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130-515: The Sub-Aqua Association ( SAA ) is a diver training organization for scubadivers in the United Kingdom . The SAA and other UK-based diving groups have traditionally used a club-based system with unpaid instructors, while other training agencies organise most of their training programs through professional instructors and dive shops. The other major club-based diving organizations in the UK are

260-492: A deck chamber . A wet bell with a gas filled dome provides more comfort and control than a stage and allows for longer time in water. Wet bells are used for air and mixed gas, and divers can decompress on oxygen at 12 metres (40 ft). Small closed bell systems have been designed that can be easily mobilised, and include a two-man bell, a launch and recovery system and a chamber for decompression after transfer under pressure (TUP). Divers can breathe air or mixed gas at

390-497: A helmet , including the standard copper helmet, and other forms of free-flow and lightweight demand helmets . The history of breath-hold diving goes back at least to classical times, and there is evidence of prehistoric hunting and gathering of seafoods that may have involved underwater swimming. Technical advances allowing the provision of breathing gas to a diver underwater at ambient pressure are recent, and self-contained breathing systems developed at an accelerated rate following

520-423: A suit of armour , with elaborate joints to allow bending, while maintaining an internal pressure of one atmosphere. An ADS can be used for dives of up to about 700 metres (2,300 ft) for many hours. It eliminates the majority of physiological dangers associated with deep diving – the occupant does not need to decompress, there is no need for special gas mixtures, and there is no danger of nitrogen narcosis – at

650-435: A consistently higher threshold of hearing underwater; sensitivity to higher frequency sounds is reduced the most. The type of headgear affects noise sensitivity and noise hazard depending on whether transmission is wet or dry. Human hearing underwater is less sensitive with wet ears than in air, and a neoprene hood causes substantial attenuation. When wearing a helmet, hearing sensitivity is similar to that in surface air, as it

780-438: A dive, kitting up for the dive, water entry, descent, breathing underwater, monitoring the dive profile (depth, time and decompression status), personal breathing gas management, situational awareness, communicating with the dive team, buoyancy and trim control, mobility in the water, ascent, emergency and rescue procedures, exit from the water, unkitting after the dive, cleaning and preparation of equipment for storage and recording

910-423: A formal training environment for the components specified by diver training standards and for which certification is issued. There are also non-formal and informal aspects where certified divers extend their competence and experience by practicing the basic skills and learning other complementary skills in the field. Prior learning may be recognised where applicable and permitted by the training standard. This

1040-414: A full-face mask or helmet, and gas may be supplied on demand or as a continuous free flow. More basic equipment that uses only an air hose is called an airline or hookah system. This allows the diver to breathe using an air supply hose from a high pressure cylinder or diving air compressor at the surface. Breathing gas is supplied through a mouth-held demand valve or light full-face mask. Airline diving

1170-412: A higher level of fitness may be needed for some applications. An alternative to self-contained breathing systems is to supply breathing gases from the surface through a hose. When combined with a communication cable, a pneumofathometer hose and a safety line it is called the diver's umbilical , which may include a hot water hose for heating, video cable and breathing gas reclaim line. The diver wears

1300-404: A large number of divers never progress beyond the entry level certification, and only dive on vacation, a system by which skills are more likely to deteriorate than improve due to long periods of inactivity. This may be mitigated by refresher courses , which tend to target skills particularly important in the specific region, and may focus on low impact diving skills, to protect the environment that

1430-615: A long history of military frogmen in various roles. They can perform roles including direct combat, reconnaissance, infiltration behind enemy lines, placing mines, bomb disposal or engineering operations. In civilian operations, police diving units perform search and rescue operations, and recover evidence. In some cases diver rescue teams may also be part of a fire department , paramedical service , sea rescue or lifeguard unit, and this may be classed as public safety diving . There are also professional media divers such as underwater photographers and videographers , who record

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1560-447: A long period of exposure, rather than after each of many shorter exposures, the overall risk of decompression injury to the diver and the total time spent decompressing are reduced. This type of diving allows greater work efficiency and safety. Commercial divers refer to diving operations where the diver starts and finishes the diving operation at atmospheric pressure as surface oriented , or bounce diving. The diver may be deployed from

1690-506: A maximum depth of 18 m, with no decompression obligation. This also encourages the diver to attend further training if they wish to achieve more than minimum competence. The training is short, convenient, and minimal. The cost is low in absolute terms, but accumulates with further training, for those few who undertake it. Professional diver training, and the associated assessment and certification of competence, are usually based on occupational health and safety legislation, and also covered by

1820-451: A measure of literacy and numeracy is necessary to allow a reasonable chance of success with the theoretical knowledge requirements, and for effective on-site communication within the dive team. The international lingua franca of offshore diving operations is English. Some training standards include an ability to swim as a prerequisite. Diver training is a form of competency-based adult education that generally occurs at least partly in

1950-454: A net positive effect, when effectively treating an underlying condition, but frequently the side effects of effective medication may have undesirable influences on the fitness of diver, and most cases of recreational drug use result in an impaired fitness to dive, and a significantly increased risk of sub-optimal response to emergencies. Formal educational prerequisites are variable. Diving skills are largely physical, but for professional diving

2080-608: A newly qualified recreational diver may dive purely for the experience of diving, most divers have some additional reason for being underwater. Recreational diving is purely for enjoyment and has several specialisations and technical disciplines to provide more scope for varied activities for which specialist training can be offered, such as cave diving , wreck diving , ice diving and deep diving . Several underwater sports are available for exercise and competition. There are various aspects of professional diving that range from part-time work to lifelong careers. Professionals in

2210-553: A similar diving reflex. The diving reflex is triggered by chilling the face and holding the breath. The cardiovascular system constricts peripheral blood vessels, slows the pulse rate, redirects blood to the vital organs to conserve oxygen, releases red blood cells stored in the spleen , and, in humans, causes heart rhythm irregularities. Aquatic mammals have evolved physiological adaptations to conserve oxygen during submersion, but apnea, slowed pulse rate, and vasoconstriction are shared with terrestrial mammals. Cold shock response

2340-406: A truly informed choice less likely. 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

2470-420: Is a branch of occupational medicine and sports medicine, and first aid for diving injuries an important part of diver education. Teaching of diving theory is usually provided as classroom lecture sessions with formative assessment tasks and exercises and a written examination for final assessment. Blended learning is used by some agencies and schools to ensure a more consistent standard. A working knowledge of

2600-846: Is a member of the British Diving Safety Group (BDSG), CMAS Europe . and the Joint Nautical Archaeology Policy Committee (JNAPC). It also collaborates with other external organisations, such as the Marine Conservation Society , Seasearch, and other environmental groups, the media, and examination boards to provide advice and expertise. The SAA also acts as an advocate for amateur divers in the UK, representing their views to government agencies and similar bodies. Diver training Recreational diver training has historically followed two philosophies, based on

2730-406: Is a response to immersion that overrides the basic homeostatic reflexes . It optimises respiration by preferentially distributing oxygen stores to the heart and brain, which allows extended periods underwater. It is exhibited strongly in aquatic mammals ( seals , otters , dolphins and muskrats ), and also exists in other mammals, including humans . Diving birds , such as penguins , have

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2860-490: Is a robot which travels underwater without requiring real-time input from an operator. AUVs constitute part of a larger group of unmanned undersea systems, a classification that includes non-autonomous ROVs, which are controlled and powered from the surface by an operator/pilot via an umbilical or using remote control. In military applications AUVs are often referred to as unmanned undersea vehicles (UUVs). People may dive for various reasons, both personal and professional. While

2990-666: Is a single club with many branches. Sub-Aqua Association member clubs maintain their independence and individual clubs organize diving programs and instruction according to the national standards of the association. The association provides regional and national support for these activities. The SAA is one of two UK affiliates to World Underwater Federation (CMAS), the international umbrella organisation for diver training organizations, and has voting rights for both CMAS Technical and Scientific Committees. Application for CMAS cards (qualification or "C-cards") for divers in Great Britain

3120-400: Is affected by the clarity and the refractive index of the medium. Visibility underwater is reduced because light passing through water attenuates rapidly with distance, leading to lower levels of natural illumination. Underwater objects are also blurred by scattering of light between the object and the viewer, resulting in lower contrast. These effects vary with the wavelength of the light, and

3250-481: Is also restricted to conditions which are not excessively hazardous, though the level of risk acceptable can vary, and fatal incidents may occur. Recreational diving (sometimes called sport diving or subaquatics) is a popular leisure activity. Technical diving is a form of recreational diving under more challenging conditions. Professional diving (commercial diving, diving for research purposes, or for financial gain) involves working underwater. Public safety diving

3380-441: Is an important aspect of recreational diver training. Professional diving operations are usually formally planned and the plan documented as a legal record that due diligence has been done for health and safety purposes. Recreational dive planning may be less formal, but for complex technical dives , can be as formal, detailed and extensive as most professional dive plans. A professional diving contractor will be constrained by

3510-403: Is considered a useful emergency skill, an important part of water sport and Navy safety training, and an enjoyable leisure activity. Underwater diving without breathing apparatus can be categorised as underwater swimming, snorkelling and freediving. These categories overlap considerably. Several competitive underwater sports are practised without breathing apparatus. Freediving precludes

3640-463: Is contact with the water as the acoustic properties are similar. When the head is exposed to the water, some sound is transmitted by the eardrum and middle ear, but a significant part reaches the cochlea independently, by bone conduction. Some sound localisation is possible, though difficult. Human hearing underwater, in cases where the diver's ear is wet, is less sensitive than in air. Frequency sensitivity underwater also differs from that in air, with

3770-587: Is done via the SAA and its qualifications are accepted worldwide through the CMAS affiliation. The association's training focuses on preparedness for the relatively cold and often visibility restricted waters around the UK. The SAA training also aims to be as comprehensive as possible, emphasizing rescue training very early in the programme. The association exercises regulation of its membership and has disqualified divers found guilty of breaches of its safety rules. The SAA

3900-403: Is essential for the assessment of the risk to which they or the people for whom they have a duty of care will be exposed while diving. 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

4030-430: Is evidence of a slight decrease in threshold for taste and smell after extended periods under pressure. There are several modes of diving distinguished largely by the breathing gas supply system used, and whether the diver is exposed to the ambient pressure. The diving equipment , support equipment and procedures are largely determined by the mode. The ability to dive and swim underwater while holding one's breath

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4160-427: Is expected to understand the hazards, risks and potential consequences of diving at work and using the equipment provided in the environment of the project, and though risk assessment and team safety on the job are primarily the responsibility of the supervisor and the employer, the diver is also responsible as a member of the team and is expected to have sufficient knowledge of the processes and risks to reasonably accept

4290-535: Is generally responsible for their own safety, and to a lesser, variable, and poorly defined extent, for the safety of their dive buddy . The primary goal of entry level diver training is to prepare the diver to dive safely in the general underwater environment that they are likely to experience during the course of a reasonably planned and executed dive in conditions similar to those in which they were trained, using similar equipment. Most further training provides knowledge and skills allowing diving in acceptable safety in

4420-568: Is immersed. Snorkelling on the surface with no intention of diving is a popular water sport and recreational activity. Scuba diving is diving with a self-contained underwater breathing apparatus , which is completely independent of surface supply. Scuba gives the diver mobility and horizontal range far beyond the reach of an umbilical hose attached to surface-supplied diving equipment (SSDE). Scuba divers engaged in armed forces covert operations may be referred to as frogmen , combat divers or attack swimmers. Open circuit scuba systems discharge

4550-476: Is limited to the physiological capacity to perform the dive on the oxygen available until it returns to a source of fresh breathing gas, usually the air at the surface. As this internal oxygen supply reduces, the animal experiences an increasing urge to breathe caused by buildup of carbon dioxide and lactate in the blood, followed by loss of consciousness due to cerebral hypoxia . If this occurs underwater, it will drown. Blackouts in freediving can occur when

4680-482: Is lost much more quickly in water than in air, so water temperatures that would be tolerable as outdoor air temperatures can lead to hypothermia, which may lead to death from other causes in inadequately protected divers. Thermoregulation of divers is complicated by breathing gases at raised ambient pressure and by gas mixtures necessary for limiting inert gas narcosis, work of breathing, and for accelerating decompression. Breath-hold diving by an air-breathing animal

4810-418: Is necessary for the diver to be competent to reasonably assess and accept the risk of a planned dive. The professional diver can to some extent rely on the diving supervisor, who is appointed to manage the risk of a diving operation, and a diver in training can expect the instructor to adequately assess risk on training dives. Certification agencies minimise their responsibility by limiting the conditions in which

4940-424: Is not greatly affected by the breathing gas or chamber atmosphere composition or pressure. Because sound travels faster in heliox than in air, voice formants are raised, making divers' speech high-pitched and distorted, and hard to understand for people not used to it. The increased density of breathing gases under pressure has a similar and additive effect. Tactile sensory perception in divers may be impaired by

5070-457: Is poorly defined and with some exceptions, the diver is not legally obliged to dive with a buddy unless they choose to. The professional diver is a member of a diving team and has legally defined duty of care to other members of the team. Recreational diver training prepares the diver for low stress diving in an environment similar to the one they were trained in, using equipment similar to that used in training. Professional diver training prepares

5200-535: Is reduced compared to that of open circuit, so a smaller cylinder or cylinders may be used for an equivalent dive duration. They greatly extend the time spent underwater as compared to open circuit for the same gas consumption. Rebreathers produce fewer bubbles and less noise than scuba which makes them attractive to covert military divers to avoid detection, scientific divers to avoid disturbing marine animals, and media divers to avoid bubble interference. A scuba diver moves underwater primarily by using fins attached to

5330-486: Is reduced core body temperature that occurs when a body loses more heat than it generates. It is a major limitation to swimming or diving in cold water. The reduction in finger dexterity due to pain or numbness decreases general safety and work capacity, which in turn increases the risk of other injuries. Non-freezing cold injury can affect the extremities in cold water diving, and frostbite can occur when air temperatures are low enough to cause tissue freezing. Body heat

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5460-409: Is regulated within the recreational diver training industry, within each certification agency, and tends to be kept to a minimum to keep costs down in a competitive environment, and because of customer pressure to minimise the effort involved. Consequently, the entry level certification for most recreational divers advises them to dive only in conditions similar to those in which they were trained, and to

5590-400: Is the physiological response of organisms to sudden cold, especially cold water, and is a common cause of death from immersion in very cold water, such as by falling through thin ice. The immediate shock of the cold causes involuntary inhalation, which if underwater can result in drowning. The cold water can also cause heart attack due to vasoconstriction; the heart has to work harder to pump

5720-406: Is the practical application of theoretical knowledge and understanding of diving to an intended underwater diving operation with the purpose of increasing the probability that a dive will be completed safely and the goals achieved. Some form of planning is done for most underwater dives, but the complexity and detail considered may vary enormously. In most professional diving, dive planning is mainly

5850-414: Is the underwater work done by law enforcement, fire rescue, and underwater search and recovery dive teams. Military diving includes combat diving, clearance diving and ships husbandry . Deep sea diving is underwater diving, usually with surface-supplied equipment, and often refers to the use of standard diving dress with the traditional copper helmet. Hard hat diving is any form of diving with

5980-414: Is typically done by assessment against the requirements of the standards using the same methods as in formal training programmes for safety-critical skills and knowledge, and by accepting verifiable evidence of experience, as in signed and witnessed logbook entries. Diving theory is the basic knowledge of the physical and physiological effects of the underwater environment on the diver. Diving physics are

6110-410: Is used for work such as hull cleaning and archaeological surveys, for shellfish harvesting, and as snuba , a shallow water activity typically practised by tourists and those who are not scuba-certified. Saturation diving lets professional divers live and work under pressure for days or weeks at a time. After working in the water, the divers rest and live in a dry pressurised underwater habitat on

6240-417: Is usually due to over-stretching the tissues in tension or shear, either directly by expansion of the gas in the closed space, or by pressure difference hydrostatically transmitted through the tissue. Barotrauma generally manifests as sinus or middle ear effects, decompression sickness, lung over-expansion injuries, and injuries resulting from external squeezes. Barotraumas of descent are caused by preventing

6370-550: Is usually the choice if safety and legal constraints allow. Higher risk work, particularly commercial diving, may be restricted to surface-supplied equipment by legislation and codes of practice. Freediving as a widespread means of hunting and gathering, both for food and other valuable resources such as pearls and coral , dates from before 4500 BCE. By classical Greek and Roman times commercial diving applications such as sponge diving and marine salvage were established. Military diving goes back at least as far as

6500-598: The British Sub-Aqua Club (BSAC) and the Scottish Sub Aqua Club , and the principal non-club-based organisation is PADI . The Sub-Aqua Association was created in 1976 to represent diving clubs outside of the BSAC branch structure. Its training structure is based on the BSAC levels and offers a full range of diving qualifications. The association is made up of independent clubs, while the BSAC

6630-482: The Peloponnesian War , with recreational and sporting applications being a recent development. Technological development in ambient pressure diving started with stone weights ( skandalopetra ) for fast descent, with rope assist for ascent. The diving bell is one of the earliest types of equipment for underwater work and exploration. Its use was first described by Aristotle in the 4th century BCE. In

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6760-593: The Second World War . Immersion in water and exposure to cold water and high pressure have physiological effects on the diver which limit the depths and duration possible in ambient pressure diving. Breath-hold endurance is a severe limitation, and breathing at high ambient pressure adds further complications, both directly and indirectly. Technological solutions have been developed which can greatly extend depth and duration of human ambient pressure dives, and allow useful work to be done underwater. Immersion of

6890-414: The diver certification organisations which issue these diver certifications . These include standard operating procedures for using the equipment and dealing with the general hazards of the underwater environment , and emergency procedures for self-help and assistance of a similarly equipped diver experiencing problems. A minimum level of fitness and health is required by most training organisations, and

7020-424: The saturation diving technique reduces the risk of decompression sickness (DCS) after long-duration deep dives. Atmospheric diving suits (ADS) may be used to isolate the diver from high ambient pressure. Crewed submersibles can extend depth range to full ocean depth , and remotely controlled or robotic machines can reduce risk to humans. The environment exposes the diver to a wide range of hazards, and though

7150-771: The standard diving dress , which made a far wider range of marine civil engineering and salvage projects practicable. Limitations in mobility of the surface-supplied systems encouraged the development of both open circuit and closed circuit scuba in the 20th century, which allow the diver a much greater autonomy. These became popular during the Second World War for clandestine military operations , and post-war for scientific , search and rescue, media diving , recreational and technical diving . The heavy free-flow surface-supplied copper helmets evolved into lightweight demand helmets , which are more economical with breathing gas, important for deeper dives using expensive helium based breathing mixtures . Saturation diving reduced

7280-472: The symptoms caused by decompression occur during or within a relatively short period of minutes to hours, or occasionally days, after a significant pressure reduction. The term "decompression" derives from the reduction in ambient pressure experienced by the organism and refers to both the reduction in pressure and the process of allowing dissolved inert gases to be eliminated from the tissues during and after this reduction in pressure. The uptake of gas by

7410-422: The 16th and 17th centuries CE, diving bells became more useful when a renewable supply of air could be provided to the diver at depth, and progressed to surface-supplied diving helmets – in effect miniature diving bells covering the diver's head and supplied with compressed air by manually operated pumps – which were improved by attaching a waterproof suit to the helmet. In the early 19th century these became

7540-534: The ability to judge relative distances of different objects, is considerably reduced underwater, and this is affected by the field of vision. A narrow field of vision caused by a small viewport in a helmet results in greatly reduced stereoacuity, and an apparent movement of a stationary object when the head is moved. These effects lead to poorer hand-eye coordination. Water has different acoustic properties from those of air. Sound from an underwater source can propagate relatively freely through body tissues where there

7670-446: The actual working skills required to do the job, and the procedures for safe operation of the work equipment other than diving equipment that may be needed. Some of the skills are common to all types of surface-supplied equipment and deployment modes, others are specific to the type of bell or stage used, or to saturation diving . There are other skills required of divers which apply to the surface support function, which are necessary as

7800-424: The aspects of physics which directly affect the underwater diver and which explain the effects that divers and their equipment are subject to underwater which differ from the normal human experience out of water. These effects are mostly consequences of immersion in water, the hydrostatic pressure of depth and the effects of the pressure on breathing gases. An understanding of the physics is useful when considering

7930-405: The boat through plastic tubes. There is no reduction valve; the diver holds the hose end in his mouth with no demand valve or mouthpiece and allows excess air to spill out between the lips. Submersibles and rigid atmospheric diving suits (ADS) enable diving to be carried out in a dry environment at normal atmospheric pressure. An ADS is a small one-person articulated submersible which resembles

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8060-415: The body from head-out immersion causes negative pressure breathing which contributes to the blood shift. The blood shift causes an increased respiratory and cardiac workload. Stroke volume is not greatly affected by immersion or variation in ambient pressure, but slowed heartbeat reduces the overall cardiac output, particularly because of the diving reflex in breath-hold diving . Lung volume decreases in

8190-424: The bottom and are usually recovered with the chamber filled with air. They decompress on oxygen supplied through built in breathing systems (BIBS) towards the end of the decompression. Small bell systems support bounce diving down to 120 metres (390 ft) and for bottom times up to 2 hours. A relatively portable surface gas supply system using high pressure gas cylinders for both primary and reserve gas, but using

8320-407: The bottom or a saturation life support system of pressure chambers on the deck of a diving support vessel , oil platform or other floating platform at a similar pressure to the work depth. They are transferred between the surface accommodation and the underwater workplace in a pressurised closed diving bell . Decompression at the end of the dive may take many days, but since it is done only once for

8450-443: The breath is held long enough for metabolic activity to reduce the oxygen partial pressure sufficiently to cause loss of consciousness. This is accelerated by exertion, which uses oxygen faster, and can be exacerbated by hyperventilation directly before the dive, which reduces the carbon dioxide level in the blood. Lower carbon dioxide levels increase the oxygen-haemoglobin affinity, reducing availability of oxygen to brain tissue towards

8580-418: The breathing gas into the environment as it is exhaled, and consist of one or more diving cylinders containing breathing gas at high pressure which is supplied to the diver through a diving regulator . They may include additional cylinders for decompression gas or emergency breathing gas. Closed-circuit or semi-closed circuit rebreather scuba systems allow recycling of exhaled gases. The volume of gas used

8710-399: The breathing gas, artifacts of the breathing apparatus, and hydrostatic pressure variations due to posture in the water. The underwater environment also affects sensory input, which can impact on safety and the ability to function effectively at depth. Decompression theory is the study and modelling of the transfer of the inert gas component of breathing gases from the gas in the lungs to

8840-565: The business structure of the training agencies. The not-for profit agencies tend to focus on developing the diver's competence in relatively fewer stages, and provide more content over a longer programme, than the for-profit agencies, which maximise profit and customer convenience by providing a larger number of shorter courses with less content and fewer skills per course. The more advanced skills and knowledge, including courses focusing on key diving skills like good buoyancy control and trim, and environmental awareness, are available by both routes, but

8970-446: The central nervous system to provide the sense of balance. Underwater, some of these inputs may be absent or diminished, making the remaining cues more important. Conflicting input may result in vertigo, disorientation and motion sickness . The vestibular sense is essential in these conditions for rapid, intricate and accurate movement. Proprioceptive perception makes the diver aware of personal position and movement, in association with

9100-403: The certification will be defined by the competence requirements for dive planning. Assessment of dive planning competence is commonly a combination of written exams on the details, and direct observation of performance of dive planning tasks. Professional divers are required to be familiar with the law regulating their occupation, and any national or international codes of practice that apply in

9230-399: The circumstances it may be established by a signed statement by the diver that he or she does not suffer from any of the listed disqualifying conditions and is able to manage the ordinary physical requirements of diving, to a detailed medical examination by a physician registered as a medical examiner of divers following a procedural checklist, and a legal document of fitness to dive issued by

9360-415: The code of practice, standing orders or regulatory legislation covering a project or specific operations within a project, and is responsible for ensuring that the scope of work to be done is within the scope of the rules relevant to that work. A recreational (including technical) diver or dive group is generally less constrained, but nevertheless is almost always restricted by some legislation, and often also

9490-437: The colour and turbidity of the water. The human eye is optimised for air vision, and when it is immersed in direct contact with water, visual acuity is adversely affected by the difference in refractive index between water and air. Provision of an airspace between the cornea and the water can compensate, but causes scale and distance distortion. Artificial illumination can improve visibility at short range. Stereoscopic acuity,

9620-451: 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, but often a lower level of understanding when the circumstances are beyond their certification level and personal experience, making

9750-550: 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

9880-430: The dive team. The underwater environment can impose severe physiological 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

10010-448: The dive will be conducted. A diving project may consist of a number of related diving operations. A documented dive plan may contain elements from the following list: For scuba dives, selection of the breathing gases and calculation of the required quantities is one of the most complex parts of dive planning, and is done in parallel with planning of the dive profile and decompression plan. The general aspects of dive planning include

10140-430: The dive, within the scope of the diver's certification. Some of these skills affect the diver's ability to minimise adverse environmental impact. Surface supplied diving skills are the skills and procedures required for the safe operation and use of surface-supplied diving equipment . Besides these skills, which may be categorised as standard operating procedures, emergency procedures and rescue procedures, there are

10270-453: The diver for a working environment in which the diver is expected to work as a member of a team, and be involved in organisation, planning, setting up of the infrastructure, selection and maintenance of the diving and work related equipment, where conditions may be less than ideal, and there may be time constraints. The professional diver must be able to make a realistic and informed decision on acceptability of risk. Recreational diver training

10400-466: The diver is also expected to work in a support capacity as a member of the diving team . Underwater diving Underwater diving , as a human activity, is the practice of descending below the water's surface to interact with the environment. It is also often referred to as diving , an ambiguous term with several possible meanings, depending on context. Immersion in water and exposure to high ambient pressure have physiological effects that limit

10530-420: The diver is considered competent. Both recreational and professional diving occur in the underwater environment, which presents the same basic hazards to both groups. The professional diver has a job to do in this environment, which may expose them to additional hazards associated with the work. The recreational diver usually has no legal duty of care to other divers. The duty of care to a recreational dive buddy

10660-408: The diving environment in which the diver is likely to operate is necessary so that the diver can to some extent understand and predict the likely conditions they will experience while diving, and the associated hazards and risks. This knowledge is also necessary for informed consent in terms of health and safety legislation, and for diving supervisors, instructors, dive leaders and recreational divers it

10790-446: The duration of a dive, but there are other problems that may result from this technological solution. Absorption of metabolically inert gases is increased as a function of time and pressure, and these may both produce undesirable effects immediately, as a consequence of their presence in the tissues in the dissolved state, such as nitrogen narcosis and high pressure nervous syndrome , or cause problems when coming out of solution within

10920-463: The employer's duty of care. The training standards are usually aligned with internationally recognised standards, and are expected to follow quality assurance procedures. The professional diver with entry level qualification is expected to perform duties as working diver, diver's attendant, and standby (rescue) diver, and must be competent and fit to perform all these tasks, as well as the basic skills of staying alive underwater and not getting injured, and

11050-414: The end of the dive ( Bohr effect ); they also suppress the urge to breathe, making it easier to hold the breath to the point of blackout. This can happen at any depth. Ascent-induced hypoxia is caused by a drop in oxygen partial pressure as ambient pressure is reduced. The partial pressure of oxygen at depth may be sufficient to maintain consciousness at that depth and not at the reduced pressures nearer

11180-547: The environmental protection suit and low temperatures. The combination of instability, equipment, neutral buoyancy and resistance to movement by the inertial and viscous effects of the water encumbers the diver. Cold causes losses in sensory and motor function and distracts from and disrupts cognitive activity. The ability to exert large and precise force is reduced. Balance and equilibrium depend on vestibular function and secondary input from visual, organic, cutaneous, kinesthetic and sometimes auditory senses which are processed by

11310-451: The expanded range of conditions, and with the equipment associated with the specific training programme. Prerequisite competences are stipulated to ensure that the diver has the skills and knowledge to seamlessly continue with further training without critical gaps in competence or understanding, which could lead to unsafe diving. Skill retention and improvement depend on practicing the skills sufficiently after initial training. Dive planning

11440-412: The expense of higher cost, complex logistics and loss of dexterity. Crewed submeribles have been built rated to full ocean depth and have dived to the deepest known points of all the oceans. Autonomous underwater vehicles (AUVs) and remotely operated underwater vehicles (ROVs) can carry out some functions of divers. They can be deployed at greater depths and in more dangerous environments. An AUV

11570-461: The feet; external propulsion can be provided by a diver propulsion vehicle , or a towboard pulled from the surface. Other equipment includes a diving mask to improve underwater vision , a protective diving suit , equipment to control buoyancy , and equipment related to the specific circumstances and purpose of the dive. Scuba divers are trained in the procedures and skills appropriate to their level of certification by instructors affiliated to

11700-430: The following, but not all of these apply to every dive, and in many cases there is no choice available to the diver, who must work within the constraints of what is available and appropriate to their level of competence. Planning of a complex dive may be an iterative process, and the order of steps may vary. Teaching of dive planning typically omits any aspects not relevant to the certification level, and to some extent

11830-425: The free change of volume of the gas in a closed space in contact with the diver, resulting in a pressure difference between the tissues and the gas space, and the unbalanced force due to this pressure difference causes deformation of the tissues resulting in cell rupture. Barotraumas of ascent are also caused when the free change of volume of the gas in a closed space in contact with the diver is prevented. In this case

11960-515: The full diver's umbilical system with pneumofathometer and voice communication, is known in the industry as "scuba replacement". Compressor diving is a rudimentary method of surface-supplied diving used in some tropical regions such as the Philippines and the Caribbean . The divers swim with a half mask and fins and are supplied with air from an industrial low-pressure air compressor on

12090-427: The harmful cold shock response, the helpful diving reflex and excessive loss of body heat. Breath-hold duration is limited by oxygen reserves, and the risk of hypoxic blackout, which has a high associated risk of drowning. Large or sudden changes in ambient pressure have the potential for injury known as barotrauma. Breathing under pressure involves several effects. Metabolically inactive gases are absorbed by

12220-473: The human body in water affects the circulation , renal system , fluid balance , and breathing, because the external hydrostatic pressure of the water provides support against the internal hydrostatic pressure of the blood. This causes a blood shift from the extravascular tissues of the limbs into the chest cavity, and fluid losses known as immersion diuresis compensate for the blood shift in hydrated subjects soon after immersion. Hydrostatic pressure on

12350-418: The increased concentration at high pressures. Hydrostatic pressure differences between the interior of the lung and the breathing gas delivery, increased breathing gas density due to ambient pressure, and increased flow resistance due to higher breathing rates may all cause increased work of breathing , fatigue of the respiratory muscles, and a physiological limit to effective ventilation. Underwater vision

12480-491: The late 20th century, where the operator controls the ROV from the surface, and autonomous underwater vehicles (AUV), which dispense with an operator altogether. All of these modes are still in use and each has a range of applications where it has advantages over the others, though diving bells have largely been relegated to a means of transport for surface-supplied divers. In some cases combinations are particularly effective, such as

12610-465: 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

12740-688: The medical examiner. The most important medical is the one before starting diving, as the diver can be screened to prevent exposure when a dangerous condition exists. Other important medicals are after some significant illness where medical intervention is needed. This has to be done by a doctor who is competent in diving medicine, and can not be done by prescriptive rules. Psychological factors can affect fitness to dive, particularly where they affect response to emergencies, or risk taking behaviour. The use of medical and recreational drugs, can also influence fitness to dive, both for physiological and behavioural reasons. In some cases prescription drug use may have

12870-443: 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

13000-444: The organism during and after changes in ambient pressure, and provides mathematical models which attempt to predict acceptably low risk and reasonably practicable procedures for decompression in the field. Both deterministic and probabilistic models have been used, and are still in use. Diving medicine, also called undersea and hyperbaric medicine (UHB), is the diagnosis, treatment and prevention of conditions caused by humans entering

13130-471: The physiological effects of diving and the hazards and risks of diving . Diving physiology is the physiological influences of the underwater environment on the physiology of air-breathing animals, and the adaptations to operating underwater, both during breath-hold dives and while breathing at ambient pressure from a suitable breathing gas supply. It, therefore, includes both the physiology of breath-hold diving in humans and other air-breathing animals, and

13260-476: The pressure difference causes a resultant tension in the surrounding tissues which exceeds their tensile strength. Besides tissue rupture, the overpressure may cause ingress of gases into the adjoining tissues and further afield by bubble transport through the circulatory system. This can cause blockage of circulation at distant sites, or interfere with the normal function of an organ by its presence. Provision of breathing gas at ambient pressure can greatly prolong

13390-459: The prevention of diving disorders, treatment of diving accidents and diving fitness. The field includes the effect of breathing gases and their contaminants under high pressure on the human body and the relationship between the state of physical and psychological health of the diver and safety. In diving accidents it is common for multiple disorders to occur together and interact with each other, both causatively and as complications. Diving medicine

13520-598: The range of physiological effects generally limited to human ambient pressure divers either freediving or using underwater breathing apparatus . Several factors influence the diver, including immersion, exposure to the water, the limitations of breath-hold endurance, variations in ambient pressure, the effects of breathing gases at raised ambient pressure, effects caused by the use of breathing apparatus, and sensory impairment. All of these may affect diver performance and safety. Immersion affects fluid balance, circulation and work of breathing. Exposure to cold water can result in

13650-674: The recreational diving industry include instructor trainers, diving instructors, assistant instructors, divemasters , dive guides, and scuba technicians. A scuba diving tourism industry has developed to service recreational diving in regions with popular dive sites. Commercial diving is industry related and includes engineering tasks such as in hydrocarbon exploration , offshore construction , dam maintenance and harbour works. Commercial divers may also be employed to perform tasks related to marine activities, such as naval diving , ships husbandry , marine salvage or aquaculture . Other specialist areas of diving include military diving , with

13780-433: The region where they will practice. National legislation will commonly be included in the curriculum for entry level professional diving, and may be recognised as prior learning for further diver training. The level of knowledge required of a diving supervisor is considerably higher, and is usually part of supervisor training and assessment. Occupational heath and safety are important aspects of professional diving. The diver

13910-420: The responsibility of the supervisor, but the diver is expected to understand the process sufficiently to know when it has been done correctly, and what variations might be acceptable. In recreational diving, unless under training, the diver is generally considered equally responsible for the planning of any dive they participate in, along with the other involved divers, so dive planning at the level of certification

14040-661: The risk assessment. Diving skills can be grouped by skills relating to the mode of diving – freediving, scuba, surface supplied or saturation diving – and whether the skill is a standard skill used in everyday diving, an emergency skill to keep oneself alive when something goes wrong, or a rescue skill to be used in the attempt to assist another diver in difficulty. Scuba skills are the skills required to dive safely using self-contained underwater breathing apparatus , (scuba). Most of these skills are relevant to both open circuit and rebreather scuba , and many are also relevant to surface-supplied diving . Those skills which are critical to

14170-604: The risks are largely controlled by appropriate diving skills , training , types of equipment and breathing gases used depending on the mode, depth and purpose of diving, it remains a relatively dangerous activity. Professional diving is usually regulated by occupational health and safety legislation, while recreational diving may be entirely unregulated. Diving activities are restricted to maximum depths of about 40 metres (130 ft) for recreational scuba diving, 530 metres (1,740 ft) for commercial saturation diving, and 610 metres (2,000 ft) wearing atmospheric suits. Diving

14300-515: The risks of decompression sickness for deep and long exposures. An alternative approach was the development of the ADS or armoured suit, which isolates the diver from the pressure at depth, at the cost of mechanical complexity and limited dexterity. The technology first became practicable in the middle 20th century. Isolation of the diver from the environment was taken further by the development of remotely operated underwater vehicles (ROV or ROUV) in

14430-451: The rules of the organisations to which the divers are affiliated. The planning of a diving operation may be simple or complex. In some cases the processes may have to be repeated several times before a satisfactory plan is achieved, and even then the plan may have to be modified on site to suit changed circumstances. The final product of the planning process may be formally documented or, in the case of recreational divers, an agreement on how

14560-842: The safety of the diver may require more practice than is usually provided during training to achieve reliable long-term proficiency Some of the skills are generally accepted by recreational diver certification agencies as necessary for any scuba diver to be considered competent to dive without direct supervision, and others are more advanced, though some diver certification and accreditation organizations may consider some of these to also be essential for minimum acceptable entry level competence. Divers are instructed and assessed on these skills during basic and advanced training, and are expected to remain competent at their level of certification, either by practice or refresher courses. The skills include selection, functional testing, preparation and transport of scuba equipment, dive planning, preparation for

14690-429: The same volume of blood throughout the body, and for people with heart disease, this additional workload can cause the heart to go into arrest. A person who survives the initial minute after falling into cold water can survive for at least thirty minutes provided they do not drown. The ability to stay afloat declines substantially after about ten minutes as the chilled muscles lose strength and co-ordination. Hypothermia

14820-454: The service provider relies on for their economic survival. Diver training is closely associated with diver certification or registration, the process of application for, and issue of, formal recognition of competence by a certification agency or registration authority. The training generally follows a programme authorised by the agency, and competence assessment follows the relevant diver training standard . Training in work skills specific to

14950-405: The shore or a diving support vessel and may be transported on a diving stage or in a diving bell. Surface-supplied divers almost always wear diving helmets or full-face diving masks . The bottom gas can be air, nitrox , heliox or trimix ; the decompression gases may be similar, or may include pure oxygen. Decompression procedures include in-water decompression or surface decompression in

15080-513: The simultaneous use of surface orientated or saturation surface-supplied diving equipment and work or observation class remotely operated vehicles. By the late 19th century, as salvage operations became deeper and longer, an unexplained malady began afflicting the divers; they would suffer breathing difficulties, dizziness, joint pain and paralysis, sometimes leading to death. The problem was already well known among workers building tunnels and bridge footings operating under pressure in caissons and

15210-472: The surface. Barotrauma , a type of dysbarism , is physical damage to body tissues caused by a difference in pressure between a gas space inside, or in contact with the body, and the surrounding gas or fluid. It typically occurs when the organism is exposed to a large change in ambient pressure, such as when a diver ascends or descends. When diving, the pressure differences which cause the barotrauma are changes in hydrostatic pressure. The initial damage

15340-416: The tissues and back during exposure to variations in ambient pressure. In the case of underwater diving, this mostly involves ambient pressures greater than the local surface pressure, but astronauts, high altitude mountaineers, and travellers in aircraft which are not pressurised to sea level pressure, are generally exposed to ambient pressures less than standard sea level atmospheric pressure. In all cases,

15470-436: The tissues and may have narcotic or other undesirable effects, and must be released slowly to avoid the formation of bubbles during decompression. Metabolically active gases have a greater effect in proportion to their concentration, which is proportional to their partial pressure, which for contaminants is increased in proportion to absolute ambient pressure. Work of breathing is increased by increased density and viscosity of

15600-406: The tissues during decompression . Other problems arise when the concentration of metabolically active gases is increased. These range from the toxic effects of oxygen at high partial pressure, through buildup of carbon dioxide due to excessive work of breathing, increased dead space , or inefficient removal, to the exacerbation of the toxic effects of contaminants in the breathing gas due to

15730-432: The tissues is in the dissolved state, and elimination also requires the gas to be dissolved, however a sufficient reduction in ambient pressure may cause bubble formation in the tissues, which can lead to tissue damage and the symptoms known as decompression sickness, and also delays the elimination of the gas. Decompression modeling attempts to explain and predict the mechanism of gas elimination and bubble formation within

15860-425: The underwater environment may be included in diver training programmes, but is also often provided independently, either as job training for a specific operation, or as generic training by specialists in the fields. Professional divers will also learn about legislative restrictions and occupational health and safety relating to diving work. Sufficient understanding of the hazards associated with diving activities

15990-527: The underwater environment. It includes the effects on the body of pressure on gases, the diagnosis and treatment of conditions caused by marine hazards and how a diver's fitness to dive affects the diver's safety. Hyperbaric medicine is a related field associated with diving, since recompression in a hyperbaric chamber is used as a treatment for two of the most significant diving-related illnesses, decompression sickness and arterial gas embolism . Diving medicine deals with medical research on issues of diving,

16120-424: The underwater world, and scientific divers in fields of study which involve the underwater environment, including marine biologists , geologists , hydrologists , oceanographers , speleologists and underwater archaeologists . The choice between scuba and surface-supplied diving equipment is based on both legal and logistical constraints. Where the diver requires mobility and a large range of movement, scuba

16250-433: The upright position, owing to cranial displacement of the abdomen from hydrostatic pressure, and resistance to air flow in the airways increases because of the decrease in lung volume. There appears to be a connection between pulmonary edema and increased pulmonary blood flow and pressure, which results in capillary engorgement. This may occur during higher intensity exercise while immersed or submerged. The diving reflex

16380-404: The use of external breathing devices, and relies on the ability of divers to hold their breath until resurfacing. The technique ranges from simple breath-hold diving to competitive apnea dives. Fins and a diving mask are often used in free diving to improve vision and provide more efficient propulsion. A short breathing tube called a snorkel allows the diver to breathe at the surface while the face

16510-455: The vestibular and visual input, and allows the diver to function effectively in maintaining physical equilibrium and balance in the water. In the water at neutral buoyancy, the proprioceptive cues of position are reduced or absent. This effect may be exacerbated by the diver's suit and other equipment. Taste and smell are not very important to the diver in the water but more important to the saturation diver while in accommodation chambers. There

16640-426: The work involved in setting up the site and demobilisation after the job. The entry requirements for diver training depend on the specific training involved, but generally include medical fitness to dive. Fitness to dive, (also medical fitness to dive), is the medical and physical suitability of a diver to function safely in the underwater environment using underwater diving equipment and procedures. Depending on

16770-431: Was a comprehensive investigation into the physiological effects of air pressure, both above and below the normal. He determined that inhaling pressurised air caused nitrogen to dissolve into the bloodstream ; rapid depressurisation would then release the nitrogen into its gaseous state, forming bubbles that could block the blood circulation and potentially cause paralysis or death. Central nervous system oxygen toxicity

16900-429: Was initially called caisson disease ; it was later renamed the bends because the joint pain typically caused the sufferer to stoop . Early reports of the disease had been made at the time of Charles Pasley 's salvage operation, but scientists were still ignorant of its causes. French physiologist Paul Bert was the first to understand it as decompression sickness (DCS). His work, La Pression barométrique (1878),

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