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Absence of oxygen to the tissues.

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.

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.

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.

An inert gas that makes up less than one percent of air.

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.

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.

A common respiratory condition manifested by narrowing of air passages.

ATmospheres Absolute. it is the total of pressures exerted by air + water.

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

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.

See buoyancy compensator.

See DSC/Chokes/Caisson’s 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.

Diving partner.

Buddy Breathing
A method of sharing air.

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.

A navigational tool to help maintain direction underwater.

Cardiopulmonary Resuscitation.  A form of external heart compression and Artifiial Respiration (A R).

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.

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.
Canadian Transport Commission.

An overlapping waistband with Velcro used to secure a Buoyancy Compensator.

A horizontal / vertical movement of water.

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.

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.

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.

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 neck’s integrity.

Clot (air bubble or blood) that obstructs a blood vessel.

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.

The temperature scale used in the United States. F=(C/.556) +32.

FFW / ffw
Feet of Fresh Water.

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.

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.

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.

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.

Garment worn on the head to reduce heat loss.

A surface-supplied compressed air apparatus.

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.

An increased amount of CO2 in the blood.

Hyperoxic / Hyperoxia
More than a normal amount of Oxygen.

A body temperature warmer than normal.

Hyperventilation (Controlled)
A technique used by breath holding divers to increase the time they can remain underwater.

Cooling of the body's core below 35C (95F) with a resulting depression of body functions.

Lower than normal O2 level in the blood.

Interstate Commerce Commission.

A constant reserve valve.

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.

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.

Fluid that takes the shape of  the container it occupies.

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.

A device that allows the diver to see underwater.

Mask Squeeze
A squeeze caused by not equalizing the mask.

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.

National Association of Underwater Instructors.

Inert gas that makes up 79% of air.

Nitrogen Narcosis
The result of the narcotic effect of nitrogen at depth.

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.

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).

An abnormal collection of air outside the lining of the lung, between the lung and the chest wall.

Force exerted on object so as to diminish its shape or volume.

Pony Bottle
A small scuba cylinder.

Pounds per Square Inch.

Purge Valve
A device that allow masks and regulators and snorkels to be cleared easily without removal.

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.

The bending of light rays in the water.

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.

The amount of salt dissolved in a liquid, measured in parts per million.

Surface Consumption Rate.  Measure used in calculations for determining air consumption rate at the surface.

Acronym for Self Contained Underwater Breathing Apparatus.

Second Stage Regulator
The part of the regulator, usually in the diver’s mouth, that reduces air pressure to the ambient pressure.

Shallow Water Blackout
A sudden unconsciousness due to hypoxia.

The body's attempt to create heat through muscular activity.

Surface Interval Group.  A place holder that allows transition from Table B to Table C.

Air spaces within the skull.

Surface Interval Time.  Length of time on the surface between two consecutive dives.

Skin Diving
Snorkel Diving

A piece of diving equipment that permits comfortable breathing at the surface when the face is immersed.

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.  

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)

Intersection between two layers of water that are of distinctly different temperatures.

A part of the body with specific characteristics, such as muscle, bone, or cartilage.
The reduction in sizeof the blood vessels in order to lessen heat loss from the blood through the skin.

Having venom.  Poisonous


Visual Inspection Program.

The distance a diver can see underwater.

Water Pressure
The pressure exerted by water only.

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.