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Glossary - G

Gas analysis A procedure whereby the fractions of gas in a breathing mixture are determined. Generally it is used to determine the fraction of oxygen to within 1 %, to control the effects of Oxygen toxicity. Most diving operations will analyse for oxygen only. In more complex Trimix's, it is be desirable to analyse for the inert gases as well.
Gas Consumption (RMV)*(Bar) = gas consumption at depth. Total gas required for a dive= the sum of the gas required at each stage of the dive. Gas required at each stage of the dive=(Bar) x (RMV) x (Time) x (Work modifier).

Bar= Pressure at each stage Bar=(depth / 10)+1
RMV= Respiratory Minute Volume (in litres per minute)
Time= Time in minutes spent at that stage/depth
Work=A modifier to take into account that you breath more when working.
     1,     at rest
     1.5   working mildly
     2      working moderately
     3-5   working heavily

Descent consumption = average depth plus time spent descending. Gas consumption during ascent is calculated by "average depth" method: (max. depth + 1st deco stop depth)/2. This average depth is then used in the gas consumption equation.

Gas Mixing Gas mixing or blending is accomplished via one of four different ways:

1. By partial pressure, where only the pressures of the constituent gases are considered in determining their percentages in the final mix.
2. By continuous flow, where the appropriate amount of each gas is metered and injected into a gas flow stream, and then delivered to a mixing chamber or compressor inlet.
3. By volume, where known volumes of each gas are delivered to a container near atmospheric pressure, then compressed into high pressure cylinders.
4. By weight, where the gases are proportioned in the final mixture by the weight that each gas adds to the initial weight of the container.

GMDSS  Global Maritime Distress and Safety System
Goody Bag Some sort of mesh bag used to collect goodies and treasures found during a dive.
GPS Global Positioning System. An electronic navigation device that uses satellites to give a precise display of your position.
Grid north Bearings taken from the grid lines on maps and charts. The grid lines vary from exactly true north-south on most maps due to curvature of the earth's surface.
Gunwale The part of a vessel where hull and deck meet. (Pronounced "gun'l")
Gymbal Compass mounting which permits the compass to work regardless of heel and roll of the vessel










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