Scuba Diving Glossary

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NARCOSIS: Depressed mental state, anywhere from confusion or drowsiness to coma.

NEGATIVE PRESSURE CHECK: A leak test performed on a rebreather. Gas is expelled from the loop to create a vacuum and observed to detect a creep in the hoses from the breathing bags.

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 deeper than 80 feet.

NITROX: Any mixture of nitrogen and oxygen that contains less than the 79% nitrogen found in ordinary air.

NOAA: Abbreviation for the National Oceanic and Atmospheric Association.

NORMOXIC: A term used for diving gases that have an equivalent amount of oxygen as normal breathing air (roughly 21%). This is usually used when diving trimix, such as "Normoxic Trimix". This would constitute a mix, or back gas, that could be used all the way to and from the surface without becoming "hypoxic" thus it would not require a "travel gas".