Underwater diving

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

Main articles: Sponge diving and Ancient divers

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.

Diving without breathing apparatus

Free diving

Main article: free-diving

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

Swimming underwater

Main article: human swimming

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

Main article: snorkeling

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

Diving with Self Contained Underwater Breathing Apparatus (SCUBA)

Main article: Scuba diving

Scuba divers are sometimes known as frogmen, particularly divers engaged on armed forces covert operations.

Open circuit

Main article: scuba set

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

Rebreather sets

Main article: rebreather

Closed-circuit breathing systems allow recycling of exhaled gases. This reduces the volume of gas used, making a rebreather lighter and more compact than an open-circuit breathing set. Rebreathers also make far fewer bubbles and less noise than open-circuit scuba; this makes them attractive to military, scientific and media divers.

Surface supplied diving

Main article: surface supplied diving

The alternative to scuba is breathing gases supplied via an umbilical 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

Main article: Saturation diving

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 habitat on or connected to a diving support vessel, oil platform or other floating work station, 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.

Diving training

Main article: Diver training

Underwater diving training should come from a qualified diving instructor, to be safe. This is available from many diving training bodies.

Basic Dive 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.

Basic underwater skills that a beginner should learn include:

• Equalization – the adjustment the Eustachian tube in the ear needs to do when submerged in the higher pressured environment underwater.
• Underwater breathing – the skill of breathing through the apparatus. All divers must get used to this way of breathing.
• Mask clearing – This is done to make sure that there will not be anything that will obstruct the diver's view as well as to remove any water that might come into the mask.
• Air sharing – the act of multiple divers sharing one air supply.
• Buoyancy – the right buoyancy allows the diver to move about underwater comfortably. Amount of equipment, buoyancy compensators, and amount of air in the lungs all come to play in maintaining buoyancy. More air in the lungs makes for more buoyancy, while less air makes for less buoyancy.
• Diving signals – diving signals may vary, but its purpose is to be able to communicate with other divers. It should be clear among a group of divers what the diving signals to be used are before the dive.

Dangers of diving

Main article: Diving hazards and precautions

• 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

Diving in submersibles

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

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, saltwater crocodiles, seasnakes and Marine Iguanas. Many mammals, birds and reptiles also dive in freshwater rivers and lakes.

Further reading

• 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.