A

Air Embolism

Air Sharing

Air Sharing Ascent

ANDI

Alpha Flag

Aqua-lung was the original name for the first open-circuit SCUBA equipment. The Aqua-lung was invented by two Frenchman Émile Gagnan and Jacques-Yves Cousteau in 1942.

Atmospheric Pressure

Is a unit of pressure, which is roughly equal to the atmospheric pressure on Earth at sea level.

Barotrauma

Barotrauma is physical damage to the body's tissues and is due to the expansion or contraction of gases putting stress on the surrounding tissues.

A common term amongst divers for decompression sickness, which is derived from the bent position a victim may take due to the pain in the joints.

Bioluminescence

Is the production and emission of light by a living organism. Bioluminescence is a natural form of chemiluminescence, when energy is released by a chemical reaction in the form of light.

Bladder

A flexible pouch which has water and gas proof walls which is used to control buoyancy.

The amount of time a dive spends on a dive from the start of the descent, until the time the diver starts the acsent.

Bourdon Tube

A "C" shaped tube which water enters one end of the tube, as the pressure increases the tube starts to straighten out. This movement is used to change the needles position on the depth gauge.

British Sub-Aqua Club (BSAC). Founded in 1953.

A procedure used by SCUBA divers using the buddy system to check each other equipment is working correctly before the start of the dive.

• B - BCD
• W - Weights
• R - Releases
• A - Air
• F - Final Check

A burst disc or rupture disc is a safety device that protects the cylinder from over pressurisation. In the event the pressure in the cylinder becomes to much the disc will rupture before the cylinder explodes.

A gaseous compound consisting of one atom of carbon and two of oxygen. A byproduct of human respiration, a build up of which induces the breathing reflex.

A colourless, odourless gaseaous compound consisting of one atom of carbon and one of oxygen. Highly toxic in large quantities when it binds with haemoglobin preventing the transport of oxygen around the body.

Is a scale and unit measurement for temperature. The symbol for degrees Celsius is °C. The unit was know as centigrade until 1948.

C-card is the generic term for any certification card issued by a recognised scuba diving instruction organisation, such as SSI or PADI.

Charles' Law

This is a law of volumes, which describes how gases tend to expand when heated. The law shows the relationship between pressure, volume and temperature of a gas; At a consent pressure, the volume of a gas expands by a constant fraction as the temperature increases.

The Confédération Mondiale des Activités Subaquatiques (CMAS) is the World Underwater Federation. Founded in 1959

An instrument that utilises the earth's natural electromagnetism to aid with orientation.

Air which is contained under pressure within a diving cylinder.

A steel or aluminium container which is used to supply a diver with air or mixed gases.

Dalton's Law

This is the law of partial pressure. Its states the total pressure exerted by a gaseous mixture is equal  to the sum of the partial pressures of the individual components.

Decompression Diving

Diving in which divers are required to stop for timed periods at various depths to allow for off-gasing of nitrogen.

Decompression Stop

A staged stop used primarily in technical diving to depths greater than 40m to allow for off-gassing of nitrogen bubbles that have saturated body tissues.

Dehydration

Is when the normal content of water  in the body is reduced, which upsets the delicate balance of minerals in your body fluid.

Deutsches Institut für Normung (German Institute for Standardization) and is used in the names of its standards. The DIN fitting that connects the first stage of a regualtor to the tank on a high pressure scuba system is named after this agency.

The angle between magnetic north and true north.

Dive Computer

A computer that allows a diver to monitor their depth, no decompression limits and dive time. Modern computers have a range of additional features such as nitrox settings, a history of dive information and dive profiles, built in compass, planning modes, wireless air integration.

Dive Tables, Decompression Tables or Tables

The dive tables were created by the US Navy and have been adapted by various diving agencies. The tables are used to provide divers with information of nitrogen absorption based on depth and time. This allows divers to plan no-decompression and repetitive square dives.

Diver Down Flag

A Diver Down Flag, or Recreational Divers Flag, is a flag which is flown from a boat or surface marker buoy to signal there is divers below. It is a red with a white stripe from the upper left corner to the lower right corner. This flag is governed by tradition, and in some places, by law.

Diver Propulsion Vehicle (DPV)

Is an item of diving equipment used by scuba divers to increase their range underwater.

A dry suit or drysuit offers thermal protection to divers while they are immersed in water. Dry suits are constructed of various water tight materials. The suit functions by preventing water coming into contact with the divers body. Usually used where the water temperature is below 15°C

Enriched-Air Nitrox (EANx)

Is a gas blend where the compositon of compressed air has been modified to contain higher percentages of oxygen, anywhere between 22 - 99%. Divers use this to increase their no-decrompression limits. Specialist training is needed as the chance of oxygen toxicity increases at depth.

Exposure Suit

A garment worn by divers to protect them from the underwater environment. Usually a wetsuit, dry suit, semi-dry or dive skins.

Fahrenheit

Is a scale and unit measurement for temperature.  The symbol for degrees Fahrenheit is °F. The freezing point of water is 32 degrees Fahrenheit (°F) and the boiling point 212 °F (at standard atmospheric pressure).

Fathom (ftm)

Is a unit of length used especially to messure depth of water. 1 fathom is equal to 6 feet or 1.8288 metres.

Fatigue

Is a state of awareness describing a range of afflictions, usually associated with physical and/or mental weakness. It is widespread in everyday life, but usually becomes more noticeable during heavy exercise.

Filling Station

A facility which provides the service of filling scuba cylinders with compressed gases.

Finning

The act of kicking your feet in a rhythmic pattern while wearing fins to increase the surface area to aid in propulsion.

Essential part of dive equipment that are worn on the feet to assist with underwater propulsion. Commonly, incorrectly referred to as "flippers", Flipper was a f***ing dolphin!!!

First Stage

The primary component of a regulator arrangement that attaches to the cylinder. Its function is to convert the high pressure air from the cylinder to an intermediate pressure, usually between 9-13 bar above ambient. Can be of a piston or diaphragm design.

Free Diving

This hardly ever happens as most reputable dive operations will charge you to dive.

The Global Positioning System is a utility which provides users with positioning and timing services, in all weather conditions any where on earth providing the GPS receiver has direct line of sight to at least 4 satellites.

The time which is taken for the body tissues to absorb or release inert gases (usually nitrogen) following changes in depth. Different tissue types have a different half-time for a given inert gas.

International Association for Handicapped Divers. Founded in 1993.

International Association of Nitrox and Technical Divers. Founded in 1985.

Inert

Is used to describe a substance that is not chemically reactive.

A lift bag is an item of diving equipment, which is used to assist divers in moving objects into a new position or bringing them to the surface. The volume of the lift bag determines the lifting capacity, a 100 litre bag can lift 100 kilogram underwater object.

Used by divers to record the experience of the dive. Such as depth, time and marine life which has been seen.

At item of diving equipment, which allows divers to see clearly underwater, by providing an air space in front of the eyes which allows the eye to focus correctly.

Mixed Gas

A mix of breathing gases which contain oxygen and one or more inert gases. Mixed gases could have only one inert gas such as Nitrox or Heliox, or multiple inert gases such as Trimix.

National Association of Scuba Diving Schools (NASDS). In 1999 NASDS merged with Scuba Schools International (SSI).

National Association of Underwater Instructors (NAUI). Founded in 1959.

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere.

Nitrogen Narcosis

Narcosis is caused when nitrogen bubbles dissolved in the body temporarily interrupt neurotransmissions in the brain leading to impairment with similar effects to alcohol. This usually affects divers at depths of 30m+ but susceptibility varies widely amongst dives and individuals. The symptoms can be easily overcome by ascent to a shallower depth.

Nitrox

See enriched air nitrox.

No Decompression Limit (NDL)

This is the length of time that a diver may stay at a given depth in order to avoid nitrogen super saturation and subsequent decompression stops. They are set by theoretical calculation and experimental evidence.

National Oceanic and Atmospheric Administration (NOAA). Founded in 1970.

No-Decompression Dive

A dive in which the use decompression stops are not necessary. The majority of recreational diving is now no decompression diving.

This is an entry-level full diver certification for scuba diving.

A mechanical gasket which is designed to create a water and/or gas tight seal.

Oxygen

Oxygen is a element that has the symbol O, atomic number of 8 and atomic mass 15.9994 u. It is a colourless, odourless and tasteless gas, which is required by all living organisms.

Oxygen Toxicity

Oxygen toxicity is a medical condition caused by exposure to oxygen at an elevated pressure. This is a concern for divers who use mixed gases such as enriched air nitrox, or exceed the recreational diving limits.

Professional Association of Diving Instructors (PADI). Founded in 1966.

Pony Bottle

Is a small independent filled cylinder, which provides a diver a redundant air source.

Pounds per square inch. Imperial messurement of pressure.

Is a scale and unit measurement for temperature. The symbol for degrees Rankine is R. Zero on the Rankine and Kelvin scales is absolute zero. The Rankine degree is defined as one degree Fahrenheit. A temperature of −459.67 °F is exactly equal to 0 R.

Sub-Aqua Association (SAA). Founded in 1976.

A precaution divers take at the end of a dive, to allow off-gasing of nitrogen. Usually performed between 3-6 metres for 3 minutes.

Salinity

Is a term which is used to describe the salt concentration in water.

Self contained underwater breathing apparatus.

Scuba Diving International. Founded in 1999.

Second Stage

This is part of the regulator which reduces pressurised breathing gases to an ambient pressure which is delivered to the diver.

A `J` or `L` shaped tube approximately 30 centimetres long with a mouth piece and the top extends out of the water. This allows a swimmer to be faced down in the water and still being able to breathe.

Swimming on or through a body of water while equipped with a diving mask, snorkel and usually fins. The equipment allows for the snorkeler to swim on the surface and observe the underwater world while still being able to breathe

Scuba Schools International. Founded in 1970.

Is an inflatable buoy used by divers, to indicate their position to boats while they are underwater.

A swell consists of a series of wind generated waves, which were generated elsewhere or some time ago, they are not affected (or hardly affected) by local wind.

Symptom

An observation which is noticed by a patient, indicating the presence of disease or abnormality.

Technical Diving International. Founded in 1993.

A form of scuba diving which exceeds the scope of recreational diving. Such as:

• Diving deeper than 40 metres (130 feet)
• Breathing gases other then air or standard nitrox
• Decompression diving, where the dive must do a decompression stop before returning to the surface.
• Special training and specialised equipment was required.

Thermocline

A distinct layer in a body of water, in which there is a temperature change of a few degrees. This can be seen by divers as a stained glass affect  in the water.

Trimix

A breathable gas which consists of oxygen, nitrogen and helium, which is used in techincal diving.

Weight belts are the most common weighting system used in diving today. They are used to counteract the buoyancy affects of diving equipment, such as diving suits and aluminium cylinders. The weights which are attached to the weight belt are usually made from lead.