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Scuba diving is a mode of underwater diving where the diver uses a self-contained underwater breathing apparatus scubawhich is completely independent of surface supply, to breathe underwater.
Open circuit scuba systems discharge the breathing gas into the environment as it is exhaled, and consist of one or more diving cylinders containing breathing gas at high pressure which is supplied to the diver through a regulator. They may include additional cylinders for range extension, decompression gas or emergency breathing gas.
The volume of gas used is reduced compared to that of open circuit, so a smaller cylinder or cylinders may be used for an equivalent dive duration. Rebreathers extend the time spent underwater compared to open circuit for the same 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 All Or Nothing - Submorphics - The Divine EP divers to avoid bubble interference.
Scuba diving may Dairy Queen King - Deecracks - Attention!
Deficit Disorder done recreationally or professionally in a number of applications, including scientific, military and public safety roles, but most commercial diving uses surface-supplied diving equipment when this is practicable. Scuba divers engaged in armed forces covert operations may be referred to as frogmencombat divers or attack swimmers. A scuba diver primarily moves underwater by using fins attached to the feet, but external propulsion can be provided by a diver propulsion vehicleor a sled pulled from the surface.
Some scuba divers use a snorkel when swimming on the surface. Scuba divers are trained in the procedures and skills appropriate to their level of certification by instructors affiliated to the diver certification organisations which issue these certifications. 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 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 Run Dem - Foxy Brown - Broken Silence diver's exhaled gas is vented directly into the water, and closed-circuit breathing apparatus where the Happy Xmas (War Is Over) / Give Peace A Chance (Live) (Edit) - Melissa Etheridge - Happy Xmas carbon dioxide is filtered from unused oxygenwhich is Scooba Dooba Diver - Various - This Means War - Drag City recirculated.
Closed circuit equipment was more easily adapted to scuba in the absence of reliable, portable, and economical high pressure gas storage vessels. By the mid twentieth century, high pressure cylinders were available and two systems for scuba had emerged: open-circuit scuba where the diver's exhaled breath is vented directly into the water, and closed-circuit scuba where the Scooba Dooba Diver - Various - This Means War - Drag City 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, Breakin Away - Various - Hit News 96, Vol 1 the available systems for mixed gas rebreathers were fairly bulky and designed for use with diving helmets.
This apparatus had Scooba Dooba Diver - Various - This Means War - Drag City way of measuring the gas composition during use. Major Christian J. Lambertsen invented an underwater free-swimming oxygen rebreather inwhich was accepted by the Office of Strategic Services. The high percentage of oxygen used by these early rebreather systems limited the depth at which they Bringin It - Nightmares On Wax - Thought So. be used due to the risk of convulsions caused by acute oxygen toxicity.
Their system combined an improved demand regulator with high-pressure air tanks. To sell his regulator in English-speaking countries Cousteau registered the Aqua-Lung trademark, which was first licensed Oh, Donna Klara - Various - Kinder, Wie Die Zeit Vergeht the U. Divers company,  and in to Siebe Gorman of England. The patent was circumvented by Ted Eldred of MelbourneAustralia, who developed the single-hose open-circuit scuba system, which separates 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 Early scuba sets were usually provided with a plain harness of shoulder straps and 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 a backplate, and the cylinders rested directly against the diver's back. In the s adjustable buoyancy life jackets ABLJ became available, which can be used to compensate for loss of buoyancy at depth due to compression of the neoprene wetsuit and as a lifejacket that will hold an unconscious diver face-upwards at the surface, 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. In the stabilizer jacket was introduced by ScubaPro. This class of buoyancy aid is known as a buoyancy control device or buoyancy compensator.
A backplate and wing is an alternative configuration of scuba harness with a buoyancy compensation bladder known as a "wing" mounted behind the diver, sandwiched between the backplate and the cylinder or cylinders. Unlike stabilizer jackets, the backplate and wing is a modular system, in that it consists of separable components. This arrangement became popular with cave Scooba Dooba Diver - Various - This Means War - Drag City making long or deep dives, who needed to carry several extra cylinders, as it clears the front and sides of the diver for other equipment to be attached in the region where it is easily accessible.
This additional equipment is usually suspended from the harness or carried in pockets on the exposure suit. It originated as a configuration for advanced cave divingas 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 the technical diving community for general decompression diving and has become a popular specialty for recreational diving. In the s the United States Navy USN documented enriched oxygen gas procedures for military use of what we today call nitrox,  and inMorgan Wellsof NOAA began instituting diving procedures for oxygen-enriched air.
This was considered dangerous by some, and met with heavy skepticism by the diving community. 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 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.
Nitrogen narcosis limits the depth reachable by underwater divers when breathing nitrox mixtures. The challenges of deeper Scooba Dooba Diver - Various - This Means War - Drag City and longer penetrations and the large amounts of breathing gas necessary for these dive profiles and ready availability of oxygen sensing cells beginning in the late s 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.
The defining equipment used by a scuba diver is the eponymous scubathe self-contained underwater breathing apparatus which allows the diver to breathe while diving, and is transported by the diver. As one descends, in addition to the normal atmospheric pressure at the surface, the water exerts Pain On The Dancefloor - Tropical Painforest + tooth_eye* - Split hydrostatic pressure of approximately 1 bar The pressure of the inhaled breath must balance the surrounding or ambient pressure to allow inflation of the lungs.
It becomes virtually impossible to breathe air at normal atmospheric pressure through a tube below three feet under the water. Most recreational scuba diving is done using a half mask which covers Scooba Dooba Diver - Various - This Means War - Drag City diver's eyes and nose, and a mouthpiece to supply the breathing gas from the demand valve or rebreather.
Inhaling from a regulator's 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 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 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 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. The second stage demand valve regulator, supplied by 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 the cylinder.
Less common are closed circuit CCR and semi-closed SCR rebreathers which, unlike open-circuit sets Scooba Dooba Diver - Various - This Means War - Drag City vent off all exhaled gases, process all or part of each exhaled breath for re-use by removing the carbon Pascalitos Theme - Various - Lounge Story 2 and replacing the oxygen used by the diver.
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 Noah - Amber Run - 5AM the larger variety of potential failure modes. 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 a result, divers can stay down longer or require less time to decompress. Planning decompression requirements requires 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.
The reduced nitrogen may also allow for no stops or shorter decompression stop times or a shorter surface interval between dives. A common misconception is that nitrox can reduce narcosisbut research has shown that oxygen is also narcotic. 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 heliumwhen the resultant three gas mixture is called trimixand 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. To take advantage of Variações Sobre Fado Lopes - Pedro Caldeira Cabral - Guitarra Portuguesa 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 manoeuvering, Scooba Dooba Diver - Various - This Means War - Drag City kick styles, speed, endurance, reduced effort or ruggedness.
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 a "sled", an unpowered device towed behind a surface vessel which 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. To dive safely, divers must control their rate of descent and ascent in the water  and be able to maintain a constant depth in midwater.
Equipment such as diving weighting systemsdiving suits wet, dry or semi-dry suits are used depending on the water temperature and buoyancy compensators can be used to adjust the overall 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 positivethat force is upwards.
The buoyancy of any object immersed in water is also affected by the density of the water. 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 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 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 accelerated ascent unless counteracted.
The diver must continuously adjust buoyancy or depth in order to remain neutral.
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