Deep diving is underwater diving to a depth beyond the norm 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 ft to lessen the risk of oxygen toxicity. At much greater depths, breathing gases become supercritical fluids , making diving with conventional equipment effectively impossible regardless of the physiological effects on the human body.
Air, for example, becomes a supercritical fluid below about metres 1, ft. 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 professional diving , a depth that requires special equipment, procedures, or advanced training may be considered a deep dive. Deep diving can mean something else in the commercial diving field. For instance early experiments carried out by COMEX using heliox and trimix attained far greater depths than any recreational technical diving. One example being its "Janus 4" open-sea dive to metres 1, ft in The open-sea diving depth record was achieved in by a team of COMEX and French Navy divers who performed pipeline connection exercises at a depth of metres 1, ft in the Mediterranean Sea as part of the "Hydra 8" programme employing heliox and hydrox.
The latter avoids the high-pressure nervous syndrome HPNS caused by helium and eases breathing due to its lower density. An atmospheric diving suit ADS allows very deep dives of up to metres 2, ft. This eliminates the problems associated with breathing pressurised gases. Assumed is the surface of the waterbody to be at or near sea level and underlies atmospheric pressure. Not included are the differing ranges of freediving β without breathing during a dive.
Deep diving has more hazards and greater risk than basic open-water diving. These bubbles produce mechanical and biochemical effects that lead to the condition. The onset of symptoms depends on the severity of the tissue gas loading and may develop during ascent in severe cases, but is frequently delayed until after reaching the surface.
