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Underwater diving

Breathhold diver with tarpon
Breathhold diver with tarpon


Topic definition

Underwater diving can be described as all of the following:

  • A human activity – intentional, purposive, conscious and subjectively meaningful sequence of actions. Underwater diving is practiced as part of an occupation, or for recreation, where the practitioner submerges below the surface of the water or other liquid for a period which may range between seconds to the order of a day at a time, either exposed to the ambient pressure or isolated by a pressure resistant suit, to interact with the underwater environment for pleasure, competitive sport, or as a means to reach a work site for profit or in the pursuit of knowledge, and may use no equipment at all, or a wide range of equipment which may include breathing apparatus, environmental protective clothing, aids to vision, communication, propulsion, maneuverability, buoyancy and safety equipment, and tools for the task at hand.
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
Surface-supplied divers riding a stage to the underwater workplace
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, and remotely controlled or robotic machines can reduce risk to humans.

The environment exposes the diver to a wide range of hazards, and though the risks are largely controlled by appropriate diving skills, training, types of equipment and breathing gases used depending on the mode, depth and purpose of diving, it remains a relatively dangerous activity. Professional diving is usually regulated by occupational health and safety legislation, while recreational diving may be entirely unregulated. Diving activities are restricted to maximum depths of about 40 metres (130 ft) for recreational scuba diving, 530 metres (1,740 ft) for commercial saturation diving, and 610 metres (2,000 ft) wearing atmospheric suits. Diving is also restricted to conditions which are not excessively hazardous, though the level of risk acceptable can vary, and fatal incidents may occur.

Recreational diving (sometimes called sport diving or subaquatics) is a popular leisure activity. Technical diving is a form of recreational diving under more challenging conditions. Professional diving (commercial diving, diving for research purposes, or for financial gain) involves working underwater. Public safety diving is the underwater work done by law enforcement, fire rescue, and underwater search and recovery dive teams. Military diving includes combat diving, clearance diving and ships husbandry. Deep sea diving is underwater diving, usually with surface-supplied equipment, and often refers to the use of standard diving dress with the traditional copper helmet. Hard hat diving is any form of diving with a helmet, including the standard copper helmet, and other forms of free-flow and lightweight demand helmets. The history of breath-hold diving goes back at least to classical times, and there is evidence of prehistoric hunting and gathering of seafoods that may have involved underwater swimming. Technical advances allowing the provision of breathing gas to a diver underwater at ambient pressure are recent, and self-contained breathing systems developed at an accelerated rate following the Second World War. (Full article...)

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Diving modes

  • Recreational scuba diver
    Recreational scuba diver
  • Atmospheric diving suit
    Atmospheric diving suit
  • Freediver with monofin, ascending
    Freediver with monofin, ascending
  • Saturation diver working on the USS Monitor wreck at 70 m (230 ft) depth.
    Saturation diver working on the USS Monitor wreck at 70 m (230 ft) depth.
  • Surface-supplied diver at the Monterey Bay Aquarium, Monterey, California
    Surface-supplied diver at the Monterey Bay Aquarium, Monterey, California
  • Surface-supplied divers riding a stage to the underwater workplace
    Surface-supplied divers riding a stage to the underwater workplace

Diving and support equipment

  • Diving cylinders to be filled at a diving air compressor station
    Diving cylinders to be filled at a diving air compressor station
  • A liveaboard dive boat on the Similan Islands, Thailand
    A liveaboard dive boat on the Similan Islands, Thailand
  • Diving regulator: The most familiar type is the single-hose open circuit scuba regulator, with first and second stages, low pressure inflator hose and submersible pressure gauge
    Diving regulator: The most familiar type is the single-hose open circuit scuba regulator, with first and second stages, low pressure inflator hose and submersible pressure gauge
  • Two divers, one wearing a 1 atmosphere diving suit and the other standard diving dress, preparing to explore the wreck of the RMS Lusitania, 1935
    Two divers, one wearing a 1 atmosphere diving suit and the other standard diving dress, preparing to explore the wreck of the RMS Lusitania, 1935
  • Israeli Navy Underwater Missions Unit transfers equipment using lifting-bags
    Israeli Navy Underwater Missions Unit transfers equipment using lifting-bags
  • A pair of demand valves fitted to a scuba regulator
    A pair of demand valves fitted to a scuba regulator
  • 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.
    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.
  • Surface supplied diver on diving stage
    Surface supplied diver on diving stage
  • Trimix scuba cylinder label
    Trimix scuba cylinder label
  • Surface supplied commercial diving equipment on display at a trade show
    Surface supplied commercial diving equipment on display at a trade show
  • Trimix scuba cylinder label
    Trimix scuba cylinder label
  • Line Arrow Marker
    Line Arrow Marker
  • Conventional scuba weight-belt with quick-release buckle
    Conventional scuba weight-belt with quick-release buckle
  • One type of nitrox cylinder identification label
    One type of nitrox cylinder identification label
  • Filling a spare air bailout cylinder
    Filling a spare air bailout cylinder

Diving procedures

  • A dive team listens to a safety brief from their dive supervisor
    A dive team listens to a safety brief from their dive supervisor
  • Diver returning from a 600 ft (183 m) dive
    Diver returning from a 600 ft (183 m) dive
  • Diver clearing ears
    Diver clearing ears
  • Air, oxygen and helium partial pressure gas blending system
    Air, oxygen and helium partial pressure gas blending system
  • A decompression dive may require the use of more than one gas mixture
    A decompression dive may require the use of more than one gas mixture
  • A Navy buddy diver team checking their gauges together
    A Navy buddy diver team checking their gauges together
  • SCUBA Diver in the mountain lake Lai da Marmorera 1,680 metres (5,510 ft) above sea level)
    SCUBA Diver in the mountain lake Lai da Marmorera 1,680 metres (5,510 ft) above sea level)
  • Divers decompressing in the water at the end of a dive
    Divers decompressing in the water at the end of a dive
  • Image 10 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...)
  • Surface-supplied diver at the Monterey Bay Aquarium, Monterey, California
    Surface-supplied diver at the Monterey Bay Aquarium, Monterey, California
  • 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.
    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.
  • Freediver with monofin, ascending
    Freediver with monofin, ascending
  • Recreational scuba diver
    Recreational scuba diver
  • Image 15In-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. 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 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 under water. 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.Several schedules have been published for in-water recompression treatment, but little data on their efficacy is available. (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. 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 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 under water. 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.

    Several schedules have been published for in-water recompression treatment, but little data on their efficacy is available. (Full article...)

Science of diving

  • Image 1In 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. A supersaturated solution is in a metastable state; it may be brought to equilibrium by forcing the excess of solute to separate from the solution. The term can also be applied to a mixture of gases. (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. A supersaturated solution is in a metastable state; it may be brought to equilibrium by forcing the excess of solute to separate from the solution. The term can also be applied to a mixture of gases. (Full article...)
  • Image 2Work 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...)
    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...)
  • 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.
    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.
  • Image 4 Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Fluids can contain suspended solid matter consisting of particles of many different sizes. While some suspended material will be large enough and heavy enough to settle rapidly to the bottom of the container if a liquid sample is left to stand (the settable solids), very small particles will settle only very slowly or not at all if the sample is regularly agitated or the particles are colloidal. These small solid particles cause the liquid to appear turbid. Turbidity (or haze) is also applied to transparent solids such as glass or plastic. In plastic production, haze is defined as the percentage of light that is deflected more than 2.5° from the incoming light direction. (Full article...)
  • These signs in English and Spanish explain how to escape from a rip current. They are posted at Mission Beach, San Diego, California. In addition to explaining how to escape, it also provides basic safety tips, such as learning to swim, not to swim alone, and to avoid the water if a swimmer is unsure that it is safe.
    These signs in English and Spanish explain how to escape from a rip current. They are posted at Mission Beach, San Diego, California. In addition to explaining how to escape, it also provides basic safety tips, such as learning to swim, not to swim alone, and to avoid the water if a swimmer is unsure that it is safe.
  • Diving reflex in a human baby
    Diving reflex in a human baby
  • A laboratory studying ambient pressure at Oregon State University
    A laboratory studying ambient pressure at Oregon State University
  • Image 8Dead space is the volume of air that is inhaled that does not take part in the gas exchange, because it either remains in the conducting airways or reaches alveoli that are not perfused or poorly perfused. It means that not all the air in each breath is available for the exchange of oxygen and carbon dioxide. Mammals breathe in and out of their lungs, wasting that part of the inhalation which remains in the conducting airways where no gas exchange can occur. (Full article...)
    Dead space is the volume of air that is inhaled that does not take part in the gas exchange, because it either remains in the conducting airways or reaches alveoli that are not perfused or poorly perfused. It means that not all the air in each breath is available for the exchange of oxygen and carbon dioxide. Mammals breathe in and out of their lungs, wasting that part of the inhalation which remains in the conducting airways where no gas exchange can occur. (Full article...)
  • Image 9In 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% helium, 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...)
    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% helium, 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...)
  • Scuba diver decompressing at a planned stop during ascent from a dive
    Scuba diver decompressing at a planned stop during ascent from a dive
  • 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. Solar tides not shown.
    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. Solar tides not shown.
  • Image 12The 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...)
    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...)
  • Scuba diver decompressing at a planned stop during ascent from a dive
    Scuba diver decompressing at a planned stop during ascent from a dive
  • Scuba diver with bifocal lenses fitted to a mask
    Scuba diver with bifocal lenses fitted to a mask
  • Image 15Cold 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. A scenario that involves fatalities occurring without continuous underwater entrapment or significant trauma, most commonly associated with high flows or cold water conditions, is frequently referred to as “flush drowning” by whitewater enthusiasts.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 tachypneia 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...)
    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. A scenario that involves fatalities occurring without continuous underwater entrapment or significant trauma, most commonly associated with high flows or cold water conditions, is frequently referred to as “flush drowning” by whitewater enthusiasts.

    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 tachypneia 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...)

Occupational diving

  • A US Navy work diver is lowered to the sea bed during a dive from the USNS Grasp (ARS 51) off the coast of St. Kitts.
    A US Navy work diver is lowered to the sea bed during a dive from the USNS Grasp (ARS 51) off the coast of St. Kitts.
  • Public safety diving team members bring in a casualty
    Public safety diving team members bring in a casualty
  • NYPD divers removing material from the Harlem Meer following a murder in the area few days prior.
    NYPD divers removing material from the Harlem Meer following a murder in the area few days prior.
  • Underwater videographer
    Underwater videographer
  • A US Navy diver at work. The umbilical supplying air from the surface is clearly visible.
    A US Navy diver at work. The umbilical supplying air from the surface is clearly visible.
  • Surface supplied diving equipment on display
    Surface supplied diving equipment on display
  • Image 7Underwater demolition refers to the deliberate destruction or neutralization of man-made or natural underwater obstacles, both for military and civilian purposes. (Full article...)
    Underwater demolition refers to the deliberate destruction or neutralization of man-made or natural underwater obstacles, both for military and civilian purposes. (Full article...)
  • Drawing to scale, underwater
    Drawing to scale, underwater
  • Image 9A 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...)
    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 serious, the decontamination team would have been wearing hazmat gear
    US Navy Diver being decontaminated after a dive. If the contamination was serious, the decontamination team would have been wearing hazmat gear
  • Image 11Salvage 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...)
    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 United States Navy Mass Communication Specialist conducting underwater photography training
    A United States Navy Mass Communication Specialist conducting underwater photography training
  • A SEAL Delivery Team member climbs aboard a delivery vehicle before launching from the back of the submarine USS Philadelphia.
    A SEAL Delivery Team member climbs aboard a delivery vehicle before launching from the back of the submarine USS Philadelphia.
  • Sponge diver putting on his diving suit in Tarpon Springs, Florida.
    Sponge diver putting on his diving suit in Tarpon Springs, Florida.

Recreational diving

Diving hazards, incidents, safety and law

  • Folding lockout hasp, allowing the use of up to six padlocks to secure a device.
    Folding lockout hasp, allowing the use of up to six padlocks to secure a device.
  • Image 2Broadly speaking, a risk assessment is the combined effort of: identifying and analyzing potential (future) events that may negatively impact individuals, assets, and/or the environment (i.e. hazard analysis); and making judgments "on the tolerability of the risk on the basis of a risk analysis" while considering influencing factors (i.e. risk evaluation).Put in simpler terms, a risk assessment determines possible mishaps, their likelihood and consequences, and the tolerances for such events. The results of this process may be expressed in a quantitative or qualitative fashion. Risk assessment is an inherent part of a broader risk management strategy to help reduce any potential risk-related consequences. (Full article...)
    Broadly speaking, a risk assessment is the combined effort of:
    1. identifying and analyzing potential (future) events that may negatively impact individuals, assets, and/or the environment (i.e. hazard analysis); and
    2. making judgments "on the tolerability of the risk on the basis of a risk analysis" while considering influencing factors (i.e. risk evaluation).


    Put in simpler terms, a risk assessment determines possible mishaps, their likelihood and consequences, and the tolerances for such events. The results of this process may be expressed in a quantitative or qualitative fashion. Risk assessment is an inherent part of a broader risk management strategy to help reduce any potential risk-related consequences. (Full article...)
  • Image 3A Job Safety Analysis (JSA) is a procedure which helps integrate accepted safety and health principles and practices into a particular task or job operation. In a JSA, each basic step of the job is to identify potential hazards and to recommend the safest way to do the job. Other terms 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, such as "operating a grinder," "using a pressurized water extinguisher" or "changing a flat tire." JSAs are not suitable for jobs defined too broadly, for example, "overhauling an engine"; or too narrowly, for example, "positioning car jack." (Full article...)
    A Job Safety Analysis (JSA) is a procedure which helps integrate accepted safety and health principles and practices into a particular task or job operation. In a JSA, each basic step of the job is to identify potential hazards and to recommend the safest way to do the job. Other terms 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, such as "operating a grinder," "using a pressurized water extinguisher" or "changing a flat tire." JSAs are not suitable for jobs defined too broadly, for example, "overhauling an engine"; or too narrowly, for example, "positioning car jack." (Full article...)
  • Image 4In tort law, a duty of care is a legal obligation that is imposed on an individual, requiring adherence to a standard of reasonable care while performing any acts that could foreseeably harm others. It is the first element that must be established to proceed with an action in negligence. The claimant must be able to show a duty of care imposed by law that the defendant has breached. In turn, breaching a duty may subject an individual to liability. The duty of care may be imposed by operation of law between individuals who have no current direct relationship (familial or contractual or otherwise) but eventually become related in some manner, as defined by common law (meaning case law).Duty of care may be considered a formalisation of the social contract, the implicit responsibilities held by individuals towards others within society. It is not a requirement that a duty of care be defined by law, though it will often develop through the jurisprudence of common law. (Full article...)
    In tort law, a duty of care is a legal obligation that is imposed on an individual, requiring adherence to a standard of reasonable care while performing any acts that could foreseeably harm others. It is the first element that must be established to proceed with an action in negligence. The claimant must be able to show a duty of care imposed by law that the defendant has breached. In turn, breaching a duty may subject an individual to liability. The duty of care may be imposed by operation of law between individuals who have no current direct relationship (familial or contractual or otherwise) but eventually become related in some manner, as defined by common law (meaning case law).

    Duty of care may be considered a formalisation of the social contract, the implicit responsibilities held by individuals towards others within society. It is not a requirement that a duty of care be defined by law, though it will often develop through the jurisprudence of common law. (Full article...)
  • Beaching a casualty while providing artificial respiration
    Beaching a casualty while providing artificial respiration
  • A dive team listens to a safety brief from their dive supervisor
    A dive team listens to a safety brief from their dive supervisor
  • Image 7Scuba 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.Scuba diving fatalities have a major financial impact by way of lost income, lost business, insurance premium increases and high litigation costs. (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.

    Scuba diving fatalities have a major financial impact by way of lost income, lost business, insurance premium increases and high litigation costs. (Full article...)
  • Image 8A code of practice can be a document that complements occupational health and safety laws and regulations to provide detailed practical guidance on how to comply with legal obligations, and should be followed unless another solution with the same or better health and safety standard is in place, or may be a document for the same purpose published by a self-regulating body to be followed by member organisations.Codes of practice published by governments do not replace the occupational health and safety laws and regulations, and are generally issued in terms of those laws and regulations. They are intended to help understand how to comply with the requirements of regulations. A workplace inspector can refer to a code of practice when issuing an improvement or prohibition notice, and they may be admissible in court proceedings. A court may use a code of practice to establish what is reasonably practicable action to manage a specific risk. Equivalent or better ways of achieving the required work health and safety may be possible, so compliance with codes of practice is not usually mandatory, providing that any alternative systems used provide a standard of health and safety equal to or better than those recommended by the code of practice.Organisational codes of practice do not have the same authority under law, but serve a similar purpose. Member organisations generally undertake to comply with the codes of practice as a condition of membership and may lose membership if found to be in violation of the code. (Full article...)
    A code of practice can be a document that complements occupational health and safety laws and regulations to provide detailed practical guidance on how to comply with legal obligations, and should be followed unless another solution with the same or better health and safety standard is in place, or may be a document for the same purpose published by a self-regulating body to be followed by member organisations.

    Codes of practice published by governments do not replace the occupational health and safety laws and regulations, and are generally issued in terms of those laws and regulations. They are intended to help understand how to comply with the requirements of regulations. A workplace inspector can refer to a code of practice when issuing an improvement or prohibition notice, and they may be admissible in court proceedings. A court may use a code of practice to establish what is reasonably practicable action to manage a specific risk. Equivalent or better ways of achieving the required work health and safety may be possible, so compliance with codes of practice is not usually mandatory, providing that any alternative systems used provide a standard of health and safety equal to or better than those recommended by the code of practice.

    Organisational codes of practice do not have the same authority under law, but serve a similar purpose. Member organisations generally undertake to comply with the codes of practice as a condition of membership and may lose membership if found to be in violation of the code. (Full article...)
  • Image 9Diving 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...)
    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...)
  • Infographic by NIOSH. Control methods at the top of graphic are potentially more effective and protective than those at the bottom. Following this hierarchy normally leads to the implementation of inherently safer systems, where the risk of illness or injury has been substantially reduced.
    Infographic by NIOSH. Control methods at the top of graphic are potentially more effective and protective than those at the bottom. Following this hierarchy normally leads to the implementation of inherently safer systems, where the risk of illness or injury has been substantially reduced.
  • Image 11Investigation of diving accidents includes investigations into the causes of reportable incidents in professional diving and recreational diving accidents, usually when there is a fatality or litigation for gross negligence.An investigation of some kind usually follows a fatal diving accident, or one in which litigation is expected. There may be several investigations with different agendas. If police are involved, they generally look for evidence of a crime. In the US the Coastguard will usually investigate if there is a death when diving from a vessel in coastal waters. Health and safety administration officials may investigate when the diver was injured or killed at work. When a death occurs during an organised recreational activity, the certification agency's insurers will usually send an investigator to look into possible liability issues. The investigation may occur almost immediately to some considerable time after the event. In most cases the body will have been recovered and resuscitation attempted, and in this process equipment is usually removed and may be damaged or lost, or the evidence compromised by handling. Witnesses may have dispersed, and equipment is often mishandled by the investigating authorities if they are unfamiliar with the equipment and store it improperly, which can destroy evidence and compromise findings.Recreational diving accidents are usually relatively uncomplicated, but accidents involving an extended range environment or specialised equipment may require expertise beyond the experience of any one investigator. This is a particular issue when rebreather equipment is involved. Investigators who are not familiar with complex equipment may not know enough about the equipment to understand that they do not know enough.For every incident in which someone is injured of killed, it has been estimated that a relatively large number of "near miss" incidents occur, which the diver manages well enough to avoid harm. Ideally these will be recorded, analysed for cause, reported, and the results made public, so that similar incidents can be avoided in the future. (Full article...)
    Investigation of diving accidents includes investigations into the causes of reportable incidents in professional diving and recreational diving accidents, usually when there is a fatality or litigation for gross negligence.

    An investigation of some kind usually follows a fatal diving accident, or one in which litigation is expected. There may be several investigations with different agendas. If police are involved, they generally look for evidence of a crime. In the US the Coastguard will usually investigate if there is a death when diving from a vessel in coastal waters. Health and safety administration officials may investigate when the diver was injured or killed at work. When a death occurs during an organised recreational activity, the certification agency's insurers will usually send an investigator to look into possible liability issues. The investigation may occur almost immediately to some considerable time after the event. In most cases the body will have been recovered and resuscitation attempted, and in this process equipment is usually removed and may be damaged or lost, or the evidence compromised by handling. Witnesses may have dispersed, and equipment is often mishandled by the investigating authorities if they are unfamiliar with the equipment and store it improperly, which can destroy evidence and compromise findings.

    Recreational diving accidents are usually relatively uncomplicated, but accidents involving an extended range environment or specialised equipment may require expertise beyond the experience of any one investigator. This is a particular issue when rebreather equipment is involved. Investigators who are not familiar with complex equipment may not know enough about the equipment to understand that they do not know enough.

    For every incident in which someone is injured of killed, it has been estimated that a relatively large number of "near miss" incidents occur, which the diver manages well enough to avoid harm. Ideally these will be recorded, analysed for cause, reported, and the results made public, so that similar incidents can be avoided in the future. (Full article...)
  • Image 12This 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...)
    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...)
  • Image 13Human factors are the physical or cognitive properties of individuals, or social behavior which is specific to humans, and influence functioning of technological systems as well as human-environment equilibria. The 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.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 commercial Scuba diving is due to this factor. The study also concluded that it would be impossible to eliminate absolutely all minor contraindications of Scuba diving, as this would result in overwhelming bureaucracy and would bring all diving to a halt. (Full article...)
    Human factors are the physical or cognitive properties of individuals, or social behavior which is specific to humans, and influence functioning of technological systems as well as human-environment equilibria. The 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.

    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 commercial Scuba diving is due to this factor. The study also concluded that it would be impossible to eliminate absolutely all minor contraindications of Scuba diving, as this would result in overwhelming bureaucracy and would bring all diving to a halt. (Full article...)
  • Example of risk assessment: A NASA model showing areas at high risk from impact for the International Space Station
    Example of risk assessment: A NASA model showing areas at high risk from impact for the International Space Station
  • Image 15Divers 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...)
    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...)

Diving medicine, disorders and treatment

  • Image 1Diving disorders, or diving related medical conditions, are conditions associated with underwater diving, and include both conditions unique to underwater diving, and those that also occur during other activities. This second group further divides into conditions caused by exposure to ambient pressures significantly different from surface atmospheric pressure, and a range of conditions caused by general environment and equipment associated with diving activities.Disorders particularly associated with diving include those caused by variations in ambient pressure, such as barotraumas of descent and ascent, decompression sickness and those caused by exposure to elevated ambient pressure, such as some types of gas toxicity. There are also non-dysbaric disorders associated with diving, which include the effects of the aquatic environment, such as drowning, which also are common to other water users, and disorders caused by the equipment or associated factors, such as carbon dioxide and carbon monoxide poisoning. General environmental conditions can lead to another group of disorders, which include hypothermia and motion sickness, injuries by marine and aquatic organisms, contaminated waters, man-made hazards, and ergonomic problems with equipment. Finally there are pre-existing medical and psychological conditions which increase the risk of being affected by a diving disorder, which may be aggravated by adverse side effects of medications and other drug use.Treatment depends on the specific disorder, but often includes oxygen therapy, which is standard first aid for most diving accidents, and is hardly ever contra-indicated for a person medically fit to dive, and hyperbaric therapy is the definitive treatment for  decompression sickness. Screening for medical fitness to dive can reduce some of the risk for some of the disorders. (Full article...)
    Diving disorders, or diving related medical conditions, are conditions associated with underwater diving, and include both conditions unique to underwater diving, and those that also occur during other activities. This second group further divides into conditions caused by exposure to ambient pressures significantly different from surface atmospheric pressure, and a range of conditions caused by general environment and equipment associated with diving activities.

    Disorders particularly associated with diving include those caused by variations in ambient pressure, such as barotraumas of descent and ascent, decompression sickness and those caused by exposure to elevated ambient pressure, such as some types of gas toxicity. There are also non-dysbaric disorders associated with diving, which include the effects of the aquatic environment, such as drowning, which also are common to other water users, and disorders caused by the equipment or associated factors, such as carbon dioxide and carbon monoxide poisoning. General environmental conditions can lead to another group of disorders, which include hypothermia and motion sickness, injuries by marine and aquatic organisms, contaminated waters, man-made hazards, and ergonomic problems with equipment. Finally there are pre-existing medical and psychological conditions which increase the risk of being affected by a diving disorder, which may be aggravated by adverse side effects of medications and other drug use.

    Treatment depends on the specific disorder, but often includes oxygen therapy, which is standard first aid for most diving accidents, and is hardly ever contra-indicated for a person medically fit to dive, and hyperbaric therapy is the definitive treatment for decompression sickness. Screening for medical fitness to dive can reduce some of the risk for some of the disorders. (Full article...)
  • In 1942–43 the UK Government carried out extensive testing for oxygen toxicity in divers. The chamber is pressurised with air to 3.7 bar. The subject in the centre is breathing 100% oxygen from a mask.
    In 1942–43 the UK Government carried out extensive testing for oxygen toxicity in divers. The chamber is pressurised with air to 3.7 bar. The subject in the centre is breathing 100% oxygen from a mask.
  • Image 3Dysbarism 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...)
    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...)
  • Image 4Compression arthralgia is pain in the joints caused by exposure to high ambient pressure at a relatively high rate of compression, experienced by underwater divers.Also referred to in the US Navy diving Manual as compression pains.Compression arthralgia has been recorded as deep aching pain in the knees, shoulders, fingers, back, hips, neck and ribs. Pain may be sudden and intense in onset and may be accompanied by a feeling of roughness in the joints.Onset commonly occurs around 60 msw (meters of sea water), and symptoms are variable depending on depth, compression rate and personal susceptibility. Intensity increases with depth and may be aggravated by exercise. Compression arthralgia is generally a problem of deep diving, particularly deep saturation diving, where at sufficient depth even slow compression may produce symptoms. Peter B. Bennett et al. showed that the use of trimix could reduce the symptoms.Fast compression (descent) may produce symptoms as shallow as 30 msw. Saturation divers generally compress much more slowly, and symptoms are unlikely at less than around 90 msw. At depths beyond 180m even very slow compression may produce symptoms. Spontaneous improvement may occur over time at depth, but this is unpredictable, and pain may persist into decompression. Symptoms may be distinguished from decompression sickness as they are present before starting decompression, and resolve with decreasing pressure, the opposite of decompression sickness. The pain may be sufficiently severe to limit the diver's capacity for work, and may also limit travel rate and depth of downward excursions. (Full article...)
    Compression arthralgia is pain in the joints caused by exposure to high ambient pressure at a relatively high rate of compression, experienced by underwater divers.
    Also referred to in the US Navy diving Manual as compression pains.

    Compression arthralgia has been recorded as deep aching pain in the knees, shoulders, fingers, back, hips, neck and ribs. Pain may be sudden and intense in onset and may be accompanied by a feeling of roughness in the joints.

    Onset commonly occurs around 60 msw (meters of sea water), and symptoms are variable depending on depth, compression rate and personal susceptibility. Intensity increases with depth and may be aggravated by exercise. Compression arthralgia is generally a problem of deep diving, particularly deep saturation diving, where at sufficient depth even slow compression may produce symptoms. Peter B. Bennett et al. showed that the use of trimix could reduce the symptoms.

    Fast compression (descent) may produce symptoms as shallow as 30 msw. Saturation divers generally compress much more slowly, and symptoms are unlikely at less than around 90 msw. At depths beyond 180m even very slow compression may produce symptoms. Spontaneous improvement may occur over time at depth, but this is unpredictable, and pain may persist into decompression. Symptoms may be distinguished from decompression sickness as they are present before starting decompression, and resolve with decreasing pressure, the opposite of decompression sickness. The pain may be sufficiently severe to limit the diver's capacity for work, and may also limit travel rate and depth of downward excursions. (Full article...)
  • Main symptoms of carbon dioxide toxicity, by increasing volume percent in air.
    Main symptoms of carbon dioxide toxicity, by increasing volume percent in air.
  • Divers breathe a mixture of oxygen, helium and nitrogen for deep dives to avoid the effects of narcosis. A cylinder label shows the maximum operating depth and mixture (oxygen/helium).
    Divers breathe a mixture of oxygen, helium and nitrogen for deep dives to avoid the effects of narcosis. A cylinder label shows the maximum operating depth and mixture (oxygen/helium).
  • Image 7In physiology, isobaric counterdiffusion (ICD) is the diffusion of different gases into and out of tissues while under a constant ambient pressure, after a change of gas composition, and the physiological effects of this phenomenon. The term inert gas counterdiffusion is sometimes used as a synonym, but can also be applied to situations where the ambient pressure changes. It has relevance in mixed gas diving and anesthesiology. (Full article...)
    In physiology, isobaric counterdiffusion (ICD) is the diffusion of different gases into and out of tissues while under a constant ambient pressure, after a change of gas composition, and the physiological effects of this phenomenon. The term inert gas counterdiffusion is sometimes used as a synonym, but can also be applied to situations where the ambient pressure changes. It has relevance in mixed gas diving and anesthesiology. (Full article...)
  • Vasily Perov: The Drowned, 1867
    Vasily Perov: The Drowned, 1867
  • Image 9Decompression 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...)
    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...)
  • Monitoring the decompression chamber during a simulated medical emergency
    Monitoring the decompression chamber during a simulated medical emergency
  • Image 11Taravana 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...)
    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...)
  • Image 12In aviation and underwater diving, alternobaric vertigo is dizziness resulting from unequal pressures being exerted between the ears due to one Eustachian tube being less patent than the other. (Full article...)
    In aviation and underwater diving, alternobaric vertigo is dizziness resulting from unequal pressures being exerted between the ears due to one Eustachian tube being less patent than the other. (Full article...)
  • Image 13Freediving 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...)
    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...)
  • PC based spirometer output
    PC based spirometer output
  • Image 15Laryngospasm is an uncontrolled or involuntary muscular contraction (spasm) of the vocal folds. The condition typically lasts less than 60 seconds, but in some cases can last 20–30 minutes and causes a partial blocking of breathing in, while breathing out remains easier. It may be triggered when the vocal cords or the area of the trachea below the vocal folds detects the entry of water, mucus, blood, or other substance.  It is characterized by stridor or retractions. Some people have frequent laryngospasms, whether awake or asleep. In an ear, nose, and throat practice, it is typically seen in people who have silent reflux disease. It is also a well known, infrequent, but serious perioperative complication.It is likely that more than 10% of drownings involve laryngospasm, but the evidence suggests that it is not usually effective at preventing water from entering the trachea. (Full article...)
    Laryngospasm is an uncontrolled or involuntary muscular contraction (spasm) of the vocal folds. The condition typically lasts less than 60 seconds, but in some cases can last 20–30 minutes and causes a partial blocking of breathing in, while breathing out remains easier. It may be triggered when the vocal cords or the area of the trachea below the vocal folds detects the entry of water, mucus, blood, or other substance. It is characterized by stridor or retractions. Some people have frequent laryngospasms, whether awake or asleep. In an ear, nose, and throat practice, it is typically seen in people who have silent reflux disease. It is also a well known, infrequent, but serious perioperative complication.

    It is likely that more than 10% of drownings involve laryngospasm, but the evidence suggests that it is not usually effective at preventing water from entering the trachea. (Full article...)

Underwater tools and weapons

  • The 5.45mm ADS rifle
    The 5.45mm ADS rifle
  • Airlift dredging
    Airlift dredging
  • Image 3Powerhead 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. (Full article...)
    Powerhead may refer to:
    (Full article...)
  • Image 4The 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...)
    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...)
  • Assembled tremie placing concrete underwater
    Assembled tremie placing concrete underwater
  • Polespear under tension with a cluster head attached.
    Polespear under tension with a cluster head attached.
  • The Gyrojet carbine and rifle at the National Firearms Museum
    The Gyrojet carbine and rifle at the National Firearms Museum
  • The APS amphibious rifle, an underwater assault rifle
    The APS amphibious rifle, an underwater assault rifle
  • Image 9A 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...)
    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...)
  • 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.
    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.
  • Israeli Navy Underwater Missions Unit transfers equipment using lifting-bags
    Israeli Navy Underwater Missions Unit transfers equipment using lifting-bags
  • OS P11
    OS P11
  • SPP-1M
    SPP-1M
  • The ASM-DT Underwater Assault Rifle
    The ASM-DT Underwater Assault Rifle
  • APS underwater rifle with 5.66-mm cartridge
    APS underwater rifle with 5.66-mm cartridge

History of underwater diving

  • Image 1Brian 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...)
    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...)
  • Image 2Captain Albert Richard Behnke Jr. USN (ret.) (August 8, 1903 – January 16, 1992) was an American physician, who was principally responsible for developing the U.S. Naval Medical Research Institute. Behnke separated the symptoms of Arterial Gas Embolism (AGE) from those of decompression sickness and suggested the use of oxygen in recompression therapy.Behnke is also known as the "modern-day father" of human body composition for his work in developing the hydrodensitometry method of measuring body density, his standard man and woman models as well as a somatogram based on anthropometric measurements. (Full article...)
    Captain Albert Richard Behnke Jr. USN (ret.) (August 8, 1903 – January 16, 1992) was an American physician, who was principally responsible for developing the U.S. Naval Medical Research Institute. Behnke separated the symptoms of Arterial Gas Embolism (AGE) from those of decompression sickness and suggested the use of oxygen in recompression therapy.

    Behnke is also known as the "modern-day father" of human body composition for his work in developing the hydrodensitometry method of measuring body density, his standard man and woman models as well as a somatogram based on anthropometric measurements. (Full article...)
  • State of the art in the late 1960s - Underwater photographer Odd Henrik Johnsen
    State of the art in the late 1960s - Underwater photographer Odd Henrik Johnsen
  • USS Westchester County  underway, c. 1960
    USS Westchester County underway, c. 1960
  • Dr. Lambertsen, U.S. Army in 1942
    Dr. Lambertsen, U.S. Army in 1942
  • Image 6The 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. (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.
    (Full article...)
  • Image 7 Capt. Charles Wesley Shilling USN (ret.) (September 21, 1901 – December 23, 1994) was an American physician who was known as a leader in the field of undersea and hyperbaric medicine, research, and education. Shilling was widely recognized as an expert on deep sea diving, naval medicine, radiation biology, and submarine capabilities. In 1939, he was Senior Medical Officer in the rescue of the submarine U.S.S. Squalus. (Full article...)
  • NOAA drawing of Dr. Bond and the SEALAB habitat. (1960s) Captain George Bond's Discoveries Enable Divers to Stay Below Indefinitely
    NOAA drawing of Dr. Bond and the SEALAB habitat. (1960s) Captain George Bond's Discoveries Enable Divers to Stay Below Indefinitely
  • An Italian manned torpedo
    An Italian manned torpedo
  • Image 10Because Egypt had such valuable cargo, it was not long before salvage attempts began. However, the Egypt′s wreck was not found until 1930. She was found lying upright in a depth of 170 metres (560 ft), making the recovery very difficult with the technology of the time. Giovanni Quaglia from the Genoese company Società Ricuperi Marittimi (So.Ri.Ma.) was in charge of the operation and decided to use a diver in an armoured suit to direct the placing of explosives to blast through the ship to expose the strong room. The diver was then used to direct a grab which picked up the gold and silver. The salvage continued until 1935 by which time 98% of the contents of the strong room had been recovered. (Full article...)
    Because Egypt had such valuable cargo, it was not long before salvage attempts began. However, the Egypt′s wreck was not found until 1930. She was found lying upright in a depth of 170 metres (560 ft), making the recovery very difficult with the technology of the time. Giovanni Quaglia from the Genoese company Società Ricuperi Marittimi (So.Ri.Ma.) was in charge of the operation and decided to use a diver in an armoured suit to direct the placing of explosives to blast through the ship to expose the strong room. The diver was then used to direct a grab which picked up the gold and silver. The salvage continued until 1935 by which time 98% of the contents of the strong room had been recovered. (Full article...)
  • Image 11 Colonel William Paul Fife USAF (Ret) (November 23, 1917 – October 13, 2008) was a United States Air Force officer that first proved the feasibility for U.S. Air Force Security Service airborne Communications Intelligence (COMINT) collection and Fife is considered the "Father of Airborne Intercept". Fife was also a hyperbaric medicine specialist who was known for his pioneering research on pressurized environments ranging from high altitude to underwater habitats. Fife was a Professor Emeritus at Texas A&M University. (Full article...)
  • Image 12The Russian government committed to raising the wreck and recovering the crew's remains in a US$65M salvage operation. They contracted with Dutch marine salvage companies Smit International and Mammoet to raise Kursk from the sea floor. It became the largest salvage operation of its type ever accomplished. The salvage operation was extremely dangerous because of the risk of radiation from the reactor. Only seven of the submarine's 24 torpedoes were accounted for. (Full article...)
    The Russian government committed to raising the wreck and recovering the crew's remains in a US$65M 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...)
  • Image 13The 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. (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.
    (Full article...)
  • Image 14Defenses against swimmer incursions are security methods developed to protect watercraft, ports and installations, and other sensitive resources in or near vulnerable waterways from potential threats or intrusions by swimmers or scuba divers. (Full article...)
    Defenses against swimmer incursions are security methods developed to protect watercraft, ports and installations, and other sensitive resources in or near vulnerable waterways from potential threats or intrusions by swimmers or scuba divers. (Full article...)
  • Image 15Operation 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...)
    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...)

Diver training, registration and certification

Underwater diving organisations

Underwater diving publications

  • Image 1The Darkness Beckons (.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free a,.mw-parser-output .citation .cs1-lock-free a{background:linear-gradient(transparent,transparent),url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited a,.mw-parser-output .id-lock-registration a,.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration a{background:linear-gradient(transparent,transparent),url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription a,.mw-parser-output .citation .cs1-lock-subscription a{background:linear-gradient(transparent,transparent),url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:linear-gradient(transparent,transparent),url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:#d33}.mw-parser-output .cs1-visible-error{color:#d33}.mw-parser-output .cs1-maint{display:none;color:#3a3;margin-left:0.3em}.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}ISBN 0-939748-32-0) is the definitive book on the history of UK cave diving.It was written by Martyn Farr, a major figure in UK diving at a time when many of the original participants were still alive and available for interview. (Full article...)
    The Darkness Beckons (ISBN 0-939748-32-0) is the definitive book on the history of UK cave diving.

    It was written by Martyn Farr, a major figure in UK diving at a time when many of the original participants were still alive and available for interview. (Full article...)
  • Image 2Shadow 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...)
    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...)
  • Image 3The 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."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...)
    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."

    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...)
  • Image 4Goldfinder 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 called Damtor 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, Damtor 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...)
    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 called Damtor 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, Damtor 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...)
  • Image 5The Silent World (subtitle: A story of undersea discovery and adventure, by the first men to swim at record depths with the freedom of fish) is a 1953 book co-authored by Captain Jacques-Yves Cousteau and Frédéric Dumas, and edited by James Dugan. (Full article...)
    The 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...)
  • Image 6The 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...)
    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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  • In 1942–43 the UK Government carried out extensive testing for oxygen toxicity in divers. The chamber is pressurised with air to 3.7 bar. The subject in the centre is breathing 100% oxygen from a mask.
    In 1942–43 the UK Government carried out extensive testing for oxygen toxicity in divers. The chamber is pressurised with air to 3.7 bar. The subject in the centre is breathing 100% oxygen from a mask.
  • Map of Bowie Seamount
    Map of Bowie Seamount
  • A recompression chamber is used to treat some diving disorders and for training divers to recognise the symptoms.
    A recompression chamber is used to treat some diving disorders and for training divers to recognise the symptoms.
  • Surface supplied diver on diving stage
    Surface supplied diver on diving stage
  • Diving cylinders to be filled at a diving air compressor station
    Diving cylinders to be filled at a diving air compressor station
  • Divers decompressing in the water at the end of a dive
    Divers decompressing in the water at the end of a dive
  • Solo diver surveying a dive site. The bailout cylinder can be seen slung at the diver's left side
    Solo diver surveying a dive site. The bailout cylinder can be seen slung at the diver's left side
  • Two United States Navy sailors demonstrate treatment for decompression sickness inside a decompression chamber
    Two United States Navy sailors demonstrate treatment for decompression sickness inside a decompression chamber
  • The hand signal "OK"
    The hand signal "OK"
  • Divers breathe a mixture of oxygen, helium and nitrogen for deep dives to avoid the effects of narcosis. A cylinder label shows the maximum operating depth and mixture (oxygen/helium).
    Divers breathe a mixture of oxygen, helium and nitrogen for deep dives to avoid the effects of narcosis. A cylinder label shows the maximum operating depth and mixture (oxygen/helium).
  • Cap badge of the Special Boat Service
    Cap badge of the Special Boat Service
  • 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.
    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.
  • 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.
    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.

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The arterial pressure can be taken in man as rapidly, simply, and accurately as the temperature can be taken with the clinical thermometer.

— Leonard Erskine Hill

Hill, A. B.; Hill, B. (1968). "The life of Sir Leonard Erskine Hill FRS (1866-1952)". Proceedings of the Royal Society of Medicine. 61 (3): 307–316. PMC 1902312. PMID 4868973.

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