Scuba is a form of underwater diving in which the diver has a self-contained underwater breathing apparatus. It allows the diver to explore ship wrecks, underwater caves and to see fish in their natural habitats. Scuba is used both recreationally and by professional divers for commercial purposes. This type of diving requires specialized training and equipment and is subject to different safety standards than recreational scuba.

A scuba set includes a mask to allow the diver to breathe easily under water, snorkel and fins to move through the water, dive computer to monitor depth and time, wetsuit or dry suit to protect against cold water, scuba tank to provide air from the surface, pony bottle for emergency use and weights to assist with buoyancy control. Other specialized tools may be included as well for specific dives, such as cameras, dive lights and other accessories.

Most common underwater emergencies are associated with a compromised breathing gas supply, such as loss of a second stage regulator, hose failure or loop flood in a rebreather. Other emergencies can include too much work of breathing, which could be caused by a gas density problem or a malfunctioning regulator. Divers are trained to donate breathing gases to each other, and also in rescue procedures for buddy separation under water.

Other hazards are related to the environment in which the diver is diving, such as currents and tides, which can affect the depth of a dive and visibility. In addition, it is a good practice to log each dive upon completion, especially for repeated dives, so that residual inert gas levels are calculated and the equipment can be maintained.