There is a vast and fascinating world beneath the sea. Scuba, the acronym for self-contained underwater breathing apparatus, is one way that people explore it. It consists of an air tank, buoyancy control device and a breathing regulator that are worn by the diver. Some people dive professionally and have advanced training and equipment, but for most recreational scuba diving is an enjoyable hobby or pastime.

A dive begins on the surface, where a diver checks the conditions before venturing below. Before entering the water, the diver puts on a wetsuit and mask to protect themselves from the cold, sand or other materials. The diver may then use a hand signal to tell the dive master they are ready to dive. If something goes wrong on a dive, the dive master will flash the signal “something is wrong” or “everything’s okay”.

Once in the water, the diver uses their tank to breathe through hoses connected to a breathing apparatus (regulator). There are two main types of scuba: open circuit, which vents all expired air into the water, and closed circuit systems that re-breathe a portion of the exhaled air with oxygen, removing carbon dioxide and adding more oxygen to make it breathable again. Some scuba divers also use helium-oxygen mixtures to allow them to go much deeper than is possible using compressed air alone.

As with any activity that involves breathing under water, scuba can pose dangers if the diver does not follow safe practices. The most serious of these dangers is running out of breathing gas on a dive, known as an out-of-air incident. This can be caused by a number of things, including decompression sickness, and it can be fatal.