These Diving Terms are brief definitions, here for the purpose of giving a basic understanding of the words you may come across when researching dive theory, dive courses or the diving industry. These descriptions do not replace proper course material, and more in-depth information about these diving terms can be found in the relevant course manuals or from your instructor.
A
AGE is a type of Decompression Illness where a bubble is trapped in the blood vessel and blocks blood flow. AGE can be caused by a diver holding their breath, ascending too quickly, or a pre-existing contributing factor. The signs and symptoms of AGE can include: blood or frothing from the mouth, unconsciousness or dizziness, chest pain, weakness or paralysis, convulsions, coughing, and shortness of breath.
A dive agency is an organisation that produces scuba diving course material and regulates the instructors who teach it.
A device used to determine the oxygen content in a scuba tank.
A barometric measurement of atmospheric pressure – 1ATA being the pressure at sea level.
B
A method of mounting a scuba cylinder or dive equipment, backmount usually consists of one or two tanks mounted to a BCD with regulators attached to provide a breathing gas to the diver.
otherwise known as a Buoyancy Control Device or BC, a jacket, or a wing, these inflatable devices are used by scuba divers to help control their depth underwater and to keep them afloat at the surface.
usually air, but also Nitrox, Trimix or Heliox, a breathing gas is simply what is contained in a scuba cylinder for divers to breathe from.
A bottom mix/gas is a term to describe a breathing gas that is used at the deepest portion of a dive. More often than not, a bottom gas is the gas with the lowest oxygen content.
The buddy system is used by scuba divers to improve safety by diving in teams of two or three – these divers are called your buddies.
BWRAF is an acronym to help divers remember the 5 points of a pre-dive check.
- B – BCD
- W – Weights
- R – Releases
- A – Air
- F – Final ok
C
A term for the system used in rebreathers [CCR – closed circuit rebreather], closed-circuit describes the recycling of breathing gases known as a ‘loop’, whereby the unit utilises two cylinders, most commonly oxygen and air, and these two gases are injected into the loop at different rates, maintaining a steady percentage of oxygen for the diver to breathe. The diver’s exhaled gas travels around the loop, passing through a scrubber, which absorbs the C02, and gets injected with oxygen before the diver inhales.
A high-pressure air compressor system that fills scuba cylinders with compressed breathing gas.
A tank, usually aluminium or steel, that is used to contain pressurised breathing gases for scuba diving.
D
A general term that includes both decompression sickness (DCS) and arterial gas embolism (AGE). /p>
DCS – (Decompression Sickness)
DCS is a condition most commonly caused by gas bubbles exiting the tissues when surfacing from a dive, but has also been associated with deeper/longer dives, diving in colder water, overexertion at depth, pre-disposing health factors, and many more. Signs and symptoms of DCS can include: a skin rash, a skin itch, fatigue, dizziness or vertigo, joint or muscle pain, numbness or paralysis, loss of consciousness, confusion or irritability, and other unusual personality changes.
AGE – Arterial Gas Embolism
AGE is a type of Decompression Illness where a bubble is trapped in the blood vessel and blocks blood flow. AGE can be caused by a diver holding their breath, ascending too quickly, or a pre-existing contributing factor. The signs and symptoms of AGE can include: blood or frothing from the mouth, unconsciousness or dizziness, chest pain, weakness or paralysis, convulsions, coughing, and shortness of breath.
DCS – (Decompression Sickness)
DCS is a condition most commonly caused by gas bubbles exiting the tissues when surfacing from a dive, but has also been associated with deeper/longer dives, diving in colder water, overexertion at depth, pre-disposing health factors, and many more. Signs and symptoms of DCS can include: a skin rash, a skin itch, fatigue, dizziness or vertigo, joint or muscle pain, numbness or paralysis, loss of consciousness, confusion or irritability, and other unusual personality changes.
Also known as an underwater scooter, is a battery-run, hand-held vehicle with a propeller used by scuba divers or snorkelers to travel underwater.
H
A gas that contains more than 21% oxygen, this term includes nitrox gases, and can be used in both recreational and technical diving.
A gas that contains less than 21% oxygen; in scuba diving hypoxic gases are usually Trimix gases, and contain less than 21% oxygen as they are not intended to be breathed at shallow depths or at the surface.
N
AGE is a type of Decompression Illness where a bubble is trapped in the blood vessel and blocks blood flow. AGE can be caused by a diver holding their breath, ascending too quickly, or a pre-existing contributing factor. The signs and symptoms of AGE can include: blood or frothing from the mouth, unconsciousness or dizziness, chest pain, weakness or paralysis, convulsions, coughing, and shortness of breath.
A gas that contains 21% oxygen. Other than air, a normoxic gas can also be Trimix with 21% oxygen.
O
A term for the system used by scuba divers whereby the unit utilises traditional scuba cylinders and regulators to provide breathing gases to the diver. In open-circuit diving, no breathing gases get recycled, and instead the exhaled gas is released into the water column.
There are two types of oxygen toxicity – CNS [central nervous system] oxygen toxicity and pulmonary oxygen toxicity.
CNS toxicity is caused by breathing a high partial pressure of oxygen; the signs and symptoms can include: convulsions, visual disturbances, ear ringing, nausea and dizziness, tingling and twitching.
Pulmonary oxygen toxicity is caused by breathing a high oxygen-content gas for a prolonged period of time; signs and symptoms can include: coughing, breathlessness and fatigue.
R
A rebreather is scuba that recycles breathing gases in a system known as a ‘loop’, whereby the unit utilises two cylinders, most commonly oxygen and air, and these two gases are injected into the loop at different rates, maintaining a steady percentage of oxygen for the diver to breathe. The diver’s exhaled gas travels around the loop, passing through a scrubber, which absorbs the C02, and gets injected with oxygen before the diver inhales.
S
Originally an acronym [self-contained underwater breathing apparatus], scuba is now a term of its own, therefore does not need to be written in capital letters. Scuba describes any self-contained breathing system used for diving, including open-circuit, semi-closed and closed-circuit systems.
An inflatable buoy which is used by divers to mark their positioning to the surface. Also known as a safety sausage, the SMB is usually inflated from below the surface, and attached to a spool, so that the diver can signal oncoming boats of their presence.
T
A breathing gas used by technical divers that is a mix of oxygen, nitrogen and helium. The main purpose of trimix is to reduce the fraction of oxygen in the breathing gas without increasing the nitrogen content, which means the gas can be breathed at deeper depths whilst also decreasing the effects of gas narcosis.
V
Usually in reference to a cylinder valve, a valve is what controls the gas flow in or out of a scuba cylinder. Gases can be filled and emptied from the same valve, and this valve is where the first stage regulator is attached for scuba diving.
Disclaimer: The Scuba Mermaid (Chi Felton) and its affiliates do not intend for any information from this entity to replace or substitute an RSTC certified scuba diving course, and at all times advise divers to dive within their certified training limits. Please seek any medical advice from a qualified hyperbaric physician.
