Diving World

Scuba diving is a very popular type of extreme sports. Simply, it is swimming underwater, or taking part in another activity, while using a scuba set. By carrying a source of breathing gas (usually compressed air), the scuba diver is able to stay underwater longer than with the simple breath-holding techniques used in snorkeling and free-diving, and is not hindered by air lines to a remote air source. The scuba diver typically swims underwater by using fins attached to the feet. However, some divers also move around with the assistance of a DPV (diver propulsion vehicle), commonly called a "scooter", or by using surface-tethered devices called sleds pulled by a boat.

The term SCUBA arose during World War II and originally referred to United States combat frogmen's oxygen rebreathers, developed by Dr. Christian Lambertsen for underwater warfare. Today, scuba typically refers to the in-line open-circuit equipment, developed by Emile Gagnan and Jacques-Yves Cousteau, in which compressed gas (usually air) is inhaled from a tank and then exhaled into the water. However, rebreathers (both semi-closed circuit and closed circuit) are also self-contained systems (as opposed to surface-supplied systems) and are therefore classified as scuba.

Although the SCUBA is an acronym for "self-contained underwater breathing apparatus", usage is mainly as a normal word "scuba", it has become acceptable to refer to scuba as "scuba equipment" or "scuba apparatus" — an example of the linguistic RAS syndrome.

Water normally contains dissolved oxygen from which fish and other aquatic animals extract all their required oxygen as the water flows past their gills. Humans lack gills and do not otherwise have the capacity to breathe underwater unaided by external devices.

Early diving experimenters quickly discovered it is not enough simply to supply air in order to breathe comfortably underwater. As one descends, in addition to the normal atmospheric pressure, water exerts increasing pressure on the chest and lungs — approximately 1 bar or 14.7 psi for every 33 feet or 10 meters of depth — so the pressure of the inhaled breath must almost exactly counter the surrounding or ambient pressure in order to inflate the lungs.

By always providing the breathing gas at ambient pressure, modern demand valve regulators ensure the diver can inhale and exhale naturally and virtually effortlessly, regardless of depth.

Because the diver's nose and eyes are covered by a diving mask; the diver cannot breathe in through the nose, except when wearing a full face diving mask. However, inhaling from a regulator's mouthpiece becomes second nature very quickly.

Divers must avoid injuries caused by changes in air pressure. The weight of the water column above the diver causes an increase in air pressure in any compressible material (wetsuit, lungs, sinus) in proportion to depth, in the same way that atmospheric air causes a pressure of 14.7 pounds-force per square inch (101.3 kPa) at sea level. Pressure injuries are called barotrauma and can be quite painful, in severe cases causing a ruptured eardrum or damage to the sinuses. To avoid them, the diver equalizes the pressure in all air spaces with the surrounding water pressure when changing depth. The middle ear and sinus are equalized using one or more of several techniques, which is referred to as clearing the ears.

The mask is equalized by periodically exhaling through the nose.

If a drysuit is worn, it too must be equalized by inflation and deflation, similar to a buoyancy compensator.