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136-443: This is a glossary of technical terms, jargon, diver slang and acronyms used in underwater diving . The definitions listed are in the context of underwater diving. There may be other meanings in other contexts. Underwater diving can be described as a human activity – intentional, purposive, conscious and subjectively meaningful sequence of actions. Underwater diving is practiced as part of an occupation, or for recreation, where

272-492: A deck chamber . A wet bell with a gas filled dome provides more comfort and control than a stage and allows for longer time in water. Wet bells are used for air and mixed gas, and divers can decompress on oxygen at 12 metres (40 ft). Small closed bell systems have been designed that can be easily mobilised, and include a two-man bell, a launch and recovery system and a chamber for decompression after transfer under pressure (TUP). Divers can breathe air or mixed gas at

408-497: A helmet , including the standard copper helmet, and other forms of free-flow and lightweight demand helmets . The history of breath-hold diving goes back at least to classical times, and there is evidence of prehistoric hunting and gathering of seafoods that may have involved underwater swimming. Technical advances allowing the provision of breathing gas to a diver underwater at ambient pressure are recent, and self-contained breathing systems developed at an accelerated rate following

544-423: A suit of armour , with elaborate joints to allow bending, while maintaining an internal pressure of one atmosphere. An ADS can be used for dives of up to about 700 metres (2,300 ft) for many hours. It eliminates the majority of physiological dangers associated with deep diving – the occupant does not need to decompress, there is no need for special gas mixtures, and there is no danger of nitrogen narcosis – at

680-477: A casing and bladder structure uses the casing for load bearing purposes and to protect the bladder, which is a replaceable part. Depending on the construction details, the diver may need to carry up to four pounds of lead (two kilos) to counteract the positive buoyancy of an empty BC. All ambient pressure gas bladder type buoyancy compensators will have some components in common: In addition some BCs may include other features: The buoyancy compensator must fit

816-435: A consistently higher threshold of hearing underwater; sensitivity to higher frequency sounds is reduced the most. The type of headgear affects noise sensitivity and noise hazard depending on whether transmission is wet or dry. Human hearing underwater is less sensitive with wet ears than in air, and a neoprene hood causes substantial attenuation. When wearing a helmet, hearing sensitivity is similar to that in surface air, as it

952-491: A correctly rigged diver to compensate for a defective BC, and unsafe in that there is no obvious way to tell which bladder is holding air, and a leak into the secondary bladder may go unnoticed until the buoyancy has increased to the extent that the diver is unable to stop the ascent, while struggling to empty the air from the wrong bladder. Monitoring the air content of two bladders is unnecessary additional task loading, which distracts attention from other matters. A variation on

1088-510: A cylinder and regulator set in order to have a complete scuba set. Some "tech-rec" (basically recreational with limited technical capability) vest BC's have the ability to carry multiple cylinders - Twin sets on the back, and sling cylinders at the sides, suspended from D-rings. The lack of flexibility of positioning the D-rings due to structural constraints on some designs is partly remedied by fitting larger numbers of D-rings, some of which may be in

1224-415: A flexible airtight bladder, thereby increasing the volume, and decreases buoyancy by releasing the gas into the water. This volume of gas will compress or expand as the ambient pressure varies with depth, following Boyle's Law , and therefore the buoyancy of the system will increase and decrease in proportion to the absolute pressure variation and the volume of gas in the bladder. The variation of buoyancy for

1360-448: A full technical rig with a thick wetsuit. Vest BCs typically provide up to about 25 kilograms of buoyancy (depending on size) and are fairly comfortable to wear, if of the correct size and adjusted to fit the diver. Vest BCs are the most common type among recreational divers because they can integrate buoyancy control, weights, attachment points for auxiliary gear, and cylinder retention in a single piece of gear. The diver need only attach

1496-414: A full-face mask or helmet, and gas may be supplied on demand or as a continuous free flow. More basic equipment that uses only an air hose is called an airline or hookah system. This allows the diver to breathe using an air supply hose from a high pressure cylinder or diving air compressor at the surface. Breathing gas is supplied through a mouth-held demand valve or light full-face mask. Airline diving

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1632-430: A gas supply to operate a buoyancy compensator, so cannot use them, though they may wear an inflatable vest lifejacket for positive buoyancy at the surface. Atmospheric pressure diving suits may use a trim tank similar to that on a submarine for small adjustments, but can be ballasted to be almost precisely neutral, and are virtually incompressible within their designed operating range. Accurate and reliable depth control

1768-483: A given change of depth will be greater near the surface than at greater depth and greater for a large volume of gas than for a small volume. The range of depths for which the diver can compensate for these changes by voluntary adjustment of lung volume while breathing effectively is therefore dependent on the volume of gas in the bladder and the nominally neutral depth, where breathing at normal tidal volume of about 500 ml results in approximate dynamic equilibrium, and

1904-412: A higher level of fitness may be needed for some applications. An alternative to self-contained breathing systems is to supply breathing gases from the surface through a hose. When combined with a communication cable, a pneumofathometer hose and a safety line it is called the diver's umbilical , which may include a hot water hose for heating, video cable and breathing gas reclaim line. The diver wears

2040-450: A horizontally trimmed diver will move towards the back of the neck when the bladder is inflated, inducing a head up trim, which can increase adverse impacts on the benthic environment. The Dacor Seachute BC4 had unique upper and lower bladders. The upper bladder was around the neck and could be inflated by the Carbon dioxide cartridge for use as a surface life jacket. The lower bladder was over

2176-445: A human activity, is the practice of descending below the water's surface to interact with the environment. It is also often referred to as diving , an ambiguous term with several possible meanings, depending on context. Immersion in water and exposure to high ambient pressure have physiological effects that limit the depths and duration possible in ambient pressure diving. Humans are not physiologically and anatomically well-adapted to

2312-615: A long history of military frogmen in various roles. They can perform roles including direct combat, reconnaissance, infiltration behind enemy lines, placing mines, bomb disposal or engineering operations. In civilian operations, police diving units perform search and rescue operations, and recover evidence. In some cases diver rescue teams may also be part of a fire department , paramedical service , sea rescue or lifeguard unit, and this may be classed as public safety diving . There are also professional media divers such as underwater photographers and videographers , who record

2448-447: A long period of exposure, rather than after each of many shorter exposures, the overall risk of decompression injury to the diver and the total time spent decompressing are reduced. This type of diving allows greater work efficiency and safety. Commercial divers refer to diving operations where the diver starts and finishes the diving operation at atmospheric pressure as surface oriented , or bounce diving. The diver may be deployed from

2584-608: A newly qualified recreational diver may dive purely for the experience of diving, most divers have some additional reason for being underwater. Recreational diving is purely for enjoyment and has several specialisations and technical disciplines to provide more scope for varied activities for which specialist training can be offered, such as cave diving , wreck diving , ice diving and deep diving . Several underwater sports are available for exercise and competition. There are various aspects of professional diving that range from part-time work to lifelong careers. Professionals in

2720-461: A runaway buoyant ascent. Several arrangements have been tried with the intention of making the arrangement acceptably safe. One is to link the inflation and deflation valves together so that both bladders are always used in parallel. In practice this requires a custom modification of two inflator units so that they can be operated together with one hand, as there is no production unit with this function available. Pull dump valves must also be connected in

2856-553: A similar diving reflex. The diving reflex is triggered by chilling the face and holding the breath. The cardiovascular system constricts peripheral blood vessels, slows the pulse rate, redirects blood to the vital organs to conserve oxygen, releases red blood cells stored in the spleen , and, in humans, causes heart rhythm irregularities. Aquatic mammals have evolved physiological adaptations to conserve oxygen during submersion, but apnea, slowed pulse rate, and vasoconstriction are shared with terrestrial mammals. Cold shock response

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2992-432: A small cylinder dedicated to this purpose, or from the diver's mouth through the oral inflation valve. Ambient pressure bladder buoyancy compensators can be broadly classified as having the buoyancy primarily in front, surrounding the torso, or behind the diver. This affects the ergonomics , and to a lesser degree, the safety of the unit. They can also be broadly classified as having the buoyancy bladder as an integral part of

3128-1350: A term may have more than one meaning depending on context, and others where several terms refer to the same concept, or there are variations in spelling. A few are loan-words from other languages. There are five sub-glossaries, listed here. The tables of content should link between them automatically: Contents:  Top A B C D E F G H I J K L M N O P Q R S T U V W X Y Z References Main article: 6061 aluminium alloy See: Aluminium alloy#Wrought alloys See: adjustable buoyancy life jacket See: Pressure measurement#Absolute, gauge and differential pressures See: auto-closure device See: yoke adaptor See: yoke fitting , and CGA 850 Main article: Activated carbon See: Diving rebreather#Active addition semi-closed circuit See: Australian Diver Accreditation Scheme See: Association of Diving Contractors International Also: "ABLJ", "Fenzy", or "horse collar buoyancy compensator" See: Buoyancy compensator (diving)#Adjustable buoyancy life jacket See: A-frame See: arterial gas embolism See: Decompression practice#Conservatism Underwater diving Underwater diving , as

3264-418: A way that they reliably operate simultaneously in parallel, and the probability of an inlet valve malfunction is doubled as they are in parallel. Another strategy is to have the inflator mechanisms on opposite sides of the body. As it is possible to inadvertently activate the inflation valve, and it can leak without the diver noticing until the buoyancy has increased significantly, this is only reliable if there

3400-499: A wide range of equipment which may include breathing apparatus, environmental protective clothing, aids to vision, communication, propulsion, maneuverability, buoyancy and safety equipment, and tools for the task at hand. Many of the terms are in general use by English speaking divers from many parts of the world, both amateur and professional, and using any of the modes of diving. Others are more specialised, variable by location, mode, or professional environment. There are instances where

3536-446: A wing type bladder integrated with the rebreather harness, with the bladder around the frame of the rebreather. Side mounted rebreathers tend to be suspended from the sides of side-mount harnesses, which include the buoyancy compensator. Inflatable buoyancy compensators of all types have been made in both single skin and casing and bladder arrangements. The strength and damage resistance of both these systems of construction depend more on

3672-406: Is a response to immersion that overrides the basic homeostatic reflexes . It optimises respiration by preferentially distributing oxygen stores to the heart and brain, which allows extended periods underwater. It is exhibited strongly in aquatic mammals ( seals , otters , dolphins and muskrats ), and also exists in other mammals, including humans . Diving birds , such as penguins , have

3808-490: Is a robot which travels underwater without requiring real-time input from an operator. AUVs constitute part of a larger group of unmanned undersea systems, a classification that includes non-autonomous ROVs, which are controlled and powered from the surface by an operator/pilot via an umbilical or using remote control. In military applications AUVs are often referred to as unmanned undersea vehicles (UUVs). People may dive for various reasons, both personal and professional. While

3944-494: Is a skill acquired by practice, and is facilitated by minimising the required BC gas volume by correct weighting. The buoyancy compensator is used by ambient pressure divers using underwater breathing apparatus to adjust buoyancy underwater or at the surface within the range of slightly negative to slightly positive, to allow neutral buoyancy to be maintained throughout the depth range of the planned dive, and to compensate for changes in weight due to breathing gas consumption during

4080-441: Is about 3 litres, or 3 kg of buoyancy, rising to about 6 kg buoyancy lost at about 60 m. This could nearly double for a large person wearing a farmer-john and jacket for cold water. This loss of buoyancy must be balanced by inflating the buoyancy compensator to maintain neutral buoyancy at depth. It must be possible to remain neutrally buoyant at the end of the dive, at the shallowest decompression stop, when almost all

4216-400: Is affected by the clarity and the refractive index of the medium. Visibility underwater is reduced because light passing through water attenuates rapidly with distance, leading to lower levels of natural illumination. Underwater objects are also blurred by scattering of light between the object and the viewer, resulting in lower contrast. These effects vary with the wavelength of the light, and

Glossary of underwater diving terminology: A–C - Misplaced Pages Continue

4352-481: Is also restricted to conditions which are not excessively hazardous, though the level of risk acceptable can vary, and fatal incidents may occur. Recreational diving (sometimes called sport diving or subaquatics) is a popular leisure activity. Technical diving is a form of recreational diving under more challenging conditions. Professional diving (commercial diving, diving for research purposes, or for financial gain) involves working underwater. Public safety diving

4488-403: Is considered a useful emergency skill, an important part of water sport and Navy safety training, and an enjoyable leisure activity. Underwater diving without breathing apparatus can be categorised as underwater swimming, snorkelling and freediving. These categories overlap considerably. Several competitive underwater sports are practised without breathing apparatus. Freediving precludes

4624-463: Is contact with the water as the acoustic properties are similar. When the head is exposed to the water, some sound is transmitted by the eardrum and middle ear, but a significant part reaches the cochlea independently, by bone conduction. Some sound localisation is possible, though difficult. Human hearing underwater, in cases where the diver's ear is wet, is less sensitive than in air. Frequency sensitivity underwater also differs from that in air, with

4760-663: Is critically important that the fully inflated buoyancy compensator can support the diver with the maximum equipment load on the surface at the start of a dive, and with maximum suit compression at the maximum depth before much gas is used up. There have been fatalities due to overloading the BC. On the other hand, buoyancy control is easiest with the lowest practicable volume of gas in the BC and dry suit, as these volumes change with depth changes, and must be adjusted to remain neutral. Measurements of volume change of neoprene foam used for wetsuits under hydrostatic compression shows that about 30% of

4896-430: Is evidence of a slight decrease in threshold for taste and smell after extended periods under pressure. There are several modes of diving distinguished largely by the breathing gas supply system used, and whether the diver is exposed to the ambient pressure. The diving equipment , support equipment and procedures are largely determined by the mode. The ability to dive and swim underwater while holding one's breath

5032-568: Is immersed. Snorkelling on the surface with no intention of diving is a popular water sport and recreational activity. Scuba diving is diving with a self-contained underwater breathing apparatus , which is completely independent of surface supply. Scuba gives the diver mobility and horizontal range far beyond the reach of an umbilical hose attached to surface-supplied diving equipment (SSDE). Scuba divers engaged in armed forces covert operations may be referred to as frogmen , combat divers or attack swimmers. Open circuit scuba systems discharge

5168-476: Is limited to the physiological capacity to perform the dive on the oxygen available until it returns to a source of fresh breathing gas, usually the air at the surface. As this internal oxygen supply reduces, the animal experiences an increasing urge to breathe caused by buildup of carbon dioxide and lactate in the blood, followed by loss of consciousness due to cerebral hypoxia . If this occurs underwater, it will drown. Blackouts in freediving can occur when

5304-482: Is lost much more quickly in water than in air, so water temperatures that would be tolerable as outdoor air temperatures can lead to hypothermia, which may lead to death from other causes in inadequately protected divers. Thermoregulation of divers is complicated by breathing gases at raised ambient pressure and by gas mixtures necessary for limiting inert gas narcosis, work of breathing, and for accelerating decompression. Breath-hold diving by an air-breathing animal

5440-405: Is necessary for safe decompression. The surface-supplied diver has the option to use the umbilical for depth control with the assistance of the line tender, and a tethered scuba diver can use the lifeline in the same way. Similarly, any diver using a shotline or jackstay to navigate between the surface and the work site can use it for depth control, making a buoyancy compensator non-essential provided

5576-482: Is necessary. Positive buoyancy at the surface is a safety requirement for any diver who must swim to or from the point of descent or surfacing, but this does not need to be precisely controllable buoyancy. The buoyancy compensator is intended to control buoyancy of a diver and their personal diving equipment, including stage and bailout cylinders, and for minor additional equipment such as reels, cameras and instruments that are lightweight or near neutral buoyancy. It

Glossary of underwater diving terminology: A–C - Misplaced Pages Continue

5712-516: Is no low pressure inflation hose connected to the backup bladder, so that it can only be inflated orally, and then always inflate the primary using low pressure gas from the regulator. This can be taken a step further by having a different style of oral inflator valve on the secondary bladder. Dual bladder buoyancy compensators are considered both unnecessary and unsafe in the DIR philosophy. Unnecessary in that there are simpler alternative methods available to

5848-431: Is not a buoyant lifting device for heavy tools and equipment. If a diving task requires the diver to work heavy, it is almost always better, and always safer, to use surface supplied equipment. If used by saturation divers to allow mid-water work, precautions must be taken to limit possible uncontrolled upward excursion. This may be possible by limiting excursion umbilical length. A buoyancy compensator works by adjusting

5984-424: Is not greatly affected by the breathing gas or chamber atmosphere composition or pressure. Because sound travels faster in heliox than in air, voice formants are raised, making divers' speech high-pitched and distorted, and hard to understand for people not used to it. The increased density of breathing gases under pressure has a similar and additive effect. Tactile sensory perception in divers may be impaired by

6120-535: Is reduced compared to that of open circuit, so a smaller cylinder or cylinders may be used for an equivalent dive duration. They greatly extend the time spent underwater as compared to open circuit for the same gas consumption. Rebreathers produce fewer bubbles and less noise than scuba which makes them attractive to covert military divers to avoid detection, scientific divers to avoid disturbing marine animals, and media divers to avoid bubble interference. A scuba diver moves underwater primarily by using fins attached to

6256-486: Is reduced core body temperature that occurs when a body loses more heat than it generates. It is a major limitation to swimming or diving in cold water. The reduction in finger dexterity due to pain or numbness decreases general safety and work capacity, which in turn increases the risk of other injuries. Non-freezing cold injury can affect the extremities in cold water diving, and frostbite can occur when air temperatures are low enough to cause tissue freezing. Body heat

6392-437: Is that the secondary bladder is a backup in case of failure of the primary bladder. The basic principle is defensible, but the arrangement can present several additional hazards, some of which have caused life-threatening incidents. Safe management of a dual bladder system requires the diver to be aware of the inflation status of each bladder at all times, and to dump gas from the correct bladder or bladders during ascent to prevent

6528-400: Is the physiological response of organisms to sudden cold, especially cold water, and is a common cause of death from immersion in very cold water, such as by falling through thin ice. The immediate shock of the cold causes involuntary inhalation, which if underwater can result in drowning. The cold water can also cause heart attack due to vasoconstriction; the heart has to work harder to pump

6664-414: Is the underwater work done by law enforcement, fire rescue, and underwater search and recovery dive teams. Military diving includes combat diving, clearance diving and ships husbandry . Deep sea diving is underwater diving, usually with surface-supplied equipment, and often refers to the use of standard diving dress with the traditional copper helmet. Hard hat diving is any form of diving with

6800-410: Is used for work such as hull cleaning and archaeological surveys, for shellfish harvesting, and as snuba , a shallow water activity typically practised by tourists and those who are not scuba-certified. Saturation diving lets professional divers live and work under pressure for days or weeks at a time. After working in the water, the divers rest and live in a dry pressurised underwater habitat on

6936-448: Is used, almost all of the variable volume is in the diving suit, and the depth range of effectively neutral buoyancy is maximised. A diver without a diving suit would be effectively neutrally buoyant over the full depth range of the dive, and only need to adjust buoyancy for mass loss as gas is used. A superficially similar system was used in the Dacor (CV Nautilus) system of the 1970s, where

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7072-417: Is usually due to over-stretching the tissues in tension or shear, either directly by expansion of the gas in the closed space, or by pressure difference hydrostatically transmitted through the tissue. Barotrauma generally manifests as sinus or middle ear effects, decompression sickness, lung over-expansion injuries, and injuries resulting from external squeezes. Barotraumas of descent are caused by preventing

7208-550: Is usually the choice if safety and legal constraints allow. Higher risk work, particularly commercial diving, may be restricted to surface-supplied equipment by legislation and codes of practice. Freediving as a widespread means of hunting and gathering, both for food and other valuable resources such as pearls and coral , dates from before 4500 BCE. By classical Greek and Roman times commercial diving applications such as sponge diving and marine salvage were established. Military diving goes back at least as far as

7344-474: The Peloponnesian War , with recreational and sporting applications being a recent development. Technological development in ambient pressure diving started with stone weights ( skandalopetra ) for fast descent, with rope assist for ascent. The diving bell is one of the earliest types of equipment for underwater work and exploration. Its use was first described by Aristotle in the 4th century BCE. In

7480-585: The Second World War . Immersion in water and exposure to cold water and high pressure have physiological effects on the diver which limit the depths and duration possible in ambient pressure diving. Breath-hold endurance is a severe limitation, and breathing at high ambient pressure adds further complications, both directly and indirectly. Technological solutions have been developed which can greatly extend depth and duration of human ambient pressure dives, and allow useful work to be done underwater. Immersion of

7616-414: The diver certification organisations which issue these diver certifications . These include standard operating procedures for using the equipment and dealing with the general hazards of the underwater environment , and emergency procedures for self-help and assistance of a similarly equipped diver experiencing problems. A minimum level of fitness and health is required by most training organisations, and

7752-424: The saturation diving technique reduces the risk of decompression sickness (DCS) after long-duration deep dives. Atmospheric diving suits (ADS) may be used to isolate the diver from high ambient pressure. Crewed submersibles can extend depth range to full ocean depth , and remotely controlled or robotic machines can reduce risk to humans. The environment exposes the diver to a wide range of hazards, and though

7888-771: The standard diving dress , which made a far wider range of marine civil engineering and salvage projects practicable. Limitations in mobility of the surface-supplied systems encouraged the development of both open circuit and closed circuit scuba in the 20th century, which allow the diver a much greater autonomy. These became popular during the Second World War for clandestine military operations , and post-war for scientific , search and rescue, media diving , recreational and technical diving . The heavy free-flow surface-supplied copper helmets evolved into lightweight demand helmets , which are more economical with breathing gas, important for deeper dives using expensive helium based breathing mixtures . Saturation diving reduced

8024-422: The 16th and 17th centuries CE, diving bells became more useful when a renewable supply of air could be provided to the diver at depth, and progressed to surface-supplied diving helmets – in effect miniature diving bells covering the diver's head and supplied with compressed air by manually operated pumps – which were improved by attaching a waterproof suit to the helmet. In the early 19th century these became

8160-534: The BC to support the full cylinders. The absolute minimum acceptable volume for the BC is enough to support the total mass of breathing gas in all the cylinders the diver will carry, plus lost volume due to suit compression at depth. This will be enough only if the diver carries no excess weight. It is easier to allow for a slight weight excess and use a slightly larger volume BC, but if taken to excess this will make buoyancy control more difficult and labour-intensive, and will use more gas, particularly during ascent when it

8296-534: The ability to judge relative distances of different objects, is considerably reduced underwater, and this is affected by the field of vision. A narrow field of vision caused by a small viewport in a helmet results in greatly reduced stereoacuity, and an apparent movement of a stationary object when the head is moved. These effects lead to poorer hand-eye coordination. Water has different acoustic properties from those of air. Sound from an underwater source can propagate relatively freely through body tissues where there

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8432-473: The advantages are less marked when used with thick, compressible, diving suits. There are three main configurations of inflatable bladder buoyancy compensation device based on buoyancy distribution: An adjustable buoyancy life jacket (ABLJ) is fitted around the neck and over the chest, secured by straps around the waist and usually between the legs. They are sometimes referred to as " horse collars " because of their resemblance, and are historically derived from

8568-466: The amount needed for undergarment loft, allowing descent by dumping from the suit. The depth range in which effectively stable neutral buoyancy can be maintained is inversely proportional to the volume of ambient pressure gas spaces in the diver's equipment (the lung volume is automatically compensated through normal breathing, and the mask is both small and reflexively maintained at constant volume by most divers). When an incompressible buoyancy compensator

8704-491: The amount of actual BC volume adjustment needed, and a skilled diver will develop the ability to adjust volume to maintain neutral buoyancy while remaining aware of the surroundings and performing other tasks. The buoyancy compensator is both an important safety device when used correctly, and a significant hazard when misused or malfunctioning. The ability to control trim effectively is dependent on both appropriate buoyancy distribution and ballast weight distribution. This too

8840-435: The average density of the diver and their attached equipment to be greater than, equal to, or less than the density of the diving medium. This can be done in either of two ways: As of 2021, the overwhelming majority of BCs are variable volume types, inflated by gas at ambient pressure, but the variable density type has been used. The common type of buoyancy compensator increases buoyancy by adding gas at ambient pressure to

8976-478: The back mounted buoyancy compensator is used without a backplate for side mount diving This arrangement is functionally similar to wearing the buoyancy compensator sandwiched between the cylinder(s) and backplate, but there is no backplate or back mounted cylinder. The buoyancy cell may be mounted between the sidemount harness and the diver, or on top of the harness. The sides of the bladder may be restrained from floating upwards when inflated by bungee cords clipped to

9112-410: The ballast water to establish positive buoyancy. If this system is used with additional sling mounted bailout or decompression cylinders a larger volume of water will be needed to compensate the additional gas usage, and the gas pressure in the buoyancy compensating cylinder will rise a bit more. The Avelo system uses this mechanism, with a rechargeable battery powered pump unit which is demountable from

9248-418: The bladder position, which is similar to a wing, being entirely behind the diver, without extensions to the sides or front. Back inflation BCs are less bulky at the sides but may have a tendency to float the diver tilted forward on the surface depending on weight and buoyancy distribution, which presents a possible hazard in an emergency if the diver is unconscious or otherwise unable to keep his or her head above

9384-399: The bladder when not inflated, although there is dispute regarding the safety and utility of this addition. The distance between boltholes on the centreline of the backplate has standardised at 11 inches (280 mm) between centres. Other back inflation buoyancy compensators are more like the jacket style regarding the structure, attachment to the diver, and accessories, differing mainly in

9520-405: The boat through plastic tubes. There is no reduction valve; the diver holds the hose end in his mouth with no demand valve or mouthpiece and allows excess air to spill out between the lips. Submersibles and rigid atmospheric diving suits (ADS) enable diving to be carried out in a dry environment at normal atmospheric pressure. An ADS is a small one-person articulated submersible which resembles

9656-415: The body from head-out immersion causes negative pressure breathing which contributes to the blood shift. The blood shift causes an increased respiratory and cardiac workload. Stroke volume is not greatly affected by immersion or variation in ambient pressure, but slowed heartbeat reduces the overall cardiac output, particularly because of the diving reflex in breath-hold diving . Lung volume decreases in

9792-424: The bottom and are usually recovered with the chamber filled with air. They decompress on oxygen supplied through built in breathing systems (BIBS) towards the end of the decompression. Small bell systems support bounce diving down to 120 metres (390 ft) and for bottom times up to 2 hours. A relatively portable surface gas supply system using high pressure gas cylinders for both primary and reserve gas, but using

9928-407: The bottom or a saturation life support system of pressure chambers on the deck of a diving support vessel , oil platform or other floating platform at a similar pressure to the work depth. They are transferred between the surface accommodation and the underwater workplace in a pressurised closed diving bell . Decompression at the end of the dive may take many days, but since it is done only once for

10064-443: The breath is held long enough for metabolic activity to reduce the oxygen partial pressure sufficiently to cause loss of consciousness. This is accelerated by exertion, which uses oxygen faster, and can be exacerbated by hyperventilation directly before the dive, which reduces the carbon dioxide level in the blood. Lower carbon dioxide levels increase the oxygen-haemoglobin affinity, reducing availability of oxygen to brain tissue towards

10200-418: The breathing gas into the environment as it is exhaled, and consist of one or more diving cylinders containing breathing gas at high pressure which is supplied to the diver through a diving regulator . They may include additional cylinders for decompression gas or emergency breathing gas. Closed-circuit or semi-closed circuit rebreather scuba systems allow recycling of exhaled gases. The volume of gas used

10336-438: The buoyancy by adding gas at ambient pressure from the breathing gas supply, rather than reducing the stored gas volume by compressing the gas. Water was added to or removed from the shell to compensate for suit compression and gas use by a manually operated valve. An inherent problem with this system is that the diver must still manually compensate for changes of buoyancy due to suit compression and expansion when changing depth, so

10472-453: The buoyancy of the diver is by varying the density of a rigid container of constant displaced volume, by adjusting the volume of added water in a normally gas filled space. This approach can also be described as buoyancy reduction, as opposed to buoyancy addition when gas is added to a flexible ambient pressure space. Such variable buoyancy pressure vessels are used by submersibles and submarines for fine buoyancy and trim control. Water from

10608-420: The buoyancy to account for gas usage and volume variation of the diving suit. One way this can be done is by pumping water into a scuba cylinder, using a flexible bladder to keep the gas and water separate, which requires a cylinder made for this purpose, with a water inlet to the space around the internal bladder, connected to a high-pressure pump and control valve system. If the weights have been optimised for

10744-446: The central nervous system to provide the sense of balance. Underwater, some of these inputs may be absent or diminished, making the remaining cues more important. Conflicting input may result in vertigo, disorientation and motion sickness . The vestibular sense is essential in these conditions for rapid, intricate and accurate movement. Proprioceptive perception makes the diver aware of personal position and movement, in association with

10880-437: The colour and turbidity of the water. The human eye is optimised for air vision, and when it is immersed in direct contact with water, visual acuity is adversely affected by the difference in refractive index between water and air. Provision of an airspace between the cornea and the water can compensate, but causes scale and distance distortion. Artificial illumination can improve visibility at short range. Stereoscopic acuity,

11016-474: The construction, or as a replaceable component supported inside the structural body. The buoyancy compensator is one of the items of diving equipment most requiring skill and attention during operation, as control is entirely manual, and adjustment is required throughout the dive as weight reduces due to gas consumption, and buoyancy of the diving suit and BC generally varies with depth. Fine buoyancy adjustment can be done by breath control on open circuit, reducing

11152-430: The cylinder harness. The air bladder extends from the back around the diver's sides or over the diver's shoulders. Wraparound bladders are favored by some divers because they make it easier to maintain upright attitude on the surface. However, some designs have a tendency to squeeze the diver's torso when inflated, and they are often bulky at the sides or front when fully inflated, and may lack sufficient volume to support

11288-422: The cylinder. This system is inherently more stable with hydrostatic pressure variation, and decreases buoyancy from the initial state, which is with a full cylinder of gas at the start of the dive. To minimise the pressure rise caused by pumping ballast water into the cylinder when it is full, weighting is done for near neutral buoyancy at the start of the dive, with just enough positive buoyancy to safely swim at

11424-402: The design details and quality of materials and manufacture than on the choice of arrangement, though maintenance may vary, as it is quicker to clean, dry and inspect a single skin than a bladder and casing, and the bladder and casing will have more components for an equivalent layout. A single skin construction uses the material of the buoyancy bladder as the structural material for the unit, and

11560-441: The difficulty of recovering from a dry-suit inversion where the air in the suit flows to the feet and the weights in the BC shift towards the head. A crotch strap will prevent this. Back inflation buoyancy compensators are typified by the stainless steel backplate and wing arrangement popular with technical divers, but other arrangements are also available. Wings or Backplate and wing consist of an inflatable bladder worn between

11696-429: The dive. Where staged cylinders are used, it may also be used to compensate for weight changes when dropping and retrieving these cylinders. Variations in the buoyancy of wetsuits depend on the volume and density of the suit and the ambient pressure, but for thick suits at depth it can be in the order of 10 kg. Variations in the buoyancy of dry suits should be compensated by maintaining a constant volume of gas inside

11832-412: The diver can find the shotline when needed. In most recreational and professional scuba, neutral buoyancy during most of the dive is necessary or desirable, as it gives the diver enhanced mobility and maneuverability, and allows the diver to avoid contact with delicate benthic organisms , and to fin without disturbing sediment which can rapidly reduce visibility. For this function a buoyancy compensator

11968-473: The diver comfortably and must stay securely in place without constraining the diver's freedom of movement. There is some conflict between allowing easy adjustment to fit a range of diver builds, and setting up the harness to optimum fit for a specific diver in a specific diving suit. This is a particular problem with jacket style BCs which are inherently less adjustable for fit than backplate harnesses, which are more adjustable, but may take more time to adjust. It

12104-540: The diver remains at that depth without additional effort. This type of buoyancy compensator functions by increasing buoyancy from the most stable state, which is empty, so weighting is done for neutral buoyancy at the condition of least mass, which is at the end of the dive with the cylinders empty, at which point the diver should be able to stay at the last decompression stop without physical effort. A few illustrative examples are presented here. They are simplified but numerically realistic: An alternative method of adjusting

12240-404: The diver sagging down in the jacket when the diver is upright when floating at the surface. Solutions to this problem include the cummerbund (a broad adjustable waist band) and the crotch strap (a strap between the legs). The crotch strap, when adjusted correctly, is effective at preventing this shift, but may prevent the weight belt from falling clear of the diver if dropped in an emergency. Fitting

12376-412: The diver's back and the cylinder(s). Invented by Greg Flanagan in 1979 for North Florida cave divers, and further developed by William Hogarth Main , the back plate and wing configuration is not a recent development, but has gained popularity because of suitability for technical diving where it is often used, as the technical diver often carries multiple cylinders on his back and/or clipped to D-rings on

12512-405: The diver's breathing gas has been used up. It is not sufficient to only be able to remain neutral with reserve gas, as if the reserve gas is nearly used up due to a problem, the diver will not want to be struggling or unable to stay down to decompress. Weighting must be sufficient to allow the diver to stay at the shallowest stop with almost empty cylinders, and available buoyancy volume must allow

12648-415: The diver's stomach area, and was inflated by LP gas from the regulator, for buoyancy control underwater. This arrangement provided better buoyancy distribution for trim control while diving than most other front inflation systems. Vest BC, stab jacket, stabiliser jacket, stabilizer, waistcoat or (disparagingly) "Poodle Vest" BCs are inflatable vests worn by the diver around the upper torso, which incorporate

12784-446: The duration of a dive, but there are other problems that may result from this technological solution. Absorption of metabolically inert gases is increased as a function of time and pressure, and these may both produce undesirable effects immediately, as a consequence of their presence in the tissues in the dissolved state, such as nitrogen narcosis and high pressure nervous syndrome , or cause problems when coming out of solution within

12920-414: The end of the dive ( Bohr effect ); they also suppress the urge to breathe, making it easier to hold the breath to the point of blackout. This can happen at any depth. Ascent-induced hypoxia is caused by a drop in oxygen partial pressure as ambient pressure is reduced. The partial pressure of oxygen at depth may be sufficient to maintain consciousness at that depth and not at the reduced pressures nearer

13056-423: The environmental conditions of diving, and various equipment has been developed to extend the depth and duration of human dives, and allow different types of work to be done. In ambient pressure diving, the diver is directly exposed to the pressure of the surrounding water. The ambient pressure diver may dive on breath-hold ( freediving ) or use breathing apparatus for scuba diving or surface-supplied diving , and

13192-547: The environmental protection suit and low temperatures. The combination of instability, equipment, neutral buoyancy and resistance to movement by the inertial and viscous effects of the water encumbers the diver. Cold causes losses in sensory and motor function and distracts from and disrupts cognitive activity. The ability to exert large and precise force is reduced. Balance and equilibrium depend on vestibular function and secondary input from visual, organic, cutaneous, kinesthetic and sometimes auditory senses which are processed by

13328-411: The equipment, and the diver is nearly at neutral buoyancy at the start of the dive, very little water needs to be added at the start of the dive, so the gas pressure is not greatly increased. More water is pumped in during the dive to compensate for the mass of gas used, but by this time the pressure will have dropped considerably. A small amount of residual gas pressure on surfacing will be enough to eject

13464-412: The expense of higher cost, complex logistics and loss of dexterity. Crewed submeribles have been built rated to full ocean depth and have dived to the deepest known points of all the oceans. Autonomous underwater vehicles (AUVs) and remotely operated underwater vehicles (ROVs) can carry out some functions of divers. They can be deployed at greater depths and in more dangerous environments. An AUV

13600-461: The feet; external propulsion can be provided by a diver propulsion vehicle , or a towboard pulled from the surface. Other equipment includes a diving mask to improve underwater vision , a protective diving suit , equipment to control buoyancy , and equipment related to the specific circumstances and purpose of the dive. Scuba divers are trained in the procedures and skills appropriate to their level of certification by instructors affiliated to

13736-425: The free change of volume of the gas in a closed space in contact with the diver, resulting in a pressure difference between the tissues and the gas space, and the unbalanced force due to this pressure difference causes deformation of the tissues resulting in cell rupture. Barotraumas of ascent are also caused when the free change of volume of the gas in a closed space in contact with the diver is prevented. In this case

13872-504: The full diver's umbilical system with pneumofathometer and voice communication, is known in the industry as "scuba replacement". Compressor diving is a rudimentary method of surface-supplied diving used in some tropical regions such as the Philippines and the Caribbean . The divers swim with a half mask and fins and are supplied with air from an industrial low-pressure air compressor on

14008-415: The harness webbing. The back-mount cylinders or rebreather assembly are fastened over the buoyancy bladder to a backplate which is strapped to the diver by the harness. The wing design frees the divers sides and front and allows for a large volume bladder with high lift capacity (60 lbs /30 liter wings are not uncommon). Some designs use elasticated webbing or bungee cords around the bladder to constrict

14144-421: The head with inflation, which adversely affects the diver's trim underwater. The ABLJ's location on the diver's chest and round the neck provides the best buoyancy distribution of the buoyancy compensator designs when it comes to floating a distressed, fatigued or unconscious diver face-up on the surface in the event of a problem. They do not normally provide good trim while immersed, as the centre of buoyancy of

14280-473: The human body in water affects the circulation , renal system , fluid balance , and breathing, because the external hydrostatic pressure of the water provides support against the internal hydrostatic pressure of the blood. This causes a blood shift from the extravascular tissues of the limbs into the chest cavity, and fluid losses known as immersion diuresis compensate for the blood shift in hydrated subjects soon after immersion. Hydrostatic pressure on

14416-418: The increased concentration at high pressures. Hydrostatic pressure differences between the interior of the lung and the breathing gas delivery, increased breathing gas density due to ambient pressure, and increased flow resistance due to higher breathing rates may all cause increased work of breathing , fatigue of the respiratory muscles, and a physiological limit to effective ventilation. Underwater vision

14552-410: The inflatable underwater demolition team (UDT) vest or Mae West life jacket issued to World War II flyers and divers. They were developed in the 1960s and have been largely superseded by wing and vest type BCs, primarily because the buoyancy is concentrated in front of the diver when full, and behind the neck when partially filled, producing a tendency to shift the diver's centre of buoyancy towards

14688-488: The late 20th century, where the operator controls the ROV from the surface, and autonomous underwater vehicles (AUV), which dispense with an operator altogether. All of these modes are still in use and each has a range of applications where it has advantages over the others, though diving bells have largely been relegated to a means of transport for surface-supplied divers. In some cases combinations are particularly effective, such as

14824-444: The order of 1.75 × 0.006 = 0.0105 m , or roughly 10 litres. The mass will depend on the specific formulation of the foam, but will probably be in the order of 4 kg, for a net buoyancy of about 6 kg at the surface. Depending on the overall buoyancy of the diver, this will generally require about 6 kg of additional weight to bring the diver to neutral buoyancy to allow reasonably easy descent The volume lost at 10 m

14960-445: The practitioner submerges below the surface of the water or other liquid for a period which may range between seconds to the order of a day at a time, either exposed to the ambient pressure or isolated by a pressure resistant suit, to interact with the underwater environment for pleasure, competitive sport, or as a means to reach a work site for profit, as a public service, or in the pursuit of knowledge, and may use no equipment at all, or

15096-476: The pressure difference causes a resultant tension in the surrounding tissues which exceeds their tensile strength. Besides tissue rupture, the overpressure may cause ingress of gases into the adjoining tissues and further afield by bubble transport through the circulatory system. This can cause blockage of circulation at distant sites, or interfere with the normal function of an organ by its presence. Provision of breathing gas at ambient pressure can greatly prolong

15232-674: The recreational diving industry include instructor trainers, diving instructors, assistant instructors, divemasters , dive guides, and scuba technicians. A scuba diving tourism industry has developed to service recreational diving in regions with popular dive sites. Commercial diving is industry related and includes engineering tasks such as in hydrocarbon exploration , offshore construction , dam maintenance and harbour works. Commercial divers may also be employed to perform tasks related to marine activities, such as naval diving , ships husbandry , marine salvage or aquaculture . Other specialist areas of diving include military diving , with

15368-436: The right place for a given diver. Three main wraparound configurations can be distinguished: BC attachment systems are generally intended to limit the shifting of the BC as a result of the lifting forces, including minimizing the tendency to slide towards the head when the diver is upright while the bladder is inflated. If the diver is wearing a weight belt, this will pull in the opposite direction to BC lift, and can result in

15504-604: The risks are largely controlled by appropriate diving skills , training , types of equipment and breathing gases used depending on the mode, depth and purpose of diving, it remains a relatively dangerous activity. Professional diving is usually regulated by occupational health and safety legislation, while recreational diving may be entirely unregulated. Diving activities are restricted to maximum depths of about 40 metres (130 ft) for recreational scuba diving, 530 metres (1,740 ft) for commercial saturation diving, and 610 metres (2,000 ft) wearing atmospheric suits. Diving

15640-512: The risks of decompression sickness for deep and long exposures. An alternative approach was the development of the ADS or armoured suit, which isolates the diver from the pressure at depth, at the cost of mechanical complexity and limited dexterity. The technology first became practicable in the middle 20th century. Isolation of the diver from the environment was taken further by the development of remotely operated underwater vehicles (ROV or ROUV) in

15776-429: The same volume of blood throughout the body, and for people with heart disease, this additional workload can cause the heart to go into arrest. A person who survives the initial minute after falling into cold water can survive for at least thirty minutes provided they do not drown. The ability to stay afloat declines substantially after about ten minutes as the chilled muscles lose strength and co-ordination. Hypothermia

15912-405: The shore or a diving support vessel and may be transported on a diving stage or in a diving bell. Surface-supplied divers almost always wear diving helmets or full-face diving masks . The bottom gas can be air, nitrox , heliox or trimix ; the decompression gases may be similar, or may include pure oxygen. Decompression procedures include in-water decompression or surface decompression in

16048-513: The simultaneous use of surface orientated or saturation surface-supplied diving equipment and work or observation class remotely operated vehicles. By the late 19th century, as salvage operations became deeper and longer, an unexplained malady began afflicting the divers; they would suffer breathing difficulties, dizziness, joint pain and paralysis, sometimes leading to death. The problem was already well known among workers building tunnels and bridge footings operating under pressure in caissons and

16184-430: The suit, by manual addition and a combination of automatic and manual dumping, independently of the adjustments to the buoyancy compensator made to compensate for gas usage. The buoyancy compensator is a standard item of scuba diving equipment, though not always necessary, and an optional item for surface-supplied diving , where neutral or positive buoyancy may not be necessary or desirable. Breathhold divers do not have

16320-452: The surface with a full tank, and pump in a relatively small volume of water to descend, which is periodically increased during the dive to compensate for mass loss of breathing gas. After surfacing, the added mass of water is released to give a comfortable positive buoyancy and minimise equipment weight when getting out of the water. If using a dry suit the initial positive buoyancy at the surface could be controlled by suit inflation in excess of

16456-472: The surface. Barotrauma , a type of dysbarism , is physical damage to body tissues caused by a difference in pressure between a gas space inside, or in contact with the body, and the surrounding gas or fluid. It typically occurs when the organism is exposed to a large change in ambient pressure, such as when a diver ascends or descends. When diving, the pressure differences which cause the barotrauma are changes in hydrostatic pressure. The initial damage

16592-427: The surroundings is injected into the tank to decrease buoyancy by ambient pressure difference or by a pump, depending on the internal gas pressure. Water can be removed in a similar way to increase buoyancy. As the tank is rigid and effectively incompressible within the range of diving depths for which it is intended, buoyancy changes due to depth variation during the dive are negligible, and the diver only needs to adjust

16728-406: The tissues during decompression . Other problems arise when the concentration of metabolically active gases is increased. These range from the toxic effects of oxygen at high partial pressure, through buildup of carbon dioxide due to excessive work of breathing, increased dead space , or inefficient removal, to the exacerbation of the toxic effects of contaminants in the breathing gas due to

16864-424: The underwater world, and scientific divers in fields of study which involve the underwater environment, including marine biologists , geologists , hydrologists , oceanographers , speleologists and underwater archaeologists . The choice between scuba and surface-supplied diving equipment is based on both legal and logistical constraints. Where the diver requires mobility and a large range of movement, scuba

17000-461: The upper torso, and it may constrain free breathing if fitted too tightly. This tendency of the inflated BC to shift towards the head is less of a problem when the weights are carried in integrated weight pockets on the BC, but it may then have a tendency to slide towards the head when deflated on an inverted diver underwater. This is less of a problem for the average recreational diver, who does not spend much time head down underwater, but can increase

17136-433: The upright position, owing to cranial displacement of the abdomen from hydrostatic pressure, and resistance to air flow in the airways increases because of the decrease in lung volume. There appears to be a connection between pulmonary edema and increased pulmonary blood flow and pressure, which results in capillary engorgement. This may occur during higher intensity exercise while immersed or submerged. The diving reflex

17272-404: The use of external breathing devices, and relies on the ability of divers to hold their breath until resurfacing. The technique ranges from simple breath-hold diving to competitive apnea dives. Fins and a diving mask are often used in free diving to improve vision and provide more efficient propulsion. A short breathing tube called a snorkel allows the diver to breathe at the surface while the face

17408-455: The vestibular and visual input, and allows the diver to function effectively in maintaining physical equilibrium and balance in the water. In the water at neutral buoyancy, the proprioceptive cues of position are reduced or absent. This effect may be exacerbated by the diver's suit and other equipment. Taste and smell are not very important to the diver in the water but more important to the saturation diver while in accommodation chambers. There

17544-421: The volume of ambient pressure gas in the rigid shell was maintained by a demand regulator automatically sensing a pressure deficit between the internal and external pressures and an automatic dump valve to release internal overpressure, much like the volume control of a rebreather loop by automatic diluent valve (ADV) and overpressure valve , but this reduced buoyancy by flooding the shell with water and increased

17680-425: The volume, and therefore 30% of surface buoyancy, is lost in about the first 10 m, another 30% by about 60 m, and the volume appears to stabilise at about 65% loss by about 100 m. The total buoyancy loss of a wetsuit is proportional to the initial uncompressed volume. An average person has a surface area of about 2 m , so the uncompressed volume of a full one piece 6 mm thick wetsuit will be in

17816-519: The waistband in front of the diver or clipped to each other, forming an elastic belt across the front of the hips, well below the diaphragm. In this application, back mount keeps the inflated bladder from occupying the space at the diver's sides where the cylinders are suspended. Some side mount harnesses are adaptable for use with a back mount cylinder as an option, without the rigid backplate. Buoyancy compensators are also used with rebreathers. In most cases back-mounted technical diving rebreathers use

17952-464: The water. A few short-lived rigid air compartment back inflation BCs were marketed in the 1970s, and the Avelo variable density system is back mounted. A hybrid arrangement is also possible, which has most of the buoyancy in the back, but has a small amount to the sides below the arms. A small proportion of wing style buoyancy compensators have been produced with a dual bladder arrangement. The intention

18088-418: The weight belt over the crotch strap after putting the BC on can be difficult. The cummerbund is an attempt to avoid this problem, as the weight belt can not be snagged on it in the same way, but the weight belt must then be worn either under the cummerbund, obstructing access to the buckle, or below the cummerbund. The effectiveness of a cummerbund depends on a waistline which is smaller than the circumference of

18224-431: Was a comprehensive investigation into the physiological effects of air pressure, both above and below the normal. He determined that inhaling pressurised air caused nitrogen to dissolve into the bloodstream ; rapid depressurisation would then release the nitrogen into its gaseous state, forming bubbles that could block the blood circulation and potentially cause paralysis or death. Central nervous system oxygen toxicity

18360-427: Was also first described in this publication and is sometimes referred to as the "Paul Bert effect". Buoyancy compensator (diving)#Adjustable buoyancy life jacket The buoyancy is usually controlled by adjusting the volume of gas in an inflatable bladder, which is filled with ambient pressure gas from the diver's primary breathing gas cylinder via a low-pressure hose from the regulator first stage, directly from

18496-429: Was initially called caisson disease ; it was later renamed the bends because the joint pain typically caused the sufferer to stoop . Early reports of the disease had been made at the time of Charles Pasley 's salvage operation, but scientists were still ignorant of its causes. French physiologist Paul Bert was the first to understand it as decompression sickness (DCS). His work, La Pression barométrique (1878),

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