Freediving in the context of "Pearl fisheries"

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 diving, as a human activity, is the practice of descending below the water's surface to interact with the environment. It is also often referred to as diving, an ambiguous term with several possible meanings, depending on context.Immersion in water and exposure to high ambient pressure have physiological effects that limit the depths and duration possible in ambient pressure diving. Humans are not physiologically and anatomically well-adapted to the environmental conditions of diving, and various equipment has been developed to extend the depth and duration of human dives, and allow different types of work to be done.

In ambient pressure diving, the diver is directly exposed to the pressure of the surrounding water. The ambient pressure diver may dive on breath-hold (freediving) or use breathing apparatus for scuba diving or surface-supplied diving, and the saturation diving technique reduces the risk of decompression sickness (DCS) after long-duration deep dives. Atmospheric diving suits (ADS) may be used to isolate the diver from high ambient pressure. Crewed submersibles can extend depth range to full ocean depth, and remotely controlled or robotic machines can reduce risk to humans.

A mode of diving, or diving mode, is a particular way to dive underwater that requires specific equipment, procedures and techniques, and may expose the diver to a particular range of hazards.

There are several modes of diving; these are distinguished by the type of breathing apparatus, diving equipment, procedures and techniques involved, and whether the diver is exposed to ambient pressure. Ambient pressure diving includes freediving and compressed-gas diving, which may also be classed as air diving, oxygen diving, and mixed gas diving by the breathing gas used, and as open-circuit, semi-closed, or closed-circuit depending on the type of breathing apparatus used. There is also atmospheric pressure diving, which involves encapsulation in an atmospheric pressure diving suit or submersible, and unmanned diving, where there are no human divers involved. The diving equipment, support equipment and procedures used largely depend on the mode of diving.

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.

The timeline of underwater diving technology is a chronological list of notable events in the history of the development of underwater diving equipment. With the partial exception of breath-hold diving, the development of underwater diving capacity, scope, and popularity, has been closely linked to available technology, and the physiological constraints of the underwater environment.

Underwater target shooting is an underwater sport/shooting sport that tests a competitors’ ability to accurately use a speargun via a set of individual and team events conducted in a swimming pool using freediving or apnea technique. The sport was developed in France during the early 1980s and is currently practiced mainly in Europe. It is known as tir sur cible subaquatique in French and as tiro al blanco subacuático in Spanish.