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For safety and efficiency, divers may need to communicate with others diving with them, or with their surface support team. The interface between air and water is an effective barrier to direct sound transmission, [9] and the natural water surface is also a barrier to visual communication across the interface due to internal reflection, particularly when not perfectly smooth.
Dive signal for out-of-air emergency. In emergencies when a diver runs out of air in the cylinder in current use, and when there is no buddy around to donate air, the use of a redundant air supply (such as independent twins or a pony bottle), allows a diver to perform an ascent in a controlled manner, breathing as normal. [8]
Technical diver during a decompression stop. There is some professional disagreement as to what exactly technical diving encompasses. [10] [11] [12] It is an arbitrary distinction, and the line has been drawn in different places by different organisations, and has shifted on a few occasions.
Communication is central to buddy and team diving. DIR divers must be competent at underwater communication by hand signals and light signals, and to use them to ensure that they are always aware of the status of the rest of the team. DIR divers have an extended range of hand signals, some particularly relevant to overhead and decompression diving.
A system recommended by some organisations, mostly those involved in technical diving (GUE, [24] CMAS-ISA, other tech and cave diving groups) is to equip the regulator normally used throughout the dive (the "primary") with a long hose, typically 1.5 to 2 metres (5 to 7 ft) long, proportional to the height of the diver. This is the regulator ...
A safety sausage or signal tube is an inflatable buoy used when the diver is at the surface to indicate the diver's position to the dive boat, reducing the risk of losing contact when air, light or sea conditions decrease the visibility of the divers from the boat.
Divers, including professionals, generally use hand signals when visibility allows. Recreational divers must be familiar with the hand signals their certification agency uses. These have to a large extent been standardized internationally and are taught in entry-level diving courses. [35] Technical divers commonly add a few more.
Scuba diving education levels as used by ISO, PADI, CMAS, SSI and NAUI This class of certification covers competence to dive within the scope of what is generally considered recreational open water diving , with no planned decompression obligations, a single air or nitrox breathing gas and relying on the buddy system or a dive leader for ...