MyOAN! Scuba Diving Jargon

A

Absolute Pressure total pressure from all sources such as atmosphere and water.

ACUC (Association of Canadian Underwater Councils) one of several agencies certifying SCUBA divers.

Air is comprised of Nitrogen 78.084%, Argon 0.934%, Oxygen 20.946%, and Carbon Dioxide 0.033%.

Air Compressor

Air Embolism obstruction of blood vessels by gas bubbles; in diving, the term is generally applied to obstruction of a vessel or vessels supplying the brain.

Alternate Air Supply either (1)an extra second stage used to provide air to another diver if they run out or have an equipment problem; or (2)a redundant air supply and regulator used primarily in the same circumstances by the diver carrying them, although they are available to others.

Alveolar Exchange transportation of oxygen to the blood and removal of carbon dioxide in the alveoli of the lungs.

Ambient Pressure total air or water pressure surrounding a diver; below the surface, is the total of the pressure exerted by the water itself plus the atmospheric pressure acting on the water (also known as absolute pressure).

Analog form of display on gauges using numerals and a needle pointing to the pressure, depth, temperature, etc.; like an "old-fashioned" clock; see new-fangled type: digital.

Archaeological Diving diving which results in the scientific study of historic or prehistoric peoples and their culture by analysis of their artifacts, inscriptions, monuments and other such remains.

Artificial Respiration any means by which an alternating increase and decrease in chest volume is artificially created while maintaining an open airway in mouth and nose passages; mouth to mouth, mouth to nose and mouth to snorkel resuscitation are examples.

Atmosphere unit of measurement for pressure exerted upon an object or person. The pressure exerted by the atmosphere at sea level is equal to the pressure exerted by 33 feet of seawater. Thus, at a depth of 33 feet there is one atmosphere (atm) of water pressure. At 66 feet, there are two atmospheres of water pressure, etc.

Atmospheric Pressure the pressure exerted by the earth's atmosphere at any given point at sea level; one atmosphere equals 14.7 pounds per square inch (psi).

B

Backward Roll Entry means of entering the water in SCUBA gear from a sitting position such as from the gunnel of a boat whereby the diver, while securely holding his mask, leans backward and rolls into the water onto his tank and shoulders.

Bailout training technique used in some SCUBA classes wherein the student jumps into the pool while holding all equipment in hand and then dons the equipment on the bottom of the pool; or, pertaining to or consisting of a means for relieving an emergency situation.

Barometric Pressure synonymous with atmospheric pressure except that it varies according to weather conditions.

Barotrauma injury due to effects of pressure.

BC or Buoyancy Compensator (See Buoyancy Control Device).

Bends (See Decompression Illness).

Bladder pouch within a Buoyancy Compensator which holds the amount of air the diver desires to provide proper buoyancy.

Bootie piece of foot protection, usually made of neoprene, worn inside an open-heeled fin; serves to protect the diver's feet while walking to and from the dive site and prevents blisters from the fins while swimming; also provides warmth, depending on thickness.

Bottle (see Tank) Bottom Time total elapsed time from the moment diver leaves the surface in descent to the time that ascent begins, measured in minutes.

Bourdon Tube curved tube (usually copper) used in analog pressure and depth gauges; pressure changes cause attached gauge needle to move around the dial.

Boyle's Law if the temperature of a gas remains unchanged, the volume of a given quantity of gas varies inversely to its pressure.

Buddy Breathing sharing of the same air supply by two or more divers; an emergency technique used when one person's air supply is exhausted or unavailable due to equipment malfunction.

Buoyancy upward force exerted upon an immersed or floating body by a fluid; neutral buoyancy allows the diver to remain at a depth without effort; positive buoyancy will cause the diver to rise toward the surface and requires effort to remain at depth; negative buoyancy results in the diver's sinking toward the bottom.

Buoyancy Control Device (BCD) an inflatable bladder, usually worn like a vest, to provide buoyancy on or below the surface; also known as Buoyancy Compensator (BC) or Vest.

C

C Card (certification card) issued by a SCUBA certifying agency evidencing the holder has successfully passed all the requirements of the agency to be a qualified diver. Must be shown before obtaining an air fill of a SCUBA tank or to go on a dive with reputable dive shops or resorts.

Cascade System type of air compressor system wherein the unit fills multiple large cylinders with air from which many SCUBA tanks can be filled as opposed to a direct fill system.

Cave Diving requiring much specialized training and equipment, this involves diving into an overhead environment including caves, abandoned mines or quarries and natural springs or sinkholes where the exit is not always visible. "Overhead environment" means a structure exists which prevents the diver from making a direct vertical ascent to the surface.

Cavern Diving requiring specialized training, this involves diving into an overhead environment including caves, abandoned mines or quarries and natural springs or sinkholes; differs from Cave Diving in that the exit should always be visible. "Overhead environment" means a structure exists which prevents the diver from making a direct vertical ascent to the surface.

CMAS (Confederation Mondiale Des Activities Subaquatiques) also known as World Diving Federation; one of several agencies certifying SCUBA divers world-wide.

Commercial Diving diving to yield or make a profit.

Compressed Air air compressed, esp. by mechanical means, to a pressure higher than the surrounding atmospheric pressure.

Compressed Air Demand-Type Unit breathing device using compressed air that is delivered to the diver through a regulator as it is demanded by inhalation; as opposed to a constant-flow unit.

Coral Reef Diving diving on a marine formation composed mainly of coral and other organic matter of which parts have solidified into limestone; usually home to many fish and other marine animals.

Crest foamy top of a wave.

Cummerbund an overlapping waistband with Velcro used to secure a Buoyancy Compensator snugly around the diver's waist.

Current a horizontal movement of water; currents can be classified as tidal and nontidal; tidal currents are caused by forces of the sun and moon and are manifested in the general rise and fall occurring at regular intervals and accompanied by movement in bodies of water; nontidal currents include the permanent currents in the general circulatory systems of the sea as well as temporary currents arising from weather conditions.

Cyalume Stick a chemical light stick usually attached to a tank valve or snorkel on a night dive making the diver visible to others; glow for several hours once activated and cannot be extinguished.

Cylinder a compressed breathing gas container (see Tank or Bottle).

D

D Ring connecting ring in the shape of the letter "D" on a BC or weight belt used for holding other accessories with snap rings.

Dalton's Law the partial pressure of a given quantity of gas is the pressure it would exert if it alone occupied the same volume; also, the total pressure of a mixture of gases is the sum of the partial pressures of the components of the mixture.

DAN (Divers Alert Network) non-profit organization formed to do medical research concerning the effects of diving on humans; operates a 24-hour medical assistance hotline for the U.S., Caribbean and Canada, and a non-emergency medical line for questions on medical problems or diving safety and acts as an advocate on issues of diving safety.

Decompression to release from pressure or compression; in diving, the term is often applied to the process of following a specific decompression table or procedure during ascent in order to release excess nitrogen.

Decompression Chamber see Hyperbaric Chamber.

Decompression Diving diving exposure requiring staged in-water stops before ascent to the surface to allow off-gassing of nitrogen.

Decompression Illness (DCI) injury resulting from formation of gas bubbles in the blood or tissues during or following ascent or decompression; in this case, the bubbles arise from gas (primarily nitrogen) that was dissolved in blood or tissues under increased pressure.

Density weight (mass) of anything per unit of volume.

Descent/Ascent Line line suspended from a boat, float or buoy used to permit divers to control their descents and ascents and to provide guidance to the bottom in poor visibility or strong currents; particularly useful on ascent to assist divers to make safety or emergency decompression stops between 10 and 15 feet.

Diaphragm dividing membrane or thin partition; the thin muscle separating the chest cavity from the abdominal cavity; the rubber (or other material) separating the demand chamber in a regulator from the surrounding water.

Digital refers to the "new" method of display on gauges showing pressure, depth, temperature, etc. by means of LED display; (like the "12:00" constantly flashing on your VCR.)

DIN tank connection high pressure system commonly used in Europe for many years, the DIN system features a regulator yoke with a captive o-ring design that allows the regulator to work with higher pressure tanks; advantages include greater air capacity, and use of more compact tanks with slight negative buoyancy; some DIN systems are capable of handling a high pressure environment up to 4350 psi; will not work with normal compressed air tank without an adapter.

Dive Computer small, portable electronic device carried by a diver designed to record data regarding the number, length and depth of dives (the dive profile), to calculate the no-decompression limits or, if necessary, the emergency decompression required and at what depth and to display the results of these operations underwater. Not a substitute for manual dive planning using dive tables.

Divemaster professional qualified to oversee SCUBA diving operations, as in group diving from boat, shore, etc. in salvage work or at a resort, and responsible for procedures, safety, and monitoring the whereabouts of divers underwater or at the surface and making rescues when necessary.

Dive Flag rectangular flag required to be flown whenever a diver is in the water to warn boaters to be on the lookout; U.S. flag is a red field with a white diagonal slash from the upper left to the lower right-hand corner, and the universal flag is a blue and white double-tailed pennant.

Dive Skin thin polyester one-piece body suit worn by divers to help protect oneself from stinging marine organisms and/or to help maintain body heat; sometimes worn under a wetsuit for additional insulation and to make it easier to don and doff a wetsuit.

Dive Table mathematical chart calculating no-decompression limits and decompression times and depths according to the total bottom time of and depths reached by the diver; designed to prevent decompression illness by estimating nitrogen build-up in the diver's body.

Doff and Don see separate listings. Also, an exercise sometimes used in SCUBA classes to familiarize participants with their gear by requiring a diver to remove and then replace gear while seated on the bottom of a pool.

Doff to remove or take off.

Don to put on or dress in.

Dry Suit one-piece coated-fabric or neoprene-foam garment worn by a SCUBA diver over special undergarments in especially cold water, protecting the skin from contact with water and having an internal, warming layer of air that can be added to in order to equalize pressure during descent.

E

Ebb Current movement of tidal current away from shore or down a tidal stream; tide that is flowing out or causing a lower water level.

Eddy circular movement of water, in a comparatively limited area, formed on the side of a main current; may be created at a point where the mainstream passes a projection or meets an opposite current.

Equalize in SCUBA diving, to relieve pressure in the inner ear canal by holding nose and gently blowing into nostrils or by moving jaw, thus making the pressure in the ear even with the ambient water pressure.

F

Farmer John/ Jane one-half of a wet suit which covers the legs and torso with straps over the shoulders--somewhat like a really tight pair of overalls.

Fins any device attached to the feet to increase area; available in two major styles: open heeled and full-footed (or shoe style).

Flood as a verb, means to fill one's mask (or, gasp, camera) with water. Flood Tide incoming tide at its greatest height; i.e., high tide.

Forward Roll Entry method of entering the water while in full SCUBA gear from a boat transom or a pier by bending at the knees and, while firmly securing the mask, rolling forward into the water landing on one's shoulders and tank.

G

Gauge Pressure on depth gauge, ignores atmospheric pressure and shows only the water pressure being measured; zero reading on the average gauge indicates atmospheric pressure; readings are expressed as pounds per square inch of gauge pressure (psig).

Giant Stride Entry most common method of entering water from a boat transom, pier, etc., where the standing diver takes a large step into the water while securely holding mask, tucking chin and bringing fins quickly together to keep himself at the surface for a controlled descent.

Goody Bag nylon mesh bag of various sizes used to 1) carry some dive gear, especially mask, fins and snorkel; and/or 2) used during a dive to carry "goodies" collected.

H

Helium extremely light gas (second only to hydrogen) used as a substitute for nitrogen in the breathing mixtures of deep commercial and military divers because it does not produce the narcotic effects under pressure that are associated with nitrogen; resulting mixture is called Heliox; use is associated with a physiological condition called high-pressure neurological syndrome, a disorder that causes muscular tremors, dizziness and nausea at extreme depth; requires special tables and is outside the scope of recreational scuba.

Hemorrhage any discharge of blood from blood vessels.

Henry's Law at a constant temperature, the amount of a gas which dissolves in a liquid, with which it is in contact, is directly proportional to the partial pressure of that gas.

High Altitude Diving is done in mountain lakes or other high altitude waters at or greater than 1,000 feet (300 meters) above sea level with increased risk of decompression sickness because of lower-than-sea-level atmospheric pressure at the surface; regular dive tables and some dive computers and depth gauges are inaccurate above sea level; special high altitude dive tables and recalibration of gauges and computer are required; specialty courses are available due to the complexity and added hazards of this activity.

Hyperbaric Chamber steel vessel in which atmospheric pressure can be raised by air compressors, used to treat divers afflicted with air embolism or decompression sickness by reducing the size of nitrogen bubbles and forcing them back into solution; the pressure is then slowly reduced allowing the diver the decompress gradually; immediate treatment is recommended; and location of nearest recompression or hyperbaric chamber should be part of all dive planning.

Hypothermia subnormal chilling of the body caused by extended exposure to cold temperatures or water of lower temperature than the human body; can be fatal if not properly or promptly treated; symptoms include shivering, slow speech and loss of coordination; shock and death are prevalent.

Hypoxia lack of oxygen absorption, frequently suffered at altitude, due to the body's inability to absorb oxygen from less dense air; symptoms include fatigue, shortness of breath, light-headedness, faintness, nausea and exhaustion.

Hemorrhage any discharge of blood from blood vessels.

Henry's Law at a constant temperature, the amount of a gas which dissolves in a liquid, with which it is in contact, is directly proportional to the partial pressure of that gas.

Hypothermia a subnormal chilling of the body.

I

J

J-Valve controlling the flow of air from the tank to the regulator, the J-valve contains a spring operated reserve mechanism that automatically shuts off the flow of air when internal tank pressure falls to 300 psi, at which point diver notices difficulty breathing and is warned to pull the lever down to again release the flow and begin the ascent.

Jetty a structure, usually made with rocks, extended into a sea, lake or river to influence the current or tide in order to protect a harbor.

K

K-Valve controlling the flow of air from the tank to the regulator, K valve operates like a faucet with a simple on/off mechanism; when open, air will flow to the demand regulator until internal tank pressure equals water pressure or the air supply is exhausted.

Kelp any large, brown, cold-water seaweed of the family Laminariaceae, used as food and in various manufacturing processes.

Kelp Surface Dive vertical, feet-first, method of descending into water of unknown depth or when obstructions or heavy plant (such as kelp) growth exists; performed by spreading arms and legs, then simultaneously bringing legs together while giving a strong downward stroke with arms thus propelling upper body out of water; body weight will then drive the diver downward; some also find this dive descent easier to equalize ears because there is less blood pressure in head than with pike (head first) dive.

Knot velocity unit of 1 nautical mile (6080.20 ft.) per hour; equivalent to 1.689 ft. per second: to convert ft. per sec. into knots, multiply by 0.592.

L

Landward in the direction of or being toward the land. Lee sheltered place or side; that side of a ship or island that is farthest from the point from which the wind or current blows.

Leeward pertaining to, or in direction of, the lee side; opposed to windward.

Lift Capacity amount of buoyancy provided by a Buoyancy Compensator; varies according to size of the BC and according to the purpose of the BC, e.g., a BC intended for use in cold fresh water will provide greater lift capacity than one intended primarily for use in warm salt water.

Low Volume Mask one which has a smaller area between the glass and the diver's face, usually with separate lenses for each eye; requires less air to purge if becomes flooded.

Low Water minimum level reached by a falling tide; i.e., low tide; the height may be solely the result of periodic tidal forces or further affected by weather conditions.

M

Martini's Law (Nitrogen Narcosis) mental effect of each 50 ft of descent breathing compressed air; is approximately equivalent to that of one (American-style) dry martini, starting at 100 ft.

Mask skirted glass window constructed to provide air space between eyes and water and to permit both eyes to see in the same plane; a regular mask covers eyes and nose only; modern mask skirts are usually made of silicone rather than the older rubber ones.

Mask Squeeze painful condition when the air inside the mask is compressed by the external pressure creating suction on the face and eyes; can be alleviated by exhaling from the nose; can cause permanent eye damage if not equalized.

Mixed Gas Diving use of any breathing medium containing a percentage of oxygen and nitrogen which differs from Compressed Air; could be a mix where helium has been added to air or a mix containing only oxygen or helium or another inert gas.

N

Narcosis reversible condition characterized by stupor or insensibility; in diving, narcosis generally refers to a state of altered mental function, ranging from mild impairment of judgment or euphoria (false sense of well-being) to complete loss of consciousness suffered a depths greater than 90 feet and caused by exposure to nitrogen; see "Martini's Law", also known as Nitrogen Narcosis or Rapture of the Deep.

N.A.S.D.S. (National Association of Scuba Diving Schools) one of several agencies certifying SCUBA divers.

N.A.U.I. (National Association of Underwater Instructors) one of several agencies certifying SCUBA divers.

Nausea any sickness of the stomach creating a desire to vomit.

Nautical Mile also known as a "geographical mile" or "sea mile"; a unit of distance designed to equal approximately 1 minute of arc of latitude, 6080.20 ft.; approximately 1.15 times as long as the statute mile of 5280 ft.

Night Diving done after dusk, giving a diver the opportunity to observe nocturnal animals such as lobsters and coral polyps which actively feed at night (or catfish in fresh water); also permits diver to approach sleeping fish which would be shy or even hide by day.

Nitrogen colorless, odorless inert gas and the most abundant component of the atmosphere (78.084%); serves primarily as a means to dilute and carry oxygen; although not used in the respiratory process, nitrogen under pressure can sedate the central nervous system: see Nitrogen Narcosis.

Nitrogen Narcosis see Narcosis.

Nitrox rather than using "Compressed Air", nitrox diving involves use of "Enriched Air" mixtures ranging from 23.5% to 40% oxygen; tanks filled with nitrox should bear indicator colors of yellow and green; requires use of DIN tank connections NOAA National Oceanic Atmospheric Administration

O

O-Ring small pliable ring at the orifice of a tank valve which enables the valve to form an airtight seal with the regulator; modern O-rings rely more on air pressure to make a seal than the pressure created by tightening the regulator yoke screw; also found on other parts of SCUBA gear.

Octopus Regulator alternate second stage air source used by a diver's buddy in an out-of-air situation (see Buddy Breathing).

Open-Heeled Fin has only a strap at the back rather than a full shoe; normally worn with booties to protect the foot; used to give a swimmer/diver greater thrust through the water while kicking.

Open-Water Diving recreational diving done in an environment other than a swimming pool but with no overhead obstacles; examples include lakes, ponds, rivers, oceans, quarries.

Oxygen an active element which is one of the most plentiful elements on earth, accounting for 20.946% of the atmosphere; phytoplankton living in the oceans are responsible for the production of over 85% of the world's supply of oxygen.

Oxygen Poisoning too much oxygen caused by the effect of the partial pressures of gases under pressure; the normal partial pressure of oxygen in air is .21 atm, or 21% at sea level; air containing the normal amount of exygen becomes toxic at a depth of 297 feet because the partial pressure of oxygen equals about 2 atmospheres; causes muscular twitching, nausea, vision and hearing problems, breathing difficulty, anxiety, confusion, unusual fatigue and clumsiness; will never be a problem for the sport diver who restricts his diving to 100-130 feet in depth; could also be caused by breathing pure oxygen at only 33 feet.

P

P.A.D.I. (Professional Association of Diving Instructors) one of several agencies which certifies SCUBA divers.

Partial Pressure pressure exerted by a specified component in a mixture of gases with the concentration of oxygen in air as 20.94 percent; if the ambient pressure is 1.0 atmosphere absolute, the partial pressure of oxygen in dry air is 0.2094 atmosphere (atm).

Physics Of Diving application of physical laws and principles to man's activities underwater.

Physiology Of Diving organic process and phenomena dealing with life and functions of organs of human beings while in a water environment.

Pike Surface Dive head-first method of propelling the diver's body down into the water; executed by starting from a face down position at the surface, then bending at the waist while lifting the legs together completely out of the water allowing the weight of the diver's legs to force him down.

Pony Bottle small air tank used as a backup source of air for returning safely to the surface in the event the primary air tank runs out or has an equipment failure.

PSI (pounds per square inch) unit of measurement for the volume of air in a SCUBA tank.

Purge remove unwanted air or water from a confined space; used to describe removing water from a snorkel or mask or air from a supply hose prior to disconnection.

Q

R

Rapture of the Deep see Nitrogen Narcosis.

Rate of Ascent speed of ascent to the surface; should not be faster than 1 ft./sec. and some organizations and computers recommend not faster than 1 ft./2 sec. especially during last 10 feet to surface.

Rebreather closed-circuit system which filters exhaled air, then recirculates it for rebreathing by the diver; requires special training and maintenance.

Recompression returning a diver to increased pressure for treatment of decompression sickness or air embolism; is properly accomplished in a recompression (or hyperbaric) chamber in accordance with specific rules and tables.

Recreational Diving generally, sport diving at 130 feet or less on compressed air only within no-decompression limits in open-water environment; other diving is considered "technical" or "commercial."

Redundant Air Supply second source of air and regulator primarily carried by the diver in case he runs out of air or has an equipment problem, although it is available for use by others.

Reef ridge or chain of rocks or sand often of coral debris at or near the surface of the water.

Regulator automatic device for maintaining or adjusting the flow of air equal to the ambient pressure of the water; includes the demand regulators used to take air from a diver's scuba cylinder and reduce it to a breathable, ambient pressure; can be open-circuit wherein exhaust is vented into the water or closed-circuit, rebreather type.

Repetitive Dive dive begun at least 10 minutes, but not more than 12 hours, after conclusion of previous dive.

Repetitive Group Designation on dive tables, letter relating directly to the amount of residual nitrogen in a diver's body for 12-hour period following a dive; used to calculate profile of next dive.

Residual Nitrogen amount of nitrogen still in solution in a diver's tissues from a dive.

Residual Nitrogen Time on dive tables, amount of time, in minutes, which must be added to the bottom time of a repetitive dive to compensate for the nitrogen still in solution in a diver's tissues from a previous dive.

Residual Volume volume of air which remains in the lungs after the most forceful exhalation.

Respiratory Minute Volume amount of air inhaled and exhaled per minute to maintain proper body function; this is variable, depending on exertion and the individual.

Rip Current strong current of limited area flowing outward from the shore, and may be visible as a band of agitated water with the regular wave pattern altered; current is caused by the rush of escaping water which is piled between shore and bar or reef by wave action through a gap in the bar or reef; such currents are dangerous to the uninitiated and are the cause of many drownings at ocean beaches; however, when located by divers they are often used to facilitate entry to areas beyond the bar or reef.

Rupture breaking apart, bursting, as an eardrum under non-equalized pressure.

S

Safety Stop voluntary stop at conclusion of dive normally made while holding an ascent/descent line at 10-15 feet to allow additional off-gassing of nitrogen as an extra measure of safety; should be done in a head-up position usually for 3-5 minutes.

Scooter powered mode of underwater transportation which pulls 1-2 divers through the water.

SCUBA (self-contained underwater breathing apparatus) any free unit containing necessary elements (gases) to support life under water. Seaward away from land toward the open sea.

Shallow Water Blackout result of excessive hyperventilation in breath-hold diving; some divers deliberately hyperventilate at surface to reduce carbon dioxide level--too much can lead to hypoxia (oxygen deficiency) before the carbon dioxide level gets to the level to tell one to breathe.

Shoal place where a sea, river, or other body of water is shallow because of a bank or bar.

Shoe Fin one with a full rubber shoe rather than just a strap; no booties are required to use this type of fin; used to give a swimmer/diver greater thrust through the water while kicking.

Shorty Farmer John/Jane that has been cut off at the knees.

Sinus Squeeze painful but usually temporary condition in sinuses in the head due to failure of pressure in sinus to equalize with ambient pressure; often caused by diving with a cold or allergy.

Skin Diving diving without the use of SCUBA.

Slack Water state of a tidal current when its velocity is near zero, especially the moment when a reversing current changes direction and its velocity is zero; occurs at high and low tide.

Slate thin piece of plastic used for underwater communication via writing with a pencil.

Snorkel J-shaped tube, the short end of which is held in the mouth, the long end protruding above the surface, permitting breathing without raising the face of the water when swimming.

Specific Gravity ratio of the density of a substance to water.

Sport Diver one who dives with or without scuba for noncommercial purposes; see Recreational Diving.

Standard Atmospheric Pressure unit of pressure used in underwater activities and called 1 atmosphere.

Suit Squeeze painful condition of body whereby increased ambient pressure causes compression of wet suit or dry suit, usually behind the knee or inside the elbow; usually can be alleviated by eliminating bunching of material in these locations; while not likely to cause permanent injury, can leave red, swollen welts.

Surf waves breaking upon a shore or shoal.

Surface Interval time spent between dives; must be at least 10 minutes in length; measured from time diver surfaces until beginning next descent.

Surge great rolling swell of water, violent rising and falling.

Swell large and more-or-less smooth wave.

Symptoms perceptible changes in body state or function that may be indicative of disease or injury; strictly, the word applies to changes perceptible to the individual himself, but it is often used to include signs, which are abnormalities that can be detected by an observer or examiner.

T

Tank hollow metal vessel, or cylinder, used to contain compressed air or other gas; integral part of self-contained underwater breathing apparatus; also called bottle.

Technical Diving diving which includes one or more of the following: deeper than 130 feet, using a breathing mixture other than compressed air, decompression or overhead diving, requiring special training and equipment.

Thermocline sharp temperature change; layer of water in an ocean or certain lakes separating an upper warmer zone from a lower colder zone; in some cases is clearly visible.

Tidal Volume volume of air passing in and out of the lungs with each natural inspiration and expiration.

Tide periodic rise and fall of water level due to the gravitational attraction of the moon and sun acting on the earth's rotating surface.

Toxic poisonous.

Toxin any poison produced by an organism such as plants and animals.

Trough hollow or low area between crests of waves.

U

Undertow current beneath surface that sweeps seaward or along a beach when waves are breaking on shore.

V

Valve device that starts, stops or regulates the flow of gas or air in diving equipment.

Venom poisonous fluid introduced into the body of the victim by biting, stinging, etc.

Venomous having a gland or glands for secreting venom; able to inflict a poisoned bite, sting or wound.

Vertigo dizzying sensation of tilting within stable surroundings; such as suffered with sea-sickness.

Volume amount of space measured by cubic units that an object or substance occupies.

W

Weights items used to allow a diver to descend in the water column against the forces buoying the diver upwards, usually lead, either solid or in shot form contained in pouches; some solid leads may have a plastic coating and are normally worn on a waist belt or as an integrated part of a Buoyancy Compensator.

Windward point or side from which the wind blows; in the direction from which the wind blows; as opposed to, leeward.

Wheel, The version of the Recreational Dive Planner, an alternative to Navy Dive Tables, used to calculate no-decompression multilevel dives, increasing dive time by giving credit for slower nitrogen uptake in shallower depths.

Wreck Diving diving on natural or man-made shipwrecks; specialty courses are available.

X

Y

YMCA (Young Men's Christian Association) one of several agencies which certify SCUBA divers.

Yoke a device for attaching regulators to tanks so as to make a leakproof seal.

Z