The diving environment exposes the diver to a wide range of hazards, and though the risks are largely controlled by appropriate diving skills, training, types of equipment and breathing gases used depending on the mode, depth and purpose of diving, it remains a relatively dangerous activity. Underwater diving is the practice of descending below the water’s surface to conduct underwater activities.
Atmospheric diving suits may be used to isolate the diver from the effects of high ambient pressure. Although not usually considered to be diving, crewed submersibles can extend depth range, while remotely controlled or robotic diving machines can reduce the risk to human divers. The saturation diving technique reduces the risk of decompression sickness after long duration deep dives.
Public safety diving is the underwater work done by law enforcement, fire rescue, and search & rescue/recovery dive teams, and may be done by professionals or volunteers. Military diving includes combat diving, clearance diving and ship’s husbandry diving. Underwater sports is a group of competitive sports using either free-diving, snorkeling or scuba technique, or a combination of these techniques.
Surface Supplied Diving
An alternative to self-contained breathing systems is to supply breathing gases from the surface through a hose. When combined with a communication cable, a pneumofathometer line and a safety line, an optional hot water hose for heating, a video cable and a gas reclaim line, it is called the diver’s umbilical. More basic equipment that may use only an air hose is called an airline or hookah system.
Compressor diving is a rudimentary method of surface-supplied diving used in some tropical regions such as the Philippines and the Caribbean. The divers swim with a half mask and fins and are supplied with air from an industrial low-pressure air compressor on the boat through plastic tubes. There is no reduction valve; the diver holds the hose end in his mouth with no demand valve or mouthpiece and allows excess air to spill out between the lips.
Submersibles and ‘hard’ atmospheric diving suits enable diving to be carried out in a dry environment at normal atmospheric pressure. An atmospheric diving suit (ADS) is a small one-person articulated submersible of anthropomorphic form which resembles a suit of armour, with elaborate joints to allow articulation while maintaining an internal pressure of one atmosphere.