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diving at a location where the water surface is more than about 300 m (980 ft) above sea level, and which requires special dive tables or dive computers to calculate allowed depths and times for safety.
the pressure on the diver at a given depth. 1 bar (100 kPa) at the surface, increasing by approximately 1 bar (100 kPa) for each 10 metres (33 ft) of depth.
absence of oxygen caused by inhaling a breathing gas that contains no oxygen or being unable to inhale any breathing gas.
a medical condition caused by gas bubbles in the bloodstream that can be caused by a too rapid ascent, in which a gas expands and a bubble blocks the arterial flow of blood.
underwater breathing equipment consisting of a diving cylinder and diving regulator.
injury caused by pressure
Bounce dive
In commercial diving, bounce diving is the alternative to saturation diving. In recreational diving, a bounce dive is a descent to maximum depth and then an ascent back to the surface with the least delay, in a dive profile resembling a spike.
a procedure carried out by SCUBA divers using the buddy system where each diver checks that the other's diving equipment is configured and functioning correctly just before the start of the dive
the use of the buddy system by scuba divers and is a set of safety procedures that improve divers' chances of avoiding or surviving accidents in or underwater by diving in a group of two divers.
Buoyancy control
the ability of a diver to control his or her depth - an essential practical diving skill
Buoyancy compensator or BCD
diving equipment worn by divers to provide buoyancy and the ability to control ascent and descent rates.
usually due to compressor maintenance errors.
is due to incomplete elimination of carbon dioxide.
is an underwater diver rescue technique used by scuba divers to safely raise an incapacitated diver to the surface from depth
a machine used to increase the volume of usable air in a diving cylinder by raising its pressure.
Controlled emergency swimming ascent (CESA)
Archaic emergency technique of swimming to surface breathing out continuously. Proper training removes the need for this practice.
DCI is caused by two different mechanisms: decompression sickness (DCS) and Arterial Gas Embolism (AGE), which result in overlapping sets of symptoms.
a potentially lethal diving disorder caused by bubbles of inert gases, such as nitrogen or helium, coming out of solution and becoming trapped in the tissues, organs and blood vessels of the body causing symptoms ranging from rashes to death. Also commonly referred to as DCS.
a pause during the ascent phase of the dive to allow safe release of inert gases from the tissues of the body and avoid decompression sickness.
Printed tables that provide divers with a way of reducing chances of Decompression Sickness. This by giving the maximum times that can be spent at depth, and by indicating the Decompression Stops and Surface Intervals needed for a particular depth and time profile to be carried out safely.
a small buoy on a line that divers inflate underwater to indicate their location to their boat.
a valve, generally placed in the diver's mouth, which provides gas from the diving regulator when the diver inhales.
Dive club
a group of people with an interest in SCUBA diving.
Flag used by a boat to indicate that it has 'divers down'.
Comes in two versions: the international maritime signal flag (international code letter flag 'A',
) and the USA red and white flag (red with white diagonal, ).
A dive profile is a two dimensional graphical representation of a dive showing depth and time. The profile is often used when describing a dive's likely decompression obligation.
Dive shop, or LDS
supplier of diving equipment or gas.
see Decompression tables.
one or more valves in series, which let the gas out of a gas cylinder in a controlled way, lowering its pressure at each stage.
a form of sign system used by SCUBA divers to communicate when underwater.
a type of recreational diving where the diver drifts with the currents caused by the tide or in a river.
a diving suit designed to provide buoyancy, thermally insulate and provide protection to the skin of the diver.
Electro-galvanic fuel cell, or O2 cell
an electrical device used to measure the concentration of oxygen gas in diving equipment.
a way of approximating the decompression requirements of breathing gas mixtures that contain nitrogen and oxygen in different proportions to those in air, known as nitrox.
a way of expressing the narcotic effect of a breathing gas mixture, for example trimix.
(Fg) Indicates the percentage of a gas present in a breathing mixture such as nitrox and trimix.
An archaic term for a scuba diver, particularly a military diver on an undercover mission.
a type of diving mask that seals the whole of the diver's face from the water and contains a mouthpiece or demand valve that provides the diver with breathing gas.
filling diving cylinders with gas mixes such as nitrox or trimix.
a potentially lethal diving disorder caused by air or other gas bubbles entering the blood stream through wounds.
Hard Hat diving
Surface supplied diving, generally in professional diving, either wearing a modern diving helmet or the old-style standard diving dress and brass helmet.
a gas blend of Helium and Oxygen in which helium replaces the normal Nitrogen in air allowing diving at greater depths than can be done with air or Trimix
High Pressure Nervous Syndrome - caused by using breathing gases that contain helium at depth.
carbon dioxide poisoning generally caused by rebreathing your own exhaled carbon dioxide. A big problem at depth especially with rebreathers or high rates of exertion.
either a deliberate and dangerous method intended to extend the duration of a free dive or the body's response to hypercapnia.
insufficient oxygen in the body - normally caused by inhaling a breathing gas that contains insufficient oxygen to support normal activities or consciousness.
a potentially lethal medical condition caused by cooling the body.
Interstitial emphysema
gas trapped in the chest after lung barotrauma.
Log Book
List of the dives a diver has recorded for proof of experience.
(MOD) the depth at which the partial pressure of oxygen (ppO2) of a gas mix exceeds a safe limit.
a dive at night - many underwater animals are nocturnal or behave differently at night.
condition caused by breathing nitrogen at high pressure (at depth). (aka "narked")
a breathing gas consisting of more than 21% oxygen and lower amounts of nitrogen. This reduces decompression obligation on shallow dives and increases microcellular safety
is caused by using breathing gases that contain oxygen at high pressure (at depth). Recreational scuba limits O2 exposure to 1.4 PO2
Partial pressure of a gas
a measure of the concentration of individual component gases of breathing gases.
collapsed lung.
breathing equipment that captures, cleanses and re-oxygenates exhaled breath so that it can be re-inhaled.
a pressure vessel used to treat divers suffering from certain diving disorders such as decompression sickness.
a type of diving that uses SCUBA equipment for the purpose of leisure and enjoyment.
Regulator
see Diving Regulator
a decompression regime used in commercial diving that allows divers to live work for weeks at a time where their tissues become saturated in high pressure gas.
can occur hours after a near drowning.
a wet suit with wrist and ankle seals to reduce entry and exit of water.
Shore diving
Scuba diving that starts from the shore line.
the practice of swimming at the surface of a body of water while equipped with a diving goggles, a shaped tube called a snorkel, and flippers.
A frowned up practice of scuba diving alone without the backup of a "dive buddy".
old-fashioned "hard hat" diving gear.
Subcutaneous emphysema
gas under the skin tissue.
Submersible pressure gauge or SPG
Gauge attached to the regulator and used to monitor pressure remaining in the scuba cylinder
Surface detection aids
equipment, such as flags, DSMBs, flares, EPIRBs and whistles, carried by divers to maintain contact with dive boats or attract rescue when lost at sea.
Surface interval
the time between dives. Divers need to track this time interval for planning decompression for the next dive.
Surface marker buoy, SMB
a small inflated buoy that divers tow when underwater on drift dives to indicate their location to their boat.
a form of SCUBA diving that exceeds the scope of recreational diving allowing deeper and longer dives.
Time to fly
Divers must wait approx. 24 hours after the last dive before flying to reduce the risk of decompression sickness.
a breathing gas consisting of oxygen, helium and nitrogen. This allows deeper diving by reducing the amount of nitrogen in the mix thereby reducing nitrogen narcosis
diving along the face of a vertical wall - requires good buoyancy control because there is no seabed to prevent the diver descending too deep.
weights, generally made of lead, to counteract the buoyancy of other diving equipment, such as diving suits and aluminium diving cylinders.
A tightly fitting neoprene thermally-insulating diving suit that allows a limited volume of water inside the suit.
diving on shipwrecks.
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