 | Portal maintenance status: (June 2018)
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ROVs can do some kinds of work without diver intervention
Topic definition
Portal scope
The scope of this portal 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
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 as diving, an ambiguous term with several possible meanings, depending on context. Immersion in water and exposure to high ambient pressure have physiological effects that limit the depths and duration possible in ambient pressure diving. Humans are not physiologically and anatomically well-adapted to the environmental conditions of diving, and various equipment has been developed to extend the depth and duration of human dives, and allow different types of work to be done.
In ambient pressure diving, the diver is directly exposed to the pressure of the surrounding water. The ambient pressure diver may dive on breath-hold (freediving) or use breathing apparatus for scuba divingorsurface-supplied diving, and the saturation diving technique reduces the risk of decompression sickness (DCS) after long-duration deep dives. Atmospheric diving suits (ADS) may be used to isolate the diver from high ambient pressure. Crewed submersibles can extend depth range to full ocean depth, and remotely controlled or robotic machines can reduce risk to humans.
The environment exposes the diver to a wide range of hazards, and though the risks are largely controlled by appropriate diving skills, training, types of equipment and breathing gases used depending on the mode, depth and purpose of diving, it remains a relatively dangerous activity. Professional diving is usually regulated by occupational health and safety legislation, while recreational diving may be entirely unregulated. Diving activities are restricted to maximum depths of about 40 metres (130 ft) for recreational scuba diving, 530 metres (1,740 ft) for commercial saturation diving, and 610 metres (2,000 ft) wearing atmospheric suits. Diving 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, and underwater search and recovery dive teams. Military diving includes combat diving, clearance diving and ships husbandry. Deep sea diving is underwater diving, usually with surface-supplied equipment, and often refers to the use of standard diving dress with the traditional copper helmet. Hard hat diving is any form of diving with a helmet, including the standard copper helmet, and other forms of free-flow and lightweight demand helmets. The history of breath-hold diving goes back at least to classical times, and there is evidence of prehistoric hunting and gathering of seafoods that may have involved underwater swimming. Technical advances allowing the provision of breathing gas to a diver underwater at ambient pressure are recent, and self-contained breathing systems developed at an accelerated rate following the Second World War. (Full article...)
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Surface-supplied diving is a modeofunderwater diving using equipment supplied with breathing gas through a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell. This is different from scuba 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. 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.
The copper helmeted free-flow standard diving dress is the version which made commercial diving a viable occupation, and although still used in some regions, this heavy equipment has been superseded by lighter free-flow helmets, and to a large extent, lightweight demand helmets, band masks and full-face diving masks. Breathing gases used include air, heliox, nitrox and trimix.
Saturation diving is a mode of surface supplied diving in which the divers live under pressure in a saturation systemorunderwater habitat and are decompressed only at the end of a tour of duty.
Airline, or hookah diving, and "compressor diving" are lower technology variants also using a breathing air supply from the surface. (Full article...)
Surface-supplied diving is a modeofunderwater diving using equipment supplied with breathing gas through a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell. This is different from scuba 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. 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.
The copper helmeted free-flow standard diving dress is the version which made commercial diving a viable occupation, and although still used in some regions, this heavy equipment has been superseded by lighter free-flow helmets, and to a large extent, lightweight demand helmets, band masks and full-face diving masks. Breathing gases used include air, heliox, nitrox and trimix.
Saturation diving is a mode of surface supplied diving in which the divers live under pressure in a saturation systemorunderwater habitat and are decompressed only at the end of a tour of duty.
Airline, or hookah diving, and "compressor diving" are lower technology variants also using a breathing air supply from the surface. (Full article...)
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 as diving, an ambiguous term with several possible meanings, depending on context.
Immersion in water and exposure to high ambient pressure have physiological effects that limit the depths and duration possible in ambient pressure diving. Humans are not physiologically and anatomically well-adapted to the environmental conditions of diving, and various equipment has been developed to extend the depth and duration of human dives, and allow different types of work to be done.
In ambient pressure diving, the diver is directly exposed to the pressure of the surrounding water. The ambient pressure diver may dive on breath-hold (freediving) or use breathing apparatus for scuba divingorsurface-supplied diving, and the saturation diving technique reduces the risk of decompression sickness (DCS) after long-duration deep dives. Atmospheric diving suits (ADS) may be used to isolate the diver from high ambient pressure. Crewed submersibles can extend depth range to full ocean depth, and remotely controlled or robotic machines can reduce risk to humans.
The environment exposes the diver to a wide range of hazards, and though the risks are largely controlled by appropriate diving skills, training, types of equipment and breathing gases used depending on the mode, depth and purpose of diving, it remains a relatively dangerous activity. Professional diving is usually regulated by occupational health and safety legislation, while recreational diving may be entirely unregulated.
Diving activities are restricted to maximum depths of about 40 metres (130 ft) for recreational scuba diving, 530 metres (1,740 ft) for commercial saturation diving, and 610 metres (2,000 ft) wearing atmospheric suits. Diving 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, and underwater search and recovery dive teams. Military diving includes combat diving, clearance diving and ships husbandry.
Deep sea diving is underwater diving, usually with surface-supplied equipment, and often refers to the use of standard diving dress with the traditional copper helmet. Hard hat diving is any form of diving with a helmet, including the standard copper helmet, and other forms of free-flow and lightweight demand helmets.
The history of breath-hold diving goes back at least to classical times, and there is evidence of prehistoric hunting and gathering of seafoods that may have involved underwater swimming. Technical advances allowing the provision of breathing gas to a diver underwater at ambient pressure are recent, and self-contained breathing systems developed at an accelerated rate following the Second World War. (Full article...)
Surface-supplied diving is a modeofunderwater diving using equipment supplied with breathing gas through a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell. This is different from scuba 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. 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.
The copper helmeted free-flow standard diving dress is the version which made commercial diving a viable occupation, and although still used in some regions, this heavy equipment has been superseded by lighter free-flow helmets, and to a large extent, lightweight demand helmets, band masks and full-face diving masks. Breathing gases used include air, heliox, nitrox and trimix.
Saturation diving is a mode of surface supplied diving in which the divers live under pressure in a saturation systemorunderwater habitat and are decompressed only at the end of a tour of duty.
Airline, or hookah diving, and "compressor diving" are lower technology variants also using a breathing air supply from the surface. (Full article...)
Scuba diving is a modeofunderwater diving whereby divers use breathing equipment that is completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The name scuba is an anacronym for "Self-Contained Underwater Breathing Apparatus" and was coined by Christian J. Lambertsen in a patent submitted in 1952. Scuba divers carry their own source of breathing gas, usually compressed air, affording them greater independence and movement than surface-supplied divers, and more time underwater than free divers. Although the use of compressed air is common, a gas blend with a higher oxygen content, known as enriched air or nitrox, has become popular due to the reduced nitrogen intake during long or repetitive dives. Also, breathing gas diluted with helium may be used to reduce the effects of nitrogen narcosis during deeper dives.
Open-circuit scuba systems discharge the breathing gas into the environment as it is exhaled, and consist of one or more diving cylinders containing breathing gas at high pressure which is supplied to the diver at ambient pressure through a diving regulator. They may include additional cylinders for range extension, decompression gasoremergency breathing gas. Closed-circuit or semi-closed circuit rebreather scuba systems allow recycling of exhaled gases. The volume of gas used is reduced compared to that of open-circuit, so a smaller cylinder or cylinders may be used for an equivalent dive duration. 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 covert military divers to avoid detection, scientific divers to avoid disturbing marine animals, and media divers to avoid bubble interference.
Scuba diving may be done recreationallyorprofessionally in a number of applications, including scientific, military and public safety roles, but most commercial diving uses surface-supplied diving equipment when this is practicable. Scuba divers engaged in armed forces covert operations may be referred to as frogmen, combat divers or attack swimmers.
A scuba diver primarily moves underwater by using fins attached to the feet, but external propulsion can be provided by a diver propulsion vehicle, or a sled pulled from the surface. Other equipment needed for scuba diving includes a mask to improve underwater vision, exposure protection by means of a diving suit, ballast weights to overcome excess buoyancy, equipment to control buoyancy, and equipment related to the specific circumstances and purpose of the dive, which may include a snorkel when swimming on the surface, a cutting tool to manage entanglement, lights, a dive computer to monitor decompression status, and signalling devices. Scuba divers are trained in the procedures and skills appropriate to their level of certification by diving instructors affiliated to the diver certification organisations which issue these certifications. These include standard operating procedures for using the equipment and dealing with the general hazards of the underwater environment, and emergency procedures for self-help and assistance of a similarly equipped diver experiencing problems. A minimum level of fitness and health is required by most training organisations, but a higher level of fitness may be appropriate for some applications. (Full article...)
Freediving, free-diving, free diving, breath-hold diving, or skin diving, is a mode of underwater diving that relies on breath-holding until resurfacing rather than the use of breathing apparatus such as scuba 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.
Examples of freediving activities are traditional fishing techniques, competitive and non-competitive freediving, competitive and non-competitive spearfishing and freediving photography, synchronised swimming, underwater football, underwater rugby, underwater hockey, underwater target shooting and snorkeling. There are also a range of "competitive apnea" disciplines; in which competitors attempt to attain great depths, times, or distances on a single breath.
Historically, the term free diving was also used to refer to scuba diving, due to the freedom of movement compared with surface supplied diving. (Full article...)
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 as diving, an ambiguous term with several possible meanings, depending on context.
Immersion in water and exposure to high ambient pressure have physiological effects that limit the depths and duration possible in ambient pressure diving. Humans are not physiologically and anatomically well-adapted to the environmental conditions of diving, and various equipment has been developed to extend the depth and duration of human dives, and allow different types of work to be done.
In ambient pressure diving, the diver is directly exposed to the pressure of the surrounding water. The ambient pressure diver may dive on breath-hold (freediving) or use breathing apparatus for scuba divingorsurface-supplied diving, and the saturation diving technique reduces the risk of decompression sickness (DCS) after long-duration deep dives. Atmospheric diving suits (ADS) may be used to isolate the diver from high ambient pressure. Crewed submersibles can extend depth range to full ocean depth, and remotely controlled or robotic machines can reduce risk to humans.
The environment exposes the diver to a wide range of hazards, and though the risks are largely controlled by appropriate diving skills, training, types of equipment and breathing gases used depending on the mode, depth and purpose of diving, it remains a relatively dangerous activity. Professional diving is usually regulated by occupational health and safety legislation, while recreational diving may be entirely unregulated.
Diving activities are restricted to maximum depths of about 40 metres (130 ft) for recreational scuba diving, 530 metres (1,740 ft) for commercial saturation diving, and 610 metres (2,000 ft) wearing atmospheric suits. Diving 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, and underwater search and recovery dive teams. Military diving includes combat diving, clearance diving and ships husbandry.
Deep sea diving is underwater diving, usually with surface-supplied equipment, and often refers to the use of standard diving dress with the traditional copper helmet. Hard hat diving is any form of diving with a helmet, including the standard copper helmet, and other forms of free-flow and lightweight demand helmets.
The history of breath-hold diving goes back at least to classical times, and there is evidence of prehistoric hunting and gathering of seafoods that may have involved underwater swimming. Technical advances allowing the provision of breathing gas to a diver underwater at ambient pressure are recent, and self-contained breathing systems developed at an accelerated rate following the Second World War. (Full article...)
Saturation diving is diving for periods long enough to bring all tissues into equilibrium with the partial pressures of the inert components of the breathing gas used. It is a diving mode that reduces the number of decompressions divers working at great depths must undergo by only decompressing divers once at the end of the diving operation, which may last days to weeks, having them remain under pressure for the whole period. A diver breathing pressurized gas accumulates dissolved inert gas used in the breathing mixture to dilute the oxygen to a non-toxic level in the tissues, which can cause potentially fatal decompression sickness ("the bends") if permitted to come out of solution within the body tissues; hence, returning to the surface safely requires lengthy decompression so that the inert gases can be eliminated via the lungs. Once the dissolved gases in a diver's tissues reach the saturation point, however, decompression time does not increase with further exposure, as no more inert gas is accumulated.
Saturation diving takes advantage of this by having divers remain in that saturated state. When not in the water, the divers live in a sealed environment which maintains their pressurised state; this can be an ambient pressure underwater habitat or a saturation system at the surface, with transfer to and from the pressurised living quarters to the equivalent depth underwater via a closed, pressurised diving bell. This may be maintained for up to several weeks, and divers are decompressed to surface pressure only once, at the end of their tour of duty. By limiting the number of decompressions in this way, and using a conservative decompression schedule the risk of decompression sickness is significantly reduced, and the total time spent decompressing is minimised. Saturation divers typically breathe a helium–oxygen mixture to prevent nitrogen narcosis, and limit work of breathing, but at shallow depths saturation diving has been done on nitrox mixtures.
Most of the physiological and medical aspects of diving to the same depths are much the same in saturation and bell-bounce ambient pressure diving, or are less of a problem, but there are medical and psychological effects of living under saturation for extended periods.
Saturation diving is a specialized form 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...)
Rebreather divingisunderwater diving using diving rebreathers, a class of underwater breathing apparatus which recirculate the breathing gas exhaled by the diver after replacing the oxygen used and removing the carbon dioxide metabolic product. Rebreather diving is practiced by recreational, military and scientific divers in applications where it has advantages over open circuit scuba, 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 for scuba applications, but are also occasionally used for bailout systems for surface-supplied diving. Gas reclaim systems used for deep heliox diving use similar technology to rebreathers, as do saturation diving life-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 potential points 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 and fault 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...)
Surface-supplied diving is a modeofunderwater diving using equipment supplied with breathing gas through a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell. This is different from scuba 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. 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.
The copper helmeted free-flow standard diving dress is the version which made commercial diving a viable occupation, and although still used in some regions, this heavy equipment has been superseded by lighter free-flow helmets, and to a large extent, lightweight demand helmets, band masks and full-face diving masks. Breathing gases used include air, heliox, nitrox and trimix.
Saturation diving is a mode of surface supplied diving in which the divers live under pressure in a saturation systemorunderwater habitat and are decompressed only at the end of a tour of duty.
Airline, or hookah diving, and "compressor diving" are lower technology variants also using a breathing air supply from the surface. (Full article...)
Scuba diving is a modeofunderwater diving whereby divers use breathing equipment that is completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The name scuba is an anacronym for "Self-Contained Underwater Breathing Apparatus" and was coined by Christian J. Lambertsen in a patent submitted in 1952. Scuba divers carry their own source of breathing gas, usually compressed air, affording them greater independence and movement than surface-supplied divers, and more time underwater than free divers. Although the use of compressed air is common, a gas blend with a higher oxygen content, known as enriched air or nitrox, has become popular due to the reduced nitrogen intake during long or repetitive dives. Also, breathing gas diluted with helium may be used to reduce the effects of nitrogen narcosis during deeper dives.
Open-circuit scuba systems discharge the breathing gas into the environment as it is exhaled, and consist of one or more diving cylinders containing breathing gas at high pressure which is supplied to the diver at ambient pressure through a diving regulator. They may include additional cylinders for range extension, decompression gasoremergency breathing gas. Closed-circuit or semi-closed circuit rebreather scuba systems allow recycling of exhaled gases. The volume of gas used is reduced compared to that of open-circuit, so a smaller cylinder or cylinders may be used for an equivalent dive duration. 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 covert military divers to avoid detection, scientific divers to avoid disturbing marine animals, and media divers to avoid bubble interference.
Scuba diving may be done recreationallyorprofessionally in a number of applications, including scientific, military and public safety roles, but most commercial diving uses surface-supplied diving equipment when this is practicable. Scuba divers engaged in armed forces covert operations may be referred to as frogmen, combat divers or attack swimmers.
A scuba diver primarily moves underwater by using fins attached to the feet, but external propulsion can be provided by a diver propulsion vehicle, or a sled pulled from the surface. Other equipment needed for scuba diving includes a mask to improve underwater vision, exposure protection by means of a diving suit, ballast weights to overcome excess buoyancy, equipment to control buoyancy, and equipment related to the specific circumstances and purpose of the dive, which may include a snorkel when swimming on the surface, a cutting tool to manage entanglement, lights, a dive computer to monitor decompression status, and signalling devices. Scuba divers are trained in the procedures and skills appropriate to their level of certification by diving instructors affiliated to the diver certification organisations which issue these certifications. These include standard operating procedures for using the equipment and dealing with the general hazards of the underwater environment, and emergency procedures for self-help and assistance of a similarly equipped diver experiencing problems. A minimum level of fitness and health is required by most training organisations, but a higher level of fitness may be appropriate for some applications. (Full article...)
Surface-supplied diving is a modeofunderwater diving using equipment supplied with breathing gas through a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell. This is different from scuba 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. 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.
The copper helmeted free-flow standard diving dress is the version which made commercial diving a viable occupation, and although still used in some regions, this heavy equipment has been superseded by lighter free-flow helmets, and to a large extent, lightweight demand helmets, band masks and full-face diving masks. Breathing gases used include air, heliox, nitrox and trimix.
Saturation diving is a mode of surface supplied diving in which the divers live under pressure in a saturation systemorunderwater habitat and are decompressed only at the end of a tour of duty.
Airline, or hookah diving, and "compressor diving" are lower technology variants also using a breathing air supply from the surface. (Full article...)
Surface-supplied diving is a modeofunderwater diving using equipment supplied with breathing gas through a diver's umbilical from the surface, either from the shore or from a diving support vessel, sometimes indirectly via a diving bell. This is different from scuba 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. 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.
The copper helmeted free-flow standard diving dress is the version which made commercial diving a viable occupation, and although still used in some regions, this heavy equipment has been superseded by lighter free-flow helmets, and to a large extent, lightweight demand helmets, band masks and full-face diving masks. Breathing gases used include air, heliox, nitrox and trimix.
Saturation diving is a mode of surface supplied diving in which the divers live under pressure in a saturation systemorunderwater habitat and are decompressed only at the end of a tour of duty.
Airline, or hookah diving, and "compressor diving" are lower technology variants also using a breathing air supply from the surface. (Full article...)
Inunderwater diving, an alternative air source, or more generally alternative breathing gas source, is a secondary supply of air or other breathing gas for use by the diver in an emergency. Examples include an auxiliary demand valve, a pony bottle and bailout bottle.
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 from buddy 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...)
Nitrox refers to any gas mixture composed (excepting trace gases) of nitrogen and oxygen. This includes atmospheric air, which is approximately 78% nitrogen, 21% oxygen, and 1% other gases, primarily argon. 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 in scuba diving, where the reduced partial pressure of nitrogen is advantageous in reducing nitrogen uptake in the body's tissues, thereby extending the practicable underwater dive time by reducing the decompression requirement, or reducing the risk of decompression sickness (also known as the bends).
Nitrox is used to a lesser extent in surface-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 of decompression 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 of oxygen toxicity and fire.
Though not generally referred to as nitrox, an oxygen-enriched air mixture is routinely provided at normal surface ambient pressure as oxygen therapy to patients with compromised respiration and circulation. (Full article...)
Adive boat is a boat that recreational diversorprofessional scuba divers use to reach a dive 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 their equipment 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 while moored, at anchor, or under way, (also known as live-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...)
Dynamic positioning (DP) is a computer-controlled system to automatically maintain a vessel's position and heading by using its own propellers and thrusters. Position reference sensors, combined with wind sensors, motion sensors and gyrocompasses, 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 and semi-submersible mobile offshore drilling units (MODU), oceanographic research vessels, cable layer ships and cruise ships.
The computer program contains a mathematical 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.
Dynamic positioning is used by much of the offshore oil industry, for example in the North Sea, Persian Gulf, Gulf of Mexico, West Africa, and off the coast of Brazil. There are currently more than 1800 DP ships. (Full article...)
Scuba diving is a modeofunderwater diving whereby divers use breathing equipment that is completely independent of a surface breathing gas supply, and therefore has a limited but variable endurance. The name scuba is an anacronym for "Self-Contained Underwater Breathing Apparatus" and was coined by Christian J. Lambertsen in a patent submitted in 1952. Scuba divers carry their own source of breathing gas, usually compressed air, affording them greater independence and movement than surface-supplied divers, and more time underwater than free divers. Although the use of compressed air is common, a gas blend with a higher oxygen content, known as enriched air or nitrox, has become popular due to the reduced nitrogen intake during long or repetitive dives. Also, breathing gas diluted with helium may be used to reduce the effects of nitrogen narcosis during deeper dives.
Open-circuit scuba systems discharge the breathing gas into the environment as it is exhaled, and consist of one or more diving cylinders containing breathing gas at high pressure which is supplied to the diver at ambient pressure through a diving regulator. They may include additional cylinders for range extension, decompression gasoremergency breathing gas. Closed-circuit or semi-closed circuit rebreather scuba systems allow recycling of exhaled gases. The volume of gas used is reduced compared to that of open-circuit, so a smaller cylinder or cylinders may be used for an equivalent dive duration. 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 covert military divers to avoid detection, scientific divers to avoid disturbing marine animals, and media divers to avoid bubble interference.
Scuba diving may be done recreationallyorprofessionally in a number of applications, including scientific, military and public safety roles, but most commercial diving uses surface-supplied diving equipment when this is practicable. Scuba divers engaged in armed forces covert operations may be referred to as frogmen, combat divers or attack swimmers.
A scuba diver primarily moves underwater by using fins attached to the feet, but external propulsion can be provided by a diver propulsion vehicle, or a sled pulled from the surface. Other equipment needed for scuba diving includes a mask to improve underwater vision, exposure protection by means of a diving suit, ballast weights to overcome excess buoyancy, equipment to control buoyancy, and equipment related to the specific circumstances and purpose of the dive, which may include a snorkel when swimming on the surface, a cutting tool to manage entanglement, lights, a dive computer to monitor decompression status, and signalling devices. Scuba divers are trained in the procedures and skills appropriate to their level of certification by diving instructors affiliated to the diver certification organisations which issue these certifications. These include standard operating procedures for using the equipment and dealing with the general hazards of the underwater environment, and emergency procedures for self-help and assistance of a similarly equipped diver experiencing problems. A minimum level of fitness and health is required by most training organisations, but a higher level of fitness may be appropriate for some applications. (Full article...)
Altitude divingisunderwater diving using scubaorsurface supplied diving equipment where the surface is 300 metres (980 ft) or more above sea level (for example, a mountain lake). Altitude is significant in diving because it affects the decompression requirement for a dive, so that the stop depths and decompression times used for dives at altitude are different from those used for the same dive profile at sea level. The U.S. Navy tables recommend that no alteration be made for dives at altitudes lower than 91 metres (299 ft) and for dives between 91 and 300 meters correction is required for dives deeper than 44 metres (144 ft) of sea water. Most recently manufactured decompression computers can automatically compensate for altitude. (Full article...)
Ear clearing, clearing the earsorequalization is any of various maneuvers to equalize the pressure in the middle ear with the outside pressure, by letting air enter along the Eustachian 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 in scuba diving, freediving/spearfishing, skydiving, fast descent in an aircraft, fast descent in a mine cage, and being put into pressure in a caisson or similar internally pressurised enclosure, or sometimes even simply travelling at fast speeds in an automobile.
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.
People who do intense weight lifting, such as squats, may experience sudden conductive hearing loss due to air pressure building up inside the ear. An ear clearing maneuver will often relieve pressure in the middle ear, or pain if any. (Full article...)
The decompression of a diver is the reduction in ambient pressure experienced during ascent from depth. It is also the process of elimination of dissolved inert gases from the diver's body which accumulate during ascent, largely during pauses in the ascent known as decompression stops, and after surfacing, until the gas concentrations reach equilibrium. Divers breathing gas at ambient pressure need to ascend at a rate determined by their exposure to pressure and the breathing gas in use. A diver who only breathes gas at atmospheric pressure when free-divingorsnorkelling will not usually need to decompress. Divers using an atmospheric diving suit do not need to decompress as they are never exposed to high ambient pressure.
When a diver descends in the water, the hydrostatic pressure, and therefore the ambient pressure, rises. Because breathing gas is supplied at ambient pressure, some of this gas dissolves into the diver's blood and is transferred by the blood to other tissues. Inert gas such as nitrogenorhelium 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's lungs, at which point the diver is saturated for that depth and breathing mixture, or the depth, and therefore the pressure, is changed, or the partial 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. If the pressure reduction is sufficient, excess gas may form bubbles, which may lead to decompression 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, the asymptomatic venous microbubbles present after most dives are eliminated from the diver's body in the alveolar 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 to sub-clinical decompression injury.
The mechanisms of bubble formation and the damage bubbles 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 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. Nevertheless, currently popular decompression procedures advise a 'safety stop' additional to any stops required by the algorithm, usually of about three to five minutes at 3 to 6 metres (10 to 20 ft), particularly 1 on an otherwise continuous no-stop ascent.
Decompression may be continuousorstaged. A staged decompression ascent is interrupted by decompression stops at calculated depth intervals, but the entire ascent is actually part of the decompression and the ascent rate is critical to harmless elimination of inert gas. A no-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 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. When time is spent on the surface between dives this is known as the "surface interval" and is considered when calculating decompression requirements for the subsequent dive.
Efficient decompression requires the diver to ascend fast enough to establish as high a decompression gradient, in as many tissues, as safely possible, without provoking the development of symptomatic bubbles. This is facilitated by the highest acceptably safe oxygen partial pressure in the breathing gas, and avoiding gas changes that could cause counterdiffusion bubble formation or growth. The development of schedules that are both safe and efficient has been complicated by the large number of variables and uncertainties, including personal variation in response under varying environmental conditions and workload. (Full article...)
Scuba skills are skills required to dive safely using self-contained underwater breathing apparatus, known as a scuba set. Most of these skills are relevant to both open-circuit scuba and rebreather scuba, and many also apply to surface-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 recreational diver certification agencies as basic and necessary in order to dive without direct supervision. Others are more advanced, although some diver 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), 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...)
To prevent or minimize decompression sickness, divers must properly plan and monitor decompression. Divers follow a decompression model to safely allow the release of excess inert gases dissolved in their body tissues, which accommodated 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 available equipment, the site and environment, and the actual dive profile. Standardized procedures have been developed which provide an acceptable level of risk in the circumstances for which they are appropriate. Different sets of procedures are used by commercial, military, scientific and recreational 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 personal dive computers in the 1990s, which facilitated decompression practice and allowed more complex dive profiles at acceptable levels of risk. (Full article...)
Wreck divingisrecreational diving where the wreckage 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 to scuttle retired ships to create artificial reef sites. Diving to crashed 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 involves penetration of the wreckage, making a direct ascent to the surface impossible for a part of the dive.
its a popular sports also in numerous countries in the world . (Full article...)
Recreational divingorsport divingisdiving for the purpose of leisure and enjoyment, usually when using scuba 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 of scuba 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 mostly open circuit scuba, though semi closed and fully automated electronic closed circuit rebreathers 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 their psychological 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 local dive sites or dive as tourists at more distant venues known for desirable underwater environments. An economically significant diving tourism industry services recreational divers, providing equipment, training and diving experiences, generally by specialist providers known as dive centers, dive schools, live-aboard, day charter and basic dive boats.
Legal constraints on recreational diving vary considerably across jurisdictions. 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, but buddy diving is generally recommended by recreational diver training agencies as safer than solo diving, and some service providers insist that customers dive in buddy pairs. The evidence supporting this policy is inconclusive. (Full article...)
Buddy breathing is a rescue technique used in scuba diving "out-of-gas" emergencies, when two divers share one demand valve, alternately breathing from it. Techniques have been developed for buddy breathing from both twin-hose and single 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 a bailout cylinder or breathing through a secondary demand valve on the rescuer's regulator.
Running out of breathing gas most commonly happens as a result of poor gas management. It can also happen due to unforeseen exertion 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 an O-ringorhose in the regulator or, in cold conditions, a freezing of water in the regulator resulting in a free flow from the demand valve. (Full article...)
Saturation diving is diving for periods long enough to bring all tissues into equilibrium with the partial pressures of the inert components of the breathing gas used. It is a diving mode that reduces the number of decompressions divers working at great depths must undergo by only decompressing divers once at the end of the diving operation, which may last days to weeks, having them remain under pressure for the whole period. A diver breathing pressurized gas accumulates dissolved inert gas used in the breathing mixture to dilute the oxygen to a non-toxic level in the tissues, which can cause potentially fatal decompression sickness ("the bends") if permitted to come out of solution within the body tissues; hence, returning to the surface safely requires lengthy decompression so that the inert gases can be eliminated via the lungs. Once the dissolved gases in a diver's tissues reach the saturation point, however, decompression time does not increase with further exposure, as no more inert gas is accumulated.
Saturation diving takes advantage of this by having divers remain in that saturated state. When not in the water, the divers live in a sealed environment which maintains their pressurised state; this can be an ambient pressure underwater habitat or a saturation system at the surface, with transfer to and from the pressurised living quarters to the equivalent depth underwater via a closed, pressurised diving bell. This may be maintained for up to several weeks, and divers are decompressed to surface pressure only once, at the end of their tour of duty. By limiting the number of decompressions in this way, and using a conservative decompression schedule the risk of decompression sickness is significantly reduced, and the total time spent decompressing is minimised. Saturation divers typically breathe a helium–oxygen mixture to prevent nitrogen narcosis, and limit work of breathing, but at shallow depths saturation diving has been done on nitrox mixtures.
Most of the physiological and medical aspects of diving to the same depths are much the same in saturation and bell-bounce ambient pressure diving, or are less of a problem, but there are medical and psychological effects of living under saturation for extended periods.
Saturation diving is a specialized form 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...)
Diver communications are the methods used by divers to communicate with each other or with surface members of the dive team. In professional diving, diver communication is usually between a single working diver and the diving 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 the helmet 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...)
Solo diving is the practice of self-sufficient underwater diving without a "dive buddy", particularly with reference to scuba diving, but the term is also applied to freediving. Professionally, solo diving has always been an option which depends on operational requirements and risk assessment. Surface supplied diving and atmospheric suit diving are commonly single diver underwater activities but are accompanied by an on-surface support team dedicated to the safety of the diver, including a stand-by diver, and are not considered solo diving in this sense.
Solo freediving has occurred for millennia as evidenced by artifacts dating back to the ancient people of Mesopotamia 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 scuba certification agencies incorporated the practice of buddy diving into their diver 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 advanced underwater 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 backup scuba equipment. In most countries there is no legal impediment to solo recreational diving, with or without certification. (Full article...)
In-water recompression (IWR) or underwater oxygen treatment is the emergency treatment of decompression sickness (DCS) by returning the diver underwater to help the gas bubbles in the tissues, which are causing the symptoms, to resolve. It is a procedure that exposes the diver to significant risk 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 to travel to the nearest recompression 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 nearby recompression 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 become paralysed, unconscious, or stop breathing while underwater. Any one of these events is likely to result in the diver drowning 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...)
Gas blending for scuba diving (or gas mixing) is the filling of diving cylinders with non-air breathing gases such as nitrox, trimix and heliox. Use of these gases is generally intended to improve overall safety of the planned dive, by reducing the risk of decompression sickness and/or nitrogen narcosis, and may improve ease of breathing.
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 to hypoxia and if it is too rich the diver may suffer oxygen 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...)
Technical diving (also referred to as tec divingortech diving) is scuba diving that exceeds the agency-specified limits of recreational 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 via appropriate skills, knowledge, and experience. Risk can also be managed by using suitable equipment and procedures. The skills may be developed through specialized training and experience. The equipment involves breathing gases other than air or standard nitrox mixtures, and multiple gas sources.
The popularisation of the term technical diving has been credited to Michael Menduno, who was editor of the (now defunct) diving magazine aquaCorps 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...)
Underwater vision is the ability to see objects underwater, and this is significantly affected by several factors. Underwater, objects are less visible because of lower levels of natural illumination caused by rapid attenuationoflight 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 absolute depth 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 the refractive indices of the two media. If one medium has a particular curved shape, it functions as a lens. The cornea, humours, and crystalline lens of the eye together form a lens that focuses images on the retina. 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 from hypermetropia. 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...)
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another.
Tide tables can be used for any given locale to find the predicted times and amplitude (or "tidal range").
The predictions are influenced by many factors including the alignment of the Sun and Moon, the phase and amplitude of the tide (pattern of tides in the deep ocean), the amphidromic systems of the oceans, and the shape of the coastline and near-shore bathymetry (see Timing). They are however only predictions, the actual time and height of the tide is affected by wind and atmospheric pressure. Many shorelines experience semi-diurnal tides—two nearly equal high and low tides each day. Other locations have a diurnal 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 the lunitidal 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 called mean sea level.
While tides are usually the largest source of short-term sea-level fluctuations, sea levels are also subject to change from thermal expansion, wind, and barometric pressure changes, resulting in storm 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 by Earth tide, though this is not as easily seen as the water tidal movements. (Full article...)
Inphysical chemistry, supersaturation occurs with a solution when the concentration of a solute exceeds the concentration specified by the value of solubilityatequilibrium. Most commonly the term is applied to a solution of a solid in a liquid, but it can also be applied to liquids and gases dissolved in a liquid. A supersaturated solution is in a metastable state; it may return to equilibrium by separation 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...)
Indiving and decompression, the oxygen window is the difference between the partial pressureofoxygen (PO2) in arterial blood and the PO2 in body tissues. It is caused by metabolic consumption of oxygen. (Full article...)
The physiology of decompression is the aspect of physiology which is affected by exposure to large changes in ambient pressure. It involves a complex interaction of gas solubility, partial pressures and concentration gradients, diffusion, bulk transport and bubble mechanics in living tissues. Gas is breathed at ambient pressure, and some of this gas dissolves into the blood and other fluids. Inert gas continues to be taken up until the gas dissolved in the tissues is in a state of equilibrium with the gas in the lungs (see: "Saturation diving"), or the ambient pressure is reduced until the inert gases dissolved in the tissues are at a higher concentration than the equilibrium state, and start diffusing out again.
The absorption of gases in liquids depends on the solubility of the specific gas in the specific liquid, the concentration of gas (customarily expressed as partial pressure) and temperature. In the study of decompression theory, the behaviour of gases dissolved in the body tissues is investigated and modeled for variations of pressure over time. Once dissolved, distribution of the dissolved gas is by perfusion, where the solvent (blood) is circulated around the diver's body, and by diffusion, where dissolved gas can spread to local regions of lower concentration when there is no bulk flow of the solvent. Given sufficient time at a specific partial pressure in the breathing gas, the concentration in the tissues will stabilise, or saturate, at a rate depending on the local solubility, diffusion rate and perfusion. If the concentration of the inert gas in the breathing gas is reduced below that of any of the tissues, there will be a tendency for gas to return from the tissues to the breathing gas. This is known as outgassing, and occurs during decompression, when the reduction in ambient pressure or a change of breathing gas reduces the partial pressure of the inert gas in the lungs.
The combined concentrations of gases in any given tissue will depend on the history of pressure and gas composition. Under equilibrium conditions, the total concentration of dissolved gases will be less than the ambient pressure, as oxygen is metabolised in the tissues, and the carbon dioxide produced is much more soluble. However, during a reduction in ambient pressure, the rate of pressure reduction may exceed the rate at which gas can be eliminated by diffusion and perfusion, and if the concentration gets too high, it may reach a stage where bubble formation can occur in the supersaturated tissues. When the pressure of gases in a bubble exceed the combined external pressures of ambient pressure and the surface tension from the bubble - liquid interface, the bubbles will grow, and this growth can cause damage to tissues. Symptoms caused by this damage are known as decompression sickness.
The actual rates of diffusion and perfusion, and the solubility of gases in specific tissues are not generally known, and vary considerably. However mathematical models have been proposed which approximate the real situation to a greater or lesser extent, and these decompression models are used to predict whether symptomatic bubble formation is likely to occur for a given pressure exposure profile. Efficient decompression requires the diver to ascend fast enough to establish as high a decompression gradient, in as many tissues, as safely possible, without provoking the development of symptomatic bubbles. This is facilitated by the highest acceptably safe oxygen partial pressure in the breathing gas, and avoiding gas changes that could cause counterdiffusion bubble formation or growth. The development of schedules that are both safe and efficient has been complicated by the large number of variables and uncertainties, including personal variation in response under varying environmental conditions and workload. (Full article...)
Athermocline (also known as the thermal layer or the metalimnion 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. an atmosphere) with a high gradient of distinct temperature differences associated with depth. In the ocean, the thermocline divides the upper mixed layer from the calm deep water below.
Depending largely on season, latitude, and turbulent mixing by wind, thermoclines may be a semi-permanent feature of the body of water in which they occur, or they may form temporarily in response to phenomena such as the radiative heating/cooling of surface water during the day/night. Factors that affect the depth and thickness of a thermocline include seasonal weather variations, latitude, and local environmental conditions, such as tides and currents. (Full article...)
Arip current (also rip) 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 the shore 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 .
A rip current is not the same thing as undertow, although some people use that term incorrectly when they are talking about 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...)
Decompression theory is the study and modelling of the transfer of the inert gas component of breathing gases from the gas in the lungs to the tissues and back during exposure to variations in ambient pressure. In the case of underwater diving and compressed air work, this mostly involves ambient pressures greater than the local surface pressure, but astronauts, high altitude mountaineers, and travellers in aircraft which are not pressurised to sea level pressure, are generally exposed to ambient pressures less than standard sea level atmospheric pressure. In all cases, the symptoms caused by decompression occur during or within a relatively short period of hours, or occasionally days, after a significant pressure reduction.
The term "decompression" derives from the reduction in ambient pressure experienced by the organism and refers to both the reduction in pressure and the process of allowing dissolved inert gases to be eliminated from the tissues during and after this reduction in pressure. The uptake of gas by the tissues is in the dissolved state, and elimination also requires the gas to be dissolved, however a sufficient reduction in ambient pressure may cause bubble formation in the tissues, which can lead to tissue damage and the symptoms known as decompression sickness, and also delays the elimination of the gas.
Decompression modeling attempts to explain and predict the mechanism of gas elimination and bubble formation within the organism during and after changes in ambient pressure, and provides mathematical models which attempt to predict acceptably low risk and reasonably practicable procedures for decompression in the field. Both deterministic and probabilistic models have been used, and are still in use.
Efficient decompression requires the diver to ascend fast enough to establish as high a decompression gradient, in as many tissues, as safely possible, without provoking the development of symptomatic bubbles. This is facilitated by the highest acceptably safe oxygen partial pressure in the breathing gas, and avoiding gas changes that could cause counterdiffusion bubble formation or growth. The development of schedules that are both safe and efficient has been complicated by the large number of variables and uncertainties, including personal variation in response under varying environmental conditions and workload. (Full article...)
The diving reflex, also known as the diving response and mammalian diving reflex, is a set of physiological responses to immersion that overrides the basic homeostatic reflexes, and is found in all air-breathing vertebrates studied to date. It optimizes respiration by preferentially distributing oxygen stores to the heart and brain, enabling submersion for an extended time.
The diving reflex is exhibited strongly in aquatic mammals, such as seals, otters, dolphins, and muskrats, and exists as a lesser response in other animals, including human babies up to 6 months old (see infant swimming), and diving birds, such as ducks and penguins. Adult humans generally exhibit a mild response, the dive-hunting Sama-Bajau people being a notable outlier.
The diving reflex is triggered specifically by chilling and wetting the nostrils and face while breath-holding, and is sustained via neural processing originating in the carotid 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 the spleen, and, in humans, heart rhythm irregularities. Although aquatic animals have evolved profound physiological adaptations to conserve oxygen during submersion, the apnea and its duration, bradycardia, vasoconstriction, and redistribution of cardiac output occur also in terrestrial animals as a neural response, but the effects are more profound in natural divers. (Full article...)
Inchemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. 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 the concentration of the solute in a saturated solution, one in which no more solute can be dissolved. At this point, the two substances are said to be at the solubility 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 a solid, a liquid, or a gas, 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 their pH 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, or ions) of the two substances, and of thermodynamic concepts such as enthalpy and entropy.
Under certain conditions, the concentration of the solute can exceed its usual solubility limit. The result is a supersaturated solution, which is metastable and will rapidly exclude the excess solute if a suitable nucleation site appears.
The concept of solubility does not apply when there is an irreversible chemical reaction between the two substances, such as the reaction of calcium hydroxide with hydrochloric acid; even though one might say, informally, that one "dissolved" the other. The solubility is also not the same as the rate 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 as geology, biology, physics, and oceanography, as well as in engineering, medicine, agriculture, and even in non-technical activities like painting, cleaning, cooking, and brewing. Most chemical reactions of scientific, industrial, or practical interest only happen after the reagents 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 form colloidal suspensions of very fine solid particles in a liquid. The quantitative solubility of such substances is generally not well-defined, however. (Full article...)
In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas mixture is the sum of the partial pressures of the gases in the mixture (Dalton's Law).
The partial pressure of a gas is a measure of thermodynamic activity of the gas's molecules. Gases dissolve, diffuse, and react according to their partial pressures but not according to their concentrations in gas mixtures or liquids. This general property of gases is also true in chemical reactions of gases in biology. For example, the necessary amount of oxygen for human respiration, and the amount that is toxic, is set by the partial pressure of oxygen alone. This is true across a very wide range of different concentrations of oxygen present in various inhaled breathing gases or dissolved in blood; consequently, mixture ratios, like that of breathable 20% oxygen and 80% Nitrogen, are determined by volume instead of by weight or mass. Furthermore, the partial pressures of oxygen and carbon dioxide are important parameters in tests of arterial blood gases. That said, these pressures can also be measured in, for example, cerebrospinal fluid. (Full article...)
Cold shock response is a series of neurogenic cardio-respiratory responses caused by sudden immersion in cold water.
In cold water immersions, such as by falling through thin ice, cold shock response is perhaps the most common cause of death. Also, the abrupt contact with very cold water may cause involuntary inhalation, which, if underwater, can result in fatal drowning.
Death which occurs in such scenarios is complex to investigate and there are several possible causes and phenomena that can take part. The cold water can cause heart attack due to severe vasoconstriction, where the heart has to work harder to pump the same volume of blood throughout the arteries. For people with pre-existing cardiovascular disease, the additional workload can result in myocardial infarction and/or acute heart failure, which ultimately may lead to a cardiac arrest. A vagal response to an extreme stimulus as this one, may, in very rare cases, render per se a cardiac arrest. Hypothermia and extreme stress can both precipitate fatal tachyarrhythmias. A more modern view suggests that an autonomic conflict — sympathetic (due to stress) and parasympathetic (due to the diving reflex) coactivation — may be responsible for some cold water immersion deaths. Gasp reflex and uncontrollable tachypnea can severely increase the risk of water inhalation and drowning.
Some people are much better prepared to survive sudden exposure to very cold water due to body and mental characteristics and due to conditioning. In fact, cold water swimming (also known as ice swimming or winter swimming) is a sport and an activity that reportedly can lead to several health benefits when done regularly. (Full article...)
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 are not perfused or poorly perfused. It means that not all the air in each breath is available for the exchange of oxygen and carbon 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...)
The ambient pressure on an object is the pressure of the surrounding medium, such as a gasorliquid, in contact with the object. (Full article...)
Recreational diver training is the process of developing knowledge and understanding of the basic principles, and the skills and procedures for the use of scuba equipment so that the diver is able to dive 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 environment hazardous 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 at Scripps 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 the certification organization that will certify the divers attending the course. The International 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 is medically 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 their diving cylinders filled. This may be an agency standard, company policy, or specified by legislation. (Full article...)
Commercial offshore diving, sometimes shortened to just offshore diving, generally refers to the branch of commercial diving, with divers working in support of the exploration and production sector of the oil and gas industry in places such as the Gulf of Mexico in the United States, the North Sea in the United Kingdom and Norway, and along the coast of Brazil. The work in this area of the industry includes maintenance of oil platforms and the building of underwater structures. In this context "offshore" implies that the diving work is done outside of national boundaries. Technically it also refers to any diving done in the international offshore waters outside of the territorial waters of a state, where national legislation does not apply. Most commercial offshore diving is in the Exclusive Economic Zone of a state, and much of it is outside the territorial waters. Offshore diving beyond the EEZ does also occur, and is often for scientific purposes.
Equipment used for commercial offshore diving tends to be surface supplied equipment but this varies according to the work and location. For instance, divers in the Gulf of Mexico may use wetsuits whilst North Sea divers need dry suits or even hot water suits because of the low temperature of the water.
Diving work in support of the offshore oil and gas industries is usually contract based.
Saturation diving is standard practice for bottom work at many of the deeper offshore sites, and allows more effective use of the diver's time while reducing the risk of decompression sickness. Surface oriented air diving is more usual in shallower water. (Full article...)
Police diving is a branch of professional diving carried out by police services. Police divers are usually professional police officers, and may either be employed full-time as divers or as general water 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 of public safety diving, and forensic diving, which is search and recovery diving for evidence and bodies. (Full article...)
Hyperbaric welding is the process of extreme welding at elevated pressures, normally underwater. Hyperbaric welding can either take place wet in the water itself or dry inside a specially constructed positive 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 repair ships, offshore oil platforms, and pipelines. 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 weld heat 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 various nondestructive testing applications), especially for wet underwater welds, because defects are difficult to detect if the defects are beneath the surface of the weld.
Underwater hyperbaric welding was invented by the Soviet metallurgist Konstantin Khrenov in 1932. (Full article...)
Army engineer divers are members of national armies who are trained to undertake tasks underwater, including reconnaissance, demolition, and salvage. These divers have similar skills and qualifications as professional divers. Army divers use both surface supplied "Hard hat" and SCUBA to perform their missions. In the United States Army, they are members of the Corps of Engineers. In the British Army, they may be Royal Engineer DiversorCommando Engineer Divers. (Full article...)
Sponge divingisunderwater diving to collect soft natural sponges for human use. (Full article...)
Aclearance diver was originally a specialist naval diver who used explosives underwater to remove obstructions to make harbours and shipping channels safe to navigate, but the term "clearance diver" was later used to include other naval underwater work. Units of clearance divers were first formed during and after World War II to clear ports and harbours in the Mediterranean and Northern Europe of unexploded ordnance and shipwrecks and booby traps laid by the Germans. (Full article...)
Public safety divingisunderwater diving conducted as part of law enforcement and search and 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...)
ADiving certificationorC-card is a document (usually a wallet sized plastic 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 in underwater diving. Divers carry a qualification record or certification card which may be required to prove their qualifications when booking a dive trip, hiring scuba equipment, having diving cylinders filled, or in the case of professional divers, seeking employment.
Although recreational certifications are issued by numerous different diver 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, a diver's logbook, or the electronic equivalent, is primarily evidence of range of diving experience. (Full article...)
Hazmat divingisunderwater diving in a known hazardous materials environment. The environment may be contaminated by hazardous materials, the diving medium may be inherently a hazardous material, or the environment in which the diving medium is situated may include hazardous materials with a significant risk of exposure to these materials to members of the diving team. Special precautions, equipment and procedures are associated with hazmat diving so that the risk can be reduced to an acceptable level. (Full article...)
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 recreational scuba 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 many training agencies, such as PADI, SSI, SDI, NASE, except NAUI, which rates a NAUI Divemaster under a NAUI Instructor but above a NAUI Assistant Instructor. The divemaster certification is generally equivalent to the requirements of ISO 24801-3 Dive Leader.
The 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 in recreational diving with the professional agencies except NAUI, where it is an optional step, because of the different position of the NAUI Divemaster in the NAUI hierarchy. (Full article...)
Underwater archaeologyisarchaeology practiced underwater. As with all other branches of archaeology, it evolved from its roots in pre-history and in the classical 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 past human life, behaviours 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 under saltorfresh water or buried beneath water-logged sediment. In recent years, the study of submerged WWII sites and of submerged aircraft in the form of underwater aviation archaeology have also emerged as bona fide activity.
Though often mistaken as such, underwater archaeology is not restricted to the study of shipwrecks. Changes in sea level because of local seismic events such as the earthquakes that devastated Port Royal and Alexandria or more widespread climatic changes on a continental 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, the North Sea was a great plain, and anthropological material, as well as the remains of animals such as mammoths, 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 of crannogs, bridges and harbours) when traces on dry land have been lost. As a result, underwater archaeological 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 rising sea levels; wells, cenotes, wrecks (shipwrecks; aircraft); the remains of structures created in water (such as crannogs, bridgesorharbours); other port-related structures; refuseordebris sites where people disposed of their waste, garbage and other items, such as ships, aircraft, munitions and machinery, by dumping 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 including prehistory, historical archaeology, maritime archaeology, and anthropology. There are many examples. One is the wreck of the VOC ship Zuytdorp 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 European pastoralists who entered the area in the mid-19th century. (Full article...)
Underwater warfare, also known as undersea warfareorsubsurface warfare, is naval warfare involving underwater vehicleorcombat operations conducted underwater. It is one of the four operational areas of naval warfare, the others being surface warfare, aerial warfare, and information warfare. Underwater warfare includes:
Underwater demolition is the deliberate destruction or neutralization of man-made or natural underwater obstacles, both for military and civilian purposes. (Full article...)
Underwater search and recovery is the process of locating and recovering underwater objects, often by divers, but also by the use of submersibles, remotely operated vehicles and electronic equipment on surface vessels.
Most underwater search and recovery is done by professional divers as part of commercial marine 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...)
Below is the list of current Commonwealth Records for finswimming. The records are ratified by the Commonwealth Finswimming Committee, which is made up of the National Finswimming Governing Bodies of Commonwealth 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 (including home nations); Australia, Canada, Cyprus, England, New Zealand, Scotland, Singapore, South Africa and Wales (). (Full article...)
Wreck divingisrecreational diving where the wreckage 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 to scuttle retired ships to create artificial reef sites. Diving to crashed 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 involves penetration of the wreckage, making a direct ascent to the surface impossible for a part of the dive.
its a popular sports also in numerous countries in the world . (Full article...)
Below is the list of current British records in finswimming. 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 with CMAS regulations. (Full article...)
Sport diving is an underwater sport that uses recreational open circuit scuba diving equipment and consists of a set of individual and team events conducted in a swimming 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 as Plongée Sportive en Piscine in French and as Buceo De Competición in Spanish. (Full article...)
Underwater sports is a group of competitive sports using one or a combination of the following underwater diving techniques - breath-hold, snorkellingorscuba, usually including the use of equipment such as diving masks and fins. These sports are conducted in the natural environment at sites such as open water and sheltered or confined water such as lakes and in artificial aquatic environments such as swimming pools. Underwater sports include the following - aquathlon (i.e. underwater wrestling), finswimming, freediving, spearfishing, sport diving, underwater football, underwater hockey, underwater ice hockey, underwater orienteering, underwater photography, underwater rugby, underwater target shooting and underwater video. (Full article...)
Underwater ice hockey (also called sub-aqua ice hockey) is a minor extreme sport that is a variant of ice hockey. It is played upside-down underneath frozen pools or ponds. Participants wear diving masks, fins, and wetsuits and use the underside of the frozen surface as the playing area or rink for a floating puck. Competitors do not use any breathing apparatus but instead surface for air every 30 seconds or so.
It is not to be confused with underwater hockey, in which the floor of a swimming pool and a sinking puck are used. (Full article...)
Skandalopetra diving (Greek: σκανταλόπετρα) dates from ancient Greece, when it was used by sponge fishermen, and has been re-discovered in recent years as a freediving discipline. It was in this discipline that the first world record in freediving was registered, when the Greek sponge fisherman Stathis Chantzis dived to a depth of 83 m (272 ft) in July 1913. It consists of a variable ballast dive using a skandalopetra tied to a rope. A companion on a boat recovers the diver by pulling the rope up after the descent, and keeps a watch on the diver from the surface. (Full article...)
Underwater photography is the process of taking photographs while under water. It is usually done while scuba diving, but can be done while diving on surface supply, snorkeling, swimming, from a submersibleorremotely operated underwater vehicle, or from automated cameras lowered from the surface.
Underwater photography can also be categorised 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 and marine mammals are common subjects, but photographers also pursue shipwrecks, submerged cave systems, underwater "landscapes", invertebrates, seaweeds, geological features, and portraits of fellow divers. (Full article...)
Underwater Target Shooting is an underwater sport/shooting sport that tests a competitors’ ability to accurately use a speargun via a set of individual and team events conducted in a swimming pool using freediving or Apnoea technique. The sport was developed in France during the early 1980s and is currently practiced mainly in Europe. It is known as Tir sur cible subaquatique in French and as Tiro al Blanco Subacuático in Spanish. (Full article...)
Shark cage divingisunderwater divingorsnorkeling where the observer remains inside a protective cage designed to prevent sharks from making contact with the divers. Shark cage diving is used for scientific observation, underwater cinematography, and as a tourist activity. Sharks may be attracted to the vicinity of the cage by the use of bait, in a procedure known as chumming, which has attracted some controversy as it is claimed to potentially alter the natural behaviour of sharks in the vicinity of swimmers.
Similar cages are also used purely as a protective measure for divers working in waters where potentially dangerous shark species are present. In this application the shark-proof cage may be used as a refuge, or as a diving stage during descent and ascent, particularly during staged decompression where the divers may be vulnerable while constrained to a specific depth in mid-water for several minutes. In other applications a mobile cage may be carried by the diver while harvesting organisms such as abalone. (Full article...)
Recreational dive sites are specific places that recreational scuba divers go to enjoy the underwater environment or for training purposes. They include technical diving sites beyond the range generally accepted for recreational 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 of diver training and leading 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, including accessibility, biodiversity, spectacular topography, historical or cultural interest and artifacts (such as shipwrecks), and water clarity. Tropical waters of high biodiversity and colourful sea life are popular recreational diving vacation 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 and cave 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...)
Doing It Right (DIR) is a holistic approach to scuba 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 the Woodville 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 several organizations, such as Global Underwater Explorers (GUE), Unified Team Diving (UTD) and InnerSpace Explorers (ISE). (Full article...)
Below is the list of current European finswimming records. The records are ratified by the CMAS Confédération Mondiale des Activités Subaquatiques (World Underwater Federation). (Full article...)
Diver rescue, usually following an accident, is the process of avoiding or limiting further exposure to diving hazards and bringing a diver to a place of safety. A safe place generally means a place where the diver cannot drown, such as a boat or dry land, where first aid can be administered and from which professional medical treatment can be sought. In the context of surface supplied diving, the place of safety for a diver with a decompression obligation is often the diving bell.
Rescue may be needed for various reasons where the diver becomes unable to manage an emergency, and there are several stages to a rescue, starting with recognising that a rescue is needed. In some cases the dive buddy identifies the need by personal observation, but in the more general case identification of the need is followed by locating the casualty. The most common and urgent diving emergencies involve loss of breathing gas, and the provision of emergency gas is the usual response. On other occasions the diver may be trapped and must be released by the rescuer. These first responses are usually followed by recovery of the distressed diver, who may be unconscious, to a place of safety with a secure supply of breathing gas, and following rescue, it may be necessary to evacuate the casualty to a place where further treatment is possible.
Recommended procedures for recovering a disabled or unresponsive scuba diver to the surface have varied over time, and to some extent depend on circumstances and the equipment in use. None are guaranteed to be successful.
In all rescue operations, the rescuer must take care of their own safety and avoid becoming another casualty. In professional diving the supervisor is responsible for initiating rescue procedures, and for ensuring the safety of the dive team. The rescue is generally carried out by the stand-by diver, and for this reason the stand-by diver must be willing and competent to perform any reasonably foreseeable rescue that may be required for a planned diving operation. A similar level of competence is desirable, but not required of recreational divers, who generally have a poorly defined duty of care to other divers, and are usually only trained in rescue and first aid as optional specialties. Nevertheless, recreational divers are usually advised by their training agencies to dive as buddy pairs so they can assist each other if one gets into difficulty. (Full article...)
Lock out, tag outorlockout–tagout (LOTO) is a safety procedure used to ensure that dangerous equipment is properly shut off and not able to be started up again prior to the completion of maintenance or repair work. It requires that hazardous energy sources be "isolated and rendered inoperative" before work is started on the equipment in question. The isolated power sources are then locked and a tag is placed on the lock identifying the worker and reason the LOTO is placed on it. The worker then holds the key for the lock, ensuring that only they can remove the lock and start the equipment. This prevents accidental startup of equipment while it is in a hazardous state or while a worker is in direct contact with it.
Lockout–tagout is used across industries as a safe method of working on hazardous equipment and is mandated by law in some countries. (Full article...)
Risk assessment determines possible mishaps, their likelihood and consequences, and the tolerances for such events. The results of this process may be expressed in a quantitativeorqualitative fashion. Risk assessment is an inherent part of a broader risk management strategy to help reduce any potential risk-related consequences.
More precisely, risk assessment identifies and analyses potential (future) events that may negatively impact individuals, assets, and/or the environment (i.e. hazard analysis). It also makes judgments "on the tolerability of the risk on the basis of a risk analysis" while considering influencing factors (i.e. risk evaluation). (Full article...)
Diving safety is the aspect of underwater diving operations and activities concerned with the safety of the participants. The safety of underwater diving depends on four factors: the environment, the equipment, behaviour of the individual diver and performance of the dive team. The underwater 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, attention and common goals.
There is a large range of hazards to which the diver may be exposed. These each have associated consequences and risks, which should be taken into account during dive planning. Where risks are marginally acceptable it may be possible to mitigate the consequences by setting contingency and emergency plans in place, so that damage can be minimised where reasonably practicable. The acceptable level of risk varies depending on legislation, codes of practice, company policy, and personal choice, with recreational divers having a greater freedom of choice.
Inprofessional diving there is a diving team to support the diving operation, and their primary function is to reduce and mitigate risk to the diver. The diving supervisor for the operation is legally responsible for the safety of the diving team. A diving contractor may have a diving superintendent or a diving safety officer tasked with ensuring the organisation has, and uses, a suitable operations manual to guide their practices. In recreational diving, the dive leader may be partly responsible for diver safety to the extent that the dive briefing is reasonably accurate and does not omit any known hazards that divers in the group can reasonably be expected to be unaware of, and not to lead the group into a known area of unacceptable risk. A certified recreational diver is generally responsible for their own safety, and to a lesser, variable, and poorly defined extent, for the safety of their dive buddy. (Full article...)
Divers face specific physical and health risks when they go underwater with scuba or other diving equipment, or use high pressure breathing gas. Some of these factors also affect people who work in raised pressure environments out of water, for example in caissons. 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 any single 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 by occupational 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 million recreational 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...)
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 are job hazard analysis (JHA), hazardous task analysis (HTA) and job 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...)
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...)
Risk management is the identification, evaluation, and prioritization of risks (defined in ISO 31000asthe effect of uncertainty on objectives) followed by coordinated and economical application of resources to minimize, monitor, and control the probability or impact of unfortunate events or to maximize the realization of opportunities.
Risks can come from various sources including uncertainty in international markets, political instability, threats from 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 unpredictable root-cause.
There are two types of events i.e. negative events can be classified as risks while positive events are classified as opportunities. Risk management standards have been developed by various institutions, including the Project Management Institute, the National Institute of Standards and Technology, actuarial societies, and ISO standards (quality management standards to help work more efficiently and reduce product failures). Methods, definitions and goals vary widely according to whether the risk management method is in the context of project management, security, engineering, industrial processes, financial portfolios, actuarial assessments, or public health and safety. Certain risk management standards have been criticized for having no measurable improvement on risk, whereas the confidence in estimates and decisions seems to increase.
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 a professional 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 also Chief Risk Officer, internal audit, and Financial risk management § Corporate finance. (Full article...)
Human factors are the physical or cognitive properties of individuals, or social behavior which is specific to humans, and influence functioning of technological systems as well as human-environment equilibria. The safetyofunderwater diving operations can be improved by reducing the frequency of human 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.
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 the underwater environment and work safely. Diving equipment is crucial because it provides life 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
Inengineering and systems theory, redundancy is the intentional duplication of critical components or functions of a system with the goal of increasing reliability of the system, usually in the form of a backup or fail-safe, or to improve actual system performance, such as in the case of GNSS receivers, or multi-threaded computer processing.
In many safety-critical systems, such as fly-by-wire and hydraulic systems in aircraft, some parts of the control system may be triplicated, which is formally termed triple 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 as human error. Electrical surges arising from lightning 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.
Redundancy is one form of robustness as practiced in computer science.
Geographic redundancy has become important in the data center industry, to safeguard data against natural disasters and political instability (see below). (Full article...)
Scuba diving fatalities are deaths occurring while scuba diving or as a consequence of scuba diving. The risks of dying during recreational, scientificorcommercial diving are small, and on scuba, deaths are usually associated with poor gas management, poor buoyancy control, equipment misuse, entrapment, rough water conditions and pre-existing health problems. Some fatalities are inevitable and caused by unforeseeable situations escalating out of control, though the majority of diving fatalities can be attributed to human error on the part of the victim.
Equipment failure is rare in open circuit scuba, and while the cause of death is commonly recorded as drowning, 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 managed ascent, 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...)
Intort law, a duty of care is a legal obligation that is imposed on an individual, requiring adherence to a standardofreasonable care to avoid careless acts that could foreseeably harm others, and lead to claim in negligence. It is the first element that must be established to proceed with an action in negligence. The claimant must be able to show a duty of care imposed by law that the defendant has breached. In turn, breaching a duty may subject an individual to liability. The duty of care may be imposed byoperation of law between individuals who have no current direct relationship (familial or contractual or otherwise) but eventually become related in some manner, as defined by common law (meaning case law).
Duty of care may be considered a formalisation of the social contract, the established and implicit responsibilities held by individuals/entities towards others within society. It is not a requirement that a duty of care be defined by law, though it will often develop through the jurisprudence of common law. (Full article...)
The civil liability of a recreational diver may include a duty of caretoanother diver during a dive. Breach of this duty that is a proximate cause of injury or loss to the other diver may lead to civil litigation for damages in compensation for the injury or loss suffered.
Participation in recreational diving implies acceptance of the inherent risks of the activity Diver training includes training in procedures known to reduce these risks to a level considered acceptable by the certification agency, and issue of certification implies that the agency accepts that the instructor 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 associated training 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 as negligence if it puts another person at risk. Recommendations generally suggest that extending the scope should be done gradually, and preferably under the guidance of a 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 in refresher courses after long periods of diving inactivity. (Full article...)
Asilt outorsilt-out is a situation when underwater visibility is rapidly reduced to functional zero by disturbing fine particulate deposits on the bottom or other solid surfaces. This can happen in scuba and surface supplied diving, or in ROV and submersible operations, and is a more serious hazard for scuba diving in penetration situations where the route to the surface may be obscured. (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., the United 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 of 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...)
In-water recompression (IWR) or underwater oxygen treatment is the emergency treatment of decompression sickness (DCS) by returning the diver underwater to help the gas bubbles in the tissues, which are causing the symptoms, to resolve. It is a procedure that exposes the diver to significant risk 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 to travel to the nearest recompression 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 nearby recompression 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 become paralysed, unconscious, or stop breathing while underwater. Any one of these events is likely to result in the diver drowning 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...)
Laryngospasm is an uncontrolled or involuntary muscular contraction (spasm) of the vocal folds. It may be triggered when the vocal cords or the area of the trachea below the vocal folds detects the entry of water, mucus, blood, or other substance. It may be associated with stridororretractions. (Full article...)
Hyperbaric treatment schedules or hyperbaric treatment tables, are planned sequences of events in chronological order for hyperbaric pressure exposures specifying the pressure profile over time and the breathing gas to be used during specified periods, for medical treatment. Hyperbaric therapy is based on exposure to pressures greater than normal atmospheric pressure, and in many cases the use of breathing gases with oxygen content greater than that of air.
A large number of hyperbaric treatment schedules are intended primarily for treatment of underwater divers and hyperbaric workers who present symptoms of decompression illness during or after a dive or hyperbaric shift, but hyperbaric oxygen therapy may also be used for other conditions.
Most hyperbaric treatment is done in hyperbaric chambers where environmental hazards can be controlled, but occasionally treatment is done in the field by in-water recompression when a suitable chamber cannot be reached in time. The risks of in-water recompression include maintaining gas supplies for multiple divers and people able to care for a sick patient in the water for an extended period of time. (Full article...)
Diving medicine, also called undersea 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 relationships of a diver's fitness to dive affect a diver's safety. Diving medical practitioners are also expected to be competent in the examination of divers and potential divers to determine fitness to dive.
Hyperbaric medicine is a corollary field associated with diving, since recompression in a hyperbaric chamber is used as a treatment for two of the most significant diving-related illnesses, decompression sickness and arterial gas embolism.
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...)
Compression arthralgia is pain in the joints caused by exposure to high ambient pressure at a relatively high rate of compression, experienced by underwater divers. Also referred to in the U.S. Navy Diving Manualascompression pains.
Compression arthralgia has been recorded as deep aching pain in the knees, shoulders, fingers, back, hips, neck and ribs. Pain may be sudden and intense in onset and may be accompanied by a feeling of roughness in the joints.
Onset commonly occurs around 60 msw (meters of sea water), and symptoms are variable depending on depth, compression rate and personal susceptibility. Intensity increases with depth and may be aggravated by exercise. Compression arthralgia is generally a problem of deep diving, particularly deep saturation diving, where at sufficient depth even slow compression may produce symptoms. Peter B. Bennett et al. (1974) found that the use of trimix could reduce the symptoms.
Fast compression (descent) may produce symptoms as shallow as 30 msw. Saturation divers generally compress much more slowly, and symptoms are unlikely at less than around 90 msw. At depths beyond 180m even very slow compression may produce symptoms. Spontaneous improvement may occur over time at depth, but this is unpredictable, and pain may persist into decompression. Symptoms may be distinguished from decompression sickness as they are present before starting decompression, and resolve with decreasing pressure, the opposite of decompression sickness. The pain may be sufficiently severe to limit the diver's capacity for work, and may also limit travel rate and depth of downward excursions. (Full article...)
Taravana is a disease often found among Polynesian island natives who habitually dive deep without breathing apparatus many times in close succession, usually for food or pearls. These free-divers may make 40 to 60 dives a day, each of 30 or 40 metres (100 to 140 feet).
Taravana seems to be decompression sickness. The usual symptoms are vertigo, nausea, lethargy, paralysis and death. The word taravanaisTuamotu Polynesian for "to fall crazily".
Taravana is also used to describe someone who is "crazy because of the sea". (Full article...)
Diving disorders, or diving related medical conditions, are conditions associated with underwater 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 to ambient pressures significantly different from surface atmospheric 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 and psychological conditions which increase the risk of being affected by a diving disorder, which may be aggravated by adverse side effects of medications and other drug use.
Treatment depends on the specific disorder, but often includes oxygen therapy, which is standard first aid for most diving accidents, and is hardly ever contra-indicated for a person medically fit to dive, and hyperbaric therapy is the definitive treatment for decompression sickness. Screening for medical fitness to dive can reduce some of the risk for some of the disorders. (Full article...)
Atremie is a watertight pipe, usually of about 250 mm inside diameter (150 to 300 mm), with a conical hopper at its upper end above the water level. It may have a loose plug or a valve at the bottom end. A tremie is used to pour concrete underwater in a way that avoids washout of cement from the mix due to turbulent water contact with the concrete while it is flowing. This produces a more reliable strength of the product. Common applications include the following.
Alimpet mine is a type of naval mine attached to a target by magnets. It is so named because of its superficial similarity to the shape of the limpet, a type of sea snail that clings tightly to rocks or other hard surfaces.
A swimmer or diver may attach the mine, which is usually designed with hollow compartments to give the mine just slight negative buoyancy, making it easier to handle underwater. (Full article...)
The M1 Underwater Defense Gun, also called the Underwater Defense Gun Mark 1 Mod 0, is an underwater firearm developed by the United States during the Cold War. Similar to other underwater firearms, it fires a special 4.25-inch (108 mm) metal dart as its projectile. (Full article...)
Apolespear (hand spearorgidgee) is an underwater tool used in spearfishing, consisting of a pole, a spear tip, and a rubber loop. Polespears are often mistakenly called Hawaiian slings, but the tools differ. A Hawaiian sling is akin to a slingshot or an underwater bow 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...)
Anairlift is device based on a pipe, used in nautical archaeology to suck small objects, sand and mud from the sea bed and to transport the resulting debris upwards and away from its source. It is a type of suction dredge. A water dredge or water eductor may be used for the same purpose.
Typically, the airlift is constructed from a 3-metre to 10 metre long, 10 cm diameter pipe. A controllable compressed air supply vents into the inside, lower end of the pipe (The input end always being the lower end). Compressed air is injected into the pipe in one to three second bursts with an interval long enough to let the resulting bubble to rise to the higher, output end of the pipe. The bubble moves water through the pipe sucking debris from the lower end and depositing it from the upper end of the pipe. Ejected debris can be either cast off (as in simply removing overburden) or collected in a mesh cage for inspection (as more often is the case in nautical archaeology). It is often designed to be hand-operated by a diver.
Airlift pumps are used by water utilities, farmers and others to extract water from deep wells. In such cases the pipes can be 30, 60 or more meters deep underground. Airlift pumps are governed by the physics of two-phase flow. (Full article...)
Aremotely operated underwater vehicle (ROUV)orremotely operated vehicle (ROV) is a free-swimming submersible craft used to perform underwater observation, inspection and physical tasks such as valve operations, hydraulic functions and other general tasks within the subsea oil 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. (Full article...)
Aspeargun is a ranged underwater fishing device designed to launch a tethered spearorharpoon to impale fish or other marine animals and targets. Spearguns are used in sport fishing and underwater target shooting. The two basic types are pneumatic and elastic (powered by rubber bands). Spear types come in a number of varieties including threaded, break-away and lined. Floats and buoys are common accessories when targeting larger fish. (Full article...)
Anunderwater firearm is a firearm designed for use underwater. Underwater firearms or needleguns usually fire flechettes or spear-like bolts instead of standard bullets. These may be fired by pressurised gas. (Full article...)
The Raid on Algiers took place on 11 December 1942, in the Algiers harbour. Italian manned torpedoes and commando frogmen from the Decima Flottiglia MAS were brought to Algiers aboard the Perla-class submarine Ambra. The participating commandos were captured after setting limpet mines which sank two Allied ships and damaged two more. (Full article...)
Captain Charles Wesley Shilling (September 21, 1901 – December 23, 1994) was an American physician who was known as a leader in the field of undersea and hyperbaric medicine, research, and education. Shilling was widely recognized as an expert on deep sea diving, naval medicine, radiation biology, and submarine capabilities. In 1939, he was Senior Medical Officer in the rescue of the submarine U.S.S. Squalus. (Full article...)
Because Egypt had such valuable cargo, it was not long before salvage attempts began. However, Egypt's wreck was not found until 1930. She was found lying upright in a depth of 128 metres (420 ft), 70 fathoms, making recovery very difficult with the technology of the time. Giovanni Quaglia from the Genoese company Società Ricuperi Marittimi (So.Ri.Ma.) was in charge of the operation and decided to use his salvage fleet with the main ship Artiglio, on which there was embarked a famous group of expert hard hat divers under the command of the chief diver Alberto Gianni, who had invented special diving equipment. Gianni located the wreck, and sent a diver in his specially-built Torretta Butoscopica armoured diving suit to direct salvage operations and the placing of explosives to blast through the ship to expose the strongroom. The diver then directed a grab which picked up the gold and silver. The salvage operation continued until 1935, by which time 98% of the contents of the strong room had been recovered.
The recovery was reported in detail by The Times reporter David Scott, who sent daily cables to the newspaper, and who later published two famous books on this adventure, the first very deep recovery by divers, Seventy Fathom deep, with the divers of salvage ship Artiglio and The Egypt's gold, which were also translated into Italian. (Full article...)
Vintage scuba is scuba equipment dating from 1975 and earlier, and the practice of diving using such equipment. (Full article...)
Brian Andrew Hills, born 19 March 1934 in Cardiff, Wales, died 13 January 2006 in Brisbane, Queensland, was a physiologist who worked on decompression theory.
Early decompression work was done with Hugh LeMessurier's aeromedicine group at the department of Physiology, University of Adelaide. His "thermodynamic decompression model" was one of the first models in which decompression is controlled by the volume of gas bubbles coming out of solution. In this model, pain only DCS is modelled by a single tissue which is diffusion-limited for gas uptake, and bubble-formation during decompression causes "phase equilibration" of partial pressures between dissolved and free gases. The driving mechanism for gas elimination in this tissue is inherent unsaturation, also called partial pressure vacancy or the oxygen window, where oxygen metabolised is replaced by more soluble carbon dioxide. This model was used to explain the effectiveness of the Torres Strait Islands pearl divers' empirically developed decompression schedules, which used deeper decompression stops and less overall decompression time than the current naval decompression schedules. This trend to deeper decompression stops has become a feature of more recent decompression models.
Hills made a significant contribution to the mainstream scientific literature of some 186 articles between 1967 and 2006. The first 15 years of this contribution are mostly related to decompression theory. Other contributions to decompression science include the development of two early decompression computers, a method to detect tissue bubbles using electrical impedance, the use of kangaroo rats as animal models for decompression sickness, theoretical and experimental work on bubble nucleation, inert gas uptake and washout, acclimatisation to decompression sickness, and isobaric counterdiffusion. (Full article...)
Simon Mitchell (born 1958) is a New Zealand physician specialising in occupational medicine, hyperbaric medicine and anesthesiology. Trained in medicine, Mitchell was awarded a PhD for his work on neuroprotection from embolic brain injury. Mitchell has also published more than 45 research and review papers in the medical literature. Mitchell is an author and avid technical diver. He also wrote two chapters of the latest edition of Bennett and Elliott's Physiology and Medicine of Diving, is the co-author of the diving textbook Deeper Into Diving with John Lippmann and co-authored the chapter on Diving and Hyperbaric Medicine in Harrison's Principles of Internal Medicine with Michael Bennett. (Full article...)
The Russian government committed to raising the wreck and recovering the crew's remains in a US$65-million salvage operation. They contracted with Dutch marine salvage companies Smit International and Mammoet to raise Kursk from the sea floor. It became the largest salvage operation of its type ever accomplished. The salvage operation was extremely dangerous because of the risk of radiation from the reactor. Only seven of the submarine's 24 torpedoes were accounted for. (Full article...)
The history of scuba diving is closely linked with the history of the 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, and closed-circuit scuba where the carbon 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 engineer Henry Fleuss in 1878, while working for Siebe Gorman in London. His self 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 through World War II, the British, Italians and Germans developed and extensively used oxygen rebreathers to equip the first frogmen. In the U.S. Major Christian J. Lambertsen invented a free-swimming oxygen 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 acute oxygen toxicity.
Although a working demand regulator system had been invented in 1864 by Auguste Denayrouze and Benoît Rouquayrol, the first open-circuit scuba system developed in 1925 by Yves 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 and Émile Gagnan designed the first successful and safe open-circuit scuba, a twin hose system known as the Aqua-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 the U.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 1960s adjustable buoyancy life jackets (ABLJ) became available, which can be used to compensate for loss of buoyancy at depth due to compression of the neoprene wetsuit and as a lifejacket 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 the stabilizer jacket was introduced by ScubaPro. 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 basic scuba 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 advanced cave 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 the technical diving community for general decompression diving, and has become a popular specialty for recreational diving.
In the 1950s the United 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 1987 Wakulla 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...)
Colonel William Paul Fife USAF (Ret) (November 23, 1917 – October 13, 2008) was a United States Air Force officer that first proved the feasibility for U.S. Air Force Security Service airborne Communications Intelligence (COMINT) collection and Fife is considered the "Father of Airborne Intercept". Fife was also a hyperbaric medicine specialist who was known for his pioneering research on pressurized environments ranging from high altitudetounderwater habitats. Fife was a Professor EmeritusatTexas A&M University. (Full article...)
Defenses against swimmer incursions are security methods developed to protect watercraft, ports and installations, and other sensitive resources in or near vulnerable waterways from potential threats or intrusions by swimmersorscuba divers. (Full article...)
The history of underwater diving starts with freediving as a widespread means of hunting and gathering, both for food and other valuable resources such as pearls and coral. By classical Greek and Roman times commercial applications such as sponge diving and marine salvage were established. Military diving also has a long history, going back at least as far as the Peloponnesian War, with recreational and sporting applications being a recent development. Technological development in ambient pressure diving started with stone weights (skandalopetra) for fast descent. In the 16th and 17th centuries diving bells became functionally useful when a renewable supply of air could be provided to the diver at depth, and progressed to surface-supplied diving helmets—in effect miniature diving bells covering the diver's head and supplied with compressed air by manually operated pumps—which were improved by attaching a waterproof suit to the helmet and in the early 19th century became the standard diving dress.
Limitations in the mobility of the surface-supplied systems encouraged the development of both open circuit and closed circuit scuba in the 20th century, which allow the diver a much greater autonomy. These also became popular during World War II for clandestine military operations, and post-war for scientific, search and rescue, media diving, recreational and technical diving. The heavy free-flow surface-supplied copper helmets evolved into lightweight demand helmets, which are more economical with breathing gas, which is particularly important for deeper dives and expensive helium based breathing mixtures, and saturation diving reduced the risks of decompression sickness for deep and long exposures.
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 of remotely operated underwater vehicles in the late 20th century, where the operator controls the ROV from the surface, and autonomous 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.
Although the pathophysiology of decompression sickness is not yet fully understood, decompression practice has reached a stage where the risk is fairly low, and most incidences are successfully treated by therapeutic recompression and hyperbaric oxygen therapy. Mixed breathing gases are routinely used to reduce the effects of the hyperbaric environment on ambient pressure divers. (Full article...)
Captain Albert Richard Behnke Jr. USN (ret.) (August 8, 1903 – January 16, 1992) was an American physician, who was principally responsible for developing the U.S. Naval Medical Research Institute. Behnke separated the symptoms of Arterial Gas Embolism (AGE) from those of decompression sickness and suggested the use of oxygeninrecompression therapy.
Behnke is also known as the "modern-day father" of human body composition for his work in developing the hydrodensitometry method of measuring body density, his standard man and woman models as well as a somatogram based on anthropometric measurements. (Full article...)
Autonomous diver is an international minimum standard for entry level recreational scuba diver certification. It describes the minimum requirements for basic training and certification for recreational scuba divers in international standard ISO 24801-2 and the equivalent European Standard EN 14153-2. Various organizations offer training that meets the requirements of the Autonomous Diver standard. A certification which corresponds to Autonomous Diver allows for independent diving with a dive buddyinopen water. Most training organizations do not recommend exceeding a depth of 18 or 20 meters at this level of certification. After completion of this certification the training can be extended to a dive leader to ISO 24801-3 or an intermediate not defined by international standards.
Before initial diver training and thereafter at regular intervals, a diver should undergo a fitness to dive examination by a diving doctor. In some countries, such an examination is required by law and it is a prerequisite for any training in many diving schools. A diving certification which corresponds to Autonomous Diver and a medical certificate may be required for renting diving equipment and taking part in organised dives. In some countries (e.g. Australia) the law requires every diver to prove basic certification before unsupervised diving activity.
Some diver training organizations offer an intermediate Supervised diver certification which corresponds to ISO 24801-1, which usually only splits the contents of the Autonomous Diver training over two courses and does not qualify the holder to take part in independent dives. (Full article...)
The Israeli Diving Federation (Hebrew: ההתאחדות הישראלית לצלילה, Hitahdut Haisraelit Letslila) (TIDF) is a non-governmental SCUBA diving training organization based in Israel.
The Israeli Diving Federation is active in varied fields. To date it has scuttled 10 vessels to serve as dive sites, and has contributed to the creation of various other dive sites such as submerged underwater archaeological theme parks, the Sculpture Garden in Eilat, and more. TIDF is active in various “green” bodies dedicated to conservation of the underwater environment, the Coral Reef, and natural as well as man-made dive sites along the coasts of Israel.
The Israeli Diving Federation certifications are respected and recognized worldwide - TIDF obtained CEN certification from the EUF certification body. (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 as freediving. 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...)
Cave-divingisunderwater diving in water-filled caves. It may be done as an extreme sport, a way of exploring flooded caves for scientific investigation, or for the search for and recovery of divers or, as in the 2018 Thai cave rescue, other cave users. The equipment used varies depending on the circumstances, and ranges from breath holdtosurface supplied, but almost all cave-diving is done using scuba equipment, often in specialised configurations with redundancies such as sidemount or backmounted twinset. Recreational cave-diving is generally considered to be a type of technical diving due to the lack of a free surface during large parts of the dive, and often involves planned decompression 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 to open water can be seen by natural light. An arbitrary distance limit to the open water surface may also be specified.
Equipment, procedures, and the requisite skills have been developed to reduce the risk of becoming lost in a flooded cave, and consequently drowning when the breathing gas supply runs out. The equipment aspect largely involves the provision of an adequate breathing gas supply to cover reasonably foreseeable contingencies, redundant dive lights and other safety critical equipment, and the use of a continuous guideline leading the divers back out of the overhead 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 of caving. Its origins in the United States are more closely associated with recreational 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, and speleologists 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 contain fauna 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...)
ADiving certificationorC-card is a document (usually a wallet sized plastic 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 in underwater diving. Divers carry a qualification record or certification card which may be required to prove their qualifications when booking a dive trip, hiring scuba equipment, having diving cylinders filled, or in the case of professional divers, seeking employment.
Although recreational certifications are issued by numerous different diver 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, a diver's logbook, or the electronic equivalent, is primarily evidence of range of diving experience. (Full article...)
Master Scuba Diver (MSD) is a scuba diving certification or recognition level offered by several North American diver training agencies, such as the National Association of Underwater Instructors (NAUI), the Professional Association of Diving Instructors (PADI), Scuba Diving International (SDI), and Scuba Schools International (SSI). Other agencies (e.g., The International Association of Nitrox and Technical Divers) offer similar programs under other names, such as "Elite Diver". Each of these (and other) agencies touts their program at this level as the highest, non-leadership program.
Most organizations have a minimum age requirement of 15 to undertake the Master Scuba Diver course, although some organizations do permit certification of "Junior" Master Scuba Divers. (Full article...)
The International Association of Nitrox and Technical Divers (IANTD) is a scuba diving organization concerned with certification and training in recreational diving, technical diving, cave diving, wreck diving, rebreather diving and diver leadership. Originally formed as the International Association of Nitrox Divers in 1985 by Dick Rutkowski it pioneered the introduction of Enriched Air Nitrox diving to the recreational diving community, before its name change in 1992 to reflect the more "technical" diving courses it had begun to teach. The European Association of Technical Divers (EATD) became part of IANTD in 1993. (Full article...)
The Sub-Aqua AssociationorSAA is a diver training organization for scubadivers in the United Kingdom. The SAA and other UK-based diving groups have traditionally used a club-based system with unpaid instructors, while other training agencies organise most of their training programs through professional instructors and dive shops. The other major club-based diving organizations in the UK are the British Sub-Aqua Club (BSAC) and the Scottish Sub Aqua Club, and the principal non-club-based organisation is PADI. (Full article...)
The Professional Association of Diving Instructors (PADI) is a recreational diving membership and diver training organization founded in 1966 by John Cronin and Ralph Erickson. PADI courses range from entry level to advanced recreational diver certification. Further, they provide several specialized diving skills courses connected with specific equipment or conditions, some diving related informational courses and a range of recreational diving instructor certifications. They also offer various technical diving courses. As of 2023, PADI is reported to have issued 29 million scuba certifications. (Full article...)
Dive RAID International (formerly RAID) is a dive training organization which was founded in 2007 to support diver training for the Poseidon Mk VI Discovery Rebreather. It has since extended its scope to include open circuit scuba training and training for both recreational and technical diving sectors as well as snorkeling and freediving. (Full article...)
The Federazione Italiana Attività Subacquee (FIAS) (Italian Underwater Activities Federation) is an Italian non-profit diver training organization. It is a member of:
The International Diving Regulators and Certifiers Forum (IDRCF) is an organisation representing a group of national regulatory and certifying bodies for occupational 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...)
Rubicon Foundation, Inc. is a non-profit organization devoted to contributing to the interdependent dynamic between research, exploration, science and education. The foundation, started in 2002, is located in Durham, North Carolina and is primarily supported by donations and grants. Funding has included the Office of Naval Research from 2008 to 2010. Gibson, Dunn & Crutcher has provided pro bono services to assist in copyright searches and support.
As of 2021, the Rubicon Research Repository is no longer available online. (Full article...)
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 at Duke University providing 24/7 telephonic hot-line diving medical assistance. Since then the organization has expanded globally and now has independent regional organizations in North America, Europe, Japan, Asia-Pacific and Southern 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...)
The Spanish Federation of Underwater Activities (Spanish: Federación Española de Actividades Subacuáticas, FEDAS) is the governing body in the field of Spanish aquatic sports. As of 2022, the federation has 895 registered clubs and 32,289 federated athlets.
It is a voting member of the Confédération Mondiale des Activités Subaquatiques (CMAS) . (Full article...)
Cave-divingisunderwater diving in water-filled caves. It may be done as an extreme sport, a way of exploring flooded caves for scientific investigation, or for the search for and recovery of divers or, as in the 2018 Thai cave rescue, other cave users. The equipment used varies depending on the circumstances, and ranges from breath holdtosurface supplied, but almost all cave-diving is done using scuba equipment, often in specialised configurations with redundancies such as sidemount or backmounted twinset. Recreational cave-diving is generally considered to be a type of technical diving due to the lack of a free surface during large parts of the dive, and often involves planned decompression 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 to open water can be seen by natural light. An arbitrary distance limit to the open water surface may also be specified.
Equipment, procedures, and the requisite skills have been developed to reduce the risk of becoming lost in a flooded cave, and consequently drowning when the breathing gas supply runs out. The equipment aspect largely involves the provision of an adequate breathing gas supply to cover reasonably foreseeable contingencies, redundant dive lights and other safety critical equipment, and the use of a continuous guideline leading the divers back out of the overhead 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 of caving. Its origins in the United States are more closely associated with recreational 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, and speleologists 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 contain fauna 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...)
The South African Underwater Sports Federation (SAUSF) is the official CMAS (World Underwater Federation) representative in the Republic of South Africa, and is affiliated to the South African Sports Confederation and Olympic Committee (SASCOC).
Formerly known as the South African Underwater Union (SAUU), the SAUSF has been responsible for the administrative duties of all underwater sports in South Africa. This originally included boating in connection with diving, and scuba training and recreational diving, but these two aspects of underwater sport developed into commercial activities and split from the SAUU to SASCA and CMAS-ISA respectively, whereas the competitive amateur sports like underwater hockey, spearfishing, finswimming and free diving remained with SAUU. (Full article...)
The Australian Underwater Federation (AUF) is the governing body for underwater sports in Australia. (Full article...)
The Cave Divers Association of Australia (CDAA) is a cave diving organisation which was formed in September 1973 to represent the interests of recreational scuba divers who dive in water‐filled caves and sinkholes principally in the Lower South East (now called the Limestone Coast) of South Australia (SA) and secondly in other parts of Australia. Its formation occurred after a series of diving fatalities in waterfilled caves and sinkholes in the Mount Gambier region between 1969 and 1973 and in parallel to a Government 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 the Nullarbor Plain and Wellington, New South Wales. (Full article...)
The Sea Research Society (SRS) is a non-profit organization promoting research and education in marine science and history. Founded in 1972 by underwater archaeologist E. Lee Spence, SRS undertakes archival research and underwater expeditions in search of historic shipwrecks. From 1972 to 1978, it also operated the College of Marine Arts. (Full article...)
British Octopush Association (BOA) is the governing body for underwater hockey in Great Britain. (Full article...)
The British Freediving Association (BFA, also known as AIDA-UK) is an organisation established in the United Kingdom during 1999 to promote the safe practice of both competition and recreational freediving. It is the British affiliate of AIDA International. The BFA is the sole body that selects teams for international competitions conducted by AIDA International and ratifies any UK record attempts. It has an inland training centre at Vobster Quay in Somerset.
The British Freediving Association organises UK Freediving pool and depth competitions every year. The Great Northern pool competition was hosted by ApneistsUK who have hosted the Pool Championships in 2010, 2011, 2012, 2013 and 2014. The last depth competition was 2012.
The organisation has a small membership, with 132 members recorded in October 2009. (Full article...)
The Cave Diving Group (CDG) is a United Kingdom-based diver training organisation specialising in cave diving.
The CDG was founded in 1946 by Graham Balcombe, making it the world's oldest continuing diving club. Graham Balcombe and Jack Sheppard pioneered cave diving in the late 1930s, notably at Wookey HoleinSomerset.
Passages through caves are often blocked by a submerged section, or sump. Cavers in many countries have tried to pass these barriers in a variety of ways; using the simple "free dive" with a lungful of air or by utilising the available diving technology of the day. (Full article...)
AIDA Hellas (AIDA, from French: Association Internationale pour le Développement de l'Apnée) is a Greek non-profit organization dedicated to the sport of freediving, officially established in 2002. It is the official national representative of AIDA InternationalinGreece, responsible for the representation of Greek freediving community internationally. It aims to the development of freediving in Greece, organizing events like educational seminars and international level sport competitions, every year. Also, it sets standards for the national record attempts and the selection of the members of the national team for AIDA World Championships.
AIDA Hellas is currently supported by more than 100 members in Greece. (Full article...)
The European Underwater and Baromedical Society (EUBS) is a primary source of information for diving and hyperbaric medicine physiology worldwide. The organization was initially formed as the European Underwater and Biomedical Society in 1971 and was an affiliate of the Undersea 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...)
The Naval Submarine Medical Research Laboratory (NSMRL) is located on the New London Submarine BaseinGroton, Connecticut. It is a subordinate command of the Naval Medical Research Command. (Full article...)
The Silent World (subtitle: A story of undersea discovery and adventure, by the first men to swim at record depths with the freedom of fish) is a 1953 book co-authored by Captain Jacques-Yves Cousteau and Frédéric Dumas, and edited by James Dugan. (Full article...)
The NOAA Diving Manual: Diving for Science and Technology is a book originally published by the US 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...)
Goldfinder is a 2001 autobiography of British diver and treasure hunter Keith Jessop. It tells the story of Jessop's life and salvaging such underwater treasures as HMS Edinburgh, one of the greatest deep sea salvage operations and most financially rewarding in history.
One day in April 1981 Jessop's survey ship Dammtor began searching for the wreck of HMS Edinburgh in the Barents Sea in the Arctic Ocean of the coast of Russia. The ship had been sunk in battle in 1942 during World War II while carrying payment for military equipment from Murmansk in Russia to Scotland. His company, called Jessop Marine, won the contract for the salvage rights to the wreck of Edinburgh because his methods, involving complex cutting machinery and divers, were deemed more appropriate for a war 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 Russian gold bullion (431 bars) from the wreck out of 465 over several days making him the greatest underwater treasurer in history.
Jessop died on 22 May 2010. (Full article...)
The Darkness Beckons (ISBN 0-939748-32-0) is a book about the history of UK cave divingbyMartyn 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...)
Shadow Divers: The True Adventure of Two Americans Who Risked Everything to Solve One of the Last Mysteries of World War II is a 2004 non-fiction book by Robert Kurson recounting of the discovery of a World War II German U-boat 60 miles (97 km) off the coast of New Jersey, United States in 1991, exploration dives, and its eventual identification as U-869 lost on 11 February 1945. (Full article...)
The Last Dive: A Father and Son's Fatal Descent into the Ocean's Depths (2000) is a non-fiction book written by diver Bernie Chowdhury and published by HarperCollins. It documents the fatal dive of Chris Rouse, Sr. and Chris "Chrissy" Rouse, Jr., a father-son team who perished off the New Jersey coast in 1992. The author is a dive expert and was a friend of the Rouses.
The divers were exploring a German U-boat in 230 feet (70 m) of water off the coast of New Jersey. Although experienced in using technical 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 the captain's log book from the so-called U-Who to "fulfill their dream of diving into fame." The U boat was subsequently identified as U-869.
Chowdhury is a technical diver who, according to writer Neal Matthews' review of Robert Kurson's book Shadow 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...)
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Kronan (ship) Mary Rose Metabolism Oxygen toxicity USS Saratoga (CV-3) Underwater diving Vasa (ship) SS Washingtonian (1913)
115 (barge) USS Arkansas (BB-33) David Attenborough William Beebe HMSAS Bloemfontein HMS Boadicea (H65) Bowie Seamount Hugh Bradner Carbon monoxide poisoning Scott Carpenter SS Cayuga SS Chester A. Congdon Decompression sickness Decompression (diving) Decompression equipment Decompression practice Dive profile Diver communications Diving cylinder SS Emperor Force SMS Geier SAS Good Hope History of decompression research and development SS Ironsides SS John V. Moran Scott Kelly (astronaut) PS Keystone State SS Manasoo USS Monitor Nitrogen narcosis Pearl and Hermes Atoll HMS Pelorus (J291) HMS Prince of Wales (53) Leni Riefenstahl HMS Safari Japanese cruiser Sakawa Scuba diving Solo diving Special Air Service Regiment Special Air Service Special Boat Service HMS Thames (1885) SAS Transvaal German submarine U-40 (1938) SS Vernon USS Yancey
Ricou Browning Scott Carpenter Darwin's Arch Deepsea Challenger Jon Lindbergh Russian submarine Losharik Pilar Luna Sinking of MV Conception Rob Stewart (filmmaker) Tham Luang cave rescue
Diver communications are the methods used by divers to communicate with each other or with surface members of the dive team. In professional diving, diver communication is usually between a single working diver and the diving 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 the helmet 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...)
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 personal dive computer. Several common types of dive profile are specifically named, and these may be characteristic of the purpose of the dive. For example, a working dive at a limited location will often follow a constant depth (square) profile, and a recreational 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 a planning tool as an indication of the risks of decompression sickness and oxygen toxicity for the exposure, to calculate a decompression schedule for the dive, and also for estimating the volume of open-circuit breathing 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 personal dive 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 a personal computer, tablet, or smartphone and displayed in graphic form as a dive profile. (Full article...)
The decompression of a diver is the reduction in ambient pressure experienced during ascent from depth. It is also the process of elimination of dissolved inert gases from the diver's body which accumulate during ascent, largely during pauses in the ascent known as decompression stops, and after surfacing, until the gas concentrations reach equilibrium. Divers breathing gas at ambient pressure need to ascend at a rate determined by their exposure to pressure and the breathing gas in use. A diver who only breathes gas at atmospheric pressure when free-divingorsnorkelling will not usually need to decompress. Divers using an atmospheric diving suit do not need to decompress as they are never exposed to high ambient pressure.
When a diver descends in the water, the hydrostatic pressure, and therefore the ambient pressure, rises. Because breathing gas is supplied at ambient pressure, some of this gas dissolves into the diver's blood and is transferred by the blood to other tissues. Inert gas such as nitrogenorhelium 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's lungs, at which point the diver is saturated for that depth and breathing mixture, or the depth, and therefore the pressure, is changed, or the partial 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. If the pressure reduction is sufficient, excess gas may form bubbles, which may lead to decompression 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, the asymptomatic venous microbubbles present after most dives are eliminated from the diver's body in the alveolar 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 to sub-clinical decompression injury.
The mechanisms of bubble formation and the damage bubbles 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 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. Nevertheless, currently popular decompression procedures advise a 'safety stop' additional to any stops required by the algorithm, usually of about three to five minutes at 3 to 6 metres (10 to 20 ft), particularly 1 on an otherwise continuous no-stop ascent.
Decompression may be continuousorstaged. A staged decompression ascent is interrupted by decompression stops at calculated depth intervals, but the entire ascent is actually part of the decompression and the ascent rate is critical to harmless elimination of inert gas. A no-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 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. When time is spent on the surface between dives this is known as the "surface interval" and is considered when calculating decompression requirements for the subsequent dive.
Efficient decompression requires the diver to ascend fast enough to establish as high a decompression gradient, in as many tissues, as safely possible, without provoking the development of symptomatic bubbles. This is facilitated by the highest acceptably safe oxygen partial pressure in the breathing gas, and avoiding gas changes that could cause counterdiffusion bubble formation or growth. The development of schedules that are both safe and efficient has been complicated by the large number of variables and uncertainties, including personal variation in response under varying environmental conditions and workload. (Full article...)
Diving disorders are medical conditions specifically arising from underwater diving. The signs and symptoms of these may present during a dive, on surfacing, or up to several hours after a dive.
The principal conditions are decompression illness (which covers decompression sickness and arterial gas embolism), nitrogen narcosis, high pressure nervous syndrome, oxygen toxicity, and pulmonary barotrauma (burst lung). Although some of these may occur in other settings, they are of particular concern during diving activities.
The disorders are caused by breathing gas at the high pressures encountered at depth, and divers will often breathe a gas mixture different from air to mitigate these effects. Nitrox, which contains more oxygen and less nitrogen, is commonly used as a breathing gas to reduce the risk of decompression sickness at recreational depths (up to about 40 metres (130 ft)). 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 and to avoid the risk of oxygen toxicity. 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 as hydreliox, a hydrogen–helium–oxygen mixture, are used at extreme depths to counteract this. (Full article...)
Solo diving is the practice of self-sufficient underwater diving without a "dive buddy", particularly with reference to scuba diving, but the term is also applied to freediving. Professionally, solo diving has always been an option which depends on operational requirements and risk assessment. Surface supplied diving and atmospheric suit diving are commonly single diver underwater activities but are accompanied by an on-surface support team dedicated to the safety of the diver, including a stand-by diver, and are not considered solo diving in this sense.
Solo freediving has occurred for millennia as evidenced by artifacts dating back to the ancient people of Mesopotamia 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 scuba certification agencies incorporated the practice of buddy diving into their diver 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 advanced underwater 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 backup scuba equipment. In most countries there is no legal impediment to solo recreational diving, with or without certification. (Full article...)
Decompression in the context of diving derives from the reduction in ambient pressure experienced by the diver during the ascent at the end of a dive or hyperbaric exposure and refers to both the reduction in pressure and the process of allowing dissolved inert gases to be eliminated from the tissues during this reduction in pressure.
When a diver descends in the water column the ambient 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's lungs, (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 as nitrogenorhelium can form bubbles in the blood and tissues of the diver if the partial pressures of the dissolved gases in the diver get too high when compared to the ambient pressure. These bubbles, and products of injury caused by the bubbles, can cause damage to tissues generally known as decompression sicknessorthe 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 other emboli 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 by Robert Boyle, who subjected experimental animals to reduced ambient pressure by use of a primitive vacuum 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...)
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 the underwater environment and work safely. Diving equipment is crucial because it provides life 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.
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