Quick Links:
A – D | E – H | I – L | M – P | Q – T | U – X | W – Z
A
Alternative Air Source:
Is a secondary supply of air or other breathing gas used by the diver in an emergency. They can include an auxiliary demand valve, a pony bottle, and a bailout bottle.
Alternobaric Vertigo:
Is the feeling of dizziness caused by the unequal increase in middle ear pressures. Vertigo may occur due to barotrauma of descent or the effects of nasal decongestants. When the pressure in both ears reaches ambient levels, the dizziness usually stops. Although most often mild, vertigo can persist until the diver reaches the surface continuing the unequal pressures, which can damage the inner ear or eardrum.
Altitude Diving:
Diving at a location where the water surface is at an altitude that requires the modification of decompression schedules more than about 300m /980ft above sea level.
Ambient Light
Is the available sunlight underwater used as a source of illumination.
Ambient Pressure:
Is the pressure of the surrounding medium. On land, that pressure comes from the weight of the atmosphere. At depth, that pressure comes from the weight of the water plus the weight of the atmosphere.
Anoxia:
Is a medical condition caused by a severe lack of oxygen in the body.
Apnea:
Is generally defined as a suspension of breathing; however, apnea has become a synonym of freediving – a form of underwater diving that relies on divers’ ability to hold their breath until resurfacing.
Ascent:
Is when the diver is moving upwards towards the surface. An ascent may be interrupted by safety stops or decompression stops.
Ascent Rate:
Is the rate of speed at which the diver ascends to the surface. It is recommended never to exceed an ascent rate of 60 feet/18 meters per minute. This is an essential part of preventing decompression sickness.
B
Backplate:
Is a plate, usually made from metal, which rests against the diver’s back and to which the primary scuba cylinders are attached. The plate is held to the body by harness straps over the shoulders and around the waist. It is most often used with a back inflation buoyancy compensator.
Backward Roll Entry:
Is a means of entering the water in scuba gear from a sitting position from the side of the boat by rolling in backward.
Bailout Bottle:
Is a cylinder with an emergency supply of air or other breathing gas to be used in case of air supply trouble.
Balanced Regulator:
Is designed to help the diver maintain consistent breathing effort regardless of external conditions, such as depth or tank pressure.
Barotrauma:
Is an injury caused by unequal pressures between a space inside the body and the ambient pressure or between two spaces within the body.
Bottom Time:
Is the time between descending below the surface to the beginning of the ascent. Bottom time is used to calculate decompression obligation.
Breath-hold Diving:
Is diving without life support apparatus while holding one’s breath.
Dive Buddy:
Is a dive partner. The Buddy System was created with the purpose of increasing divers’ safety.
Buddy Breathing:
In case of an emergency, two divers share the same air supply. This can happen when one diver’s air supply is exhausted or unavailable due to equipment malfunction.
Buoyancy:
Is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. Objects that float are positively buoyant, those that sink are negatively buoyant, and those that stay where placed are neutrally buoyant.
Buoyancy Compensator:
An inflatable vest worn by the diver can be automatically or orally inflated to help control buoyancy, also known as a BC or BCD.
Buoyancy Control:
Is the skill of maintaining the appropriate buoyancy at all times during the dive.
C
Carbon Dioxide:
CO2 is an odorless, tasteless gas that is a byproduct of metabolism and is excreted by the lungs in exhaled air.
Carbon Dioxide Toxicity:
Is an occurrence of toxic effects, such as headache, shortness of breath, or even sudden blackout, caused by the buildup of CO2 in the blood.
C-card (certification card):
A card issued to a diver by a certification agency is evidence that the diver successfully completed training. You may be required to show your certification card when booking a dive trip, renting scuba equipment, or filling dive tanks.
Cf (cubic foot):
A measure of volume often used to mark the size of scuba cylinders. Standard cylinder sizes are 80cf and 100cf.
Compressed Air:
Air at a pressure greater than ambient. This is typically normal atmospheric air for recreational diving but compressed about 200 times to 200 bar (or 3000 psi).
Confined Water:
Confined water is a controlled environment that is not affected by geographic or weather conditions but is used for safe training purposes. An example of confined water is a swimming pool.
Cyanosis:
Is a bluish coloration on the skin or mucous membranes that appears when the tissues near the skin surface are low on oxygen
D
DAN:
Divers Alert Network is a group of nonprofit organizations that provides emergency and informational advice and assistance for its members and the diving community. DAN America and DAN Europe also collect and maintain databases on diving accidents, treatment, and fatalities, used for research and statistical reference.
Decompression:
Is a change from one ambient pressure to a lower ambient pressure that occurs during the ascent. During decompression, gas pressure within the body is reduced, and dissolved inert gases are eliminated from the tissues.
Decompression Algorithm:
Is a set of step-by-step procedures designed to calculate the decompression stops needed for a particular dive profile.
Decompression Chamber:
A hyperbaric (decompression) chamber is a sealed chamber in which a high-pressure environment can vary air pressure is used primarily to treat decompression sickness.
Decompression Illness:
DCI, also called generalized barotrauma or the bends, refers to injuries caused by a rapid decrease in the pressure that surrounds you, of either air or water.
Decompression Sickness:
DCS results when sudden decompression causes nitrogen bubbles to form in the body’s tissues.
Decompression Stop:
A decompression stop is a pause during the diver’s ascent, made to allow the body to expel dissolved gases, primarily nitrogen, in the blood. Failure to perform decompression stops leads to decompression sickness, caused by the gases expanding and turning into bubbles.
Deep Diving:
A dive deeper than 60 feet/18 meters. This type of diving requires additional preparation, planning, and skills.
Depth Gauge:
Is a calibrated device that displays how far a diver is below the surface.
Dive Computer:
Is a device that allows monitoring time and depth of a dive, calculates nitrogen levels in the body, and determines a safe ascent profile using mathematical algorithms.
Dive Flag:
Is a flag used to signal boats in the area that divers are below the surface.
Divemaster:
A Divemaster is the first level of being a professional diver. DM’s can help Instructors and lead recreational dives.
Dive Tables (also called decompression tables):
Dive tables are used to determine how long you can safely stay underwater at a given depth, both for the initial dive and for subsequent dives.
Diving signals:
Are hand or light signals used by scuba divers to communicate with each other when underwater.
Drift Diving:
Is a type of scuba diving, where a diver is transported underwater by drifting with currents.
Drysuit:
A watertight exposure suit designed to keep the diver dry and provide insulation with a layer of gas, such as air.
E
EAN (Enriched Air Nitrox):
Nitrox is a breathing gas that contains more oxygen and less nitrogen. Recreational divers use it to increase the bottom time or safety margin by decreasing the amount of nitrogen absorbed.
Equalization:
Is the procedure used to balance the pressure of a gas-filled space with the ambient pressure by forcing air into that space.
Exposure Protection:
Exposure protection suits range from thin wetsuits to heavy dry suits and are designed to prevent abrasions and decreases in core body temperatures.
F
First Stage:
The first stage is a regulator that is attached to the tank valve. It takes the high pressure in the tank (3,000 PSI +) and drops the pressure to intermediate pressure to the 2nd stage regulator.
Mask Fog:
Condensation of water vapor on the inside surface of a mask results in reduced visibility.
Freediving:
Is holding your breath while diving underwater without using a breathing apparatus.
Free Flow:
When your regulator malfunctions and the valve sticks in the open position, causing a constant rate of airflow.
Frenzel Maneuver:
Is one of the methods for equalizing the middle ear by pinching the nose closed and moving the back of the tongue upwards.
G
Gas Blending:
Gas blending is when scuba tanks are filled with non-air breathing gases. Mixes can include Nitrox, trimix, and heliox.
Gas embolism:
A condition when a gas bubble enters the blood vessel and blocks it.
Gas Saturation:
A state occurs when the level of dissolved gas in a particular body tissue has reached its maximum.
Giant Stride Entry:
This is the most common method used to enter the water. Using this method, a standing diver takes a large step into the water while securely holding his mask and loose gear.
H
Hood:
A garment that is used for thermal head protection while diving in cold water environments. Hoods are usually made from neoprene or latex.
Hyperthermia:
When a body temperature is higher than normal, hyperthermia can result from overheating in a wet suit in diving.
Hypothermia:
When the body temperature is lower than normal.
Hypoventilation:
Breathing at an abnormally low rate leads to elevated carbon dioxide levels in the blood.
Hypoxia:
Abnormally low oxygen level in the body that is insufficient to support normal activities or consciousness.
I
IP (Intermediate Pressure, or Interstage Pressure):
IP is the reduced pressure between a diving regulator’s first and second stages. Also referred to as LP (Low Pressure) in this context.
J
Jonline:
Is a short line often used by scuba divers to fasten themselves to an anchor line or down line during safety and decompression stops.
K
Knot:
A nautical term, Knots, are used to measure the speed of boats.
L
Lanyard:
A rope or a cord is usually worn around the neck or wrist. Lanyards can be used to secure or lower things, such as a knife, compass, regulator, etc.
Lift bag:
It is an air-tight bag with straps that can be tied to an object, which, once the bag is inflated, will be lifted to the surface by the bag’s buoyancy.
Lift Capacity:
It is the amount of buoyancy provided by a BCD. A BCD for cold freshwater will provide greater lift capacity than in warm saltwater.
Logbook:
Is a record of the diver’s dive history that proves the number of dives, dive depth, and dive experience.
Low Volume (low profile) Mask:
It is a mask with a small amount of air space inside it. Low volume masks sit closer to the diver’s face and require less air to purge if flooded.
M
Scuba Diving Mask:
It is a piece of dive gear that allows scuba divers, freedivers, and snorkelers to see clearly underwater. There are many different types of masks in the market today.
Mask Squeeze:
This happens when the mask creates suction on the face and eyes that can possibly lead to tissue swelling if the mask is not equalized.
Mixed Gas:
They are breathing gases other than air. Common mixes could include helium and air.
MOD/ODL:
Maximum operating depth/oxygen depth limit is the depth limit a diver can safely achieve using a particular gas mixture.
Multilevel Diving:
This is a dive profile where a diver spends time at several different depths on a single dive.
N
Narcosis:
Is a reversible change in consciousness that occurs while a person is diving at deep depths.
NDL (No decompression limit):
The maximum time a diver can spend at a specified depth without the need to make mandatory decompression stops during the ascent.
Neoprene:
Is a synthetic rubber material that maintains flexibility used in manufacturing most wetsuits and some drysuits.
Nitrogen:
Is an inert gas that makes up approximately 78% of air.
Nitrogen narcosis:
Is a reversible change in consciousness that occurs while a person is diving at deep depths. Nitrogen narcosis usually begins to manifest itself at depths of 30 m and greater.
Nitrox:
Is any mixture of nitrogen and oxygen containing less than 78% of Nitrogen.
O
Octopus Regulator:
Also known as an Octo, this is a 2nd Stage regulator used as an alternative air source in an emergency.
Off-gassing:
Is a diffusion of gas out of the tissues into the blood and its further movement to the lungs, where the gas is eliminated by exhalation.
Open-water Diving:
Is recreational diving in an environment other than a swimming pool but with no overhead obstacles; for instance, lakes, ponds, rivers, oceans.
O-ring:
O-Rings prevent leaks between parts and seams of scuba gear and are a vital part of scuba equipment.
Overhead:
Is anytime you are in an environment underwater that does not allow for a direct ascent to the surface.
Overweighting:
Carrying more weight than is necessary to achieve neutral buoyancy at all times in a dive.
Oxygen:
Is a gas vital for all life and makes up about 21% of the air by volume.
Oxygen Toxicity:
Is damage or injury caused by breathing oxygen at either too high pressure or concentration.
P
PADI:
Professional Association of Diving Instructors is one of the largest scuba certifying agencies in the world.
Partial Pressure:
Is When each gas contributes to the total pressure of the gas mixture.
Pony Bottle:
A “pony” is a small diving cylinder with an independent regulator that provides an additional alternative air source in case of emergency.
Primary Light:
The main light used on a dive and is usually the most powerful.
Purge Valve:
This allows 2nd stage regulators, masks, or snorkels to be cleared easily.
Q
R
Recreational Dive Planner:
Developed by DSAT, the planner calculates the no-stop time during underwater diving.
Dive Reel:
Is a mechanism used to store, deploy and recover long line.
Scuba Regulator:
A scuba regulator is your life support system while diving that connects your air supply in your tank, allowing you to breathe underwater.
Repetitive Dive:
Is any dive done within a specific time frame after a previous dive. All in all, any dive whose profile is affected by a dive prior is considered repetitive.
Reserve Gas:
Gas not intended to be used during the dive is reserved for contingencies.
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 spaces, such as sinuses, middle ear, inside mask, due to inability to release pressure on ascent from a dive.
Rip Current:
Rip currents are powerful, narrow channels of fast-moving water.
S
Safety Sausage (SMB or surface marker buoy):
A buoy that a diver tows to indicate their location to people at the surface.
Safety Stop:
Is a voluntary stop (not required by the decompression schedule), typically 3 minutes at 5 meters / 15 feet, as the diver ascends at the end of a dive.
Saturation:
Is 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.
Scuba:
Is an acronym meaning Self Contained Underwater Breathing Apparatus.
Second Stage:
Is the device that you breathe from, and its purpose is to reduce the pressure of the gas you will breathe to equal the surrounding pressure.
Sidemount:
A specific dive equipment configuration with diving cylinders mounted alongside the diver, below the shoulders, and along the hips, instead of on the diver’s back.
Dive Slate:
Is a rigid plastic tablet used for writing messages or notes underwater during the dive.
Snorkel:
Is a breathing tube attached to your mask and extends above the surface of the water. It allows you to breathe while your face is underwater.
Snorkeling:
Is swimming at the surface while breathing through a snorkel and using a mask to view underwater.
Snorkel Keeper:
Is a device used to hold a snorkel in place by fixing it to the mask strap.
Solo Diving :
Is the practice of scuba diving alone without a “dive buddy.”
Speargun:
Is a weapon for shooting fish underwater.
Standard Operating Procedure:
An SOP is a procedure, usually compiled by a diver certification organization, prescribing the processes to be followed when performing specified tasks.
Submersible Pressure Gauge:
Is a gauge to monitor the air supply of your scuba tank during the course of a dive.
Surface Air Consumption (SAC):
Your SAC rate measures the amount of air you consume while breathing for one minute on the surface.
Surface Interval:
Is the length of time on the surface between two consecutive dives.
T
Technical Diving:
A form of diving that exceeds the limits of recreational scuba diving and carries greater technical complexity and higher inherent risk.
Travel Gas:
Is a gas mixture used for descent and/or ascent when the bottom gas is not suitable for breathing at shallower depths.
Trimix:
Is a mixture of helium, nitrogen, and oxygen, used for deep diving.
Trim Weight:
Is ballast weight used to improve diver’s trim.
Turn the Dive:
Start the return on a dive that has reached the planned turning point in depth, time, gas supply, or distance.
U
Unbalanced Regulator:
Is a regulator where you will have to put in more effort to breathe as the pressure in the air tank decreases.
Upstream:
Against the current or flow.
Upwelling:
Upwellings occur when strong offshore winds blow out towards the sea. As the surface water is pushed away from shore, cold water from the deep travels up to take its place.
V
Vertigo:
The feeling of dizziness and off-balance can be a sign of ear barotraumas, from minor ear squeeze to perforation of the eardrum.
Visibility:
The distance a diver can see underwater is measured in feet or meters.
Visual Inspection (VIP):
Is the internal and external inspection of a scuba tank performed annually.
W
Water Pressure:
Is the force per unit area exerted by the weight of water and is given in units of atmospheres or ATA’s.
Weight System:
Is a system such as a nylon “weight belt,” or is integrated (built) into BCD’s that hold lead weights needed to compensate for increased buoyancy.
Wet Notes:
Is a small notebook made from waterproof paper used to communicate underwater.
Wet Suit:
Is a garment, usually made of foamed neoprene, that provides thermal protection while also providing abrasion resistance and buoyancy.
Wing:
A back inflation buoyancy compensator cell.
Working Pressure:
Is the maximum filling pressure rating for the scuba cylinder.
Wreck Diving:
Diving on natural or manufactured shipwrecks.
Z
Zip Tie (also cable tie, tie wrap):
Is a self-locking plastic strip used to connect objects.
Z-knife:
Is a line cutting tool with a replaceable blade in a slot.
