Scuba diving glossary

Recreational and technical diving terms.

AIDA: Association Internationale pour le Développement de l'Apnée. International freediving / breath-hold diving organization that certifies freedivers and governs competitive apnea.
Algorithm (decompression): Mathematical model that calculates the absorption and elimination of inert gases in diver tissues. Common algorithms include ZHL-16C (Bühlmann), RGBM (Reduced Gradient Bubble Model), and VPM (Variable Permeability Model).
Apnea / Freediving: Breath-hold diving without breathing apparatus. Freediving is the recreational and competitive form of apnea.
BCD / BC (Buoyancy Compensator Device): Inflatable vest or wing that allows the diver to control buoyancy in the water column. Main styles: jacket, wing (backplate+wing), and mono.
CMAS: Confédération Mondiale des Activités Subaquatiques. IOC-recognized world organization for underwater activities; issues recreational and technical dive certifications using a star-rating system.
DCS (Decompression Sickness): Also called "the bends". Occurs when dissolved nitrogen forms bubbles in tissues due to ascending too fast. Treatment requires a hyperbaric chamber.
DIN: Regulator-to-cylinder connection where the first stage screws directly into the valve (rated up to 300 bar). More secure than yoke/A-clamp for high pressures and technical diving.
Dive Computer: Electronic device that measures depth and bottom time in real time, calculates the decompression profile, and alerts the diver to no-decompression limits (NDL) or required stops.
Divemaster: First professional-level certification in PADI (and equivalent in other agencies). A Divemaster can guide certified divers and assist instructors but cannot teach independently.
Drysuit: Waterproof diving suit that keeps the diver dry. Used in cold water (typically < 12 °C) and inflated with gas for buoyancy control. Requires specific training.
Equalization (ear): Technique to equalize middle-ear pressure with ambient pressure when descending. The Valsalva maneuver (pinch nose and blow gently) is most common; Frenzel and other methods are more efficient.
Halocline: Transition layer between water masses of different salinity. Visually similar to a thermocline; creates optical distortion in caves and cenotes.
Helium / Trimix: Helium is added to gas mixes in deep technical diving to reduce nitrogen narcosis and oxygen toxicity. Trimix = oxygen + nitrogen + helium in variable proportions.
Hypoxia: Insufficient oxygen in tissues. In diving it can result from using hypoxic mixes (< 21 % O₂) at shallow depths or from CO₂ buildup in closed-circuit rebreathers.
Kelp: Giant macroalgae (genera Macrocystis and Lessonia) that form underwater forests. Common in Patagonian Atlantic waters and around Ushuaia; requires good buoyancy control to navigate.
NAUI: National Association of Underwater Instructors. US-founded (1960) diving certification agency for recreational and technical diving.
Nitrogen narcosis: Narcotic effect produced by nitrogen under elevated pressure (typically from 30–40 m). Can cause euphoria, disorientation, and impaired judgment. Reverses upon ascent.
Nitrox / EAN (Enriched Air Nitrox): Oxygen–nitrogen mix with O₂ concentration above 21 %. Reduces nitrogen loading and extends bottom time on repetitive dives. Requires a dedicated certification.
No-decompression limit (NDL): Maximum bottom time at a given depth that allows direct ascent to the surface with only a safety stop, without mandatory decompression stops.
Octopus: Additional second-stage regulator (alternate air source) used to share gas with a buddy in an emergency. Typically on a long yellow or green hose.
Open Water Diver (OWD): Entry-level SCUBA certification. Permits diving to 18 m (20 m depending on agency) with a certified buddy without instructor supervision.
PADI: Professional Association of Diving Instructors. The world's largest recreational diving certification organization, with hundreds of affiliated centers in Argentina.
Rescue Diver: Rescue diving certification (PADI or equivalent). Trains the diver to prevent and manage dive emergencies, assist distressed divers, and apply first aid.
Safety stop: A 3-minute stop at 5 m depth at the end of every dive, recommended even when no mandatory decompression stops are required. Reduces DCS risk.
SSI: Scuba Schools International. Recreational and technical diving certification agency with a strong presence in Argentina and Latin America.
Thermocline: Layer of water where temperature drops abruptly over a few meters of depth. Can reduce visibility and requires buoyancy adjustment when crossing it.
Twin set / Doubles: Two paired cylinders (typically 2×10 L or 2×12 L) connected by a manifold. Standard in technical diving for extended gas capacity.
Visibility: Maximum horizontal distance at which objects can be seen underwater. In Argentina: 5–15 m in the South Atlantic, up to 20 m in Golfo Nuevo (Puerto Madryn), > 20 m in Patagonian lakes.
Wetsuit: Neoprene diving suit that allows a thin water layer between the suit and the body; body heat warms that layer for thermal insulation. Typical thicknesses: 3 mm (warm water) to 7 mm (cold water).
Wing: Back-mounted BCD bladder attached to a backplate. Standard in technical diving and preferred by many advanced recreational divers for streamlined profile.
Wreck: Sunken vessel accessible for underwater exploration. Argentina has notable wrecks including the Monte Cervantes in Ushuaia and the Corvette Swift in Puerto Deseado.
Yoke (A-Clamp): Regulator-to-cylinder connection using a clamp, limited to cylinders up to 232 bar. The most common connection type for recreational diving in Argentina.