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This article refers to underwater diving by humans. For other uses of the term diving, see dive (disambiguation) and diving

Signal flag A(Alpha) - "I have a diver down - Keep clear"

Informal Recreational diving flag

Underwater diving is the practice of going underwater, either with breathing apparatus (scuba diving and surface supplied diving) or by breath-holding (free-diving).

Recreational diving is a popular activity (also called sports diving or subaquatics). Professional diving (commercial diving or diving for financial gain) takes a range of diving activities to the underwater work site.

Levels of training and types of equipment and breathing gases used differ between types of diving.

History[link]

Underwater diving for commercial, rather than recreational purposes may have begun in Ancient Greece, since both Plato and Homer mention the sponge as being used for bathing. The island of Kalymnos was a main centre of diving for sponges. By using weights of as much as 15 kilograms (33 lb) to speed the descent, breath-holding divers would descend to depths up to 30 metres (98 ft) for as much as 5 minutes to collect sponges.^[1]

Diving without breathing apparatus[link]

Free diving[link]

Free diving includes a range of activities from simple breath-hold diving to competitive apnoea dives.

Swimming underwater[link]

The ability to dive and swim underwater can be a useful emergency skill, and is an important part of watersport and navy safety training. More generally, entering water from a height is an enjoyable leisure activity, as is underwater swimming with or without breathing apparatus.

Snorkeling[link]

The addition of a short breathing tube (snorkel) allows the diver to breathe while remaining immersed, but close to the surface.

Scuba diving[link]

Scuba (Self Contained Underwater Breathing Apparatus) divers are sometimes known as frogmen, particularly divers engaged on armed forces covert operations.

Open circuit[link]

Breathing systems consist of one or more diving cylinders containing breathing gas at high pressure connected to a diving regulator.

Rebreathers[link]

Closed-circuit or semi-closed circuit breathing systems allow recycling of exhaled gases. This reduces the volume of gas used, meaning a smaller cylinder, or cylinders, than open circuit scuba, and giving the ability to spend far more time underwater compared to open circut for the same gas consumption. Rebreathers also make far fewer bubbles and less noise than scuba; this makes them attractive to military, scientific and media divers.

Surface supplied diving[link]

Surface supplied commercial diving equipment on display at a trade show

The alternative to self contained breathing systems is breathing gases supplied via an umbilical hose or hoses from the surface, often from a diving support vessel but sometimes, indirectly via a diving bell. Surface-supplied divers almost always wear diving helmets or full face diving masks. An alternative to scuba diving, called "SNUBA" or "hooka" diving, has the diver supplied via an umbilical from a small cylinder or compressor on the surface. It is popular for light work such as hull cleaning, and also as a tourist activity for those who are not scuba-certified.

Saturation diving[link]

Saturation diving lets professional divers live and work at depth for days or weeks at a time. This type of diving allows greater economy of work and enhanced safety. After working in the water, divers rest and live in a dry pressurized underwater habitat on the bottom or a system of pressure chambers on the deck of a diving support vessel, oil platform or other floating work station, in either case, the stay at the same pressure as the work depth. They may be transferred in a diving bell. Decompression at the end of the dive may take many days.

Diver training[link]

Underwater diver training is normally given by a qualified instructor who is a member of one of many diving training agencies or is registered with a government agency.

Basic diver training entails the learning of skills required for the safe conduct of activities in an underwater environment, such as the buddy system, dive planning, and use of dive tables.

Some of the skills which an entry level diver will normally learn include:

• Ear equalization – normally a Valsalva maneuver. This maneovre is where the diver pushes air into the Eustachian tube by closing his nose and exhaling against the closed nostrils.
• Underwater breathing – the skill of breathing through the apparatus.
• Mask clearing – the skill of clearing water from the mask.
• Air sharing – assisting another diver by providing air from one's own supply, or receiving air supplied by another diver.
• Emergency ascents - how to return to the surface without injury in the event of a breathing supply interruption.
• Buoyancy control – neutral buoyancy allows the diver to move about underwater comfortably. The type and thickness of exposure suit used, size and type of cylinder used, fresh or salt water, other equipment carried all affect the buoyancy characteristics of the diver.
• Diving signals – used to communicate underwater. There are many standard signals, but also many which vary between divers. An entry level diver will normally learn the standard signals such as ok, problem, up, down, etc

Dangers of diving[link]

• Decompression sickness
• Nitrogen narcosis
• Drowning
• Barotrauma
• Oxygen toxicity
• Shallow water blackout
• Deep water blackout
• On jumping into water: divers sometimes jump into water feet first from some height above the water (e.g. from a large boat or from a pier). Jumping into the water headfirst is unsafe for those wearing any sort of scuba or snorkelling equipment. In particular, an open-circuit scuba on the back is big and hard and heavy and during a headfirst dive into water may cause back or neck injury or break the neck.

Other forms of underwater diving[link]

Diving in submersibles[link]

Submarines, submersibles and 'hard' diving suits enable undersea diving to be carried out within a dry environment at normal atmospheric pressure, albeit more remotely. Underwater robots and remotely operated vehicles and also carry out some functions of divers at greater depths and in more dangerous environments. See also Sea Trek.

Diving by other animals[link]

Humans are not the only air-breathing creatures to dive. Marine mammals such as seals, dolphins and whales, dive to feed and catch prey under the sea as do penguins and many seabirds, as well as various reptiles: turtles^[2], saltwater crocodiles, seasnakes and Marine Iguanas. Many mammals, birds and reptiles also dive in freshwater rivers and lakes. A compilation of the diving records by several air-breathing animals can be found on the Penguiness Book page (http://penguinessbook.scarmarbin.be/).

Further reading[link]

• Lang, Michael A., and Alf O. Brubakk, eds. The Future of Diving: 100 Years of Haldane and Beyond. Washington, D.C.: Smithsonian Institution Scholarly Press, 2009.

References[link]

See Also[link]

Underwater diving portal

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