Scuba diving...
Is a mode of underwater diving in which a scuba diver uses a selfcontained
underwater breathing apparatus (scuba) to breathe underwater.
Unlike other modes of diving, which rely either on breath-hold or on
breathing supplied under pressure from the surface, scuba divers carry their
own source of breathing gas, usually compressed air, allowing them greater
freedom of movement than with an air line or diver's umbilical and longer
underwater endurance than breath-hold. Scuba equipment may be open
circuit, in which exhaled gas is expelled to the surroundings, or a closed or
semi-closed circuit rebreather, in which the breathing gas is scrubbed to
remove carbon dioxide, and the oxygen used is replenished from a supply of
feed gas before being re-breathed.
Scuba diving may be done recreationally or professionally in a number of
applications, including scientific, military and public safety roles, but most
commercial diving uses surface supplied diving equipment when this is
practicable.
A scuba diver primarily moves underwater by using fins attached to the
feet, but external propulsion can be provided by a diver propulsion vehicle,
or a sled pulled from the surface. Other equipment includes a dive mask to
improve underwater vision, a protective diving suit, equipment to control
buoyancy, and equipment related to the specific circumstances and purpose
of the dive. Scuba divers are trained in the procedures and skills appropriate
to their level of certification by instructors affiliated to the diver certification
organisations which issue these certifications. These include standard
operating procedures for using the equipment and dealing with the general
hazards of the underwater environment, and emergency procedures for selfhelp
and assistance of a similarly equipped diver experiencing problems. A
minimum level of fitness and health is required by most training
organisations, but a higher level of fitness may be appropriate for some
applications.