H
- Haldanian
-
also Haldanean
Further information: Decompression (diving)#Critical ratio hypothesis
Decompression models based on the principles described by John Scott Haldane.
- half duplex
-
Voice communications system where users take turns to send and receive.
- half mask
- Diver's mask which covers the eyes and nose but not the mouth.
- half times
- see tissue half times
- halocline
-
A strong variation in salinity over a small depth range within a body of water. Often visble as a blurred or shimmering region due to uneven refractive index.
- hard hat diving
- Surface supplied diving, generally in professional diving, either wearing a modern diving helmet or the old-style standard diving dress and brass helmet.
- hardwire communications
- Voice communications using a cable for transmission.
- heavy gear
- see standard diving dress
- heliox
-
Mixtures of helium and oxygen for use as a breathing gas.
- heliair
-
Trimix blends made by topping up helium with air.
- helium analyzer
-
An instrument used to identify the presence and concentration of helium in a mixture of gases
- helmet diving
- see hard hat diving
- HID light
- High intensity discharge light: Used in cave diving light heads (q.v.).
- HIRA
- Hazard Identification and Risk Analysis: A risk management procedure for identifying hazards and assessing the risk associated with them and ways to reduce the risk to an acceptable level.
- Hogarthian configuration
- A scuba combination of backplate, wing, one-piece harness with crotch-strap, regulator arrangement including long-hose primary with a necklaced secondary demand valve, and, if used with twin cylinders, an isolation manifold.
- Hog looped
- A scuba configuration where the primary demand valve has a long hose which is routed under the righr arm, usually tucked under a light battery canister on the waist belt of the harness, and around behind the neck to reach the mouth from the right hand side. Part of the Hogarthian configuration (q.v.).
- hookah
-
also hooka and airline diving
Further information: Surface-supplied diving#Airline
Also known as airline diving; surface supplied diving where the breathing air is supplied to the diver by a simple hose. The diver usually breathes through a mouth held demand valve.
- hopcalite
-
Catalyst sometimes used in air filters to oxidise carbon monoxide to carbon dioxide. Hopcalite is a mixture of manganese oxide, copper oxide and a small amount of silver oxide.
- horse collar
- see adjustable bouyancy lifejacket
- hot water suit
-
Further information: Diving suit#Hot water suit
An insulated pipe in the umbilical line, which links the diver to the surface support, carries the hot water from a heater on the surface down to the suit. The diver controls the flow rate of the water allowing him to vary the warmth of the suit.
- HPNS
-
High-pressure nervous syndrome: A neurological and physiological diving disorder that results when a diver descends below about 500 feet (150 m) while breathing a helium–oxygen mixture.
- H-valve
- Cylinder valve body with two outlets and two valve mechanisms which can be independently controlled so that two regulator first stages can be fitted. Similar to Y-valve but in configuration where the second valve is parallel to the primary, though the secondary valve can sometimes be swivelled.
- hydrostatic pressure
-
Pressure due to the weight of the water column above a point at depth.
- hydrostatic test
-
Non-destructive test to revalidate pressure vessels which uses water as a test medium. The vessel is pressurised to the test pressure (q.v.) and measured for permanent set.
- hydreliox
-
Deep diving breathing gas mixture of hydrogen, helium and oxygen.
- hydrox
-
Deep diving breathing gas mixture of hydrogen and oxygen.
- hyperbaric lifeboat
- A lifeboat with a hyperbaric chamber and life support system built into it for evacuating saturation divers in an emergency.
- hyperfilter
- Additional filter to produce air of oxygen compatible quality. This may be built into the filling system or temporarily connected when required.
- hypercapnia
-
Excessive level of carbon dioxide in the body.
- hyperventilation
- 1. A deliberate deep breathing to reduce blood carbon dioxide level to extend the duration of a free dive.
- 2. Rapid breathing as the body's response to hypercapnia.
- 3. Rapid, often shallow breathing, associated with panic.
- hypothermia
- hypoxia
-
Abnormally low tissue oxygen concentration: Insufficient oxygen in the body to support normal activities or consciousness.
Read more about this topic: Glossary Of SCUBA Diving