Scuba Diving

Scuba diving is swimming underwater, or taking part in another activity, while using a scuba set. By carrying a source of breathing gas (usually compressed air), the scuba diver is able to stay underwater longer than with the simple breath-holding techniques used in snorkeling and free-diving, and is not hindered by air lines to a remote air source. The scuba diver typically swims underwater by using fins attached to the feet. However, some divers also move around with the assistance of a DPV (diver propulsion vehicle), commonly called a "scooter", or by using surface-tethered devices called sleds pulled by a boat.



Over 70% of the earth's surface is covered with water. The allure and mystery of the underwater world has inspired the human imagination since prehistory, from the mythological monsters described by seafaring people, to the science fiction of Jules Verne and the modern underwater adventures in Hollywood films. Breath-hold diving, dangerous though it can be, has been used to collect pearls, sponges and valuable commodities from the sea floor for many generations.
Advances in underwater exploration began nearly three centuries ago using diving bells and large cumbersome sealed suits using pumped air from the surface. Only very recently advances in technology and mechanics have allowed people to visit this domain safely for exploration using comfortable, self-contained air delivery systems.

EQUIPMENTS
A scuba set is an independent breathing set that provides a scuba diver with the breathing gas necessary to breathe underwater during scuba diving. It is much used for sport diving and some sorts of work diving.
The word SCUBA is an acronym for Self-Contained Underwater Breathing Apparatus.

Modern scuba sets are of two types,

open-circuit
In Europe, it is often called an Aqualung. Here the diver breathes in from the equipment and the exhaled gas goes to waste in the surrounding water. This type of equipment is relatively simple, making it cheaper and more reliable.

closed-circuit/semi-closed circuit
It is also referred to as a Rebreather. diver breathes in from the set, and breathes back into the set where the exhaled gas is processed to make it fit to breathe again. These existed before the open-circuit sets and are still used, but they are used less than open-circuit sets.

Wonders of the Sea