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131-434: The lake given its location is the backdrop for year-round, water-based recreation opportunities, including boating, fishing, swimming, scuba diving and water-skiing. Houseboats and other boating equipment can be rented from the park unit's concessionaires . Amistad National Recreation Area in addition provides opportunities for picnicking, hiking, camping and hunting. The area is rich in archeology and rock art, and contains

262-410: A dive leader and may be escorted by another dive leader. The reasons to dive for recreational purposes are many and varied, and many divers will go through stages when their personal reasons for diving change, as the initial novelty of the alien environment becomes familiar and skills develop to the point where the diver is able to pay more attention to the surroundings. Many people start diving for

393-406: A diver propulsion vehicle , or a sled pulled from the surface. Other equipment needed for scuba diving includes a mask to improve underwater vision, exposure protection by means of a diving suit , ballast weights to overcome excess buoyancy, equipment to control buoyancy , and equipment related to the specific circumstances and purpose of the dive, which may include a snorkel when swimming on

524-498: A "single-hose" open-circuit 2-stage demand regulator, connected to a single back-mounted high-pressure gas cylinder, with the first stage connected to the cylinder valve and the second stage at the mouthpiece. This arrangement differs from Émile Gagnan's and Jacques Cousteau 's original 1942 "twin-hose" design, known as the Aqua-lung, in which the cylinder pressure was reduced to ambient pressure in one or two stages which were all in

655-402: A "sled", an unpowered device towed behind a surface vessel that conserves the diver's energy and allows more distance to be covered for a given air consumption and bottom time. The depth is usually controlled by the diver by using diving planes or by tilting the whole sled. Some sleds are faired to reduce drag on the diver. To dive safely, divers must control their rate of descent and ascent in

786-431: A backplate, and the cylinders rested directly against the diver's back. Early scuba divers dived without a buoyancy aid. In an emergency they had to jettison their weights. In the 1960s adjustable buoyancy life jackets (ABLJ) became available, which can be used to compensate for loss of buoyancy at depth due to compression of the neoprene wetsuit and as a lifejacket that will hold an unconscious diver face-upwards at

917-497: A clearly visible route adequately illuminated by ambient light . Some organisations extend the scope of recreational diving to allow short decompression obligations which can be done without gas switching . Depth limitations are imposed by the certification agencies, and relate to the competency associated with the specific certification. Entry level divers may be restricted to a depth of 18 or 20 metres (59 or 66 ft), and more advanced divers to 30, 40, 50 or 60 m depending on

1048-421: A day, to complex specialties which may take several days to weeks, and require several classroom sessions, confined water skills training and practice, and a substantial number of open-water dives, followed by rigorous assessment of knowledge and skills. Details on the approximate duration of training can be found on the websites of most certification agencies, but accurate schedules are generally only available from

1179-440: 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, un-kitting after the dive, cleaning and preparation of equipment for storage, and recording

1310-422: A frame and skirt, which are opaque or translucent, therefore the total field-of-view is significantly reduced and eye-hand coordination must be adjusted. Divers who need corrective lenses to see clearly outside the water would normally need the same prescription while wearing a mask. Generic corrective lenses are available off the shelf for some two-window masks, and custom lenses can be bonded onto masks that have

1441-402: A line held by the diver indicates the position of the diver to the surface personnel. This may be an inflatable marker deployed by the diver at the end of the dive, or a sealed float, towed for the whole dive. A surface marker also allows easy and accurate control of ascent rate and stop depth for safer decompression. Various surface detection aids may be carried to help surface personnel spot

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1572-423: A long time, recreational underwater excursions were limited by breath-hold time. The invention of the aqualung in 1943 by Émile Gagnan and Jacques-Yves Cousteau and the wetsuit in 1952 by University of California, Berkeley physicist, Hugh Bradner and its development over subsequent years led to a revolution in recreational diving. However, for much of the 1950s and early 1960s, recreational scuba diving

1703-448: A low-pressure hose from the first stage, delivers the breathing gas at ambient pressure to the diver's mouth. The exhaled gases are exhausted directly to the environment as waste through a non-return valve on the second stage housing. The first stage typically has at least one outlet port delivering gas at full tank pressure which is connected to the diver's submersible pressure gauge or dive computer, to show how much breathing gas remains in

1834-408: A mask than normal-sighted people. Diving masks and helmets solve this problem by providing an air space in front of the diver's eyes. The refraction error created by the water is mostly corrected as the light travels from water to air through a flat lens, except that objects appear approximately 34% bigger and 25% closer in water than they actually are. The faceplate of the mask is supported by

1965-409: A minimum task loading on the diver and as far as possible to fail safe and give the diver ample warning to bail out to open circuit and abort the dive. Open water is the definitive environment for recreational diving, and in this context implies that there is no physical or physiological barrier to the diver concluding the dive at any time by a direct ascent to the surface, either vertically, or via

2096-504: A more conservative approach for a SCR than for a CCR, but decompression computers with a real-time oxygen partial pressure input can optimise decompression for these systems. Because rebreathers produce very few bubbles, they do not disturb marine life or make a diver's presence known at the surface; this is useful for underwater photography, and for covert work. For some diving, gas mixtures other than normal atmospheric air (21% oxygen, 78% nitrogen , 1% trace gases) can be used, so long as

2227-420: A number of applications, including scientific, military and public safety roles, but most commercial diving uses surface-supplied diving equipment when this is practicable. Scuba divers engaged in armed forces covert operations may be referred to as frogmen , combat divers or attack swimmers. A scuba diver primarily moves underwater by using fins attached to the feet, but external propulsion can be provided by

2358-423: A result, divers can stay down longer or require less time to decompress. A semi-closed circuit rebreather injects a constant mass flow of a fixed breathing gas mixture into the breathing loop, or replaces a specific percentage of the respired volume, so the partial pressure of oxygen at any time during the dive depends on the diver's oxygen consumption and/or breathing rate. Planning decompression requirements requires

2489-524: A safe continuous maximum, which reduces the inert gas (nitrogen and/or helium) partial pressure in the breathing loop. Minimising the inert gas loading of the diver's tissues for a given dive profile reduces the decompression obligation. This requires continuous monitoring of actual partial pressures with time and for maximum effectiveness requires real-time computer processing by the diver's decompression computer. Decompression can be much reduced compared to fixed ratio gas mixes used in other scuba systems and, as

2620-401: A shorter surface interval between dives. The increased partial pressure of oxygen due to the higher oxygen content of nitrox increases the risk of oxygen toxicity, which becomes unacceptable below the maximum operating depth of the mixture. To displace nitrogen without the increased oxygen concentration, other diluent gases can be used, usually helium , when the resultant three gas mixture

2751-478: A single front window or two windows. As a diver descends, they must periodically exhale through their nose to equalise the internal pressure of the mask with that of the surrounding water. Swimming goggles are not suitable for diving because they only cover the eyes and thus do not allow for equalisation. Failure to equalise the pressure inside the mask may lead to a form of barotrauma known as mask squeeze. Masks tend to fog when warm humid exhaled air condenses on

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2882-463: A surface breathing gas supply, and therefore has a limited but variable endurance. The name scuba is an acronym for " Self-Contained Underwater Breathing Apparatus " and was coined by Christian J. Lambertsen in a patent submitted in 1952. Scuba divers carry their own source of breathing gas , usually compressed air , affording them greater independence and movement than surface-supplied divers , and more time underwater than free divers. Although

3013-509: A tropical coral reef ). The removal ("ditching" or "shedding") of diver weighting systems can be used to reduce the diver's weight and cause a buoyant ascent in an emergency. Diving suits made of compressible materials decrease in volume as the diver descends, and expand again as the diver ascends, causing buoyancy changes. Diving in different environments also necessitates adjustments in the amount of weight carried to achieve neutral buoyancy. The diver can inject air into dry suits to counteract

3144-403: A tube below 3 feet (0.9 m) under the water. Most recreational scuba diving is done using a half mask which covers the diver's eyes and nose, and a mouthpiece to supply the breathing gas from the demand valve or rebreather. Inhaling from a mouthpiece becomes second nature very quickly. The other common arrangement is a full-face mask which covers the eyes, nose and mouth, and often allows

3275-468: A wide variety of plant and animal life. In the fall, monarch butterflies by the thousands pass through the area during their 3,000 mile (4,800 km) migration from southern Canada to central Mexico. There are opportunities for hunting as provided for under state and federal law at Amistad given its status as a recreation area. Bow-hunting for white-tailed deer , javelina , turkey, rabbit, mouflon sheep , aoudad sheep , blackbuck antelope and feral hog

3406-464: Is diving for the purpose of leisure and enjoyment, usually when using scuba equipment . The term "recreational diving" may also be used in contradistinction to " technical diving ", a more demanding aspect of recreational diving which requires more training and experience to develop the competence to reliably manage more complex equipment in the more hazardous conditions associated with the disciplines. Breath-hold diving for recreation also fits into

3537-435: Is a particular aspect where most of the basic hand signals are common to most recreational diver training agencies. This does not mean that there is no variation. There are some procedures such as emergency donation of air which are quite strongly polarized between those who advocate donation of the secondary (octopus) regulator and those who advocate donating the primary regulator . Length of regulator hose and position of

3668-413: Is a risk of getting the anti-fog agent in the eyes. Water attenuates light by selective absorption. Pure water preferentially absorbs red light, and to a lesser extent, yellow and green, so the colour that is least absorbed is blue light. Dissolved materials may also selectively absorb colour in addition to the absorption by the water itself. In other words, as a diver goes deeper on a dive, more colour

3799-437: Is absorbed by the water, and in clean water the colour becomes blue with depth. Colour vision is also affected by the turbidity of the water which tends to reduce contrast. Artificial light is useful to provide light in the darkness, to restore contrast at close range, and to restore natural colour lost to absorption. Dive lights can also attract fish and a variety of other sea creatures. Protection from heat loss in cold water

3930-486: Is also commonly referred to as the scuba set. As one descends, in addition to the normal atmospheric pressure at the surface, the water exerts increasing hydrostatic pressure of approximately 1 bar (14.7 pounds per square inch) for every 10 m (33 feet) of depth. The pressure of the inhaled breath must balance the surrounding or ambient pressure to allow controlled inflation of the lungs. It becomes virtually impossible to breathe air at normal atmospheric pressure through

4061-543: Is available. These can be broadly distinguished as environmental and equipment specialties. Environmental specialties: Equipment specialties: Many diver training agencies such as ACUC , BSAC , CMAS , IANTD , NAUI , PADI , PDIC , SDI , and SSI offer training in these areas, as well as opportunities to move into professional dive leadership , instruction , technical diving , public safety diving and others. Recreational scuba diving grew out of related activities such as Snorkeling and underwater hunting . For

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4192-544: Is below 15 °C (60 °F) or for extended immersion in water above 15 °C (60 °F), where a wetsuit user would get cold, and with an integral helmet, boots, and gloves for personal protection when diving in contaminated water. Dry suits are designed to prevent water from entering. This generally allows better insulation making them more suitable for use in cold water. They can be uncomfortably hot in warm or hot air, and are typically more expensive and more complex to don. For divers, they add some degree of complexity as

4323-467: Is called trimix , and when the nitrogen is fully substituted by helium, heliox . For dives requiring long decompression stops, divers may carry cylinders containing different gas mixtures for the various phases of the dive, typically designated as travel, bottom, and decompression gases. These different gas mixtures may be used to extend bottom time, reduce inert gas narcotic effects, and reduce decompression times. Back gas refers to any gas carried on

4454-417: Is competent and willing to assist. Many recreational diver training organisations exist, throughout the world, offering diver training leading to certification: the issuing of a " diver certification card ", also known as a "C-card," or qualification card. Recreational diver training courses range from minor specialties which require one classroom session and an open water dive, and which may be completed in

4585-414: Is exhaled, and consist of one or more diving cylinders containing breathing gas at high pressure which is supplied to the diver at ambient pressure through a diving regulator . They may include additional cylinders for range extension, decompression gas or emergency breathing gas . Closed-circuit or semi-closed circuit rebreather scuba systems allow recycling of exhaled gases. The volume of gas used

4716-400: Is facilitated by ascending on a line with a buoy at the top. The diver can remain marginally negative and easily maintain depth by holding onto the line. A shotline or decompression buoy are commonly used for this purpose. Precise and reliable depth control are particularly valuable when the diver has a large decompression obligation, as it allows the theoretically most efficient decompression at

4847-421: Is greater per unit of depth near the surface. Minimising the volume of gas required in the buoyancy compensator will minimise the buoyancy fluctuations with changes in depth. This can be achieved by accurate selection of ballast weight, which should be the minimum to allow neutral buoyancy with depleted gas supplies at the end of the dive unless there is an operational requirement for greater negative buoyancy during

4978-794: Is inconclusive. Recreational diving may be considered to be any underwater diving that is not occupational, professional, or commercial, in that the dive is fundamentally at the discretion of the diver, who dives either to their own plan, or to a plan developed in consensus with the other divers in the group, though dives led by a professional dive leader or instructor for non-occupational purposes are also legally classified as recreational dives in some legislations. The full scope of recreational diving includes breath-hold diving and surface supplied diving – particularly with lightweight semi-autonomous airline systems such as snuba – and technical diving (including penetration diving ), as all of these are frequently done for recreational purposes, but common usage

5109-533: Is known as a buoyancy control device or buoyancy compensator. A backplate and wing is an alternative configuration of a scuba harness with a buoyancy compensation bladder known as a "wing" mounted behind the diver, sandwiched between the backplate and the cylinder or cylinders. Unlike stabilizer jackets, the backplate and wing is a modular system, in that it consists of separable components. This arrangement became popular with cave divers making long or deep dives, who needed to carry several extra cylinders, as it clears

5240-491: Is mostly for open water scuba diving with limited decompression. Scuba diving implies the use of an autonomous breathing gas supply carried by the diver, the self-contained underwater breathing apparatus which provides the name for this mode of diving. Scuba may be the simpler and more popular open circuit configuration or one of the more complex and expensive closed or semi-closed rebreather arrangements. Rebreathers used for recreational diving are generally designed to require

5371-438: Is not generally a contravention of the training agencies' recommendations. The initial training for open water certification for a person who is medically fit to dive and a reasonably competent swimmer is relatively short. The minimum number of open-water dives required for certification is usually four, but instructors are generally required by training standards to ensure that the diver is sufficiently skilled to dive safely in

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5502-621: Is now commonly referred to as technical diving for decades. One reasonably widely held definition is that any dive in which at some point of the planned profile it is not physically possible or physiologically acceptable to make a direct and uninterrupted vertical ascent to surface air is a technical dive. The equipment often involves breathing gases other than air or standard nitrox mixtures, multiple gas sources, and different equipment configurations. Over time, some equipment and techniques developed for technical diving have become more widely accepted for recreational diving. Oxygen toxicity limits

5633-612: Is permitted during certain times of the year in prescribed hunt areas. Though rifles and handguns are not permitted, shotguns may be used to hunt dove, quail, duck and rabbit in accordance with relevant regulations. Elite scuba divers have begun to explore the system of deep underwater caves beneath the surface of the reservoir. The dive requires exotic gas mixes, pre-placement of gas cylinders, and extensive decompression times at depth. These caves are considered hazardous and should not be attempted by anyone without extensive training and preparation. The National Park Service initially managed

5764-430: Is recovered; this has advantages for research, military, photography, and other applications. Rebreathers are more complex and more expensive than open-circuit scuba, and special training and correct maintenance are required for them to be safely used, due to the larger variety of potential failure modes. In a closed-circuit rebreather the oxygen partial pressure in the rebreather is controlled, so it can be maintained at

5895-546: Is reduced compared to that of open-circuit, so a smaller cylinder or cylinders may be used for an equivalent dive duration. Rebreathers extend the time spent underwater compared to open-circuit for the same metabolic gas consumption; they produce fewer bubbles and less noise than open-circuit scuba, which makes them attractive to covert military divers to avoid detection, scientific divers to avoid disturbing marine animals, and media divers to avoid bubble interference. Scuba diving may be done recreationally or professionally in

6026-402: Is upwards. The buoyancy of any object immersed in water is also affected by the density of the water. The density of fresh water is about 3% less than that of ocean water. Therefore, divers who are neutrally buoyant at one dive destination (e.g. a freshwater lake) will predictably be positively or negatively buoyant when using the same equipment at destinations with different water densities (e.g.

6157-417: Is usually limited as far as possible by waivers which they require the customer to sign before engaging in any diving activity. The extent of responsibility of recreational buddy divers is unclear, but buddy diving is generally recommended by recreational diver training agencies as safer than solo diving , and some service providers insist that customers dive in buddy pairs. The evidence supporting this policy

6288-422: Is usually provided by wetsuits or dry suits. These also provide protection from sunburn, abrasion and stings from some marine organisms. Where thermal insulation is not important, lycra suits/diving skins may be sufficient. A wetsuit is a garment, usually made of foamed neoprene, which provides thermal insulation, abrasion resistance and buoyancy. The insulation properties depend on bubbles of gas enclosed within

6419-544: The Aqua-Lung trademark, which was first licensed to the U.S. Divers company, and in 1948 to Siebe Gorman of England. Siebe Gorman was allowed to sell in Commonwealth countries but had difficulty in meeting the demand and the U.S. patent prevented others from making the product. The patent was circumvented by Ted Eldred of Melbourne , Australia, who developed the single-hose open-circuit scuba system, which separates

6550-527: The Duke University Medical Center Hyperbaric Laboratory started work which identified the use of trimix to prevent the symptoms of high-pressure nervous syndrome . Cave divers started using trimix to allow deeper dives and it was used extensively in the 1987 Wakulla Springs Project and spread to the north-east American wreck diving community. The challenges of deeper dives and longer penetrations and

6681-833: The Professional Association of Diving Instructors (PADI) announced full educational support for nitrox. The use of a single nitrox mixture has become part of recreational diving, and multiple gas mixtures are common in technical diving to reduce overall decompression time. Technical diving is recreational scuba diving that exceeds the generally accepted recreational limits and may expose the diver to hazards beyond those normally associated with recreational diving, and to greater risks of serious injury or death. These risks may be reduced by appropriate skills, knowledge and experience, and by using suitable equipment and procedures. The concept and term are both relatively recent advents, although divers had already been engaging in what

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6812-630: The Scripps Institution of Oceanography where Andy Rechnitzer , Bob Dill and Connie Limbaugh taught the first scuba courses in the United States, then in 1953 Trevor Hampton created the first British diving school, the British Underwater Centre and in 1954 when Los Angeles County created an Underwater Instructor Certification Course based on the training that they received from the scientific divers of

6943-604: The Scripps Institution of Oceanography . Early instruction developed in the format of amateur teaching within a club environment, as exemplified by organizations such as the Scottish Sub Aqua Club and the British Sub Aqua Club from 1953, Los Angeles County from 1954 and the YMCA from 1959. Professional instruction started in 1959 when the non-profit NAUI was formed, which later effectively

7074-401: The carbon dioxide is removed from the diver's exhaled breath which has oxygen added and is recirculated. Oxygen rebreathers are severely depth-limited due to oxygen toxicity risk, which increases with depth, and the available systems for mixed gas rebreathers were fairly bulky and designed for use with diving helmets. The first commercially practical scuba rebreather was designed and built by

7205-427: The history of scuba equipment . By the turn of the twentieth century, two basic architectures for underwater breathing apparatus had been pioneered; open-circuit surface supplied equipment where the diver's exhaled gas is vented directly into the water, and closed-circuit breathing apparatus where the diver's carbon dioxide is filtered from exhaled unused oxygen , which is then recirculated, and oxygen added to make up

7336-474: The technical diving community for general decompression diving , and has become a popular speciality for recreational diving. In the 1950s the United States Navy (USN) documented enriched oxygen gas procedures for military use of what is today called nitrox, and in 1970, Morgan Wells of NOAA began instituting diving procedures for oxygen-enriched air. In 1979 NOAA published procedures for

7467-577: The Poseidon Mk6 or variable nitrox mixtures such as provided by the earlier semi-closed circuit Dräger Ray rebreather. Emergency gas supplies are either by sharing with a dive buddy or from a bailout cylinder for open circuit diving, and by bailout to open circuit for rebreather diving. Most recreational diving officially applies the buddy system , but in reality there are a significant proportion of dives which are either effectively solo dives or where larger groups of nominally paired divers follow

7598-444: The adventure of experiencing a different environment and the ability to maneuver fairly freely in three dimensions, but the novelty wears off after a while. This may be replaced by the satisfaction of developing the skills to operate in a wider range of environments, and developing excellence in those skills, the addition of compatible interests and activities to complement the basic activity, like underwater photography and an interest in

7729-417: The average lung volume in open-circuit scuba, but this feature is not available to the closed circuit rebreather diver, as exhaled gas remains in the breathing loop. This is a skill that improves with practice until it becomes second nature. Buoyancy changes with depth variation are proportional to the compressible part of the volume of the diver and equipment, and to the proportional change in pressure, which

7860-445: The bare minimum as specified by RSTC and ISO, and others requiring a greater level of competence with associated assumption of lower risk to the diver and dive buddy, and less likelihood of environmental damage. Entry level training may include skills for assisting or rescue of another diver, but this is not always the case. Divers without rescue training are routinely assigned to dive as buddy pairs to follow organizational protocols. This

7991-400: The breathing apparatus, diving suit , buoyancy control and weighting systems, fins for mobility, mask for improving underwater vision, and a variety of safety equipment and other accessories. The defining equipment used by a scuba diver is the eponymous scuba , the self-contained underwater breathing apparatus which allows the diver to breathe while diving, and is transported by the diver. It

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8122-450: The broader scope of the term, but this article covers the commonly used meaning of scuba diving for recreational purposes, where the diver is not constrained from making a direct near-vertical ascent to the surface at any point during the dive , and risk is considered low. The equipment used for recreational diving is mostly open circuit scuba , though semi closed and fully automated electronic closed circuit rebreathers may be included in

8253-477: The buoyancy of a lifting device such as a buoyancy compensator, inflatable surface marker buoy or small lifting bag. The breathing gas is generally provided from a high-pressure diving cylinder through a scuba regulator. By always providing the appropriate breathing gas at ambient pressure, demand valve regulators ensure the diver can inhale and exhale naturally and without excessive effort, regardless of depth, as and when needed. The most commonly used scuba set uses

8384-432: The certification and agency. Junior divers may be restricted to shallower depths generally confined to a depth of 12 metres (40 ft). Recreational diving is generally limited to the use of air or a single nitrox mixture with an oxygen fraction not exceeding 40% for the planned dive, but this does not preclude constant oxygen partial pressure nitrox provided by electronically controlled closed circuit rebreathers like

8515-445: The cold inside of the faceplate. To prevent fogging many divers spit into the dry mask before use, spread the saliva over the inside of the glass and rinse it out with a little water. The saliva residue allows condensation to wet the glass and form a continuous wet film, rather than tiny droplets. There are several commercial products that can be used as an alternative to saliva, some of which are more effective and last longer, but there

8646-508: The commercial diver training standards of several countries, including the United Kingdom, Australia, South Africa, and Canada, consider the competence provided by the recreational diver training industry minimum standard to be inadequate for safe diving, particularly occupational diving, where the diver has a legal duty of care towards other members of the dive team, even though the responsibility for occupational dive planning and safety

8777-426: The compression effect and squeeze . Buoyancy compensators allow easy and fine adjustments in the diver's overall volume and therefore buoyancy. Neutral buoyancy in a diver is an unstable state. It is changed by small differences in ambient pressure caused by a change in depth, and the change has a positive feedback effect. A small descent will increase the pressure, which will compress the gas-filled spaces and reduce

8908-413: The convenience of the diver, and profit for the agency, or in the case of club oriented systems, for the overall benefit of the club community: Activities: Some recreational diving activities require skills sufficiently beyond the basic recreational open water diving skill set that they are classed by the recreational diver training industry as specialties, and for which further training and certification

9039-433: The cylinder. Less common are closed circuit (CCR) and semi-closed (SCR) rebreathers which, unlike open-circuit sets that vent off all exhaled gases, process all or part of each exhaled breath for re-use by removing the carbon dioxide and replacing the oxygen used by the diver. Rebreathers release few or no gas bubbles into the water, and use much less stored gas volume, for an equivalent depth and time because exhaled oxygen

9170-424: The depth and duration of a dive to avoid decompression sickness. Traditionally this was done by using a depth gauge and a diving watch, but electronic dive computers are now in general use, as they are programmed to do real-time modelling of decompression requirements for the dive, and automatically allow for surface interval. Many can be set for the gas mixture to be used on the dive, and some can accept changes in

9301-453: The depth reachable by underwater divers when breathing nitrox mixtures. In 1924 the US Navy started to investigate the possibility of using helium and after animal experiments, human subjects breathing heliox 20/80 (20% oxygen, 80% helium) were successfully decompressed from deep dives, In 1963 saturation dives using trimix were made during Project Genesis , and in 1979 a research team at

9432-439: The details of the environment, including exploration and study and recording of aspects of the environment. Experience of the underwater environment varies depending on where the diver has access to suitable sites - there is more to see on a coastal reef than in most freshwater lakes, and scuba diving tourism can make a wide variety of more entertaining and challenging sites available. Exploration can also extend beyond tourism to

9563-399: The direction of intended motion and will reduce induced drag. Streamlining dive gear will also reduce drag and improve mobility. Balanced trim which allows the diver to align in any desired direction also improves streamlining by presenting the smallest section area to the direction of movement and allowing propulsion thrust to be used more efficiently. Occasionally a diver may be towed using

9694-423: The dive, within the scope of the diver's certification. A significant amount of harmonization of training standards and standard and emergency procedures has developed over the years, largely due to organisations like World Recreational Scuba Training Council . This allows divers trained by the various certifying organisations to dive together with a minimum of confusion, which enhances safety. Diver communications

9825-514: The dive. Buoyancy and trim can significantly affect drag of a diver. The effect of swimming with a head up angle of about 15°, as is quite common in poorly trimmed divers, can be an increase in drag in the order of 50%. The ability to ascend at a controlled rate and remain at a constant depth is important for correct decompression. Recreational divers who do not incur decompression obligations can get away with imperfect buoyancy control, but when long decompression stops at specific depths are required,

9956-524: The diver after ascent. In addition to the surface marker buoy, divers may carry mirrors, lights, strobes, whistles, flares or emergency locator beacons . Divers may carry underwater photographic or video equipment, or tools for a specific application in addition to diving equipment. Professional divers will routinely carry and use tools to facilitate their underwater work, while most recreational divers will not engage in underwater work. Recreational diving Recreational diving or sport diving

10087-418: The diver is competent in their use. The most commonly used mixture is nitrox, also referred to as Enriched Air Nitrox (EAN or EANx), which is air with extra oxygen, often with 32% or 36% oxygen, and thus less nitrogen, reducing the risk of decompression sickness or allowing longer exposure to the same pressure for equal risk. The reduced nitrogen may also allow for no stops or shorter decompression stop times or

10218-435: The diver to breathe through the nose. Professional scuba divers are more likely to use full-face masks, which protect the diver's airway if the diver loses consciousness. Open-circuit scuba has no provision for using the breathing gas more than once for respiration. The gas inhaled from the scuba equipment is exhaled to the environment, or occasionally into another item of equipment for a special purpose, usually to increase

10349-475: The diver to carry an alternative gas supply sufficient to allow the diver to safely reach a place where more breathing gas is available. For open water recreational divers this is the surface. A bailout cylinder provides emergency breathing gas sufficient for a safe emergency ascent. For technical divers on a penetration dive, it may be a stage cylinder positioned at a point on the exit path. An emergency gas supply must be sufficiently safe to breathe at any point on

10480-467: The diver to navigate, a compass may be carried, and where retracing a route is critical, as in cave or wreck penetrations, a guide line is laid from a dive reel. In less critical conditions, many divers simply navigate by landmarks and memory, a procedure also known as pilotage or natural navigation. A scuba diver should always be aware of the remaining breathing gas supply, and the duration of diving time that this will safely support, taking into account

10611-669: The diver's back, usually bottom gas. To take advantage of the freedom of movement afforded by scuba equipment, the diver needs to be mobile underwater. Personal mobility is enhanced by swimfins and optionally diver propulsion vehicles. Fins have a large blade area and use the more powerful leg muscles, so are much more efficient for propulsion and manoeuvering thrust than arm and hand movements, but require skill to provide fine control. Several types of fin are available, some of which may be more suited for maneuvering, alternative kick styles, speed, endurance, reduced effort or ruggedness. Neutral buoyancy will allow propulsive effort to be directed in

10742-559: The diver, clipped to the harness below the shoulders and along the hips, instead of on the back of the diver. It originated as a configuration for advanced cave diving , as it facilitates penetration of tight sections of caves since sets can be easily removed and remounted when necessary. The configuration allows easy access to cylinder valves and provides easy and reliable gas redundancy. These benefits for operating in confined spaces were also recognized by divers who made wreck diving penetrations. Sidemount diving has grown in popularity within

10873-481: The divers attending the course. Diver training can be divided into entry-level training, which are those skills and knowledge considered essential for the diver to dive unsupervised at an acceptably low level of risk by the certifying agency, and further skills and knowledge which allow better performance and extend the environmental capacity and equipment choices of the diver. There is a significant variation in entry-level training, with some training agencies requiring

11004-512: The diving engineer Henry Fleuss in 1878, while working for Siebe Gorman in London. His self-contained breathing apparatus consisted of a rubber mask connected to a breathing bag, with an estimated 50–60% oxygen supplied from a copper tank and carbon dioxide scrubbed by passing it through a bundle of rope yarn soaked in a solution of caustic potash, the system giving a dive duration of up to about three hours. This apparatus had no way of measuring

11135-400: The equipment and dealing with the general hazards of the underwater environment , and emergency procedures for self-help and assistance of a similarly equipped diver experiencing problems. A minimum level of fitness and health is required by most training organisations, but a higher level of fitness may be appropriate for some applications. The history of scuba diving is closely linked with

11266-442: The equipment they are breathing from at the time. Several systems are in common use depending on the planned dive profile. Most common, but least reliable, is relying on the dive buddy for gas sharing using a secondary second stage, commonly called an octopus regulator connected to the primary first stage. This system relies entirely on the dive buddy being immediately available to provide emergency gas. More reliable systems require

11397-509: The first stage and demand valve of the pressure regulator by a low-pressure hose, puts the demand valve at the diver's mouth, and releases exhaled gas through the demand valve casing. Eldred sold the first Porpoise Model CA single-hose scuba early in 1952. Early scuba sets were usually provided with a plain harness of shoulder straps and a waist belt. The waist belt buckles were usually quick-release, and shoulder straps sometimes had adjustable or quick-release buckles. Many harnesses did not have

11528-424: The following items: Basic equipment, which can be used for most modes of ambient pressure diving: A scuba set, comprising: Auxiliary equipment to enhance safety. For solo diving a bailout cylinder is considered standard for dives where there is an appreciable risk of entrapment, or where a direct controlled emergency swimming ascent is not an acceptable option to manage an out-of-air incident at any point in

11659-403: The front and sides of the diver for other equipment to be attached in the region where it is easily accessible. This additional equipment is usually suspended from the harness or carried in pockets on the exposure suit. Sidemount is a scuba diving equipment configuration which has basic scuba sets , each comprising a single cylinder with a dedicated regulator and pressure gauge, mounted alongside

11790-724: The gas composition during use. During the 1930s and all through World War II , the British, Italians and Germans developed and extensively used oxygen rebreathers to equip the first frogmen . The British adapted the Davis Submerged Escape Apparatus and the Germans adapted the Dräger submarine escape rebreathers, for their frogmen during the war. In the U.S. Major Christian J. Lambertsen invented an underwater free-swimming oxygen rebreather in 1939, which

11921-432: The gas mix during the dive. Most dive computers provide a fairly conservative decompression model, and the level of conservatism may be selected by the user within limits. Most decompression computers can also be set for altitude compensation to some degree, and some will automatically take altitude into account by measuring actual atmospheric pressure and using it in the calculations. If the dive site and dive plan require

12052-450: The housing mounted to the cylinder valve or manifold. The "single-hose" system has significant advantages over the original system for most applications. In the "single-hose" two-stage design, the first stage regulator reduces the cylinder pressure of up to about 300 bars (4,400 psi) to an intermediate pressure (IP) of about 8 to 10 bars (120 to 150 psi) above ambient pressure. The second stage demand valve regulator, supplied by

12183-608: The international standards. Under most entry-level programs ( SEI , SDI , PADI , BSAC, SSAC , NAUI , SSI , and PDIC ), divers can complete a certification with as few as four open water dives. This complies with the minimum requirements of ISO 24801-2 Autonomous diver. Such a qualification allows divers to rent equipment, receive air fills, and dive without supervision to depths typically restricted to 18 meters (60 feet) with an equally qualified buddy in conditions similar to, or easier than those in which they were trained. Certification agencies advise their students to dive within

12314-429: The large amounts of breathing gas necessary for these dive profiles and ready availability of oxygen-sensing cells beginning in the late 1980s led to a resurgence of interest in rebreather diving. By accurately measuring the partial pressure of oxygen, it became possible to maintain and accurately monitor a breathable gas mixture in the loop at any depth. In the mid-1990s semi-closed circuit rebreathers became available for

12445-427: The local environment before certification is issued, and this may require further training and experience beyond the required minimum. Many dive shops in popular holiday locations offer courses intended to teach a novice to dive in a few days, which can be combined with diving on the vacation. Other instructors and dive schools will provide more thorough training, which generally takes longer. Skills and knowledge beyond

12576-540: The lowest reasonably practicable risk. Ideally the diver should practice precise buoyancy control when the risk of decompression sickness due to depth variation violating the decompression ceiling is low. Water has a higher refractive index than air – similar to that of the cornea of the eye. Light entering the cornea from water is hardly refracted at all, leaving only the eye's crystalline lens to focus light. This leads to very severe hypermetropia . People with severe myopia , therefore, can see better underwater without

12707-466: The material, which reduce its ability to conduct heat. The bubbles also give the wetsuit a low density, providing buoyancy in water. Suits range from a thin (2 mm or less) "shortie", covering just the torso, to a full 8 mm semi-dry, usually complemented by neoprene boots, gloves and hood. A good close fit and few zips help the suit to remain waterproof and reduce flushing – the replacement of water trapped between suit and body by cold water from

12838-527: The minimum requirement are generally labelled Advanced skills , and these may include skills such as competent buoyancy control, which are included in the entry level skills by other agencies. Many skills which are considered advanced by recreational training agencies are considered basic entry-level skills for professional divers. Each diver certification agency has its own set of diver training standards for each level of certification that they issue. Although these standards are usually available on request or on

12969-500: The organisation's website, the assessment criteria are often not available to the public, making a direct comparison of standards difficult. Most agencies comply with the minimum requirements of the World Recreational Scuba Training Council (WRSTC) or ISO for the relevant certification (ISO 24801-2 Autonomous diver, and ISO 24801-3 Dive leader ), but most certification levels are not defined by

13100-409: The outside. Improved seals at the neck, wrists and ankles and baffles under the entry zip produce a suit known as "semi-dry". A dry suit also provides thermal insulation to the wearer while immersed in water, and normally protects the whole body except the head, hands, and sometimes the feet. In some configurations, these are also covered. Dry suits are usually used where the water temperature

13231-410: The overall buoyancy. When divers want to remain at constant depth, they try to achieve neutral buoyancy. This minimises the effort of swimming to maintain depth and therefore reduces gas consumption. The buoyancy force on the diver is the weight of the volume of the liquid that they and their equipment displace minus the weight of the diver and their equipment; if the result is positive , that force

13362-469: The planned dive profile at which it may be needed. This equipment may be a bailout cylinder , a bailout rebreather , a travel gas cylinder, or a decompression gas cylinder. When using a travel gas or decompression gas, the back gas (main gas supply) may be the designated emergency gas supply. Cutting tools such as knives, line cutters or shears are often carried by divers to cut loose from entanglement in nets or lines. A surface marker buoy (SMB) on

13493-726: The planned dive profile. Some 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

13624-468: The presence of the divers. The high percentage of oxygen used by these early rebreather systems limited the depth at which they could be used due to the risk of convulsions caused by acute oxygen toxicity . Although a working demand regulator system had been invented in 1864 by Auguste Denayrouze and Benoît Rouquayrol , the first open-circuit scuba system developed in 1925 by Yves Le Prieur in France

13755-1116: The range of environments and venues the diver can enjoy at an acceptable level of risk. Reasons to dive and preferred diving activities may vary during the personal development of a recreational diver, and may depend on their psychological profile and their level of dedication to the activity. Most divers average less than eight dives per year, but some total several thousand dives over a few decades and continue diving into their 60s and 70s, occasionally older. Recreational divers may frequent local dive sites or dive as tourists at more distant venues known for desirable underwater environments . An economically significant diving tourism industry services recreational divers, providing equipment, training and diving experiences, generally by specialist providers known as dive centers , dive schools , live-aboard , day charter and basic dive boats . Legal constraints on recreational diving vary considerably across jurisdictions . Recreational diving may be industry regulated or regulated by law to some extent. The legal responsibility for recreational diving service providers

13886-424: The recreational scuba market, followed by closed circuit rebreathers around the turn of the millennium. Rebreathers are currently manufactured for the military, technical and recreational scuba markets, but remain less popular, less reliable, and more expensive than open-circuit equipment. Scuba diving equipment, also known as scuba gear, is the equipment used by a scuba diver for the purpose of diving, and includes

14017-443: The remainder were more advanced certifications. Scuba-diving has become a popular leisure activity, and many diving destinations have some form of dive shop presence that can offer air fills, equipment sale, rental and repair, and training. In tropical and sub-tropical parts of the world, there is a large market for 'holiday divers'; people who train and dive while on holiday, but rarely dive close to home. Technical diving and

14148-417: The risk of decompression sickness is increased by depth variations while at a stop. Decompression stops are typically done when the breathing gas in the cylinders has been largely used up, and the reduction in weight of the cylinders increases the buoyancy of the diver. Enough weight must be carried to allow the diver to decompress at the end of the dive with nearly empty cylinders. Depth control during ascent

14279-584: The safety, comfort and convenience of the gear encouraging more people to train and use it. Until the early 1950s, navies and other organizations performing professional diving were the only providers of diver training, but only for their own personnel and only using their own types of equipment. The first scuba diving school was opened in France to train the owners of the Cousteau and Gagnan designed twin-hose scuba. The first school to teach single hose scuba

14410-472: The scientific use of nitrox in the NOAA Diving Manual. In 1985 IAND (International Association of Nitrox Divers) began teaching nitrox use for recreational diving. This was considered dangerous by some, and met with heavy skepticism by the diving community. Nevertheless, in 1992 NAUI became the first existing major recreational diver training agency to sanction nitrox, and eventually, in 1996,

14541-444: The scope of recreational diving. Risk is managed by training the diver in a range of standardised procedures and skills appropriate to the equipment the diver chooses to use and the environment in which the diver plans to dive. Further experience and development of skills by practice will improve the diver's ability to dive safely. Specialty training is made available by the recreational diver training industry and diving clubs to increase

14672-681: The scope of their experience and training, and to extend their training to suit the conditions in which they plan to dive. In the 1980s, several agencies with DEMA collaborated to author ANSI Standard Z86.3 (1989), Minimum Course Content For Safe Scuba Diving which defines their training as the Accepted Industry Practices . The International Standards Organisation has since published ISO 24801 and ISO 24802 which define minimum training standards for two levels of recreational diver and for recreational diving instructors. A few recreational certification agencies such as GUE , and

14803-457: The search for previously unvisited sites and the satisfaction of being the first to be there and in some cases, tell the story. Reasons to dive include: There are many recreational diving activities, and equipment and environmental specialties which require skills additional to those provided by the entry level courses, These skills were originally developed by trial and error, but training programmes are offered by most diver training agencies for

14934-496: The secondary second stage depend on the donation technique. There are also variations in procedures for self rescue in an out-of-air situation, and in procedures for bringing an unresponsive casualty to the surface . Solo diving, once considered technical diving and discouraged by most certification agencies , is now seen by many experienced divers and some certification agencies as an acceptable practice for those divers suitably trained and experienced. Rather than relying on

15065-554: The site as the Amistad Recreation Area under a cooperative agreement with the International Boundary and Water Commission effective November 11, 1965. Amistad was reauthorized as a national recreation area and NPS park unit on November 28, 1990. Scuba diving Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of

15196-408: The specific school or instructor who will present that course, as this will depend on the local conditions and other constraints. Diving instructors affiliated to a diving certification agency may work independently or through a university, a dive club, a dive school or a dive shop. They will offer courses that should meet, or exceed, the standards of the certification organisation that will certify

15327-416: The suit must be inflated and deflated with changes in depth in order to avoid "squeeze" on descent or uncontrolled rapid ascent due to over-buoyancy. Dry suit divers may also use the gas argon to inflate their suits via low pressure inflator hose. This is because the gas is inert and has a low thermal conductivity. Unless the maximum depth of the water is known, and is quite shallow, a diver must monitor

15458-411: The surface, a cutting tool to manage entanglement, lights , a dive computer to monitor decompression status , and signalling devices . Scuba divers are trained in the procedures and skills appropriate to their level of certification by diving instructors affiliated to the diver certification organisations which issue these certifications. These include standard operating procedures for using

15589-506: The surface, and that can be quickly inflated. The first versions were inflated from a small disposable carbon dioxide cylinder, later with a small direct coupled air cylinder. A low-pressure feed from the regulator first-stage to an inflation/deflation valve unit an oral inflation valve and a dump valve lets the volume of the ABLJ be controlled as a buoyancy aid. In 1971 the stabilizer jacket was introduced by ScubaPro . This class of buoyancy aid

15720-400: The time required to surface safely and an allowance for foreseeable contingencies. This is usually monitored by using a submersible pressure gauge on each cylinder. Any scuba diver who will be diving below a depth from which they are competent to do a safe emergency swimming ascent should ensure that they have an alternative breathing gas supply available at all times in case of a failure of

15851-430: The total volume of diver and equipment. This will further reduce the buoyancy, and unless counteracted, will result in sinking more rapidly. The equivalent effect applies to a small ascent, which will trigger an increased buoyancy and will result in an accelerated ascent unless counteracted. The diver must continuously adjust buoyancy or depth in order to remain neutral. Fine control of buoyancy can be achieved by controlling

15982-412: The traditional buddy diving safety system, solo divers rely on self-sufficiency and are willing to take responsibility for their own safety while diving. Buddy diving is the more generally advocated procedural alternative, on the principle that in case of an emergency, a dive buddy can assist the diver in difficulty, but this is only valid if the buddy is close enough to help, notices the problem, and

16113-597: The use of rebreathers are increasing, particularly in areas of the world where deeper wreck diving is the main underwater attraction. Generally, recreational diving depths are limited by the training agencies to a maximum of between 30 and 40 meters (100 and 130 feet), beyond which a variety of safety issues such as oxygen toxicity and nitrogen narcosis significantly increase the risk of diving using recreational diving equipment and practices, and specialized skills and equipment for technical diving are needed. The standard recreational open circuit scuba equipment includes

16244-404: The use of compressed air is common, a gas blend with a higher oxygen content, known as enriched air or nitrox , has become popular due to the reduced nitrogen intake during long or repetitive dives. Also, breathing gas diluted with helium may be used to reduce the effects of nitrogen narcosis during deeper dives. Open-circuit scuba systems discharge the breathing gas into the environment as it

16375-410: The volume when necessary. Closed circuit equipment was more easily adapted to scuba in the absence of reliable, portable, and economical high-pressure gas storage vessels. By the mid-twentieth century, high pressure gas cylinders were available and two systems for scuba had emerged: open-circuit scuba where the diver's exhaled breath is vented directly into the water, and closed-circuit scuba where

16506-422: The water and be able to maintain a constant depth in midwater. Ignoring other forces such as water currents and swimming, the diver's overall buoyancy determines whether they ascend or descend. Equipment such as diving weighting systems , diving suits (wet, dry or semi-dry suits are used depending on the water temperature) and buoyancy compensators(BC) or buoyancy control device(BCD) can be used to adjust

16637-582: Was a manually adjusted free-flow system with a low endurance, which limited its practical usefulness. In 1942, during the German occupation of France , Jacques-Yves Cousteau and Émile Gagnan designed the first successful and safe open-circuit scuba, known as the Aqua-Lung . Their system combined an improved demand regulator with high-pressure air tanks. This was patented in 1945. To sell his regulator in English-speaking countries Cousteau registered

16768-504: Was a sport limited to those who were able to afford or make their own kit, and prepared to undergo intensive training to use it. As the sport became more popular, manufacturers became aware of the potential market, and equipment began to appear that was easy to use, affordable and reliable. Continued advances in SCUBA technology, such as buoyancy compensators , improved diving regulators , wet or dry suits , and dive computers , increased

16899-502: Was accepted by the Office of Strategic Services . In 1952 he patented a modification of his apparatus, this time named SCUBA (an acronym for "self-contained underwater breathing apparatus"), which became the generic English word for autonomous breathing equipment for diving, and later for the activity using the equipment. After World War II, military frogmen continued to use rebreathers since they do not make bubbles which would give away

17030-502: Was split, to form the for-profit PADI in 1966. The National Association of Scuba Diving Schools (NASDS) started with their dive center based training programs in 1962 followed by SSI in 1970. Professional Diving Instructors College was formed in 1965, changing its name in 1984 to Professional Diving Instructors Corporation (PDIC). In 2009 PADI alone issued approximately 950,000 diving certifications. Approximately 550,000 of these certifications were "entry level" certifications and

17161-531: Was started in 1953, in Melbourne, Australia , at the Melbourne City Baths. RAN Commander Batterham organized the school to assist the inventor of the single hose regulator , Ted Eldred . However, neither of these schools was international in nature. There were no formal training courses available to civilians who bought the early scuba equipment. Some of the first training started in 1952 at

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