Early ideas of autonomous under-water systems appear in Twenty Thousand Leagues Under the Sea

Scuba Diving is the use of independent breathing equipment to stay underwater for long periods for recreational diving and professional diving. Generally the diver swims underwater, but walking and the use of diver propulsion vehicles is possible while breathing from scuba equipment.

The two types of scuba equipment are the "open-circuit" Aqua-lung and the "closed-circuit" rebreather.

Issues that diving poses

Also see Diving disorders for a longer description of these issues followed by an extensive discussion of physical and medical risks.

Equipment to allow underwater breathing

The two most common types of equipment are:

• surface supplied diving, where the diver's breathing gas (usually air) is pumped down from the surface. Standard diving dress is a historically interesting type of surface supplied diving equipment.
• scuba, where the breathing gas supply is carried by the diver.

There is no single optimal breathing gas mix for every type of dive

A wide variety of breathing gas mixes have been used for diving. Each mix must contain sufficient oxygen to sustain life and consciousness. Mixes may contain other gases such as nitrogen and helium. As the concentration of gases increases with the depth of the dive and some gases are toxic at high concentrations, the design of breathing gas mixes depends on the depth of the dive.

Need to avoid injury caused by changes in water pressure

Pressure injuries are called barotrauma. They are caused by pressure differences between the outside and trapped air spaces inside the diver or the diver's equipment. To avoid them, the diver "equalises" the pressure in all air spaces with the surrounding water pressure when changing depth.

Need to avoid decompression sickness

Decompression sickness can be prevented by decompression stops and a slow ascent using dive computers or decompression tables for guidance.

Need to see underwater

Diving masks and diving helmets solve this problem. Occasionally commando frogmen use special contact lenses instead, to avoid searchlight beams reflecting off a mask window.

Controlling buoyancy underwater

This is needed to descend and ascend safely and at will. Diving weighting systems, diving suits and buoyancy compensators all contribute to the diver's buoyancy.

Avoiding losing body heat

This causes hypothermia. Water conducts heat from the diver 25 times better than air. Except in very warm water, the diver needs the thermal insulation provided by a diving suit.

Avoiding skin cuts and grazes

Diving suits also help prevent the diver's skin being damaged by rough or sharp underwater objects and marine animals.

Diving longer and deeper safely

There are a number of techniques to increase the diver's ability dive deeper and longer:

• technical diving - use of SCUBA breathing gases other than air
• 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 dive

Being mobile underwater

• The diver needs to be mobile underwater. Personal mobility is enhanced by fins worn on the feet and Diver Propulsion Vehicles. Other equipment to improve mobility includes diving bells and diving shots.

See also

• Timeline of underwater technology
• Diving equipment
• Diver training
• Diving locations
• Diving activities
• Diving physics
• List of SCUBA magazines
• DIR diving
• Diving Glossary

External links

• Divers Alert Network (http://www.diversalertnetwork.org/)
• Brief history of diving (http://scuba.rinkes.nl/) - From antiquity to the present.
• Top Scuba Sites (http://www.topscubasites.com/) - Scuba sites as ranked by user popularity.
• Scuba Diving Cozumel (http://www.scuba-diving-cozumel.com) - Information for scuba divers traveling to Cozumel, Mexico.
• Scuba Monster (http://www.scubamonster.com/Uwe/ForumList.aspx) - Scuba Usenet discussions and archive.
• NAUI Worldwide (http://www.nauiww.org/) is the world's oldest not-for-profit membership training agency organized solely to support and promote dive safety through education.
• Australia Underwater (http://www.underwater.com.au/) - All about diving in Australia - includes photo gallery from all around Australia.