Scuba diving

Scuba Diving is swimming (or occasionally walking) underwater wearing a breathing set designed to be used underwater at depth. It provides a supply of breathing gas (usually air), allowing him to stay underwater for long periods for recreational diving and professional diving.

The word SCUBA is an acronym for Self Contained Underwater Breathing Apparatus. (These initials likely originated in the US Navy during WWII to refer to US commando frogman's rebreathers.) As with radar, the acronym has become so familiar that it is often not capitalised. Nowadays it usually means open-circuit underwater breathing sets.

The breathing sets used are described on the pages scuba sets and rebreather.
The history of scuba diving and underwater breathing sets is described at Scuba sets#History.

Problems that arise in diving

Also see Diving disorder for a longer description.

Need to breathe underwater

The two most common techniques used here are scuba and surface supplied diving. Standard diving dress is a historically interesting type of surface supplied diving equipment.

Need to avoid injury caused by changes in water pressure

Such injuries are classed as barotrauma. They are caused by pressure differences between the outside and trapped air spaces inside the diver or his kit. To avoid them, ensure that the pressure in all air spaces is the same as the surrounding water pressure when changing depth. This is known as "equalizing". This need arises with:-

• The air spaces in the ears, and the sinuses. The risk is burst eardrum. Here, the diver can use the valsalva maneouvre, to let air into the middle ears via the Eustachian tubes. Sometimes swallowing will open the Eustachian tubes and equalize the ears.
• The lungs. The risk is burst lung. To equalize, always breathe normally and never hold the breath. This risk does not arise when snorkel diving from the surface, unless you breathe in underwater from some source or another.
• The air inside the usual eyes-and-nose diving mask. The main risk is bleeding round the eyes. Here, let air into the mask through the nose. Do not dive in eyes-only goggles as sometimes seen on land with industrial breathing sets.
• Air spaces inside a dry suit. The main risk is folds of skin getting pinched inside folds of the drysuit. Most modern drysuits have a tube connection to feed air in from the cylinder. Air must be injected on the descent and vented on the ascent.
• In extreme depths (>100m/300ft), the lungs fill with blood, to avoid collapse of the alveoli. It is also possible to equalize by allowing surrounding water (or any liquid) to enter the sinuses and eustachian tubes. This is only likely to happen in unadvisable circumstances.

Need to avoid decompression illness

Decompression illness 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 seachlight 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 umbilicals 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.

Related topics

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

External links

• Divers Alert Network
• Brief history of diving - From antiquity to the present.
• Top Scuba Sites - Scuba sites as ranked by user popularity.
• Scuba Monster - Scuba Usenet discussions and archive.
• NAUI Worldwide is the world's oldest not-for-profit membership training agency organized solely to support and promote dive safety through education.