Diving support equipment

USS Arkansas (BB-33) was a dreadnought battleship, the second member of the Wyoming class, built by the United States Navy. She was the third ship of the US Navy named in honor of the 25th state, and was built by the New York Shipbuilding Corporation. She was laid down in January 1910, launched in January 1911, and commissioned into the Navy in September 1912. Arkansas was armed with a main battery of twelve 12-inch (305 mm) guns and capable of a top speed of 20.5 knots (38.0 km/h; 23.6 mph).

A frogman is someone who is trained in scuba diving or swimming underwater in a tactical capacity that includes military, and in some European countries, police work. Such personnel are also known by the more formal names of combat diver, combatant diver, or combat swimmer. The word frogman first arose in the stage name the "Fearless Frogman" of Paul Boyton in the 1870s and later was claimed by John Spence, an enlisted member of the U.S. Navy and member of the OSS Maritime Unit, to have been applied to him while he was training in a green waterproof suit.

Professional diving is underwater diving where the divers are paid for their work. Occupational diving has a similar meaning and applications. The procedures are often regulated by legislation and codes of practice as it is an inherently hazardous occupation and the diver works as a member of a team. Due to the dangerous nature of some professional diving operations, specialized equipment such as an on-site hyperbaric chamber and diver-to-surface communication system is often required by law, and the mode of diving for some applications may be regulated.

A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed habitats. Oxygen is the essential component for any breathing gas. Breathing gases for hyperbaric use have been developed to improve on the performance of ordinary air by reducing the risk of decompression sickness, reducing the duration of decompression, reducing nitrogen narcosis or reducing work of breathing and allowing safer deep diving.

Association Internationale pour le Développement de l'Apnée (AIDA) (English: International Association for the Development of Apnea) is a worldwide rule- and record-keeping body for competitive breath holding events, also known as freediving. It sets standards for safety, comparability of Official World Record attempts and freedive education. AIDA International is the parent organization for national clubs of the same name. AIDA World Championships are periodically held.

The Johnson Sea Link accident was a June 1973 incident that claimed the lives of two divers. During a seemingly routine dive off Key West, the submersible Johnson Sea Link was trapped for over 24 hours in the wreckage of the destroyer USS Fred T. Berry, which had been sunk to create an artificial reef. Although the submersible was eventually recovered by the rescue vessel A.B. Wood II, two of the four occupants died of carbon dioxide poisoning: 31-year-old Edwin Clayton Link (son of Edwin Albert Link, the submersible's designer) and 51-year-old diver Albert Dennison Stover. The submersible's pilot, Archibald "Jock" Menzies, and ichthyologist Robert Meek survived. Over the next two years, Edwin Link designed an unmanned Cabled Observation and Rescue Device (CORD) that could free a trapped submersible.

In physiology, respiration is the transport of oxygen from the outside environment to the cells within tissues, and the removal of carbon dioxide in the opposite direction to the environment by a respiratory system.

Underwater habitats are underwater structures in which people can live for extended periods and carry out most of the basic human functions of a 24-hour day, such as working, resting, eating, attending to personal hygiene, and sleeping. In this context, 'habitat' is generally used in a narrow sense to mean the interior and immediate exterior of the structure and its fixtures, but not its surrounding marine environment. Most early underwater habitats lacked regenerative systems for air, water, food, electricity, and other resources. However, some underwater habitats allow for these resources to be delivered using pipes, or generated within the habitat, rather than manually delivered.

Risk assessment determines possible mishaps, their likelihood and consequences, and the tolerances for such events. The results of this process may be expressed in a quantitative or qualitative fashion. Risk assessment is an inherent part of a broader risk management strategy to help reduce any potential risk-related consequences.

Motion sickness occurs due to a difference between actual and expected motion. Symptoms commonly include nausea, vomiting, cold sweat, headache, dizziness, tiredness, loss of appetite, and increased salivation. Complications may rarely include dehydration, electrolyte problems, or a lower esophageal tear.