A form of underwater swimming with the aid of a self-contained underwater breathing apparatus (abbreviated as scuba), or aqualung. The first such device was developed by French naval officer Jacques Yves Cousteau and engineer Emil Gagnan in 1943. The Confédération Mondiale des Activités Subaquatique (World Underwater Federation) was founded in 1959.
Scuba diving is the term used to describe the use of a self-contained breathing set to stay underwater for periods of time greater than the average individual can breath-hold. The diver carries all equipment necessary for diving and is not reliant upon equipment elsewhere (e.g. on the surface) to supply breathing gas or other support during the dive. Some divers also move around with the assistance of a DPV (Diver Propulsion Vehicle), commonly referred to as a "scooter", or by using surface-tethered devices called sleds, which are pulled by a boat.
Scuba diving is still evolving, but general classifications have grown up to describe various diving activities. These classifications include, but are not limited to:
recreational diving public safety diving technical diving (also called Tech Divers) Cave diving Deep diving Ice diving Wreck diving military diving: this includes combat divers and armed forces work divers. commercial diving. scientific diving.Within recreational diving there are those who are considered professional divers, because they maintain a professional standard of training and skills (and must, in theory, according to the laws of the area, carry professional liability insurance).
Some consider technical diving to be a subset of recreational diving, but others separate it out due to the extensively different training equipment and knowledge needed for technical dives.
Public safety diving and military diving might likewise be classified as commercial diving because public safety divers and military divers make a living from their pursuit of diving. However, public safety divers (police or rescue) and military divers have a different mission from the typical commercial diver.
Scientific diving is used by marine scientists, including marine biologists, as a tool for collecting their research data.
History of diving
Men and women have practiced breath-hold diving (Free-diving) for centuries. mother-of-pearl ornaments), and depictions of divers in ancient drawings. In ancient Greece, breath-hold divers are known to have hunted for sponges and engaged in military exploits. Until humans found a way to breathe underwater, however, each dive was necessarily short and frantic.
One of the major hurdles of diving is to stay under water for a longer period of time.
In the 16th century people began to use diving bells supplied with air from the surface, the first effective means of staying under water for any length of time.
In 16th century England and France, full diving suits made of leather were used to depths of 60 feet. Soon helmets were made of metal to withstand even greater water pressure and divers went deeper. Their studies helped explain effects of water pressure on the body, and also defined safe limits for compressed air diving.
See also: Timeline of underwater technology
Diving Issues
This section looks at some of the physiological issues posed by diving. See Diving hazards and precautions.
Breathing underwater
Water normally contains dissolved oxygen from which fish and other aquatic animals extract all their required oxygen as the water flows past their gills.
Early diving experimenters quickly discovered it is not enough to simply supply air in order to breathe comfortably underwater.
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.
Typically the diver's nose and eyes are encapsulated in a diving mask, such that the nose cannot participate in inhalation except when wearing a full face diving mask.
The most commonly used Scuba set today is the open circuit 2-stage diving regulator, coupled to a single pressurized gas cylinder.
For more information, see diving regulator.
Less common (but becoming increasingly so) are the closed and/or semi-closed rebreather units.
On deeper or more prolonged dives, gas mixtures other than normal atmospheric air are used, such as air with enriched oxygen content, known as nitrox, or oxygen with helium and a reduced percentage of nitrogen, known as trimix. In cases of technical dives multiple cylinders may be carried, each containing a different gas mixture for a distinct phase of the dive, typically designated as Travel, Bottom and Decompression.
Injuries due to changes in water pressure
The diver must avoid injury caused by changes in water pressure. They are caused by pressure differences between the outside and trapped air spaces inside the diver or the diver's equipment.
Effects of breathing high pressure gas
Decompression sickness
The diver must avoid the formation of gas bubbles in the body, called decompression sickness or 'the bends', by releasing the water pressure on the body slowly at the end of the dive. This is done by making safety stops or decompression stops and ascending slowly using dive computers or decompression tables for guidance.
Nitrogen narcosis
Nitrogen narcosis or inert gas narcosis is a reversible alteration in consciousness producing a state similar to alcohol intoxication in divers who breathe high pressure gas at depth. Being "narced" can impair judgement and make diving very dangerous.
Need to see underwater
Water has a higher refractive index than air. Diving masks and diving helmets solve this problem by creating an air partition between the diver's eyes and the water.
Divers who require corrective lenses to see clearly outside the water would normally require the same prescription while wearing a mask.
Occasionally commando frogmen use special contact lenses instead, to see underwater without the large glass surface of a diving mask which can reflect light and give away the frogman's position.
Controlling buoyancy underwater
To dive safely, divers need to be able to control their rate of descent and ascent in the water. Ignoring other forces such as water currents and swimming, diver's overall buoyancy determines whether a diver ascends or descends. Equipment such as the diving weighting systems, diving suits (Wet, Dry & When divers want to remain at constant depth, they try to achieve neutral buoyancy.
The volumes and weights of the diver and all equipment attached to the diver, contribute to the diver's overall buoyancy. Diving weighting systems can be used to reduce the diver's weight and cause an ascent in an emergency. Diving suits, mostly being made of compressible materials, reduce in volume as the diver descends and expand as the diver ascends creating unwanted buoyancy changes. The diver can inject air into some diving suits to counteract this effect and squeeze. For open circuit divers, changes in the diver's lung volume can be used to adjust buoyancy.
Avoiding losing body heat
Water conducts heat from the diver 25 times better than air, which can lead to hypothermia.
The second way in which wetsuits reduce heat loss is to trap a thin layer of water between the diver's skin and the insulating suit itself. Provided the wetsuit is reasonably well-sealed at all openings (neck, wrists, legs), this reduces water flow over the surface of the skin, reducing loss of body heat by convection, and therefore keeps the diver warm (this is the principle employed in the use of a "Semi-Dry")
In the case of a dry suit, it does exactly that: keeps a diver dry. both systems have their good and bad points but generally they can be reduced to:
Membrane: high level of diver manoeuverability due to the thinness of the material, however that also means that heavy weight undersuit is required if diving in cooler water.Avoiding skin cuts and grazes
Diving suits also help prevent the diver's skin being damaged by rough or sharp underwater objects, marine animals or coral.
Diving longer and deeper safely
There are a number of techniques to increase the diver's ability dive deeper and longer:
technical diving - diving deeper than 130 feet and/or using mixed gases. surface supplied diving - use of umbilical gas supply and diving helmets. saturation diving - long-term use of underwater habitats under pressure and a gradual release of pressure over several days in a decompression chamber at the end of a diveBeing mobile underwater
The diver needs to be mobile underwater. Streamlining dive gear will reduce drag and improve mobility. Other equipment to improve mobility includes diving bells and diving shots.
Scuba dive training and certification agencies
See main article: List of diver training organizations
Recreational Scuba diving does not have a centralized certifying or regulatory agency, and is mostly self regulated. There are, however, several large diving organizations that train and certify divers and dive instructors, and many diving related sales and rental outlets require proof of diver certification from one of these organizations prior to selling or renting certain diving products or services.
The largest international certification agencies that are currently recognized by most diving outlets for diver certification include:
ACUC - American Canadian Underwater Certifications Inc. British Sub Aqua Club (BSAC) - based in the United Kingdom, mostly for UK divers and clubs CEDIP - European Committee of Professional Diving Instructors - (http://www.cedip.org/) based in Europe since 1992 but international certifications are recognized all over the world. (see Cedip on French Wiki pages) Confédération Mondiale des Activités Subaquatiques (CMAS) National Association of Underwater Instructors (NAUI) - based in the USA Professional Association of Diving Instructors (PADI) - based in the USA, largest recreational dive training and certification organization in the world Scuba Schools International (SSI) - based in the USA YMCA SCUBA - based in the USA, part of Young Men's Christian Association (YMCA), a Christian related organization (open to all faiths, ages and genders despite the historic name) List of scuba diving instructor organizations
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