The scope of thisportal includes the technology supporting diving activities, the physiological and medical aspects of diving, the skills and procedures of diving and the training and registration of divers, underwater activities which are to some degree dependent on diving, economical, commercial, safety, and legal aspects of diving, biographical information on notable divers, inventors and manufacturers of diving related equipment and researchers into aspects of diving.
Introduction to underwater diving
Surface-supplied divers riding a stage to the underwater workplace
Underwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment. It is also often referred to asdiving, an ambiguous term with several possible meanings, depending on context.Immersion in water and exposure to highambient pressure havephysiological effects that limit the depths and duration possible inambient pressure diving. Humans are not physiologically and anatomically well-adapted to 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 forscuba diving orsurface-supplied diving, and thesaturation diving technique reduces the risk ofdecompression sickness (DCS) after long-duration deep dives.Atmospheric diving suits (ADS) may be used to isolate the diver from high ambient pressure. Crewedsubmersibles can extend depth range tofull 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 the risks are largely controlled by appropriatediving skills,training, types ofequipment andbreathing 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 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 is the underwater work done by law enforcement, fire rescue, andunderwater search and recovery dive teams.Military diving includes combat diving,clearance diving andships husbandry.Deep sea diving is underwater diving, usually with surface-supplied equipment, and often refers to the use ofstandard diving dress with the traditional copper helmet.Hard hat diving is any form of diving with ahelmet, including the standard copper helmet, and other forms offree-flow andlightweight demand helmets.The history of breath-hold diving goes back at least to classical times, and there is evidence of prehistorichunting 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 theSecond World War. (Full article...)
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Index of underwater diving is an alphabetical list of the articles and redirects to sections of the articles representing common dive related topics, (also not always up to date). It has sub-indexes for some of the associated groups of articles, such as:
TheGlossary of underwater diving terminology is an alphabetical list of terms commonly used in diving and their meanings in this context. A useful quick reference. A definition will often contain a link to a detailed main article, or a section of an article on the term. If you can't find a term and are reasonably sure itis a diving term in general use in English, leave a note on the talk page.
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Surface-supplied diver at theMonterey Bay Aquarium, Monterey, California Surface-supplied diving is amode of underwater diving using equipment supplied withbreathing gas through adiver's umbilical from the surface, either from the shore or from adiving support vessel, sometimes indirectly via adiving bell. This is different fromscuba diving, where the diver's breathing equipment is completely self-contained and there is no essential link to the surface. The primary advantages of conventional surface supplied diving are lower risk of drowning and considerably larger breathing gas supply than scuba, allowing longer working periods and safer decompression. It is also nearly impossible for the diver to get lost. Disadvantages are the absolute limitation on diver mobility imposed by the length of the umbilical, encumbrance by the umbilical, and high logistical and equipment costs compared with scuba. The disadvantages restrict use of this mode of diving to applications where the diver operates within a small area, which is common in commercial diving work.
Air-line, or hookah diving, and "compressor diving" are lower technology variants also using a breathing air supply from the surface. (Full article...)
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2nd Reconnaissance Battalion combat diver training with the Dräger LAR V rebreather
Rebreather diving isunderwater diving usingdiving rebreathers, a class of underwater breathing apparatus which recirculates thebreathing gas exhaled by the diver after replacing theoxygen used and removing thecarbon dioxide metabolic product. Rebreather diving is practiced by recreational, military and scientific divers in applications where it has advantages over open circuitscuba, and surface supply of breathing gas is impracticable. The main advantages of rebreather diving are extended gas endurance, low noise levels, and lack of bubbles.
Rebreathers are generally used forscuba applications, but are also occasionally used forbailout systems forsurface-supplied diving.Gas reclaim systems used for deep heliox diving use similar technology to rebreathers, as dosaturation divinglife-support systems, but in these applications the gas recycling equipment is not carried by the diver.Atmospheric diving suits also carry rebreather technology to recycle breathing gas as part of the life-support system, but this article covers the procedures of ambient pressure diving using rebreathers carried by the diver.
Rebreathers are generally more complex to use than open circuit scuba, and have more potentialpoints of failure, so acceptably safe use requires a greater level of skill, attention and situational awareness, which is usually derived from understanding the systems, diligent maintenance and overlearning the practical skills of operation andfault recovery. Fault tolerant design can make a rebreather less likely to fail in a way that immediately endangers the user, and reduces the task loading on the diver which in turn may lower the risk of operator error. (Full article...)
Image 3
Surface-supplied divers riding a stage to the underwater workplace
Underwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment. It is also often referred to asdiving, an ambiguous term with several possible meanings, depending on context. Immersion in water and exposure to highambient pressure havephysiological effects that limit the depths and duration possible inambient pressure diving. Humans are not physiologically and anatomically well-adapted to 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 forscuba diving orsurface-supplied diving, and thesaturation diving technique reduces the risk ofdecompression sickness (DCS) after long-duration deep dives.Atmospheric diving suits (ADS) may be used to isolate the diver from high ambient pressure. Crewedsubmersibles can extend depth range tofull 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 the risks are largely controlled by appropriatediving skills,training, types ofequipment andbreathing 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 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 is the underwater work done by law enforcement, fire rescue, andunderwater search and recovery dive teams.Military diving includes combat diving,clearance diving andships husbandry. Deep sea diving is underwater diving, usually with surface-supplied equipment, and often refers to the use ofstandard diving dress with the traditional copper helmet.Hard hat diving is any form of diving with ahelmet, including the standard copper helmet, and other forms offree-flow andlightweight demand helmets. The history of breath-hold diving goes back at least to classical times, and there is evidence of prehistorichunting 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 theSecond World War. (Full article...)
Image 4
Surface-supplied diver at theMonterey Bay Aquarium, Monterey, California Surface-supplied diving is amode of underwater diving using equipment supplied withbreathing gas through adiver's umbilical from the surface, either from the shore or from adiving support vessel, sometimes indirectly via adiving bell. This is different fromscuba diving, where the diver's breathing equipment is completely self-contained and there is no essential link to the surface. The primary advantages of conventional surface supplied diving are lower risk of drowning and considerably larger breathing gas supply than scuba, allowing longer working periods and safer decompression. It is also nearly impossible for the diver to get lost. Disadvantages are the absolute limitation on diver mobility imposed by the length of the umbilical, encumbrance by the umbilical, and high logistical and equipment costs compared with scuba. The disadvantages restrict use of this mode of diving to applications where the diver operates within a small area, which is common in commercial diving work.
Air-line, or hookah diving, and "compressor diving" are lower technology variants also using a breathing air supply from the surface. (Full article...)
Open-circuit scuba systems discharge the breathing gas into the environment as it is exhaled and consist of one or morediving cylinders containing breathing gas at high pressure which is supplied to the diver atambient pressure through adiving regulator. They may include additional cylinders for range extension,decompression gas oremergency breathing gas. Closed-circuit or semi-closed circuitrebreather scuba systems allow recycling of exhaled gases. The volume of gas used is reduced compared to that of open-circuit, making longer dives feasible. Rebreathers extend the time spent underwater compared to open-circuit for the same metabolic gas consumption. They produce fewer bubbles and less noise than open-circuit scuba, which makes them attractive to covertmilitary divers to avoid detection,scientific divers to avoid disturbing marine animals, andmedia diver to avoid bubble interference.
Scuba diving may be donerecreationally orprofessionally in several applications, including scientific, military and public safety roles, but mostcommercial diving uses surface-supplied diving equipment for breathing gas security when this is practicable. Scuba divers engaged in armed forces covert operations may be referred to asfrogmen, combat divers or attack swimmers.
Freediving,free-diving,free diving,breath-hold diving, orskin diving, is a mode ofunderwater diving that relies onbreath-holding (apnea) until resurfacing rather than the use of breathing apparatus such asscuba gear. Besides the limits of breath-hold, immersion in water and exposure to high ambient pressure also have physiological effects that limit the depths and duration possible in freediving.
Open-circuit scuba systems discharge the breathing gas into the environment as it is exhaled and consist of one or morediving cylinders containing breathing gas at high pressure which is supplied to the diver atambient pressure through adiving regulator. They may include additional cylinders for range extension,decompression gas oremergency breathing gas. Closed-circuit or semi-closed circuitrebreather scuba systems allow recycling of exhaled gases. The volume of gas used is reduced compared to that of open-circuit, making longer dives feasible. Rebreathers extend the time spent underwater compared to open-circuit for the same metabolic gas consumption. They produce fewer bubbles and less noise than open-circuit scuba, which makes them attractive to covertmilitary divers to avoid detection,scientific divers to avoid disturbing marine animals, andmedia diver to avoid bubble interference.
Scuba diving may be donerecreationally orprofessionally in several applications, including scientific, military and public safety roles, but mostcommercial diving uses surface-supplied diving equipment for breathing gas security when this is practicable. Scuba divers engaged in armed forces covert operations may be referred to asfrogmen, combat divers or attack swimmers.
Anatmospheric diving suit (ADS),atmospheric pressure diving suit orsingle atmosphere diving suit is a small one-person articulatedsubmersible which resembles asuit of armour, with pressure-tight joints to allow articulation while maintaining a constant internal volume and an internal pressure of one atmosphere. An ADS can enable diving at depths of up to 2,300 feet (700 m) for many hours by eliminating the majority of significant physiological dangers associated withdeep diving. The occupant of an ADS does not need todecompress, and there is no need for specialbreathing gas mixtures, so there is no danger ofdecompression sickness ornitrogen narcosis when the ADS is functioning properly. An ADS can permit less-skilled swimmers to complete deep dives, albeit at the expense of dexterity.
Atmospheric diving suits in current use include theNewtsuit, Exosuit, Hardsuit and the WASP, all of which are self-contained hard suits that incorporate propulsion units. The Hardsuit is constructed fromcast aluminum (forged aluminum in a version constructed for the US Navy for submarine rescue); the upper torso hull is made from castaluminum, while the bottom dome is machined aluminum. The WASP is ofglass-reinforced plastic (GRP) body tube construction. (Full article...)
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Two very different modes of diving: Ambient pressure open circuit scuba diving (left) and atmospheric pressure diving in a pressure resistant suit (right) Amode of diving, ordiving mode, is a particular way todive underwater that requiresspecific equipment, procedures and techniques, and may expose the diver to aparticular range of hazards.
There are several modes of diving; these are distinguished by the type ofbreathing apparatus, diving equipment, procedures and techniques involved, and whether the diver is exposed to ambient pressure.Ambient pressure diving includesfreediving and compressed-gas diving, which may also be classed asair diving,oxygen diving, andmixed gas diving by the breathing gas used, and asopen-circuit,semi-closed, orclosed-circuit depending on the type of breathing apparatus used. There is alsoatmospheric pressure diving, which involves encapsulation in anatmospheric pressure diving suit orsubmersible, andunmanned diving, where there are no human divers involved. Thediving equipment,support equipment andprocedures used largely depend on the mode of diving.
In certain circumstances, some modes of diving may be impracticable, unsafe, not permitted by the governing organisation, or illegal. All modes of diving carry a certain amount of risk; this is mitigated withplanning,training, and the appropriate equipment. (Full article...)
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Saturation diver working on theUSSMonitor wreck at 70 m (230 ft) depth Saturation diving is anambient pressure diving technique which allows a diver to remain at working depth for extended periods during which thebody tissues becomesaturated withmetabolically inert gas from thebreathing gas mixture. Once saturated, the time required fordecompression to surface pressure will not increase with longer exposure. The diver undergoes a single decompression to surface pressure at the end of the exposure of several days to weeks duration. The ratio of productive working time at depth to unproductive decompression time is thereby increased, and the health risk to the diver incurred by decompression is minimised. Unlike other ambient pressure diving, the saturation diver is only exposed to external ambient pressure while at diving depth.
Most saturation diving procedures are common to all surface-supplied diving, but there are some which are specific to the use of a closed bell, the restrictions of excursion limits, and the use of saturation decompression.
Surface saturation systems transport the divers to the worksite in a closed bell, usesurface-supplied diving equipment, and are usually installed on anoffshore platform ordynamically positioneddiving support vessel. Divers operating fromunderwater habitats may use surface-supplied equipment from the habitat orscuba equipment, and access the water through awet porch, but will usually have to surface in a closed bell, unless the habitat includes adecompression chamber. The life support systems provide breathing gas, climate control, and sanitation for the personnel under pressure, in the accommodation and in the bell and the water. There are also communications, fire suppression and other emergency services. Bell services are provided via the bell umbilical and distributed to divers through excursion umbilicals. Life support systems for emergency evacuation are independent of the accommodation system as they must travel with the evacuation module.
Saturation diving is a specializedmode of diving; of the 3,300 commercial divers employed in the United States in 2015, 336 were saturation divers. Special training and certification is required, as the activity is inherently hazardous, and a set of standard operating procedures, emergency procedures, and a range of specialised equipment is used to control the risk, that require consistently correct performance by all the members of an extended diving team. The combination of relatively large skilled personnel requirements, complex engineering, and bulky, heavy equipment required to support a saturation diving project make it an expensive diving mode, but it allows direct human intervention at places that would not otherwise be practical, and where it is applied, it is generally more economically viable than other options, if such exist. (Full article...)
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Surface-supplied diver at theMonterey Bay Aquarium, Monterey, California Surface-supplied diving is amode of underwater diving using equipment supplied withbreathing gas through adiver's umbilical from the surface, either from the shore or from adiving support vessel, sometimes indirectly via adiving bell. This is different fromscuba diving, where the diver's breathing equipment is completely self-contained and there is no essential link to the surface. The primary advantages of conventional surface supplied diving are lower risk of drowning and considerably larger breathing gas supply than scuba, allowing longer working periods and safer decompression. It is also nearly impossible for the diver to get lost. Disadvantages are the absolute limitation on diver mobility imposed by the length of the umbilical, encumbrance by the umbilical, and high logistical and equipment costs compared with scuba. The disadvantages restrict use of this mode of diving to applications where the diver operates within a small area, which is common in commercial diving work.
Air-line, or hookah diving, and "compressor diving" are lower technology variants also using a breathing air supply from the surface. (Full article...)
Image 12
Surface-supplied diver at theMonterey Bay Aquarium, Monterey, California Surface-supplied diving is amode of underwater diving using equipment supplied withbreathing gas through adiver's umbilical from the surface, either from the shore or from adiving support vessel, sometimes indirectly via adiving bell. This is different fromscuba diving, where the diver's breathing equipment is completely self-contained and there is no essential link to the surface. The primary advantages of conventional surface supplied diving are lower risk of drowning and considerably larger breathing gas supply than scuba, allowing longer working periods and safer decompression. It is also nearly impossible for the diver to get lost. Disadvantages are the absolute limitation on diver mobility imposed by the length of the umbilical, encumbrance by the umbilical, and high logistical and equipment costs compared with scuba. The disadvantages restrict use of this mode of diving to applications where the diver operates within a small area, which is common in commercial diving work.
Air-line, or hookah diving, and "compressor diving" are lower technology variants also using a breathing air supply from the surface. (Full article...)
Image 13
Surface-supplied diver at theMonterey Bay Aquarium, Monterey, California Surface-supplied diving is amode of underwater diving using equipment supplied withbreathing gas through adiver's umbilical from the surface, either from the shore or from adiving support vessel, sometimes indirectly via adiving bell. This is different fromscuba diving, where the diver's breathing equipment is completely self-contained and there is no essential link to the surface. The primary advantages of conventional surface supplied diving are lower risk of drowning and considerably larger breathing gas supply than scuba, allowing longer working periods and safer decompression. It is also nearly impossible for the diver to get lost. Disadvantages are the absolute limitation on diver mobility imposed by the length of the umbilical, encumbrance by the umbilical, and high logistical and equipment costs compared with scuba. The disadvantages restrict use of this mode of diving to applications where the diver operates within a small area, which is common in commercial diving work.
Air-line, or hookah diving, and "compressor diving" are lower technology variants also using a breathing air supply from the surface. (Full article...)
Image 14
Surface-supplied diver at theMonterey Bay Aquarium, Monterey, California Surface-supplied diving is amode of underwater diving using equipment supplied withbreathing gas through adiver's umbilical from the surface, either from the shore or from adiving support vessel, sometimes indirectly via adiving bell. This is different fromscuba diving, where the diver's breathing equipment is completely self-contained and there is no essential link to the surface. The primary advantages of conventional surface supplied diving are lower risk of drowning and considerably larger breathing gas supply than scuba, allowing longer working periods and safer decompression. It is also nearly impossible for the diver to get lost. Disadvantages are the absolute limitation on diver mobility imposed by the length of the umbilical, encumbrance by the umbilical, and high logistical and equipment costs compared with scuba. The disadvantages restrict use of this mode of diving to applications where the diver operates within a small area, which is common in commercial diving work.
Air-line, or hookah diving, and "compressor diving" are lower technology variants also using a breathing air supply from the surface. (Full article...)
The helium is included as a substitute for some of the nitrogen, to reduce thenarcotic effect of the breathing gas at depth and to reduce thework of breathing. With a mixture of three gases it is possible to create mixes suitable for different depths or purposes by adjusting the proportions of each gas. Oxygen content can be optimised for the depth to limit the risk oftoxicity, and the inert component balanced between nitrogen (which is cheap but narcotic) and helium (which is not narcotic and reduces work of breathing, but is more expensive and can increaseheat loss).
The mixture of helium and oxygen with a 0% nitrogen content is generally known asheliox. This is frequently used as a breathing gas in deep commercial diving operations, where it is often recycled to save the expensive helium component. Analysis of two-component gases is much simpler than three-component gases. (Full article...)
Dynamic positioning (DP) is a computer-controlled system to automatically maintain avessel's position and heading by using its own propellers and thrusters. Position reference sensors, combined with wind sensors, motion sensors andgyrocompasses, provide information to the computer pertaining to the vessel's position and the magnitude and direction of environmental forces affecting its position. Examples of vessel types that employ DP include ships andsemi-submersible mobileoffshore drilling units (MODU), oceanographic research vessels,cable layer ships andcruise ships.
The computer program contains amathematical model of the vessel that includes information pertaining to the wind and current drag of the vessel and the location of the thrusters. This knowledge, combined with the sensor information, allows the computer to calculate the required steering angle and thruster output for each thruster. This allows operations at sea where mooring or anchoring is not feasible due to deep water, congestion on the sea bottom (pipelines, templates) or other problems.
Dynamic positioning may either be absolute in that the position is locked to a fixed point over the bottom, or relative to a moving object like another ship or an underwater vehicle. One may also position the ship at a favorable angle towards wind, waves and current, called weathervaning.
Abailout bottle (BoB) or, more formally,bailout cylinder is ascuba cylinder carried by an underwater diver for use as an emergency supply of breathing gas in the event of a primary gas supply failure. A bailout cylinder may be carried by a scuba diver in addition to the primary scuba set, or by a surface supplied diver using either free-flow or demand systems. The bailout gas is not intended for use during the dive except in an emergency. The term may refer to just the cylinder, or the bailout set or emergency gas supply (EGS), which is the cylinder with the gas delivery system attached. The bailout set or bailout system is the combination of the emergency gas cylinder with the gas delivery system to the diver, which includes adiving regulator with either ademand valve, abailout block, or abailout valve (BOV).
Insolo diving, abuddy bottle is a bailout cylinder carried as a substitute for an emergency gas supply from adiving buddy. A bailout cylinder for recreational scuba diving is often a small cylinder, known as apony bottle, with a normal scuba regulator set, or a smaller cylinder with a combined first and second stage integrated with the cylinder valve, known as "Spare air", after a well known example of the type.
There are several categories ofdecompression equipment used to help diversdecompress, which is the process required to allowambient pressure divers to return to the surface safely after spending time underwater at higher ambient pressures.
Decompression obligation for a givendive profile must be calculated and monitored to ensure that the risk ofdecompression sickness is controlled. Some equipment is specifically for these functions, both during planning before the dive and during the dive. Other equipment is used to mark the underwater position of the diver, as a position reference in low visibility or currents, or to assist the diver's ascent and control the depth.
Decompression may be shortened ("accelerated") by breathing an oxygen-rich "decompression gas" such as anitrox blend or pureoxygen. The high partial pressure of oxygen in such decompression mixes produces the effect known as theoxygen window. This decompression gas is often carried by scuba divers in side-slung cylinders.Cave divers who can only return by a single route, can leave decompression gas cylinders attached to the guideline ("stage" or "drop cylinders") at the points where they will be used.Surface-supplied divers will have the composition of the breathing gas controlled at thegas panel.
Divers with long decompression obligations may be decompressed inside gas filledhyperbaric chambers in the water or at the surface, and in the extreme case,saturation divers are only decompressed at the end of a project, contract, or tour of duty that may be several weeks long. (Full article...)
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Two divers, one wearing a 1 atmosphere diving suit and the other standard diving dress, preparing to explore the wreck of theRMS Lusitania, 1935
Adiving suit is a garment or device designed to protect a diver from theunderwater environment. A diving suit may also incorporate abreathing gas supply (such as for astandard diving dress oratmospheric diving suit), but in most cases the term applies only to the environmental protective covering worn by the diver. The breathing gas supply is usually referred to separately. There is no generic term for the combination of suit and breathing apparatus alone. It is generally referred to asdiving equipment or dive gear along with any other equipment necessary for the dive.
Israeli Navy Underwater Missions Unit transfers equipment using lifting-bags
Alifting bag is an item ofdiving equipment consisting of a robust andair-tight bag with straps, which is used to lift heavy objects underwater by means of the bag'sbuoyancy. The heavy object can either be moved horizontally underwater by thediver or sent unaccompanied to the surface.
Lift bag appropriate capacity should match the task at hand. If the lift bag is grossly oversized a runaway or otherwise out of control ascent may result. Commercially available lifting bags may incorporate dump valves to allow the operator to control the buoyancy during ascent, but this is a hazardous operation with high risk of entanglement in an uncontrolled lift or sinking. If a single bag is insufficient, multiple bags may be used, and should be distributed to suit the load.
There are also lifting bags used on land as short lift jacks for lifting cars or heavy loads or lifting bags which are used in machines as a type of pneumatic actuator which provides load over a large area. These lifting bags of the AS/CR type are for example used in the brake mechanism of rollercoasters. (Full article...)
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Conventional scuba weight-belt with quick-release buckle
Adiving weighting system is ballast weight added to a diver or diving equipment to counteract excess buoyancy. They may be used by divers or on equipment such as diving bells, submersibles or camera housings.
Divers weardiver weighting systems,weight belts orweights to counteract thebuoyancy of otherdiving equipment, such asdiving suits and aluminiumdiving cylinders, and buoyancy of the diver. The scuba diver must be weighted sufficiently to be slightly negatively buoyant at the end of the dive when most of the breathing gas has been used, and needs to maintain neutral buoyancy at safety or obligatory decompression stops. During the dive, buoyancy is controlled by adjusting the volume of air in thebuoyancy compensation device (BCD) and, if worn, thedry suit, in order to achieve negative, neutral, or positive buoyancy as needed. The amount of weight required is determined by the maximum overall positive buoyancy of the fully equipped but unweighted diver anticipated during the dive, with an empty buoyancy compensator and normally inflated dry suit. This depends on the diver's mass and body composition, buoyancy of other diving gear worn (especially thediving suit), watersalinity, weight of breathing gas consumed, and water temperature. It normally is in the range of 2 kilograms (4.4 lb) to 15 kilograms (33 lb). The weights can be distributed to trim the diver to suit the purpose of the dive.
Surface-supplied divers may be more heavily weighted to facilitate underwater work, and may be unable to achieve neutral buoyancy, and rely on the diving stage, bell, umbilical, lifeline, shotline or jackstay for returning to the surface.
Freedivers may also use weights to counteract buoyancy of a wetsuit. However, they are more likely to weight for neutral buoyancy at a specific depth, and their weighting must take into account not only the compression of the suit with depth, but also the compression of the air in their lungs, and the consequent loss of buoyancy. As they have no decompression obligation, they do not have to be neutrally buoyant near the surface at the end of a dive.
If the weights have a method of quick release, they can provide a useful rescue mechanism: they can be dropped in an emergency to provide an instant increase in buoyancy which should return the diver to the surface. Dropping weights increases the risk ofbarotrauma anddecompression sickness due to the possibility of an uncontrollable ascent to the surface. This risk can only be justified when the emergency is life-threatening or the risk of decompression sickness is small, as is the case in freediving and scuba diving when the dive is well short of the no-decompression limit for the depth. Often divers take great care to ensure the weights are not dropped accidentally, and heavily weighted divers may arrange their weights so subsets of the total weight can be dropped individually, allowing for a somewhat more controlled emergency ascent.
The weights are generally made oflead because of its highdensity, reasonably low cost, ease ofcasting into suitable shapes, and resistance tocorrosion. The lead can be cast in blocks, cast shapes with slots for straps, or shaped as pellets known as "shot" and carried in bags. There is some concern that lead diving weights may constitute atoxic hazard to users and environment, but little evidence of significant risk. (Full article...)
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A snorkeller wearing a clear silicone diving mask
Adiving mask (alsohalf mask,free-diving mask,snorkelling mask orscuba mask) is an item ofdiving equipment that allowsunderwater divers, includingscuba divers,underwater hockey players,underwater rugby players,free-divers, andsnorkellers to clearly seeunderwater.Surface supplied divers usually use afull face mask ordiving helmet, but in some systems the half mask may be used. When thehuman eye is in direct contact with water as opposed toair, its normal environment,light entering the eye isrefracted by a different angle and the eye is unable tofocus the light on the retina. By providing an air space in front of the eyes, the eye is able to focus nearly normally. The shape of the air space in the mask slightly affects the ability to focus. Corrective lenses can be fitted to the inside surface of the viewport or contact lenses may be worn inside the mask to allow normal vision for people with focusing defects.
When the diver descends, theambient pressure rises, and it becomes necessary to equalise the pressure inside the mask with the external ambient pressure to avoid thebarotrauma known asmask squeeze. This is done by allowing sufficient air to flow out through the nose into the mask to relieve the pressure difference, which requires the nose to be included in the airspace of the mask. Equalisation during ascent is automatic as excess air inside the mask easily leaks out past the seal.
A wide range of viewport shapes and internal volumes are available, and each design will generally fit some shapes of face better than others. A good comfortable fit and a reliable seal around the edges of the rubber skirt is important to the correct function of the mask. National and international standards relating to diving masks provide a means of ensuring that they are manufactured to a suitable quality. (Full article...)
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A liveaboard dive boat on theSimilan Islands,Thailand Adive boat is aboat thatrecreational divers orprofessional scuba divers use to reach adive site which they could not conveniently reach by swimming from the shore. Dive boats may be propelled by wind or muscle power, but are usually powered by internal combustion engines. Some features, like convenient access from the water, are common to all dive boats, while others depend on the specific application or region where they are used. The vessel may be extensively modified to make it fit for purpose, or may be used without much adaptation if it is already usable.
Dive boats may simply transport divers and theirequipment to and from the dive site for a single dive, or may provide longer term support and shelter for day trips or periods of several consecutive days. Deployment of divers may be whilemoored, atanchor, orunder way, (also known aslive-boating or live-boat diving). There are a range of specialised procedures for boat diving, which include water entry and exit, avoiding injury by the dive boat, and keeping the dive boat crew aware of the location of the divers in the water.
There are also procedures used by the boat crew, to avoid injuring the divers in the water, keeping track of where they are during a dive, recalling the divers in an emergency, and ensuring that none are left behind. (Full article...)
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Surface supplied commercial diving equipment on display at a trade show
Diving equipment, orunderwater diving equipment, isequipment used byunderwater divers to make diving activities possible, easier, safer and/or more comfortable. This may be equipment primarily intended for this purpose, or equipment intended for other purposes which is found to be suitable for diving use.
The fundamental item of diving equipment used by divers other thanfreedivers, isunderwater breathing apparatus, such asscuba equipment, andsurface-supplied diving equipment, but there are other important items of equipment that make diving safer, more convenient or more efficient. Diving equipment used byrecreational scuba divers, also known as scuba gear, is mostly personal equipment carried by the diver, butprofessional divers, particularly when operating in the surface supplied orsaturation mode, use a large amount of support equipment not carried by the diver.
Equipment which is used for underwater work or other activities which is not directly related to the activity of diving, or which has not been designed or modified specifically for underwater use by divers is not considered to be diving equipment. (Full article...)
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Nitrox refers to anygas mixture composed (excepting trace gases) ofnitrogen andoxygen. It is usually used for mixtures that contain less than 78% nitrogen by volume. In the usual application,underwater diving, nitrox is normally distinguished from air and handled differently. The most common use of nitrox mixtures containing oxygen in higher proportions than atmospheric air is inscuba diving, where the reducedpartial pressure of nitrogen is advantageous in reducing nitrogen uptake in thebody's tissues, thereby extending the practicable underwater dive time by reducing thedecompression requirement, or reducing the risk ofdecompression sickness (also known asthe bends). The two most common recreational diving nitrox mixes are 32% and 36% oxygen, which have maximum operating depths of about 110 feet (34 meters) and 95 feet (29 meters) respectively.
Nitrox is used to a lesser extent insurface-supplied diving, as these advantages are reduced by the more complex logistical requirements for nitrox compared to the use of simple low-pressure compressors for breathing gas supply. Nitrox can also be used in hyperbaric treatment ofdecompression illness, usually at pressures where pure oxygen would be hazardous. Nitrox is not a safer gas than compressed air in all respects; although its use can reduce the risk of decompression sickness, it increases the risks ofoxygen toxicity and fire.
Though not generally referred to as nitrox, an oxygen-enriched air mixture is routinely provided at normal surface ambient pressure asoxygen therapy to patients with compromised respiration and circulation. (Full article...)
Diving cylinders are usually manufactured from aluminum or steel alloys, and when used on a scuba set are normally fitted with one of two common types ofscuba cylinder valve for filling and connection to the regulator. Other accessories such asmanifolds, cylinder bands, protective nets and boots and carrying handles may be provided. Various configurations of harness may be used by the diver to carry a cylinder or cylinders while diving, depending on the application. Cylinders used for scuba typically have an internal volume (known as water capacity) of between 3 and 18 litres (0.11 and 0.64 cu ft) and a maximum working pressure rating from 184 to 300bars (2,670 to 4,350 psi). Cylinders are also available in smaller sizes, such as 0.5, 1.5 and 2 litres; however these are usually used for purposes such as inflation ofsurface marker buoys,dry suits, andbuoyancy compensators rather than breathing. Scuba divers may dive with a single cylinder, a pair of similar cylinders, or a main cylinder and a smaller"pony" cylinder, carried on the diver's back or clipped onto the harness at the side. Paired cylinders may be manifolded together or independent. Intechnical diving, more than two scuba cylinders may be needed to carry different gases. Larger cylinders, typically up to 50 litre capacity, are used as on-board emergency gas supply on diving bells. Large cylinders are also used forsurface supply through adiver's umbilical, and may be manifolded together on a frame for transportation.
Theselection of an appropriate set of scuba cylinders for a diving operation is based on theestimated amount of gas required to safely complete the dive. Diving cylinders are most commonly filled with air, but because the main components of air can cause problems when breathed underwater at higher ambient pressure, divers may choose to breathe from cylinders filled with mixtures of gases other than air. Many jurisdictions have regulations that govern the filling, recording of contents, and labeling for diving cylinders. Periodictesting and inspection of diving cylinders is often obligatory to ensure the safety of operators of filling stations. Pressurized diving cylinders are considereddangerous goods for commercial transportation, and regional andinternational standards for colouring and labeling may also apply. (Full article...)
An alternative air source may be fully redundant (completely independent of any part of the main air supply system) or non-redundant, if it can be compromised by any failure of the main air supply. From the diver's point of view, air supplied by a buddy or rescue diver is fully redundant, as it is unaffected by the diver's own air supply in any way, but a second regulator on a double cylinder valve or a secondary demand valve (octopus) is not redundant to the diver carrying it, as it is attached to his or her main air supply. Decompression gas can be considered an alternative gas supply only when the risk of breathing it at the current depth is acceptable.
Effective use of any alternate air source requires competence in the associated skill set. The procedures for receiving air from another diver or from one's own equipment are most effective and least likely to result in a life-threatening incident if well trained to the extent that they do not distract the diver from other essential matters. A major difference frombuddy breathing is that the diver using a redundant alternative air source need not alternate breathing with the donor, which can be a substantial advantage in many circumstances. There is a further significant advantage when the alternate air source is carried by the diver using it, in that it is not necessary to locate the buddy before it is available, but this comes at the cost of extra equipment. (Full article...)
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Trimix scuba cylinder label
Abreathing gas is a mixture of gaseous chemical elements and compounds used forrespiration.Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed habitats. Oxygen is the essential component for any breathing gas. Breathing gases for hyperbaric use have been developed to improve on the performance of ordinary air by reducing the risk ofdecompression sickness, reducing the duration ofdecompression, reducingnitrogen narcosis or reducingwork of breathing and allowing saferdeep diving. (Full article...)
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Line Arrow Marker
Incave (and occasionally wreck) diving,line markers are used for orientation as a visual and tactile reference on a permanent guideline. Directional markers (commonly a notched acute isosceles triangle in basic outline), are also known as line arrows or Dorff arrows, and point the way to an exit. Line arrows may mark the location of a "jump" location in a cave when two are placed adjacent to each other. Two adjacent arrows facing away from each other, mark a point in the cave where the diver is equidistant from two exits. Arrow direction can be identified by feel in low visibility.
Non-directional markers ("cookies") are purely personal markers that mark specific spots, or the direction of one's chosen exit at line intersections where there are options. Their shape does not provide a tactile indication of direction as this could cause confusion in low visibility. One important reason to be adequately trained before cave diving is that incorrect marking can confuse and fatally endanger not only oneself, but also other divers. (Full article...)
Diver clearing ears Ear clearing,clearing the ears orequalization is any of various maneuvers to equalize the pressure in themiddle ear with theoutside pressure, by letting air enter along theEustachian tubes, as this does not always happen automatically when the pressure in the middle ear is lower than the outside pressure. This need can arise inscuba diving,freediving/spearfishing,skydiving, fast descent in anaircraft, fast descent in amine cage, and being put into pressure in acaisson or similar internally pressurised enclosure, or sometimes even simply travelling at fast speeds in anautomobile.
Normally the ears will clear automatically during a reduction in ambient pressure, but if they do not, a reverse squeeze may occur, which can also require clearing to avoid causing injury to the eardrum or inner ear. (Full article...)
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Beginner diver inSt. Croix,United States Virgin Islands Recreational diving orsport diving isdiving for the purpose of leisure and enjoyment, usually when usingscuba equipment. The term "recreational diving" may also be used in contradistinction to "technical diving", a more demanding aspect of recreational diving which requires more training and experience to develop the competence to reliably manage more complex equipment in the more hazardous conditions associated with the disciplines.Breath-hold diving for recreation also fits into the broader scope of the term, but this article covers the commonly used meaning ofscuba diving for recreational purposes, where the diver is not constrained from making a direct near-vertical ascent to the surface at any point during the dive, and risk is considered low.
The equipment used for recreational diving is mostlyopen circuit scuba, though semi closed and fully automated electronic closed circuitrebreathers may be included in the scope of recreational diving. Risk is managed by training the diver in a range of standardised procedures and skills appropriate to the equipment the diver chooses to use and the environment in which the diver plans to dive. Further experience and development of skills by practice will improve the diver's ability to dive safely. Specialty training is made available by the recreational diver training industry and diving clubs to increase the range of environments and venues the diver can enjoy at an acceptable level of risk.
Reasons to dive and preferred diving activities may vary during the personal development of a recreational diver, and may depend on theirpsychological profile and their level of dedication to the activity. Most divers average less than eight dives per year, but some total several thousand dives over a few decades and continue diving into their 60s and 70s, occasionally older. Recreational divers may frequent localdive sites or dive as tourists at more distant venues known for desirableunderwater environments. Aneconomically significantdiving tourism industry services recreational divers, providing equipment, training and diving experiences, generally by specialist providers known asdive centers,dive schools,live-aboard,day charter andbasic dive boats.
Legal constraints on recreational diving vary considerably acrossjurisdictions. Recreational diving may be industry regulated or regulated by law to some extent. The legal responsibility for recreational diving service providers is usually limited as far as possible by waivers which they require the customer to sign before engaging in any diving activity. The extent of responsibility of recreational buddy divers is unclear, butbuddy diving is generally recommended by recreational diver training agencies as safer thansolo diving, and some service providers insist that customers dive in buddy pairs. The evidence supporting this policy is inconclusive: it may or may not reduce average risk to the clients by imposing a burden on some to the advantage of others, and may reduce liability risk for the service provider. (Full article...)
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A shotline with decompression trapeze provides a relatively safe and convenient place for in-water decompression.
Dive planning is the process of planning an underwater diving operation. The purpose of dive planning is to increase the probability that a dive will be completed safely and the goals achieved. Some form of planning is done for most underwater dives, but the complexity and detail considered may vary enormously.
Professional diving operations are usually formally planned and the plan documented as a legal record that due diligence has been done for health and safety purposes.Recreational dive planning may be less formal, but for complextechnical dives, can be as formal, detailed and extensive as most professional dive plans. A professional diving contractor will be constrained by the code of practice, standing orders or regulatory legislation covering a project or specific operations within a project, and is responsible for ensuring that the scope of work to be done is within the scope of the rules relevant to that work. A recreational (including technical) diver or dive group is generally less constrained, but nevertheless is almost always restricted by some legislation, and often also the rules of the organisations to which the divers are affiliated.
The planning of a diving operation may be simple or complex. In some cases the processes may have to be repeated several times before a satisfactory plan is achieved, and even then the plan may have to be modified on site to suit changed circumstances. The final product of the planning process may be formally documented or, in the case of recreational divers, an agreement on how the dive will be conducted. A diving project may consist of a number of related diving operations.
A documented dive plan may contain elements from the following list:
Divers using the anchor cable as an aid to depth control during a decompression stop during ascent.
To prevent or minimizedecompression sickness,divers must properly plan, conduct, and monitordecompression. Divers follow adecompression model to allow the release of excess inert gases dissolved in their body tissues at acceptable risk, which accumulated as a result of breathing at ambient pressures greater than surface atmospheric pressure. Decompression models take into account variables such as depth and time of dive,breathing gasses, altitude, and equipment to develop appropriate procedures for safe ascent.
Decompression may be continuous or staged, where the ascent is interrupted by stops at regular depth intervals, but the entire ascent is part of the decompression, and ascent rate can be critical to harmless elimination of inert gas. What is commonly known as no-decompression diving, or more accurately no-stop decompression, relies on limiting ascent rate for avoidance of excessive bubble formation. Staged decompression may include deep stops depending on the theoretical model used for calculating the ascent schedule. Omission of decompression theoretically required for a dive profile exposes the diver to significantly higher risk of symptomatic decompression sickness, and in severe cases, serious injury or death. The risk is related to the severity of exposure and the level of supersaturation of tissues in the diver. Procedures for emergency management of omitted decompression and symptomatic decompression sickness have been published. These procedures are generally effective, but vary in effectiveness from case to case.
The procedures used for decompression depend on the mode of diving, the availableequipment, the site and environment, and the actualdive profile. Standardized procedures have been developed which provide an acceptablelevel of risk in the circumstances for which they are appropriate. Different sets of procedures are used bycommercial,military,scientific andrecreational divers, though there is considerable overlap where similar equipment is used, and some concepts are common to all decompression procedures. In particular, all types of surface oriented diving benefited significantly from the acceptance of personaldive computers in the 1990s, which facilitateddecompression practice and allowed more complex dive profiles at acceptable levels of risk. (Full article...)
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The instructor monitors a trainee practicing diving skills. Scuba skills are skills required to dive safely using self-contained underwater breathing apparatus, known as ascuba set. Most of these skills are relevant to bothopen-circuit scuba andrebreather scuba, and many also apply tosurface-supplied diving. Some scuba skills, which are critical to divers' safety, may require more practice than standard recreational training provides to achieve reliable competence.
Some skills are generally accepted by recreationaldiver certification agencies as basic and necessary in order to dive without direct supervision. Others are more advanced, although somediver certification and accreditation organizations may require these to endorse entry-level competence. Instructors assess divers on these skills during basic and advanced training. Divers are expected to remain competent at their level of certification, either by practice or through refresher courses. Some certification organizations recommend refresher training if a diver has a lapse of more than six to twelve months without a dive.
Skill categories include selection, functional testing, preparation and transport of scuba equipment, dive planning, preparation for a dive, kitting up for the dive, water entry, descent, breathing underwater, monitoring the dive profile (depth, time, and decompression status) and progress of the dive, personal breathing gas management, situational awareness, communicating with the dive team, buoyancy and trim control, mobility in the water, ascent, emergency and rescue procedures, exit from the water, removal of equipment after the dive, cleaning and preparation of equipment for storage and recording the dive, within the scope of the diver's certification. (Full article...)
Filling cylinders with a mixture of gases has dangers for both the filler and the diver. During filling there is a risk of fire due to use of oxygen and a risk of explosion due to the use of high-pressure gases. The composition of the mix must be safe for the depth and duration of the planned dive. If the concentration of oxygen is too lean the diver may lose consciousness due tohypoxia and if it is too rich the diver may sufferoxygen toxicity. The concentration of inert gases, such as nitrogen and helium, are planned and checked to avoid nitrogen narcosis and decompression sickness.
Methods used include batch mixing by partial pressure or by mass fraction, and continuous blending processes. Completed blends are analysed for composition for the safety of the user. Gas blenders may be required by legislation to prove competence if filling for other persons. (Full article...)
Open-circuit scuba systems discharge the breathing gas into the environment as it is exhaled and consist of one or morediving cylinders containing breathing gas at high pressure which is supplied to the diver atambient pressure through adiving regulator. They may include additional cylinders for range extension,decompression gas oremergency breathing gas. Closed-circuit or semi-closed circuitrebreather scuba systems allow recycling of exhaled gases. The volume of gas used is reduced compared to that of open-circuit, making longer dives feasible. Rebreathers extend the time spent underwater compared to open-circuit for the same metabolic gas consumption. They produce fewer bubbles and less noise than open-circuit scuba, which makes them attractive to covertmilitary divers to avoid detection,scientific divers to avoid disturbing marine animals, andmedia diver to avoid bubble interference.
Scuba diving may be donerecreationally orprofessionally in several applications, including scientific, military and public safety roles, but mostcommercial diving uses surface-supplied diving equipment for breathing gas security when this is practicable. Scuba divers engaged in armed forces covert operations may be referred to asfrogmen, combat divers or attack swimmers.
Wreck diving isrecreational diving where thewreckage of ships, aircraft and other artificial structures are explored. The term is used mainly by recreational and technical divers. Professional divers, when diving on a shipwreck, generally refer to the specific task, such as salvage work, accident investigation or archaeological survey. Although most wreck dive sites are at shipwrecks, there is an increasing trend toscuttle retired ships to create artificial reef sites. Diving tocrashed aircraft can also be considered wreck diving. The recreation of wreck diving makes no distinction as to how the vessel ended up on the bottom.
Some wreck diving involvespenetration of the wreckage, making a direct ascent to the surface impossible for a part of the dive. (Full article...)
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A Navy buddy diver team checking their gauges together
Buddy diving is the use of thebuddy system byscuba divers andfreedivers. It is a set of safety procedures intended to improve the chances of avoiding or survivingaccidents in orunder water by having divers dive in a group of two or sometimes three. When using the buddy system, members of the group dive together and co-operate with each other, so that they can help orrescue each other in the event of an emergency. This is most effective if both divers are competent in all relevant skills and sufficiently aware of the situation that they can respond in time, which is a matter of both attitude and competence.
Inrecreational diving, a pair of divers is usually considered best for buddy diving. With threesomes, one diver can easily lose the attention of the other two, and groups of more than three divers are not using the buddy system. The system is likely to be effective in mitigating out-of-air emergencies, non-diving medical emergencies and entrapment inropes ornets. When used with thebuddy check it can help avoid the omission, misuse and failure ofdiving equipment.
Intechnical diving activities such ascave diving, threesomes are considered an acceptable practice. This is usually referred to as team diving to distinguish it from buddy diving in pairs. Freedivers may also operate in groups of three, to make more efficient use of dive time, as a recently surfaced diver requires recovery time before they are ready to stand by for another diver's dive.
When professional divers dive as buddy pairs their responsibility to each other is specified as part of standard operating procedures, code of practice or governing legislation. (Full article...)
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DiverTrevor Jackson returning from a 178 m (584 ft) wreck dive Technical diving (also referred to astec diving ortech diving) isscuba diving that exceeds theagency-specified limits ofrecreational diving for non-professional purposes. Technical diving may expose the diver to hazards beyond those normally associated with recreational diving, and to a greater risk of serious injury or death. Risk may be reduced by using suitable equipment and procedures, which require appropriate knowledge and skills. The required knowledge and skills are preferably developed through specialised training, adequate practice, and experience. The equipment involvesbreathing gases other thanair or standardnitrox mixtures, and multiple gas sources.
Most technical diving is done within the limits of training and previous experience, but by its nature, technical diving includes diving which pushes the boundaries of recognised safe practice, and new equipment and procedures are developed and honed by technical divers in the field. Where these divers are sufficiently knowledgeable, skilled, prepared and lucky, they survive and eventually their experience is integrated into the body of recognised practice.
The popularisation of the termtechnical diving has been credited to Michael Menduno, who was editor of the (now defunct) diving magazineaquaCorps Journal, but the concept and term,technical diving, go back at least as far as 1977, and divers have been engaging in what is now commonly referred to as technical diving for decades. (Full article...)
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Dive profile of an actual dive as recorded by a personal dive computer and displayed on a desktop screen using dive logging software. In this case depth is in metres. Adive profile is a description of a diver's pressure exposure over time. It may be as simple as just a depth and time pair, as in: "sixty for twenty," (abottom time of 20 minutes at a depth of 60 feet) or as complex as a second by second graphical representation of depth and time recorded by a personaldive computer. Several common types of dive profile are specifically named, and these may be characteristic of the purpose of the dive. For example, aworking dive at a limited location will often follow a constant depth (square) profile, and arecreational dive is likely to follow a multilevel profile, as the divers start deep and work their way up a reef to get the most out of the available breathing gas. The names are usually descriptive of the graphic appearance.
The intended dive profile is useful as aplanning tool as an indication of the risks ofdecompression sickness andoxygen toxicity for the exposure, to calculate a decompression schedule for the dive, and also for estimating the volume of open-circuitbreathing gas needed for a planned dive, as these depend in part upon the depth and duration of the dive. A dive profile diagram is conventionally drawn with elapsed time running from left to right and depth increasing down the page.
Many personaldive computers record the instantaneous depth at small time increments during the dive. This data can sometimes be displayed directly on the dive computer or more often downloaded to apersonal computer, tablet, or smartphone and displayed in graphic form as a dive profile. (Full article...)
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Scuba divers practicing buddy breathing technique during formal training Buddy breathing is a rescue technique used inscuba diving"out-of-gas" emergencies, when two divers share onedemand valve, alternately breathing from it. Techniques have been developed for buddy breathing from bothtwin-hose andsingle-hose regulators, but to a large extent it has been superseded by safer and more reliable techniques using additional equipment, such as the use of abailout cylinder or breathing through asecondary demand valve on the rescuer's regulator.
Running out ofbreathing gas most commonly happens as a result of poorgas management, but it can also happen due to unforeseen exertion, stress, or breathing equipment failure. Equipment failure resulting in the loss of all gas could be caused by failure of a pressure retaining component such as anO-ring orhose in the regulator or, in cold conditions, a freezing of water in the regulator resulting in afreeflow from the demand valve. The need for buddy breathing can be avoided by use of alternative techniques and equipment.
Buddy breathing originated frommilitary diving following a prohibition on the training and practice offree ascents. Minor variations on the basic technique were taught by different agencies at different times, and different techniques were needed for single hose and twin hose regulators. As buddy breathing has been found to require more intensive practice than is usually provided duringentry level training to be reliably used in a real emergency without endangering the buddy, and more reliable alternatives are affordably available, the procedure has been deprecated by most recreational diver training agencies in favour of more reliable and safer alternatives which are quicker to learn, and where appropriate,emergency swimming ascent.
The term has also been used for air sharing between scuba divers using an octopus demand valve, and between firefighting breathing apparatus. (Full article...)
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The hand signal "OK" Diver communications are the methods used bydivers to communicate with each other or with surface members of the dive team. Inprofessional diving, diver communication is usually between a single working diver and thediving supervisor at the surface control point. This is considered important both for managing the diving work, and as a safety measure for monitoring the condition of the diver. The traditional method of communication was by line signals, but this has been superseded by voice communication, and line signals are now used in emergencies when voice communications have failed. Surface supplied divers often carry a closed circuit video camera on thehelmet which allows the surface team to see what the diver is doing and to be involved in inspection tasks. This can also be used to transmit hand signals to the surface if voice communications fails. Underwater slates may be used to write text messages which can be shown to other divers, and there are some dive computers which allow a limited number of pre-programmed text messages to be sent through-water to other divers or surface personnel with compatible equipment.
Communication between divers and between surface personnel and divers is imperfect at best, and non-existent at worst, as a consequence of the physical characteristics of water. This prevents divers from performing at their full potential. Voice communication is the most generally useful format underwater, as visual forms are more affected by visibility, and written communication and signing are relatively slow and restricted by diving equipment.
Recreational divers do not usually have access to voice communication equipment, and it does not generally work with a standard scuba demand valve mouthpiece, so they use other signals. Hand signals are generally used when visibility allows, and there are a range of commonly used signals, with some variations. These signals are often also used by professional divers to communicate with other divers. There is also a range of other special purpose non-verbal signals, mostly used for safety and emergency communications. (Full article...)
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Solo diver surveying a dive site. The bailout cylinder can be seen slung at the diver's left side
Solo diving is the practice of self-sufficientunderwater diving without a "dive buddy", particularly with reference toscuba diving, but the term is also applied tofreediving. Professionally, solo diving has always been an option which depends on operational requirements and risk assessment.Surface supplied diving andatmospheric suit diving are commonly single diver underwater activities but are accompanied by an on-surfacesupport team dedicated to the safety of the diver, including astand-by diver, and are not considered solo diving in this sense.
Solo freediving has occurred formillennia as evidenced by artifacts dating back to the ancient people ofMesopotamia when people dived to gather food and to collect pearl oysters. It wasn't until the 1950s, with the development of formalised scuba diving training, that recreational solo diving was deemed to be dangerous, particularly for beginners. In an effort to mitigate associated risks, some scubacertification agencies incorporated the practice ofbuddy diving into theirdiver training programmes. The true risk of solo diving relative to buddy diving in the same environmental conditions has never been reliably established, and may have been significantly overstated by some organisations, though it is generally recognised that buddy and team diving, when performed as specified in the manuals, will enhance safety to some extent depending on circumstances.
Some divers, typically those with advancedunderwater skills, prefer solo diving over buddy diving and acknowledge responsibility for their own safety. One of the more controversial reasons given being the uncertain competence of arbitrarily allocated dive buddies imposed on divers by service providers protected from liability by waivers. Others simply prefer solitude while communing with nature, or find the burden of continuously monitoring another person reduces their enjoyment of the activity, or engage in activities which are incompatible with effective buddy diving practices, and accept the possibility of slightly increased risk, just as others accept the increased risk associated with deeper dives, planned decompression, or penetration under an overhead.
The recreational solo diver uses enhanced procedures, skills and equipment to mitigate the risks associated with not having another competent diver immediately available to assist if something goes wrong. The skills and procedures may be learned through a variety of effective methods to achieve appropriate competence, including formal training programmes with associated assessment and certification. Recreational solo diving, once discouraged by most training agencies, has been accepted since the late 1990s by some agencies that will train and certify experienced divers skilled in self-sufficiency and the use of redundant backupscuba equipment. In most countries there is no legal impediment to solo recreational diving, with or without certification. (Full article...)
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In-water recompression (IWR) orunderwater oxygen treatment is the emergency treatment ofdecompression sickness (DCS) by returning thediverunderwater to help the gas bubbles in the tissues, which are causing the symptoms, to resolve. It is a procedure that exposes the diver to significantrisk which should be compared with the risk associated with the available options and balanced against the probable benefits. Some authorities recommend that it is only to be used when the time totravel to the nearestrecompression chamber is too long to save the victim's life; others take a more pragmatic approach and accept that in some circumstances IWR is the best available option. The risks may not be justified for case of mild symptoms likely to resolve spontaneously, or for cases where the diver is likely to be unsafe in the water, but in-water recompression may be justified in cases where severe outcomes are likely if not recompressed, if conducted by a competent and suitably equipped team.
Carrying out in-water recompression when there is a nearbyrecompression chamber or without suitable equipment and training is never a desirable option. The risk of the procedure is due to the diver suffering from DCS being seriously ill and may becomeparalysed,unconscious, orstop breathing while underwater. Any one of these events is likely to result in the diverdrowning or asphyxiating or suffering further injury during a subsequent rescue to the surface. This risk can be reduced by improving airway security by using surface supplied gas and a helmet or full-face mask. Risk of injury during emergency surfacing is minimised by treatment on 100% oxygen, which is also the only gas with a reliable record of positive outcomes. Early recompression on oxygen has a high rate of complete resolution of symptoms, even for shallower and shorter treatment than the highly successful US Navy Treatment Table 6.
Several schedules have been published for in-water recompression treatment, but little data on their efficacy is available. The Australian Navy tables and US Navy Tables may have the largest amount of empirical evidence supporting their efficacy. (Full article...)
Inphysical chemistry,supersaturation occurs with asolution when the concentration of asolute exceeds theconcentration specified by the value ofsolubility atequilibrium. Most commonly the term is applied to a solution of asolid in aliquid, but it can also be applied to liquids andgases dissolved in a liquid. A supersaturated solution is in ametastable state; it may return to equilibrium byseparation of the excess of solute from the solution, by dilution of the solution by adding solvent, or by increasing the solubility of the solute in the solvent. (Full article...)
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Upwelling is anoceanographic phenomenon that involveswind-driven motion of dense, cooler, and usually nutrient-richwater from deep water towards theocean surface. It replaces the warmer and usually nutrient-depletedsurface water. The nutrient-rich upwelled water stimulates the growth and reproduction ofprimary producers such asphytoplankton. Thebiomass of phytoplankton and the presence of cool water in those regions allow upwelling zones to be identified by coolsea surface temperatures (SST) and high concentrations ofchlorophyll a.
The increased availability of nutrients in upwelling regions results in high levels ofprimary production and thusfishery production. Approximately 25% of the total globalmarine fish catches come from five upwellings, which occupy only 5% of the total ocean area. Upwellings that are driven by coastalcurrents or diverging open ocean have the greatest impact on nutrient-enriched waters and global fishery yields. (Full article...)
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Simplified schematic of only the lunar portion of Earth's tides, showing (exaggerated) high tides at the sublunar point and itsantipode for the hypothetical case of an ocean of constant depth without land, and on the assumption that Earth is not rotating; otherwise there is a lag angle. Solar tides not shown. Tides are the rise and fall ofsea levels caused by the combined effects of thegravitational forces exerted by theMoon (and to a much lesser extent, theSun) and are also caused by theEarth andMoon orbiting one another.
Tide tables can be used for any given locale to find the predicted times andamplitude (or "tidal range"). The predictions are influenced by many factors including the alignment of the Sun and Moon, thephase and amplitude of the tide (pattern of tides in the deep ocean), theamphidromic systems of the oceans, and the shape of thecoastline and near-shorebathymetry (seeTiming). They are however only predictions, and the actual time and height of the tide is affected by wind andatmospheric pressure. Many shorelines experiencesemi-diurnal tides—two nearly equal high and low tides each day. Other locations have adiurnal tide—one high and low tide each day. A "mixed tide"—two uneven magnitude tides a day—is a third regular category.
Tides vary on timescales ranging from hours to years due to a number of factors, which determine thelunitidal interval. To make accurate records,tide gauges at fixed stations measure water level over time. Gauges ignore variations caused by waves with periods shorter than minutes. These data are compared to the reference (or datum) level usually calledmean sea level.
While tides are usually the largest source of short-term sea-level fluctuations, sea levels are also subject to change fromthermal expansion, wind, and barometric pressure changes, resulting instorm surges, especially in shallow seas and near coasts.
Tidal phenomena are not limited to the oceans, but can occur in other systems whenever a gravitational field that varies in time and space is present. For example, the shape of the solid part of the Earth is affected slightly byEarth tide, though this is not as easily seen as the water tidal movements. (Full article...)
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Work of breathing (WOB) is the energy expended toinhale andexhale abreathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not particularly useful without a reference to volume or time. It can be calculated in terms of the pulmonary pressure multiplied by the change in pulmonary volume, or in terms of the oxygen consumption attributable to breathing.
In a normal resting state the work of breathing constitutes about 5% of the total body oxygen consumption. It can increase considerably due to illness or constraints on gas flow imposed bybreathing apparatus,ambient pressure, orbreathing gas composition. (Full article...)
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Graph showing a tropical ocean thermocline (depth vs. temperature). Note the rapid change between 100 and 1000 meters. The temperature is nearly constant after 1500 meters depth.
Athermocline (also known as thethermal layer or themetalimnion in lakes) is a distinct layer based on temperature within a large body of fluid (e.g.water, as in an ocean or lake; or air, e.g. anatmosphere) with a high gradient of distinct temperature differences associated with depth. In theocean, the thermocline divides the uppermixed layer from the calm deep water below.
Depending largely onseason,latitude, andturbulent mixing bywind, thermoclines may be a semi-permanent feature of thebody of water in which they occur, or they may form temporarily in response to phenomena such as the radiativeheating/cooling of surface water during the day/night. Factors that affect the depth and thickness of a thermocline includeseasonal weather variations, latitude, and local environmental conditions, such astides andcurrents. (Full article...)
Diving reflex in a humanbaby Thediving reflex, also known as thediving response andmammalian diving reflex, is a set ofphysiological responses to immersion that overrides the basichomeostaticreflexes, and is found in all air-breathing vertebrates studied to date. It optimizesrespiration by preferentially distributing oxygen stores to the heart and brain, enabling submersion for an extended time.
The diving reflex is triggered specifically by chilling and wetting thenostrils and face while breath-holding, and is sustained via neural processing originating in thecarotid chemoreceptors. The most noticeable effects are on the cardiovascular system, which displays peripheral vasoconstriction, slowed heart rate, redirection of blood to the vital organs to conserve oxygen, release of red blood cells stored in thespleen, and, in humans, heart rhythm irregularities. Although aquatic animals have evolved profound physiological adaptations to conserve oxygen during submersion, theapnea and its duration,bradycardia,vasoconstriction, and redistribution ofcardiac output occur also in terrestrial animals as a neural response, but the effects are more profound in natural divers. (Full article...)
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Example of a dissolved solid (left) Inchemistry,solubility is the ability of asubstance, thesolute, to form asolution with another substance, thesolvent.Insolubility is the opposite property, the inability of the solute to form such a solution.
The extent of the solubility of a substance in a specific solvent is generally measured as theconcentration of the solute in asaturated solution, one in which no more solute can be dissolved. At this point, the two substances are said to be at thesolubility equilibrium. For some solutes and solvents, there may be no such limit, in which case the two substances are said to be "miscible in all proportions" (or just "miscible").
The solute can be asolid, aliquid, or agas, while the solvent is usually solid or liquid. Both may be pure substances, or may themselves be solutions. Gases are always miscible in all proportions, except in very extreme situations, and a solid or liquid can be "dissolved" in a gas only by passing into the gaseous state first.
The solubility mainly depends on the composition of solute and solvent (including theirpH and the presence of other dissolved substances) as well as on temperature and pressure. The dependency can often be explained in terms of interactions between the particles (atoms,molecules, orions) of the two substances, and ofthermodynamic concepts such asenthalpy andentropy.
Under certain conditions, the concentration of the solute can exceed its usual solubility limit. The result is asupersaturated solution, which ismetastable and will rapidly exclude the excess solute if a suitablenucleation site appears.
The concept of solubility does not apply when there is an irreversiblechemical reaction between the two substances, such as the reaction ofcalcium hydroxide withhydrochloric acid; even though one might say, informally, that one "dissolved" the other. The solubility is also not the same as therate of solution, which is how fast a solid solute dissolves in a liquid solvent. This property depends on many other variables, such as the physical form of the two substances and the manner and intensity of mixing.
The concept and measure of solubility are extremely important in many sciences besides chemistry, such asgeology,biology,physics, andoceanography, as well as inengineering,medicine,agriculture, and even in non-technical activities likepainting,cleaning,cooking, andbrewing. Most chemical reactions of scientific, industrial, or practical interest only happen after thereagents have been dissolved in a suitable solvent.Water is by far the most common such solvent.
The term "soluble" is sometimes used for materials that can formcolloidal suspensions of very fine solid particles in a liquid. The quantitative solubility of such substances is generally not well-defined, however. (Full article...)
Thephysiology of underwater diving is the physiological adaptations to diving of air-breathingvertebrates that have returned to the ocean from terrestrial lineages. They are a diverse group that includesea snakes,sea turtles, themarine iguana,saltwater crocodiles,penguins,pinnipeds,cetaceans,sea otters,manatees anddugongs. All known diving vertebrates dive to feed, and the extent of the diving in terms of depth and duration are influenced by feeding strategies, but also, in some cases, with predator avoidance. Diving behaviour is inextricably linked with the physiological adaptations for diving and often the behaviour leads to an investigation of the physiology that makes the behaviour possible, so they are considered together where possible. Most diving vertebrates make relatively short shallow dives. Sea snakes, crocodiles, and marine iguanas only dive in inshore waters and seldom dive deeper than 10 meters (33 feet). Some of these groups can make much deeper and longer dives.Emperor penguins regularly dive to depths of 400 to 500 meters (1,300 to 1,600 feet) for 4 to 5 minutes, often dive for 8 to 12 minutes, and have a maximum endurance of about 22 minutes.Elephant seals stay at sea for between 2 and 8 months and dive continuously, spending 90% of their time underwater and averaging 20 minutes per dive with less than 3 minutes at the surface between dives. Their maximum dive duration is about 2 hours and they routinely feed at depths between 300 and 600 meters (980 and 1,970 feet), though they can exceed depths of 1,600 meters (5,200 feet).Beaked whales have been found to routinely dive to forage at depths between 835 and 1,070 meters (2,740 and 3,510 feet), and remain submerged for about 50 minutes. Their maximum recorded depth is 1,888 meters (6,194 feet), and the maximum duration is 85 minutes.
Air-breathingmarine vertebrates that dive to feed must deal with the effects of pressure at depth,hypoxia duringapnea, and the need to find and capture their food. Adaptations to diving can be associated with these three requirements. Adaptations to pressure must deal with the mechanical effects of pressure on gas-filled cavities,solubility changes of gases under pressure, and possible direct effects of pressure on the metabolism, while adaptations tobreath-hold capacity include modifications to metabolism,perfusion, carbon dioxide tolerance, and oxygen storage capacity. Adaptations to find and capture food vary depending on the food, but deep-diving generally involves operating in a dark environment.
Diving vertebrates have increased the amount of oxygen stored in their internal tissues. This oxygen store has three components; oxygen contained in the air in the lungs, oxygen stored byhaemoglobin in the blood, and bymyoglobin, in muscle tissue, The muscle and blood of diving vertebrates have greater concentrations of haemoglobin and myoglobin than terrestrial animals. Myoglobin concentration in locomotor muscles of diving vertebrates is up to 30 times more than in terrestrial relatives. Haemoglobin is increased by both a relatively larger amount of blood and a larger proportion of red blood cells in the blood compared with terrestrial animals. The highest values are found in the mammals which dive deepest and longest.
Body size is a factor in diving ability. A larger body mass correlates to a relatively lowermetabolic rate, while oxygen storage is directly proportional to body mass, so larger animals should be able to dive for longer, all other things being equal. Swimming efficiency also affects diving ability, as low drag and high propulsive efficiency requires less energy for the same dive. Burst and glidelocomotion is also often used to minimise energy consumption, and may involve using positive or negativebuoyancy to power part of the ascent or descent.
The responses seen in seals diving freely at sea are physiologically the same as those seen during forced dives in the laboratory. They are not specific to immersion in water, but are protective mechanisms againstasphyxia which are common to all mammals but more effective and developed in seals. The extent to which these responses are expressed depends greatly on the seal's anticipation of dive duration. The regulation ofbradycardia andvasoconstriction of the dive response in both mammals anddiving ducks can be triggered by facial immersion, wetting of the nostrils andglottis, or stimulation oftrigeminal andglossopharyngeal nerves. Animals cannot convert fats to glucose, and in many diving animals, carbohydrates are not readily available from the diet, nor stored in large quantities, so as they are essential foranaerobic metabolism, they could be a limiting factor.
Decompression sickness (DCS) is a disease associated with metabolically inert gas uptake at pressure, and its subsequent release into the tissues in the form of bubbles. Marine mammals were thought to be relatively immune to DCS due to anatomical, physiological and behavioural adaptations that reduce tissue loading with dissolved nitrogen during dives, but observations show that gas bubbles may form, and tissue injury may occur under certain circumstances. Decompression modelelling using measured dive profiles predict the possibility of high blood and tissue nitrogen tensions. (Full article...)
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Dead space is the volume of air that is inhaled that does not take part in the gas exchange, because it either remains in the conducting airways or reaches alveoli that arenot perfused or poorly perfused. It means that not all the air in eachbreath is available for the exchange ofoxygen andcarbon dioxide.Mammals breathe in and out of their lungs, wasting that part of the inhalation which remains in the conducting airways where no gas exchange can occur. (Full article...)
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Theatmospheric pressure is roughly equal to the sum of partial pressures of constituent gases – oxygen, nitrogen,argon,water vapor, carbon dioxide, etc.
In a mixture ofgases, each constituent gas has apartial pressure which is the notionalpressure of that constituent gas as if it alone occupied the entirevolume of the original mixture at the sametemperature. Thetotal pressure of anideal gas mixture is the sum of the partial pressures of the gases in the mixture (Dalton's Law).
Inrespiratory physiology, the partial pressure of a dissolved gas in liquid (such as oxygen in arterial blood) is also defined as the partial pressure of that gas as it would be undissolved in gas phase yet in equilibrium with the liquid. This concept is also known asblood gas tension. In this sense, the diffusion of a gas liquid is said to be driven by differences in partial pressure (not concentration). Inchemistry andthermodynamics, this concept is generalized to non-ideal gases and instead calledfugacity. The partial pressure of a gas is a measure of itsthermodynamic activity. Gases dissolve, diffuse, and react according to their partial pressures and not according to theirconcentrations in a gas mixture or as a solute in solution. This general property of gases is also true in chemical reactions of gases in biology. (Full article...)
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Turbidity standards of 5, 50, and 500 NTU Turbidity is the cloudiness orhaziness of afluid caused by large numbers of individualparticles that are generally invisible to thenaked eye, similar tosmoke in air. The measurement of turbidity is a key test of bothwater clarity andwater quality.
Fluids can contain suspended solid matter consisting of particles of many different sizes. While some suspended material will be large enough and heavy enough to settle rapidly to the bottom of the container if a liquid sample is left to stand (thesettable solids), very small particles will settle only very slowly or not at all if the sample is regularly agitated or the particles arecolloidal. These small solid particles cause the liquid to appear turbid.
Turbidity (or haze) is also applied to transparent solids such as glass or plastic. In plastic production, haze is defined as the percentage of light that is deflected more than 2.5° from the incoming light direction. (Full article...)
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Signs explaining how to escape from a rip current, posted atMission Beach, San Diego,California Arip current (or justrip) is a specific type of water current that can occur near beaches where waves break. A rip is a strong, localized, and narrow current of water that moves directly away from theshore by cutting through the lines of breaking waves, like a river flowing out to sea. The force of the current in a rip is strongest and fastest next to the surface of the water.
Rip currents can be hazardous to people in the water. Swimmers who are caught in a rip current and who do not understand what is happening, or who may not have the necessary water skills, may panic, or they may exhaust themselves by trying to swim directly against the flow of water. Because of these factors, rip currents are the leading cause of rescues by lifeguards at beaches. In the United States they cause an average of 71 deaths by drowning per year between 2013 and 2022.
A rip current is not the same thing asundertow, although that term is used incorrectly when referred to a rip current. Contrary to popular belief, neither rip nor undertow can pull a person down and hold them under the water. A rip simply carries floating objects, including people, out to just beyond the zone of the breaking waves, at which point the current dissipates and releases everything it is carrying. (Full article...)
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Scuba diver with bifocal lenses fitted to a mask
Underwater vision is the ability to see objectsunderwater, and this is significantly affected by several factors. Underwater, objects are less visible because of lower levels of natural illumination caused by rapidattenuation oflight with distance passed through the water. They are also blurred by scattering of light between the object and the viewer, also resulting in lower contrast. These effects vary with wavelength of the light, and color and turbidity of the water. The vertebrate eye is usually either optimised for underwater vision or air vision, as is the case in the human eye. The visual acuity of the air-optimised eye is severely adversely affected by the difference in refractive index between air and water when immersed in direct contact. Provision of an airspace between the cornea and the water can compensate, but has the side effect of scale and distance distortion. The diver learns to compensate for these distortions. Artificial illumination is effective to improve illumination at short range.
Stereoscopic acuity, 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 associated loss of hand-eye coordination. At very short range in clear water distance is underestimated, in accordance with magnification due to refraction through the flat lens of the mask, but at greater distances - greater than arm's reach, the distance tends to be overestimated to a degree influenced by turbidity. Both relative and absolutedepth perception are reduced underwater. Loss of contrast results in overestimation, and magnification effects account for underestimation at short range. Divers can to a large extent adapt to these effects over time and with practice.
Light rays bend when they travel from one medium to another; the amount of bending is determined by therefractive indices of the two media. If one medium has a particular curved shape, it functions as alens. Thecornea, humours, andcrystalline lens of the eye together form a lens that focuses images on theretina. The eye of most land animals is adapted for viewing in air. Water, however, has approximately the same refractive index as the cornea (both about 1.33), effectively eliminating the cornea's focusing properties. When immersed in water, instead of focusing images on the retina, they are focused behind the retina, resulting in an extremely blurred image fromhypermetropia. This is largely avoided by having an air space between the water and the cornea, trapped inside the mask or helmet.
Water attenuates light due to absorption and as light passes through water colour is selectively absorbed by the water. Color absorption is also affected by turbidity of the water and dissolved material. Water preferentially absorbs red light, and to a lesser extent, yellow, green and violet light, so the color that is least absorbed by water is blue light. Particulates and dissolved materials may absorb different frequencies, and this will affect the color at depth, with results such as the typically green color in many coastal waters, and the dark red-brown color of many freshwater rivers and lakes due to dissolved organic matter.
Visibility is a term which generally predicts the ability of some human, animal, or instrument to optically detect an object in the given environment, and may be expressed as a measure of the distance at which an object or light can be discerned. Factors affecting visibility include illumination, length of the light path, particles which cause scattering, dissolved pigments which absorb specific colours, and salinity and temperature gradients which affect refractive index. Visibility can be measured in any arbitrary direction, and for various colour targets, but horizontal visibility of a black target reduces the variables and meets the requirements for a straight-forward and robust parameter for underwater visibility. Instruments are available for field estimates of visibility from the surface, which can inform the dive team on probable complications. (Full article...)
A SEAL Delivery Team member climbs aboard a delivery vehicle before launching from the back of the submarineUSSPhiladelphia. Afrogman is someone who is trained inscuba diving orswimming underwater. The term often applies more to professional rather than recreational divers, especially those working in a tactical capacity that includesmilitary, and in some European countries,police work. Such personnel are also known by the more formal names ofcombat diver,combatant diver, orcombat swimmer. The wordfrogman first arose in the stage name the "Fearless Frogman" ofPaul Boyton in the 1870s and later was claimed byJohn Spence, an enlisted member of the U.S. Navy and member of theOSS Maritime Unit, to have been applied to him while he was training in a green waterproof suit.
The termfrogman is occasionally used to refer to a civilian scuba diver, such as in apolice diving role.
In the United Kingdom, police divers have often been called "police frogmen". Some countries' tactical diver organizations include a translation of the wordfrogman in their official names, e.g., Denmark'sFrømandskorpset; others call themselves "combat divers" or similar. (Full article...)
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Nesconset fire department scuba rescue team on training exercise
Public safety diving isunderwater diving conducted as part oflaw enforcement andfire/rescue. Public safety divers differ from recreational, scientific and commercial divers who can generally plan the date, time, and location of a dive, and dive only if the conditions are conducive to the task. Public safety divers respond to emergencies 24 hours a day, 7 days a week, and may be required to dive in the middle of the night, during inclement weather, in zero visibility "black water," or in waters polluted by chemicals and biohazards. (Full article...)
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NYPD divers removing material from theHarlem Meer following a murder in the area few days prior. Police diving is a branch ofprofessional diving carried out bypolice services. Police divers are usually professional police officers, and may either be employed full-time as divers or as generalwater police officers, or be volunteers who usually serve in other units but are called in if their diving services are required.
The duties carried out by police divers include rescue diving for underwater casualties, under the general classification ofpublic safety diving, and forensic diving, which is search and recovery diving forevidence and bodies. (Full article...)
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Instructor and learner divers practicing scuba skills in confined water
Depending on the jurisdiction, there will generally be specific published codes of practice and guidelines for training, competence and registration of diving instructors, as they have a duty of care to their clients, and operate in an environment with intrinsic hazards which may be unfamiliar to the lay person. Training and assessment will generally follow adiver training standard, and may use adiver training manual as source material.
Recreational diving instructors are usually registered members of one or more recreational diver certification agencies, and are generally registered to train and assess divers against specified certification standards. Originally these standards were at the discretion of each training and certification agency, but inter-agency and international standards now exist to ensure that the basic skills required for acceptable safety are included as a minimum standard for both instructors and recreational divers. Military diving instructors are generally members of the armed force for which they train personnel. Commercial diving instructors may be required to register with national government appointed organisations, and comply with specific training and assessment standards, but there may be other requirements in some parts of the world. (Full article...)
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Underwater welding Hyperbaric welding is the process of extremewelding at elevatedpressures, normallyunderwater. Hyperbaric welding can either take placewet in the water itself ordry inside a specially constructedpositive pressure enclosure and hence a dry environment. It is predominantly referred to as "hyperbaric welding" when used in a dry environment, and "underwater welding" when in a wet environment. The applications of hyperbaric welding are diverse—it is often used to repairships, offshoreoil platforms, andpipelines.Steel is the most common material welded.
Dry welding is used in preference to wet underwater welding when high quality welds are required because of the increased control over conditions which can be maintained, such as through application of prior and post weldheat treatments. This improved environmental control leads directly to improved process performance and a generally much higher quality weld than a comparative wet weld. Thus, when a very high quality weld is required, dry hyperbaric welding is normally utilized. Research into using dry hyperbaric welding at depths of up to 1,000 metres (3,300 ft) is ongoing. In general, assuring the integrity of underwater welds can be difficult (but is possible using variousnondestructive testing applications), especially for wet underwater welds, because defects are difficult to detect if the defects are beneath the surface of the weld.
Public safety diving team members bring in a casualty Underwater search and recovery is the process of locating and recoveringunderwater objects, often bydivers, but also by the use of submersibles, remotely operated vehicles and electronic equipment on surface vessels.
Most underwater search and recovery is done byprofessional divers as part of commercialmarine salvage operations, military operations, emergency services, or law enforcement activities.
Minor aspects of search and recovery are also considered within the scope of recreational diving. (Full article...)
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NAUI Nitrox diver certification card
ADiving certification orC-card is adocument (usually a wallet sizedplastic card) recognizing that an individual or organization authorized to do so, "certifies" that the bearer has completed a course of training as required by the agency issuing the card. This is assumed to represent a defined level of skill and knowledge inunderwater diving. Divers carry a qualification record orcertification card which may be required to prove their qualifications when booking a dive trip, hiringscuba equipment, havingdiving cylinders filled, or in the case of professional divers, seeking employment.
Although recreational certifications are issued by numerous differentdiver training agencies, the entry-level grade is not always equivalent. Different agencies will have different entry-level requirements as well as different higher-level grades, but all are claimed to allow a diver to develop their skills and knowledge in achievable steps.
In contradistinction, adiver's logbook, or the electronic equivalent, is primarily evidence of range of diving experience. (Full article...)
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AUS Navy diver at work. The umbilical supplying air from the surface is clearly visible.
Professional diving isunderwater diving where the divers are paid for their work.Occupational diving has a similar meaning and applications. Theprocedures are often regulated by legislation and codes of practice as it is an inherentlyhazardous occupation and the diver works as a member of ateam. Due to the dangerous nature of some professional diving operations, specialized equipment such as an on-sitehyperbaric chamber and diver-to-surface communication system is often required by law, and themode of diving for some applications may be regulated.
Underwater photography can also be categorized as an art form and a method for recording data. Successful underwater imaging is usually done with specialized equipment and techniques. However, it offers exciting and rare photographic opportunities. Animals such as fish andmarine mammals are common subjects, but photographers also pursueshipwrecks, submerged cave systems, underwater "landscapes",invertebrates,seaweeds, geological features, andportraits of fellow divers. (Full article...)
Scuba diving education levels as used by ISO, PADI, CMAS, SSI and NAUI Recreational diver training is the process of developing knowledge and understanding of the basic principles, and the skills and procedures for the use ofscuba equipment so that the diver is able todive for recreational purposes with acceptable risk using the type of equipment and in similar conditions to those experienced during training.
Not only is the underwater environmenthazardous but the diving equipment itself can be dangerous. There are problems that divers must learn to avoid and manage when they do occur. Divers need repeated practice and a gradual increase in challenge to develop and internalise the skills needed to control the equipment, to respond effective if they encounter difficulties, and to build confidence in their equipment and themselves. Diver practical training starts with simple but essential procedures, and builds on them until complex procedures can be managed effectively. This may be broken up into several short training programmes, with certification issued for each stage, or combined into a few more substantial programmes with certification issued when all the skills have been mastered.
Many diver training organizations exist, throughout the world, offering diver training leading to certification: the issuing of a "diving certification card," also known as a "C-card," or qualification card. This diving certification model originated atScripps Institution of Oceanography in 1952 after two divers died while using university-owned equipment and the SIO instituted a system where a card was issued after training as evidence of competence. Diving instructors affiliated to a diving certification agency may work independently or through a university, a dive club, a dive school or a dive shop.
They will offer courses that should meet or exceed the standards of thecertification organization that will certify the divers attending the course. TheInternational Organization for Standardization has approved six recreational diving standards that may be implemented worldwide, and some of the standards developed by the(United States) RSTC are consistent with the applicable ISO Standards:
The initial open water training for a person who ismedically fit to dive and a reasonably competent swimmer is relatively short. Many dive shops in popular holiday locations offer courses intended to teach a novice to dive in a few days, which can be combined with diving on the vacation. Other instructors and dive schools will provide more thorough training, which generally takes longer. Dive operators,dive shops, and cylinder filling stations may refuse to allow uncertified people to dive with them, hire diving equipment or have theirdiving cylinders filled. This may be an agency standard, company policy, or specified by legislation. (Full article...)
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Drawing to scale, underwater Underwater archaeology isarchaeology practicedunderwater. As with all other branches of archaeology, it evolved from its roots in pre-history and in theclassical era to include sites from the historical and industrial eras.
Its acceptance has been a relatively late development due to the difficulties of accessing and working underwater sites, and because the application of archaeology to underwater sites initially emerged from the skills and tools developed by shipwreck salvagers. As a result, underwater archaeology initially struggled to establish itself as actual archaeological research. This changed when universities began teaching the subject and a theoretical and practical base for the sub-discipline was firmly established in the late 1980s.
Underwater archaeology now has a number of branches including,maritime archaeology: the scientifically based study of pasthuman life, behaviors and cultures and their activities in, on, around and (lately) under the sea, estuaries and rivers. This is most often effected using the physical remains found in, around or undersalt orfresh water or buried beneath water-loggedsediment. In recent years, the study of submergedWWII sites and of submerged aircraft in the form of underwateraviation archaeology have also emerged as bona fide activity.
Though often mistaken as such, underwater archaeology is not restricted to the study ofshipwrecks. Changes insea level because of localseismic events such as the earthquakes that devastatedPort Royal andAlexandria or more widespreadclimatic changes on acontinental scale mean that some sites of human occupation that were once on dry land are now submerged. At the end of the last ice age, theNorth Sea was a great plain, andanthropological material, as well as the remains of animals such asmammoths, are sometimes recovered by trawlers. Also, because human societies have always made use of water, sometimes the remains of structures that these societies built underwater still exist (such as the foundations ofcrannogs,bridges andharbors) when traces on dry land have been lost. As a result, underwaterarchaeological sites cover a vast range including: submerged indigenous sites and places where people once lived or visited that have been subsequently covered by water due to risingsea levels; wells,cenotes, wrecks (shipwrecks;aircraft); the remains of structures created in water (such as crannogs, bridges or harbors); other port-related structures;refuse ordebris sites where people disposed of theirwaste, garbage and other items, such as ships, aircraft, munitions and machinery, bydumping into the water.
Underwater archaeology is often complementary to archaeological research on terrestrial sites because the two are often linked by many and various elements including geographic, social, political, economic and other considerations. As a result, a study of an archaeological landscape can involve a multidisciplinary approach requiring the inclusion of many specialists from a variety of disciplines includingprehistory,historical archaeology,maritime archaeology, andanthropology. There are many examples. One is the wreck of the VOC shipZuytdorp lost in 1711 on the coast of Western Australia, where there remains considerable speculation that some of the crew survived and, after establishing themselves on shore, intermixed with indigenous tribes from the area. The archaeological signature at this site also now extends into the interaction between indigenous people and the Europeanpastoralists who entered the area in the mid-19th century. (Full article...)
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Adivemaster (DM) is a role that includes organising and leading recreational dives, particularly in a professional capacity, and is a qualification used in many parts of the world in recreationalscuba diving for a diver who has supervisory responsibility for a group of divers and as a dive guide. As well as being a generic term, 'Divemaster' is the title of the first professional rating of manytraining agencies, such asPADI,SSI,SDI,NASE, exceptNAUI, which rates a NAUI Divemaster under a NAUI Instructor but above a NAUI Assistant Instructor. The divemaster certification is generally equivalent to the requirements ofISO 24801-3Dive Leader.
The British Sub-Aqua Club (BSAC) recognizes several agencies' divemaster certificates as equivalent to BSAC Dive Leader, but not to BSAC Advanced Diver. The converse may not be true.
The certification is a prerequisite for training as an instructor inrecreational diving with the professional agencies exceptNAUI, where it is an optional step, because of the different position of the NAUI Divemaster in the NAUI hierarchy. (Full article...)
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Underwater videographer Underwater videography is the branch of electronicunderwater photography concerned with capturingunderwater moving images as arecreational diving, scientific, commercial,documentary, orfilmmaking activity. Although technological changes since 1909 have improved the ease of operation and quality of images, significant challenges in the form of protecting equipment from water, low light levels, and the usual hazards of diving must be addressed. (Full article...)
Underwater ice hockey (also calledsub-aqua ice hockey) is a minorextreme sport that is a variant ofice hockey. It is played upside-down underneath frozen pools or ponds. Participants weardiving masks,fins, andwetsuits and use the underside of the frozen surface as the playing area orrink for a floating puck. Competitors do not use any breathing apparatus but instead surface for air every 30 seconds or so.
US Navy servicemen practiseunderwater search and rescue scenarios involving combative or panicky victims, which corresponds to certain aquathlonic disciplines
Aquathlon (also known asunderwater wrestling) is anunderwater sport, where two competitors wearing masks and fins wrestle underwater in an attempt to remove a ribbon from each other's ankle band in order to win the bout. The "combat" takes place in a 5-metre (16 ft) square ring within a swimming pool, and is made up of three 30-second rounds, with a fourth round played in the event of a tie. The sport originated during the 1980s in the former USSR (now Russia) and was first played at international level in 1993. It was recognised by theConfédération Mondiale des Activités Subaquatiques (CMAS) in 2008. Combat aquathlon practice training engagements not onlyunder water, but also afloat, above the water surface, both with or withoutdiving gear, utilizing dummy weapons (rubber knives, bayonetted rifles, etc.) or barehanded, combined with grappling and choking techniques in order to neutralize orsubmit the opponent. (Full article...)
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Sport diving is anunderwater sport that uses recreationalopen circuitscuba diving equipment and consists of a set of individual and team events conducted in aswimming pool that test the competitors' competency in recreational scuba diving techniques. The sport was developed in Spain during the late 1990s and is currently played mainly in Europe. It is known asPlongée Sportive en Piscine in French and asBuceo De Competición in Spanish. (Full article...)
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DiverTrevor Jackson returning from a 178 m (584 ft) wreck dive Technical diving (also referred to astec diving ortech diving) isscuba diving that exceeds theagency-specified limits ofrecreational diving for non-professional purposes. Technical diving may expose the diver to hazards beyond those normally associated with recreational diving, and to a greater risk of serious injury or death. Risk may be reduced by using suitable equipment and procedures, which require appropriate knowledge and skills. The required knowledge and skills are preferably developed through specialised training, adequate practice, and experience. The equipment involvesbreathing gases other thanair or standardnitrox mixtures, and multiple gas sources.
Most technical diving is done within the limits of training and previous experience, but by its nature, technical diving includes diving which pushes the boundaries of recognised safe practice, and new equipment and procedures are developed and honed by technical divers in the field. Where these divers are sufficiently knowledgeable, skilled, prepared and lucky, they survive and eventually their experience is integrated into the body of recognised practice.
The popularisation of the termtechnical diving has been credited to Michael Menduno, who was editor of the (now defunct) diving magazineaquaCorps Journal, but the concept and term,technical diving, go back at least as far as 1977, and divers have been engaging in what is now commonly referred to as technical diving for decades. (Full article...)
Recreational diver over a coral reef in the Red Sea Recreational dive sites are specific places that recreationalscuba divers go to enjoy the underwater environment or for training purposes. They includetechnical diving sites beyond the range generally accepted forrecreational diving. In this context all diving done for recreational purposes is included.Professional diving tends to be done where the job is, and with the exception ofdiver training andleading groups of recreational divers, does not generally occur at specific sites chosen for their easy access, pleasant conditions or interesting features.
Recreational dive sites may be found in a wide range of bodies of water, and may be popular for various reasons, includingaccessibility,biodiversity, spectacular topography,historical or cultural interest and artifacts (such asshipwrecks), andwater clarity. Tropical waters of high biodiversity and colourful sea life are popularrecreational diving tourism destinations. South-east Asia, the Caribbean islands, the Red Sea and the Great Barrier Reef of Australia are regions where the clear, warm, waters, reasonably predictable conditions and colourful and diverse sea life have made recreational diving an economically important tourist industry.
Recreational divers may accept a relatively high level of risk to dive at a site perceived to be of special interest.Wreck diving andcave diving have their adherents, and enthusiasts will endure considerable hardship, risk and expense to visit caves and wrecks where few have been before. Some sites are popular almost exclusively for their convenience for training and practice of skills, such as flooded quarries. They are generally found where more interesting and pleasant diving is not locally available, or may only be accessible when weather or water conditions permit.
While divers may choose to get into the water at any arbitrary place that seems like a good idea at the time, a popular recreational dive site will usually be named, and a geographical position identified and recorded, describing the site with enough accuracy to recognise it, and hopefully, find it again. (Full article...)
The goal of the game is tomanoeuvre (bycarrying andpassing) a slightlynegatively buoyantball from one side of a pool to the other by players who are completely submergedunderwater.Scoring is achieved by placing the ball (under control) in thegutter on the side of the pool. Variations include using a toy rubber torpedo as the ball, and weighing down buckets to rest on the bottom and serve as goals.
Earlycivilizations were familiar with the custom of spearing fish from rivers and streams using sharpened sticks. Modern spearfishing usually involves the use ofunderwater swimming gear andslingshot-like elasticspearguns orcompressed gas powered pneumatic spearguns, which launch a tethereddart-likeprojectile to strike the target fish. Specialised techniques and equipment have been developed for various types of aquatic environments and target fish. Spearfishing uses nobait and is highly selective, with noby-catch, but inflicts lethal injury to the fish and thus precludescatch and release.
Spearfishing may be done usingfree-diving,snorkelling, orscuba diving techniques, but spearfishing while using scuba equipment is illegal in some countries. The use of mechanically powered spearguns is also outlawed in some countries and jurisdictions such asNew Zealand. (Full article...)
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DIR divers
Doing It Right (DIR) is aholistic approach toscuba diving that encompasses several essential elements, including fundamental diving skills, teamwork, physical fitness, and streamlined and minimalistic equipment configurations. DIR proponents maintain that through these elements, safety is improved by standardizing equipment configuration and dive-team procedures for preventing and dealing with emergencies.
DIR evolved out of the efforts of divers involved in theWoodville Karst Plain Project (WKPP) during the 1990s, who were seeking ways of reducing the fatality rate in those cave systems. The DIR philosophy is now used as a basis for teaching scuba diving from entry-level to technical and cave qualifications by severalorganizations, such asGlobal Underwater Explorers (GUE), Unified Team Diving (UTD) and InnerSpace Explorers (ISE). (Full article...)
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Below is the list of currentBritish records infinswimming. The records are ratified by the British Finswimming Association.
This list echoes that found on the Monofin website. These records are correct as of 1 April 2018.
In December 2017 British Finswimming Association made a decision to maintain the National records separately for adults and juniors in line withCMAS regulations. (Full article...)
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Below is the list of current Commonwealth Records forfinswimming. The records are ratified by the Commonwealth Finswimming Committee, which is made up of the National Finswimming Governing Bodies ofCommonwealth of Nations. The First Commonwealth Championships were held in Hobart, Tasmania, Australia in February 2007.
This page does not include the Commonwealth Finswimming Championship Records. This list echoes that found on the Swansea Finswimming Club Website and the British Finswimming Association documents website. These records are correct as of 4 December 2008. Times set before the First Commonwealth Championships have been allowed. All records have been accepted as a result of documentary evidence of the events or time-trials that they were set at.
Currently there are only four nations hold records: Australia (10), England (8), New Zealand (7) and Singapore (5). Finswimming is currently competed in eight Commonwealth Countries (includinghome nations); Australia, Canada, Cyprus, England, New Zealand, Scotland, Singapore, South Africa and Wales (). (Full article...)
Equipment failure is rare inopen circuit scuba, and while the cause of death is commonly recorded asdrowning, this is mainly the consequence of an uncontrollable series of events taking place in water.Arterial gas embolism is also frequently cited as a cause of death, and it, too, is the consequence of other factors leading to an uncontrolled and badly managedascent, possibly aggravated by medical conditions. About a quarter of diving fatalities are associated with cardiac events, mostly in older divers. There is a fairly large body of data on diving fatalities, but in many cases, the data is poor due to the standard of investigation and reporting. This hinders research that could improve diver safety.
For diving facilities, scuba diving fatalities have a major financial impact by way of lost income, lost business, insurance premium increases and high litigation costs. (Full article...)
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Divers face specific physical andhealth risks when they gounderwater withscuba or otherdiving equipment, or use high pressurebreathing gas. Some of these factors also affect people who work in raised pressure environments out of water, for example incaissons. This article lists hazards that a diver may be exposed to during a dive, and possible consequences of these hazards, with some details of the proximate causes of the listed consequences. A listing is also given of precautions that may be taken to reduce vulnerability, either by reducing the risk or mitigating the consequences. A hazard that is understood and acknowledged may present a lower risk if appropriate precautions are taken, and the consequences may be less severe if mitigation procedures are planned and in place.
Ahazard is any agent or situation that poses a level of threat to life, health, property, or environment. Most hazards remain dormant or potential, with only a theoretical risk of harm, and when a hazard becomes active, and produces undesirable consequences, it is called an incident and may culminate in an emergency or accident. Hazard and vulnerability interact with likelihood of occurrence to create risk, which can be the probability of a specific undesirable consequence of a specific hazard, or the combined probability of undesirable consequences of all the hazards of a specific activity. The presence of a combination of several hazards simultaneously is common in diving, and the effect is generally increased risk to the diver, particularly where the occurrence of an incident due to one hazard triggers other hazards with a resulting cascade of incidents. Many diving fatalities are the result of a cascade of incidents overwhelming the diver, who should be able to manage anysingle reasonably foreseeable incident. The assessed risk of a dive would generally be considered unacceptable if the diver is not expected to cope with any single reasonably foreseeable incident with a significant probability of occurrence during that dive. Precisely where the line is drawn depends on circumstances. Commercial diving operations tend to be less tolerant of risk than recreational, particularly technical divers, who are less constrained byoccupational health and safety legislation.
Decompression sickness and arterial gas embolism in recreational diving are associated with certain demographic, environmental, and dive style factors. A statistical study published in 2005 tested potential risk factors: age, gender, body mass index, smoking, asthma, diabetes, cardiovascular disease, previous decompression illness, years since certification, dives in last year, number of diving days, number of dives in a repetitive series, last dive depth, nitrox use, and drysuit use. No significant associations with decompression sickness or arterial gas embolism were found for asthma, diabetes, cardiovascular disease, smoking, or body mass index. Increased depth, previous DCI, days diving, and being male were associated with higher risk for decompression sickness and arterial gas embolism. Nitrox and drysuit use, greater frequency of diving in the past year, increasing age, and years since certification were associated with lower risk, possibly as indicators of more extensive training and experience.
Statistics show diving fatalities comparable to motor vehicle accidents of 16.4 per 100,000 divers and 16 per 100,000 drivers.Divers Alert Network 2014 data shows there are 3.174 millionrecreational scuba divers in America, of which 2.351 million dive 1 to 7 times per year and 823,000 dive 8 or more times per year. It is reasonable to say that the average would be in the neighbourhood of 5 dives per year. (Full article...)
Investigation of diving accidents includes investigations into the causes of reportable incidents in professional diving and recreational diving accidents, usually when there is a fatality or litigation for gross negligence.
An investigation of some kind usually follows a fatal diving accident, or one in which litigation is expected. There may be several investigations with different agendas. If police are involved, they generally look for evidence of a crime. In the U.S., theUnited States Coast Guard will usually investigate if there is a death when diving from a vessel in coastal waters. Health and safety administration officials may investigate when the diver was injured or killed at work. When a death occurs during an organised recreational activity, the certification agency's insurers will usually send an investigator to look into possible liability issues. The investigation may occur almost immediately to some considerable time after the event. In most cases the body will have been recovered and resuscitation attempted, and in this process equipment is usually removed and may be damaged or lost, or the evidence compromised by handling. Witnesses may have dispersed, and equipment is often mishandled by the investigating authorities if they are unfamiliar with the equipment and store it improperly, which can destroy evidence and compromise findings.
Recreational diving accidents are usually relatively uncomplicated, but accidents involving an extended range environment or specialised equipment may require expertise beyond the experience of any one investigator. This is a particular issue when rebreather equipment is involved. Investigators who are not familiar with complex equipment may not know enough about the equipment to understand that they do not know enough.
For every incident in which someone is injured or killed, it has been estimated that a relatively large number of "near miss" incidents occur, which the diver manages well enough to avoid harm. Ideally these will be recorded, analysed for cause, reported, and the results made public, so that similar incidents can be avoided in the future. (Full article...)
Participation in recreational diving impliesacceptance of the inherent risks of the activity.Diver training includes training in procedures known to reduce these risks to a level considered acceptable by thecertification agency, and issue of certification implies that the agency accepts that theinstructor has assessed the diver to be sufficiently competent in these skills at the time of assessment and to be competent to accept the associated risks. Certification relates to a set of skills and knowledge defined by the associatedtraining standard, which also specifies the limitations on the scope of diving activities for which the diver is deemed competent. These limitations involve depth, environment and equipment that the diver has been trained to use. Intentionally diving significantly beyond the scope of certified competence is at the diver's risk, and may be construed asnegligence if it puts another person at risk. Recommendations generally suggest that extending the scope should be done gradually, and preferably under the guidance of another diver experienced in similar conditions. The training agencies usually specify that any extension of scope should only be done by further training under a registered instructor, but this is not always practicable, or even possible, as there can always be circumstances that differ from those experienced during training.
Retention of skills requires exercise of those skills, and prolonged periods between dives will degrade skills by unpredictable amounts. This is recognised by training agencies, which require instructors to keep in date, and recommend that divers take part inrefresher courses after long periods of diving inactivity. (Full article...)
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Divers face specific physical andhealth risks when they gounderwater withscuba or otherdiving equipment, or use high pressurebreathing gas. Some of these factors also affect people who work in raised pressure environments out of water, for example incaissons. This article lists hazards that a diver may be exposed to during a dive, and possible consequences of these hazards, with some details of the proximate causes of the listed consequences. A listing is also given of precautions that may be taken to reduce vulnerability, either by reducing the risk or mitigating the consequences. A hazard that is understood and acknowledged may present a lower risk if appropriate precautions are taken, and the consequences may be less severe if mitigation procedures are planned and in place.
Ahazard is any agent or situation that poses a level of threat to life, health, property, or environment. Most hazards remain dormant or potential, with only a theoretical risk of harm, and when a hazard becomes active, and produces undesirable consequences, it is called an incident and may culminate in an emergency or accident. Hazard and vulnerability interact with likelihood of occurrence to create risk, which can be the probability of a specific undesirable consequence of a specific hazard, or the combined probability of undesirable consequences of all the hazards of a specific activity. The presence of a combination of several hazards simultaneously is common in diving, and the effect is generally increased risk to the diver, particularly where the occurrence of an incident due to one hazard triggers other hazards with a resulting cascade of incidents. Many diving fatalities are the result of a cascade of incidents overwhelming the diver, who should be able to manage anysingle reasonably foreseeable incident. The assessed risk of a dive would generally be considered unacceptable if the diver is not expected to cope with any single reasonably foreseeable incident with a significant probability of occurrence during that dive. Precisely where the line is drawn depends on circumstances. Commercial diving operations tend to be less tolerant of risk than recreational, particularly technical divers, who are less constrained byoccupational health and safety legislation.
Decompression sickness and arterial gas embolism in recreational diving are associated with certain demographic, environmental, and dive style factors. A statistical study published in 2005 tested potential risk factors: age, gender, body mass index, smoking, asthma, diabetes, cardiovascular disease, previous decompression illness, years since certification, dives in last year, number of diving days, number of dives in a repetitive series, last dive depth, nitrox use, and drysuit use. No significant associations with decompression sickness or arterial gas embolism were found for asthma, diabetes, cardiovascular disease, smoking, or body mass index. Increased depth, previous DCI, days diving, and being male were associated with higher risk for decompression sickness and arterial gas embolism. Nitrox and drysuit use, greater frequency of diving in the past year, increasing age, and years since certification were associated with lower risk, possibly as indicators of more extensive training and experience.
Statistics show diving fatalities comparable to motor vehicle accidents of 16.4 per 100,000 divers and 16 per 100,000 drivers.Divers Alert Network 2014 data shows there are 3.174 millionrecreational scuba divers in America, of which 2.351 million dive 1 to 7 times per year and 823,000 dive 8 or more times per year. It is reasonable to say that the average would be in the neighbourhood of 5 dives per year. (Full article...)
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Human factors are the physical orcognitive properties of individuals, or socialbehavior which is specific to humans, and which influence functioning of technological systems as well as human-environment equilibria. Thesafety ofunderwater diving operations can be improved by reducing the frequency ofhuman error and the consequences when it does occur. Human error can be defined as an individual's deviation from acceptable or desirable practice which culminates in undesirable or unexpected results. Human factors include both the non-technical skills that enhance safety and the non-technical factors that contribute to undesirable incidents that put the diver at risk.
[Safety is] An active, adaptive process which involves making sense of the task in the context of the environment to successfully achieve explicit and implied goals, with the expectation that no harm or damage will occur. – G. Lock, 2022
Dive safety is primarily a function of four factors: the environment, equipment, individual diver performance and dive team performance. The water is a harsh and alien environment which can impose severe physical and psychological stress on a diver. The remaining factors must be controlled and coordinated so the diver can overcome the stresses imposed by theunderwater environment and work safely.Diving equipment is crucial because it provideslife support to the diver, but the majority of dive accidents are caused by individual diver panic and an associated degradation of the individual diver's performance. – M.A. Blumenberg, 1996
Human error is inevitable and most errors are minor and do not cause significant harm, but others can have catastrophic consequences. Examples of human error leading to accidents are available in vast numbers, as it is the direct cause of 60% to 80% of all accidents. In a high risk environment, as is the case in diving, human error is more likely to have catastrophic consequences. A study by William P. Morgan indicates that over half of all divers in the survey had experienced panic underwater at some time during their diving career. These findings were independently corroborated by a survey that suggested 65% ofrecreational divers have panicked under water.Panic frequently leads to errors in a diver's judgment or performance, and may result in an accident. Human error and panic are considered to be the leading causes of dive accidents and fatalities.
Only 4.46% of therecreational diving fatalities in a 1997 study were attributable to a single contributory cause. The remaining fatalities probably arose as a result of a progressive sequence of events involving two or more procedural errors or equipment failures, and since procedural errors are generally avoidable by a well-trained, intelligent and alert diver, working in an organised structure, and not under excessive stress, it was concluded that the low accident rate in professional scuba diving is due to these factors. The study also concluded that it would be impossible to eliminate absolutely all minor contraindications for scuba diving, as this would result in overwhelming bureaucracy and would bring all diving to a halt.
Human factors engineering (HFE), also known as human factors andergonomics, is the application of psychological and physiological principles to the engineering and design of equipment, procedures, processes, and systems. Primary goals of human factors engineering are to reducehuman error, increase productivity and system availability, and enhance safety, health and comfort with a specific focus on the interaction between the human and equipment. (Full article...)
Example of risk assessment: ANASA model showing areas at high risk from impact for theInternational Space Station Risk management is the identification, evaluation, and prioritization ofrisks, followed by the minimization, monitoring, and control of the impact or probability of those risks occurring. Risks can come from various sources (i.e,threats) including uncertainty ininternational markets,political instability, dangers of project failures (at any phase in design, development, production, or sustaining of life-cycles),legal liabilities,credit risk,accidents,natural causes and disasters, deliberate attack from an adversary, or events of uncertain or unpredictableroot-cause. Retail traders also apply risk management by using fixed percentage position sizing and risk-to-reward frameworks to avoid large drawdowns and support consistent decision-making under pressure.
Strategies to manage threats (uncertainties with negative consequences) typically include avoiding the threat, reducing the negative effect or probability of the threat, transferring all or part of the threat to another party, and even retaining some or all of the potential or actual consequences of a particular threat. The opposite of these strategies can be used to respond to opportunities (uncertain future states with benefits).
As aprofessional role, a risk manager will "oversee the organization's comprehensive insurance and risk management program, assessing and identifying risks that could impede the reputation, safety, security, or financial success of the organization", and then develop plans to minimize and/or mitigate any negative (financial) outcomes. Risk analysts support the technical side of the organization's risk management approach: once risk data has been compiled and evaluated, analysts share their findings with their managers, who use those insights to decide among possible solutions. See alsoChief Risk Officer,internal audit, andFinancial risk management § Corporate finance. (Full article...)
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Risk assessment is a process for identifying hazards, potential (future) events which may negatively impact on individuals, assets, and/or the environment because of those hazards, their likelihood and consequences, and actions which can mitigate these effects. The output from such a process may also be called a risk assessment.Hazard analysis forms the first stage of a risk assessment process. Judgments "on the tolerability of the risk on the basis of a risk analysis" (i.e. risk evaluation) also form part of the process. The results of a risk assessment process may be expressed in aquantitative orqualitative fashion.
Risk assessment forms a key part of a broaderrisk management strategy to help reduce any potential risk-related consequences. (Full article...)
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Acode of practice can be a document that complements occupational health and safety laws and regulations to provide detailed practical guidance on how to comply with legal obligations, and should be followed unless another solution with the same or better health and safety standard is in place, or may be a document for the same purpose published by a self-regulating body to be followed by member organisations.
Codes of practice published by governments do not replace the occupational health and safety laws and regulations, and are generally issued in terms of those laws and regulations. They are intended to help understand how to comply with the requirements of regulations. A workplace inspector can refer to a code of practice when issuing an improvement or prohibition notice, and they may be admissible in court proceedings. A court may use a code of practice to establish what is reasonably practicable action to manage a specific risk. Equivalent or better ways of achieving the required work health and safety may be possible, so compliance with codes of practice is not usually mandatory, providing that any alternative systems used provide a standard of health and safety equal to or better than those recommended by the code of practice.
Organisational codes of practice do not have the same authority under law, but serve a similar purpose. Member organisations generally undertake to comply with the codes of practice as a condition of membership and may lose membership if found to be in violation of the code. (Full article...)
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Common redundant power supply Inengineering andsystems theory,redundancy is the intentional duplication of critical components or functions of a system with the goal of increasing reliability of thesystem, usually in the form of a backup orfail-safe, or to improve actual system performance, such as in the case ofGNSS receivers, ormulti-threaded computer processing.
In manysafety-critical systems, such asfly-by-wire andhydraulic systems inaircraft, some parts of the control system may be triplicated, which is formally termedtriple modular redundancy (TMR). An error in one component may then be out-voted by the other two. In a triply redundant system, the system has three sub components, all three of which must fail before the system fails. Since each one rarely fails, and the sub components are designed to preclude common failure modes (which can then be modelled as independent failure), the probability of all three failing is calculated to be extraordinarily small; it is often outweighed by other risk factors, such ashuman error.Electrical surges arising fromlightning strikes are an example of a failure mode which is difficult to fully isolate, unless the components are powered from independent power busses and have no direct electrical pathway in their interconnect (communication by some means is required for voting). Redundancy may also be known by the terms "majority voting systems" or "voting logic".
Redundancy sometimes produces less, instead of greater reliability – it creates a more complex system which is prone to various issues, it may lead to human neglect of duty, and may lead to higher production demands which by overstressing the system may make it less safe.
Diving safety is the aspect ofunderwater diving operations and activities concerned with thesafety of the participants. The safety of underwater diving depends on four factors: the environment, the equipment, behaviour of the individual diver and performance of thediving team. Theunderwater environment can impose severe physical and psychological stress on a diver, and is mostly beyond the diver's control. Equipment is used to operate underwater for anything beyond very short periods, and the reliable function of some of the equipment is critical to even short-term survival. Other equipment allows the diver to operate in relative comfort and efficiency, or to remain healthy over the longer term. The performance of the individual diver depends on learned skills, many of which are not intuitive, and the performance of the team depends on competence, communication, preparation, attention and common goals.
There is alarge range of hazards to which the diver may be exposed. These each have associated consequences and risks, which should be taken into account duringdive planning. Where risks are marginally acceptable it may be possible to mitigate the consequences by setting contingency and emergency plans in place, so that harm can be minimised where reasonably practicable. The acceptable level of risk varies depending onlegislation,codes of practice,company policy, andpersonal choice, with recreational divers having a greater freedom of choice.
Ajob safety analysis (JSA) is a procedure that helps integrate accepted safety and health principles and practices into a particular task or job operation. The goal of a JSA is to identify potential hazards of a specific role and recommend procedures to control or prevent these hazards.
Other terms often used to describe this procedure arejob hazard analysis (JHA),hazardous task analysis (HTA) andjob hazard breakdown.
The terms "job" and "task" are commonly used interchangeably to mean a specific work assignment. Examples of work assignments include "operating a grinder," "using a pressurized water extinguisher" or "changing a flat tire." Each of these tasks have different safety hazards that can be highlighted and fixed by using the job safety analysis. (Full article...)
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Hazard control methods at the top of the graphic are potentially more effective and protective than those at the bottom. Following thishierarchy of controls normally leads to the implementation of inherently safer systems, where the risk of illness or injury has been substantially reduced. Hierarchy of hazard control is a system used in industry to prioritize possible interventions to minimize or eliminate exposure tohazards. It is a widely accepted system promoted by numerous safety organizations. This concept is taught tomanagers in industry, to be promoted as standard practice in theworkplace. It has also been used to inform public policy, in fields such asroad safety. Various illustrations are used to depict this system, most commonly a triangle.
The hazard controls in the hierarchy are, in order of decreasing priority:
The system is not based on evidence of effectiveness; rather, it relies on whether the elimination of hazards is possible. Eliminating hazards allows workers to be free from the need to recognize and protect themselves against these dangers. Substitution is given lower priority than elimination because substitutes may also present hazards. Engineering controls depend on a well-functioning system and human behaviour, while administrative controls and personal protective equipment are inherently reliant on human actions, making them less reliable. (Full article...)
A Sechrist Monoplace hyperbaric oxygen chamber at theMoose Jaw Union Hospital, Saskatchewan, Canada
Hyperbaric medicine is medical treatment in which an increase in barometric pressure of typically air or oxygen is used. The immediate effects include reducing the size ofgas emboli and raising the partial pressures of the gases present. Initial uses were indecompression sickness, and it also effective in certain cases ofgas gangrene andcarbon monoxide poisoning. There are potential hazards. Injury can occur at pressures as low as 2psig (13.8 kPa) if a person is rapidly decompressed. If oxygen is used in the hyperbaric therapy, this can increase the fire hazard.
Hyperbaric oxygen therapy (HBOT), is the medical use of greater than 99%oxygen at an ambient pressure higher thanatmospheric pressure, and therapeutic recompression. The equipment required consists of apressure vessel for human occupancy (hyperbaric chamber), which may be of rigid or flexible construction, and a means of a controlled atmosphere supply. Treatment gas may be the ambient chamber gas, or delivered via abuilt-in breathing system. Operation is performed to a predetermined schedule by personnel who may adjust the schedule as required.
Chambers used in the US made for hyperbaric medicine fall under the jurisdiction of the federal Food and Drug Administration (FDA). The FDA requires hyperbaric chambers to comply with theAmerican Society of Mechanical Engineers PVHO Codes and the National Fire Protection Association Standard 99, Health Care Facilities Code. Similar conditions apply in most other countries.
Dysbarism ordysbaric disorders are medical conditions resulting from changes inambient pressure. Various activities are associated with pressure changes.Underwater diving is a frequently cited example, but pressure changes also affect people who work in other pressurized environments (for example,caisson workers), and people who move between differentaltitudes. A dysbaric disorder may beacute orchronic. (Full article...)
Oxygen is required for normalcellular metabolism. However, excessively high concentrations can result inoxygen toxicity, leading to lung damage andrespiratory failure. Higher oxygen concentrations can also increase the risk of airway fires, particularly while smoking. Oxygen therapy can also dry out the nasal mucosa without humidification. In most conditions, an oxygen saturation of 94–96% is adequate, while in those at risk ofcarbon dioxide retention, saturations of 88–92% are preferred. In cases of carbon monoxide toxicity orcardiac arrest, saturations should be as high as possible. Whileair is typically 21% oxygen by volume, oxygen therapy can increase O2 content of air up to 100%.
Freediving blackout,breath-hold blackout, orapnea blackout is a class ofhypoxic blackout, aloss of consciousness caused bycerebral hypoxia towards the end of a breath-hold (freedive or dynamicapnea) dive, when the swimmer does not necessarily experience an urgent need to breathe and has no other obvious medical condition that might have caused it. It can be provoked byhyperventilating just before a dive, or as a consequence of the pressure reduction on ascent, or a combination of these. Victims are often established practitioners of breath-hold diving, are fit, strong swimmers and have not experienced problems before. Blackout may also be referred to as asyncope orfainting.
Divers and swimmers who black out orgrey out underwater during a dive will usuallydrown unless rescued and resuscitated within a short time. Freediving blackout has a high fatality rate, and mostly involves males younger than 40 years, but is generally avoidable. Risk cannot be quantified, but is clearly increased by any level of hyperventilation.
Freediving blackout can occur on any dive profile: at constant depth, on an ascent from depth, or at the surface following ascent from depth and may be described by a number of terms depending on the dive profile and depth at which consciousness is lost. Blackout during a shallow dive differs from blackout during ascent from a deep dive in that blackout during ascent is precipitated by depressurisation on ascent from depth while blackout in consistently shallow water is a consequence ofhypocapnia following hyperventilation. (Full article...)
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Main symptoms of carbon dioxide toxicity, by increasingvolume percent in air.
Hypercapnia (from theGreekhyper, "above" or "too much" andkapnos, "smoke"), also known ashypercarbia andCO2 retention, is a condition of abnormally elevatedcarbon dioxide (CO2) levels in the blood. Carbon dioxide is agaseous product of thebody'smetabolism and is normally expelled through thelungs. Carbon dioxide may accumulate in any condition that causeshypoventilation, a reduction ofalveolar ventilation (the clearance of air from the small sacs of the lung wheregas exchange takes place) as well as resulting from inhalation of CO2. Inability of the lungs to clear carbon dioxide, or inhalation of elevated levels of CO2, leads torespiratory acidosis. Eventually the body compensates for the raised acidity by retaining alkali in the kidneys, a process known as "metabolic compensation".
Acute hypercapnia is calledacute hypercapnic respiratory failure (AHRF) and is a medical emergency as it generally occurs in the context of acute illness. Chronic hypercapnia, where metabolic compensation is usually present, may cause symptoms but is not generally an emergency. Depending on the scenario both forms of hypercapnia may be treated with medication, with mask-basednon-invasive ventilation or withmechanical ventilation.
Hypercapnia is a hazard of underwater diving associated with breath-hold diving, scuba diving, particularly on rebreathers, and deep diving where it is associated with highwork of breathing caused by increased breathing gas density due to the high ambient pressure. (Full article...)
Since bubbles can form in or migrate to any part of the body, DCS can produce many symptoms, and its effects may vary from joint pain and rashes to paralysis and death. DCS often causes air bubbles to settle in major joints like knees or elbows, causing individuals to bend over in excruciating pain, hence its common name, the bends. Individual susceptibility can vary from day to day, and different individuals under the same conditions may be affected differently or not at all. The classification of types of DCS according to symptoms has evolved since its original description in the 19th century. The severity of symptoms varies from barely noticeable to rapidly fatal.
Decompression sickness can occur after an exposure to increased pressure while breathing a gas with a metabolically inert component, then decompressing too fast for it to be harmlessly eliminated through respiration, or by decompression by an upward excursion from a condition of saturation by the inert breathing gas components, or by a combination of these routes. Theoretical decompression risk is controlled by the tissue compartment with the highest inert gas concentration, which for decompression from saturation, is the slowest tissue to outgas.
The risk of DCS can be managed through properdecompression procedures, and contracting the condition has become uncommon. Its potential severity has driven much research to prevent it, and divers almost universally usedecompression schedules ordive computers to limit their exposure and to monitor their ascent speed. If DCS is suspected, it is treated byhyperbaric oxygen therapy in arecompression chamber. Where a chamber is not accessible within a reasonable time frame, in-water recompression may be indicated for a narrow range of presentations, if there are suitably skilled personnel and appropriate equipment available on site. Diagnosis is confirmed by a positive response to the treatment. Early treatment results in a significantly higher chance of successful recovery. (Full article...)
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Latent hypoxia affects the diver on ascent
Latent hypoxia is a condition where the oxygen content of the lungs and arterial blood is sufficient to maintain consciousness at a raised ambient pressure, but not when the pressure is reduced to normal atmospheric pressure.
It usually occurs when adiver at depth has a lung gas and blood oxygen concentration that is sufficient to support consciousness at the pressure at that depth, but would be insufficient at surface pressure. This problem is associated withfreediving blackout and the presence ofhypoxic breathing gas mixtures inunderwater breathing apparatus, particularly indiving rebreathers.
The term latent hypoxia strictly refers to the situation while the potential victim is at depth, still conscious, and not yet hypoxic, but is also loosely applied to the consequential blackout, which is a form of hypoxic blackout also referred to asblackout of ascent or deep water blackout, though deep water blackout is also used to refer to the final stage ofnitrogen narcosis. (Full article...)
Hypothermia is defined as a bodycore temperature below 35.0 °C (95.0 °F) in humans. Symptoms depend on the temperature. In mild hypothermia, there isshivering and mental confusion. In moderate hypothermia, shivering stops and confusion increases. In severe hypothermia, there may be hallucinations andparadoxical undressing, in which a person removes their clothing, as well as an increased risk of theheart stopping.
Hypothermia has two main types of causes. It classically occurs from exposure to cold weather and cold water immersion. It may also occur from any condition that decreases heat production or increases heat loss. Commonly, this includesalcohol intoxication but may also includelow blood sugar,anorexia, and advanced age.Body temperature is usually maintained near a constant level of 36.5–37.5 °C (97.7–99.5 °F) throughthermoregulation. Efforts to increase body temperature involve shivering, increased voluntary activity, and putting on warmer clothing. Hypothermia may be diagnosed based on either a person's symptoms in the presence of risk factors or by measuring a person's core temperature.
The treatment of mild hypothermia involves warm drinks, warm clothing, and voluntary physical activity. In those with moderate hypothermia, heating blankets and warmedintravenous fluids are recommended. People with moderate or severe hypothermia should be moved gently. In severe hypothermia,extracorporeal membrane oxygenation (ECMO) orcardiopulmonary bypass may be useful. In those without apulse,cardiopulmonary resuscitation (CPR) is indicated along with the above measures. Rewarming is typically continued until a person's temperature is greater than 32 °C (90 °F). If there is no improvement at this point or the blood potassium level is greater than 12 millimoles per litre at any time, resuscitation may be discontinued.
Hypothermia is the cause of at least 1,500 deaths a year in the United States. It is more common in older people and males. One of the lowest documented body temperatures from which someone with accidental hypothermia has survived is 12.7 °C (54.9 °F) in a 2-year-old boy from Poland named Adam. Survival after more than six hours of CPR has been described. In individuals for whom ECMO or bypass is used, survival is around 50%. Deaths due to hypothermia have played an important role in many wars.
The term is fromGreek ῠ̔πο (ypo), meaning "under", and θέρμη (thérmē), meaning "heat". The opposite of hypothermia ishyperthermia, an increased body temperature due to failed thermoregulation. (Full article...)
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Diving disorders, ordiving related medical conditions, are conditions associated withunderwater diving, and include both conditions unique to underwater diving, and those that also occur during other activities. This second group further divides conditions caused by exposure toambient pressures significantly different from surfaceatmospheric pressure, and a range of conditions caused by general environment and equipment associated with diving activities.
Disorders particularly associated with diving include those caused by variations in ambient pressure, such as barotraumas of descent and ascent, decompression sickness and those caused by exposure to elevated ambient pressure, such as some types of gas toxicity. There are also non-dysbaric disorders associated with diving, which include the effects of the aquatic environment, such as drowning, which also are common to other water users, and disorders caused by the equipment or associated factors, such as carbon dioxide and carbon monoxide poisoning. General environmental conditions can lead to another group of disorders, which include hypothermia and motion sickness, injuries by marine and aquatic organisms,contaminated waters, man-made hazards, and ergonomic problems with equipment. Finally there are pre-existing medical andpsychological conditions which increase the risk of being affected by a diving disorder, which may be aggravated by adverse side effects ofmedications and other drug use.
Treatment depends on the specific disorder, but often includesoxygen therapy, which is standard first aid for most diving accidents, and is hardly ever contra-indicated for a person medically fit to dive, andhyperbaric therapy is the definitive treatment for decompression sickness. Screening formedical fitness to dive can reduce some of the risk for some of the disorders. (Full article...)
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PC-based spirometer output Fitness to dive (more specificallymedical fitness to dive) refers to the medical and physical suitability of adiver to function safely in an underwater environment usingdiving equipment and related procedures. Depending on the circumstances, it may be established with a signed statement by the diver that they do not have any of the listed disqualifying conditions. The diver must be able to fulfill the ordinary physical requirements of diving as per the detailed medical examination by a physician registered as amedical examiner of divers following a procedural checklist. A legal document of fitness to dive issued by the medical examiner is also necessary.
The most important medical is the one before starting diving, as the diver can be screened to prevent exposure in the event of an imminent danger. The other important medicals are after some significant illness, where medical intervention is needed and has to be done by a doctor proficient in diving medicine, and can not be done by prescriptive rules.
Psychological factors can affect fitness to dive, particularly where they affect response to emergencies, or risk-taking behavior. The use of medical and recreational drugs can also influence fitness to dive, both for physiological and behavioral reasons. In some cases, prescription drug use might have a net positive effect when viably treating an underlying condition. However, the side effects of viable medication frequently have undesirable influences on the fitness of a diver. Most cases of recreational drug use result in an impaired fitness to dive, and a significantly increased risk of sub-optimal response to emergencies. (Full article...)
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Inphysiology,isobaric counterdiffusion (ICD) is thediffusion of different gases into and out oftissues while under a constantambient pressure, after a change of gas composition, and the physiological effects of this phenomenon. The terminert gas counterdiffusion is sometimes used as a synonym, but can also be applied to situations where the ambient pressure changes. It has relevance in mixed gasdiving andanesthesiology. (Full article...)
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Arecompression chamber is used to treat some diving disorders. Diving medicine, also calledundersea and hyperbaric medicine (UHB), is the diagnosis, treatment and prevention of conditions caused by humans entering the undersea environment. It includes the effects on the body of pressure on gases, the diagnosis and treatment of conditions caused by marine hazards and how aspects of a diver's fitness to dive affect the diver's safety. Diving medical practitioners are also expected to be competent in the examination of divers and potential divers to determinefitness to dive.
Diving medicine deals with medical research on issues of diving, the prevention of diving disorders, treatment of diving accidents and diving fitness. The field includes the effect of breathing gases and their contaminants under high pressure on the human body and the relationship between the state of physical and psychological health of the diver and safety.
In diving accidents it is common for multiple disorders to occur together and interact with each other, both causatively and as complications.
Diving medicine is a branch of occupational medicine and sports medicine, and at first aid level, an important part of diver education. (Full article...)
Drowning is a type ofsuffocation induced by the submersion of the mouth and nose in a liquid. Submersion injury refers to both drowning and near-miss incidents. Most instances of fatal drowning occur alone or in situations where others present are either unaware of the victim's situation or unable to offer assistance. After successfulresuscitation, drowning victims may experience breathing problems, confusion, orunconsciousness. Occasionally, victims may not begin experiencing these symptoms until several hours after they are rescued. An incident of drowning can also cause further complications for victims due tolow body temperature,aspiration, oracute respiratory distress syndrome (respiratory failure from lung inflammation).
Drowning is more likely to happen when spending extended periods near large bodies of water. Risk factors for drowning include alcohol use, drug use,epilepsy, minimal swim training or a complete lack of training, and, in the case of children, a lack of supervision. Common drowning locations include natural and man-made bodies of water,bathtubs, andswimming pools.
Drowning occurs when a person spends too much time with their nose and mouth submerged in a liquid to the point of being unable to breathe. If this is not followed by an exit to the surface,low oxygen levels andexcess carbon dioxide in the blood trigger a neurological state of breathing emergency, which results in increased physical distress and occasionalcontractions of the vocal folds. Significant amounts of water usually only enter the lungs later in the process.
While the word "drowning" is commonly associated with fatal results, drowning may be classified into three different types: drowning that results in death, drowning that results in long-lasting health problems, and drowning that results in no health complications. Sometimes the term "near-drowning" is used in the latter cases. Among children who survive, health problems occur in about 7.5% of cases.
Steps to prevent drowning include teaching children and adults to swim and to recognise unsafe water conditions, never swimming alone, use ofpersonal flotation devices on boats and when swimming in unfavourable conditions, limiting or removing access to water (such as with fencing of swimming pools), and exercising appropriate supervision. Treatment of victims who are not breathing should begin with opening the airway and providing five breaths ofmouth-to-mouth resuscitation.Cardiopulmonary resuscitation (CPR) is recommended for a person whoseheart has stopped beating and has been underwater for less than an hour. (Full article...)
In-water recompression (IWR) orunderwater oxygen treatment is the emergency treatment ofdecompression sickness (DCS) by returning thediverunderwater to help the gas bubbles in the tissues, which are causing the symptoms, to resolve. It is a procedure that exposes the diver to significantrisk which should be compared with the risk associated with the available options and balanced against the probable benefits. Some authorities recommend that it is only to be used when the time totravel to the nearestrecompression chamber is too long to save the victim's life; others take a more pragmatic approach and accept that in some circumstances IWR is the best available option. The risks may not be justified for case of mild symptoms likely to resolve spontaneously, or for cases where the diver is likely to be unsafe in the water, but in-water recompression may be justified in cases where severe outcomes are likely if not recompressed, if conducted by a competent and suitably equipped team.
Carrying out in-water recompression when there is a nearbyrecompression chamber or without suitable equipment and training is never a desirable option. The risk of the procedure is due to the diver suffering from DCS being seriously ill and may becomeparalysed,unconscious, orstop breathing while underwater. Any one of these events is likely to result in the diverdrowning or asphyxiating or suffering further injury during a subsequent rescue to the surface. This risk can be reduced by improving airway security by using surface supplied gas and a helmet or full-face mask. Risk of injury during emergency surfacing is minimised by treatment on 100% oxygen, which is also the only gas with a reliable record of positive outcomes. Early recompression on oxygen has a high rate of complete resolution of symptoms, even for shallower and shorter treatment than the highly successful US Navy Treatment Table 6.
Several schedules have been published for in-water recompression treatment, but little data on their efficacy is available. The Australian Navy tables and US Navy Tables may have the largest amount of empirical evidence supporting their efficacy. (Full article...)
TheGyrojet is a family of uniquefirearms developed in the 1960s named for the method ofgyroscopically stabilizing its projectiles. Rather than inertbullets, Gyrojets fire smallrockets called Microjets which have little recoil and do not require a heavy barrel or chamber to resist the pressure of the combustion gases. Velocity on leaving the tube was very low, but increased to around 1,250 feet per second (380 m/s) at 30 feet (9.1 m). The result is a very lightweight and transportable weapon.
Long out of production, today they are a coveted collector's item with prices for even the most common model ranging above $4,000. They are rarely fired; ammunition is scarce and can cost over $800 per round. (Full article...)
Polespear under tension with a cluster head attached.
Apolespear (hand spear orgidgee) is an underwater tool used inspearfishing, consisting of a pole, aspear tip, and arubber loop. Polespears are often mistakenly calledHawaiian slings, but the tools differ. A Hawaiian sling is akin to aslingshot or an underwaterbow and arrow, since the spear and the propelling device are separate, while a polespear has the sling (rubber loop) attached to the spear. (Full article...)
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Speargun Aspeargun is a ranged underwaterfishing device designed to launch a tetheredspear orharpoon to impalefish or othermarine animals and targets. Spearguns are used insport fishing and underwatertarget shooting. The two basic types arepneumatic andelastic (powered byrubber bands). Spear types come in a number of varieties including threaded, break-away and lined.Floats andbuoys are common accessories when targeting larger fish. (Full article...)
Alimpet mine is a type ofnaval mine attached to a target bymagnets. It is so named because of its superficial similarity to the shape of thelimpet, a type ofsea snail that clings tightly to rocks or other hard surfaces.
A swimmer ordiver may attach the mine, which is usually designed with hollow compartments to give the mine just slight negativebuoyancy, making it easier to handle underwater. (Full article...)
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TheM1 Underwater Defense Gun, also called theUnderwater Defense Gun Mark 1 Mod 0, is anunderwater firearm developed by the United States during theCold War. Similar to other underwater firearms, it fires a special 4.25-inch (108 mm) metal dart as its projectile. (Full article...)
Under water, ordinary bullets are inaccurate and have a very short range. The APS fires a 120-millimetre-long (4.7 in), 5.66 mm calibre steel bolt specially designed for this weapon. Its magazine holds 26 rounds. The APS's barrel is notrifled; the fired projectile is kept in line byhydrodynamic effects; as a result, the APS is somewhat inaccurate when fired out of water.
The APS has a longer range and more penetrating power thanspearguns. This is useful in such situations such as shooting an opposing diver through a reinforceddry suit, a protectivehelmet (whether air-holding or not), thick tough parts ofbreathing sets and theirharnesses, and the plastic casings and transparent covers of somesmall underwater vehicles.
The APS is more powerful than a pistol, but is bulkier, heavier and takes longer to aim, particularly swinging its long barrel and large flat magazine sideways through water. (Full article...)
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The ROV Hercules recovers an experiment from theNew England Seamounts. Aremotely operated underwater vehicle (ROUV) orremotely operated vehicle (ROV) is a free-swimming submersible craft. ROVs are used to perform underwater observation, inspection, and physical tasks such as valve operations,hydraulic functions, and other general tasks within the subseaoil and gas industry, military, scientific and other applications. ROVs can also carry tooling packages for undertaking specific tasks such as pull-in and connection of flexible flowlines and umbilicals, and component replacement. They are often used to do research and commercial work at great depths beyond the capacities of mostsubmersibles and divers. Most users of the machines use the term "remotely operated vehicle" (ROV). (Full article...)
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SPP-1M
TheSPP-1 underwater pistol was made in theSoviet Union for use by Sovietfrogmen as anunderwater firearm. It was developed in the late 1960s and accepted for use in 1975. Under water, standard bullets are inaccurate and have very short range. This pistol instead fires a round-based 4.5 millimetres (0.18 in) caliber steel dart about 115 millimetres (4.5 in) long, weighing 12.8 grams (0.45 oz), which has longer range and more penetrating power than aspeargun. The complete cartridge is 145 millimetres (5.7 in) long and weighs 17.5 grams (0.62 oz). (Full article...)
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Israeli Navy Underwater Missions Unit transfers equipment using lifting-bags
Alifting bag is an item ofdiving equipment consisting of a robust andair-tight bag with straps, which is used to lift heavy objects underwater by means of the bag'sbuoyancy. The heavy object can either be moved horizontally underwater by thediver or sent unaccompanied to the surface.
Lift bag appropriate capacity should match the task at hand. If the lift bag is grossly oversized a runaway or otherwise out of control ascent may result. Commercially available lifting bags may incorporate dump valves to allow the operator to control the buoyancy during ascent, but this is a hazardous operation with high risk of entanglement in an uncontrolled lift or sinking. If a single bag is insufficient, multiple bags may be used, and should be distributed to suit the load.
There are also lifting bags used on land as short lift jacks for lifting cars or heavy loads or lifting bags which are used in machines as a type of pneumatic actuator which provides load over a large area. These lifting bags of the AS/CR type are for example used in the brake mechanism of rollercoasters. (Full article...)
Thehistory of scuba diving is closely linked with the history ofdiving equipment. By the turn of the twentieth century, two basic architectures for underwater breathing apparatus had been pioneered; open-circuit surface supplied equipment where the diver's exhaled gas is vented directly into the water, and closed-circuit breathing apparatus where the diver's carbon dioxide is filtered from the exhaled breathing gas, which is then recirculated, and more gas added to replenish the oxygen content. Closed circuit equipment was more easily adapted to scuba in the absence of reliable, portable, and economical high pressure gas storage vessels. By the mid-twentieth century, high pressure cylinders were available and two systems for scuba had emerged:open-circuit scuba where the diver's exhaled breath is vented directly into the water, andclosed-circuit scuba where thecarbon dioxide is removed from the diver's exhaled breath which has oxygen added and is recirculated. Oxygen rebreathers are severely depth limited due to oxygen toxicity risk, which increases with depth, and the available systems for mixed gas rebreathers were fairly bulky and designed for use with diving helmets. The first commercially practical scuba rebreather was designed and built by the diving engineerHenry Fleuss in 1878, while working forSiebe Gorman in London. Hisself contained breathing apparatus consisted of a rubber mask connected to a breathing bag, with an estimated 50–60% oxygen supplied from a copper tank and carbon dioxide scrubbed by passing it through a bundle of rope yarn soaked in a solution of caustic potash. During the 1930s and all throughWorld War II, the British, Italians and Germans developed and extensively used oxygen rebreathers to equip the firstfrogmen. In the U.S. MajorChristian J. Lambertsen invented a free-swimmingoxygen rebreather. In 1952 he patented a modification of his apparatus, this time named SCUBA, an acronym for "self-contained underwater breathing apparatus," which became the generic English word for autonomous breathing equipment for diving, and later for the activity using the equipment. After World War II, military frogmen continued to use rebreathers since they do not make bubbles which would give away the presence of the divers. The high percentage of oxygen used by these early rebreather systems limited the depth at which they could be used due to the risk of convulsions caused by acuteoxygen toxicity.
Although a working demand regulator system had been invented in 1864 byAuguste Denayrouze andBenoît Rouquayrol, the first open-circuit scuba system developed in 1925 byYves Le Prieur in France was a manually adjusted free-flow system with a low endurance, which limited the practical usefulness of the system. In 1942, during the German occupation of France,Jacques-Yves Cousteau andÉmile Gagnan designed the first successful and safe open-circuit scuba, a twin hose system known as theAqua-Lung. Their system combined an improved demand regulator with high-pressure air tanks. This was patented in 1945. To sell his regulator in English-speaking countries Cousteau registered the Aqua-Lung trademark, which was first licensed to theU.S. Divers company, and in 1948 to Siebe Gorman of England.
Early scuba sets were usually provided with a plain harness of shoulder straps and waist belt. Many harnesses did not have a backplate, and the cylinders rested directly against the diver's back. Early scuba divers dived without a buoyancy aid. In an emergency they had to jettison their weights. In the 1960sadjustable buoyancy life jackets (ABLJ) became available, which can be used to compensate for loss of buoyancy at depth due to compression of theneoprenewetsuit and as alifejacket that will hold an unconscious diver face-upwards at the surface. The first versions were inflated from a small disposable carbon dioxide cylinder, later with a small direct coupled air cylinder. A low-pressure feed from the regulator first-stage to an inflation/deflation valve unit an oral inflation valve and a dump valve lets the volume of the ABLJ be controlled as a buoyancy aid. In 1971 thestabilizer jacket was introduced byScubaPro. This class of buoyancy aid is known as a buoyancy control device or buoyancy compensator. A backplate and wing is an alternative configuration of scuba harness with a buoyancy compensation bladder known as a "wing" mounted behind the diver, sandwiched between the backplate and the cylinder or cylinders. This arrangement became popular with cave divers making long or deep dives, who needed to carry several extra cylinders, as it clears the front and sides of the diver for other equipment to be attached in the region where it is easily accessible. Sidemount is a scuba diving equipment configuration which has basicscuba sets, each comprising a single cylinder with a dedicated regulator and pressure gauge, mounted alongside the diver, clipped to the harness below the shoulders and along the hips, instead of on the back of the diver. It originated as a configuration for advancedcave diving, as it facilitates penetration of tight sections of cave, as sets can be easily removed and remounted when necessary. Sidemount diving has grown in popularity within thetechnical diving community for generaldecompression diving, and has become a popular specialty for recreational diving.
In the 1950s theUnited States Navy (USN) documented procedures for military use of what is now called nitrox, and in 1970,Morgan Wells, of NOAA, began instituting diving procedures for oxygen-enriched air. In 1979 NOAA published procedures for the scientific use of nitrox in the NOAA Diving Manual. In 1985 IAND (International Association of Nitrox Divers) began teaching nitrox use for recreational diving. After initial resistance by some agencies, the use of a single nitrox mixture has become part of recreational diving, and multiple gas mixtures are common in technical diving to reduce overall decompression time.Oxygen toxicity limits the depth when breathing nitrox mixtures. In 1924 the U.S. Navy started to investigate the possibility of using helium and after animal experiments, human subjects breathing heliox 20/80 (20% oxygen, 80% helium) were successfully decompressed from deep dives, Cave divers started using trimix to allow deeper dives and it was used extensively in the 1987Wakulla Springs Project and spread to the north-east American wreck diving community. The challenges of deeper dives and longer penetrations and the large amounts of breathing gas necessary for these dive profiles and ready availability of oxygen sensing cells beginning in the late 1980s led to a resurgence of interest in rebreather diving. By accurately measuring the partial pressure of oxygen, it became possible to maintain and accurately monitor a breathable gas mixture in the loop at any depth. In the mid-1990s semi-closed circuit rebreathers became available for the recreational scuba market, followed by closed circuit rebreathers around the turn of the millennium. Rebreathers are currently (2018) manufactured for the military, technical and recreational scuba markets. (Full article...)
Decompression in the context ofdiving derives from the reduction inambient pressure experienced by the diver during the ascent at the end of a dive or hyperbaric exposure and refers to both the reduction inpressure and the process of allowing dissolvedinert gases to be eliminated from thetissues during this reduction in pressure.
When a diver descends in the water column theambient pressure rises.Breathing gas is supplied at the same pressure as the surrounding water, and some of this gas dissolves into the diver's blood and other tissues. Inert gas continues to be taken up until the gas dissolved in the diver is in a state of equilibrium with the breathing gas in the diver'slungs, (see: "Saturation diving"), or the diver moves up in the water column and reduces the ambient pressure of the breathing gas until the inert gases dissolved in the tissues are at a higher concentration than the equilibrium state, and start diffusing out again. Dissolved inert gases such asnitrogen orhelium can form bubbles in the blood and tissues of the diver if thepartial pressures of the dissolved gases in the diver get too high when compared to theambient pressure. These bubbles, and products of injury caused by the bubbles, can cause damage to tissues generally known asdecompression sickness orthe bends. The immediate goal of controlled decompression is to avoid development of symptoms of bubble formation in the tissues of the diver, and the long-term goal is to also avoid complications due to sub-clinical decompression injury.
The symptoms of decompression sickness are known to be caused by damage resulting from the formation and growth of bubbles of inert gas within the tissues and by blockage of arterial blood supply to tissues by gas bubbles and otheremboli consequential to bubble formation and tissue damage. The precise mechanisms of bubble formation and the damage they cause has been the subject of medical research for a considerable time and several hypotheses have been advanced and tested. Tables and algorithms for predicting the outcome of decompression schedules for specified hyperbaric exposures have been proposed, tested, and used, and usually found to be of some use but not entirely reliable. Decompression remains a procedure with some risk, but this has been reduced and is generally considered to be acceptable for dives within the well-tested range of commercial, military and recreational diving.
The first recorded experimental work related to decompression was conducted byRobert Boyle, who subjected experimental animals to reduced ambient pressure by use of a primitivevacuum pump. In the earliest experiments the subjects died from asphyxiation, but in later experiments, signs of what was later to become known as decompression sickness were observed. Later, when technological advances allowed the use of pressurisation of mines and caissons to exclude water ingress, miners were observed to present symptoms of what would become known as caisson disease, the bends, and decompression sickness. Once it was recognized that the symptoms were caused by gas bubbles, and that recompression could relieve the symptoms, further work showed that it was possible to avoid symptoms by slow decompression, and subsequently various theoretical models have been derived to predict low-risk decompression profiles and treatment of decompression sickness. (Full article...)
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Olterra at anchor shortly before being broken up atVado Ligure, 1961
Behnke is also known as the "modern-day father" of humanbody composition for his work in developing thehydrodensitometry method of measuring body density, his standard man and woman models as well as a somatogram based onanthropometric measurements. (Full article...)
While serving as Officer-in-Charge at the Naval Medical Research Laboratory in Groton, Connecticut, he conducted his earliest experiments into saturation diving techniques. In 1957, Bond began the Genesis project to prove that humans could in fact withstand prolonged exposure to differentbreathing gases and increased environmental pressures. Once saturation is achieved, the amount of time needed fordecompression depends only on the depth and gases breathed. This was the beginning ofsaturation diving and the US Navy's Man-in-the-Sea Program.
The first two phases of Project Genesis involved exposing animals to saturation in various breathing gases. In 1962, interest inhelium-oxygen atmospheres for crewed space flights made Phase C possible. Phase C involved saturation of three subjects at one atmosphere (surface) in a 21.6% oxygen, 4% nitrogen, and 74.4% helium environment for six days. In phase D experiments at theUnited States Navy Experimental Diving Unit in 1963, the subjects performed the world's first saturation dive at a depth of 100 feet of seawater (fsw) in a 7% oxygen, 7% nitrogen, and 86% helium environment for 6 days. In phase E trials in 1963 divers were saturated for 12 days at 198 fsw breathing 3.9% oxygen, 6.5% nitrogen and 89.6% helium. A 27-hour linear ascent was made from saturation.
"Papa Topside" Bond initiated and served as the Senior Medical Officer andprincipal investigator of the US NavySEALAB program. SEALAB I was lowered off the coast ofBermuda in 1964 to a depth of 192 fsw below the sea's surface. The experiment was halted after 11 days due to an approachingtropical storm. SEALAB I proved that saturation diving in the open ocean was a viable means for expanding our ability to live and work in the sea. The experiment also provided engineering solutions to habitat placement, habitat umbilicals, humidity, and helium speech descrambling. SEALAB II was launched off the coast of California in 1965 to assess the feasibility of utilizing saturation techniques and tools to accomplish a variety of tasks that would be difficult or impossible to accomplish by repeated dives from the surface. In addition to physiological testing, the divers tested new tools, methods of salvage, and an electrically heated drysuit. SEALAB III was placed in water three times as deep to test new salvage techniques and foroceanographic andfishery studies. On February 15, 1969, SEALAB III was lowered to 610 fsw (185 m), offSan Clemente Island, California. The habitat soon began to leak and six divers were sent to repair it, but they were unsuccessful. During the second attempt, aquanautBerry L. Cannon died, and the program came to a halt. (Full article...)
The sinking was a cause of embarrassment to France and PresidentFrançois Mitterrand. They initially denied responsibility, but two French agents were captured byNew Zealand Police and charged witharson,conspiracy to commit arson,willful damage andmurder. It resulted in a scandal that led to the resignation of theFrench Defence MinisterCharles Hernu, while the two agents pleaded guilty tomanslaughter and were sentenced to ten years in New Zealand prison. Despite being sentenced to ten years' imprisonment, due to pressures from the French state they spent merely two years confined to the French Polynesian island ofHao before being freed by the French government.
France was also forced to apologise and had to pay reparations to New Zealand, Pereira's family and Greenpeace. (Full article...)
An alternative approach was the development of the "single atmosphere" or armoured suit, which isolates the diver from the pressure at depth, at the cost of great 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 ofremotely operated underwater vehicles in the late 20th century, where the operator controls the ROV from the surface, andautonomous underwater vehicles, 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 the simultaneous use of surface orientated or saturation surface-supplied diving equipment and work or observation class remotely operated vehicles.
A commando team observed British naval traffic in the area from Spain during 1982, waiting to attack a target of opportunity when ordered, usingfrogmen and Italianlimpet mines.
The plan was to launch divers fromAlgeciras, have them swim across the bay, to Gibraltar, under cover of darkness, attach the mines to a British naval ship and swim back to Algeciras. The timed detonators would cause the mines to explode after the divers had time to safely swim back across the bay. The plan was foiled when the Spanish police became suspicious of their behaviour and arrested them before any attack could be mounted. (Full article...)
Mitchell is anauthor and avidtechnical diver. He authored two chapters of the latest edition ofBennett and Elliott's Physiology and Medicine of Diving, is the co-author of the diving textbookDeeper Into Diving with John Lippmann, and co-authored the chapter on Diving and Hyperbaric Medicine inHarrison'sPrinciples of Internal Medicine with Michael Bennett. (Full article...)
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Operation Thunderhead was a highly classified combat mission conducted by U.S. NavySEAL Team One andUnderwater Demolition Team 11 (UDT-11) in 1972. The mission was conducted off the coast of North Vietnam during the Vietnam War to rescue two U.S. airmen said to be escaping from a prisoner of war prison in Hanoi. The prisoners, including Air Force ColonelJohn A. Dramesi were planning to steal a boat and travel down theRed River to theGulf of Tonkin.
Lieutenant Melvin Spence Dry was killed on the mission. He was the last SEAL lost during the Vietnam War. His father, retired Navy Captain Melvin H. Dry, spent the rest of his life trying to learn the circumstances surrounding his son's death. The details, however, were long shrouded in secrecy. (Full article...)
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Edward D. Thalmann, MD, expert in hyperbaric medicine
Christian James Lambertsen (May 15, 1917 – February 11, 2011) was an American medical researcher. He was aenvironmental medicine anddiving medicine specialist who was principally responsible for developing theUnited States Navyfrogmen'srebreathers in the early 1940s for underwater warfare. Lambertsen designed a series of rebreathers in 1940 (patent filing date: 16 Dec 1940) and in 1944 (patent issue date: 2 May 1944) and first called his inventionbreathing apparatus. Later, after the war, he called itLaru (acronym forLambertsen Amphibious Respiratory Unit) and finally, in 1952, he changed his invention's name again to SCUBA (Self Contained Underwater Breathing Apparatus). Althoughdiving regulator technology was invented byÉmile Gagnan andJacques-Yves Cousteau in 1943 and was unrelated to rebreathers, the current use of the word SCUBA is largely attributed tothe Gagnan-Cousteau invention. The US Navy considers Lambertsen to be "the father of the Frogmen". (Full article...)
Scuba diving education levels as used by ISO, PADI, CMAS, SSI and NAUI Open Water Diver (OWD) is an entry-levelautonomous divercertification forrecreational scuba diving. Although different agencies use different names, similar entry-level courses are offered by allrecreational diving agencies and consist of a combination of knowledge development (theory), confined water dives (practical training) and open water dives (experience) suitable to allow the diver to dive onopen circuit scuba, inopen water to a limited depth and in conditions similar to those in which the diver has been trained or later gained appropriate experience, to an acceptable level of safety. (Full article...)
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TheInternational Association for Handicapped Divers (or "IAHD") is a non-profit organization with its headquarters inMiddenmeer,the Netherlands. The organization was established in 1993, with the aim to promote, develop and conduct programs for the training in scuba diving of people with a disability. From 1993 to date (2008) IAHD have educated and certified over 5500divers and dive professionals worldwide. As the IAHD is a non-profit foundation, all the people on the board are volunteers. There are also volunteers in regions around the world.
Physical exercise helps people improve their health both physically and mentally. A person with a disability gets these benefits as well as increased social activity by taking up an activity like scuba diving. Being involved with such activities may even result in giving a person with a disability a renewed interest in life and provide positive and lasting benefits.
The risks in training a disabled person in diving are no higher than for able bodied people. Instructors may have to alter some of the techniques and some equipment may also need changing to meet the individual's need. In some cases extra pool or open water training may be needed. In some extreme cases even individual lessons may be needed. IAHD believes that people with a disability should be in a regular class at some point in their training. (Full article...)
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TheInternational Diving Educators Association (IDEA) is an American diving training organization that was originally established in 1952 as part of the Florida Skin Divers Association (FSDA).
In the early days, Scuba Instructor training and certification was handled by the FSDA Scuba Training Committee which was also in charge of Standards & Procedures and new diver certifications. By 1976 there were more FSDA instructors outside of Florida than within the state.
In February 1976, the membership voted to expand the Scuba Training Committee to an international certification agency. The name was changed to the International Diving Educators Association (IDEA). In 1979, IDEA was reorganized and incorporated. IDEA made its first international appearance as a member of the Diving Equipment Manufacturers Association (DEMA) in Las Vegas in 1980. IDEA grew into over 30 foreign countries and across the continental United States. In 1996 IDEA became the fourth largest certification agency worldwide.
IDEA is American owned and operated by US military veterans and first responders. In 1987 the majority of certification agencies agreed to form a not-for-profit agency known as the Recreational Scuba Training Council (RSTC). The purpose of the RSTC is to allow member associations a vehicle for developing standards and to monitor quality control for the mutual benefit of the recreational diving industry and the general public.
IDEA, along with the other members of the RSTC, developed the standards for the Entry Level Scuba standards registered and approved by ANSI. IDEA has affiliates operating in Asia and Europe.
TheAustralian Diver Accreditation Scheme (ADAS) is an international commercial and occupationaldiver certification scheme. It has mutual recognition arrangements with other equivalent national schemes. ADAS qualifications have international recognition.
Training is provided by Accredited Training Establishments (ATEs) which are required to operate at the level of international best practice as defined by ADAS.
The scheme provides the following services:
developing training courses to meet industry needs
certification of divers
accreditation of training establishments
national and international lobbying for the improved safety of divers
promoting the mobility of ADAS licence holders around the world.
This article lists notableunderwater diver certification agencies. These include certification incave diving,commercial diving,recreational diving,technical diving andfreediving.Diver certification agencies are organisations which issue certification of competence in diving skills under their own name, and which train, assess, certify and register the instructors licensed to present courses following the standards for the certification they issue. They are expected to providequality assurance for the training done to their standards by licensed schools and instructors. (Full article...)
TheSpanish Federation of Underwater Activities (Spanish:Federación Española de Actividades Subacuáticas,FEDAS) is the governing body in the field of Spanish aquatic sports. As of 2023, the federation has 897 registered clubs and 31,828 federated athletes.
Scuba diving education levels as used by ISO, PADI, CMAS, SSI and NAUI Advanced Open Water Diver (AOWD) is arecreational scuba diving certification level provided by several divertraining agencies. Agencies offering this level of training under this title includeProfessional Association of Diving Instructors (PADI), andScuba Schools International (SSI). Other agencies offer similar training under different titles. Advanced Open Water Diver is one step up from entry level certification as a beginner autonomous scuba diver. A major difference betweenAutonomous diver equivalentOpen Water Diver (OWD) certification and AOWD is that the depth limit is increased from 18 to 30 metres (60 to 100 ft).
Prerequisite certification level for AOWD training is OWD or a recognized equivalent (ISO 24801-2). Certification requirements for AOWD includes theory learning and assessment, practical training and assessment, and a minimum requirement for number of logged dives, that varies between agencies. SSI requires 24 logged dives. PADI requires 5 dives on course, and the prerequisite is OWD which requires 4 open water dives. No additional logged dives are specified. (Full article...)
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The International Diving Regulators and Certifiers Forum (IDRCF) is an organisation representing a group of national regulatory and certifying bodies foroccupational diving, and other interested and affected parties. The IDRCF confirmed its principles and purpose at their meeting in London in September 2009. The statement of principles and purpose states “The forum has agreed to work together towards mutual recognition to identify and implement best practice in diver training and assessment with the objective of harmonising cross-border diver training outside Europe.”
The organisation has since changed its name to International Diving Regulators and Certifiers Forum (IDRCF) (Full article...)
Association Internationale pour le Développement de l'Apnée (AIDA) (English:International Association for the Development of Apnea) is a worldwide rule- and record-keeping body for competitive breath holding events, also known asfreediving. It sets standards for safety, comparability of Official World Record attempts and freedive education. AIDA International is the parent organization for national clubs of the same name.AIDA World Championships are periodically held. (Full article...)
TheNational Speleological Society (NSS) is an organization formed in 1941 to advance theexploration, conservation, study, and understanding ofcaves in theUnited States. Originally headquartered in Washington D.C., its current offices are inHuntsville, Alabama. The organization engages in the research and scientific study, restoration, exploration, and protection of caves. It has more than 10,000 members in more than 250grottos.
Since 1974 there has been a cave diving section of the society. (Full article...)
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TheDiving Medical Advisory Council (DMAC) is an independent organisation of diving medical specialists, mostly from across Northern Europe which exists to provide expert advice about medical and some safety aspects of commercial diving. The advice is published in the form of guidance documents, which are made available for download.
The committee has also issued position statements on the following subjects:
Commercial Diving and Health (October 2006)
Health Surveillance of Commercial Divers (April 2008)
Exercise Testing in Medical Assessment of Commercial Divers (October 2009)
Requirement for Air Diving to 50 msw in Commercial Diver Training (March 2013)
Deep Saturation Diving (April 2013)
Education and Training in Diving Medicine (November 2014)
A cave diver running a reel with guide line into the overhead environment
Cave-diving isunderwater diving in water-filledcaves. It may be done as anextreme sport, a way of exploring flooded caves for scientific investigation, or for thesearch for and recovery of divers or, as in the2018 Thai cave rescue, other cave users. The equipment used varies depending on the circumstances, and ranges frombreath hold tosurface supplied, but almost all cave-diving is done usingscuba equipment, often in specialised configurations withredundancies such assidemount or backmounted twinset. Recreational cave-diving is generally considered to be a type oftechnical diving due to the lack of afree surface during large parts of the dive, and often involves planneddecompression stops. A distinction is made by recreational diver training agencies between cave-diving and cavern-diving, where cavern diving is deemed to be diving in those parts of a cave where the exit toopen water can be seen by natural light. An arbitrary distance limit to the open water surface may also be specified.
Equipment,procedures, and the requisiteskills have been developed to reduce the risk of becoming lost in a flooded cave, and consequently drowning when thebreathing gas supply runs out. The equipment aspect largely involves the provision of an adequate breathing gas supply to cover reasonably foreseeable contingencies, redundantdive lights and other safety critical equipment, and the use of acontinuous guideline leading the divers back out of theoverhead environment. The skills and procedures include effective management of the equipment, and procedures to recover from foreseeable contingencies and emergencies, both by individual divers, and by the teams that dive together.
In the United Kingdom, cave-diving developed from the locally more common activity ofcaving. Its origins in the United States are more closely associated withrecreational scuba diving. Compared to caving and scuba diving, there are relatively few practitioners of cave-diving. This is due in part to the specialized equipment and skill sets required, and in part because of the high potential risks due to the specific environment.
Despite these risks, water-filled caves attract scuba divers,cavers, andspeleologists due to their often unexplored nature, and present divers with a technical diving challenge. Underwater caves have a wide range of physical features, and can containfauna not found elsewhere. Several organisations dedicated to cave diving safety and exploration exist, and several agencies provide specialised training in the skills and procedures considered necessary for acceptable safety. (Full article...)
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TheCave Divers Association of Australia (CDAA) is acave diving organisation which was formed in September 1973 to represent the interests ofrecreational scuba divers who dive in water-filled caves andsinkholes principally in the Lower South East (now called theLimestone Coast) ofSouth Australia (SA) and secondly in other parts of Australia. Its formation occurred after a series of diving fatalities in waterfilled caves and sinkholes in theMount Gambier region between 1969 and 1973 and in parallel to aGovernment of South Australia inquiry into these deaths. The CDAA's major achievement has been the dramatic reduction of fatalities via the introduction of a site rating scheme and an associated testing system which was brought in during the mid-1970s. While its major area of operation is in the Limestone Coast region of SA, it administers and supports cave diving activity in other parts of Australia including theNullarbor Plain andWellington, New South Wales. (Full article...)
ARSBC Headquarters - Vancouver Maritime Museum TheArtificial Reef Society of British Columbia (ARSBC) is a registered non-profit society based inVancouver,British Columbia (BC), and has been a registered tax-deductible charity inCanada since 1992. Its aim is to create environmentally and economically sustainableartificial reefs (ARs) in British Columbia and around the world for the protection and enhancement of sensitive marine habitats, while also providing interesting destinations for the enjoyment ofscuba divers.
The Society operates without any paid employees. Instead, it is driven by a dedicated volunteer Board of Directors alongside hundreds of volunteers hailing from British Columbia, Alberta, and the northwest United States, all actively involved in its projects, and is based out of theVancouver Maritime Museum.
Since its founding in 1991, eight ships and oneBoeing 737 have been sunk off the west coast of BC. These wreckages act as a safe starting point for creating additional biodiversity, similar toship graveyards, and other man-made structures that became ARs without the toxic leaching hazardous materials such as paints andheavy metals.
The Artificial Reef Society of BC is a member of the Association of British Columbia Marine Industries as listed on their website. (Full article...)
TheEuropean Underwater and Baromedical Society (EUBS) is a primary source of information fordiving andhyperbaric medicine physiology worldwide. The organization was initially formed as theEuropean Underwater and Biomedical Society in 1971 and was an affiliate of theUndersea Medical Society for several years. Its purpose is promoting the advancement of diving and hyperbaric medicine and the education of those involved in the field; EUBS provides a forum and a journal for exchange of information and promotes research into diving medicine. (Full article...)
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Divers Alert Network (DAN) is a group of not-for-profit organizations dedicated to improving diving safety for all divers. It was founded in Durham, North Carolina, United States, in 1980 atDuke University providing 24/7 telephonic hot-line diving medical assistance. Since then the organization has expanded globally and now has independent regional organizations inNorth America,Europe,Japan,Asia-Pacific andSouthern Africa.
The DAN group of organizations provide similar services, some only to members, and others to any person on request. Member services usually include a diving accident hot-line, and diving accident and travel insurance. Services to the general public usually include diving medical advice and training in first aid for diving accidents. DAN America and DAN Europe maintain databases on diving accidents, treatment and fatalities, and crowd-sourced databases on dive profiles uploaded by volunteers which are used for ongoing research programmes. They publish research results and collaborate with other organizations on projects of common interest. (Full article...)
TheUndersea and Hyperbaric Medical Society (UHMS) is an organization based in the US which supports research on matters of hyperbaric medicine and physiology, and provides a certificate of added qualification for physicians with an unrestricted license to practice medicine and for limited licensed practitioners, at the completion of the Program for Advanced Training in Hyperbaric Medicine. They support an extensive library and are a primary source of information fordiving andhyperbaric medicine physiology worldwide. (Full article...)
One day in April 1981 Jessop'ssurvey shipDammtor began searching for the wreck ofHMS Edinburgh in theBarents Sea in theArctic Ocean of the coast of Russia. The ship had been sunk in battle in 1942 duringWorld War II while carrying payment formilitary equipment fromMurmansk in Russia to Scotland. His company, Jessop Marine, won the contract for the salvage rights to the wreck ofEdinburgh because his methods, involving complex cutting machinery and divers, were deemed more appropriate for awar grave, compared to the explosives-oriented methods of other companies.
In late April 1981, the survey ship discovered the ship's final resting place at an approximate position of 72.00°N, 35.00°E, at a depth of 245 metres (804 ft) within ten days of the start of the operation. Using specialist camera equipment,Dammtor took detailed film of the wreck, which allowed Jessop and his divers to carefully plan the salvage operation.
Later that year, on 30 August, the dive-support vessel Stephaniturm journeyed to the site, and salvage operations began in earnest. Leading the operation undersea, by mid-September of that year Jessop was able to salvage over $100,000,000 in Russiangold bullion (431 bars) from the wreck out of 465. (Full article...)
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The Darkness Beckons (ISBN0-939748-32-0) is a book about the history ofUKcave diving byMartyn Farr. It is considered the definitive work on the subject. Farr was a major figure in UK diving at a time when many of the original participants were still alive and available for interview. The first edition of the book was published in 1980. A second edition was published in 1991, followed by a substantially rewritten third edition on 3 July 2017. (Full article...)
The divers were exploring a German U-boat in 230 feet (70 m) of water off the coast of New Jersey. Although experienced in usingtechnical diving gas mixtures such as "trimix" (adding helium gas to the nitrogen and oxygen found in air), they were diving on just compressed air. The pair had set out to retrieve thecaptain's log book from the so-calledU-Who to "fulfill their dream of diving into fame." The U-boat was subsequently identified asU-869.
Chowdhury is a technical diver who, according to writer Neal Matthews' review ofRobert Kurson's bookShadow Divers (2004), "was among the first to adapt cave-diving principles to deep-water wrecks". Also according to Matthews, "His book documents how the clashes of equipment philosophy between cave divers and wreck divers mirrored the clash of diving subcultures." (Full article...)
TheNOAA Diving Manual: Diving for Science and Technology is a book originally published by theUS Department of Commerce for use as training and operational guidance for National Oceanographic and Atmospheric Administration divers. NOAA also publish a Diving Standards and Safety Manual (NDSSM), which describes the minimum safety standards for their diving operations. Several editions of the diving manual have been published, and several editors and authors have contributed over the years. The book is widely used as a reference work by professional and recreational divers. (Full article...)
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Solo diver surveying a dive site. The bailout cylinder can be seen slung at the diver's left side
Solo diving is the practice of self-sufficientunderwater diving without a "dive buddy", particularly with reference toscuba diving, but the term is also applied tofreediving. Professionally, solo diving has always been an option which depends on operational requirements and risk assessment.Surface supplied diving andatmospheric suit diving are commonly single diver underwater activities but are accompanied by an on-surfacesupport team dedicated to the safety of the diver, including astand-by diver, and are not considered solo diving in this sense.
Solo freediving has occurred formillennia as evidenced by artifacts dating back to the ancient people ofMesopotamia when people dived to gather food and to collect pearl oysters. It wasn't until the 1950s, with the development of formalised scuba diving training, that recreational solo diving was deemed to be dangerous, particularly for beginners. In an effort to mitigate associated risks, some scubacertification agencies incorporated the practice ofbuddy diving into theirdiver training programmes. The true risk of solo diving relative to buddy diving in the same environmental conditions has never been reliably established, and may have been significantly overstated by some organisations, though it is generally recognised that buddy and team diving, when performed as specified in the manuals, will enhance safety to some extent depending on circumstances.
Some divers, typically those with advancedunderwater skills, prefer solo diving over buddy diving and acknowledge responsibility for their own safety. One of the more controversial reasons given being the uncertain competence of arbitrarily allocated dive buddies imposed on divers by service providers protected from liability by waivers. Others simply prefer solitude while communing with nature, or find the burden of continuously monitoring another person reduces their enjoyment of the activity, or engage in activities which are incompatible with effective buddy diving practices, and accept the possibility of slightly increased risk, just as others accept the increased risk associated with deeper dives, planned decompression, or penetration under an overhead.
The recreational solo diver uses enhanced procedures, skills and equipment to mitigate the risks associated with not having another competent diver immediately available to assist if something goes wrong. The skills and procedures may be learned through a variety of effective methods to achieve appropriate competence, including formal training programmes with associated assessment and certification. Recreational solo diving, once discouraged by most training agencies, has been accepted since the late 1990s by some agencies that will train and certify experienced divers skilled in self-sufficiency and the use of redundant backupscuba equipment. In most countries there is no legal impediment to solo recreational diving, with or without certification. (Full article...)
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Cap badge of the Special Boat Service
TheSpecial Boat Service (SBS) is thespecial forces unit of the United Kingdom'sRoyal Navy. The SBS can trace its origins back to theSecond World War when the Army Special Boat Section was formed in 1940. After the Second World War, the Royal Navy formed special forces with several name changes—Special Boat Company was adopted in 1951 and re-designated as the Special Boat Squadron in 1974—until on 28 July 1987 when the unit was renamed as the Special Boat Service after assuming responsibility formaritimecounter-terrorism. Most of the operations conducted by the SBS are highlyclassified, and are rarely commented on by theBritish government or theMinistry of Defence, owing to their sensitive nature.
Since bubbles can form in or migrate to any part of the body, DCS can produce many symptoms, and its effects may vary from joint pain and rashes to paralysis and death. DCS often causes air bubbles to settle in major joints like knees or elbows, causing individuals to bend over in excruciating pain, hence its common name, the bends. Individual susceptibility can vary from day to day, and different individuals under the same conditions may be affected differently or not at all. The classification of types of DCS according to symptoms has evolved since its original description in the 19th century. The severity of symptoms varies from barely noticeable to rapidly fatal.
Decompression sickness can occur after an exposure to increased pressure while breathing a gas with a metabolically inert component, then decompressing too fast for it to be harmlessly eliminated through respiration, or by decompression by an upward excursion from a condition of saturation by the inert breathing gas components, or by a combination of these routes. Theoretical decompression risk is controlled by the tissue compartment with the highest inert gas concentration, which for decompression from saturation, is the slowest tissue to outgas.
The risk of DCS can be managed through properdecompression procedures, and contracting the condition has become uncommon. Its potential severity has driven much research to prevent it, and divers almost universally usedecompression schedules ordive computers to limit their exposure and to monitor their ascent speed. If DCS is suspected, it is treated byhyperbaric oxygen therapy in arecompression chamber. Where a chamber is not accessible within a reasonable time frame, in-water recompression may be indicated for a narrow range of presentations, if there are suitably skilled personnel and appropriate equipment available on site. Diagnosis is confirmed by a positive response to the treatment. Early treatment results in a significantly higher chance of successful recovery. (Full article...)
Decompression in the context ofdiving derives from the reduction inambient pressure experienced by the diver during the ascent at the end of a dive or hyperbaric exposure and refers to both the reduction inpressure and the process of allowing dissolvedinert gases to be eliminated from thetissues during this reduction in pressure.
When a diver descends in the water column theambient pressure rises.Breathing gas is supplied at the same pressure as the surrounding water, and some of this gas dissolves into the diver's blood and other tissues. Inert gas continues to be taken up until the gas dissolved in the diver is in a state of equilibrium with the breathing gas in the diver'slungs, (see: "Saturation diving"), or the diver moves up in the water column and reduces the ambient pressure of the breathing gas until the inert gases dissolved in the tissues are at a higher concentration than the equilibrium state, and start diffusing out again. Dissolved inert gases such asnitrogen orhelium can form bubbles in the blood and tissues of the diver if thepartial pressures of the dissolved gases in the diver get too high when compared to theambient pressure. These bubbles, and products of injury caused by the bubbles, can cause damage to tissues generally known asdecompression sickness orthe bends. The immediate goal of controlled decompression is to avoid development of symptoms of bubble formation in the tissues of the diver, and the long-term goal is to also avoid complications due to sub-clinical decompression injury.
The symptoms of decompression sickness are known to be caused by damage resulting from the formation and growth of bubbles of inert gas within the tissues and by blockage of arterial blood supply to tissues by gas bubbles and otheremboli consequential to bubble formation and tissue damage. The precise mechanisms of bubble formation and the damage they cause has been the subject of medical research for a considerable time and several hypotheses have been advanced and tested. Tables and algorithms for predicting the outcome of decompression schedules for specified hyperbaric exposures have been proposed, tested, and used, and usually found to be of some use but not entirely reliable. Decompression remains a procedure with some risk, but this has been reduced and is generally considered to be acceptable for dives within the well-tested range of commercial, military and recreational diving.
The first recorded experimental work related to decompression was conducted byRobert Boyle, who subjected experimental animals to reduced ambient pressure by use of a primitivevacuum pump. In the earliest experiments the subjects died from asphyxiation, but in later experiments, signs of what was later to become known as decompression sickness were observed. Later, when technological advances allowed the use of pressurisation of mines and caissons to exclude water ingress, miners were observed to present symptoms of what would become known as caisson disease, the bends, and decompression sickness. Once it was recognized that the symptoms were caused by gas bubbles, and that recompression could relieve the symptoms, further work showed that it was possible to avoid symptoms by slow decompression, and subsequently various theoretical models have been derived to predict low-risk decompression profiles and treatment of decompression sickness. (Full article...)
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In 1942–43 the UK Government carried out extensive testing for oxygen toxicity in divers. The chamber is pressurised with air to 3.7 bar. The subject in the centre is breathing 100% oxygen from a mask.
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecularoxygen (O 2) at increasedpartial pressures. Severe cases can result incell damage and death, with effects most often seen in thecentral nervous system,lungs, and eyes. Historically, the central nervous system condition was called thePaul Bert effect, and the pulmonary condition theLorrain Smith effect, after the researchers who pioneered the discoveries and descriptions in the late 19th century. Oxygen toxicity is a concern forunderwater divers, those on high concentrations of supplemental oxygen, and those undergoinghyperbaric oxygen therapy.
The result of breathing increased partial pressures of oxygen ishyperoxia, an excess of oxygen in body tissues. The body is affected in different ways depending on the type of exposure. Central nervous system toxicity is caused by short exposure to high partial pressures of oxygen at greater than atmospheric pressure. Pulmonary and ocular toxicity result from longer exposure to increased oxygen levels at normal pressure. Symptoms may include disorientation, breathing problems, and vision changes such asmyopia. Prolonged exposure to above-normal oxygen partial pressures, or shorter exposures to very high partial pressures, can causeoxidative damage tocell membranes, collapse of thealveoli in the lungs,retinal detachment, andseizures. Oxygen toxicity is managed by reducing the exposure to increased oxygen levels. Studies show that, in the long term, a robust recovery from most types of oxygen toxicity is possible.
Protocols for avoidance of the effects of hyperoxia exist in fields where oxygen is breathed at higher-than-normal partial pressures, includingunderwater diving using compressedbreathing gases, hyperbaric medicine,neonatal care andhuman spaceflight. These protocols have resulted in the increasing rarity of seizures due to oxygen toxicity, with pulmonary and ocular damage being largely confined to the problems of managing premature infants.
In recent years, oxygen has become available for recreational use inoxygen bars. TheUS Food and Drug Administration has warned those who have conditions such as heart or lung disease not to use oxygen bars. Scuba divers use breathing gases containing up to 100% oxygen, and should have specific training in using such gases. (Full article...)
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The hand signal "OK" Diver communications are the methods used bydivers to communicate with each other or with surface members of the dive team. Inprofessional diving, diver communication is usually between a single working diver and thediving supervisor at the surface control point. This is considered important both for managing the diving work, and as a safety measure for monitoring the condition of the diver. The traditional method of communication was by line signals, but this has been superseded by voice communication, and line signals are now used in emergencies when voice communications have failed. Surface supplied divers often carry a closed circuit video camera on thehelmet which allows the surface team to see what the diver is doing and to be involved in inspection tasks. This can also be used to transmit hand signals to the surface if voice communications fails. Underwater slates may be used to write text messages which can be shown to other divers, and there are some dive computers which allow a limited number of pre-programmed text messages to be sent through-water to other divers or surface personnel with compatible equipment.
Communication between divers and between surface personnel and divers is imperfect at best, and non-existent at worst, as a consequence of the physical characteristics of water. This prevents divers from performing at their full potential. Voice communication is the most generally useful format underwater, as visual forms are more affected by visibility, and written communication and signing are relatively slow and restricted by diving equipment.
Recreational divers do not usually have access to voice communication equipment, and it does not generally work with a standard scuba demand valve mouthpiece, so they use other signals. Hand signals are generally used when visibility allows, and there are a range of commonly used signals, with some variations. These signals are often also used by professional divers to communicate with other divers. There is also a range of other special purpose non-verbal signals, mostly used for safety and emergency communications. (Full article...)
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Arecompression chamber is used to treat some diving disorders and for training divers to recognise the symptoms.
The disorders are caused bybreathing gas at the high pressures encountered at the depth of the water and divers will often breathe a gas mixture different from air to mitigate these effects.Nitrox, which contains moreoxygen and lessnitrogen, is commonly used as a breathing gas to reduce the risk of decompression sickness atrecreational depths (up to 34 meters or 112 feet for 32% oxygen).Helium may be added to reduce the amount of nitrogen and oxygen in the gas mixture when diving deeper, to reduce the effects of narcosis, to avoid the risk of oxygen toxicity, and to reducework of breathing. This is complicated at depths beyond about 150 metres (500 ft), because a helium–oxygen mixture (heliox) then causes high pressure nervous syndrome. More exotic mixtures such ashydreliox, a hydrogen–helium–oxygen mixture, are used at extreme depths to counteract this. (Full article...)
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Divers breathe a mixture of oxygen, helium and nitrogen for deep dives to avoid the effects of narcosis. A cylinder label shows the maximum operating depth and mixture (oxygen/helium).
Nitrogen narcosis (also known asnarcosis while diving,inert gas narcosis,raptures of the deep,Martini effect) is a reversible alteration inconsciousness that occurs whilediving at depth. It is caused by theanesthetic effect of certain gases at highpartial pressure. The Greek wordνάρκωσις (narkōsis), "the act of making numb", is derived fromνάρκη (narkē), "numbness, torpor", a term used byHomer andHippocrates. Narcosis produces a state similar todrunkenness (alcohol intoxication), ornitrous oxide inhalation. It can occur during shallow dives, but does not usually become noticeable at depths less than 30 metres (98 ft).
Except forhelium and probablyneon, allgases that can be breathed have a narcotic effect, although widely varying in degree. The effect is consistently greater for gases with a higherlipid solubility, and although the mechanism of this phenomenon is stillnot fully clear, there is good evidence that the two properties are mechanistically related. As depth increases, the mental impairment may become hazardous. Divers can learn to cope with some of the effects of narcosis, but it is impossible to develop atolerance. Narcosis can affect all ambient pressure divers, although susceptibility varies widely among individuals and from dive to dive. The main modes of underwater diving that deal with its prevention and management arescuba diving andsurface-supplied diving at depths greater than 30 metres (98 ft).
Narcosis may be completely reversed in a few minutes by ascending to a shallower depth, with no long-term effects. Thus narcosis while diving in open water rarely develops into a serious problem as long as the divers are aware of its symptoms, and are able to ascend to manage it. Diving much beyond 40 m (130 ft) is generally considered outside the scope ofrecreational diving. To dive at greater depths, as narcosis andoxygen toxicity become critical risk factors, gas mixtures such astrimix orheliox are used. These mixtures prevent or reduce narcosis by replacing some or all of the inert fraction of the breathing gas with non-narcotic helium. There is a synergy betweencarbon dioxide toxicity and inert gas narcosis which is recognised but not fully understood. Conditions where high work of breathing due to gas density occur tend to exacerbate this effect. (Full article...)
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Surface supplied diver on diving stage
There are several categories ofdecompression equipment used to help diversdecompress, which is the process required to allowambient pressure divers to return to the surface safely after spending time underwater at higher ambient pressures.
Decompression obligation for a givendive profile must be calculated and monitored to ensure that the risk ofdecompression sickness is controlled. Some equipment is specifically for these functions, both during planning before the dive and during the dive. Other equipment is used to mark the underwater position of the diver, as a position reference in low visibility or currents, or to assist the diver's ascent and control the depth.
Decompression may be shortened ("accelerated") by breathing an oxygen-rich "decompression gas" such as anitrox blend or pureoxygen. The high partial pressure of oxygen in such decompression mixes produces the effect known as theoxygen window. This decompression gas is often carried by scuba divers in side-slung cylinders.Cave divers who can only return by a single route, can leave decompression gas cylinders attached to the guideline ("stage" or "drop cylinders") at the points where they will be used.Surface-supplied divers will have the composition of the breathing gas controlled at thegas panel.
Divers with long decompression obligations may be decompressed inside gas filledhyperbaric chambers in the water or at the surface, and in the extreme case,saturation divers are only decompressed at the end of a project, contract, or tour of duty that may be several weeks long. (Full article...)
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Divers decompressing in the water at the end of a dive Thedecompression of adiver is the reduction inambient pressure experienced during ascent from depth or depressurisation of adiving chamber. It is also the process of elimination of dissolvedmetabolically inert gases from the diver's body tissues which accumulated during the dive. Gas elimination also occurs during pauses in the ascent known as decompression stops, where the pressure is held constant, and after surfacing, until the gas concentrations reach equilibrium. Divers breathing gas at ambient pressure need to ascend at a rate determined by their recent exposure to pressure and the breathing gas in use. A diver who only breathes gas at atmospheric pressure whenfree-diving orsnorkelling will not usually need to decompress. Divers using anatmospheric diving suit do not need to decompress as they are never exposed to high ambient pressure.
When an ambient pressure diver descends in the water, thehydrostatic pressure, and therefore the ambient pressure, rises. Becausebreathing gas is supplied at ambientpressure, some of this gas dissolves into the diver's blood and is transferred by the blood to other tissues where it may accumulate by diffusion. Inert gas such asnitrogen orhelium continues to be taken up until the gas dissolved in the diver is in a state of equilibrium with the breathing gas in the diver'slungs, at which point the diver issaturated for that depth and breathing mixture, or the depth, and therefore the pressure, is changed, or thepartial pressures of the gases are changed by modifying the breathing gas mixture. During ascent, the ambient pressure is reduced, and at some stage the inert gases dissolved in any given tissue will be at a higher concentration than the equilibrium state and start to diffuse out again to the blood and be eliminated in the lungs. If the pressure reduction is sufficient, excess gas may form bubbles, which may lead todecompression sickness, a possibly debilitating or life-threatening condition. It is essential that divers manage their decompression to avoid excessive bubble formation and decompression sickness. A mismanaged decompression usually results from reducing the ambient pressure too quickly for the amount of gas in solution to be eliminated safely. These bubbles may block arterial blood supply to tissues or directly cause tissue damage. If the decompression is effective, theasymptomaticvenous microbubbles present after most dives are eliminated from the diver's body in thealveolar capillary beds of the lungs. If they are not given enough time, or more bubbles are created than can be eliminated safely, the bubbles grow in size and number causing the symptoms and injuries of decompression sickness. The immediate goal of controlled decompression is to avoid development of symptoms of bubble formation in the tissues of the diver, and the long-term goal is to avoid complications due tosub-clinical decompression injury.
The mechanisms of bubble formation and the damage bubbles cause has been the subject ofmedical research for a considerable time and severalhypotheses have been advanced and tested. Tables andalgorithms for predicting the outcome of decompression schedules for specified hyperbaric exposures have been proposed, tested and used, and in many cases, superseded. Although constantly refined and generally considered acceptably reliable, the actual outcome for any individual diver remains slightly unpredictable. Although decompression retains some risk, this is now generally considered acceptable for dives within the well tested range of normal recreational and professional diving.
Decompression may becontinuous orstaged. A staged decompression ascent is interrupted bydecompression stops at specified depth intervals, but the entire ascent is actually part of the decompression and the ascent rate is important for harmless elimination of inert gas. Ano-decompression dive, or more accurately, a dive with no-stop decompression, relies on limiting the ascent rate for avoidance of excessive bubble formation in the fastest tissues. The elapsed time at surface pressure immediately after a dive is known as the surface interval, is also an important part of decompression, and can be thought of as the last decompression stop of a dive. It can take up to 24 hours for the body to return to its normal atmospheric levels of inert gas saturation after a dive. (Full article...)
The volcano has a flat-topped summit rising about 3,000 m (10,000 ft) above theseabed, to 24 m (79 ft) belowsea level. The seamount lies at the southern end of a long underwater volcanicmountain range called the Pratt-Welker orKodiak-Bowie Seamount chain, stretching from theAleutian Trench in the north almost to Haida Gwaii in the south.
Bowie Seamount lies on thePacific Plate, a large segment of the Earth's surface which moves in a northwestern direction under the Pacific Ocean. It is adjacent to two other submarine volcanoes;Hodgkins Seamount on its northern flank andGraham Seamount on its eastern flank. (Full article...)
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Dive profile of an actual dive as recorded by a personal dive computer and displayed on a desktop screen using dive logging software. In this case depth is in metres. Adive profile is a description of a diver's pressure exposure over time. It may be as simple as just a depth and time pair, as in: "sixty for twenty," (abottom time of 20 minutes at a depth of 60 feet) or as complex as a second by second graphical representation of depth and time recorded by a personaldive computer. Several common types of dive profile are specifically named, and these may be characteristic of the purpose of the dive. For example, aworking dive at a limited location will often follow a constant depth (square) profile, and arecreational dive is likely to follow a multilevel profile, as the divers start deep and work their way up a reef to get the most out of the available breathing gas. The names are usually descriptive of the graphic appearance.
The intended dive profile is useful as aplanning tool as an indication of the risks ofdecompression sickness andoxygen toxicity for the exposure, to calculate a decompression schedule for the dive, and also for estimating the volume of open-circuitbreathing gas needed for a planned dive, as these depend in part upon the depth and duration of the dive. A dive profile diagram is conventionally drawn with elapsed time running from left to right and depth increasing down the page.
Many personaldive computers record the instantaneous depth at small time increments during the dive. This data can sometimes be displayed directly on the dive computer or more often downloaded to apersonal computer, tablet, or smartphone and displayed in graphic form as a dive profile. (Full article...)
Diving cylinders are usually manufactured from aluminum or steel alloys, and when used on a scuba set are normally fitted with one of two common types ofscuba cylinder valve for filling and connection to the regulator. Other accessories such asmanifolds, cylinder bands, protective nets and boots and carrying handles may be provided. Various configurations of harness may be used by the diver to carry a cylinder or cylinders while diving, depending on the application. Cylinders used for scuba typically have an internal volume (known as water capacity) of between 3 and 18 litres (0.11 and 0.64 cu ft) and a maximum working pressure rating from 184 to 300bars (2,670 to 4,350 psi). Cylinders are also available in smaller sizes, such as 0.5, 1.5 and 2 litres; however these are usually used for purposes such as inflation ofsurface marker buoys,dry suits, andbuoyancy compensators rather than breathing. Scuba divers may dive with a single cylinder, a pair of similar cylinders, or a main cylinder and a smaller"pony" cylinder, carried on the diver's back or clipped onto the harness at the side. Paired cylinders may be manifolded together or independent. Intechnical diving, more than two scuba cylinders may be needed to carry different gases. Larger cylinders, typically up to 50 litre capacity, are used as on-board emergency gas supply on diving bells. Large cylinders are also used forsurface supply through adiver's umbilical, and may be manifolded together on a frame for transportation.
Theselection of an appropriate set of scuba cylinders for a diving operation is based on theestimated amount of gas required to safely complete the dive. Diving cylinders are most commonly filled with air, but because the main components of air can cause problems when breathed underwater at higher ambient pressure, divers may choose to breathe from cylinders filled with mixtures of gases other than air. Many jurisdictions have regulations that govern the filling, recording of contents, and labeling for diving cylinders. Periodictesting and inspection of diving cylinders is often obligatory to ensure the safety of operators of filling stations. Pressurized diving cylinders are considereddangerous goods for commercial transportation, and regional andinternational standards for colouring and labeling may also apply. (Full article...)
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For Cousteau there existed only Cousteau. He never acknowledged others or corrected the impression that he wasn’t the first in diving or in underwater photography.
— Hans Hass, in Ecott, Tim. (2001):Neutral Buoyancy
Vitello, Paul (July 7, 2013)."Hans Hass, Early Undersea Explorer, Dies at 94".New York Times. Retrieved17 July 2018. A version of this article appears in print on July 7, 2013, on Page A18 of the New York edition with the headline: Hans Hass, 94, Early Explorer of the World Beneath the Sea.
This portal is within the scope ofWikiProject Underwater diving, a subject-area collaboration for underwater diving topics, andWikiProject Portals, a collaboration on portal design, development, and maintenance.
Women Divers Hall of Fame members. If any of these go blue, check and where appropriate add to membership list to WDHOF article. In date as of July 2022.
Stand-by diver – A member of a dive team who is ready to assist or rescue the working diver
Saturation diving skills – Surface-supplied diving skills specific to saturation operations Sat diving standard procedures and emergency procedures, closed bell rescue etc. (Split fromSurface supplied diving skills?)
Very low priority
Bailout gas – Emergency breathing gas supply carried by the diver
Bottom gas – Gas breathed during the deep part of a dive
Breathing air – Air quality suitable for safe breathing
Decompression gas – Oxygen-rich gas used for accelerated decompression
Emergency gas supply – Alternative independent breathing gas supply carried by a diver
Australian Diver Accreditation Scheme – Australian based international occupational diver accreditation organisation – content other than training standards needed
Diver rescue – Rescue of a distressed or incapacitated diver - add decompression, surface supply and bell procedures.
Diver training – Processes to develop the skills and knowledge to dive safely underwater – More needed on military diver training
Diving instructor – Person who trains and assesses underwater divers – Several empty sections. May be possible to use summaries copied from other article for some of them.
Diving medicine#History – Diagnosis, treatment and prevention of disorders caused by underwater diving and Ethical and medicolegal issues (empty section)
Diving procedures – Standardised methods of doing things that are known to work effectively and acceptably safely – finish link annotations
Dutch Springs – Flooded quarry in Pennsylvania used as a recreational diving site
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Category:Underwater diving safety
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