One of the higher strength aluminum alloys with excellent forming characteristics and good corrosion resistance, including resistance to salt water.
The pressure that includes the effect of atmospheric pressure. When used with the unit 'atmosphere' it is abbreviated 'ata.'
Acetal resin is a high performance-engineering polymer used as a lightweight metal replacement. It has excellent strength and a high resistance to impact.
Advanced Nitrox training
A gas mixture containing 21% oxygen, 78% nitrogen, and 1% other gasses (mainly argon); compressed air is used for recreational scuba diving.
A term used to describe a wing-style buoyancy compensator.
A set of equations incorporated into diving computers in order to compute nitrogen uptake and elimination from changes in depth and elapsed time.
Alternate air source
A secondary regulator used by a diver in place of the primary regulator in order to make a safe, emergency ascent while still breathing normally.
The surrounding light underwater that occurs naturally from the sun.
The surrounding pressure; on land, comes from the weight of the atmosphere. At depth underwater, comes from the weight of the water, plus the weight of the atmosphere. One atmosphere is approximately 14.7 pounds of pressure per square inch.
A pressure gauge that uses a needle moving around a dial to provide tank pressure.
An inert gas that makes up less than one percent of air. Often used as drysuit inflation in cold water due to its insulating properties.
A line suspended from a boat or a buoy that allows a diver to use as a means to control their rate of ascent or descent.
An early Scubapro backpack buoyancy compensator that used shot for weight. By pulling a pin, the shot could be released in an emergency. Considered a more comfortable alternative to a lead weight belt.
Abbreviation for atmosphere absolute; 1 ata is the atmospheric pressure at sea level.
Pressure of the atmosphere at a given altitude or location.
Axial flow scrubber
A type of scrubber canister used in rebreathers where exhaust gas comes in at one end and exits the other end.
A compass heading or angle.
Breathing gas that is carried in primary cylinders on a diver's back.
The center plate of a harness-style BCD. Can be constructed of aluminum, steel, ABS plastic or ballistic nylon.
Back up light
Dive lights carried as an emergency light in the event a primary light fails.
A tank carried on a dive that is designated for emergency use and not intended as a primary breathing gas.
A tough, synthetic nylon fabric originally developed in WWII to protect wearers from flying debris and shrapnel. Ballistic nylon fabric resists tears and abrasions like no other fabric of its kind. Ounce for ounce, it is more durable than other fabrics: it?s resistant to abrasions, tears, and scuffs and is a true high performance fabric.
Measurement of pressure slightly more than an atmosphere. 1 ATA = 1.0132 bar. 1 bar = 14.5083 psi.
Basic Cave training
This course covers the basic principles of actual cave diving. Accident analysis forms the basis of the training. The basis of this course is aimed at perfecting basic skills and the mastering of techniques and procedures required for the most elementary of cave dives. Cave dives are planned around very limited penetrations so that the diver may progress into cave diving at a conservative pace. The Basic Cave Diver course is not intended to train divers for all facets of cave diving. This course develops the minimum skills and knowledge required for limited penetration cave diving. Dive planning, cave environment, procedures, techniques, problem solving, and other specialized needs of cavern/cave diving are covered.
BC or BCD
Abbreviation for buoyancy compensator
A rotating ring on a compass or watch.
A bifocal lens helps a diver who has difficulty seeing items that are close up, such as gauges or a compass. Often called "gauge readers," they can be added to a dive mask.
The inner air cell of a buoyancy compensator, which holds the amount of air used to provide proper buoyancy.
Slang term used to describe a scuba tank or cylinder.
A gas that is specified for use at the deepest portions of a dive, usually when other decompression gases are present. Bottom mix may be air, nitrox or helium.
The time between descending below the surface to the beginning of ascent.
A depth (pressure) activated time device that automatically starts as a diver descends. Can be mechanical or electronic.
Bourdon tube gauge
A gauge containing a closed coiled tube, which expands with pressure and causes the gauge needle to rotate. As the gauge pressure increases the tube will tend to uncoil and reduced pressured cause the tube to coil more tightly. Connected to the indicator needle, the movement of the tube causes the needle to rise or fall, depending on the pressure.
A woven nylon line that has better abrasion resistance than twisted line.
The load that will cause a line or rope to fail.
Describes CO2 entering the inhalation side of the breathing loop on a Rebreather from the absorbent canister.
The part of a Rebreather system that includes the mouthpiece, hoses, inhalation bag, exhalation bag and absorbent canister.
Term used by solo divers for an independent stage bottle that is carried for emergency gas in place of a dive buddy.
The upward force exerted on an object in liquid, whether the object sinks or floats. Objects that float are positively buoyant, those that sink are negatively buoyant and those that stay where placed are neutrally buoyant.
An inflatable vest worn by the diver that can be automatically or orally inflated to help control buoyancy; abbreviated BC or BCD (Buoyancy Control Device).
Thin copper disk held in place with a vented plug. Designed to rupture if tank pressure is greatly exceeded.
A technique for mounting a primary canister light on the bottom of a set of double tanks. Very popular in the 1980's and 1990's, when massive battery canisters were not conducive to belt mounting. Is also popular in sidemount diving.
A manual addition valve that allows direct addition of gas into the breathing loop on a Rebreather.
The band that attaches a scuba cylinder to a BC by a 'camming' action when closing the buckle.
A large, primary light with a battery pack contained in a canister. Typically has longer burn times than smaller, flashlight-style lights.
The chemical injury a Rebreather diver may sustain when water floods the scrubber canister and combines with the hydroxide chemical. Highly dangerous and can cause significant damage to the mouth or trachea if inhaled.
Requiring much specialized training and equipment, this involves diving into an overhead environment including caves, abandoned mines or quarries and natural springs or sinkholes where the exit is not always visible. 'Overhead environment' means a structure exists which prevents the diver from making a direct vertical ascent to the surface.
Cave Sidemount training
Designed to expose the experienced cave diver to alternative cylinder and harness configurations when back-mounted cylinders are not appropriate or available. Strong emphasis on gear configuration along with awareness and safety precautions specific to sidemount diving.
Requiring specialized training, this involves diving into an overhead environment including caves, abandoned mines or quarries and natural springs or sinkholes; differs from Cave Diving in that the exit should always be visible. 'Overhead environment' means a structure exists which prevents the diver from making a direct vertical ascent to the surface.
Teaches fundamental skills for safe cavern diving. 100-foot depth limit (30m), 200-foot (61m) combined depth & penetration limit, no decompression, daylight zone only. Class is taught in open water gear with slight modifications. Course is for recreational divers who wish to safely enjoy the beauty of cavern diving OR for the diver who is curious if cave diving might be of interest to them.
CCR Cave training
Designed for the experienced cave diver who has transitioned from open circuit to rebreather. Emphasis is on gas planning and management as well as safety and emergency skills specific to the cave rebreather diver.
European manufacturing certificate of approval for use of sale.
Metric unit for temperature. C=(F-32) x .556
Describes the settling of absorbent chemical in an improperly packed Rebreather scrubber canister. As the absorbent material settles, a passageway for exhaled, carbon dioxide-rich gas passes through the scrubber without having the carbon dioxide removed. Not a prominent problem in cartridge-style scrubbers.
A valve that only allows a fluid or gas to flow in one direction. The mushroom valve used in a second stage regulator is one example. Check valves are also required in the hose assembly of a Rebreather, both on the inhalation and exhalation side of the loop to keep the gas flowing in the proper direction.
Closed circuit SCUBA
A SCUBA system designed to allow divers to re-breath exhaled air after removal of CO2 and addition of supplemental 02. In contrast to 'Open Circuit', closed circuit scuba is noiseless and produces no bubbles.
A device that monitors nitrogen in the body during a dive though mathematical algorithms. The device allows divers to multilevel dive and extend bottom time beyond what a dive table allows.
The breathing bag portion of a Rebreather system. Named 'counter lung' because it operates opposite (or counter) to the diver's lungs.
The waist band on a buoyancy compensator.
The technically correct term for describing a SCUBA tank.
A series of webbing loops sewn into a chain that allows for multiple accessory attachment points on the front or side of a pocket or harness. Widely used in the backpacking industry.
Slang term for decompression.
A nitrox mix used to accelerate decompression. Can vary from a relatively low oxygen mix up to pure oxygen.
Any change from one ambient pressure to a lower ambient pressure, always results in a reduction of gas pressure within the body.
Any dive where the diver is exposed to a higher pressure than when the dive began, the decompression occurs as the diver ascends.
A specified time and depth that a diver must remain to eliminate diluent/inert gas.
For recreational divers a deep dive is a dive below 60 ft. For technical divers a deep dive is a dive below recreational limits of 130 ft.
Pioneered by Richar Pyle, a scientific diver in Hawaii, who made careful note of physical symptoms after surfacing from numerous deep dives. Deep stops are found to help keep the diluent gas tension at reasonable levels during ascent.
Delrin is the brand name for acetal resin.
A device that indicates how far a diver is below the surface.
A line suspended from a boat, float or buoy used to permit divers to control their descents and ascents and to provide guidance to the bottom in poor visibility or strong currents; particularly useful on ascent to assist divers to make safety or emergency decompression stops between 10 and 15 feet.
Diaphragm first stage
A regulator first stage that uses a flexible diaphragm to keep water from contacting the internal parts, which helps to reduce corrosion or contamination.
Deutsches Institut fur Normung. Used to describe a valve connection for cylinder to regulator.
Identified by pressure rating of 200 bar or 300 bar
Abbreviation for 'Doing It Right,' a term coined by a group of divers to describe a particular style of equipment configuration, diving style and philosophy.
Device that constantly measures depth and time, based on a pre-programmed algorithm, the computer calculates tissue nitrogen uptake and elimination in several theoretical compartments and provides a continuous readout of the dive profile, including: depth, elapsed time of the dive, duration at current depth before decompression becomes mandatory, and a warning if the rate of ascent is too fast.
The first dive gear manufacturer to provide specialized diving equipment to the cave and wreck diving communities. Established in 1984.
Two cylinders banded together and often connected by a manifold to allow longer dive time and redundant gas versus a single cylinder.
Down stream valve
A style of second stage design where the gas flow is always positive, flowing outward from the regulator so that in the event of a failure, it will fail leaking, not shut off.
Abbreviation for diver propulsion vehicle. Used to traverse quickly over long distances underwater.
A water-tight garment that keeps the diver's body warm through the use of insulating undergarments.
Abbreviation for Enriched Air Nitrox. May be used with numeric values to identify specific oxygen content of a gas such as EAN32.
Abbreviation for general nitrox values or where the specific oxygen value is not known or specified.
Enriched Air Nitrox
A breathing gas that contains more oxygen than normal air and a corresponding decrease in the amount of nitrogen.
A perflourinated material used to make o-rings. More resistant to oxygen erosion that standard o-rings.
The one-way valve incorporated in the exhaust hose to keep the gas flowing in the proper direction or to prevent excessive back pressure.
Garment worn to prevent decreases in core body temperature and abrasions. Protection can range from thin body suits to heavy dry suits.
The temperature scale used in the United States. F=(C/.556) +32
feet of fresh water. Measurement of depth in fresh water.
Regulator attached to the SCUBA cylinder valve that lowers the tank pressure to ambient pressure plus a pre-determined pressure (e.g., ambient + 140 psi).
A visual indicating device that shows the flow rate, usually for an oxygen analyzer or to verify the flow rate in a Rebreather system. Is often used to describe a restricted orifice that 'meters' out gas for oxygen analysis.
A restriction placed in a flow line to keep the volume of gas limited. Commonly used with low pressure hoses to allow an oxygen sensor to accurately determine the fraction of gas without having to worry about variations in pressure caused by flow.
feet of sea water. Measurement of depth in sea water.
Full cave training
Emphasis is upon dive planning and skill perfection through actual cave dives. Techniques learned through the earlier Basic Cave Diver and Cavern Diver courses are critiqued and expanded. Exposure to more sophisticated cave-diving scenarios is the foundation of this training. Complex cave dive planning and execution is emphasized.
Wraps that are used to squeeze the airspace in the lower legs of a dry suit to help maintain buoyancy control and body positioning (trim).
The corrosion that occurs when two or more different metals are placed in contact with each other. Depending on each metal's electro negativity, the rate of corrosion can be low or high. When water, particularly sea water, is added to the process, large amounts of metal can corrode away very fast.
A metal preservation and protection technique that uses thin rust resistant zinc coating on steel.
Pressure that does not include the effect of the atmosphere. Most SPGs as well as automotive tire gauges fall into this category.
A gauge reader is a non-prescription bifocal lens that helps a diver who can see well into the distance, but has difficulty reading gauges up close.
A sealed lead-acid battery that is used in dive lights and DPVs. The term 'gel' is used to show that the electrolyte, a sulphuric acid paste, is not a liquid sloshing around inside the battery, which allows the battery to be operated in any position without fear of spilling.
Slang for the yellow nylon permanent line installed in cave systems in Florida and Mexico. Usually of kern mantle construction for durability and long life.
Grade 304 Stainless Steel
Grade 304 is the standard ?18/8? stainless and is the most versatile and most widely used stainless steel with excellent forming and welding characteristics. Stainless steel is highly resistant to staining, rust and corrosion. This grade of stainless steel has outstanding toughness, even in cryogenic temperatures.
Grade 316 Stainless Steel
Grade 316 stainless steel, often known as ?marine grade? stainless has excellent corrosion resistant properties, particularly high in resistance to pitting and crevice corrosion in chloride environments. This grade of stainless steel has outstanding toughness, even in cryogenic temperatures.
Grade 440 Stainless Steel
Grade 440 stainless steel is also known as razor blade steel, as it is one of the hardest stainless steels. It can be sharpened and allows for much better edge retention. Its very high carbon content gives it its strength, hardness and wear resistance. It is moderately corrosion resistant although its corrosion resistance is lower than the commonly used 304 and 416 grades.
A dual outlet valve used with single cylinders to provide dual high pressure outlet for the use of dual regulators.
Referring to descriptions of gas mechanisms by J.S. Haldane, typically with tissue saturation and desaturation.
Slang for deco stop
The webbing used to hold a backplate on a diver.
Mixture of helium and oxygen, usually reserved for very deep diving.
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.
Abbreviation for High Intensity Discharge. Technology used in underwater lighting that allows significant high power intensity lighting with very low battery power requirements. The color temperature is white-blue; more pleasing to the eyes.
High pressure cylinder
Typically refers to steel cylinders used at pressures of 3,500 psi (230 bar).
The Hogarthian configuration is named after Florida cave diver, William 'Bill' Hogarth Main. It is based on reducing equipment to a minimum streamlined configuration in order to maximize gas efficiency, which including sufficient redundancy for extended decompression dives.
Garment worn over the head to reduce thermal loss.
A hose specifically designed for high pressures so it will not rupture with dive cylinder pressures.
Abbreviation for International Association of Nitrox and Trimix Divers, the first established recreational-technical diving organization. Originally established by Dick Rutkowski, retired NOAA Deputy Diving Director. Current headed by Tom Mount.
A technique of diving double cylinders without a manifold, requiring a complete regulator setup for each cylinder. Favored in some European countries and by sidemount divers.
The valve on a buoyancy compensator where a low pressure hose from the second stage can be used for inflation. Usually includes an oral inflation mouthpiece.
A step down pressure from the high pressure scuba cylinder to the ambient pressure at depth. Makes regulator function more stable and predictable. Common IP ranges from 120 to 180 psi (8 to 12 bar).
Abbreviation for intermediate pressure
An older style of cylinder valve with a spring activated reserve that served to release remaining cylinder gas for ascent. Used before SPGs were widely available.
A reel that has the handle located on one side, rather than on top. Named after Florida cave diver, Woody Jasper, who used this design to quickly payout exploration line when exploring new cave passage.
A length of line typically used to attach to an anchor line to provide spacing for decompressing divers at the same stop depth.
Standard on-off cylinder valve used on today's cylinders.
An irregular limestone geologic area that may have a series of sinkholes, fissures, cracks, caverns and underground streams caused by erosion by carbon dioxide enriched water.
Named after Lord Kelvin, a British physicist, it is the metric unit of thermodynamic temperature, where zero degrees Kelvin is defined as the point where atomic motion ceases (= -273.15 degrees Celcius).
A style of rope construction that uses a central set of core lines covered with a tightly braided sheath.
Kilogram. Metric measure of weight. 1 kg = 2.21 pounds.
British term for dive equipment
Term used by cave explorers to describe placing initial exploration line in a virgin cave system.
Abbreviation for light emitting diode. Light technology using diodes, rather than traditional bulbs, that are robust, rugged and have an incredibly long life compared to a conventional bulb.
A bag used by divers to float or lift objects underwater.
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.
Low pressure cylinder
Describes steel cylinders that have fill pressures in the 2,400 psi range (160 bar).
Low pressure inflator
An extra hose from the first stage regulator that provides air to inflate the BC.
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.
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.
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.
Military-standard polypropylene is a tough, heat-resistant, semi-rigid material that offers a combination of outstanding physical, chemical, and mechanical properties not found in any other thermoplastic. It has superior working temperature and tensile strength and is light in weight, resistant to staining, and has a low moisture absorption rate.
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).
Abbreviation for maximum operating depth. 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).
meters of sea water. Measurement of depth in sea water.
Spending a period of time at several different depth on a single dive.
Small, flexible valves used as exhaust valves in a second stage and also as a check valve used in the mouthpiece of a Rebreather.
National Association of Underwater Instructors. It is one of the oldest certifying agencies.
Abbreviation for Nickel Metal Hydride, a high capacity rechargeable battery. More tolerant to abuse and resistant to overcharging.
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).
The narcotic effect on the body based on higher than normal nitrogen pressure.
Any mixture of nitrogen and oxygen that contains less than the 79% nitrogen as found in ordinary air.
Learn how to choose the proper blend of Nitrox for your dive profile, determine maximum depth limits for your Nitrox mixture, analyze your breathing mixture, and plan and safely execute each dive. Includes the physiology of oxygen and nitrogen; advantages, disadvantages, and risks of Nitrox; oxygen toxicity; hazards and precautions of handling oxygen; the concept of Equivalent Air Depth; use of EANx with standard Air Dive Tables; common gas mixing procedures; and more.
Method used to squeeze into small holes when diving. Requires diver to remove cylinders and push them ahead of the diver.
National Speleological Society - Cave Diving Section
Common sealing device for scuba equipment constructed of butyl, nitrile, Viton or EPDM. Measured by both its physical size as well as its hardness knows as 'durometer.'
O2ptima CCR Training
Teaches fundamental rebreather skills on the O2ptima CCR. Open water, 140 foot max depth (160 foot if recreational Trimix certified), maximum 15 minute decompression. Minimum of 500 minutes of confined and open water training. Students must have their own O2ptima CCR unit.
Short for 'octopus, ' which is a device a diver can use in place of the primary regulator, in order to make an ascent while still breathing normally.
An alternate second stage air source used by a diver's buddy in an out-of-air situation, or reserve 2nd stage regulator.
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.
Open water sidemount training
Program covers benefits of sidemounting in open water with a strong emphasis on gear configuration. Covers both sidemount-style diving along with sidemount stage diving with backmounted primary tanks.
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.
Object that has been cleaned to remove contaminants that could react with high pressures of oxygen, specifically hydrocarbons (oils and silicones).
Materials that are suitable for exposure to oxygen.
Drysuit accessory that allows a diver to void the bladder during a dive. Used in conjunction with a condom catheter.
Professional Association of Diving Instructors. It is one of the largest SCUBA certifying agencies.
Pressure exerted by a single component of a gas within a gas mixture, or dissolved in a liquid.
Fifteen-mil polyether aromatic polyurethane is excellent at maintaining flexibility in low temperature environments and can be welded, which eliminates fittings and reduces failure points. It has very good chemical and abrasion resistance and excellent strength. It also resists the growth of microorganisms.
A small scuba cylinder strapped to a divers main tank for emergency use.
Pounds per square inch, a common measurement of air pressure.
A style of absorbent carbon dioxide scrubber canister where the gas flows from the center to the outside.
Diving apparatus that recycles exhaled gas, scrubbing the carbon dioxide and adjusting the amount of oxygen metabolized.
Diving to prescribed limits, including a depth no greater than 130 fsw, using only compressed air, and never requiring a decompression stop.
Technique of carrying back up equipment in the event of primary equipment failure during a dive.
Device used to allow a diver to breathe gas from a high pressure cylinder at a suitable breathing pressure.
Radio Frequency welding, sometimes known as RF, Dielectric or High Frequency (HF) welding, is the process of fusing materials together by applying radio frequency energy to the area to be joined. The resulting weld can be as strong as the original materials.
Slang term used for a diver propulsion vehicle.
Abbreviation for semi-closed Rebreather.
Component of a Rebreather system that contains a chemical that reacts with carbon dioxide to remove exhaled gas.
Acronym meaning Self Contained Underwater Breathing Apparatus.
Scuba Diving International. The recreational scuba training and certification arm of TDI.
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.
The pressure which a device is rated to work, not the test or hydrostatic pressure.
Technique of carrying cylinders on the side of a diver to allow passage through tight restrictions or passageways.
A single dive cylinder.
Abbreviation for submersible pressure gauge.
A cylinder used to carry decompression gas to extend dive time or assist with decompression.
Submersible pressure gauge
Gauge to monitor air supply during the course of a dive.
Slang term used to describe boat clips that are notorious for snagging line as a diver traverses through a wreck or cave.
SuperFabric® brand material
SuperFabric® brand technology is an advanced, multi-step engineered process that takes ordinary fabrics and transforms them into a variety of unique, protective solutions, known collectively as SuperFabric® brand materials. These new protective fabrics can be engineered for optimum resistance to cuts, punctures, and abrasions, while remaining highly flexible.
Surface Interval Clothing
Surface Interval: ˈsər-fəs ˈin-tər-vəl The amount of time spent on the surface between two dives.
Surface Interval Clothing is a team of divers who are dedicated to creating designer clothing for diving enthusiasts and non-divers who like great looking apparel. They can be contacted at www.Store.SurfaceIntervalClothing.com
The U.S. Navy treatment procedure for decompression sickness that is the most commonly used, consisting of oxygen breathing with air breaks at a maximum pressure of 2.8 ATA with typical treatment times of 285 minutes.
Slang term for scuba cylinder.
Technical Diving International. Maine-based certification agency for technical aspects of recreational scuba.
Term used to describe diving that is beyond typical recreational limits and/or diving in an overhead environment. Technical divers are still recreational divers as opposed to commercial divers.
Mixture of helium, nitrogen and oxygen, used for very deep diving.
Trimix I training
Learn how to execute and plan dives using normoxic Trimix (16-percent oxygen) utilizing 100-percent oxygen for decompression. Depth up to 200-feet (61m).
A valve that works against pressure, rather than flow with the pressure. When an upstream valve fails, it fails in the 'off' position, unlike downstream valves, which fail by free flowing.
A weight placed between a set of cylinders to offset undesired buoyancy or trim.
Visual Inspection Program. Standardized visual tank inspection performed by a trained equipment technician, performed annually.
A trademarked perflourinated material used to make o-rings. More resistant to oxygen erosion that standard o-rings.
Any suit that provides thermal protection underwater by trapping a layer of water betweens the diver's skin and the suit.
A back mounted buoyancy compensator popularized by cave divers and later used by many technical divers.
Work of Breathing (WOB): Hydrostatic
This is the result of the resistive WOB and the effects of the position of the counter lungs about the body when the rebreather and diver are submerged in water. For example, a back-mounted- counter lung rebreather may have a good resistive WOB, but when in a horizontal swimming position the distance from the diver’s lungs (hence pressure difference between the counter lungs and the lung centroid) when combined with the resistive WOB create an excessive pressure which causes the diver to suck against in order to take a breath. In this case the inhale pressure would be excessive (because the diver is inhaling gas from a lower pressure) and the exhale would be easy having breathed out into a lower pressure. Chest mounted counter lungs have the reverse affect in the same swim position.
Work of Breathing (WOB): Resistive
This is purely a result of the gas flow restrictions within the unit. In other words how much the size of the pipes and orifices generate a resistance to breathing. Such things as small mouthpiece mushroom valves, small hoses, counter lungs with insufficient volume or room to expand and long absorbent paths within a canister are common elements which go to make up a resistive breathing circuit.
Resistive WOB is also a function of gas density and hence depth. The deeper the dive and the higher the gas density the greater the WOB. WOB is also a function of ventilation or breathing rate. The more gas flow (higher breathing rate) the mores resistance is generated. A rebreather that breathes OK on the surface may well not at 40m on an air diluent. This why current European CE standards and military test standards insist on a resistive WOB measurement at depth and with different ventilation rates and normally in two orientations (swimming positions).
Diving on natural or man-made shipwrecks.
A dual outlet valve used with single cylinders that is shaped in the form of the letter 'Y.' Also known as a sling-shot valve.