Diving masks and diving helmets and fullface masks solve this problem by creating an air space in front of the diver's eyes.[1] 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 salt water than they actually are. Therefore total field-of-view is significantly reduced and eye-hand coordination must be adjusted.
(This affects underwater photography: a camera seeing through a flat window in its casing is affected the same as its user's eye seeing through a flat mask window, and so its user must focus for the apparent distance to target, not for the real distance.)
Divers who need corrective lenses to see clearly outside the water would normally need the same prescription while wearing a mask. Generic and custom corrective lenses are available for some two-window masks. Custom lenses can be bonded onto masks that have a single front window.
A "double-dome mask" has curved windows in an attempt to cure these faults, but this causes a refraction problem of its own.
On rare occasions, commando frogmen use special contact lenses instead, to see underwater without the large glass surface of a diving mask, which can reflect light and give away the frogman's position.
As a diver changes depth, he must periodically exhale through his nose to equalize the internal pressure of the mask with that of the surrounding water. Swimming goggles which only cover the eyes do not allow for equalization and thus are not suitable for diving.
[edit]Controlling buoyancy underwater
Diver under the Salt Pier in Bonaire.
To dive safely, divers need to be able to control their rate of descent and ascent in the water.[2] Ignoring other forces such as water currents and swimming, the diver's overall buoyancy determines whether he ascends or descends. Equipment such as the diving weighting systems, diving suits (Wet, Dry & Semi-dry suits are used depending on the water temperature) and buoyancy compensators can be used to adjust the overall buoyancy.[1] When divers want to remain at constant depth, they try to achieve neutral buoyancy. This minimizes gas consumption caused by swimming to maintain depth.
The downward force on the diver is the weight of the diver and his equipment minus the weight of the same volume of the liquid that he is immersed in; if the result is negative, that force is upwards. Diving weighting systems can be used to reduce the diver's weight and cause an ascent in an emergency. Diving suits, mostly being made of compressible materials, shrink as the diver descends, and expand as the diver ascends, creating unwanted buoyancy changes. The diver can inject air into some diving suits to counteract this effect and squeeze. Buoyancy compensators allow easy and fine adjustments in the diver's overall volume and therefore buoyancy. For open circuit divers, changes in the diver's lung volume can be used to adjust buoyancy.
[edit]Avoiding losing body heat
Main article: Diving suit
Water conducts heat from the diver 25 times[10] better than air, which can lead to hypothermia even in mild water temperatures.[2] Symptoms of hypothermia include impaired judgment and dexterity[11], which can quickly become deadly in an aquatic environment. In all but the warmest waters, divers need the thermal insulation provided by wetsuits or drysuits.[1]
In the case of a wetsuit, the suit is designed to minimize heat loss. Wetsuits are generally made of neoprene that has small gas cells, generally nitrogen, trapped in it during the manufacturing process. The poor thermal conductivity of this expanded cell neoprene means that wetsuits reduce loss of body heat by conduction to the surrounding water. The neoprene in this case acts as an insulator.
The second way in which wetsuits reduce heat loss is to trap a thin layer of water between the diver's skin and the insulating suit itself. Body heat then heats the trapped water. Provided the wetsuit is reasonably well-sealed at all openings (neck, wrists, legs), this reduces water flow over the surface of the skin, reducing loss of body heat by convection, and therefore keeps the diver warm (this is the principle employed in the use of a "Semi-Dry")
Spring suit and steamer
In the case of a drysuit, it does exactly that: keeps a diver dry. The suit is sealed so that frigid water cannot penetrate the suit. Drysuit undergarments are often worn under a drysuit as well, and help to keep layers of air inside the suit for better thermal insulation. Some divers carry an extra gas bottle dedicated to filling the dry suit. Usually this bottle contains argon gas, because of its better insulation as compared with air.[12]
Drysuits fall into two main categories neoprene and membrane; both systems have their good and bad points but generally their thermal properties can be reduced to:
Membrane: usually a trilaminate construction; owing to the thinness of the material (around 1 mm), these require an undersuit, usually of high insulation value if diving in cooler water.
Neoprene: a similar construction to wetsuits; these are often considerably thicker (7-8 mm) and have sufficient insulation to allow a lighter-weight undersuit (or none at all); however on deeper dives the neoprene can compress to as little as 2 mm thus losing a proportion of their insulation. Compressed or crushed neoprene may also be used (where the neoprene is pre-compressed to 2-3 mm) which avoids the variation of insulating properties with depth.
[edit]Avoiding skin cuts and grazes
Diving suits also help prevent the diver's skin being damaged by rough or sharp underwater objects, marine animals or coral.
[edit]Diving longer and deeper safely
There are a number of techniques to increase the diver's ability to dive deeper and longer:
Technical diving - diving deeper than 40 metres (130 ft), using mixed gases, and/or entering overhead environments (caves or wrecks)
surface supplied diving - use of umbilical gas supply and diving helmets.[1]
saturation diving - long-term use of underwater habitats under pressure and a gradual release of pressure over several days in a decompression chamber at the end of a dive.[1]
[edit]Being mobile underwater
The diver needs to be mobile underwater. Streamlining dive gear will reduce drag and improve mobility. Personal mobility is enhanced by swimfins and Diver Propulsion Vehicles. Other equipment to improve mobility includes diving bells and diving shots.
scuba diving does not have a centralized certifying or regulatory agency, and is mostly self regulated. There are, however, several large diving organizations that train and certify divers and dive instructors, and many diving related sales and rental outlets require proof of diver certification from one of these organizations prior to selling or renting certain diving products or services.
The largest international certification agencies that are currently recognized by most diving outlets for diver certification include:
American Canadian Underwater Certifications (ACUC) (formerly Association of Canadian Underwater Councils) - originated in Canada in 1969 and expanded internationally in 1984
British Sub Aqua Club (BSAC) - based in the United Kingdom, founded in 1953 and is the largest dive club in the world
European Committee of Professional Diving Instructors (CEDIP) based in Europe since 1992 (see Cedip on French Wiki pages)
Confédération Mondiale des Activités Subaquatiques (CMAS), the World Underwater Federation
National Association of Underwater Instructors (NAUI) - based in the United States
Professional Diving Instructors Corporation (PDIC) - based in the United States
Professional Association of Diving Instructors (PADI) - based in the United States, largest recreational dive training and certification organization in the world
Scottish Sub Aqua Club (SSAC or ScotSAC) the National Governing Body for the sport of diving in Scotland.
International Training SDI, TDI & ERDi -based in the United States, TDI is the world's largest technical diving agency, SDI is the recreational division focusing on new methods and online courses, and ERDi is the public safety component.
Scuba Schools International (SSI) - based in the United States with 35 Regional Centers and Area Offices around the globe.
YMCA scuba - based in the U.S., part of Young Men's Christian Association (YMCA), a Christian related organization (open to all faiths, ages and genders despite the historic name)
(This affects underwater photography: a camera seeing through a flat window in its casing is affected the same as its user's eye seeing through a flat mask window, and so its user must focus for the apparent distance to target, not for the real distance.)
Divers who need corrective lenses to see clearly outside the water would normally need the same prescription while wearing a mask. Generic and custom corrective lenses are available for some two-window masks. Custom lenses can be bonded onto masks that have a single front window.
A "double-dome mask" has curved windows in an attempt to cure these faults, but this causes a refraction problem of its own.
On rare occasions, commando frogmen use special contact lenses instead, to see underwater without the large glass surface of a diving mask, which can reflect light and give away the frogman's position.
As a diver changes depth, he must periodically exhale through his nose to equalize the internal pressure of the mask with that of the surrounding water. Swimming goggles which only cover the eyes do not allow for equalization and thus are not suitable for diving.
[edit]Controlling buoyancy underwater
Diver under the Salt Pier in Bonaire.
To dive safely, divers need to be able to control their rate of descent and ascent in the water.[2] Ignoring other forces such as water currents and swimming, the diver's overall buoyancy determines whether he ascends or descends. Equipment such as the diving weighting systems, diving suits (Wet, Dry & Semi-dry suits are used depending on the water temperature) and buoyancy compensators can be used to adjust the overall buoyancy.[1] When divers want to remain at constant depth, they try to achieve neutral buoyancy. This minimizes gas consumption caused by swimming to maintain depth.
The downward force on the diver is the weight of the diver and his equipment minus the weight of the same volume of the liquid that he is immersed in; if the result is negative, that force is upwards. Diving weighting systems can be used to reduce the diver's weight and cause an ascent in an emergency. Diving suits, mostly being made of compressible materials, shrink as the diver descends, and expand as the diver ascends, creating unwanted buoyancy changes. The diver can inject air into some diving suits to counteract this effect and squeeze. Buoyancy compensators allow easy and fine adjustments in the diver's overall volume and therefore buoyancy. For open circuit divers, changes in the diver's lung volume can be used to adjust buoyancy.
[edit]Avoiding losing body heat
Main article: Diving suit
Water conducts heat from the diver 25 times[10] better than air, which can lead to hypothermia even in mild water temperatures.[2] Symptoms of hypothermia include impaired judgment and dexterity[11], which can quickly become deadly in an aquatic environment. In all but the warmest waters, divers need the thermal insulation provided by wetsuits or drysuits.[1]
In the case of a wetsuit, the suit is designed to minimize heat loss. Wetsuits are generally made of neoprene that has small gas cells, generally nitrogen, trapped in it during the manufacturing process. The poor thermal conductivity of this expanded cell neoprene means that wetsuits reduce loss of body heat by conduction to the surrounding water. The neoprene in this case acts as an insulator.
The second way in which wetsuits reduce heat loss is to trap a thin layer of water between the diver's skin and the insulating suit itself. Body heat then heats the trapped water. Provided the wetsuit is reasonably well-sealed at all openings (neck, wrists, legs), this reduces water flow over the surface of the skin, reducing loss of body heat by convection, and therefore keeps the diver warm (this is the principle employed in the use of a "Semi-Dry")
Spring suit and steamer
In the case of a drysuit, it does exactly that: keeps a diver dry. The suit is sealed so that frigid water cannot penetrate the suit. Drysuit undergarments are often worn under a drysuit as well, and help to keep layers of air inside the suit for better thermal insulation. Some divers carry an extra gas bottle dedicated to filling the dry suit. Usually this bottle contains argon gas, because of its better insulation as compared with air.[12]
Drysuits fall into two main categories neoprene and membrane; both systems have their good and bad points but generally their thermal properties can be reduced to:
Membrane: usually a trilaminate construction; owing to the thinness of the material (around 1 mm), these require an undersuit, usually of high insulation value if diving in cooler water.
Neoprene: a similar construction to wetsuits; these are often considerably thicker (7-8 mm) and have sufficient insulation to allow a lighter-weight undersuit (or none at all); however on deeper dives the neoprene can compress to as little as 2 mm thus losing a proportion of their insulation. Compressed or crushed neoprene may also be used (where the neoprene is pre-compressed to 2-3 mm) which avoids the variation of insulating properties with depth.
[edit]Avoiding skin cuts and grazes
Diving suits also help prevent the diver's skin being damaged by rough or sharp underwater objects, marine animals or coral.
[edit]Diving longer and deeper safely
There are a number of techniques to increase the diver's ability to dive deeper and longer:
Technical diving - diving deeper than 40 metres (130 ft), using mixed gases, and/or entering overhead environments (caves or wrecks)
surface supplied diving - use of umbilical gas supply and diving helmets.[1]
saturation diving - long-term use of underwater habitats under pressure and a gradual release of pressure over several days in a decompression chamber at the end of a dive.[1]
[edit]Being mobile underwater
The diver needs to be mobile underwater. Streamlining dive gear will reduce drag and improve mobility. Personal mobility is enhanced by swimfins and Diver Propulsion Vehicles. Other equipment to improve mobility includes diving bells and diving shots.
scuba diving does not have a centralized certifying or regulatory agency, and is mostly self regulated. There are, however, several large diving organizations that train and certify divers and dive instructors, and many diving related sales and rental outlets require proof of diver certification from one of these organizations prior to selling or renting certain diving products or services.
The largest international certification agencies that are currently recognized by most diving outlets for diver certification include:
American Canadian Underwater Certifications (ACUC) (formerly Association of Canadian Underwater Councils) - originated in Canada in 1969 and expanded internationally in 1984
British Sub Aqua Club (BSAC) - based in the United Kingdom, founded in 1953 and is the largest dive club in the world
European Committee of Professional Diving Instructors (CEDIP) based in Europe since 1992 (see Cedip on French Wiki pages)
Confédération Mondiale des Activités Subaquatiques (CMAS), the World Underwater Federation
National Association of Underwater Instructors (NAUI) - based in the United States
Professional Diving Instructors Corporation (PDIC) - based in the United States
Professional Association of Diving Instructors (PADI) - based in the United States, largest recreational dive training and certification organization in the world
Scottish Sub Aqua Club (SSAC or ScotSAC) the National Governing Body for the sport of diving in Scotland.
International Training SDI, TDI & ERDi -based in the United States, TDI is the world's largest technical diving agency, SDI is the recreational division focusing on new methods and online courses, and ERDi is the public safety component.
Scuba Schools International (SSI) - based in the United States with 35 Regional Centers and Area Offices around the globe.
YMCA scuba - based in the U.S., part of Young Men's Christian Association (YMCA), a Christian related organization (open to all faiths, ages and genders despite the historic name)
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