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All Terms
Abdominal hernia
A weakness of the abdominal wall through which the intestines or other intraabdominal contents protrude. Dangerous to a diver if a loop of air-containing intestine is trapped outside the abdomen.
Pressure calculated by using a vacuum as the zero point and including the gauge and atmospheric pressure in the calculation.
Actual bottom time (ABT)
Total elapsed time in minutes from leaving the surface until ascent is initiated.
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.
A hormone secreted by the adrenal gland into the circulatory system which stimulates the heart, blood vessels and respiratory system.
Australian Diver Accreditation Scheme: An international commercial and occupational diver certification scheme.
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.
Abbreviation for arterial gas embolism.
A gas mixture containing 21% oxygen, 78% nitrogen, and 1% other gasses (mainly argon); compressed air is used for recreational scuba diving.
Air compressor
A machine that compresses or pressurizes air; for scuba purposes, air is compressed from the atmospheric level (14.7 psi at sea level) to the capacity of the tank, usually between 2500-3000 psi.
Air Consumption
The depletion of breathing gas by a diver during the course of a dive.
Air Dome
A section of cave which traps air or other gas at the top. This gas is not directly connected to the surface.
Air embolism
A condition that occurs when air enters the bloodstream through ruptured alveoli into the pulmonary capillaries. The air in the bloodstream then forms bubbles, which can block blood flow to the body's tissues.
Air pressure
The force per unit area exerted by the weight of air; at sea level the air pressure is 14.7 psi. (air pressure decreases with altitude.)
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.
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. Sometimes refered as a Red Tide.
A set of equations incorporated into diving computers in order to compute nitrogen uptake and elimination from changes in depth and elapsed time.
Alpha flag
an International maritime signal flag, meaning, 'Diver down, keep clear'.
Alternate air source
A redundant air supply. A device a diver can use in place of the primary regulator, in order to make an safe ascent while still breathing normally. This can be either an octopus second stage or a separate tank and regulator, sometimes called a pony tank.
Alternoberic Vertigo
Un-even release of pressure from the inner ear. Causing vertigo, dizziness and spins.
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.
altitude sickness
An illness brought on by the sudden reduction in pressure of ascent to altitude.
Air sac at the terminus of a bronchus where oxygen and carbon dioxide transfer occurs.
Ambient Light
It is the available sunlight underwater used as a source of illumination.
Ambient pressure
The surrounding pressure; on land, comes from the weight of the atmosphere (see air pressure), at depth, comes from the weight of the water plus the weight of the atmosphere. One atmospere is about 14.7 pounds of pressure per square inch.
Analog instrument
Device that uses a needle moving around a dial to provide information.
Anchor Line
A rope, cable or chain that attaches a boat to its anchor.
American Nitrox Divers Incorporated
Any reduction in the oxygen carrying capacity of the red blood cells.
A medical condition caused by a severe lack of oxygen in the body.
Medications that reduce the clotting ability of the blood. Particularly dangerous to divers due to barotrauma of air-filled body cavities.
An impairment of language ability which may range from having difficulty remembering words to being completely unable to speak, read, or write.
Aqua Lung
The first self-contained-underwater-breathing-apparatus that used compressed air and a two-stage on demand regulator. The aqua lung was designed by Jacques Cousteau and Emile Gagnan.
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.
Archimedes principle
Any object wholly or partly immersed in fluid will be buoyed up by a force equal to the weight of the fluid displaced by the object.
An inert gas that makes up less than one percent of air (sometimes used as a dry suit gas).
Irregularities in the rhythm and rate of the heart, particularly dangerous to divers due to the underwater environment.
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
The condition characterized by bubble(s) of air from a ruptured lung segment under pressure; the bubbles enter the pulmonary circulation and travel to the arterial circulation, where they may cause a stroke.
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.
Artificial Spit
Small bottles of "special" liquid used by divers to keep their masks defogged. There are many diffrent manufactures that offer a gel, paste or spray.
Ascent Bottle
An extra cylinder of air used on deep dives to allow decompression stops without fear of running out of air.
Ascent Bottle
An extra cylinder of air used on deep dives to allow decompression stops without fear of running out of air. They come in many different sizes from 6 c.f. to a full 80 c.f. tank.
Ascent rate
The rate at which depth is reduced at the end of a dive. An important component of decompression.
Ascent/Decent line
Line suspended from a boat or a buoy for a diver to use to control their rate of ascent or descent.
A common condition manifested by narrowing of air passages within the lungs. One reason for the narrowing is excess mucous in the airway.
Atmosphere absolute; 1 ata is the atmospheric pressure at sea level; is measured with a barometer.
The blanket of air surrounding the earth, from sea level to outer space. Also, a unit of pressure; "one atmospheres is pressure of the atmosphere at sea level, I.e., 760 mm Hg. Two atmosphere is twice this pressure, 1520 mm Hg, etc. Abbreviated atm.
Atmosphere Absolute
The ambient pressure including the air column over the water. The air column = 1 atm. at sea level. In sea water, another atmosphere is added each 33 FSW (Feet of Sea Water) . There is an increase in pressure per foot of sea water equivalent to 1/33 or .03030303 . So ATA may be calculated by multiplying the depth (FSW) by .0303030 and then adding 1 for the air above the water. i.e. the ATA at 46 FSW = (46 * .0303030) + 1 = 2.3939 ATA. to convert ATA to FSW. ATA - 1 * 33 = FSW.
Atmospheric pressure
Pressure of the atmosphere at a given altitude or location.
Australian Underwater Federation
Aquatic World Awareness, Responsibility and Education. A PADI nonprofit environmental foundation that provides financial support for aquatic preservation endeavors, develops conservation-oriented educational materials and initiates public awareness campaigns.
Axial flow scrubber
An axial scrubber is a scrubber design in which the breathing gases move from top to bottom (or vise-versa) through the scrubber.
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.
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.
When suspended particles in the water, such as sand, are illuminated by light from a flash, they reflect the light back to the lens. The particles appear as specks or snow in the photo.
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 drections 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.
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. Checking for an all clear is recommended.
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.
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.
Balanced regulator
Regulator designed to provide a consistent demand effort not affected by cylinder gas pressure or depth.
Barometric pressure
Same as atmospheric pressure with the exception that it varies with the weather.
Any disease or injury due to unequal pressures between a space inside the body and the ambient pressure, or between two spaces within the body; examples include arterial gas embolism and pneumothorax.
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.
See buoyancy compensator.
Beach Master or Beach Marshal
A person on the beach who records when divers enter and exit the water. Typically used during scuba classes to keep track of the students, watch the gear, provide assistance when required.
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.
Bell man
Standby diver 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 umbilical
The combined supply and return hoses and cables for life-support, power and communications between a diving bell and the support platform.
A form of decompression sickness caused by dissolved nitrogen leaving the tissues too quickly on ascent; is manifestation of decompression sickness.
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.
A pouch within a Buoyancy Compensator which holds the amount of air the diver desires to provide proper buoyancy.
Body suit
Garment that provides full length abrasion protection.
A 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. May come in a varying sole thickness.
Bottom time
The time between descending below the surface to the beginning of ascent.
The front end of a boat.
Boyle's law
At a fixed temperature for a fixed mass of gas, pressure times volume is a constant value.
Breath-hold diving
Diving without life support apparatus, while holding one's breath.
Britsh Thermal Units or calories; measurment of heat.
A collection of air or gas surrounded by a permeable membrane through which gases can enter or exit.
Diving partner.
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.
Buddy System
Pair or sometimes threesome of divers that dive together as a team for safety.
The upward force exerted on an object in liquid, whether the object sinks or floats. Objects that float are positively buoyant, those that sink are negatively buoyant and those that stay where placed are neutrally buoyant.
Buoyancy compensator
An inflatable vest worn by the diver that can be automatically or orally inflated to help control buoyancy; abbreviated BC or BCD (Buoyancy Control Device).
Burst disk
Thin copper disk held in place with a vented plug. Designed to rupture if tank pressure is greatly exceeded.
Cerebral arterial gas embolism.
Capillary depth gauge
Made up of a small tube. Uses Boyle's law to determine depth.
Carbon dioxide
CO2; an odorless, tasteless gas that is a byproduct of metabolism; is excreted by the lungs in exhaled air.
Carbon dioxide toxicity
Problems resulting from buildup of CO2 in the blood; they may range from headache and shortness of breath, all the way to sudden blackout.
Carbon monoxide
CO; odorless, tasteless, highly poisonous gas given off by incomplete combustion of hydrocarbon fuels.
Carbon monoxide poisoning
CO bonds with hemoglobin and prevents blood cells from carrying oxygen. This causes oxygen deprivation in the tissues and can even cause death.
Carbon monoxide toxicity
Illness from inhaling excess CO; problems may range from headache to unconsciousness and death.
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.
Refers to a divers certification card for a specific level of achievement.
Course Director. Level of instructor certification authorized to conduct instructor training.
Cave Diving Association of Australia. The CDAA was formed in September 1973.
Centers for Disease Control and Prevention. An U.S. government agency within the Department of Health and Human Services which, among other functions, maintains the Traveler Hotline with information on geographic distribution of diseases and inoculations required/recommended for travel toother countries.
Metric unit for temperature. C=(F-32) x .556
cubic foot. A measure of volume. Scuba cylinders are manufactured in standard sizes, such as 30, 50, 72 and 80 cf.
Charles's Law
The amount of change in either volume or pressure of a given volume of gas is directly proportional to the change in the absolute temperature.
Closed circuit scuba
Apparatus designed to allow divers to re-breath exhaled air after removal of CO2 and addition of supplemental 02. In contrast to "Open Circuit", closed circuit scuba is noiseless and produces no bubbles.
The Confédération Mondiale des Activités Subaquatiques (CMAS) is the World Underwater Federation. CMAS is the international umbrella organisation for diver training organizations. It was founded in Brussels on September 28, 1958. One of the founding members was the French underwater pioneer Philippe Tailliez. As such, it is one of the world's oldest scuba diving organizations.
Combat swimmer
Person trained in scuba diving or swimming underwater in a military capacity which can include combat
A theoretical division of the body with an arbitrarily assigned half time for nitrogen uptake and elimination. In designing decompression tables the body is divided into finite number of compartments for purposes of making calculations.
A device that monitors nitrogen in the body during a dive though mathematical algorithms. The device allows divers to multilevel dive and extend bottom time beyond what a dive table allows.
Invertebrates that secrete an internal, hard skeleton structure composed of calcium carbonate, which is absorbed from the surrounding water.
Core temperature
The internal temperature of the body, 98.6F is the normal temperature of the human body. Deviation from this temperature even a few degrees could be life threatening.
An overlapping waistband with Velcro used to secure a Buoyancy Compensator snugly around the diver's waist.
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. For general rules: 1 to 2 kt current is Light, 2 to 3kt current is Mild, 3 to 4kt is Strong and 5kt is Very Strong for the average diver!
Divers Alert Network. Nonprofit organization that provides emergency and informational advice and assistance for diving injuries, promotes diving-related medical research and education, collects injury statistics, and offers dive safety services to its members and the diving community.
Dalton's Law
The total pressure exerted by a mixture of gases is equal to the sum of the pressures of each gas of the different gases making up the mixture. Each gas acting as if it were alone were present and occupied the total volume.
Deco Mix
Gas mixture used during decompression.
Any change from one ambient pressure to a lower ambient pressure, always results in a reduction of gas pressure within the body.
Decompression dive
Any dive where the diver is exposed to a higher pressure than when the dive began, the decompression occurs as the diver ascends.
Decompression illness
DCI; a term to encompass all bubble-related problems arising from decompression, including both decompression sickness and arterial gas embolism.
Decompression sickness
DCS; a general term for all problems resulting from nitrogen leaving the body when ambient pressure is lowered. Can be divided into Type I (musculoskeletal and/or skin manifestations only) or the more serous Type II (neurologic, cardiac, and/or pulmonary manifestations).
Decompression stop
On ascent from a dive, a specified time spent at a specific depth, for the purpose of nitrogen off-gassing. When not mandatory it is called a safety stop.
Deep diving
For recreational divers a deep dive is a dive below 60 ft.
Dive Equipment & Marketing Association. Not-for-profit organization of equipment manufacturers, training agencies, dive media, travel companies and dive retailers that seeks to promote scuba diving and snorkeling to the general public.
Depth gauge
A device that indicates how far a diver is below the surface.
Descent/Ascent Line
A 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.
A 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.
Deutsches Institut fur Normung. Design of tank valve popular in Europe in which the first-stage regulator screws into the tank valve. Recommended for high pressure tanks.
Dive computer
Device that constantly measures depth and time, based on a pre-programmed algorithm, the computer calculates tissue nitrogen uptake and elimination in several theoretical compartments and provides a continuous readout of the dive profile, including: depth, elapsed time of the dive, duration at current depth before decompression becomes mandatory, and a warning if the rate of ascent is too fast.
Dive Flag
May be either a red rectangle with a white diagonal stripe or a blue and white double tailed pennant. Flags are used to warn watercraft to stay away because there are divers below.
Dive lights
Specially designed underwater lights used for night, cave or wreck diving.
Dive Master
A professional level diver who leads a group of less experienced divers underwater. He works with an Instructor during classes.
Dive Profile
a two dimensional representation of the two most important characteristics of the dive that a diver must monitor to dive safely: depth and time. The profile is often used when describing a dive's likely decompression obligation.
Dive Shop
A supplier of diving equipment or training, or organizer of dive expeditions.
Dive Tables
A printed collection of dive times for specific depths, by which the divers can avoid contacting DCS. Most tables are based on Haldanian theory for nitrogen up-take and elimination.
Diver propulsion vehicle
Motorized vehicle used by divers to cove long distances underwater without having to kick.
Department of Transportation. U.S. government agency that regulates the manufacture, testing and transport of compressed gas containers, including scuba cylinders. DOT stamp appears on scuba tanks, followed by the alphabetic designation for the steel or aluminum alloy the tank is made of and the maximum fill pressure.
Diver propulsion vehicle, underwater scooter that allows a dive to cover an increased distance underwater. Popular at some resorts.
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.
A death caused by inability to inhale anything but water. The process of experiencing respiratory impairment from submersion/immersion in liquid.
Dry Suit
A water-tight garment that keeps the diver's body warm by providing insulation with a layer of gas, such as air, for diving in waters that are too cold for comfortable wetsuit protection, usually below 65'F.
A medical conditions resulting from changes in ambient pressure.
Enriched Air Nitrox. A N2/O2 (nitrogen/oxygen) breathing gas containing more oxygen (typically 32 or 36 percent) and less nitrogen than plain air. Used by recreational divers to increase either bottom time or safety margin by decreasing the amount of nitrogen absorbed. Requires predive testing of gas mixture and adherence to strict depth restrictions.
Ebb Current
A movement of tidal current away from shore or down a tidal stream; tide that is flowing out or causing a lower water level.
Electronic closed circuit re-breather. Sometime ECCCR for electronically controlled closed circuit re-breather.
A 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.
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 aluminum cylinders. Also called Visual Plus inspection. Required for cylinders of AA6351 alloy.
E-L algorithm
Exponential-Linear algorithm of 2008 US Navy tables, assumes exponential in gassing and a combination of linear and exponential outgassing rates.
Electro-galvanic fuel cell
An electrical device used to measure the concentration of oxygen gas in diving equipment.
The act of forcing air into an open space to offset increasing water pressure.
Eustachian tube
A short tube connecting the back of the nose to the middle ear. If clogged, by mucus, equalization is next to impossible.
Exposure protection
Garment worn to prevent decreases in core body temperature and abrasions. Protection can range from thin body suits to heavy dry suits.
The temperature scale used in the United States. F=(C/.556) +32
A linear unit of measurement (equal to 6 feet) for water depth - commonly used by fishermen. Depth = V x T/2
feet of fresh water. Measurement of depth in fresh water.
First Stage
Regulator attached to the scuba tank that lowers the tank pressure to ambient pressure plus a pre-determined pressure (e.g., ambient + 140 psi).
Foramen Oval
The opening between the left and right atria of the fetal heart which remains open in about 30% of people, allowing passage of bubbles into the arterial circulation which is believed to cause symptoms of arterial gas embolism.
Forward Roll Entry
A 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.
Free Diving
Diving without any scuba or other equipment and synonymous with breath-hold diving.
Frenzel maneuver
Technique for equalizing 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.
A scuba diver, particularly a military diver on an undercover mission.
feet of sea water. Measurement of depth in sea water.
Feet of sea water; used to indicate either an actual depth, or just a pressure equal to that depth (e.g., in an hyperbaric chamber).
Kitchen on a boat.
Gas absorption and elimination
Dissolved gases such as nitrogen are absorbed into the blood and tissues during the course of the dive. The level of saturation depends on the depth of the dive. The elimination of these gases is very important in preventing decompression sickness. The length of time required for elimination depends on the duration and depth of the dive.
Gas Analysis
A procedure whereby the fractions of gas in a breathing mixture are determined. Generally it is used to determine the fraction of oxygen to within 1 %, to control the effects of Oxygen toxicity. Most diving operations will analyse for oxygen only. In more complex Trimix's, it is be desirable to analyse for the inert gases as well.
Gas Laws
Laws that predict how gases will behave with changes in pressure, temperature and volume.
Gas Saturation
Gas saturation occurs when the level of dissolved gas in a particular body tissue has reached its maximum.
Gauge pressure
Pressure exclusive of atmospheric pressure, when diving, gauge pressure is due to the water pressure.
Gorman Dive Adventures and Travel.
Giant Stride Entry
The 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.
GoPro cameras. Hero 3 Black, Siver and White. Miniture camera for all sports, above water and under. GoPro is a brand of the privately owned San Mateo, California company Woodman Labs that features "wearable" camera/camcorders such as helmet cameras that are targeted at adventure video/photography.
global positioning system. A worldwide system of navigation based on a ring of stationary satellites. Small, even handheld, GPS devices can be used to accurately determine speed and direction of travel, and pinpoint dive site locations.
Granny Line
Also known as a Gerry Line. A line which goes from the stern platform or hang bar to the anchor line.
Related to Haldane's theory that nitrogen is absorbed up and released in an exponential manner during a dive, and that there is some safe ratio of pressure change for ascent.
Half Time
Half the time it takes for a dissolved gas in a tissue (such as nitrogen) to equililbrate to a new pressure, or to reach full saturation at a new pressure. Theoretical tissue half times are used in designing dive tables and algorithms for dive computers.
A Halocline is a change in the salt content of the water, but is not often apparent to divers unless severe enough to cause buoyancy changes.
Hang Tank
An extra tank, ideally of deco mix, staged at the decompression stop. Normally found at the rear of a dive boat in case of emergencies.
Restroom on a boat.
Mixture of helium and oxygen, usually reserved for very deep diving.
Second lightest gas; does not cause problems of narcosis to the same extent as seen with nitrogen, and is therefore used for very deep diving.
Henry's Law
The amount of any given gas that will dissolve in a liquid at a given temperature is a function of the partial pressure of the gas in contact with the liquid and the solubility coeffient of the gas in the liquid.
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.
High pressure nervous syndrome
Abbr. HPNS; A condition which results from breathing Helium under high pressures. Early symptoms of HPNS are somtimes seen as shallow as 300FSW but more commonly over 600FSW. The severity also depends on the mix of breathing gases, Nitrogen can often moderate the affects of HPNS. The early symptoms include muscle tremors, followed by changes in electroencephalogram (EEG) readings, impaired motor and problem solving skills. Other symptoms can include euphoria, nausea, vomiting, lack of appetite and drowsiness. Symptoms sometimes moderate or entirely dissapear with continued exposure.
Hogarthian Principles
The Hogarthian configuration is named after Bill 'Hogarth' Main. It is based on reducing equipment to a minimum streamlined configuration that nevertheless includes sufficient redundancy for extended decompression dives.
Garment worn over the head to reduce thermal loss.
A surface-supplied compressed air apparatus, for use in shallow diving in calm waters. The air is delivered to one or more divers through a long hose.
The common term for the hydrostatic test required on scuba cylinders every five years to determine whether the tank walls are still strong enough for safe usage.
An inert gas, and lightest of all the elements, has been used in experimental diving situations.
Hydrostatic Test
Pressure test in which the tank is filled with water instead of air and raised to five thirds the maximum working pressure, causing the water to expand and be displaced.
Hyperbaric Chamber
Air-tight chamber that can simulate the ambient pressure at altitude or at depth, is used for treating decompression illness.
A higher than normal P02level in the blood.
Hyperoxic and hyperoxia
In general, these terms relate to a more than a normal amount of Oxygen. Hyperoxic refers to a mixture of gases with higher than normal Oxygen content (above 21%). Hyperoxia is the physiological condition associated with breathing too high of a partial pressure of Oxygen. The human body has a limit on both the partial pressure of Oxygen it can tolerate and the long term dosage of Oxygen. The partial pressure upper limit is generally considered to be approximately 1.6 ppO2 but most divers leave some margin for error and a more typical upper limit is 1.4 ppO2. When high partial pressures of Oxygen are inspired, convulsions may occur with little or no warning.
A body temperature warmer than normal, less common in diving than Hypothermia, but can occur from overheating in a wet suit.
Over breathing to the extent that the blood carbon dioxide level is lowered, may lead to tingling in fingers and dizziness.
A subnormal chilling of the body.
Under breathing to the extent that the blood carbon dioxide level is elevated, may be manifested by carbon dioxide narcosis.
Lower than normal PO2 level in the blood, insufficient oxygen in the blood.
A body temperature colder than normal (98.6F), severe problems start to manifest when body temperature reaches about 95'F.
International Association of Nitrox and Technical Divers. IANTD is the only EANx agency that offers training in all aspects of EANx through continuing education programs. This allows you to expand your knowledge and training with the top professionals in the field. IANTD instructors are well trained, highly experienced and extremely qualified. IANTD Standards and Procedures provide for the highest level of EANx education and training available. IANTD (IAND, Inc.) was founded by Dick Rutkowski, the former dive supervisor for the National Oceanic and Atmospheric Administration (NOAA). Mr. Rutkowski introduced the recreational diving community to the technology of EANx. This program was developed through NOAA during his tenure. Today the board of directors and the membership of IANTD are composed of many of the most experienced divers in the world pertaining to the use of breathing gases other than air.
Immersion Hypothermia
The lowering of body temperature when a diver is fully immersed in cold water without proper thermal protection.
Inflator Valve
A manually operated valve that puts compressed air into the buoyancy bladders of a BCD or into a dry suit.
An animal without a backbone, (vertebrate)
Jellyfish are members of the cnidarians group of invertebrates. They are transparent and bell shaped with tentacles hanging down from their body. They are free-floating and seem serene, but in their tentacles there are stinging mechanisms that are used to catch prey and for defense.
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.
Jon Line
Is a line with a hook device that is designed to attach to any thickness anchor or down line that allows the diver to stay in the water column regardless of wave action during deco stops.
Contains a spring loaded valve that shuts off a divers air supply at approx. 300psi.
Kelp Surface Dive
A 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.
Kilogram. Metric measure of weight. 1 kg = 2.21 pounds.
The 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.
A simple on and off valve.
Lift Bag
After being tied to an object to be lifted, the bag is inflated and will start to rise.
Lift Capacity
The 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.
Live aboard
A dive boat with sleeping and eating accommodations. Commercial live aboard boats are usually between 50 and 130 feet long, and can carry from 10 to 30 divers for up to a week or more.
A diary of a divers dive history. Provides evidence of the depth and breadth of a divers experience.
Low Volume Mask
A mask 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.
Used on double cylinder systems. Has 2 valves similar to single tank systems attached by a heavy duty crosspiece with a valve in the center.
Marco Photography
A method of getting close-up pictures of a subject by using Marco accessories attached to the camera's lens. Where the size of the image projected in the film or lens is equal or smaller than the real object.
A 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
A 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.
Mask squeeze
Occurs in rapid descents where the diver neglects to equalize his/her mask. The increase pressure causes tissues around the eyes to swell.
Mediastinal emphysema
Air from an over expanding lung escapes into the center of the chest. This puts pressure on the heart and major blood vessels, interfering with circulation. Symptoms are shortness of breath and feeling faint.
Middle ear
Air containing space of the ear bordered on one side by the tympanic membrane, which is exposed to any change in ambient pressure. Air pressure in the middle ear space can only be equalized through the Eustachian tube, which controls the middle ear to the back of the nose.
Mixed gas
Any non-air mixture (e.g., nitrox), although some authors use the term only for mixes that contain a gas in addition to (or in place of) nitrogen (e.g., helium).
maximum operating depth/oxygen depth limit. The deepest that a diver can safely go using a particular gas mixture. For example, the MOD for EAN32 (32 per- cent oxygen) is 132 fsw (40 m).
Multilevel diving
Spending a period of time at several different depth on a single dive.
Depressed mental state, anywhere from confusion or drowsiness to coma.
National Associatio of Underwater Instructors. It is one of the oldest certifying agencies.
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.
Inert gas that makes up 79% of air. Nitrogen is inert in that it does not enter into any chemical reation in the body, but it can cause problems under pressure (see nitrogen narcosis, decompression sickness).
Nitrogen Narcosis
Depressed mental state from high nitrogen pressure; usually does not begin to manifest on compressed air until below 80 fsw.
Any mixture of nitrogen and oxygen that contains less than the 79% nitrogen as found in ordinary air.
Abbreviation for the National Oceanic and Atmospheric Association.
Octopus Regulator
An alternate second stage air source used by a diver's buddy in an out-of-air situation, or reserve 2nd stage regulator.
Oxygen enriched air - synonym for nitrox.
Open circuit scuba
Apparatus used in recreational diving. Exhaled air is expelled into the water as bubbles, no part is re-breathed by the diver.
Open-Water Diving
The recreational diving done in an environment other than a swimming pool but with no overhead obstacles; examples include lakes, ponds, rivers, oceans, quarries.
Often seen as using the chemistry abbreviation 02, gas vital for all life on this planet; makes up about 21% of the air by volume.
Oxygen Therapy
Administration of any gas, for medical purposes, that contains more than 21% oxygen.
Oxygen Toxicity
Damage or injury from inhaling too much oxygen; can arise from either too high an oxygen concentration or oxygen pressure. One of the most dramatic manifestations of oxygen toxicity while diving can be seizure.
Oxygen Window
Difference between total gas pressures in arterial and venous blood; exist because oxygen is partly metabolized by the tissues, so venous oxygen pressure is lower than arterial oxygen pressure.
Professional Association of Diving Instructors. It is one of the largest certifying agencies.
Partial Pressure
Pressure exerted by a single component of a gas within a gas mixture, or dissolved in a liquid.
Am abnormal collection of air outside the lining of the lung, between the lung and the chest wall, often a consequence of pressure injuries (barotraumas).
Pony Bottle
A small scuba cylinder strapped to a divers main tank with an independent regulator. Used for emergency use in the event a diver's main air supply fails.
Any force exerted over an area.
Pounds per square inch, a common measurement of air pressure.
Purge Valve
Allow masks to be cleared without removal. Allows snorkels to be cleared easily.
A closed-circuit system which filters exhaled air, then recirculates it for rebreathing by the diver; requires special training and maintenance.
Recreational scuba diving
Diving to prescribed limits, including a depth no greater than 130 fsw, using only compressed air, and never requiring a decompression stop.
In scuba, any device that changes air pressure from one level to a lower level.
Repetitive Dive
Any dive whose profile is affected by a previous dive is considered repetitive.
Residual Nitrogen Time
The time it would take to off-gas any extra nitrogen remaining after a dive. Residual Nitrogen Time is always taken into consideration when determining the safe duration for any repetitive dive.
Reverse squeeze
Pain or discomfort in enclosed space (e.g., sinuses, middle ear, inside mask) on ascent from a dive.
Rip Current
A 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.
Rule of Thirds
An air management technique. Use a third of the tank to get to your destination, a third to get back, and the last third belongs to your buddy in case of an emergency.
Safety Stop
On ascent from a dive, a specified time spent at a specified depth, for purposes of nitrogen off gassing. By definition it is not a mandatory for a safe ascent from a dive.
The amount of salt dissolved in a liquid, measured in parts per million.
Supplied Air Snorkeling for Youth/Supplied Air Snorkeling for Adults. BC-like PFD mounted with small compressed air cylinder and regulator that allows snorkeler to breathe comfortably on the surface but prohibits him from descending. SPG submersible pressure gauge. Required scuba gear that displays the amount of air pressure in the scuba cylinder; can be either analog or digital.
The degree to which a gas is dissolved in the blood or tissues, full saturation occurs when the pressure of gas dissolved in the blood or tissues is the same as the surrounding pressure of that gas.
Saturation Diving
Diving performed after the body is fully saturated with nitrogen. To become fully saturated the diver must stay under water for a much longer period than is allowed in recreational scuba diving tables.
surface consumption rate. Measure used in calculations for determining air consumption rate at various depths.
Acronym meaning Self Contained Underwater Breathing Apparatus.
Scuba Resort
a place providing recreation and entertainment to vacationers with the main attraction as that of scuba diving. It may include training, Beach and/or boat diving and many specialties such as wall, drift, wreck, eco-diving and many others. It can be an All-Inclusive, a Live Aboard and or a land base operation. It will normally be supported by one or many of the training agencies.
Scuba Diving International. The recreational scuba training and certification arm of TDI.
Sea Level
The altitude of the world's oceans; all oceans are at sea level.
Second Stage Regulator
The regulator that follows, in line, the first stage regulator, and delivers compressed air to the diver. Usually associated with the mouthpiece.
Shallow Water Blackout
A sudden unconsciousness, from hypoxia, that occurs among some breath hold dives. Often occurs near the surface after a deeper dive, hence "Shallow Water".
The body's attempt to create heat through muscular activity.
Shore (Beach) Diving
Scuba diving that starts from the shore line.
Air spaces within the skull that are in contact with ambient pressure through openings into the back of the nasal passages.
Skin Diving
Another name for breath-hold diving; diving without the use of a breathing equipment (may include a snorkel).
Scuba Lifesaving and Accident Management. YMCA diver rescue course.
A surface-supplied compressed air apparatus, for use in shallow diving in calm waters. The air is delivered to one or more divers through a long hose.
Solo Diving
Solo diving is the practice of scuba diving alone without a "dive buddy". Solo diving, once discouraged, is now beginning to gain acceptance among experienced divers who have skills in self-sufficiency and redundant backup equipment.
Pain or discomfort in an enclosed (sinuses, Middle ear, inside a mask), caused by shrinkage of that space, occurs on decent.
The back end of a boat.
Scuba Travel Ventures
A heavy walled vessel that can withstand pressures under water and allow occupants to breath air at sea level pressures and travels under its own power.
Submersible Pressure Gauge
Gauge to monitor air supply during the course of a dive.
Super saturation
An unstable situation where the pressure of a gas dissolved in the blood or tissues is higher than the ambient pressure of that gas.
Surface Interval
Length of time on the surface, usually out of the water, between two consecutive dives.
Surface supplied compressed air diving
Diving with the air continuously supplied by a compressor on the surface can be used for both sport and professional diving.
Tank Boot
Flat-bottomed, plastic, vinyl or rubber devices that fit over the rounded end of a scuba tank, allowing the tank to stand up.
Technical Diving International. Maine-based certification agency for technical aspects of recreational scuba.
thal-uh-suh-fahyl (Noun) Lover of the sea, one who feels safe/comfortable around seas, oceans
Intersection between two layers of water of that are of distinctly different temperatures, usually the colder layer is deeper.
A part of the body characterized by specific characteristics, such as muscle, bone, or cartilage. The term is also used to refer to any part of the body with a specific half time for loading and unloading nitrogen or even a theoretical compartment.
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.
Material used for dry suit shells made of a layer of waterproof rubber laminated between two layers of woven textile.
Mixture of helium, nitrogen and oxygen, used for very deep diving.
Transfer Under Pressure: Transfer of personnel between hyperbaric environments, usually between a closed bell and a saturation system, or between a portable recompression chamber and a multi-occupant chamber.
The cloudiness or haziness of a fluid caused by individual particles (suspended solids) that may be invisible to the naked eye, similar to smoke in air.
Turn the dive
Start the return on a dive which has reached the planned turning point in terms of depth, time, gas supply or distance.
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.
Unbalanced Regulator
An unbalanced first stage regulator is affected by tank pressure. The tank pressure works to force the piston in the first stage open. As the gas in the tank diminishes, it is easier for the piston to be forced into a closed position. This makes it increasingly harder to breath from the first stage as the dive progresses. This is an older style regulator and has pretty much vanished from today's scuba gear market.
A subsurface flow of water returning seaward from shore as result of wave action.
U-Pattern Search
A U shape search pattern that requires on line. This type of search pattern is suitable over many different bottom terrains and is a frequently used search pattern. A search team swims along the bottom in a long straight line, turns 90 degrees and swims for a short length, and then swims another long length.
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.
Against the flow. Moving against the current.
Upwelling is vertical water movement. This occurs when surface water is moved away (offshore) due to winds blowing from north top south and acting as a force on the surface waters. Because water from somewhere has to fill the space left by the offshore movement of surface water, water fills in from below, creating a vertical current of water.
Valsalva Maneuver
A method of manually equalizing the inner ear. The pressure on the inside of the eardrum is increased by closing the nasal passage (pinching the nose shut) and blowing gently, forcing air into the inner ear via the Eustachian tube.
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
A 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.
The constriction of the blood vessels in order to reduce heat loss from the blood through the skin.
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.
Having a gland or glands for secreting venom; able to inflict a poisoned bite, sting or wound.
A sign of ear barotraumas and should not be ignored. Causes may range from minor ear squeeze to perforation of the eardrum to inner ear barotraumas.
1. Glass or plastic window on a diving helmet or full face mask. 2. Window on a hyperbaric chamber.
Visual Inspection Program. Standardized visual tank inspection performed by a trained equipment technician, performed annually.
The distance a diver can see underwater measured in feet. Normally vertically not up and down.
Visual gap
Gap between guidelines which is small enough that each line can be seen from the other.
Visual inspection
Internal and external inspection of a pressure vessel as part of revalidation procedure.
Visual jump
The procedure of crossing a visual gap (q.v.) without the use of a jump line.
Synthetic elastomer suitable for oxygen service O-rings.
Wall Diving
Occurs on rock and reefs that run vertically, usually run from shallow to deep.
Water capacity
Of a cylinder: The internal volume. The amount of water it would hold at ambient pressure at 20 °C (68 °F)
Water Pressure
Force per unit area exerted by the weight of water, each 33 feet of sea water exerts a pressure equivalent to one atmosphere, or 14.7psa.
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.
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.
Wet filling
Filling scuba cylinders using a water bath for cooling the cylinders.
Wet pot
Water filled hyperbaric chamber.
Wet Suit
Any suit that provides thermal protection underwater by trapping a layer of water betweens the diver's skin and the suit.
A dive table used to plan muti-level dives.
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.
A point or side from which the wind blows; in the direction from which the wind blows; as opposed to, leeward.
Wreck Diving
Diving on natural or man-made shipwrecks; specialty courses are available.
Wrist slate
A small plastic writing surface attached to the diver's wrist. Can come with mutiple slates and a pencil.
To swing off course. This is normally caused by bad steering or the action of the waves.
Yoke fitting/valve
A fitting or valve used to connect a regulator or filling whip to a diving cylinder using the "international" connection.
Dual orifice valve.
In general terms, the zenith is the direction pointing directly "above" a particular location; that is, it is one of two vertical directions at the location, orthogonal to a horizontal flat surface there. The concept of "above" is more specifically defined in astronomy, geophysics and related sciences (e.g., meteorology) as the vertical direction opposite to the net gravitational force at a given location. The opposite direction, i.e. the direction of the gravitational force is called the nadir. The term zenith also refers to the highest point reached by a celestial body during its apparent orbit around a given point of observation.
Zip tie
(also cable tie, tie wrap) Self-locking plastic strip used to connect objects together.
Line cutting tool with a replaceable blade in a slot.
Zoom Lens
A lens that combines a range of focal lengths.

There are 339 scuba glossary terms listed.

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