Glossary of Scuba Diving Terms (H)

Understanding That Strange Scuba Language

Welcome to our glossary of scuba diving terms. Diving, like many sports, has its own language. Our scuba glossary is for anyone interested in understanding the scuba diving definitions, scuba diving terms or scuba slang found in this strange scuba communication that divers use.

Our glossary of scuba diving terms is easy to use. Just click on the letter that corresponds to the first letter of the word that you are looking for. All the words that begin with that letter will be displayed.

We will be constantly updating our glossary of scuba diving terms. If you think we have missed a term or you can not find the word you are looking for, please let us know. We will add it and the best definition we can find to our glossary of scuba diving terms.

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H

Haldane's theory that nitrogen is absorbed and released in an exponential manner during a dive, and that there is some safe ratio of pressure change for ascent.

Half the time it takes for a dissolved gas in a tissue (such as nitrogen) to equilibrate to a new pressure, or to reach full saturation at a new pressure. Theoretical tissue half times are used in designing dive tables and algorithms for dive computers.

A Halocline is a change between layers of fluids of different densities. The most important to divers is the salt content of the water. This is not often apparent unless the change is big enough to cause buoyancy changes.

An extra tank staged at the decompression stop. A hang tank found on the ascent line of a dive boat in case of emergencies.

Bathroom on a boat.

Mixture of helium and oxygen that is most commonly use for very deep diving.

Second lightest gas. Helium does not cause problems of narcosis to the same extent as seen with nitrogen, and is therefore used for very deep diving.

The amount of any given gas that will dissolve in a liquid at a given temperature is a function of the partial pressure of the gas in contact with the liquid and the solubility coeffient of the gas in the liquid.

Diving in mountain lakes or other high altitude waters at or greater than 1,000 feet (300 meters) above sea level. This type of diving has an increased risk of decompression sickness because of lower-than-sea-level atmospheric pressure at the surface. This requires special dive tables, dive computers and depth gauges. Specialty courses are available due to the complexity and added hazards of this activity.

Garment worn over the head to reduce thermal loss. .

A surface-supplied compressed air apparatus. This is used for diving in shallow, calm waters. The air is delivered to one or more divers through a long hose.

Pressure test in which the tank is filled with water instead of air and raised to five thirds the maximum working pressure, causing the water to expand and be displaced.

Air-tight chamber that can simulate the ambient pressure at altitude or at depth is used for treating decompression illness.

In general, these terms relate to a more than a normal amount of Oxygen. Hypoxic refers to a mixture of gases with higher than normal Oxygen content (above 21%). Hypoxia is the physiological condition associated with breathing too high of a partial pressure of Oxygen. The human body has a limit on both the partial pressure of Oxygen it can tolerate and the long term dosage of Oxygen. The partial pressure upper limit is generally considered to be approximately 1.6 ppO2 but most divers leave some margin for error and a more typical upper limit is 1.4 ppO2. When high partial pressures of Oxygen are inspired, convulsions may occur with little or no warning.

A body temperature warmer than normal. This is less common in diving than Hypothermia, but can occur from overheating in a wet suit.

Over breathing to the extent that the blood carbon dioxide level is lowered. This may lead to tingling in fingers and dizziness.

A subnormal chilling of the body.

Under breathing to the extent that the blood carbon dioxide level is elevated. This may be manifested by carbon dioxide narcosis.

A body temperature colder than normal (98.6F). Severe problems will start to show.