Glossary of SCUBA Diving - A

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AA6061

Aluminium Alloy 6061 (not subject to sustained load cracking). Currently (2012) used for diving cylinders.

AA6351

Aluminium Alloy 6351 (subject to sustained load cracking – requires periodical eddy current testing). No longer used for new cylinder manufacture, but many cylinders still in service.

ABLJ

see adjustable buoyancy life jacket

A-clamp fitting/valve

see yoke fitting/valve.

A-clamp adaptor

see yoke adaptor

activated carbon

activated charcoal

A filter medium used to remove oil, water and odours from breathing air.

ADAS

Australian Diver Accreditation Scheme: An international commercial and occupational diver certification scheme.

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.

ADV

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.

A-frame

Gantry or davit for launching and recovering bells, stages or large ROVs. Usually deployed by hydraulic rams which swing the frame over the deck or overboard as required. The load is hoisted and lowered by cables from the top of the frame.

AGE

see arterial gas embolism

airlift

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.

air top

1. Completing a planned breathing gas mix by topping up with compressed air.

2. Topping up a partly used breathing gas mix with compressed air, providing a different mixture which is analysed after the fill.

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.

alternative air source

A secondary supply of air or other breathing gas used by the diver in an emergency

alternobaric vertigo

Dizziness caused by a difference of pressure between the middle ears.

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.

ambient pressure

Pressure of the surroundings.

anoxia

Completely lacking in oxygen.

aphasia

An impairment of language ability which may range from having difficulty remembering words to being completely unable to speak, read, or write

apnea

1. Suspension of breathing, breath-hold.

2. Free-diving.

Aqua-lung

arterial bubble model

Further information: Decompression (diving)#The arterial bubble decompression 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

Blockage of an artery by a gas bubble. A possible consequence of lung overpressure injury.

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.

ascent rate

Further information: Decompression (diving)#No decompression dives, ascent rate and safety stops

The rate at which depth is reduced at the end of a dive. An important component of decompression.

atmospheric diving suit

Also ADS

A small one-man articulated submersible of anthropomorphic form which resembles a suit of armour, with elaborate pressure joints to allow articulation while maintaining an internal pressure of one atmosphere.

attack swimmer

see combat swimmer