- This article is an introduction to underwater diving by humans. For other uses of the term diving, see dive (disambiguation) and diving
Recreational diving is a popular activity (also called sports diving or subaquatics). Professional diving (commercial diving, diving for scientific research purposes or diving for financial gain) takes a range of diving activities to the underwater work site.
Freediver with monofin, ascending.
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 (skandalopetra) 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.
Methods of underwater diving 
Diving without breathing apparatus 
Free diving 
Free diving does not involve the use of external breathing devices, but relies on a diver's ability to hold his or her breath until resurfacing. It includes a range of activities from simple breath-hold diving to competitive apnoea dives.
Swimming underwater 
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.
The addition of a short breathing tube known as a snorkel allows the diver to breathe with the face remaining immersed, but at the surface.
Scuba diving 
Scuba diving is diving with a Self Contained Underwater Breathing Apparatus, which is completely independent of surface supply, and provides the diver with the advantages of mobility and horizontal range far beyond what is possible when supplied from the surface by the umbilical hoses of Surface-supplied diving equipment (SSDE).
Some scuba divers have been referred to as frogmen, particularly divers engaged on armed forces covert operations
Open circuit 
Open circuit scuba systems discharge the breathing gas into the environment as it is exhaled, and consist of one or more diving cylinders containing breathing gas at high pressure connected to a primary diving regulator, and may include additional cylinders for decompression gas or emergency breathing gas.
Closed-circuit or semi-closed circuit breathing systems allow recycling of exhaled gases. This reduces the volume of gas used, so that a smaller cylinder, or cylinders, than open circuit scuba may be used for the equivalent dive duration, and giving the ability to spend far more time underwater compared to open circuit for the same gas consumption. Rebreathers also produce far less bubble volume and less noise than scuba, which makes them attractive to military, scientific and media divers.
Surface supplied diving 
An alternative to self-contained breathing systems is to supply breathing gases from the surface. A diver's umbilical, or airline hose, from the surface provides gas, communications and a safety line, with options for a hot water hose for heating, a video cable and gas reclaim line.
Surface oriented diving 
Surface oriented, or bounce diving, is how commercial divers refer to diving operations where the diver starts and finishes the diving operation at atmospheric pressure. The alternative is saturation diving.
The diver may be deployed directly, often from a diving support vessel or indirectly via a diving bell. Surface-supplied divers almost always wear diving helmets or full face diving masks. The bottom mix can be air or mixed gas, the decompression mix nitrox or pure oxygen. Decompression procedures include in-water decompression or surface decompression in a deck chamber.
A wet bell with a gas filled dome provides more comfort and control than a stage and allows for longer time in water. Wet bells are used for air and mixed gas, and divers can decompress on oxygen at 12 m.
Small closed bell systems have been designed that can be easily mobilized, and include a two-man bell, a handling frame and a chamber for decompression after transfer under pressure (TUP). Divers can breathe air or mixed gas at the bottom but are usually recovered in the chamber filled with air. They decompress on oxygen supplied through built in breathing systems (BIBS) towards the end of the decompression. Small bell systems support bounce diving down to 120 m and for bottom times up to 2 hours.
An alternative to scuba diving, called "SNUBA" or "hooka" diving, has the diver supplied via an airline from a small cylinder or compressor at the surface. It is used for light work such as hull cleaning and archaeological surveys, for shellfish harvesting, and as a shallow water tourist activity for those who are not scuba-certified.
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 underwater habitat on the bottom or a saturation life support system of pressure chambers on the deck of a diving support vessel, oil platform or other floating work station. In either case, they stay at a similar pressure to the work depth. They may be transferred in a closed diving bell, also known as a personnel transfer capsule. Decompression at the end of the dive may take many days, but since it is done only once for a long period of exposure, rather than after each of many shorter exposures, the overall risk of decompression injury to the diver and the total time spent decompressing are reduced.
Reasons for diving 
Diving may be done for a number of reasons, both personal and professional.
Divers may be employed professionally to perform tasks underwater.
Commercial divers are employed to perform tasks related to industries involving underwater work, including civil engineering tasks such as in oil exploration, offshore construction dam maintenance and harbour works. Commercial divers may also be employed to perform tasks specifically related to marine activities, such as naval diving, including the repair and inspection of boats and ships, salvage of wrecks or aquaculture.
There are a fair number of divers who work, full or part-time, in the recreational diving community as instructors, assistant instructors, divemasters and dive guides. In some jurisdictions the professional nature, with particular reference to responsibility for health and safety of the clients, of recreational diver instruction, dive leadership for reward and dive guiding is recognised by national legislation.
Other specialist areas of diving include military diving, with a long history of military frogmen in various roles. They can perform roles including direct combat, infiltration behind enemy lines, placing mines, bomb disposal or engineering operations.
In civilian operations, many police forces operate police diving teams to perform search and recovery or search and rescue operations and to assist with the detection of crime which may involve bodies of water. In some cases diver rescue teams may also be part of a fire department, paramedical service or lifeguard unit, and may be classed as public safety diving.
Lastly, there are professional divers involved with the water itself, such as underwater photography or underwater film makers, who set out to document the underwater world, or scientific diving, including marine biology, geology, hydrology, oceanography and underwater archaeology.
The choice between scuba and surface supplied diving equipment is based on both legal and logistical constraints. Where the diver requires mobility and a large range of movement, scuba is usually the choice if safety and legal constraints allow. Higher risk work, particularly commercial diving, may be restricted to surface supplied equipment by legislation and codes of practice.
Reasons for diving may include:
|Diving activities||Classification||Scuba or Surface Supplied Diving Equipment|
|aquarium maintenance in large public aquariums||commercial, scientific||Scuba, SSDE|
|boat and ship inspection, cleaning and maintenance||commercial, naval||SSDE, occasionally scuba|
|cave diving||technical, recreational, scientific||Scuba, occasionally SSDE|
|civil engineering in harbors, water supply, and drainage systems||commercial||Almost exclusively SSDE|
|crude oil industry and other offshore construction and maintenance||commercial||Almost exclusively SSDE|
|demolition and salvage of ship wrecks||commercial, naval||SSDE, sometimes scuba|
|professional diver training||professional||SSDE or scuba as appropriate|
|recreational diver training||professional, recreational||Scuba|
|fish farm maintenance||commercial||Scuba, SSDE|
|fishing, e.g. for abalones, crabs, lobsters, pearls, scallops, sea crayfish, sponges||commercial||Scuba, SSDE|
|frogman, manned torpedo||military||Scuba|
|harbor clearance and maintenance||commercial, military||Almost exclusively SSDE|
|media diving: making television programs, etc.||professional||Scuba, occasionally SSDE|
|mine clearance and bomb disposal, disposing of unexploded ordnance||military, naval||Scuba, occasionally SSDE|
|pleasure, leisure, sport||recreational||Almost exclusively scuba|
|policing/security: diving to investigate or arrest unauthorized divers||police diving, military, naval||Scuba|
|search and recovery diving||commercial, public safety, police diving||Scuba, SSDE|
|search and rescue diving||police, naval, public service||Scuba, occasionally SSDE|
|spear fishing||professional (occasionally), recreational||Scuba|
|surveys and mapping||scientific, recreational||Scuba, SSDE|
|scientific diving (marine biology, oceanography, hydrology, geology, palaeontology, diving physiology and medicine)||scientific||Scuba, occasionally SSDE|
|underwater archaeology (shipwrecks; harbors, and buildings)||scientific, recreational||Scuba, SSDE|
|underwater inspections and surveys||commercial, military||SSDE, sometimes scuba|
|underwater photography||professional, recreational||Scuba, SSDE|
|underwater sport||recreational||Snorkel, breathhold and Scuba|
|underwater tour guiding||professional, recreational||Scuba|
|underwater tourism||recreational||Scuba, occasionally Snuba|
|underwater welding||commercial||Almost exclusively SSDE|
Diver training 
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, and includes procedures and skills for the use of diving equipment, safety, emergency self-help and rescue procedures, dive planning, and use of dive tables.
Some of the skills which an entry level diver will normally learn include:
- Ear equalization and equalisation of other air spaces.
- 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.
- Use of bailout systems (professional divers)
- Buoyancy control – neutral buoyancy allows the diver to move about underwater comfortably.
- Diving signals – used to communicate underwater. Professional divers will also learn other methods of communication.
Hazards of diving 
Divers face specific physical and health risks when they go underwater with scuba or other diving equipment, or use high pressure breathing gas. The hazards can be listed under several categories:
- The aquatic environment
- Use of breathing equipment in an underwater environment
- Exposure to a pressurised environment and pressure changes, which includes:
- Pressure changes during descent
- Pressure changes during ascent
- Breathing gases at high ambient pressure
- The specific diving environment
- Pre-existing physiological and psychological conditions in the diver
- Diver behaviour and competence
- Failure of diving equipment other than breathing apparatus
- Hazards of the dive task and special equipment
- Hazards related to access to and egress from the water.
The presence of a combination of several hazards simultaneously is common in diving, and the effect is generally increased risk to the diver, particularly where the occurrence of an incident due to one hazard triggers other hazards with a resulting cascade of incidents. Many diving fatalities are the result of a cascade of incidents overwhelming the diver, who should be able to manage any single reasonably foreseeable incident.
The assessed risk of a dive would generally be considered unacceptable if the diver is not expected to cope with any single reasonably foreseeable incident with a significant probability of occurrence during that dive. Precisely where the line is drawn depends on circumstances. Commercial diving operations tend to be less tolerant of risk than recreational, particularly technical divers, who are less constrained by occupational health and safety legislation.
According to a North American 1972 analysis of calendar year 1970 data, diving was, based on man hours, 96 times more dangerous than driving an automobile. According to a 2000 Japanese study, every hour of recreational diving is 36 to 62 times riskier than automobile driving.
Consequences of diving hazards range from merely annoying through to rapidly fatal, and are listed in the article on Diving hazards and precautions and discussed in detail in other articles linked from that article.
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.
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.
- Sandra Hendrikse and André Merks (12 May 2009). "Diving the Skafandro suit". Diving Heritage. Retrieved 2009-10-16.
- Imbert, Jean Pierre (February 2006). "Commercial Diving: 90m Operational Aspects". In Lang and Smith. Advanced Scientific Diving Workshop (Smithsonian Institution). Retrieved 2012-06-30.
- HSE press release E061:05 - 5 May 2005 HSE issues warning over recreational dive training http://www.hse.gov.uk/press/2005/e05061.htm
- Statutory Instruments 1997 No. 2776 HEALTH AND SAFETY, The Diving at Work Regulations 1997, http://www.legislation.gov.uk/uksi/1997/2776/contents/made
- Lansche, James M (1972). "Deaths During Skin and Scuba Diving in California in 1970". California Medicine 116 (6): 18–22. PMC 1518314. PMID 5031739.
- Ikeda, T; Ashida, H (2000). "Is recreational diving safe?". Undersea and Hyperbaric Medical Society. Retrieved 2009-08-08.
- Here you can see Underwater divers and turtles near Sipadan. It was filmed by Christoph Brüx
Further reading 
- Cousteau J.Y. (1953) Le Monde du Silence, translated as The Silent World, Hamish Hamilton Ltd., London; ASIN B000QRK890
- Lang M.A. & Brubakk A.O. (eds., 2009) The Future of Diving: 100 Years of Haldane and Beyond, Smithsonian Institution Scholarly Press, Washington DC