A recreational activity enjoyed around the world, scuba (an acronym for Self-Contained Underwater Breathing Apparatus) allows people to explore underwater environments at much greater depths than snorkeling. It is often used for exploration of shipwrecks, underwater caves or seeing fish and other marine life in their natural habitat. However, scuba is also employed for many jobs such as underwater construction, military diving and search and rescue operations.

Scuba is a safe hobby if the equipment is maintained properly. Divers must undergo training to learn how to use their scuba gear, understand dive physiology and the principles of decompression diving. They are taught to recognise and respond appropriately to common dive emergencies such as running out of air, being lost underwater or a decompression illness.

When scuba diving, it is recommended that divers log their dives to record key information such as depth and time of the dive. This enables them to calculate residual inert gas levels and prepare for future dives. It is also a good practice to perform a buddy check before each dive.

The most urgent scuba emergency is running out of breathing gas under water, usually referred to as an Out-of-Air incident. Divers are trained in procedures to donate and receive breathing gas from each other and may carry an independent alternative air supply if they do not choose to rely on their buddies.

A scuba tank is connected to a buoyancy control device, or BCD, by a low-pressure inflator hose and a high-pressure hose with gauges that display the remaining amount of air. Divers can adjust the air supply in their BCD to achieve a neutral buoyancy on the surface or a controlled descent and ascent.