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Scuba Diving Glossary
ABSOLUTE PRESSURE: Pressure calculated by using a vacuum as the zero point and including the gauge and atmospheric pressure in the calculation.
ADRENALINE: A hormone secreted by the adrenal gland into the circulatory system which stimulates the heart, blood vessels, and respiratory system.
AIR: The primary breathing gas used by Scuba divers. Air is made up of approximately 20.95% Oxygen, O2, 78.08% Nitrogen, N2, 0.03% Carbon Dioxide, CO2, and 0.94% trace elements or gases. For most non scientific purposes or applications, these values are rounded up to 21% O2 and 79% N2.
AIR COMPRESSOR: A machine that compresses or pressurizes air; for Scuba purposes, air is compressed from the atmospheric level (14.7 psi at sea level) to the capacity of the tank, usually between 2500-3000 psi.
AIR EMBOLISM: A condition that occurs when air enters the bloodstream through ruptured alveoli into the pulmonary capillaries. The air in the bloodstream then forms bubbles, which can block blood flow to the body's tissues.
AIR PRESSURE: The force per unit area exerted by the weight of air; at sea level the air pressure is 14.7 psi (air pressure decreases with altitude).
ALGORITHM: A set of equations incorporated into diving computers in order to compute nitrogen uptake and elimination from changes in depth and elapsed time.
ALTERNATE AIR SOURCE: A device a diver can use in place of the primary regulator, in order to make an ascent while still breathing normally.
AMBIENT PRESSURE: The surrounding pressure; on land, comes from the weight of the atmosphere (see air pressure), at depth, comes from the weight of the water plus the weight of the atmosphere.
ANALOG INSTRUMENT: A device that uses a needle moving around a dial to provide information.
ARCHIMEDES PRINCIPLE: Any object wholly or partly immersed in fluid will be buoyed up by a force equal to the weight of the fluid displaced by the object.
ARGON: An inert gas that makes up less than one percent of air (sometimes used as a drysuit gas).
ARTERIAL GAS EMBOLISM: The condition characterized by bubble(s) of air from a ruptured lung segment under pressure; the bubbles enter the pulmonary circulation and travel to the arterial circulation, where they may cause a stroke.
ASCENT / DESCENT LINE: A line suspended from a boat or a buoy for a diver to use to control their rate of ascent or descent.
ASTHMA: A common condition manifested by narrowing of air passages within the lungs. One reason for the narrowing is excess mucous in the airways.
ATA: "Atmosphere Absolute" - 1 ata is the atmospheric pressure at sea level; is measured with a barometer.
ATMOSPHERE: The blanket of air surrounding the earth from sea level to outer space. Also, a unit of pressure; "one atmosphere" is the pressure of the atmosphere at sea level, i.e., 760 mm Hg. Two atmospheres is twice this pressure, 1520 mm Hg, etc. Abbreviated atm.
ATMOSPHERIC PRESSURE: Pressure of the atmosphere at a given altitude or location.