Portal:Underwater diving
Underwater diving
Scuba divers decompressing in the water
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 diving or surface-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...)
How to use this portal
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- Outline of underwater diving is a hierarchical list of all the articles, but may not always be up to date.
- Index of underwater diving is an alphabetical list of the articles and redirects to sections of the articles representing common dive related topics, (also not always up to date). It has sub-indexes for some of the associated groups of articles, such as:
- The Glossary of underwater diving terminology is an alphabetical list of terms commonly used in diving and their meanings in this context. A useful quick reference. A definition will often contain a link to a detailed main article, or a section of an article on the term. If you can't find a term and are reasonably sure it is a diving term in general use in English, leave a note on the talk page.
Category:Underwater diving and the associated subcategories should also list all the articles, probably in a different hierarchical structure to that used for the navbox and outline list. Sometimes the category system can be more appropriate for finding information. It is also helpful for maintenance of Wikipedia and keeping track of the connectedness of articles.
If you have unlimited time and no special target, you can go down the rabbit-hole – Read the topic root article Underwater diving, and click on any link that looks interesting. Read until you find another interesting link and click on that, otherwise click your browser arrow to go back, and carry on. Stop when reality intrudes or you get bored, tired, thirsty or a fire breaks out.
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Diving modes
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Surface-supplied diver at the Monterey Bay Aquarium, Monterey, California
Surface-supplied diving is a mode of underwater 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 system or underwater 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...) -
Saturation diver working on the USS Monitor wreck at 70 m (230 ft) depth.
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...) -
Surface-supplied diver at the Monterey Bay Aquarium, Monterey, California
Surface-supplied diving is a mode of underwater 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 system or underwater 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...) -
Recreational scuba diver
Scuba diving is a mode of underwater 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 acronym 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 gas or emergency 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 recreationally or professionally 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 diver at the Monterey Bay Aquarium, Monterey, California
Surface-supplied diving is a mode of underwater 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 system or underwater 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...) -
A freediver on the ocean floor
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...) -
Surface-supplied divers riding a stage to the underwater workplace
Underwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment. It is also often referred to 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 diving or surface-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 diver at the Monterey Bay Aquarium, Monterey, California
Surface-supplied diving is a mode of underwater 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 system or underwater 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...) -
An atmospheric diving suit (ADS), or single atmosphere diving suit is a small one-person articulated submersible which resembles a suit of armour, with elaborate pressure joints to allow articulation while maintaining an internal pressure of one atmosphere. An ADS can enable diving at depths of up to 2,300 feet (700 m) for many hours by eliminating the majority of significant physiological dangers associated with deep diving. The occupant of an ADS does not need to decompress, and there is no need for special breathing gas mixtures, so there is little danger of decompression sickness or nitrogen narcosis when the ADS is functioning properly. An ADS can permit less skilled swimmers to complete deep dives, albeit at the expense of dexterity.
Atmospheric diving suits in current use include the Newtsuit, Exosuit, Hardsuit and the WASP, all of which are self-contained hard suits that incorporate propulsion units. The Hardsuit is constructed from cast aluminum (forged aluminum in a version constructed for the US Navy for submarine rescue); the upper hull is made from cast aluminum, while the bottom dome is machined aluminum. The WASP is of glass-reinforced plastic (GRP) body tube construction. (Full article...) -
Surface-supplied diver at the Monterey Bay Aquarium, Monterey, California
Surface-supplied diving is a mode of underwater 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 system or underwater 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 diver at the Monterey Bay Aquarium, Monterey, California
Surface-supplied diving is a mode of underwater 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 system or underwater 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 divers riding a stage to the underwater workplace
Underwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment. It is also often referred to 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 diving or surface-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...) -
Recreational scuba diver
Scuba diving is a mode of underwater 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 acronym 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 gas or emergency 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 recreationally or professionally 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...) -
2nd Reconnaissance Battalion combat diver training with the Dräger LAR V rebreather
Rebreather diving is underwater 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...)
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Diving and support equipment
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In cave (and occasionally wreck) diving, line markers are used for orientation as a visual and tactile reference on a permanent guideline. Directional markers (commonly a notched acute isosceles triangle in basic outline), are also known as line arrows or Dorff arrows, and point the way to an exit. Line arrows may mark the location of a "jump" location in a cave when two are placed adjacent to each other. Two adjacent arrows facing away from each other, mark a point in the cave where the diver is equidistant from two exits. Arrow direction can be identified by feel in low visibility.
Non-directional markers ("cookies") are purely personal markers that mark specific spots, or the direction of one's chosen exit at line intersections where there are options. Their shape does not provide a tactile indication of direction as this could cause confusion in low visibility. One important reason to be adequately trained before cave diving is that incorrect marking can confuse and fatally endanger not only oneself, but also other divers. (Full article...) -
A pair of demand valves fitted to a scuba regulator
In underwater 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...) -
Diving equipment, or underwater diving equipment, is equipment used by underwater divers to make diving activities possible, easier, safer and/or more comfortable. This may be equipment primarily intended for this purpose, or equipment intended for other purposes which is found to be suitable for diving use.
The fundamental item of diving equipment used by divers other than freedivers, is underwater breathing apparatus, such as scuba equipment, and surface-supplied diving equipment, but there are other important items of equipment that make diving safer, more convenient or more efficient. Diving equipment used by recreational scuba divers, also known as scuba gear, is mostly personal equipment carried by the diver, but professional divers, particularly when operating in the surface supplied or saturation mode, use a large amount of support equipment not carried by the diver.
Equipment which is used for underwater work or other activities which is not directly related to the activity of diving, or which has not been designed or modified specifically for underwater use by divers is not considered to be diving equipment. (Full article...) -
Trimix scuba cylinder label
Trimix is a breathing gas consisting of oxygen, helium and nitrogen and is used in deep commercial diving, during the deep phase of dives carried out using technical diving techniques, and in advanced recreational diving.
The helium is included as a substitute for some of the nitrogen, to reduce the narcotic effect of the breathing gas at depth. With a mixture of three gases it is possible to create mixes suitable for different depths or purposes by adjusting the proportions of each gas. Oxygen content can be optimised for the depth to limit the risk of toxicity, and the inert component balanced between nitrogen (which is cheap but narcotic) and helium (which is not narcotic and reduces work of breathing, but is more expensive and increases heat loss).
The mixture of helium and oxygen with a 0% nitrogen content is generally known as heliox. This is frequently used as a breathing gas in deep commercial diving operations, where it is often recycled to save the expensive helium component. Analysis of two-component gases is much simpler than three-component gases. (Full article...) -
A diving mask (also half mask, dive mask or scuba mask) is an item of diving equipment that allows underwater divers, including scuba divers, free-divers, and snorkelers, to see clearly underwater. Surface supplied divers usually use a full face mask or diving helmet, but in some systems the half mask may be used. When the human eye is in direct contact with water as opposed to air, its normal environment, light entering the eye is refracted by a different angle and the eye is unable to focus the light on the retina. By providing an air space in front of the eyes, the eye is able to focus nearly normally. The shape of the air space in the mask slightly affects the ability to focus. Corrective lenses can be fitted to the inside surface of the viewport or contact lenses may be worn inside the mask to allow normal vision for people with focusing defects.
When the diver descends, the ambient pressure rises, and it becomes necessary to equalise the pressure inside the mask with the external ambient pressure to avoid the barotrauma known as mask squeeze. This is done by allowing sufficient air to flow out through the nose into the mask to relieve the pressure difference, which requires the nose to be included in the airspace of the mask. Equalisation during ascent is automatic as excess air inside the mask easily leaks out past the seal.
A wide range of viewport shapes and internal volumes are available, and each design will generally fit some shapes of face better than others. A good comfortable fit and a reliable seal around the edges of the rubber skirt is important to the correct function of the mask. National and international standards relating to diving masks provide a means of ensuring that they are manufactured to a suitable quality. (Full article...) -
A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed habitats. Oxygen is the essential component for any breathing gas. Breathing gases for hyperbaric use have been developed to improve on the performance of ordinary air by reducing the risk of decompression sickness, reducing the duration of decompression, reducing nitrogen narcosis or allowing safer deep diving. (Full article...) -
A diving suit is a garment or device designed to protect a diver from the underwater environment. A diving suit may also incorporate a breathing gas supply (such as for a standard diving dress or atmospheric diving suit), but in most cases the term applies only to the environmental protective covering worn by the diver. The breathing gas supply is usually referred to separately. There is no generic term for the combination of suit and breathing apparatus alone. It is generally referred to as diving equipment or dive gear along with any other equipment necessary for the dive.
Diving suits can be divided into two classes: "soft" or ambient pressure diving suits – examples are wetsuits, dry suits, semi-dry suits and dive skins – and "hard" or atmospheric pressure diving suits, armored suits that keep the diver at atmospheric pressure at any depth within the operating range of the suit. Hot water suits are actively heated wetsuits. (Full article...) -
Offshore support vessel Toisa Perseus with, in the background, the fifth-generation deepwater drillship Discoverer Enterprise, over the Thunder Horse Oil Field. Both are equipped with DP systems.
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...) -
One type of nitrox cylinder identification label
Nitrox refers to any gas mixture composed (excepting trace gases) of nitrogen and oxygen that contains less than 78% nitrogen. 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). The two most common recreational diving nitrox mixes are 32% and 36% oxygen, which have maximum operating depths of about 110 feet (34 meters) and 95 feet (29 meters respectively.
Nitrox is used to a lesser extent 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...) -
A diving weighting system is ballast weight added to a diver or diving equipment to counteract excess buoyancy. They may be used by divers or on equipment such as diving bells, submersibles or camera housings.
Divers wear diver weighting systems, weight belts or weights to counteract the buoyancy of other diving equipment, such as diving suits and aluminium diving cylinders, and buoyancy of the diver. The scuba diver must be weighted sufficiently to be slightly negatively buoyant at the end of the dive when most of the breathing gas has been used, and needs to maintain neutral buoyancy at safety or obligatory decompression stops. During the dive, buoyancy is controlled by adjusting the volume of air in the buoyancy compensation device (BCD) and, if worn, the dry suit, in order to achieve negative, neutral, or positive buoyancy as needed. The amount of weight required is determined by the maximum overall positive buoyancy of the fully equipped but unweighted diver anticipated during the dive, with an empty buoyancy compensator and normally inflated dry suit. This depends on the diver's mass and body composition, buoyancy of other diving gear worn (especially the diving suit), water salinity, weight of breathing gas consumed, and water temperature. It normally is in the range of 2 kilograms (4.4 lb) to 15 kilograms (33 lb). The weights can be distributed to trim the diver to suit the purpose of the dive.
Surface-supplied divers may be more heavily weighted to facilitate underwater work, and may be unable to achieve neutral buoyancy, and rely on the diving stage, bell, umbilical, lifeline, shotline or jackstay for returning to the surface.
Free divers may also use weights to counteract buoyancy of a wetsuit. However, they are more likely to weight for neutral buoyancy at a specific depth, and their weighting must take into account not only the compression of the suit with depth, but also the compression of the air in their lungs, and the consequent loss of buoyancy. As they have no decompression obligation, they do not have to be neutrally buoyant near the surface at the end of a dive.
If the weights have a method of quick release, they can provide a useful rescue mechanism: they can be dropped in an emergency to provide an instant increase in buoyancy which should return the diver to the surface. Dropping weights increases the risk of barotrauma and decompression sickness due to the possibility of an uncontrollable ascent to the surface. This risk can only be justified when the emergency is life-threatening or the risk of decompression sickness is small, as is the case in free diving and scuba diving when the dive is well short of the no-decompression limit for the depth. Often divers take great care to ensure the weights are not dropped accidentally, and heavily weighted divers may arrange their weights so subsets of the total weight can be dropped individually, allowing for a somewhat more controlled emergency ascent.
The weights are generally made of lead because of its high density, reasonably low cost, ease of casting into suitable shapes, and resistance to corrosion. The lead can be cast in blocks, cast shapes with slots for straps, or shaped as pellets known as "shot" and carried in bags. There is some concern that lead diving weights may constitute a toxic hazard to users and environment, but little evidence of significant risk. (Full article...) -
A bailout bottle (BoB) or, more formally, bailout cylinder is a scuba cylinder carried by an underwater diver for use as an emergency supply of breathing gas in the event of a primary gas supply failure. A bailout cylinder may be carried by a scuba diver in addition to the primary scuba set, or by a surface supplied diver using either free-flow or demand systems. The bailout gas is not intended for use during the dive except in an emergency, and would be considered a fully redundant breathing gas supply if used correctly. The term may refer to just the cylinder, or the bailout set or emergency gas supply (EGS), which is the cylinder with the gas delivery system attached. The bailout set or bailout system is the combination of the emergency gas cylinder with the gas delivery system to the diver, which includes a diving regulator with either a demand valve, a bailout block, or a bailout valve (BOV).
In solo diving, a buddy bottle is a bailout cylinder carried as a substitute for an emergency gas supply from a diving buddy. A bailout cylinder for recreational scuba diving is often a small cylinder, known as a pony bottle, with a normal scuba regulator set, or a smaller cylinder with a combined first and second stage integrated with the cylinder valve, known as "Spare air", after a well known example of the type.
Rebreathers also have bailout systems, often including an open-circuit bailout bottle. (Full article...) -
A lifting bag is an item of diving equipment consisting of a robust and air-tight bag with straps, which is used to lift heavy objects underwater by means of the bag's buoyancy. The heavy object can either be moved horizontally underwater by the diver or sent unaccompanied to the surface.
Lift bag appropriate capacity should match the task at hand. If the lift bag is grossly oversized a runaway or otherwise out of control ascent may result. Commercially available lifting bags may incorporate dump valves to allow the operator to control the buoyancy during ascent, but this is a hazardous operation with high risk of entanglement in an uncontrolled lift or sinking. If a single bag is insufficient, multiple bags may be used, and should be distributed to suit the load.
There are also lifting bags used on land as short lift jacks for lifting cars or heavy loads or lifting bags which are used in machines as a type of pneumatic actuator which provides load over a large area. These lifting bags of the AS/CR type are for example used in the brake mechanism of rollercoasters. (Full article...) -
A diving cylinder or diving gas cylinder is a gas cylinder used to store and transport high pressure gas used in diving operations. This may be breathing gas used with a scuba set, in which case the cylinder may also be referred to as a scuba cylinder, scuba tank or diving tank. When used for an emergency gas supply for surface supplied diving or scuba, it may be referred to as a bailout cylinder or bailout bottle. It may also be used for surface-supplied diving or as decompression gas . A diving cylinder may also be used to supply inflation gas for a dry suit or buoyancy compensator. Cylinders provide gas to the diver through the demand valve of a diving regulator or the breathing loop of a diving re-breather.
Diving cylinders are usually manufactured from aluminum or steel alloys, and when used on a scuba set are normally fitted with one of two common types of cylinder valve for filling and connection to the regulator. Other accessories such as manifolds, cylinder bands, protective nets and boots and carrying handles may be provided. Various configurations of harness may be used by the diver to carry a cylinder or cylinders while diving, depending on the application. Cylinders used for scuba typically have an internal volume (known as water capacity) of between 3 and 18 litres (0.11 and 0.64 cu ft) and a maximum working pressure rating from 184 to 300 bars (2,670 to 4,350 psi). Cylinders are also available in smaller sizes, such as 0.5, 1.5 and 2 litres, however these are usually used for purposes such as inflation of surface marker buoys, dry suits and buoyancy compensators rather than breathing. Scuba divers may dive with a single cylinder, a pair of similar cylinders, or a main cylinder and a smaller "pony" cylinder, carried on the diver's back or clipped onto the harness at the side. Paired cylinders may be manifolded together or independent. In technical diving, more than two scuba cylinders may be needed.
When pressurized, the gas is compressed up to several hundred times atmospheric pressure. The selection of an appropriate set of diving cylinders for a diving operation is based on the amount of gas required to safely complete the dive. Diving cylinders are most commonly filled with air, but because the main components of air can cause problems when breathed underwater at higher ambient pressure, divers may choose to breathe from cylinders filled with mixtures of gases other than air. Many jurisdictions have regulations that govern the filling, recording of contents, and labeling for diving cylinders. Periodic testing and inspection of diving cylinders is often obligatory to ensure the safety of operators of filling stations. Pressurized diving cylinders are considered dangerous goods for commercial transportation, and regional and international standards for colouring and labeling may also apply. (Full article...) -
A liveaboard dive boat on the Similan Islands, Thailand
A dive boat is a boat that recreational divers or professional 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...) -
There are several categories of decompression equipment used to help divers decompress, which is the process required to allow divers to return to the surface safely after spending time underwater at higher ambient pressures.
Decompression obligation for a given dive profile must be calculated and monitored to ensure that the risk of decompression sickness is controlled. Some equipment is specifically for these functions, both during planning before the dive and during the dive. Other equipment is used to mark the underwater position of the diver, as a position reference in low visibility or currents, or to assist the diver's ascent and control the depth.
Decompression may be shortened ("accelerated") by breathing an oxygen-rich "decompression gas" such as a nitrox blend or pure oxygen. The high partial pressure of oxygen in such decompression mixes produces the effect known as the oxygen window. This decompression gas is often carried by scuba divers in side-slung cylinders. Cave divers who can only return by a single route, can leave decompression gas cylinders attached to the guideline ("stage" or "drop cylinders") at the points where they will be used. Surface-supplied divers will have the composition of the breathing gas controlled at the gas panel.
Divers with long decompression obligations may be decompressed inside gas filled hyperbaric chambers in the water or at the surface, and in the extreme case, saturation divers are only decompressed at the end of a project, contract, or tour of duty that may be several weeks long. (Full article...)
Diving procedures
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A freediver on the ocean floor
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...) -
A shotline with decompression trapeze provides a relatively safe and convenient place for in-water decompression.
Dive planning is the process of planning an underwater diving operation. The purpose of dive planning is to increase the probability that a dive will be completed safely and the goals achieved. Some form of planning is done for most underwater dives, but the complexity and detail considered may vary enormously.
Professional diving operations are usually formally planned and the plan documented as a legal record that due diligence has been done for health and safety purposes. Recreational dive planning may be less formal, but for complex technical dives, can be as formal, detailed and extensive as most professional dive plans. A professional diving contractor will be constrained by the code of practice, standing orders or regulatory legislation covering a project or specific operations within a project, and is responsible for ensuring that the scope of work to be done is within the scope of the rules relevant to that work. A recreational (including technical) diver or dive group is generally less constrained, but nevertheless is almost always restricted by some legislation, and often also the rules of the organisations to which the divers are affiliated.
The planning of a diving operation may be simple or complex. In some cases the processes may have to be repeated several times before a satisfactory plan is achieved, and even then the plan may have to be modified on site to suit changed circumstances. The final product of the planning process may be formally documented or, in the case of recreational divers, an agreement on how the dive will be conducted. A diving project may consist of a number of related diving operations.
A documented dive plan may contain elements from the following list:- Overview of diving activities
- Schedule of diving operations
- Specific dive plan information
- Budget
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SCUBA Diver in the mountain lake Lai da Marmorera 1,680 metres (5,510 ft) above sea level)
Altitude diving is underwater diving using scuba or surface 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...) -
Diver at the wreck of the Hilma Hooker, Netherlands Antilles.
Wreck diving is recreational 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. (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-ring or hose 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...) -
Dive profile of an actual dive as recorded by a personal dive computer and displayed on a desktop screen using dive logging software. In this case depth is in metres.
A dive 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," (a bottom 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...) -
A decompression dive may require the use of more than one gas mixture
Scuba gas planning is the aspect of dive planning and of gas management which deals with the calculation or estimation of the amounts and mixtures of gases to be used for a planned dive. It may assume that the dive profile, including decompression, is known, but the process may be iterative, involving changes to the dive profile as a consequence of the gas requirement calculation, or changes to the gas mixtures chosen. Use of calculated reserves based on planned dive profile and estimated gas consumption rates rather than an arbitrary pressure is sometimes referred to as rock bottom gas management. The purpose of gas planning is to ensure that for all reasonably foreseeable contingencies, the divers of a team have sufficient breathing gas to safely return to a place where more breathing gas is available. In almost all cases this will be the surface.
Gas planning includes the following aspects:- Choice of breathing gases
- Choice of scuba configuration
- Estimation of gas required for the planned dive, including bottom gas, travel gas, and decompression gases, as appropriate to the profile.
- Estimation of gas quantities for reasonably foreseeable contingencies. Under stress it is likely that a diver will increase breathing rate and decrease swimming speed. Both of these lead to a higher gas consumption during an emergency exit or ascent.
- Choice of cylinders to carry the required gases. Each cylinder volume and working pressure must be sufficient to contain the required quantity of gas.
- Calculation of the pressures for each of the gases in each of the cylinders to provide the required quantities.
- Specifying the critical pressures of relevant gas mixtures for appropriate stages (waypoints) of the planned dive profile (gas matching).
Gas planning is one of the stages of scuba gas management. The other stages include:- Knowledge of personal and team members' gas consumption rates under varying conditions
- basic consumption at the surface for variations in workload
- variation in consumption due to depth variation
- variation in consumption due to dive conditions and personal physical and mental condition
- Monitoring the contents of the cylinders during a dive
- Awareness of the critical pressures and using them to manage the dive
- Efficient use of the available gas during the planned dive and during an emergency
- Limiting the risk of equipment malfunctions that could cause a loss of breathing gas
The term "rock bottom gas planning" is used for the method of gas planning based on a planned dive profile where a reasonably accurate estimate of the depths, times, and level of activity is available, so the calculations for gas mixtures and the appropriate quantities of each mixture are known well enough to make fairly rigorous calculations useful. Simpler, easier, and fairly arbitrary rules of thumb are commonly used for dives which do not require long decompression stops. These methods are often adequate for low risk dives, but relying on them for more complex dive plans can put divers at significantly greater risk if they are unaware of the limitations of each method and apply them inappropriately. (Full article...) -
Saturation diver working on the USS Monitor wreck at 70 m (230 ft) depth.
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...) -
A dive team listens to a safety brief from their dive supervisor
The diving supervisor is the professional diving team member who is directly responsible for the diving operation's safety and the management of any incidents or accidents that may occur during the operation; the supervisor is required to be available at the control point of the diving operation for the diving operation's duration, and to manage the planned dive and any contingencies that may occur. Details of competence, requirements, qualifications, registration and formal appointment differ depending on jurisdiction and relevant codes of practice. Diving supervisors are used in commercial diving, military diving, public safety diving and scientific diving operations.
The control point is the place where the supervisor can best monitor the status of the diver and progress of the dive. For scuba dives this is commonly on deck of the dive boat where there is a good view of the surface above the operational area, or on the shore at a nearby point where the divers can be seen when surfaced. For surface supplied diving, the view of the water is usually still necessary, and a view of the line tenders handling the umbilicals is also required, unless there is live video feed from the divers and two-way audio communications with the tenders. The control position also includes the gas panel and communications panel, so the supervisor can remain as fully informed as practicable of the status of the divers and their life support systems during the dive. For bell diving and saturation diving the situation is more complex and the control position may well be inside a compartment where the communications, control and monitoring equipment for the bell and life-support systems are set up.
In recreational diving the term is used to refer to persons managing a recreational dive, with certification such as Divemaster,
Dive Control Specialist, Dive Coordinator, etc. (Full article...) -
Ice diving is a type of penetration diving where the dive takes place under ice. Because diving under ice places the diver in an overhead environment typically with only a single entry/exit point, it requires special procedures and equipment. Ice diving is done for purposes of recreation, scientific research, public safety (usually search and rescue/recovery) and other professional or commercial reasons.
The most obvious hazards of ice diving are getting lost under the ice, hypothermia, and regulator failure due to freezing. Scuba divers are generally tethered for safety. This means that the diver wears a harness to which a line is secured, and the other end of the line is secured above the surface and monitored by an attendant. Surface supplied equipment inherently provides a tether, and reduces the risks of regulator first stage freezing as the first stage can be managed by the surface team, and the breathing gas supply is less limited. For the surface support team, the hazards include freezing temperatures and falling through thin ice. (Full article...) -
Diver Trevor Jackson returning from a 600 ft (183 m) dive
Technical diving (also referred to as tec diving or tech 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...) -
Divers decompressing in the water at the end of a dive
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-diving or snorkelling 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 nitrogen or helium 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 continuous or staged. 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...) -
The instructor monitors a trainee practicing diving skills.
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...) -
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...) -
Beginner diver in St. Croix, United States Virgin Islands
Recreational diving or sport diving is diving 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...)
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Science of diving
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In diving and decompression, the oxygen window is the difference between the partial pressure of oxygen (PO2) in arterial blood and the PO2 in body tissues. It is caused by metabolic consumption of oxygen. (Full article...)
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Scuba diver with bifocal lenses fitted to a mask
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 attenuation of light 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...) -
Scuba diver decompressing at a planned stop during ascent from a dive
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...) -
Work of breathing (WOB) is the energy expended to inhale and exhale a breathing gas. It is usually expressed as work per unit volume, for example, joules/litre, or as a work rate (power), such as joules/min or equivalent units, as it is not particularly useful without a reference to volume or time. It can be calculated in terms of the pulmonary pressure multiplied by the change in pulmonary volume, or in terms of the oxygen consumption attributable to breathing.
In a normal resting state the work of breathing constitutes about 5% of the total body oxygen consumption. It can increase considerably due to illness or constraints on gas flow imposed by breathing apparatus, ambient pressure, or breathing gas composition. (Full article...) -
The physiology of underwater diving is the physiological adaptations to diving of air-breathing vertebrates that have returned to the ocean from terrestrial lineages. They are a diverse group that include sea snakes, sea turtles, the marine iguana, saltwater crocodiles, penguins, pinnipeds, cetaceans, sea otters, manatees and dugongs. All known diving vertebrates dive to feed, and the extent of the diving in terms of depth and duration are influenced by feeding strategies, but also, in some cases, with predator avoidance. Diving behaviour is inextricably linked with the physiological adaptations for diving and often the behaviour leads to an investigation of the physiology that makes the behaviour possible, so they are considered together where possible. Most diving vertebrates make relatively short shallow dives. Sea snakes, crocodiles, and marine iguanas only dive in inshore waters and seldom dive deeper than 10 meters (33 feet). Some of these groups can make much deeper and longer dives. Emperor penguins regularly dive to depths of 400 to 500 meters (1,300 to 1,600 feet) for 4 to 5 minutes, often dive for 8 to 12 minutes, and have a maximum endurance of about 22 minutes. Elephant seals stay at sea for between 2 and 8 months and dive continuously, spending 90% of their time underwater and averaging 20 minutes per dive with less than 3 minutes at the surface between dives. Their maximum dive duration is about 2 hours and they routinely feed at depths between 300 and 600 meters (980 and 1,970 feet), though they can exceed depths of 1,600 meters (5,200 feet). Beaked whales have been found to routinely dive to forage at depths between 835 and 1,070 meters (2,740 and 3,510 feet), and remain submerged for about 50 minutes. Their maximum recorded depth is 1,888 meters (6,194 feet), and the maximum duration is 85 minutes.
Air-breathing marine vertebrates that dive to feed must deal with the effects of pressure at depth, hypoxia during apnea, and the need to find and capture their food. Adaptations to diving can be associated with these three requirements. Adaptations to pressure must deal with the mechanical effects of pressure on gas-filled cavities, solubility changes of gases under pressure, and possible direct effects of pressure on the metabolism, while adaptations to breath-hold capacity include modifications to metabolism, perfusion, carbon dioxide tolerance, and oxygen storage capacity. Adaptations to find and capture food vary depending on the food, but deep-diving generally involves operating in a dark environment.
Diving vertebrates have increased the amount of oxygen stored in their internal tissues. This oxygen store has three components; oxygen contained in the air in the lungs, oxygen stored by haemoglobin in the blood, and by myoglobin, in muscle tissue, The muscle and blood of diving vertebrates have greater concentrations of haemoglobin and myoglobin than terrestrial animals. Myoglobin concentration in locomotor muscles of diving vertebrates is up to 30 times more than in terrestrial relatives. Haemoglobin is increased by both a relatively larger amount of blood and a larger proportion of red blood cells in the blood compared with terrestrial animals. The highest values are found in the mammals which dive deepest and longest.
Body size is a factor in diving ability. A larger body mass correlates to a relatively lower metabolic rate, while oxygen storage is directly proportional to body mass, so larger animals should be able to dive for longer, all other things being equal. Swimming efficiency also affects diving ability, as low drag and high propulsive efficiency requires less energy for the same dive. Burst and glide locomotion is also often used to minimise energy consumption, and may involve using positive or negative buoyancy to power part of the ascent or descent.
The responses seen in seals diving freely at sea are physiologically the same as those seen during forced dives in the laboratory. They are not specific to immersion in water, but are protective mechanisms against asphyxia which are common to all mammals but more effective and developed in seals. The extent to which these responses are expressed depends greatly on the seal's anticipation of dive duration.
The regulation of bradycardia and vasoconstriction of the dive response in both mammals and diving ducks can be triggered by facial immersion, wetting of the nostrils and glottis, or stimulation of trigeminal and glossopharyngeal nerves.
Animals cannot convert fats to glucose, and in many diving animals, carbohydrates are not readily available from the diet, nor stored in large quantities, so as they are essential for anaerobic metabolism, they could be a limiting factor.
Decompression sickness (DCS) is a disease associated with metabolically inert gas uptake at pressure, and its subsequent release into the tissues in the form of bubbles. Marine mammals were thought to be relatively immune to DCS due to anatomical, physiological and behavioural adaptations that reduce tissue loading with dissolved nitrogen during dives, but observations show that gas bubbles may form, and tissue injury may occur under certain circumstances. Decompression modelelling using measured dive profiles predict the possibility of high blood and tissue nitrogen tensions. (Full article...) -
In physical chemistry, supersaturation occurs with a solution when the concentration of a solute exceeds the concentration specified by the value of solubility at equilibrium. 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...)
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Scuba diver decompressing at a planned stop during ascent from a dive
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 atmospheric pressure is roughly equal to the sum of partial pressures of constituent gases – oxygen, nitrogen, argon, water vapor, carbon dioxide, etc.
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...) -
Graph showing a tropical ocean thermocline (depth vs. temperature). Note the rapid change between 100 and 1000 meters. The temperature is nearly constant after 1500 meters depth.
A thermocline (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...) -
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...) -
Example of a dissolved solid (left)
In chemistry, 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...) -
Simplified schematic of only the lunar portion of Earth's tides, showing (exaggerated) high tides at the sublunar point and its antipode for the hypothetical case of an ocean of constant depth without land, and on the assumption that Earth is not rotating; otherwise there is a lag angle. Solar tides not shown.
Tides are the rise and fall 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...) -
Diving reflex in a human baby
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...) -
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water from deep water towards the ocean surface. It replaces the warmer and usually nutrient-depleted surface water. The nutrient-rich upwelled water stimulates the growth and reproduction of primary producers such as phytoplankton. The biomass of phytoplankton and the presence of cool water in those regions allow upwelling zones to be identified by cool sea surface temperatures (SST) and high concentrations of chlorophyll a.
The increased availability of nutrients in upwelling regions results in high levels of primary production and thus fishery production. Approximately 25% of the total global marine fish catches come from five upwellings, which occupy only 5% of the total ocean area. Upwellings that are driven by coastal currents or diverging open ocean have the greatest impact on nutrient-enriched waters and global fishery yields. (Full article...) -
Signs explaining how to escape from a rip current, posted at Mission Beach, San Diego, California
A rip current (or just 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 as of 2022[update].
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...)
Occupational diving
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Sponge diver putting on his diving suit in Tarpon Springs, Florida.
Sponge diving is underwater diving to collect soft natural sponges for human use. (Full article...) -
Underwater welding
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...) -
A divemaster (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...) -
US Navy Diver being decontaminated after a dive. If the contamination was severe, the decontamination team would have been wearing hazmat gear.
Hazmat diving is underwater 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. These are based on preventing contact of the hazardous materials with the divers and other personnel, generally by encapsulating the affected personnel in personal protective equipment (PPE) appropriate to the hazard, and by effective decontamination after contact between the PPE and the hazardous materials.
There are a few well known environments, like nuclear power plant cooling systems, sewage treatment plants and sewers which require routine maintenance by divers, and which are well documented, with well-known and consistent hazards, for which standard operating procedures will have been developed, and other environments where the need for diving work is unusual and the hazards less well documented, and must be managed on a case-by-case basis, following an approved code of practice. Hazmat diving is a particular class of diving in high risk environments, normally only done by specially trained professional divers. (Full article...) -
US Navy diver dredging an excavation site during an underwater recovery operation, searching for personnel who went missing during WWII off the coast of Koror
Salvage diving is the diving work associated with the recovery of all or part of ships, their cargoes, aircraft, and other vehicles and structures which have sunk or fallen into water. In the case of ships it may also refer to repair work done to make an abandoned or distressed but still floating vessel more suitable for towing or propulsion under its own power. The recreational/technical activity known as wreck diving is generally not considered salvage work, though some recovery of artifacts may be done by recreational divers.
Most salvage diving is commercial work, or military work, depending on the diving contractor and the purpose for the salvage operation, Similar underwater work may be done by divers as part of forensic investigations into accidents, in which case the procedures may be more closely allied with underwater archaeology than the more basic procedures of advantageous cost/benefit expected in commercial and military operations.
Clearance diving, the removal of obstructions and hazards to navigation, is closely related to salvage diving, but has a different purpose, in that the objects to be removed are not intended to be recovered, just removed or reduced to a condition where they no longer constitute a hazard or obstruction. Many of the techniques and procedures used in clearance diving are also used in salvage work. (Full article...) -
A US Navy work diver is lowered to the sea bed during a dive from the USNS Grasp (T-ARS-51) off the coast of St. Kitts.
A clearance 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...) -
An ama pearl diver in Japan
Pearl hunting, also known as pearl fishing or pearling, is the activity of recovering or attempting to recover pearls from wild molluscs, usually oysters or mussels, in the sea or freshwater. Pearl hunting was prevalent in the Persian Gulf region and Japan for thousands of years. On the northern and north-western coast of Western Australia pearl diving began in the 1850s, and started in the Torres Strait Islands in the 1860s, where the term also covers diving for nacre or mother of pearl found in what were known as pearl shells.
In most cases the pearl-bearing molluscs live at depths where they are not manually accessible from the surface, and diving or the use of some form of tool is needed to reach them. Historically the molluscs were retrieved by freediving, a technique where the diver descends to the bottom, collects what they can, and surfaces on a single breath. The diving mask improved the ability of the diver to see while underwater. When the surface-supplied diving helmet became available for underwater work, it was also applied to the task of pearl hunting, and the associated activity of collecting pearl shell as a raw material for the manufacture of buttons, inlays and other decorative work. The surface supplied diving helmet greatly extended the time the diver could stay at depth, and introduced the previously unfamiliar hazards of barotrauma of ascent and decompression sickness. (Full article...) -
Public safety diving team members bring in a casualty
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...) -
ROKS Lee Jongmoo (SS-066) and USS Columbus (SSN-762) off the coast of Hawaii; a United States Navy P-3 Orion can be seen observing them nearby.
Underwater warfare, also known as undersea warfare or subsurface warfare, is naval warfare involving underwater vehicle or combat 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:- Actions by submarines actions, and anti-submarine warfare, i.e. warfare between submarines, other submarines and surface ships; combat airplanes and helicopters may also be engaged when launching special dive-bombs and torpedo-missiles against submarines;
- Underwater special operations, considering:
- Military diving sabotage against ships and ports.
- Anti-frogman techniques.
- Reconnaissance tasks.
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A SEAL Delivery Team member climbs aboard a delivery vehicle before launching from the back of the submarine USS Philadelphia.
A frogman is someone who is trained in scuba diving or swimming underwater in a tactical capacity that includes military, and in some European countries, police work. Such personnel are also known by the more formal names of combat diver, combatant diver, or combat swimmer. The word frogman first arose in the stage name the "Fearless Frogman" of Paul Boyton in the 1870s and later was claimed by John Spence, an enlisted member of the U.S. Navy and member of the OSS Maritime Unit, to have been applied to him while he was training in a green waterproof suit.
The term frogman is occasionally used to refer to a civilian scuba diver, such as in a police diving role.
In the United Kingdom, police divers have often been called "police frogmen".
Some countries' tactical diver organizations include a translation of the word frogman in their official names, e.g., Denmark's Frømandskorpset; others call themselves "combat divers" or similar. (Full article...) -
Scuba diving education levels as used by ISO, PADI, CMAS, SSI and NAUI
Recreational diver training is the process of developing knowledge and understanding of the basic principles, and the skills and procedures for the use 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...) -
NYPD divers removing material from the Harlem Meer following a murder in the area few days prior.
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...) -
Surface supplied diving equipment on display
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...) -
A US Navy diver at work. The umbilical supplying air from the surface is clearly visible.
Professional diving is underwater diving where the divers are paid for their work. Occupational diving has a similar meaning and applications. The procedures are often regulated by legislation and codes of practice as it is an inherently hazardous occupation and the diver works as a member of a team. Due to the dangerous nature of some professional diving operations, specialized equipment such as an on-site hyperbaric chamber and diver-to-surface communication system is often required by law, and the mode of diving for some applications may be regulated.
There are several branches of professional diving, the best known of which is probably commercial diving and its specialised applications, offshore diving, inshore civil engineering diving, marine salvage diving, hazmat diving, and ships husbandry diving. There are also applications in scientific research, marine archaeology, fishing and aquaculture, public service, law enforcement, military service, media work and diver training.
Any person wishing to become a professional diver normally requires specific training that satisfies any regulatory agencies which have regional or national authority, such as US Occupational Safety and Health Administration, United Kingdom Health and Safety Executive or South African Department of Employment and Labour. International recognition of professional diver qualifications and registration exists between some countries. (Full article...) -
Instructor and learner divers practicing scuba skills in confined water
A diving instructor is a person who trains, and usually also assesses competence, of underwater divers. This includes freedivers, recreational divers including the subcategory technical divers, and professional divers which includes military, commercial, public safety and scientific divers.
Depending on the jurisdiction, there will generally be specific published codes of practice and guidelines for training, competence and registration of diving instructors, as they have a duty of care to their clients, and operate in an environment with intrinsic hazards which may be unfamiliar to the lay person. Training and assessment will generally follow a diver training standard, and may use a diver training manual as source material.
Recreational diving instructors are usually registered members of one or more recreational diver certification agencies, and are generally registered to train and assess divers against specified certification standards. Originally these standards were at the discretion of each training and certification agency, but inter-agency and international standards now exist to ensure that the basic skills required for acceptable safety are included as a minimum standard for both instructors and recreational divers. Military diving instructors are generally members of the armed force for which they train personnel. Commercial diving instructors may be required to register with national government appointed organisations, and comply with specific training and assessment standards, but there may be other requirements in some parts of the world. (Full article...)
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Recreational diving
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Spearfisher Monument in Croatia
Spearfishing is fishing using handheld elongated, sharp-pointed tools such as a spear, gig, or harpoon, to impale the fish in the body. It was one of the earliest fishing techniques used by mankind, and has been deployed in artisanal fishing throughout the world for millennia. Early civilizations were familiar with the custom of spearing fish from rivers and streams using sharpened sticks.
Modern spearfishing usually involves the use of underwater swimming gear and slingshot-like elastic spearguns or compressed gas powered pneumatic spearguns, which launch a tethered dart-like projectile to strike the target fish. Specialised techniques and equipment have been developed for various types of aquatic environments and target fish. Spearfishing uses no bait and is highly selective, with no by-catch, but inflicts lethal injury to the fish and thus precludes catch and release.
Spearfishing may be done using free-diving, snorkelling, or scuba diving techniques, but spearfishing while using scuba equipment is illegal in some countries. The use of mechanically powered spearguns is also outlawed in some countries and jurisdictions such as New Zealand. (Full article...) -
Sharks swimming outside shark-proof cage with people inside
Shark cage diving is underwater diving or snorkeling 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...) -
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...)
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Underwater football is a two-team underwater sport that shares common elements with underwater hockey and underwater rugby. As with both of those games, it is played in a swimming pool with snorkeling equipment (mask, snorkel, and fins).
The goal of the game is to manoeuvre (by carrying and passing) a slightly negatively buoyant ball from one side of a pool to the other by players who are completely submerged underwater. Scoring is achieved by placing the ball (under control) in the gutter on the side of the pool. Variations include using a toy rubber torpedo as the ball, and weighing down buckets to rest on the bottom and serve as goals.
It is played in the Canadian provinces of Alberta, Manitoba, Newfoundland and Labrador and Saskatchewan. (Full article...) -
Diver Trevor Jackson returning from a 600 ft (183 m) dive
Technical diving (also referred to as tec diving or tech 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...) -
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...)
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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...) -
Divers Alert Network (DAN) is a group of not-for-profit organisations dedicated to improving diving safety for all divers. It was founded in Durham, North Carolina, in 1980 at Duke University to provide 24/7 telephone diving medical assistance. Since then the organisation has expanded globally and now has independent regional organisations in North America, Europe, Japan, Asia-Pacific and Southern Africa.
DAN publishes research results on a wide range of matters relating to diving safety and medicine and diving accident analysis, including annual reports on decompression illness and diving fatalities. Most are freely available on the internet, many of these were at the now defunct Rubicon Research Repository.[needs update]
This list includes publications where one or more authors are staff or members of one of the DAN affiliates, where a large part of the data is from one of the DAN Databases, or where the research was funded by DAN. (Full article...) -
Recreational diver over a coral reef in the Red Sea
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 tourism destinations. South-east Asia, the Caribbean islands, the Red Sea and the Great Barrier Reef of Australia are regions where the clear, warm, waters, reasonably predictable conditions and colourful and diverse sea life have made recreational diving an economically important tourist industry.
Recreational divers may accept a relatively high level of risk to dive at a site perceived to be of special interest. Wreck diving 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...) -
A United States Navy Mass Communication Specialist conducting underwater photography training
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 submersible or remotely 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...) -
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...) -
Diver at the wreck of the Hilma Hooker, Netherlands Antilles.
Wreck diving is recreational 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. (Full article...) -
Aquathlon (also known as underwater wrestling) is an underwater sport, where two competitors wearing masks and fins wrestle underwater in an attempt to remove a ribbon from each other's ankle band in order to win the bout. The "combat" takes place in a 5-metre (16 ft) square ring within a swimming pool, and is made up of three 30-second rounds, with a fourth round played in the event of a tie. The sport originated during the 1980s in the former USSR (now Russia) and was first played at international level in 1993. It was recognised by the Confédération Mondiale des Activités Subaquatiques (CMAS) in 2008. Combat aquathlon practice training engagements not only under water, but also afloat, above the water surface, both with or without diving gear, utilizing dummy weapons (rubber knives, bayonetted rifles, etc.) or barehanded, combined with grappling and choking techniques in order to neutralize or submit the opponent. (Full article...) -
DIR divers
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...) -
Finswimming is an underwater sport consisting of four techniques involving swimming with the use of fins either on the water's surface using a snorkel with either monofins or bifins or underwater with monofin either by holding one's breath or using open circuit scuba diving equipment. Events exist over distances similar to swimming competitions for both swimming pool and open water venues. Competition at world and continental level is organised by the Confédération Mondiale des Activités Subaquatiques (CMAS, World Underwater Federation). The sport's first world championship was held in 1976. It also has been featured at the World Games as a trend sport since 1981 and was demonstrated at the 2015 European Games in June 2015. (Full article...)
Diving hazards, incidents, safety and law
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Lockout Tagout hasp can accommodate up to 6 padlocks, can be used during group LOTO procedure.
Lock out, tag out or lockout–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 that worker 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...) -
Human factors are the physical or cognitive properties of individuals, or social behavior which is specific to humans, and which influence functioning of technological systems as well as human-environment equilibria. The safety of underwater 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.
Human factors include both the non-technical skills that enhance safety and the non-technical factors that contribute to undesirable incidents that put the diver at risk.[Safety is] An active, adaptive process which involves making sense of the task in the context of the environment to successfully achieve explicit and implied goals, with the expectation that no harm or damage will occur. – G. Lock, 2022
Dive safety is primarily a function of four factors: the environment, equipment, individual diver performance and dive team performance. The water is a harsh and alien environment which can impose severe physical and psychological stress on a diver. The remaining factors must be controlled and coordinated so the diver can overcome the stresses imposed by 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
Human error is inevitable and most errors are minor and do not cause significant harm, but others can have catastrophic consequences. Examples of human error leading to accidents are available in vast numbers, as it is the direct cause of 60% to 80% of all accidents.
In a high risk environment, as is the case in diving, human error is more likely to have catastrophic consequences. A study by William P. Morgan indicates that over half of all divers in the survey had experienced panic underwater at some time during their diving career. These findings were independently corroborated by a survey that suggested 65% of recreational divers have panicked under water. Panic frequently leads to errors in a diver's judgment or performance, and may result in an accident. Human error and panic are considered to be the leading causes of dive accidents and fatalities.
Only 4.46% of the recreational diving fatalities in a 1997 study were attributable to a single contributory cause. The remaining fatalities probably arose as a result of a progressive sequence of events involving two or more procedural errors or equipment failures, and since procedural errors are generally avoidable by a well-trained, intelligent and alert diver, working in an organised structure, and not under excessive stress, it was concluded that the low accident rate in professional scuba diving is due to these factors. The study also concluded that it would be impossible to eliminate absolutely all minor contraindications for scuba diving, as this would result in overwhelming bureaucracy and would bring all diving to a halt.
Human factors engineering (HFE), also known as human factors and ergonomics, is the application of psychological and physiological principles to the engineering and design of equipment, procedures, processes, and systems. Primary goals of human factors engineering are to reduce human error, increase productivity and system availability, and enhance safety, health and comfort with a specific focus on the interaction between the human and equipment. (Full article...) -
Hazard control methods at the top of the graphic are potentially more effective and protective than those at the bottom. Following this hierarchy of controls normally leads to the implementation of inherently safer systems, where the risk of illness or injury has been substantially reduced.
Hierarchy of hazard control is a system used in industry to prioritize possible interventions to minimize or eliminate exposure to hazards. It is a widely accepted system promoted by numerous safety organizations. This concept is taught to managers in industry, to be promoted as standard practice in the workplace. It has also been used to inform public policy, in fields such as road safety. Various illustrations are used to depict this system, most commonly a triangle.
The hazard controls in the hierarchy are, in order of decreasing priority:
The system is not based on evidence of effectiveness; rather, it relies on whether the elimination of hazards is possible. Eliminating hazards allows workers to be free from the need to recognize and protect themselves against these dangers. Substitution is given lower priority than elimination because substitutes may also present hazards. Engineering controls depend on a well-functioning system and human behavior, while administrative controls and personal protective equipment are inherently reliant on human actions, making them less reliable. (Full article...) -
A task load indicates the degree of difficulty experienced when performing a task, and task loading describes the accumulation of tasks that are necessary to perform an operation. A light task loading can be managed by the operator with capacity to spare in case of contingencies. Task loads are primarily associated with underwater diving. They are also associated with workloads in other environments, such as aircraft cockpits and command and control stations.
Task loads may be measured and compared. NASA uses six sub-scales in their task load rating procedure. Three of these relate to the demands on the subject and the other three to interactions between subject and task. Ratings contain a large personal component and may vary considerably between subjects, and over time as experience is gained.- Mental Demands: How much mental and perceptual effort is required;
- Physical Demands: How much physical effort is required;
- Temporal Demands: How much time pressure the subject feels;
- Own Performance: Rating of how successfully the task was performed;
- Effort: Rating of how much effort was put into the task; and
- Frustration: Rating of how frustrating or satisfying the task was to perform.
In underwater diving, task loading increases the risk of failure by the diver to undertake some key basic function which would normally be routine for safety underwater. A heavy task loading may overwhelm the diver if something does not go according to plan. This is particularly a problem in scuba diving, where the breathing gas supply is limited and delays may cause decompression obligations. The same workload may be a light task loading to a skilled diver with considerable experience of all the component tasks, and heavy task loading for a diver with little experience of some of the tasks.
Excessive task loading is implicated in many diving accidents, and may be limited by adding tasks one at a time, and adequately developing the requisite skills for each before adding more. (Full article...) -
Scuba diving fatalities are deaths occurring while scuba diving or as a consequence of scuba diving. The risks of dying during recreational, scientific or commercial 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...) -
This list identifies the legislation governing underwater diving activities listed by region. Some legislation affects only professional diving, other may affect only recreational diving, or all diving activities. The list includes primary and delegated legislation, and international standards for the conduct of diving adopted by national states, but does not include legislation or standards relating to manufacture or testing of diving equipment. (Full article...)
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Example of risk assessment: A NASA model showing areas at high risk from impact for the International Space Station
Risk management is the identification, evaluation, and prioritization of risks, followed by the minimization, monitoring, and control of the impact or probability of those risks occurring.
Risks can come from various sources (i.e, threats) including uncertainty in international markets, political instability, dangers of project failures (at any phase in design, development, production, or sustaining of life-cycles), legal liabilities, credit risk, accidents, natural causes and disasters, deliberate attack from an adversary, or events of uncertain or unpredictable root-cause.
There are two types of events wiz. Risks and Opportunities. 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 International Organization for Standardization. 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...) -
Common redundant power supply
In engineering 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...) -
A dive team listens to a safety brief from their dive supervisor
The diving supervisor is the professional diving team member who is directly responsible for the diving operation's safety and the management of any incidents or accidents that may occur during the operation; the supervisor is required to be available at the control point of the diving operation for the diving operation's duration, and to manage the planned dive and any contingencies that may occur. Details of competence, requirements, qualifications, registration and formal appointment differ depending on jurisdiction and relevant codes of practice. Diving supervisors are used in commercial diving, military diving, public safety diving and scientific diving operations.
The control point is the place where the supervisor can best monitor the status of the diver and progress of the dive. For scuba dives this is commonly on deck of the dive boat where there is a good view of the surface above the operational area, or on the shore at a nearby point where the divers can be seen when surfaced. For surface supplied diving, the view of the water is usually still necessary, and a view of the line tenders handling the umbilicals is also required, unless there is live video feed from the divers and two-way audio communications with the tenders. The control position also includes the gas panel and communications panel, so the supervisor can remain as fully informed as practicable of the status of the divers and their life support systems during the dive. For bell diving and saturation diving the situation is more complex and the control position may well be inside a compartment where the communications, control and monitoring equipment for the bell and life-support systems are set up.
In recreational diving the term is used to refer to persons managing a recreational dive, with certification such as Divemaster,
Dive Control Specialist, Dive Coordinator, etc. (Full article...) -
A job 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...) -
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.
A hazard 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...) -
A silt out or silt-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...)
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Beaching a casualty while providing artificial respiration
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...) -
The civil liability of a recreational diver may include a duty of care to another 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...) -
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.
In professional 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...)
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Diving medicine, disorders and treatment
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Decompression Illness (DCI) comprises two different conditions caused by rapid decompression of the body. These conditions present similar symptoms and require the same initial first aid. Scuba divers are trained to ascend slowly from depth to avoid DCI. Although the incidence is relatively rare, the consequences can be serious and potentially fatal, especially if untreated. (Full article...)
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Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen (O
2) at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lungs, and eyes. Historically, the central nervous system condition was called the Paul Bert effect, and the pulmonary condition the Lorrain Smith effect, after the researchers who pioneered the discoveries and descriptions in the late 19th century. Oxygen toxicity is a concern for underwater divers, those on high concentrations of supplemental oxygen, and those undergoing hyperbaric oxygen therapy.
The result of breathing increased partial pressures of oxygen is hyperoxia, an excess of oxygen in body tissues. The body is affected in different ways depending on the type of exposure. Central nervous system toxicity is caused by short exposure to high partial pressures of oxygen at greater than atmospheric pressure. Pulmonary and ocular toxicity result from longer exposure to increased oxygen levels at normal pressure. Symptoms may include disorientation, breathing problems, and vision changes such as myopia. Prolonged exposure to above-normal oxygen partial pressures, or shorter exposures to very high partial pressures, can cause oxidative damage to cell membranes, collapse of the alveoli in the lungs, retinal detachment, and seizures. Oxygen toxicity is managed by reducing the exposure to increased oxygen levels. Studies show that, in the long term, a robust recovery from most types of oxygen toxicity is possible.
Protocols for avoidance of the effects of hyperoxia exist in fields where oxygen is breathed at higher-than-normal partial pressures, including underwater diving using compressed breathing gases, hyperbaric medicine, neonatal care and human spaceflight. These protocols have resulted in the increasing rarity of seizures due to oxygen toxicity, with pulmonary and ocular damage being largely confined to the problems of managing premature infants.
In recent years, oxygen has become available for recreational use in oxygen bars. The US Food and Drug Administration has warned those who have conditions such as heart or lung disease not to use oxygen bars. Scuba divers use breathing gases containing up to 100% oxygen, and should have specific training in using such gases. (Full article...) -
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 taravana is Tuamotu Polynesian for "to fall crazily".
Taravana is also used to describe someone who is "crazy because of the sea". (Full article...) -
Monitoring the decompression chamber during a simulated medical emergency
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...) -
Latent hypoxia affects the diver on ascent
Latent hypoxia is a condition where the oxygen content of the lungs and arterial blood is sufficient to maintain consciousness at a raised ambient pressure, but not when the pressure is reduced to normal atmospheric pressure. It usually occurs when a diver at depth has a lung gas and blood oxygen concentration that is sufficient to support consciousness at the pressure at that depth, but would be insufficient at surface pressure. This problem is associated with freediving blackout and the presence of hypoxic breathing gas mixtures in underwater breathing apparatus, particularly in diving rebreathers.
The term latent hypoxia strictly refers to the situation while the potential victim is at depth, still conscious, and not yet hypoxic, but is also loosely applied to the consequential blackout, which is a form of hypoxic blackout also referred to as blackout of ascent or deep water blackout, though deep water blackout is also used to refer to the final stage of nitrogen narcosis. (Full article...) -
A recompression chamber is used to treat some diving disorders.
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 aspects of a diver's fitness to dive affect the diver's safety. Diving medical practitioners are also expected to be competent in the examination of divers and potential divers to 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...) -
Monitoring the decompression chamber during a simulated medical emergency
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...) -
Freediving blackout, breath-hold blackout, or apnea blackout is a class of hypoxic blackout, a loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold (freedive or dynamic apnea) dive, when the swimmer does not necessarily experience an urgent need to breathe and has no other obvious medical condition that might have caused it. It can be provoked by hyperventilating just before a dive, or as a consequence of the pressure reduction on ascent, or a combination of these. Victims are often established practitioners of breath-hold diving, are fit, strong swimmers and have not experienced problems before. Blackout may also be referred to as a syncope or fainting.
Divers and swimmers who black out or grey out underwater during a dive will usually drown unless rescued and resuscitated within a short time. Freediving blackout has a high fatality rate, and mostly involves males younger than 40 years, but is generally avoidable. Risk cannot be quantified, but is clearly increased by any level of hyperventilation.
Freediving blackout can occur on any dive profile: at constant depth, on an ascent from depth, or at the surface following ascent from depth and may be described by a number of terms depending on the dive profile and depth at which consciousness is lost. Blackout during a shallow dive differs from blackout during ascent from a deep dive in that blackout during ascent is precipitated by depressurisation on ascent from depth while blackout in consistently shallow water is a consequence of hypocapnia following hyperventilation. (Full article...) -
Hypothermia is defined as a body core temperature below 35.0 °C (95.0 °F) in humans. Symptoms depend on the temperature. In mild hypothermia, there is shivering and mental confusion. In moderate hypothermia, shivering stops and confusion increases. In severe hypothermia, there may be hallucinations and paradoxical undressing, in which a person removes their clothing, as well as an increased risk of the heart stopping.
Hypothermia has two main types of causes. It classically occurs from exposure to cold weather and cold water immersion. It may also occur from any condition that decreases heat production or increases heat loss. Commonly, this includes alcohol intoxication but may also include low blood sugar, anorexia and advanced age. Body temperature is usually maintained near a constant level of 36.5–37.5 °C (97.7–99.5 °F) through thermoregulation. Efforts to increase body temperature involve shivering, increased voluntary activity, and putting on warmer clothing. Hypothermia may be diagnosed based on either a person's symptoms in the presence of risk factors or by measuring a person's core temperature.
The treatment of mild hypothermia involves warm drinks, warm clothing, and voluntary physical activity. In those with moderate hypothermia, heating blankets and warmed intravenous fluids are recommended. People with moderate or severe hypothermia should be moved gently. In severe hypothermia, extracorporeal membrane oxygenation (ECMO) or cardiopulmonary bypass may be useful. In those without a pulse, cardiopulmonary resuscitation (CPR) is indicated along with the above measures. Rewarming is typically continued until a person's temperature is greater than 32 °C (90 °F). If there is no improvement at this point or the blood potassium level is greater than 12 millimoles per litre at any time, resuscitation may be discontinued.
Hypothermia is the cause of at least 1,500 deaths a year in the United States. It is more common in older people and males. One of the lowest documented body temperatures from which someone with accidental hypothermia has survived is 12.7 °C (54.9 °F) in a 2-year-old boy from Poland named Adam. Survival after more than six hours of CPR has been described. In individuals for whom ECMO or bypass is used, survival is around 50%. Deaths due to hypothermia have played an important role in many wars.
The term is from Greek ῠ̔πο (ypo), meaning "under", and θέρμη (thérmē), meaning "heat". The opposite of hypothermia is hyperthermia, an increased body temperature due to failed thermoregulation. (Full article...) -
Hypercapnia (from the Greek hyper = "above" or "too much" and kapnos = "smoke"), also known as hypercarbia and CO2 retention, is a condition of abnormally elevated carbon dioxide (CO2) levels in the blood. Carbon dioxide is a gaseous product of the body's metabolism and is normally expelled through the lungs. Carbon dioxide may accumulate in any condition that causes hypoventilation, a reduction of alveolar ventilation (the clearance of air from the small sacs of the lung where gas exchange takes place) as well as resulting from inhalation of CO2. Inability of the lungs to clear carbon dioxide, or inhalation of elevated levels of CO2, leads to respiratory acidosis. Eventually the body compensates for the raised acidity by retaining alkali in the kidneys, a process known as "metabolic compensation".
Acute hypercapnia is called acute hypercapnic respiratory failure (AHRF) and is a medical emergency as it generally occurs in the context of acute illness. Chronic hypercapnia, where metabolic compensation is usually present, may cause symptoms but is not generally an emergency. Depending on the scenario both forms of hypercapnia may be treated with medication, with mask-based non-invasive ventilation or with mechanical ventilation.
Hypercapnia is a hazard of underwater diving associated with breath-hold diving, scuba diving, particularly on rebreathers, and deep diving where it is associated with increased breathing gas density due to the high ambient pressure. (Full article...) -
Oxygen therapy, also referred to as supplemental oxygen, is the use of oxygen as medical treatment. Supplemental oxygen can also refer to the use of oxygen enriched air at altitude. Acute indications for therapy include hypoxemia (low blood oxygen levels), carbon monoxide toxicity and cluster headache. It may also be prophylactically given to maintain blood oxygen levels during the induction of anesthesia. Oxygen therapy is often useful in chronic hypoxemia caused by conditions such as severe COPD or cystic fibrosis. Oxygen can be delivered via nasal cannula, face mask, or endotracheal intubation at normal atmospheric pressure, or in a hyperbaric chamber. It can also be given through bypassing the airway, such as in ECMO therapy.
Oxygen is required for normal cellular metabolism. However, excessively high concentrations can result in oxygen toxicity, leading to lung damage and respiratory failure. Higher oxygen concentrations can also increase the risk of airway fires, particularly while smoking. Oxygen therapy can also dry out the nasal mucosa without humidification. In most conditions, an oxygen saturation of 94–96% is adequate, while in those at risk of carbon dioxide retention, saturations of 88–92% are preferred. In cases of carbon monoxide toxicity or cardiac arrest, saturations should be as high as possible. While air is typically 21% oxygen by volume, oxygen therapy can increase O2 content of air up to 100%.
The medical use of oxygen first became common around 1917, and is the most common hospital treatment in the developed world. It is currently on the World Health Organization's List of Essential Medicines. Home oxygen can be provided either by oxygen tanks or oxygen concentrator. (Full article...) -
Narcosis while diving (also known as nitrogen narcosis, inert gas narcosis, raptures of the deep, Martini effect) is a reversible alteration in consciousness that occurs while diving at depth. It is caused by the anesthetic effect of certain gases at high partial pressure. The Greek word νάρκωσις (narkōsis), "the act of making numb", is derived from νάρκη (narkē), "numbness, torpor", a term used by Homer and Hippocrates. Narcosis produces a state similar to drunkenness (alcohol intoxication), or nitrous oxide inhalation. It can occur during shallow dives, but does not usually become noticeable at depths less than 30 metres (98 ft).
Except for helium and probably neon, all gases that can be breathed have a narcotic effect, although widely varying in degree. The effect is consistently greater for gases with a higher lipid solubility, and although the mechanism of this phenomenon is still not fully clear, there is good evidence that the two properties are mechanistically related. As depth increases, the mental impairment may become hazardous. Divers can learn to cope with some of the effects of narcosis, but it is impossible to develop a tolerance. Narcosis can affect all ambient pressure divers, although susceptibility varies widely among individuals and from dive to dive. The main modes of underwater diving that deal with its prevention and management are scuba diving and surface-supplied diving at depths greater than 30 metres (98 ft).
Narcosis may be completely reversed in a few minutes by ascending to a shallower depth, with no long-term effects. Thus narcosis while diving in open water rarely develops into a serious problem as long as the divers are aware of its symptoms, and are able to ascend to manage it. Diving much beyond 40 m (130 ft) is generally considered outside the scope of recreational diving. To dive at greater depths, as narcosis and oxygen toxicity become critical risk factors, gas mixtures such as trimix or heliox are used. These mixtures prevent or reduce narcosis by replacing some or all of the inert fraction of the breathing gas with non-narcotic helium.
There is a synergy between carbon dioxide toxicity, and inert gas narcosis which is recognised but not fully understood. Conditions where high work of breathing due to gas density occur tend to exacerbate this effect. (Full article...) -
Drowning is a type of suffocation induced by the submersion of the mouth and nose in a liquid. Submersion injury refers to both drowning and near-miss incident. Most instances of fatal drowning occur alone or in situations where others present are either unaware of the victim's situation or unable to offer assistance. After successful resuscitation, drowning victims may experience breathing problems, confusion, or unconsciousness. Occasionally, victims may not begin experiencing these symptoms until several hours after they are rescued. An incident of drowning can also cause further complications for victims due to low body temperature, aspiration, or acute respiratory distress syndrome (respiratory failure from lung inflammation).
Drowning is more likely to happen when spending extended periods of time near large bodies of water. Risk factors for drowning include alcohol use, drug use, epilepsy, minimal swim training or a complete lack of training, and, in the case of children, a lack of supervision. Common drowning locations include natural and man-made bodies of water, bathtubs, and swimming pools.
Drowning occurs when a person spends too much time with their nose and mouth submerged in a liquid to the point of being unable to breathe. If this is not followed by an exit to the surface, low oxygen levels and excess carbon dioxide in the blood trigger a neurological state of breathing emergency, which results in increased physical distress and occasional contractions of the vocal folds. Significant amounts of water usually only enter the lungs later in the process.
While the word "drowning" is commonly associated with fatal results, drowning may be classified into three different types: drowning that results in death, drowning that results in long-lasting health problems, and drowning that results in no health complications. Sometimes the term "near-drowning" is used in the latter cases. Among children who survive, health problems occur in about 7.5% of cases.
Steps to prevent drowning include teaching children and adults to swim and to recognise unsafe water conditions, never swimming alone, use of personal flotation devices on boats and when swimming in unfavourable conditions, limiting or removing access to water (such as with fencing of swimming pools), and exercising appropriate supervision. Treatment of victims who are not breathing should begin with opening the airway and providing five breaths of mouth-to-mouth resuscitation. Cardiopulmonary resuscitation (CPR) is recommended for a person whose heart has stopped beating and has been underwater for less than an hour. (Full article...) -
Dysbarism refers to medical conditions resulting from changes in ambient pressure. Various activities are associated with pressure changes. Underwater diving is the most frequently cited example, but pressure changes also affect people who work in other pressurized environments (for example, caisson workers), and people who move between different altitudes. (Full article...)
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Decompression sickness (DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompression. DCS most commonly occurs during or soon after a decompression ascent from underwater diving, but can also result from other causes of depressurisation, such as emerging from a caisson, decompression from saturation, flying in an unpressurised aircraft at high altitude, and extravehicular activity from spacecraft. DCS and arterial gas embolism are collectively referred to as decompression illness.
Since bubbles can form in or migrate to any part of the body, DCS can produce many symptoms, and its effects may vary from joint pain and rashes to paralysis and death. DCS often causes air bubbles to settle in major joints like knees or elbows, causing individuals to bend over in excruciating pain, hence its common name, the bends. Individual susceptibility can vary from day to day, and different individuals under the same conditions may be affected differently or not at all. The classification of types of DCS according to symptoms has evolved since its original description in the 19th century. The severity of symptoms varies from barely noticeable to rapidly fatal.
Decompression sickness can occur after an exposure to increased pressure while breathing a gas with a metabolically inert component, then decompressing too fast for it to be harmlessly eliminated through respiration, or by decompression by an upward excursion from a condition of saturation by the inert breathing gas components, or by a combination of these routes. Theoretical decompression risk is controlled by the tissue compartment with the highest inert gas concentration, which for decompression from saturation is the slowest tissue to outgas.
The risk of DCS can be managed through proper decompression procedures, and contracting the condition has become uncommon. Its potential severity has driven much research to prevent it, and divers almost universally use decompression schedules or dive computers to limit their exposure and to monitor their ascent speed. If DCS is suspected, it is treated by hyperbaric oxygen therapy in a recompression chamber. Where a chamber is not accessible within a reasonable time frame, in-water recompression may be indicated for a narrow range of presentations, if there are suitably skilled personnel and appropriate equipment available on site. Diagnosis is confirmed by a positive response to the treatment. Early treatment results in a significantly higher chance of successful recovery. (Full article...)
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Underwater tools and weapons
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The Hawaiian sling is a device used in spearfishing. The sling operates much like a bow and arrow does on land, but energy is stored in rubber tubing rather than a wooden or fiberglass bow. (Full article...)
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The APS underwater assault rifle (APS stands for Avtomat Podvodny Spetsialnyy (Автомат Подводный Специальный) or "Special Underwater Assault Rifle") is an underwater firearm designed by the Soviet Union in the early 1970s. It was adopted in 1975. Made by the Tula Arms Plant (Тульский Оружейный Завод, Tul'skiy Oruzheynyy Zavod) in Russia, it is exported by Rosoboronexport.
Under water, ordinary bullets are inaccurate and have a very short range. The APS fires a 120-millimetre-long (4.7 in), 5.66 mm calibre steel bolt specially designed for this weapon. Its magazine holds 26 rounds. The APS's barrel is not rifled; the fired projectile is kept in line by hydrodynamic effects; as a result, the APS is somewhat inaccurate when fired out of water.
The APS has a longer range and more penetrating power than spearguns. This is useful in such situations such as shooting an opposing diver through a reinforced dry suit, a protective helmet (whether air-holding or not), thick tough parts of breathing sets and their harnesses, and the plastic casings and transparent covers of some small underwater vehicles.
The APS is more powerful than a pistol, but is bulkier, heavier and takes longer to aim, particularly swinging its long barrel and large flat magazine sideways through water. (Full article...) -
A limpet 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...) -
Speargun
A speargun is a ranged underwater fishing device designed to launch a tethered spear or harpoon 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...) -
Powerhead may refer to:
- Powerhead (firearm), a direct-contact, underwater firearm
- Powerhead (aquarium), a submersible aquarium pump
- Powerhead (rocket engine), the preburners and turbopumps of a pump-fed rocket engine (excludes the engine combustion chamber and nozzle)
- Powerhead (pump), the mechanical drive of any one of several non-aquarium pump types; marine propeller powerhead, fountain powerhead, etc.
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The Gyrojet is a family of unique firearms developed in the 1960s named for the method of gyroscopically stabilizing its projectiles. Rather than inert bullets, Gyrojets fire small rockets called Microjets which have little recoil and do not require a heavy barrel or chamber to resist the pressure of the combustion gases. Velocity on leaving the tube was very low, but increased to around 1,250 feet per second (380 m/s) at 30 feet (9.1 m). The result is a very lightweight and transportable weapon.
Long out of production, today they are a coveted collector's item with prices for even the most common model ranging above $1,000. They are rarely fired; ammunition is scarce and can cost over $200 per round. (Full article...) -
Polespear under tension with a cluster head attached.
A polespear (hand spear or gidgee) 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...) -
The ADS (Russian: АДС - Автомат Двухсредный Специальный - Special Dual-environment Automatic rifle) is a Russian assault rifle specially made for combat divers. It is of a bullpup layout and is chambered in the 5.45×39mm M74 round. The ADS can adapt a suppressor and optical sights. (Full article...) -
The Heckler & Koch P11 is an underwater firearm developed in 1976 by Heckler & Koch. It is loaded using a pepper-box-like assembly, containing five sealed barrels each containing an electrically-fired projectile. Two styles of barrel assembly can be used: one containing five 7.62×36mm flechette darts for use underwater, or five 133-grain bullets for use above water. (Full article...) -
The SPP-1 underwater pistol was made in the Soviet Union for use by Soviet frogmen as an underwater firearm. It was developed in the late 1960s and accepted for use in 1975. Under water, ordinary-shaped bullets are inaccurate and very short-range. As a result, this pistol fires a round-based 4.5 millimetres (0.18 in) caliber steel dart about 115 millimetres (4.5 in) long, weighing 12.8 grams (0.45 oz), which has longer range and more penetrating power than speargun spears. The complete cartridge is 145 millimetres (5.7 in) long and weighs 17.5 grams (0.62 oz). (Full article...) -
The APS amphibious rifle, an underwater assault rifle
An underwater 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...) -
ROV at work in an underwater oil and gas field. The ROV is using a torque wrench to adjust a valve on a subsea structure.
A remotely operated underwater vehicle (ROUV) or remotely 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. They are often used to visit wrecks at great depths beyond the capacities of submersibles for research purposes, such as the Titanic, amongst others. (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...)
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The ASM-DT is a Russian prototype folding-stock underwater firearm. It emerged in the 1990s. (Full article...) -
Assembled tremie placing concrete underwater
A tremie 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 usually 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:- Caissons, which are the foundations of bridges, among other things, that span bodies of water.
- Pilings.
- Monitoring wells. Builders use tremie methods for materials other than concrete, and for industries other than construction. For example, bentonite slurries for monitoring wells are often emplaced via tremie pipe.
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History of underwater diving
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16th century Islamic painting of Alexander the Great lowered in a glass diving bell.
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...) -
The timeline of underwater diving technology is a chronological list of notable events in the history of the development of underwater diving equipment. With the partial exception of breath-hold diving, the development of underwater diving capacity, scope, and popularity, has been closely linked to available technology, and the physiological constraints of the underwater environment.
Primary constraints are:- the provision of breathing gas to allow endurance beyond the limits of a single breath,
- safely decompressing from high underwater pressure to surface pressure,
- the ability to see clearly enough to effectively perform the task,
- and sufficient mobility to get to and from the workplace.
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Scuba diver of the late 1960s
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...) -
The timeline of underwater diving technology is a chronological list of notable events in the history of the development of underwater diving equipment. With the partial exception of breath-hold diving, the development of underwater diving capacity, scope, and popularity, has been closely linked to available technology, and the physiological constraints of the underwater environment.
Primary constraints are:- the provision of breathing gas to allow endurance beyond the limits of a single breath,
- safely decompressing from high underwater pressure to surface pressure,
- the ability to see clearly enough to effectively perform the task,
- and sufficient mobility to get to and from the workplace.
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Robert William Hamilton Jr. (1930 – 16 September 2011), known as Bill, was an American physiologist known for his work in hyperbaric physiology. (Full article...) -
This is a listing of researchers who have made discoveries or inventions relating to the science and technology of underwater diving.
Divers who have become notable due to their exploits are not listed here, unless they have published research findings or invented an important item of diving related equipment. For these, see Outline of underwater divers. (Full article...) -
Captain George Foote Bond (November 14, 1915 – January 3, 1983) was a United States Navy physician who was known as a leader in the field of undersea and hyperbaric medicine and the "Father of Saturation Diving".
While serving as Officer-in-Charge at the Naval Medical Research Laboratory in Groton, Connecticut, he conducted his earliest experiments into saturation diving techniques.
In 1957, Bond began the Genesis project to prove that humans could in fact withstand prolonged exposure to different breathing gases and increased environmental pressures. Once saturation is achieved, the amount of time needed for decompression depends only on the depth and gases breathed. This was the beginning of saturation diving and the US Navy's Man-in-the-Sea Program.
The first two phases of Project Genesis involved exposing animals to saturation in various breathing gases. In 1962, interest in helium-oxygen atmospheres for crewed space flights made Phase C possible. Phase C involved saturation of three subjects at one atmosphere (surface) in a 21.6% oxygen, 4% nitrogen, and 74.4% helium environment for six days. In phase D experiments at the United States Navy Experimental Diving Unit in 1963, the subjects performed the world's first saturation dive at a depth of 100 feet of seawater (fsw) in a 7% oxygen, 7% nitrogen, and 86% helium environment for 6 days. In phase E trials in 1963 divers were saturated for 12 days at 198 fsw breathing 3.9% oxygen, 6.5% nitrogen and 89.6% helium. A 27-hour linear ascent was made from saturation.
"Papa Topside" Bond initiated and served as the Senior Medical Officer and principal investigator of the US Navy SEALAB program. SEALAB I was lowered off the coast of Bermuda in 1964 to a depth of 192 fsw below the sea's surface. The experiment was halted after 11 days due to an approaching tropical storm. SEALAB I proved that saturation diving in the open ocean was a viable means for expanding our ability to live and work in the sea. The experiment also provided engineering solutions to habitat placement, habitat umbilicals, humidity, and helium speech descrambling. SEALAB II was launched off the coast of California in 1965 to assess the feasibility of utilizing saturation techniques and tools to accomplish a variety of tasks that would be difficult or impossible to accomplish by repeated dives from the surface. In addition to physiological testing, the divers tested new tools, methods of salvage, and an electrically heated drysuit. SEALAB III was placed in water three times as deep to test new salvage techniques and for oceanographic and fishery studies. On February 15, 1969, SEALAB III was lowered to 610 fsw (185 m), off San Clemente Island, California. The habitat soon began to leak and six divers were sent to repair it, but they were unsuccessful. During the second attempt, aquanaut Berry L. Cannon died, and the program came to a halt. (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...) -
Christian James Lambertsen (May 15, 1917 – February 11, 2011) was an American environmental medicine and diving medicine specialist who was principally responsible for developing the United States Navy frogmen's rebreathers in the early 1940s for underwater warfare. Lambertsen designed a series of rebreathers in 1940 (patent filing date: 16 Dec 1940) and in 1944 (patent issue date: 2 May 1944) and first called his invention breathing apparatus. Later, after the war, he called it Laru (acronym for Lambertsen Amphibious Respiratory Unit) and finally, in 1952, he changed his invention's name again to SCUBA (Self Contained Underwater Breathing Apparatus). Although diving regulator technology was invented by Émile Gagnan and Jacques-Yves Cousteau in 1943 and was unrelated to rebreathers, the current use of the word SCUBA is largely attributed to the Gagnan-Cousteau invention. The US Navy considers Lambertsen to be "the father of the Frogmen". (Full article...) -
Capt. Edward Deforest Thalmann, USN (ret.) (April 3, 1945 – July 24, 2004) was an American hyperbaric medicine specialist who was principally responsible for developing the current United States Navy dive tables for mixed-gas diving, which are based on his eponymous Thalmann Algorithm (VVAL18). At the time of his death, Thalmann was serving as assistant medical director of the Divers Alert Network (DAN) and an assistant clinical professor in anesthesiology at Duke University's Center for Hyperbaric Medicine and Environmental Physiology. (Full article...) -
Operation Thunderhead was a highly classified combat mission conducted by U.S. Navy SEAL Team One and Underwater Demolition Team 11 (UDT-11) in 1972. The mission was conducted off the coast of North Vietnam during the Vietnam War to rescue two U.S. airmen said to be escaping from a prisoner of war prison in Hanoi. The prisoners, including Air Force Colonel John A. Dramesi were planning to steal a boat and travel down the Red River to the Gulf of Tonkin.
Lieutenant Melvin Spence Dry was killed on the mission. He was the last SEAL lost during the Vietnam War. His father, retired Navy Captain Melvin H. Dry, spent the rest of his life trying to learn the circumstances surrounding his son's death. The details, however, were long shrouded in secrecy. (Full article...) -
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...) -
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...)
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This painting, An Experiment on a Bird in the Air Pump by Joseph Wright of Derby, 1768, depicts an experiment originally performed by Robert Boyle in 1660.
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 nitrogen or helium 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 sickness or the 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...) -
The Raid on Alexandria (Operazione EA 3) was carried out on 19 December 1941 by Italian Navy (Regia Marina) divers of the Decima Flottiglia MAS (Decima Flottiglia Motoscafi Armati Siluranti [10th Flotilla MAS]), who attacked and sank two Royal Navy battleships at their moorings and damaged an oil tanker and a destroyer in the harbour of Alexandria, Egypt, using manned torpedoes.
The attacks came at a difficult time for the Mediterranean Fleet, after the loss of the aircraft carrier HMS Ark Royal and the battleship Barham to U-boats, the loss of ships during the Battle of Crete and the sinking of much of Force K on an Italian minefield, the day before the human torpedo attack on Alexandria. Ships also had to be sent to the Eastern Fleet. (Full article...)
Diver training, registration and certification
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The Federazione Italiana Attività Subacquee (FIAS) (Italian Underwater Activities Federation) is an Italian non-profit diver training organization. It is a member of:
- CMAS (Confédération Mondiale des Activités Subaquatiques)
- EUF (European Underwater Federation)
- CIAS (Confederazione Italiana delle Attività Subacquee).
It counts in Italy 130 distinct federated clubs (34 sezioni territoriali and 96 circoli). (Full article...) -
Recreational diver course referral is a system intended to facilitate completion of training for open water recreational scuba diving students who intend to do their training dives at a place different from the venue for the theory and confined water training. Referral systems within a specific training agency were the original format, but as more universally recognised training standard such as those of the recreational Scuba Training Council, and more recently the ISO and EUF standards have been adopted by most training agencies, it has become possible to expand the system to function across agencies. Referrals within a certification agency are relatively uncontroversial as the agency training standards are expected to be fairly uniform. Cross-agency referrals can occasionally raise problems where the standards differ significantly, as the instructor completing the training may not be entirely familiar with the relevant s requirements.
Equipment rental and where appropriate, boat dives may be included in the package. Not all diver training agencies, schools and instructors participate in inter-agency referrals. (Full article...) -
The World Underwater Federation or CMAS (Confédération Mondiale des Activités Subaquatiques) is an international federation that represents underwater activities in underwater sport and underwater sciences, and oversees an international system of recreational snorkel and scuba diver training and recognition. It is also known by its Spanish name, Confederación Mundial De Actividades Subacuáticas. Its foundation in Monaco during January 1959 makes it one of the world's oldest underwater diving organisations. (Full article...)
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The United Diving Instructors (UDI) is the diver training organization founded in 1983 by Z. Fisher and H. G. Golzing in California, United States. (Full article...) -
The British Sub-Aqua Club or BSAC has been recognised since 1954 by UK Sport as the national governing body of recreational diving in the United Kingdom.
The club was founded in 1953 and at its peak in the mid-1990s had over 50,000 members declining to over 30,000 in 2009. It is a diver training organization that operates through its associated network of around 1,100 local, independent diving clubs and around 400 diving schools worldwide. The old logo featured the Roman god Neptune (Greek god Poseidon), god of the sea. The new logo, as of 2017, features a diver with the updated BSAC motto "Dive with us".
BSAC is unusual for a diver training agency in that most BSAC instructors are volunteers, giving up their spare time to train others, unlike many other agencies, in which instructors are paid employees, or self-employed.
Given that UK waters are relatively cold and have restricted visibility, BSAC training is regarded by its members as more comprehensive than some. Specifically it places emphasis on rescue training very early in the programme. BSAC also maintains links with other organisations, such as NACSAC.
Science writer and science fiction author Arthur C. Clarke was a famous member of BSAC.[full citation needed]
The current President of BSAC is William, Prince of Wales. His father Charles III, and grandfather Philip also held that position and his brother Harry, Duke of Sussex also trained with BSAC. (Full article...) -
The International Association for Handicapped Divers (or "IAHD") is a non-profit organization with its headquarters in Middenmeer, the Netherlands. The organization was established in 1993, with the aim to promote, develop and conduct programs for the training in scuba diving of people with a disability. From 1993 to date (2008) IAHD have educated and certified over 5500 divers and dive professionals worldwide. As the IAHD is a non-profit foundation, all the people on the board are volunteers. There are also volunteers in regions around the world.
Physical exercise helps people improve their health both physically and mentally. A person with a disability gets these benefits as well as increased social activity by taking up an activity like scuba diving. Being involved with such activities may even result in giving a person with a disability a renewed interest in life and provide positive and lasting benefits.
The risks in training a disabled person in diving are no higher than for able bodied people. Instructors may have to alter some of the techniques and some equipment may also need changing to meet the individual's need. In some cases extra pool or open water training may be needed. In some extreme cases even individual lessons may be needed. IAHD believes that people with a disability should be in a regular class at some point in their training. (Full article...) -
Typical UK sump access conditions
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 Hole in Somerset.
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...) -
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...)
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A divemaster (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...) -
Technical Diving International (TDI) claims to be the largest technical diving certification agency in the world, and one of the first agencies to offer mixed gas and rebreather training. TDI specializes in more advanced Scuba diving techniques, particularly diving with rebreathers and use of breathing gases such as trimix and heliox.
TDI provides courses and certification for divers and for instructors. (Full article...) -
International Diving Schools Association (IDSA) was formed in 1982 with the primary purpose of developing common international standards for commercial diver training.
The Association is concerned with offshore, inshore and inland commercial diving and some specialist non-diving qualifications such as diving supervisors, diving medical technicians and life support technicians. It has published international diver training standards based on the consensus of members which provide a basic standard of comparison for commercial diver training standards, with the stated intention of:-- Improving safety
- Providing contractors with a direct input to the diver training syllabus
- Enabling contractors to bid across national borders on a more even playing field
- Improving diver quality
- Providing divers with greater job opportunities
IDSA provides a Table of Equivalence of various national commercial diver training standards.
IDSA standards are recognized in the Danish, Norwegian and Italian (Sicily) legislation. (Full article...) -
The Fédération Française d'Études et de Sports Sous-Marins (FFESSM) is a French sports federation specialized in recreational and competition underwater sports, like scuba diving and freediving. It is the main diver training organization in France.
The historical ancestor of the federation was created in 1948 under the name "Federation of societies for underwater fishing and swimming", and merged in 1955 with the "French federation of underwater activities" to become the current organization. It is one of the founding members of the Confédération Mondiale des Activités Subaquatiques (CMAS, World Confederation of Underwater Activities) created in 1959.
It has 140,000 members, 6,000 instructors, in 2,500 clubs. The federation has a delegation from the French Ministry of Sports to organize and develop scuba diving and related activities nationwide. (Full article...) -
The Professional Diving Instructors Corporation (PDIC) is an international SCUBA training and certification agency. It has an estimated 5 million active recreational divers.
Founded in 1969, PDIC was established out of the need to properly train SCUBA instructors.
After more than ten years of training exclusively instructors, the decision was made to offer training starting at the open water level.
PDIC is a founding member of the (United States) Recreational Scuba Training Council and is recognised as a scuba training and certification provider by several state and national organisations in the USA. (Full article...) -
The World Recreational Scuba Training Council (WRSTC) was founded in 1999 and is dedicated to creating minimum recreational diving training standards for the various recreational scuba diving certification agencies across the world. The WRSTC restricts its membership to national or regional councils. These councils consist of individual training organizations who collectively represent at least 50% of the annual diver certifications in the member council's country or region. A national council is referred to as a RSTC (Recreational Scuba Training Council).
Significant training organisations which are not associated with WRSTC via membership of its regional RSTCs include Confédération Mondiale des Activités Subaquatiques (CMAS). (Full article...) -
The Sub-Aqua Association (SAA) 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...)
Underwater diving organisations
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The Nautical Archaeology Society (NAS) is a charity registered in England and Wales and in Scotland and is a company limited by guarantee.
The charitable aims and object of the company are to further research in Nautical Archaeology and publish the results of such research and to advance education and training in the techniques pertaining to the study of Nautical Archaeology for the benefit of the public.
Nautical archaeology is an archaeological sub-discipline more generally known as maritime archaeology. It encompasses the archaeology of shipwrecks, underwater archaeology in seas and elsewhere and the archaeology of related features.
The society's logo is derived from the image of a merchant sailing ship on a Bichrome Ware Cypro-Archaic pottery jug 750-600BC, thought to be from the Karpas Peninsula in North Cyprus. The ancient vessel is part of the British Museum's collection (GR 1926.6-28.9). An analysis of how the iconography on this pot has been misinterpreted in recent history and how the image has been adapted for the society's logo, can be read in the editorial of the society's publication the International Journal of Nautical Archaeology (2000) 29.1: 1–2. (Full article...) -
Save Ontario Shipwrecks (SOS) is a Provincial Heritage Organization in Ontario, Canada. SOS is a public charitable organization which operates through Local Chapter Committees supported by a Provincial Board of Directors and Provincial Executive. (Full article...)
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The Undersea and Hyperbaric Medical Society (UHMS) is an organization based in the US which supports research on matters of hyperbaric medicine and physiology, and provides a certificate of added qualification for physicians with an unrestricted license to practice medicine and for limited licensed practitioners, at the completion of the Program for Advanced Training in Hyperbaric Medicine. They support an extensive library and are a primary source of information for diving and hyperbaric medicine physiology worldwide. (Full article...)
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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...)
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The Aerospace Medical Association (AsMA) is the largest professional organization in the fields of aviation, space, and environmental medicine. The AsMA membership includes aerospace and hyperbaric medical specialists, scientists, flight nurses, physiologists, and researchers from all over the world. (Full article...)
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Comhairle Fo-Thuinn (pronounced [ˈkoːɾˠl̠ʲə fˠɔˈhiːnʲ]; Irish for "Under-Wave Council"; CFT), also known as Irish Underwater Council (IUC) and trading as Diving Ireland, is the national governing body for recreational diving and underwater sports in Ireland. (Full article...)
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The Woodville Karst Plain Project or WKPP, is a project and organization that maps the underwater cave systems underlying the Woodville Karst Plain. This plain is a 450-square-mile (1,200 km2) area that runs from Tallahassee, Florida, U.S. to the Gulf of Mexico and includes numerous first magnitude springs, including Wakulla Springs, and the Leon Sinks Cave System, the longest underwater cave in the United States. The project grew out of a cave diving research and exploration group established in 1985 and incorporated in 1990 (by Bill Gavin and Bill Main, later joined by Parker Turner, Lamar English and Bill McFaden, at the time the chairman of the NACD Exploration and Survey Committee).
WKPP is the only organization currently allowed to dive some of these caves – which are all on State, Federal, or private land – due to the extreme nature of the systems and the discipline required to safely explore them, although these caves were explored extensively prior to the establishment of the WKPP.
WKPP divers hold every deep (below −190 feet (−58 m)) distance record in underwater cave diving. WKPP director Casey McKinlay and Jarrod Jablonski hold the world's record for the greatest distance below −190 feet (−58 m)) from air in a cave dive - 25,789 feet (7,860 m) each way at Wakulla Spring at an average depth of −275 feet (−84 m). This record dive required more than 29 hours submersion including 16 hours of decompression (also a record). The WKPP also hold the world's record for the longest traverse between two known entry points - 35,791 feet (10,909 m) one way between Turner Sink and Wakulla Spring at an average depth of −275 feet (−84 m). The WKPP is also responsible for exploring and mapping more cave passageway below 190 ft than any other organization in the world - 108,584 feet (33,096 m). In total, WKPP explorers have mapped and explored 144,192 feet (43,950 m) as of June, 2018.
The data gathered by WKPP divers has allowed planners a better definition of what to expect from the underground aquifer system and how best to handle issues relating to such things as surface water runoff and other nonpoint source pollution issues. WKPP mapping has resulted in the State of Florida and the U.S. Department of Agriculture establishing a "greenway" surrounding the Leon Sinks cave system and a "protection zone" for Edward Ball Wakulla Springs State Park, as well as numerous improvements in water management district operations, DOT road-building, and development planning. WKPP data has been the basis for multi-million dollar land purchase decisions to protect critical "below the surface" resources requiring protection. (Full article...) -
British Underwater Sports Association (BUSA) is the British affiliate of the Sports Committee of Confédération Mondiale des Activités Subaquatiques (CMAS).
It was created in 1997 to fill the vacancy on the CMAS Sport Committee for the United Kingdom caused by the expulsion of the British Sub-Aqua Club from CMAS in order to ensure ongoing access to international competition offered by CMAS for British underwater sports teams.
Its members include the British Finswimming Association, British Octopush Association and British Spearfishing Association.
Its role is exclusively one of representation of British underwater sports at the international level. It does not have any recognition from the British government or the governments of the four constituent countries of the UK. BUSA members seeking government funding for sporting activities are required to obtain a letter of support from the National Governing Body (NGB) for Sub Aqua in their country. These include the BSAC for the UK and England, Northern Ireland Federation of Sub-Aqua Clubs for Northern Ireland, the Scottish Sub Aqua Club for Scotland and the Welsh Association of Sub Aqua Clubs for Wales. However, in June 2013, UK Sport and Sport England reportedly published their requirements for the acceptance of BUSA as the NGB for underwater sports in the UK. (Full article...) -
The Southern African Underwater and Hyperbaric Medical Association (SAUHMA) is an organisation of voluntary members with a special interest in the subject of underwater and/or hyperbaric medicine, recognised by the Council of the South African Medical Association as a special interest group. The Association promotes the practice and facilitates the study of underwater and hyperbaric medicine. Membership includes members and associate members, and may include medical practitioners; registered nurses; registered paramedics; qualified hyperbaric chamber operators; diving instructors; dive operators, and any other person with a special interest underwater or hyperbaric medicine. (Full article...)
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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...)
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The European Diving Technology Committee eV. (EDTC) is an association registered in Kiel, Federal Republic of Germany for the purpose of making professional diving safer by creating international standards. Membership is open to all countries of the continent of Europe, with each country having one representative from the medical, industrial, government and trade union sectors. Some major diving industry associations are also involved. As of May 2016, 22 nations and 6 international non-governmental organisations were represented in the EDTC. (Full article...)
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The South Pacific Underwater Medicine Society (SPUMS) is a primary source of information for diving and hyperbaric medicine physiology worldwide. (Full article...)
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Divers Alert Network (DAN) is a group of not-for-profit organizations dedicated to improving diving safety for all divers. It was founded in Durham, North Carolina, United States, in 1980 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 Australian Underwater Federation (AUF) is the governing body for underwater sports in Australia. (Full article...)
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DDRC Healthcare is a not-for-profit organization and a registered UK charity (no. 279652) based in Plymouth in the United Kingdom. They offer global services relating to diving medicine.
The organisation employs approximately 60 staff (2023) as regular employees and contracted staff. The organization was established in 1980 at Fort Bovisand in Devon, England - to research the effects of underwater diving on human physiology. (Full article...)
Underwater diving publications
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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...)
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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...)
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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...) -
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 diving by Martyn 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...)
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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...)
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The Special Boat Service (SBS) is the special forces unit of the United Kingdom's Royal Navy. The SBS can trace its origins back to the Second World War when the Army Special Boat Section was formed in 1940. After the Second World War, the Royal Navy formed special forces with several name changes—Special Boat Company was adopted in 1951 and re-designated as the Special Boat Squadron in 1974—until on 28 July 1987 when the unit was renamed as the Special Boat Service after assuming responsibility for maritime counter-terrorism. Most of the operations conducted by the SBS are highly classified, and are rarely commented on by the British government or the Ministry of Defence, owing to their sensitive nature.
The Special Boat Service is the maritime special forces unit of the United Kingdom Special Forces and is described as the sister unit of the British Army 22 Special Air Service Regiment (22 SAS), with both under the operational control of the Director Special Forces. In October 2001, full command of the SBS was transferred from the Commandant General Royal Marines to the Commander-in-Chief Fleet. On 18 November 2003, the SBS were given their own cap badge with the motto "By Strength and Guile". SBS operators are mostly recruited from the Royal Marines Commandos. (Full article...) -
There are several categories of decompression equipment used to help divers decompress, which is the process required to allow divers to return to the surface safely after spending time underwater at higher ambient pressures.
Decompression obligation for a given dive profile must be calculated and monitored to ensure that the risk of decompression sickness is controlled. Some equipment is specifically for these functions, both during planning before the dive and during the dive. Other equipment is used to mark the underwater position of the diver, as a position reference in low visibility or currents, or to assist the diver's ascent and control the depth.
Decompression may be shortened ("accelerated") by breathing an oxygen-rich "decompression gas" such as a nitrox blend or pure oxygen. The high partial pressure of oxygen in such decompression mixes produces the effect known as the oxygen window. This decompression gas is often carried by scuba divers in side-slung cylinders. Cave divers who can only return by a single route, can leave decompression gas cylinders attached to the guideline ("stage" or "drop cylinders") at the points where they will be used. Surface-supplied divers will have the composition of the breathing gas controlled at the gas panel.
Divers with long decompression obligations may be decompressed inside gas filled hyperbaric chambers in the water or at the surface, and in the extreme case, saturation divers are only decompressed at the end of a project, contract, or tour of duty that may be several weeks long. (Full article...) -
Decompression sickness (DCS; also called divers' disease, the bends, aerobullosis, and caisson disease) is a medical condition caused by dissolved gases emerging from solution as bubbles inside the body tissues during decompression. DCS most commonly occurs during or soon after a decompression ascent from underwater diving, but can also result from other causes of depressurisation, such as emerging from a caisson, decompression from saturation, flying in an unpressurised aircraft at high altitude, and extravehicular activity from spacecraft. DCS and arterial gas embolism are collectively referred to as decompression illness.
Since bubbles can form in or migrate to any part of the body, DCS can produce many symptoms, and its effects may vary from joint pain and rashes to paralysis and death. DCS often causes air bubbles to settle in major joints like knees or elbows, causing individuals to bend over in excruciating pain, hence its common name, the bends. Individual susceptibility can vary from day to day, and different individuals under the same conditions may be affected differently or not at all. The classification of types of DCS according to symptoms has evolved since its original description in the 19th century. The severity of symptoms varies from barely noticeable to rapidly fatal.
Decompression sickness can occur after an exposure to increased pressure while breathing a gas with a metabolically inert component, then decompressing too fast for it to be harmlessly eliminated through respiration, or by decompression by an upward excursion from a condition of saturation by the inert breathing gas components, or by a combination of these routes. Theoretical decompression risk is controlled by the tissue compartment with the highest inert gas concentration, which for decompression from saturation is the slowest tissue to outgas.
The risk of DCS can be managed through proper decompression procedures, and contracting the condition has become uncommon. Its potential severity has driven much research to prevent it, and divers almost universally use decompression schedules or dive computers to limit their exposure and to monitor their ascent speed. If DCS is suspected, it is treated by hyperbaric oxygen therapy in a recompression chamber. Where a chamber is not accessible within a reasonable time frame, in-water recompression may be indicated for a narrow range of presentations, if there are suitably skilled personnel and appropriate equipment available on site. Diagnosis is confirmed by a positive response to the treatment. Early treatment results in a significantly higher chance of successful recovery. (Full article...) -
Solo diver surveying a dive site. The bailout cylinder can be seen slung at the diver's left side
Solo diving is the practice of self-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...) -
A recompression chamber is used to treat some diving disorders and for training divers to recognise the symptoms.
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 34 meters or 112 feet for 32% oxygen). Helium may be added to reduce the amount of nitrogen and oxygen in the gas mixture when diving deeper, to reduce the effects of narcosis 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...) -
A diving cylinder or diving gas cylinder is a gas cylinder used to store and transport high pressure gas used in diving operations. This may be breathing gas used with a scuba set, in which case the cylinder may also be referred to as a scuba cylinder, scuba tank or diving tank. When used for an emergency gas supply for surface supplied diving or scuba, it may be referred to as a bailout cylinder or bailout bottle. It may also be used for surface-supplied diving or as decompression gas . A diving cylinder may also be used to supply inflation gas for a dry suit or buoyancy compensator. Cylinders provide gas to the diver through the demand valve of a diving regulator or the breathing loop of a diving re-breather.
Diving cylinders are usually manufactured from aluminum or steel alloys, and when used on a scuba set are normally fitted with one of two common types of cylinder valve for filling and connection to the regulator. Other accessories such as manifolds, cylinder bands, protective nets and boots and carrying handles may be provided. Various configurations of harness may be used by the diver to carry a cylinder or cylinders while diving, depending on the application. Cylinders used for scuba typically have an internal volume (known as water capacity) of between 3 and 18 litres (0.11 and 0.64 cu ft) and a maximum working pressure rating from 184 to 300 bars (2,670 to 4,350 psi). Cylinders are also available in smaller sizes, such as 0.5, 1.5 and 2 litres, however these are usually used for purposes such as inflation of surface marker buoys, dry suits and buoyancy compensators rather than breathing. Scuba divers may dive with a single cylinder, a pair of similar cylinders, or a main cylinder and a smaller "pony" cylinder, carried on the diver's back or clipped onto the harness at the side. Paired cylinders may be manifolded together or independent. In technical diving, more than two scuba cylinders may be needed.
When pressurized, the gas is compressed up to several hundred times atmospheric pressure. The selection of an appropriate set of diving cylinders for a diving operation is based on the amount of gas required to safely complete the dive. Diving cylinders are most commonly filled with air, but because the main components of air can cause problems when breathed underwater at higher ambient pressure, divers may choose to breathe from cylinders filled with mixtures of gases other than air. Many jurisdictions have regulations that govern the filling, recording of contents, and labeling for diving cylinders. Periodic testing and inspection of diving cylinders is often obligatory to ensure the safety of operators of filling stations. Pressurized diving cylinders are considered dangerous goods for commercial transportation, and regional and international standards for colouring and labeling may also apply. (Full article...) -
This painting, An Experiment on a Bird in the Air Pump by Joseph Wright of Derby, 1768, depicts an experiment originally performed by Robert Boyle in 1660.
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 nitrogen or helium 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 sickness or the 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...) -
Bowie Seamount, or SG̱aan Ḵinghlas ("Supernatural One Looking Outward") in the Haida language, is a large submarine volcano in the northeastern Pacific Ocean, located 180 km (110 mi) west of Haida Gwaii, British Columbia, Canada. The seamount is also known as Bowie Bank. The English name for the feature is after William Bowie of the United States Coast and Geodetic Survey.
The volcano has a flat-topped summit rising about 3,000 m (10,000 ft) above the seabed, to 24 m (79 ft) below sea level. The seamount lies at the southern end of a long underwater volcanic mountain range called the Pratt-Welker or Kodiak-Bowie Seamount chain, stretching from the Aleutian Trench in the north almost to Haida Gwaii in the south.
Bowie Seamount lies on the Pacific Plate, a large segment of the Earth's surface which moves in a northwestern direction under the Pacific Ocean. It is adjacent to two other submarine volcanoes; Hodgkins Seamount on its northern flank and Graham Seamount on its eastern flank. (Full article...) -
Narcosis while diving (also known as nitrogen narcosis, inert gas narcosis, raptures of the deep, Martini effect) is a reversible alteration in consciousness that occurs while diving at depth. It is caused by the anesthetic effect of certain gases at high partial pressure. The Greek word νάρκωσις (narkōsis), "the act of making numb", is derived from νάρκη (narkē), "numbness, torpor", a term used by Homer and Hippocrates. Narcosis produces a state similar to drunkenness (alcohol intoxication), or nitrous oxide inhalation. It can occur during shallow dives, but does not usually become noticeable at depths less than 30 metres (98 ft).
Except for helium and probably neon, all gases that can be breathed have a narcotic effect, although widely varying in degree. The effect is consistently greater for gases with a higher lipid solubility, and although the mechanism of this phenomenon is still not fully clear, there is good evidence that the two properties are mechanistically related. As depth increases, the mental impairment may become hazardous. Divers can learn to cope with some of the effects of narcosis, but it is impossible to develop a tolerance. Narcosis can affect all ambient pressure divers, although susceptibility varies widely among individuals and from dive to dive. The main modes of underwater diving that deal with its prevention and management are scuba diving and surface-supplied diving at depths greater than 30 metres (98 ft).
Narcosis may be completely reversed in a few minutes by ascending to a shallower depth, with no long-term effects. Thus narcosis while diving in open water rarely develops into a serious problem as long as the divers are aware of its symptoms, and are able to ascend to manage it. Diving much beyond 40 m (130 ft) is generally considered outside the scope of recreational diving. To dive at greater depths, as narcosis and oxygen toxicity become critical risk factors, gas mixtures such as trimix or heliox are used. These mixtures prevent or reduce narcosis by replacing some or all of the inert fraction of the breathing gas with non-narcotic helium.
There is a synergy between carbon dioxide toxicity, and inert gas narcosis which is recognised but not fully understood. Conditions where high work of breathing due to gas density occur tend to exacerbate this effect. (Full article...) -
The hand signal "OK"
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...) -
Divers decompressing in the water at the end of a dive
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-diving or snorkelling 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 nitrogen or helium 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 continuous or staged. 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...) -
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen (O
2) at increased partial pressures. Severe cases can result in cell damage and death, with effects most often seen in the central nervous system, lungs, and eyes. Historically, the central nervous system condition was called the Paul Bert effect, and the pulmonary condition the Lorrain Smith effect, after the researchers who pioneered the discoveries and descriptions in the late 19th century. Oxygen toxicity is a concern for underwater divers, those on high concentrations of supplemental oxygen, and those undergoing hyperbaric oxygen therapy.
The result of breathing increased partial pressures of oxygen is hyperoxia, an excess of oxygen in body tissues. The body is affected in different ways depending on the type of exposure. Central nervous system toxicity is caused by short exposure to high partial pressures of oxygen at greater than atmospheric pressure. Pulmonary and ocular toxicity result from longer exposure to increased oxygen levels at normal pressure. Symptoms may include disorientation, breathing problems, and vision changes such as myopia. Prolonged exposure to above-normal oxygen partial pressures, or shorter exposures to very high partial pressures, can cause oxidative damage to cell membranes, collapse of the alveoli in the lungs, retinal detachment, and seizures. Oxygen toxicity is managed by reducing the exposure to increased oxygen levels. Studies show that, in the long term, a robust recovery from most types of oxygen toxicity is possible.
Protocols for avoidance of the effects of hyperoxia exist in fields where oxygen is breathed at higher-than-normal partial pressures, including underwater diving using compressed breathing gases, hyperbaric medicine, neonatal care and human spaceflight. These protocols have resulted in the increasing rarity of seizures due to oxygen toxicity, with pulmonary and ocular damage being largely confined to the problems of managing premature infants.
In recent years, oxygen has become available for recreational use in oxygen bars. The US Food and Drug Administration has warned those who have conditions such as heart or lung disease not to use oxygen bars. Scuba divers use breathing gases containing up to 100% oxygen, and should have specific training in using such gases. (Full article...) -
Dive profile of an actual dive as recorded by a personal dive computer and displayed on a desktop screen using dive logging software. In this case depth is in metres.
A dive 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," (a bottom 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...)
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For Cousteau there existed only Cousteau. He never acknowledged others or corrected the impression that he wasn’t the first in diving or in underwater photography.
— Hans Hass, in Ecott, Tim. (2001): Neutral Buoyancy
Vitello, Paul (July 7, 2013). "Hans Hass, Early Undersea Explorer, Dies at 94". New York Times. Retrieved 17 July 2018. A version of this article appears in print on July 7, 2013, on Page A18 of the New York edition with the headline: Hans Hass, 94, Early Explorer of the World Beneath the Sea.
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