Scuba Diving Glossary A - G |
Scuba Diving Glossary H - Z
Haldanian
Related to Haldane's theory that nitrogen is absorbed up and released in an
exponential manner during a dive, and that there is some safe ratio of pressure
change for ascent.
Half Time
Half the time it takes for a dissolved gas in a tissue (such as nitrogen) to
equililbrate 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.
Head
Restroom on a boat.
Heliox
Mixture of helium and oxygen, usually reserved for very deep diving.
Helium
Second lightest gas; does not cause problems of narcosis to the same extent as
seen with nitrogen, and is therefore used for very deep diving.
Henry's Law
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.
High Altitude Diving
Is done in mountain lakes or other high altitude waters at or greater than 1,000
feet (300 meters) above sea level with increased risk of decompression sickness
because of lower-than-sea-level atmospheric pressure at the surface; regular
dive tables and some dive computers and depth gauges are inaccurate above sea
level; special high altitude dive tables and recalibration of gauges and
computer are required; specialty courses are available due to the complexity and
added hazards of this activity.
High pressure nervous syndrome
Abbr. HPNS; A condition which results from breathing Helium under high
pressures. Early symptoms of HPNS are somtimes seen as shallow as 300FSW but
more commonly over 600FSW. The severity also depends on the mix of breathing
gases, Nitrogen can often moderate the affects of HPNS. The early symptoms
include muscle tremors, followed by changes in electroencephalogram (EEG)
readings, impaired motor and problem solving skills. Other symptoms can include
euphoria, nausea, vomiting, lack of appetite and drowsiness. Symptoms sometimes
moderate or entirely dissapear with continued exposure.
Hogarthian Principles
The Hogarthian configuration is named after Bill 'Hogarth' Main. It is based on
reducing equipment to a minimum streamlined configuration that nevertheless
includes sufficient redundancy for extended decompression dives.
Hoods
Garment worn over the head to reduce thermal loss.
Hookah
A surface-supplied compressed air apparatus, for use in shallow diving in calm
waters. The air is delivered to one or more divers through a long hose.
Hydro
The common term for the hydrostatic test required on scuba cylinders every five
years to determine whether the tank walls are still strong enough for safe
usage.
Hydrogen
An inert gas, and lightest of all the elements, has been used in experimental
diving situations.
Hydrostatic Test
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.
Hyperbaric Chamber
Air-tight chamber that can simulate the ambient pressure at altitude or at
depth, is used for treating decompression illness.
Hypercapnia
A higher than normal P02level in the blood.
Hyperoxic and hyperoxia
In general, these terms relate to a more than a normal amount of Oxygen.
Hyperoxic refers to a mixture of gases with higher than normal Oxygen content
(above 21%). Hyperoxia 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.
Hyperthermia
A body temperature warmer than normal, less common in diving than Hypothermia,
but can occur from overheating in a wet suit.
Hyperventilation
Over breathing to the extent that the blood carbon dioxide level is lowered, may
lead to tingling in fingers and dizziness.
Hypothermia
A subnormal chilling of the body.
Hypoventilation
Under breathing to the extent that the blood carbon dioxide level is elevated,
may be manifested by carbon dioxide narcosis.
Hypoxia
Lower than normal PO2 level in the blood, insufficient oxygen in the blood.
Hyprthermia
A body temperature colder than normal (98.6F), severe problems start to manifest
when body temperature reaches about 95'F.
Jetty
A structure, usually made with rocks, extended into a sea, lake or river to
influence the current or tide in order to protect a harbor.
J-Valve
Contains a spring loaded valve that shuts off a divers air supply at approx.
300psi.
Kelp Surface Dive
A vertical, feet-first, method of descending into water of unknown depth or when
obstructions or heavy plant (such as kelp) growth exists; performed by spreading
arms and legs, then simultaneously bringing legs together while giving a strong
downward stroke with arms thus propelling upper body out of water; body weight
will then drive the diver downward; some also find this dive descent easier to
equalize ears because there is less blood pressure in head than with pike (head
first) dive.
Kilo/kg
Kilogram. Metric measure of weight. 1 kg = 2.21 pounds.
Knot
The velocity unit of 1 nautical mile (6080.20 ft.) per hour; equivalent to 1.689
ft. per second: to convert ft. per sec. into knots, multiply by 0.592.
K-Valve
A simple on and off valve.
Lift Bag
After being tied to an object to be lifted, the bag is inflated and will start
to rise.
Lift Capacity
The amount of buoyancy provided by a Buoyancy Compensator; varies according to
size of the BC and according to the purpose of the BC, e.g., a BC intended for
use in cold fresh water will provide greater lift capacity than one intended
primarily for use in warm salt water.
Live aboard
A dive boat with sleeping and eating accommodations. Commercial live aboard
boats are usually between 50 and 130 feet long, and can carry from 10 to 30
divers for up to a week or more.
Logbook
A diary of a divers dive history. Provides evidence of the depth and breadth of
a divers experience.
Low Volume Mask
A mask which has a smaller area between the glass and the diver's face, usually
with separate lenses for each eye; requires less air to purge if becomes flooded
Manifold
Used on double cylinder systems. Has 2 valves similar to single tank systems
attached by a heavy duty crosspiece with a valve in the center.
Marco Photography
A method of getting close-up pictures of a subject by using Marco accessories
attached to the camera's lens.
Mask
A skirted glass window constructed to provide air space between eyes and water
and to permit both eyes to see in the same plane; a regular mask covers eyes and
nose only; modern mask skirts are usually made of silicone rather than the older
rubber ones.
Mask Squeeze
A painful condition when the air inside the mask is compressed by the external
pressure creating suction on the face and eyes; can be alleviated by exhaling
from the nose; can cause permanent eye damage if not equalized.
Mask squeeze
Occurs in rapid descents where the diver neglects to equalize his/her mask. The
increase pressure causes tissues around the eyes to swell.
Mediastinal emphysema
Air from an over expanding lung escapes into the center of the chest. This puts
pressure on the heart and major blood vessels, interfering with circulation.
Symptoms are shortness of breath and feeling faint.
Middle ear
Air containing space of the ear bordered on one side by the tympanic membrane,
which is exposed to any change in ambient pressure. Air pressure in the middle
ear space can only be equalized through the Eustachian tube, which controls the
middle ear to the back of the nose.
Mixed gas
Any non-air mixture (e.g., nitrox), although some authors use the term only for
mixes that contain a gas in addition to (or in place of) nitrogen (e.g.,
helium).
MOD/ODL
maximum operating depth/oxygen depth limit. The deepest that a diver can safely
go using a particular gas mixture. For example, the MOD for EAN32 (32 per- cent
oxygen) is 132 fsw (40 m).
Multilevel diving
Spending a period of time at several different depth on a single dive
Narcosis
Depressed mental state, anywhere from confusion or drowsiness to coma.
NAUI
National Associatio 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 reation 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
Am 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 for emergency use.
Pressure
Any force exerted over an area.
PSI
Pounds per square inch, a common measurement of air pressure.
Purge Valve
Allow masks to be cleared without removal. Allows snorkels to be cleared easily
Rebreather
A closed-circuit system which filters exhaled air, then recirculates it for
rebreathing by the diver; requires special training and maintenance.
Recreational scuba diving
Diving to prescribed limits, including a depth no greater than 130 fsw, using
only compressed air, and never requiring a decompression stop.
Regulator
In scuba, any device that changes air pressure from one level to a lower level.
Repetitive Dive
Any dive whose profile is affected by a previous dive is considered repetitive.
Residual Nitrogen Time
The time it would take to off-gas any extra nitrogen remaining after a dive.
Residual Nitrogen Time is always taken into consideration when determining the
safe duration for any repetitive dive.
Reverse squeeze
Pain or discomfort in enclosed space (e.g., sinuses, middle ear, inside mask) on
ascent from a dive.
Rip Current
A strong current of limited area flowing outward from the shore, and may be
visible as a band of agitated water with the regular wave pattern altered;
current is caused by the rush of escaping water which is piled between shore and
bar or reef by wave action through a gap in the bar or reef; such currents are
dangerous to the uninitiated and are the cause of many drownings at ocean
beaches; however, when located by divers they are often used to facilitate entry
to areas beyond the bar or reef.
Safety Stop
On ascent from a dive, a specified time spent at a specified depth, for purposes
of nitrogen off gassing. By definition it is not a mandatory for a safe ascent
from a dive.
Salinity
The amount of salt dissolved in a liquid, measured in parts per million.
SASY/SASA
Supplied Air Snorkeling for Youth/Supplied Air Snorkeling for Adults. BC-like
PFD mounted with small compressed air cylinder and regulator that allows
snorkeler to breathe comfortably on the surface but prohibits him from
descending. SPG submersible pressure gauge. Required scuba gear that displays
the amount of air pressure in the scuba cylinder; can be either analog or
digital.
Saturation
The degree to which a gas is dissolved in the blood or tissues, full saturation
occurs when the pressure of gas dissolved in the blood or tissues is the same as
the surrounding pressure of that gas.
Saturation Diving
Diving performed after the body is fully saturated with nitrogen. To become
fully saturated the diver must stay under water for a much longer period than is
allowed in recreational scuba diving tables.
SCR
surface consumption rate. Measure used in calculations for determining air
consumption rate at various depths.
SCUBA
Acronym meaning Self Contained Underwater Breathing Apparatus.
Scuba Resort
a place providing recreation and entertainment to vacationers with the main
attraction as that of scuba diving. It may include training, Beach and/or boat
diving and many specialties such as wall, drift, wreck, eco-diving and many
others. It can be an All-Inclusive, a Live Aboard and or a land base operation.
It will normally be supported by one or many of the training agencies.
SDI
Scuba Diving International. The recreational scuba training and certification
arm of TDI.
Sea Level
The altitude of the world's oceans; all oceans are at sea level.
Second Stage Regulator
The regulator that follows, in line, the first stage regulator, and delivers
compressed air to the diver. Usually associated with the mouthpiece.
Shallow Water Blackout
A sudden unconsciousness, from hypoxia, that occurs among some breath hold
dives. Often occurs near the surface after a deeper dive, hence "Shallow Water".
Shivering
The body's attempt to create heat through muscular activity.
Sinuses
Air spaces within the skull that are in contact with ambient pressure through
openings into the back of the nasal passages.
Skin Diving
Another name for breath-hold diving; diving without the use of a breathing
equipment (may include a snorkel).
SLAM
Scuba Lifesaving and Accident Management. YMCA diver rescue course.
SNUBA
A surface-supplied compressed air apparatus, for use in shallow diving in calm
waters. The air is delivered to one or more divers through a long hose.
Squeeze
Pain or discomfort in an enclosed (sinuses, Middle ear, inside a mask), caused
by shrinkage of that space, occurs on decent.
Stern
The back end of a boat.
Submarine
A heavy walled vessel that can withstand pressures under water and allow
occupants to breath air at sea level pressures and travels under its own power.
Submersible Pressure Gauge
Gauge to monitor air supply during the course of a dive.
Super saturation
An unstable situation where the pressure of a gas dissolved in the blood or
tissues is higher than the ambient pressure of that gas.
Surface Interval
Length of time on the surface, usually out of the water, between two consecutive
dives.
Surface supplied compressed air diving
Diving with the air continuously supplied by a compressor on the surface can be
used for both sport and professional diving.
Tank Boot
Flat-bottomed, plastic, vinyl or rubber devices that fit over the rounded end of
a scuba tank, allowing the tank to stand up.
TDI
Technical Diving International. Maine-based certification agency for technical
aspects of recreational scuba.
Thermocline
Intersection between two layers of water of that are of distinctly different
temperatures, usually the colder layer is deeper.
Tissue
A part of the body characterized by specific characteristics, such as muscle,
bone, or cartilage. The term is also used to refer to any part of the body with
a specific half time for loading and unloading nitrogen or even a theoretical
compartment.
Trimix
Mixture of helium, nitrogen and oxygen, used for very deep diving.
Vasoconstriction
The constriction of the blood vessels in order to reduce heat loss from the
blood through the skin.
Venomous
Having a gland or glands for secreting venom; able to inflict a poisoned bite,
sting or wound.
Vertigo
A sign of ear barotraumas and should not be ignored. Causes may range from minor
ear squeeze to perforation of the eardrum to inner ear barotraumas.
VIP
Visual Inspection Program. Standardized visual tank inspection performed by a
trained equipment technician, performed annually.
Visibility
The distance a diver can see underwater measured in feet. Normally horizontally,
not up and down.
1. Wall Diving
Occurs on rock and reefs that run vertically, usually run from shallow to deep.
Water Pressure
Force per unit area exerted by the weight of water, each 33 feet of sea water
exerts a pressure equivalent to one atmosphere, or 14.7psa.
Wet Suit
Any suit that provides thermal protection underwater by trapping a layer of
water betweens the diver's skin and the suit.
Wheel
A dive table used to plan muti-level dives.
Windward
A point or side from which the wind blows; in the direction from which the wind
blows; as opposed to, leeward.
Wreck Diving
Diving on natural or man-made shipwrecks; specialty courses are available
Y-valve
Dual orifice valve.
Zoomlens
A lens that combines a range of focal lengths
