Underwater diving in the context of "Nitrox"

Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air in vehicle tires and shock absorbers are commonly used for improved traction and reduced vibration. Compressed air is an important medium for the transfer of energy in industrial processes and is used for power tools such as air hammers, drills, wrenches, and others, as well as to atomize paint, to operate air cylinders for automation, and can also be used to propel vehicles. Brakes applied by compressed air made large railway trains safer and more efficient to operate. Compressed air brakes are also found on large highway vehicles.

Compressed air is used as a breathing gas by underwater divers. The diver may carry it in a high-pressure diving cylinder, or supplied from the surface at lower pressure through an air line or diver's umbilical. Similar arrangements are used in breathing apparatus used by firefighters, mine rescue workers and industrial workers in hazardous atmospheres.

In physiology, dehydration is a lack of total body water that disrupts metabolic processes. It occurs when free water loss exceeds intake, often resulting from excessive sweating, health conditions, or inadequate consumption of water. Mild dehydration can also be caused by immersion diuresis, which may increase risk of decompression sickness in divers.

Most people can tolerate a 3–4% decrease in total body water without difficulty or adverse health effects. A 5–8% decrease can cause fatigue and dizziness. Loss of over 10% of total body water can cause physical and mental deterioration, accompanied by severe thirst. Death occurs with a 15 and 25% loss of body water. Mild dehydration usually resolves with oral rehydration, but severe cases may need intravenous fluids.

Google Street View is a technology featured in Google Maps and Google Earth that provides interactive panoramas from positions along many streets in the world. Google Street View displays interactive panoramas of stitched VR photographs. Most photography is done by car, but some is done by tricycle, camel, boat, snowmobile, underwater apparatus, and on foot.

First launched in 2007 in several cities in the United States, Street View has since expanded to include all of the country's major and minor cities, as well as the cities and rural areas of many other countries worldwide. As of 2017, Street View had coverage in 83 countries. Street View has been used for research in fields like urban analytics and geographic information science. Street View imagery has also been used in artistic work.

An environmental suit is a suit designed specifically for a particular environment, usually one otherwise hostile to humans. An environment suit is typically a one-piece garment, and many types also feature a helmet or other covering for the head. Where the surrounding environment is especially dangerous the suit is completely sealed.

The first environmental suits were diving suits designed to protect a diver from the surrounding water (see timeline of underwater technology). Later developments were designed to protect the wearer from the cold (for example wetsuits and other ambient pressure suits) or from undersea high pressure and the resulting decompression sickness (for example atmospheric diving suits). Protecting the wearer from cold is also a feature of ski suits.

Sportswear or activewear is athletic clothing, including footwear, worn for sports activity or physical exercise. Sport-specific clothing is worn for most sports and physical exercise, for practical, comfort or safety reasons.

Typical sport-specific garments include tracksuits, shorts, football or basketball jerseys, t-shirts and polo shirts. Specialized garments include swimsuits (for swimming), wet suits (for diving or surfing), ski suits (for skiing) and leotards and tights (for gymnastics or aerobics). Sports footwear includes football boots (also referred to as cletes), trainers, riding boots, tennis shoes (or running shoes), or ice skates. Sportswear also includes sports bras for running, crop tops, or a bikini top. Sportswear is often worn as casual fashion clothing.

Ama (海女, "sea women") are Japanese divers famous for collecting pearls, though traditionally their main catch is seafood. The vast majority of ama are women.

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 mask (also half mask, free-diving mask, snorkelling mask or scuba mask) is an item of diving equipment that allows underwater divers, including scuba divers, underwater hockey players, underwater rugby players, free-divers, and snorkellers to clearly see underwater. Surface supplied divers usually use a full face mask or diving helmet, but in some systems the half mask may be used. When the human eye is in direct contact with water as opposed to air, its normal environment, light entering the eye is refracted by a different angle and the eye is unable to focus the light on the retina. By providing an air space in front of the eyes, the eye is able to focus nearly normally. The shape of the air space in the mask slightly affects the ability to focus. Corrective lenses can be fitted to the inside surface of the viewport or contact lenses may be worn inside the mask to allow normal vision for people with focusing defects.

When the diver descends, the ambient pressure rises, and it becomes necessary to equalise the pressure inside the mask with the external ambient pressure to avoid the barotrauma known as mask squeeze. This is done by allowing sufficient air to flow out through the nose into the mask to relieve the pressure difference, which requires the nose to be included in the airspace of the mask. Equalisation during ascent is automatic as excess air inside the mask easily leaks out past the seal.

Underwater work is work done underwater, generally by divers during diving operations, but includes work done underwater by remotely operated underwater vehicles and crewed submersibles.

Underwater work is the activity required to achieve the purpose of the diving operation additional to the activities required for safe diving in the specific underwater environment of the worksite, including finding and identifying the workplace, and where necessary, making it safe to do the planned work. Some of these activities have a wide range of applications in work suitable for a given diving mode, and are likely to be considered basic skills and learned during professional diver training programmes for the relevant mode. Others are specialist skils and are more likely to be learned on the job or on skills training programmes not directly related to diving.

Decompression sickness (DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompression. DCS most commonly occurs during or soon after a decompression ascent from underwater diving, but can also result from other causes of depressurization, such as emerging from a caisson, decompression from saturation, flying in an unpressurised aircraft at high altitude, and extravehicular activity from spacecraft. DCS and arterial gas embolism are collectively referred to as decompression illness.

Since bubbles can form in or migrate to any part of the body, DCS can produce many symptoms, and its effects may vary from joint pain and rashes to paralysis and death. DCS often causes air bubbles to settle in major joints like knees or elbows, causing individuals to bend over in excruciating pain, hence its common name, the bends. Individual susceptibility can vary from day to day, and different individuals under the same conditions may be affected differently or not at all. The classification of types of DCS according to symptoms has evolved since its original description in the 19th century. The severity of symptoms varies from barely noticeable to rapidly fatal.