Absolute Pressure The sum of gauge (water) pressure and atmospheric pressure.
Absolute Temperature The temperature when everything freezes -273C (Celcius) - 0oK (Kelvin).
Actual Bottom Time (ABT) See Bottom Time.
Air A gas mixture containing 21% oxygen, 78% nitrogen, and 1% other gasses.
Air Compressor A machine that compresses or pressurizes gas.
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 obstruct blood flow.
Air Consumption The rate at which air is used in a dive.
Algorithm A set of numbers in a chart. Dive tables are an algorithm.
Alpha Flag It is the international diver down flag. It represents the letter "A" in flag signals.
Ambient Light Available sunlight underwater.
Ambient Pressure The surrounding pressure acting on the diver from all directions.
Analog Watch Timing device that uses two hands moving around the clock.
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.
Argon An inert gas that makes up less than one percent of air.
Arrhythmia Irregularity in the rhythm and rate of the heart.
Arterial Gas Embolism (AGE) A condition that occurs when air bubbles enter the bloodstream. It will eventually cause blockage.
Artificial Respiration (A R / Rescue Breathing) Ventilating for another.
ACUC American Canadian Underwater Certification.
Ascent/Decent Line A line suspended from a boat or a buoy for a diver to use to control their rate of ascent or descent.
Ascent Time The period of time from when the bottom time ends to the first safety / decompression stop.
Ascent Rate The speed at which the diver travels to the surface. ACUC recommends a rate of 50 ft/min +/- 10 ft.
Asthma A common respiratory condition manifested by narrowing of air passages.
ATA ATmospheres Absolute. it is the total of pressures exerted by air + water.
Atmosphere A unit of pressure measurement. The gasses that surround the earth.
Atmospheres Absolute All the pressure acting on a body (including air + water).
Atmospheric Pressure Pressure of the atmosphere at a given altitude or location. At sea level, atmospheric pressure is 14.7psi.
Back Roll Entry Means of entering the water in SCUBA gear from a sitting position such as from the gunnels of a boat. The diver leans backward and rolls into the water onto his tank and shoulders.
Bailout Entry Exercise wherein the student jumps into the pool, while holding all equipment, then dons the equipment on the bottom of the pool.
Pulmonary Barotraumas Lung injuries due to pressure.
BC or BCD See buoyancy compensator.
Bends See DSC/Chokes/Caissons Disease.
Body Suit Garment that provides protection from sun, temperature, abrasion and marine injuries.
Boot / Bootie Protective footwear.
Bottom Time (Actual Bottom Time) The time that begins when the diver leaves the surface and ends when the diver begins a direct ascent to the surface.
Boyle's Law At a constant temperature the volumes of the gas varies inversely with the absolute pressure while the density of the gas varies directly with the absolute pressure.
Buddy Diving partner.
Buddy Breathing A method of sharing air.
Buoyancy The ability to float. The three types are: positive, negative and neutral.
Buoyancy Compensator Device (BC/BCD) An inflatable device worn by the diver to help control buoyancy.
Burst Disk A safety device in the tank valve that will rupture if the working pressure of the tank is exceeded.
Capillary Depth Gauge A gauge formed by a transparent tube that shows air compression at the depth.
Carbon Dioxide(CO2) Odourless, colourless, tasteless gas. It is a by-product of metabolism. It is part of exhaled air.
Carbon Dioxide Poisoning CO2 build-up.
Carbon Monoxide (CO) A product of incomplete combustion.
Carbon Monoxide Poisoning A condition caused by inhaling carbon monoxide.
Cave Diving / Cavern Diving Diving into an overhead environment and requires special training and cetification.
Compass A navigational tool to help maintain direction underwater.
CPR Cardiopulmonary Resuscitation. A form of external heart compression and Artifiial Respiration (A R).
Celsius Metric unit for temperature. Water freezes at 0o C and boils at 100oC.
Cu Ft / cu. ft (Cubic Foot) An imperial measure of volume.
Charles Law If the pressure is kept constant, the volume of a gas will vary directly as the absolute temperature.
Closed Circuit Scuba (Rebreather) A breathing device that reduces CO2 levels in the fixed air supply.
Coral Colonies of invertebrates.
Cone Shell Univalved mollusc shaped like a cone. Many are venomous.
Core Temperature The internal temperature of the body (37oC / 97.6oF. CTC Canadian Transport Commission.
Cummerbund An overlapping waistband with Velcro used to secure a Buoyancy Compensator.
Current A horizontal / vertical movement of water.
D.A.N. Divers Alert Network.
Dalton's Law The total pressure exerted by a mixture of gases is equal to the sum of the pressures that would be exerted by each of the different gases ,if it were alone was present and occupied the total volume.
Decompression A gradual safe reduction of bubbles in divers.
Decompression Dive A dive having a mandatory decompression stop.
Decompression Illness (DCI) A term to encompass all bubble-related problems.
Decompression Sickness (DCS) A general term for all problems resulting when nitrogen leaves the body too quickly.
Decompression Stop (DS) A mandatory off gassing stop made when ascending
Deep Dive For recreational divers, a deep dive is a dive below 70 ft.
Depth The deepest point of the dive.
Depth Gauge A measuring device that indicates the depth of the dive.
Descent/Ascent Line A line suspended from a boat, float or buoy used to permit divers to control their rate of descent and ascent.
Descent Rate The speed at which the diver travels to the bottom. ACUC recommends no greater rate than 75 ft/min.
Descent Time The amount of time it takes a diver to descend to the bottom.
Diaphragm 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.
DIN Valve (Deutsches Institut fur Normung) Design of tank valve popular in Europe in which the first-stage regulator screws into the tank valve.
Dive Computer A device that uses time and depth to calculate decompression requirements.
Dive Flag See "Diver Down" and "Alpha" flags.
Dive Light A light designed specifically for underwater use.
Decompression Tables A series of charts used to calculate the uptake and release of nitrogen by the tissues.
Doff and Don (Ditch and Recovery) Removal and replacement of equipment.
Dry Suit A suit that allows the diver to stay dry in the water.
Duck Dive Head first surface dive.
Eddy Test A test to measure the tank necks integrity.
Embolus Clot (air bubble or blood) that obstructs a blood vessel.
Equalization The method of balancing external and internal pressure.
Equipment Squeeze The squeeze caused by air trapped in dive equipment (mask, suit).
Eustachian Tube A short tube connecting the back of the throat to the middle ear.
Exposure Suit Garment worn to prevent decrease in core body temperature and protect from marine life injury.
Fahrenheit The temperature scale used in the United States. F=(C/.556) +32.
FFW / ffw Feet of Fresh Water.
Fins Devices worn on the feet to allow comfortable, relaxed propulsion.
First Stage Part of the regulator attached to the scuba tank that lowers the tank pressure to intermediate pressure.
FT / ft (Foot) Unit of measurement (12" or 30.48cm).
Forward Roll Entry A method of entering the water by bending at the waist, rolling forward into the water and landing on one's shoulders and tank.
Free Diving Breath hold diving.
FSW / fsw Feet of Sea Water.
Gas A form of matter (vapour) that takes the shape of the container it occupies. it is affected by change in pressure.
Gas Laws Laws that predict how gases will behave with changes in pressure, temperature and volume.
Gauge Pressure Pressure exclusive of atmospheric pressure. When diving, gauge pressure is due to the water pressure. 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.
GPS (Global Positioning System) An electronic devicethat uses a worldwide system of navigation.
Haldanian Related to Haldane's theory o decompression.
Half Life Half the time it takes for a dissolved gas in a tissue (such as nitrogen) to equilibrate 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.
Heliox Mixture of helium and oxygen, usually reserved for very deep diving.
Helium 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.
Hood Garment worn on the head to reduce heat loss.
Hookah A surface-supplied compressed air apparatus.
Hydro Hydrostatic Test
Hyperbaric Chamber (Recompression Chamber) Air-tight chamber that can simulate the ambient pressure at altitude or at depth. It is used for treating decompression illness and other medical conditions.
Hypercapnia An increased amount of CO2 in the blood.
Hyperoxic / Hyperoxia More than a normal amount of Oxygen.
Hyperthermia A body temperature warmer than normal.
Hyperventilation (Controlled) A technique used by breath holding divers to increase the time they can remain underwater.
Hypothermia Cooling of the body's core below 35C (95F) with a resulting depression of body functions.
Hypoxia Lower than normal O2 level in the blood.
ICC Interstate Commerce Commission.
J-Valve A constant reserve valve.
Kelp Marine plant. Grows to varying heights.
Kelp Surface Dive A vertical, feet-first, surface dive.
Kilo (KG / kg) Kilogram. Metric measure of weight. 1 kg = 2.21 pounds.
K-Valve A simple on and off valve.
Light Absorption The decrease in light intensity with depth and the subsequent loss of colour.
Lift Bag A device used to lift objects iunder the water.
Lift Capacity The amount of buoyancy provided by a Buoyancy Compensator.
Liquid Fluid that takes the shape of the container it occupies.
Logbook A record of a diver's dive history.
Low Volume Mask A mask which has a smaller air space between the glass and the diver's face.
Mask A device that allows the diver to see underwater.
Mask Squeeze A squeeze caused by not equalizing the mask.
Matter Anything that occupies space and has weight.
Mediastinal Emphysema A type of pulmonary barotrauma where air collects in the middle of the chest.
Middle Ear Area of the ear from the ear drum to the inner ear and eustachian tube.
MNDT (Maximum No Decompression Time) The period of dive a diver can stay at a specific depth without requiring a decompression stop.
MSW / msw Meters of Sea Water
Multilevel Diving Spending a period of time at several different depths on a single dive.
NAUI National Association of Underwater Instructors.
Nitrogen Inert gas that makes up 79% of air.
Nitrogen Narcosis The result of the narcotic effect of nitrogen at depth.
Nitrox Enriched air
No Decompression Dive Any dive that does not require a mandatory decompression stop.
NPT (Nitrogen Penalty Time) The time that represents the amount of residual nitrogen in the diver's tissues following a surface interval.
Octopus Regulator An alternate second stage air source.
Open Circuit Scuba Apparatus used in recreational diving where exhaled air is expelled into the water.
Open-Water Diving Recreational diving done in an environment other than a swimming pool, with direct access to the surface.
Oxygen (O2) Colourless, tasteless, odourless gas. It makes up about 21% of the air by volume.
Oxygen Therapy Administration of a gas, for medical purposes, that contains more than 21% oxygen.
Oxygen Toxicity Damage or injury from inhaling oxygen at elevated partial pressures.
PADI Professional Association of Diving Instructors.
Partial Pressure Pressure exerted by a single component of a gas within a gas mixture, or dissolved in a liquid. Obtained by multiplying the fraction of the gas (in decimals) by the pressure (ATA).
Pneumothorax An abnormal collection of air outside the lining of the lung, between the lung and the chest wall.
Pressure Force exerted on object so as to diminish its shape or volume.
Pony Bottle A small scuba cylinder.
PSI Pounds per Square Inch.
Purge Valve A device that allow masks and regulators and snorkels to be cleared easily without removal.
Rebreather See Closed Circuit System .
Recreational Scuba Diving Sport Diving) Diving to within prescribed limits (130 fsw), using only compressed air, and never requiring a decompression stop.
Refraction The bending of light rays in the water.
Regulator A specialized device that changes air pressure from one level to a lower level. It allows a diver to breathe underwater.
Repetitive Dive The following dive in the series of dives.
RNG (Residual Nitrogen Group) A letter designation representing the amount of surplus nitrogen remaining in the diver's tissuesat the completion of the dive.
Reverse Squeeze Squeeze that occurs because of reduced pressure.
Safety Stop (S) A recommended stop(s) to assist in the off gassing of nitrogen.
Salinity The amount of salt dissolved in a liquid, measured in parts per million.
SCR Surface Consumption Rate. Measure used in calculations for determining air consumption rate at the surface.
SCUBA Acronym for Self Contained Underwater Breathing Apparatus.
Second Stage Regulator The part of the regulator, usually in the divers mouth, that reduces air pressure to the ambient pressure.
Shallow Water Blackout A sudden unconsciousness due to hypoxia.
Shivering The body's attempt to create heat through muscular activity.
SIG Surface Interval Group. A place holder that allows transition from Table B to Table C.
Sinuses Air spaces within the skull.
SIT Surface Interval Time. Length of time on the surface between two consecutive dives.
Skin Diving Snorkel Diving
Snorkel A piece of diving equipment that permits comfortable breathing at the surface when the face is immersed.
Solids Have definite shape, constant density and have little or no reaction to pressure.
Sport Diver Flag (Diver Down Flag) A red rectangular flag with a white diagonal stripe from the top of the hoist to the bottom of the fty.
Squeeze Tissue damage due to pressure differences in rigid containers.
Submersible Pressure Gauge (SPG) An underwater pressure gauge.
Swim Away A type of ditch and recovery
Tank Boot Flat-bottomed, plastic, vinyl or rubber device that fits over the bottom end of a scuba tank.
Tank Protector / Skin Coloured, plastic sleeve that prevents the tank from being scratched.
Tank Valve Device used to control the rate of gas leaving a tank.
TBT (Total Bottom Time) Sum of the Actual bottom Time and the Nitrogen Penalty Time (ABT + NPT)
Thermocline Intersection between two layers of water that are of distinctly different temperatures.
Tissue A part of the body with specific characteristics, such as muscle, bone, or cartilage. Vasoconstriction The reduction in sizeof the blood vessels in order to lessen heat loss from the blood through the skin.
Venomous Having venom. Poisonous
Vertigo Dizziness
VIP Visual Inspection Program.
Visibility The distance a diver can see underwater.
Water Pressure The pressure exerted by water only.
Weight Amount of gravitational pull exerted by an object. property of matter represented as an amount per unit volume.
Wet Suit Neoprene suit that provides thermal protection. It is not waterproof.
Wreck Diving Diving on natural or man-made shipwrecks.
