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Scuba Diving Lundy Island

Scuba diving is a mode of underwater diving in which a scuba diver uses a self-contained underwater breathing apparatus (scuba) to breathe underwater. Unlike other modes of diving, which rely either on breath-hold or on breathing supplied under pressure from the surface, scuba divers carry their own source of breathing gas, usually compressed air, allowing them greater freedom of movement than with an air line or diver s umbilical and longer underwater endurance than breath-hold. Scuba equipment may be open circuit, in which exhaled gas is expelled to the surroundings, or a closed or semi-closed circuit rebreather, in which the breathing gas is scrubbed to remove carbon dioxide, and the oxygen used is replenished from a supply of feed gas before being re-breathed. Scuba diving may be done recreationally or professionally in a number of applications, including scientific, military and public safety roles, but most commercial diving uses surface supplied diving equipment when this is practicable. A scuba diver primarily moves underwater by using fins attached to the feet, but external propulsion can be provided by a diver propulsion vehicle, or a sled pulled from the surface. Other equipment includes a dive mask to improve underwater vision, a protective diving suit, equipment to control buoyancy, and equipment related to the specific circumstances and purpose of the dive. Scuba divers are trained in the procedures and skills appropriate to their level of certification by instructors affiliated to the diver certification organisations which issue these certifications. These include standard operating procedures for using the equipment and dealing with the general hazards of the underwater environment, and emergency procedures for self-help and assistance of a similarly equipped diver experiencing problems. A minimum level of fitness and health is required by most training organisations, but a higher level of fitness may be appropriate for some applications. Diving masks and helmets solve this problem by providing an air space in front of the diver s eyes. The refraction error created by the water is mostly corrected as the light travels from water to air through a flat lens, except that objects appear approximately 34% bigger and 25% closer in water than they actually are. Therefore, total field-of-view is significantly reduced and eye–hand coordination must be adjusted. This also affects underwater photography: a camera seeing through a flat port in its housing is affected in the same way as its user s eye seeing through a flat mask viewport, and so its operator must focus for the apparent distance to target, not for the real distance. This is only relevant for manual focusing. Cylindrically curved faceplates such as those used for firefighting full-face masks produce severely distorted views underwater. Commando frogmen concerned about revealing their position when light reflects from the glass surface of their diving masks may instead use special contact lenses to see underwater. Dive lights Water attenuates light by selective absorption. Pure water preferentially absorbs red light, and to a lesser extent, yellow and green, so the color that is least absorbed is blue light. Environmental protection Protection from heat loss in cold water is usually provided by wet suits or dry suits. Wetsuits A wetsuit is a garment, usually made of foamed neoprene, which provides thermal insulation, abrasion resistance and buoyancy. A good close fit and few zips helps the suit to remain waterproof and reduce flushing - the replacement of water trapped between suit and body by cold water from the outside. Suits range from a thin (2 mm or less) shortie , covering just the torso, to a full 8 mm semi-dry, usually complemented by neoprene boots, gloves and hood. Dry suits A dry suit provides thermal insulation to the wearer while immersed in water, and normally protects the whole body except the head, hands, and sometimes the feet. In some configurations, these are also covered. Dry suits are designed to prevent water entering. This generally allows better insulation making them more suitable for use in cold water.