Scuba Glossary: N - O - P


Narcosis  –  Depressed mental state, anywhere from confusion or drowsiness to coma.

NAUI  –  National Association of Underwater Instructors. It is one of the oldest certifying agencies.

Nautical Mile  –  Also known as a “geographical mile” or “sea mile”; a unit of distance designed to equal approximately 1 minute of arc of latitude, 6080.20 ft.; approximately 1.15 times as long as the statute mile of 5280 ft.

Nitrogen  –  Inert gas that makes up 79% of air. Nitrogen is inert in that it does not enter into any chemical reaction in the body, but it can cause problems under pressure (see nitrogen narcosis, decompression sickness).

Nitrogen Narcosis  –  Depressed mental state from high nitrogen pressure; usually does not begin to manifest on compressed air until below 80 fsw.

Nitrox  –  Any mixture of nitrogen and oxygen that contains less than the 79% nitrogen as found in ordinary air.

NOAA  –  Abbreviation for the National Oceanic and Atmospheric Association.


Octopus Regulator  –  An alternate second stage air source used by a diver’s buddy in an out-of-air situation, or reserve 2nd stage regulator.

OEA  –  Oxygen enriched air – synonym for nitrox.

Open circuit scuba  –  Apparatus used in recreational diving. Exhaled air is expelled into the water as bubbles, no part is re-breathed by the diver.

Open-Water Diving  –  The recreational diving done in an environment other than a swimming pool but with no overhead obstacles; examples include lakes, ponds, rivers, oceans, quarries.

Oxygen  –  Often seen as using the chemistry abbreviation 02, gas vital for all life on this planet; makes up about 21% of the air by volume.

Oxygen Therapy  –  Administration of any gas, for medical purposes, that contains more than 21% oxygen.

Oxygen Toxicity  –  Damage or injury from inhaling too much oxygen; can arise from either too high an oxygen concentration or oxygen pressure. One of the most dramatic manifestations of oxygen toxicity while diving can be seizure.

Oxygen Window  –  Difference between total gas pressures in arterial and venous blood; exist because oxygen is partly metabolized by the tissues, so venous oxygen pressure is lower than arterial oxygen pressure.


PADI  –  Professional Association of Diving Instructors. It is one of the largest certifying agencies.

Partial Pressure  –  Pressure exerted by a single component of a gas within a gas mixture, or dissolved in a liquid.

Pneumothorax  –  An abnormal collection of air outside the lining of the lung, between the lung and the chest wall, often a consequence of pressure injuries (barotraumas).

Pony Bottle  –  A small scuba cylinder strapped to a divers main tank with an independent regulator. Used for emergency use in the event a diver’s main air supply fails.

Port  –  Nautical terms which refer to the left sides of a ship as perceived by a person on board facing the bow (front). In lay terms, when standing on the bridge of a ship (or any watercraft) looking toward the front of the ship, port refers to the left side.

Pressure  –  Any force exerted over an area.

PSI  –  Pounds per square inch, a common measurement of air pressure.

Pulmonary  Toxicity  –  The toxic effects of oxygen at partial pressures between 0.45 ATA and 1.6 ATA are primarily on the lungs while the toxic effect at pO2s over 1.6 ATA are primarily on the brain.

Purge Valve  –  Allow masks to be cleared without removal. Allows snorkels to be cleared easily.

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