Scuba set in the context of "Diving equipment"

Scuba diving is an underwater diving mode where divers use breathing equipment completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The word scuba is an acronym for "Self-Contained Underwater Breathing Apparatus" and was coined by Christian J. Lambertsen in a patent submitted in 1952. Scuba divers carry their source of breathing gas, affording them greater independence and movement than surface-supplied divers, and more time underwater than freedivers. Although compressed air is commonly used, other gas blends are also employed.

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 which is supplied to the diver at ambient pressure through a diving regulator. They may include additional cylinders for range extension, decompression gas or emergency breathing gas. Closed-circuit or semi-closed circuit rebreather scuba systems allow recycling of exhaled gases. The volume of gas used is reduced compared to that of open-circuit, making longer dives feasible. Rebreathers extend the time spent underwater compared to open-circuit for the same metabolic gas consumption. They produce fewer bubbles and less noise than open-circuit scuba, which makes them attractive to covert military divers to avoid detection, scientific divers to avoid disturbing marine animals, and media diver to avoid bubble interference.

Cocos Island (Spanish: Isla del Coco) is a volcanic island in the Pacific Ocean administered by Costa Rica, approximately 550 km (342 mi; 297 nmi) southwest of the Costa Rican mainland. It constitutes the 11th of the 15 districts of Puntarenas Canton of the Province of Puntarenas. With an area of approximately 23.85 km (9.21 sq mi), the island is roughly rectangular in shape. It is the southernmost point of geopolitical North America if non-continental islands are included, and the only landmass above water on the Cocos tectonic plate.

The entirety of Cocos Island has been designated a Costa Rican National Park since 1978, and has no permanent inhabitants other than Costa Rican park rangers. While previously being portrayed as the largest uninhabited island within the tropics, this has been labeled a false claim, as the island of Fernandina in the Galapagos archipelago is also uninhabited and far larger in area. Surrounded by deep waters with counter-currents, Cocos Island is admired by scuba divers for its populations of hammerhead sharks, rays, dolphins and other large marine species. The wet climate and oceanic qualities give Cocos an ecological character that is not shared with either the Galápagos Archipelago or any of the other islands (for example, Malpelo, Gorgona or Coiba) in the eastern Pacific Ocean. Because of the unique ecology of the island and its surrounding waters, Cocos Island National Park became a UNESCO World Heritage Site in 1997. The island can only be reached by sea, which usually takes 36 to 48 hours.

Freediving, free-diving, free diving, breath-hold diving, or skin diving, is a mode of underwater diving that relies on breath-holding (apnea) until resurfacing rather than the use of breathing apparatus such as scuba gear.Besides the limits of breath-hold, immersion in water and exposure to high ambient pressure also have physiological effects that limit the depths and duration possible in freediving.

Examples of freediving activities are traditional fishing techniques, competitive and non-competitive freediving, competitive and non-competitive spearfishing and freediving photography, synchronised swimming, underwater football, underwater rugby, underwater hockey, underwater target shooting and snorkeling. There are also a range of competitive apnea disciplines; in which competitors attempt to attain great depths, times, or distances on a single breath.

A diving helmet is a rigid head enclosure with a breathing gas supply used in underwater diving. They are worn mainly by professional divers engaged in surface-supplied diving, though some models can be used with scuba equipment. The upper part of the helmet, known colloquially as the hat or bonnet, may be sealed directly to the diver using a neck dam, connected to a diving suit by a lower part, known as a breastplate, or corselet, depending on regional language preferences, or simply rest on the diver's shoulders, with an open bottom, for shallow water use.

The helmet isolates the diver's head from the water, allows the diver to see clearly underwater, provides the diver with breathing gas, protects the diver's head when doing heavy or dangerous work, and usually provides voice communications with the surface (and possibly other divers). If a helmeted diver becomes unconscious but is still breathing, most helmets will remain in place and continue to deliver breathing gas until the diver can be rescued. In contrast, the scuba regulator used by recreational divers must be held in the mouth by bite grips, and it can fall out of an unconscious diver's mouth and result in drowning.

A diving cylinder or diving gas cylinder is a gas cylinder used to store and transport high-pressure gas used in diving operations. This may be breathing gas used with a scuba set, in which case the cylinder may also be referred to as a scuba cylinder, scuba tank or diving tank. When used for an emergency gas supply for surface-supplied diving or scuba, it may be referred to as a bailout cylinder or bailout bottle. It may also be used for surface-supplied diving or as decompression gas. A diving cylinder may also be used to supply inflation gas for a dry suit, buoyancy compensator, decompression buoy, or lifting bag. Cylinders provide breathing gas to the diver by free-flow or through the demand valve of a diving regulator, or via the breathing loop of a diving rebreather.

Diving cylinders are usually manufactured from aluminum or steel alloys, and when used on a scuba set are normally fitted with one of two common types of scuba cylinder valve for filling and connection to the regulator. Other accessories such as manifolds, cylinder bands, protective nets and boots and carrying handles may be provided. Various configurations of harness may be used by the diver to carry a cylinder or cylinders while diving, depending on the application. Cylinders used for scuba typically have an internal volume (known as water capacity) of between 3 and 18 litres (0.11 and 0.64 cu ft) and a maximum working pressure rating from 184 to 300 bars (2,670 to 4,350 psi). Cylinders are also available in smaller sizes, such as 0.5, 1.5 and 2 litres; however these are usually used for purposes such as inflation of surface marker buoys, dry suits, and buoyancy compensators rather than breathing. Scuba divers may dive with a single cylinder, a pair of similar cylinders, or a main cylinder and a smaller "pony" cylinder, carried on the diver's back or clipped onto the harness at the side. Paired cylinders may be manifolded together or independent. In technical diving, more than two scuba cylinders may be needed to carry different gases. Larger cylinders, typically up to 50 litre capacity, are used as on-board emergency gas supply on diving bells. Large cylinders are also used for surface supply through a diver's umbilical, and may be manifolded together on a frame for transportation.

Christian James Lambertsen (May 15, 1917 – February 11, 2011) was an American medical researcher. He was a environmental medicine and diving medicine specialist who was principally responsible for developing the United States Navy frogmen's rebreathers in the early 1940s for underwater warfare. Lambertsen designed a series of rebreathers in 1940 (patent filing date: 16 Dec 1940) and in 1944 (patent issue date: 2 May 1944) and first called his invention breathing apparatus. Later, after the war, he called it Laru (acronym for Lambertsen Amphibious Respiratory Unit) and finally, in 1952, he changed his invention's name again to SCUBA (Self Contained Underwater Breathing Apparatus). Although diving regulator technology was invented by Émile Gagnan and Jacques-Yves Cousteau in 1943 and was unrelated to rebreathers, the current use of the word SCUBA is largely attributed to the Gagnan-Cousteau invention. The US Navy considers Lambertsen to be "the father of the Frogmen".

Diving equipment, or underwater diving equipment, is equipment used by underwater divers to make diving activities possible, easier, safer and/or more comfortable. This may be equipment primarily intended for this purpose, or equipment intended for other purposes which is found to be suitable for diving use.

The fundamental item of diving equipment used by divers other than freedivers, is underwater breathing apparatus, such as scuba equipment, and surface-supplied diving equipment, but there are other important items of equipment that make diving safer, more convenient or more efficient. Diving equipment used by recreational scuba divers, also known as scuba gear, is mostly personal equipment carried by the diver, but professional divers, particularly when operating in the surface supplied or saturation mode, use a large amount of support equipment not carried by the diver.