Deep diving is underwater diving to a depth beyond the normal range accepted by the associated community. In some cases this is a prescribed limit established by an authority, while in others it is associated with a level of certification or training, and it may vary depending on whether the diving is recreational, technical or commercial. Nitrogen narcosis becomes a hazard below 30 metres (98 ft) and hypoxic breathing gas is required below 60 metres (200 ft) to lessen the risk of oxygen toxicity.
For some recreational diving agencies, "Deep diving", or "Deep diver" may be a certification awarded to divers that have been trained to dive to a specified depth range, generally deeper than 30 metres (98 ft). However, the Professional Association of Diving Instructors (PADI) defines anything from 18 to 30 metres (59 to 98 ft) as a "deep dive" in the context of recreational diving (other diving organisations vary), and considers deep diving a form of technical diving. In technical diving, a depth below about 60 metres (200 ft) where hypoxic breathing gas becomes necessary to avoid oxygen toxicity may be considered a deep dive. In professional diving, a depth that requires special equipment, procedures, or advanced training may be considered a deep dive.
