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Scuba Diving Glossary
SAC RATE: Short for Surface Air Consumption Rate. SAC Rate is the volume of gas a diver breathes on the surface at sea level. This measurement of gas volume is used as an index to determine the amount of gas needed/planned for a particular dive. With all the various gases in use today, the term is more correctly called Surface Consumption Rate (SCR).
SAFETY STOP: On ascent from a dive, a specified time spent at a specific depth, for purposes of nitrogen off gassing. By definition, it is not mandatory for safe ascent from the dive.
SALINITY: The amount of salt dissolved in a liquid, measured in parts per million.
SATURATION: The degree to which a gas is dissolved in the blood or tissues; full saturation occurs when the pressure of a gas dissolved in the blood or tissues is the same as the surrounding pressure of that gas.
SATURATION DIVING: Diving performed after the body is fully saturated with nitrogen. To become fully saturated the diver must stay under water for a much longer period than is allowed in recreational Scuba diving tables.
SCUBA: Acronym meaning Self Contained Underwater Breathing Apparatus.
SCUBA CYLINDER: A Scuba or diving cylinder, also known as a tank, is used to store and transport high pressure breathing gas to a diver through the demand valve of a regulator.
SEA LEVEL: The altitude of the world's oceans; all oceans are at sea level.
SECOND STAGE REGULATOR: The regulator that follows, in line, the first stage regulator, and delivers compressed air to the diver. Usually associated with the mouthpiece.
SERGEANT MAJOR: The Sergeant Major (Abudefduf saxatilis, family Pomacentridae) is a large, colorful damselfish. It earns its name from its brightly striped sides, which are reminiscent of the insignia of a military Sergeant Major. It grows to a length of about 15cm (6 inches). They are popular aquarium fish, although their aggressively territorial nature can pose problems if not closely watched.
SHALLOW WATER BLACKOUT: A sudden unconsciousness, from hypoxia, that occurs among some breath hold divers. Often occurs near the surface after a deeper dive, hence "shallow water."
SHIPWRECK DIVING: Commonly known as wreck diving, this type of diving focuses on the practices and techniques used while exploring shipwrecks. Shipwreck diving enables sport divers to visit the past and make interesting artifact finds while exploring the remains of sunken ships. This enables the sport diving community to make its own contribution to historians and archaeologists by giving them the information needed for wreck identification and further research.
SHIVERING: The body's attempt to create heat through muscular activity.
SINUSES: Air spaces within the skull that are in contact with ambient pressure through openings into the back of the nasal passages.
SKIN DIVING: Another name for breath-hold diving; diving without the use of breathing equipment (may include a snorkel).
SKIRT: The part of the diving mask typically made of rubber or silicone that creates a watertight seal with the diver's face.
SNUBA: A surface supplied compressed air apparatus, for use in shallow diving in calm waters. The air is delivered to one or more divers through a long hose.
SPLIT FIN: A fin having a split at the end of the blade. Split fins operate similarly to a propeller, by creating suction and lift forces to move the diver forward. Water flowing toward the center of the fin's 'paddle' portion also gains speed as it focuses, creating a 'scooping' or channeling effect.
SQUEEZE: Pain or discomfort in an enclosed space (sinuses, middle ears, inside a mask) caused by shrinkage of that space, occurs on descent.
STOPLIGHT PARROTFISH: A sex-changing fish inhabiting coral reefs in Florida, the Bahamas, the Caribbean, eastern Gulf of Mexico, Bermuda, and Brazil. Its typical length is between 30 and 45 cm, but it can reach 60 cm at times. The common name, stoplight, comes from the marked yellow spot near the pectoral fin.
SUBMARINE: A heavy walled vessel that can withstand pressures under water and allow occupants to breathe air at sea level pressure and travels under its own power.
SUBMERSIBLE PRESSURE GAUGE: A gauge to monitor air supply during the course of a dive.
SUPERSATURATION: An unstable situation where the pressure of a gas dissolved in the blood or tissues is higher than the ambient pressure surrounding that gas.
SURFACE INTERVAL: The length of time on the surface, usually out of the water, between two consecutive dives.
SURFACE SUPPLIED COMPRESSED AIR DIVING: Diving with the air continuously supplied by a compressor on the surface; can be used for both sport and professional diving.