can affect decompression

ALUMINA Aluminium Oxide. sed as a dessecant in compressor filters, usually in the form of activated alumina.

ALUMINIUM Metal element. Ductile, malleable and light in weight. Resistant to corrosion. A useful component of an alloy

ALVEOLUS Terminal air-sac in the lungs where gaseous exchange takes place. Cavity or socket in jaw bone into which a tooth fits.

AMBIENT Immediately surrounding. Generally used of temperature or pressure.

AMPHORA Ancient earthenware vase. In ancient times used for the transport and storage of liquids, especially oil or wine.

ANAESTHETIC A substance in gas or liquid form, which causes a loss of feeling, insensibility or unconsciousness. Nitrogen Narcosis-Chloroform

ANALGESIC A remedy which relieves pain.

ANALYSIS Air Testing.

ANCHOR In effect a weighted hook placed on or in the sea bed and attached to a boat via a rope or chain. Horizontal pull is needed for efficient anchoring (anchor warp). Holding power depends on bottom - anchor size C.Q.R - Danforth - Fisherman Anchor

ANCHOR SIZE Calculations for fisherman anchor - upto 9ft (3m) boat - 4lbs (1-8 kgs), add 1 lb (0.45 kgs) per extra foot or 300mm. Reduce weight by a quarter for Danforth or C.Q.R., but increase weight by a quarter for over-night mooring.

ANCHOR WARP Minimum length is 3 times the maximum depth at the site. The optimum lenth is 5 times the depth. Anchor should be attached to warp by a spliced eye.

ANCHORING The practice of dropping and securing the anchor to hold the vessel in a specific place.

ANKLE STRAPS Fixe-palms - ill

ANNEAL A heat treatment for metal or glass. Material is heated then cooled. It has the effect of hardening some metals, eg, duralumin and softening other, eg, copper.

ANODE Positive Electrode.

ANOXIA Total lack of oxygen, this is rare. Acute anoxia (instantaneous anoxia) occurs when cylinders have been filled with, eg, nitrogen only. Unconciousness occurs within 30 seconds - hypoxia.

ANTICYCLONE Meteorlogical state of high atmospheric pressure, usually denoting fine weather.

ANTIHISTAMINE A group of drugs which (among other things) helps control travel sickness. Not as effective as hyoscine, but better tolerated for long journeys. Can cause drowsiness and add to the effects of hypnotic drugs and/or alcohol. Should not be taken before or during a dive.

ANXIETY Mental state which can increase exhaustion and the effects of cold. It ofter precedes panic.

AQUALUNG The common british name for Scuba

AQUAPLANE A predominantly flat surface or board towed by a boat and controlled by a diver, so that he may cover a large area rapidly when searching

ARC (electric) Highly luminous, high temperature discharge. Used in underwater cutting and welding. Also the source of light in arc-lights.

ARCHIMEDES PRINCIPLE (Law) When a body is wholly or partially immersed in a fluid, eg, water, it experiences an apparent up thrust. This up-thrust is equal to the weight of fluid displaced.

ARGON An inertgas occurring as 0.8% of atmospheric air. Used in filling electric lamps and as a substitute for Oxygen in the oxy-arc cutting torch.

ARTERY A major blood vessel which carries blood away from the heart.

ARTIFICIAL RESPIRATION A means of oxygenating the blood of a person with out the help of that person - Resuscitation

ASCENT ASSISTED An ascent where both divers ascend sharing one aqualung.

ASCENT BUOYANT Ascent where extra buoyancy has been gained by inflating a lifejacket or to a lesser extent by dropping the weightbelt. It cannot be stopped unless relief valves are fitted to the lifejacket and frequently involves acceleration near the surface. Many Navies use this method for submarine escape.

ASCENT EMERGENCY Any Ascent other than normal.

ASCENT FREE Ascent without using the aqualung and with additional buoyancy.

ASCENT HAZARDS Hitting a surface obstruction. Barotrauma through breath-holding, ascending too fast or having a lung lesion. Decompression sickness. Exhaustion from surfacing when heavy or negatively buoyant. Losing your Buddy.

ASCENT NORMAL Fin gently to the surface at 15m (18m or 60ft on some tables) per minute, keeping in contact with your buddy and glancing towards the surface for obstructions, eg boats. The hand is usually held above the head.

ASCENT RATE Ascent Normal

ASDIC Anti Submarine Detection Investigation Committee - Sonar.

ASEPTIC BONE NECROSIS Non-Infectious death of bone leading to arthritis and possible bone collapse. A long term effect of living under pressure of possibly undetected decompression sickness.

ASPHYXIA Suffocation - inability to draw air into the lungs. The usual cause of death in drowning.

ASPIRIN A drug (acetylsalycilic acid) used alone or with other ingredients to relieve pain (analgesic) or reduce temperature (anti-pyretic). It may increase body heat loss in a diver.

ASTERN Behind a boat.

ASTHMA Spasm of muscles within the lungs affecting respiration. emotionally induced asthma is a disqualifying factor for divers. Advice should be sought from a diving doctor.

AT(S) Abbreviation for the unit of pressure atmosphere(s).

ATA Abbreviation of atmosphere absolute pressure.

ATMOSPHERE The air surrounding the earth. A unit of pressure equivalent to that exerted on the surface of the Earth by the atmosphere.

ATMOSPHERIC PRESSURE At zero Degree C (32 Degree F) at sea level, equivalents 14-7 psi, 1014 milibars (approx one bar) 102 kN/m2 - 1033.3 gm/cm2

ATRIUM An upper chamber of the heart which receives blood from the veins and passes it to the ventricle. The left atrium receives oxygenated blood, the right one de-oxygenated blood, the right one de-oxygenated blood.

ATTENDANT The person above water who cares for a diver under water. He helps him get ready and enter the water, attends the safety line constantly and helps the diver leave the water.

AURAL Pertaining to the ear and/or hearing.

AURAL BAROTRAUMA Damage to the ear(s) due to pressure changes during descent or ascent - Ear Clearing

AURICLE Atrium

AVOGADRO'S HYPOTHESIS (Law) Equal volumes of gases at the same temperature and pressure contain the same number of molecules.

B B B

B.O.D. Biochemical Oxygen Demand. A way of expressing the amount of oxygen needed to purify sewage or other contaminated water. A high B.O.D. indicates the death of large numbers of fish and other animals in the water.

B.S.I. British Standards Institution - A non profit makingconcern which sets standard of quality for equipment, apparatus. Goods approved are marked with the Kite Mark.

B.S.P. British Standard Pipe thread used on metal pipes; also used for the pillar valve thread on some air cylinders.

BACK PACK Harness

BACKING When the wind changes direction in an anti-clockwise manner.

BAG LIFTING A bag designed to be inflated with air to lift objects. Particularly useful in salvage work. To allow for air expansion as the bag ascends, it must either be open at the bottom or be fitted with a pressure relief valve.

BALANCED VALVE A valve controlling the passage of high pressure air in such a way that the air pressure does not affect the force needed to operate the valve - downstream - upstream.

BALLOON SURFACING A diver in a drysuit, who over-inflates the suit surfacing rapidly, tends to come up spreaeagled with his suit swollen or ballooning.

BANGSTICK An explosive device commonly carrying a 12 bore or smaller cartridge at the end. On contact with the victim (usually a shark) the cartridge detonates and the shock wave kills the shark.

BAR A unit of pressure approximating that one "atmosphere; 1000 millibars; atmospheric pressure;millibar.

BAROMETER Instrument for measuring atmospheric pressure.

BAROMETRIC Appertaining to pressure as measured by a Barometer.

BAROTRAUMA Physical damage to the body as a direct result of expanding or contracting air; aural barotrauma; burst ears; embolism; emphysema; pneumothorax; reversed ears; squeeze.

BARTON, OTIS American geologist and engineer who designed Beebe's bathysphere. He and Beebe made the first test descent down to 800 ft in June 1930. Later in 1934, the two of them reached 3,028 ft in the bathysphere.

BASIC EQUIPMENT The minium necessary for snorkelling or skin diing, ie, mask, fins and snorkel.

BASIC TRAINING The minimum training given to enable a diver to use scuba under water - this only covers a swimming pool or hazard free, still, shallow, open water.

BATHYMETER A simple depth gauge depending on the effect of pressure (according to Boyles Law) on a bubble or air trapped in a capillary tube.

BATHYSCAPHE Deep diving vehicle carrying its own buoyancy as a (virtually) incompressible liquid, eg, petrol. Invented by Prof Auguste Piccard, one version reached a depth of 35,800 ft (approx 12,000m) in 1960.

BATHYSPHERE A pressure proof sphere lowered to great depths on a cable from a surface vessel. Designed by Otis Barton and shared by Dr william Beebe, it descended to 3,028 ft (approx 1,000m) in 1934.

BEAM The width of a boat.

BEAM SEA A sea running at right angles to the vessel's course, causing the vessel to roll.

BEARING The angular directions of an object expressed with reference to a compass bearing or another object.

BEARING, COMPASS A bearing in terms of compass degrees from North. May be magnetic or true.

BEARING, HAND Bearing taken with a hand-held compass.

BEARING, TRANSIT Bearings taken by lining up two objects - usually fixed items such as buildings - ashore.

BEATING THE LUNG Breathing or attempting to breathe faster that the scuba unit can deliver air. This leads to panix, hypoxia, etc

BEAUFORT WIND SCALE A system for assessing conditions at sea.

BEEBE, DR WILLIAM Beebe was an academically trained American scientist, who was already famous before he went under water with a Dunn helmet in the 1920s. He later descended to 3,028 ft in the bathysphere with Barton.

BEHNKE, DR AR A US navy doctor, Behnke did valuable research work on helium mixtures and takes in conjunction with Dr O.D. Yarborough, starting in 1937.

BELAY To make a rope fast; To stop any activity.

BELL, DIVING Diving Bell

BELLONI Italian Designer of a system of escape from submerged submarines. The system is described by him as the tube (or trunk) and tub method on the Torricelli Barometric Principle

BEND (KNOT) A knot joining one piece of rope to anouther; hitch (knot)

BENDS A form of decompression sickness, so called because certain bent positions ease the pain.

BERRIED Bearing eggs on the outer surface of the body, eg, crabs.

BEZEL A rotating collar round a watch used to note elapsed time on a diving watch.

BILGE The very bottom of a boat inboard. The lowest part other than the keel outboard.

BILLY, SHARK A short stick with or without a point or nail in the end used for fending off sharks. It is not intended to wound.

BIOLOGY The study of life and living things.

BLACKOUT Unconsciousness; shallow water blackout; syncope.

BLEEDING Loss of blood from the body; The release of small quantities of air from a cylinder; The release of small quantities of fluid from a hydraulic system.

BLOB BUOY A small surface buoy towed on a line by a diver. Used to indicate his underwater position to anyone on the surface.

BLOOD PRESSURE Usually measured as the height of a column of mercury which the blood can support. Measured in the brachial artery, the systolic pressure is 120-140 mm Mercury and 70 mm mercury diastolic.

BLOWING UP Another name for balloon surfacing.

BOAT BOX A waterproof container of tools, spares, flares, first aid kits, etc, carried on a small diving boat.

BOLLARD A post, aboard or ashore, used for fastening a line when mooring a boat.

BOLT GUN Gun using an explosive cartridge to fire a steel bolt into iron, steel or concrete.

BONE NECROSIS Aseptic bone necrosis.

BOOT Rubber or plastic receptacle fitted to the base of an air cylinder to protect it and enable it to stand upright; Shoe or foot fitting part of a wet suit, sometimes called a bootee.

BORELLI, ALFONSO An italian who designed an independent diving dress in 1679. It included claw-like footwear, but the diver walked on the sea bed.

BORGHESE, PRINCE VALERIO He commanded an Italian submarine in General Franco's service during the Spanish Civil War. Commander of the Italian underwater Chariot team during World War II.

BOTTLE Name for any size of cylinder containing compressed air:tank

BOTTOM TIME The time elapsed from leaving the surface until starting the ascent. This is the time required for decompression calculations.

BOURDON TUBE A curved metal tube which tends to straighten when subjected to internal pressure. It is the pressure detector in most pressure gauges and many depth gauges.

BOUTAN, LOUIS Underwater photography pioneer. Lecturer in the Faculty of Science of Paris, attached to the Arago Lab in Banyuls, France. In 1893 outan applied himself ro the problem of photography unrder water. Working with a clumsy helmet suit, he first experimented with a completely flooded camera,using specially varnished plates. Dissatisfied he developed a watertight camera and succeeded in taking some of the 1st underwater pictures.

BOW The front end of a boat.

BOWER ANCHOR The main anchor.

BOWLINE One of the most usefull knots used for securing safety lines to divers.

BOYLE, ROBERT An Englishman, Boyle was one of the first people to study the effect of decompression. His book, New Experiments, physicomechanical, touching the spring of air and it's effects, was written in 1660; it explained the barometer and outlined Boyle's Law.

BOYLES LAW At a constant temperature, the absolute pressure of a gas is inversely proportional to its volume.

BRADYCARDIA Slowing of the heartbeat. It occurs when the face is immersed in water. Diving mammals display extreme bradycardia, eg, the pulse in seals, normally about 80/minute, falls to 8/minute during a dive.

BRASS An alloy of copper and zinc; restoration

BREATH-HOLDING volantary cessation of breathing. Only possible by great willpower in concious persons. The time can be extended by hyperventilation.

BREATHING The process of moving air in and out of the lungs.

BREATHING RESISTANCE Personal resistance stated to be 4cm water/litre air/second. Add equipment resistance to total 7.5 cm water/litre air/second as desirable limit, but up to 12 cm water/litre air/second may be accepted occassionally.

BREATHLESSNESS A diving hazard which can lead to panic.Stages Transitory - initial breathlessness during oxygen debit situation. CO2 is soon eliminated and respiration becomes normal; Slight Carbon Dioxide poisoning:

BREATHLESSNESS Severe Corbon Dioxide Poisoning leading to unconciousness. Causes-emotional stress, physical exertion and fatigue; poor breathing technique:cold hangover:poor physical fitness:beating the lung

BROACH TO Boating term meaning to turn (involuntarily) broadside on to the waves. This can lead to swamping or capsizing.

BRONZE MEDALLION Award of the Royal Life Saving Society; sub-aqua bronze medallion.

BRONZE, PHOSPHOR Bronze improved by the addition of up to 1% phosphorus.

BROUSSARD, HENRI Leading French underwater pioneer. The initiative for the first Underwater Archaeology Conference, held at Cannes in 1955 cam from Broussard.

BUBBLE TROUBLE Slang term for Barotrauma.

BUCKLE A fastening for belts and harnesses:quick release.

BUDDY Diving Companion.

BUDDY BREATHING Sharing one regulator mouthpiece under water.

BUG BAG Bag carried by divers for collecting crabs, lobsters, crawfish, et.

BUOY Floating object, oftern anchored to the bottom used to indicate position/direction/obstruction for navigation or reference.

BUOYAGE A system of using buoys as navigation aids. The lateral system is used in Britain, and the cardinal system in the rest of Europe.

BUOYANCY The assessment of floating ability of a diver or object. floating is positive buoyancy, sinking is negative buoyancy and doing neith is neutral buoyancy.

BUOYANCY COMPENSATOR VEST Sililar to ABLJ but inferior it is a bag that is inflated (partly or fully) by means of the diver's exhaled air (co2), therefore useless for breathing in the case of regulator failure. Only favoured in the USA and South Pacific areas.

BURST EAR Name given to a form of Barotrauma in which the ear drum ruptures inwards due to excess external pressure. If this happens, the entry of cold water so near the balance organs of the inner ear can give rise to nausea, vertigo, disorientation or even unconsciousness.

BURST LUNG Resulting from excessive pressure within the lungs related to ambient pressure. Oftern caused by breath-holding during ascent, but sometime due to local obstruction or a cyst within the lung.

C C C

C.M.A.S. Confederation Mondiale des Activites Subaquatiques (the World Underwater Federation). An international association of diving federations and clubs.

C.Q.R. Very efficient pattern of anchor shaped like a plough. Holding power almost twice that of fisherman anchor. Very reliable except in shingle; anchor; anchor size; anchor warp; anchoring.

C.V.L.J. Constant volume lifejacket. Dated term for A.B.L.J.

CABLE 1/10 of a nautical mile. Taken to be 600 feet.

CABLE-LAID Rope consisting of three right-handed hawsers, twisted together left-handedly. Weaker but more flexible than standard ropes.

CADAQUES' BELL In 1678 a diving bell - the designer is unknown - was functioning regularly in the little Spanish harbour of Cadaques. It was about 4m high and it enabled two Arabs to work on a wreck for about one hour. It has also been called the Catalan Bell.

CAISSON DISEASE Name for decompression sickness, so called because it was found in workmen working under pressure in Caissons (similar to diving bells)

CAM-CLEAT A cleat which holds a rope firmly between two cams. The greater the strain on the rope, the more securely do the cams hold. The rope is easily released when the strain is eased.

CANNON Big Gun, certainly in use in England in 1378; issued to the Royal Navy in 1412. Last used about 1850.

CAPACITOR A device used for storing an electrical charge which can be released very rapidly. Used in photographic electronic flash guns.

CAPILLARY Very small-bore tube: The smallest blood vessels joining arteries to veins.

CARBON An element which is essential to life. Activated carbon is one ingredient used to filter compressed air for breathing. It is a superb adsorbent of gases and vapours.

CARBON DIOXIDE An oxide of carbon produced by combustion or respiration. It is heavier than air, generally odourless, colourless and tasteless. It will not support life. About 0.7 to 0.85 cu ft of carbon dioxide are produced/man/hour on the surface.

CARBON DIOXIDE POISONING Due to CO2 (carbon dioxide) in inspired air, poor air supply or failure of absorbent in re-breather sets. Symptons - Breathlessness and panting, dizzyness, nausea, headaches, anxiety and general distress, sweating, palpitations, loss of consciousness.

CARBON DIOXIDE POISONING In ordinary air the CO2 content is 0.03%, 3% may be breathed for several days, 6% has an effect in only 15 minutes and 10% causes unconsciousness and death. Air Purity

CARBON MONOXIDE An oxide of carbon formed by incomplete combustion of carbonaceous fuelds. It is highly toxic combining irreversibly with the haemoglobin in the blood and interfering with the transport of oxygen.

CARBONATED A liquid containing carbon dioxide dissolved in the liquid under pressure, eg fizzy drinks.

CARBONIC ACID A weak acid formed by dissolving carbon dioxide in water.

CARDIAC ARREST When the heart has stopped beating. This can result from a heart attack:drugs:electric shock:anoxia (prolonged hypoxia)

CARDIAC MASSAGE A means of squeezing the heart from outside the body to keep the blood circulating. Will sometime re-start a heart that has stopped beating.

CAROTID Main arteries supplying oxygenated blood to the head and brains. They have a very strong pulse.

CATALYST A substance often finely divided metal which assists, initiates or speeds a chemical reaction, without itself being consumed in the process.

CATHODE Negative electrode.

C-CARD A card certifying that the holder has received a certain amount of diving training (USA).

CENTIMETRE Unit of length being one hundredth of a metre.

CENTRAL NERVOUS SYSTEM The brain and spinal cord.

CENTROID The centre of breathing pressure which is found 19 cm inferior and 7 cm posterior to the sternal notch.

CEREBRAL HYPOXIA Hypoxia, Cerebral.

CHALK A sedimentary rock. Calcium carbonate. It is used to prevent stickiness of rubber and neoprene surfaces, french chalk.

CHAMBER A pressurized metal container used for compression, re-compression or de-compression.

CHARCOAL An impure form of carbon formed by heating wood or bones in the absence of air. As activated carbon, it is a useful filter medium for compressors.

CHARGING CLAMP Device for connecting a high pressure hose to an air cylinder. also used on regulators.

CHARGING PRESSURE (CP) The maximum pressure to which a cylinder may be charged for normal use. Should not be exceeded, even by the legendary plus 10% to allow for cooling.

CHARLES'S LAW (Gay Lussac) If the pressure is kept constant, the volume of a given mass of gas will vary directly as the absolute temperature.

CHART A map of the coast and the sea bottom, including depths of water. Essential for navigation at sea.

CHART DATUM The plane from which heights and depths are measured. Chart Datum is set at a level below which the tide seldom falls. It approximates to the level of the lowest astronmical tide.

CHLORINE A green gas used to kill germs in swimming pools. It is used at extremely small dilutions.

CHLOROFORM An anaesthetic gas. It is liquid at room temperature, and is sometimes used as a solvent for perspex (acrylic).

CHOKES A serious form of decompression sickness.

CHURCHILL, OWEN Los Angeles yachtsman, bought de Corlieu fins in Tahiti in 1938. Obtained a license from de Corlieu and patented his own improvements. He sold 946 pairs in 1940 and manufactured 25,000 for Allied Frogmen and swimmers during World War II.

CIRCUIT TRAINING A regimen for physical fitness.

CIRCULATION The network of blood vessels, arteries, arterioles, cappillaries, venules and veins, through which the blood travels.

CLAM CLEAT A cleat which holds a rope firmly between two shaped, grooved arms. The greater the tension, the tighter the rope is held, yet is it easily released by reversing the direction of strain.

CLARK, DR EUGENIE Noted American ichthyologist. Director of the Vanderbilt Oceanographic Research Station. Florida. author of Lady with a Spear.

CLARKE, ARTHUR C Full time Amercan author of fiction and non-fiction. Thogh his subjects are mainly science fiction and space travel, he has also writen many books about the underwater world. eg, The Coast of Coral.

CLAUSTROPHOBIA An obsessional neurosis characterised by fear of small spaces or of being shut in. Sometimes dangerous to divers in wrecks and in conditions of zero visibility. Panic is the great danger.

CLEARING EARS Equalising the pressure on each side of the ear drum by yawning, swallowing, or the valsalva manoeuvre.

CLEARING MASK Blowing water out from a flooded mask by exhaling air through the nose.

CLEARING TUBES Clearing the water from the regulator tubes and mouthpiece by exhaling air, pressing the purge valve or holding the mouthpiece up above the first stage.

CLOSED CIRCUIT Breathing apparatus in which the exhaled gases of respiration are re-circulated to be cleaned of carbon-dioxide and re-charged with oxygen. Open Circuit.

CLOTHING Dry Suits - Wet Suits

CLOVE HITCH A knot which is commonly used for attaching a rope to a spar or bollard.

CNS Central Nervous System

CO2 Scientific shorthand for (strictly speaking) one molecule of carbon dioxide. In diving terminology it refers to carbon dioxide in general.

COLD INFECTIONS An infection of the nose and respiratory passages. The profuse mucus secretions can block the sinuses and Eustachian tubes, making diving painful or even dangerous.

COLD TEMPERATURE Hypothermia

COLIC A digestive upset usually due to gas; divers colic.

COLOUR Sensation received by the eyes, caused by radiations of light of different wavelengths. Under water colours fade as the water itself absorbs the colour. Red goes first: at a depth of only 1m red is fading. At 10m reds are virtually absent, while orange and yellow are fading. At 20m virtually the only colour present is a fairly uniform blue-green.

COLOUR This does not mean that colour colour is absent underwater, only that the depth of the water prevents you seeing it. If an artificial light source is taken under water, a torch or flash gun for example you will be able to see the colours once again where the light falls on them. This us why underwater photographers so frequently use artificial illumination of some sort.

COLOUR TRIANGLE The effects of adding together lights of different colours. Blue+green+redd=White. Blue+green=Cyan, Blue+red=Magenta, Green+Red=Yellow, Red, Blue and green are primary colours; cyan, magenta and yellow are secondary colours.

COMA A state of unconsciousness. The patient is totally without sensation of response.

COMA POSITION The position in which all unconsious persons should be placed as long as they are breathing. They must also be transported or carried in this position. with one exception - a fractured spine.

COMMUNICATE The means by which divers comunicate with each other underwater or above, via rope signals, surface cover to shore, shore to surface cover, etc. It includes arn signals, ropes, torches (for night diving),etc.

COMPASS A device for drawing circles. A magnetic instrument used for determining the direction of North; nowadays calibrated in 360 degrees in a clockwise direction.

COMPENSATOR Dent or facility in a face mask to enable the diver to seal his nostrils when clearing his ears.

COMPLEMENTAL AIR Inspiratory reserve;lung volume.

COMPRESSOR Mechanical device using external power to compress air. This is usually done in a number of stages, with interstage cooling and final filtration of the air.

CONCENTRATION CELL CORROSION This occurs on metal when the formation of anodes or cathodes is due to differences in the environment, eg, in crevices between gaskets, under deposits and scale, tc. It is usually associated with stagnant conditions. It may leat to pitting. Oxygen (dissolved in the water) accelerates corrosion.

CONCENTRATION CELL CORROSION Fe + 2 H2O + O2 - FE (OH)2. Iron goes into solution at the anode; oxygen is reduced at the cathode. Further oxidation is probable converting 2 Fe (oh2) into fe (OH)3. High po2 is of course normal within aqualung cylinders. Chloride ions (found in sea water) tend to migrate toward corrosion aras. This strimulates and accelerates corrosion in these areas. Corrosion pits typically appear are autocatalytic.

CONCRETE Engineering material consisting of a hydraulic cementing substance, aggregate and water. Sometimes iron rods are added as reinforcement. Strong in compression, weaker in tension. concrete will set under water, which makes it a useful underwater engineering material.

CONDENSATION Small droplets of water often in the form of mist, which forms when moist air comes into contact with a cold surface.

CONDERT, CHARLES Worked as a diver in the East River, Brooklyn, New York, up to 1832. He used a free-diver apparatus, independent of surface air. He was drowned in the East River in August 1832, probably because of a malfunction in his suit.

CONSTANT VOLUME LIFEJACKET Original name of the A.B.L.J.

CONSTANT VOLUME SUIT A dry suit in which nips or squeezes are prevented by air pressurisation and over inflation is prevented by pressure relief valves. The inflation can be provided straight from an air cylinder or as is often the case through a regulator connection.

CONTACT LENS An eyesight correction lens worn inside the eyelids and in contact with the conjunctiva (surface of the eyeball).

CONTAMINATION The presence of harmful impurities, eg, oil in compressed breathing air.

CONTENTS GAUGE A gauge which indicates the pressure of air inside a cylinder. Simple calculations will give the volume of air left in the cylinder.

CONTINENTAL SHELF Region of relatively shallow water (down to 600 feet or 200 metres) surrounding each continent. It forms a definate shelf.

CONTRAST Visual effect due to strong differences in luminance, reflection or colour. One of the more important means of visual comunication under water.

CONVERSIONS (random examples) miles to kilometres x 8/5;kilometres to miles x 5/8; miles to nautical miles - 1/8; nautical miles to miles +1/7;psi to feet (fresh water) x 2.31;psi to feet (sea water) x 2.25 Metres to feet x 3.28; litres to pints x 1.76; psi to atmosphers divide by 14.7 or x 0.068