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Cave diving is underwater diving in caves which are at least partially filled with water. The equipment used varies depending on the circumstances, and ranges from breath hold to surface supplied, but almost all cave diving is done using scuba equipment, often in specialised configurations. Cave diving is generally considered to be a type of technical diving due to the lack of a free surface during large parts of the dive, and often involves decompression. In the United Kingdom it is an extension of the more common sport of caving, and in the United States an extension of the more common sport of scuba diving. Compared to caving and scuba diving, there are relatively few practitioners of cave diving. This is due in part to the specialized equipment (such as rebreathers, diver propulsion vehicles and dry suits) and skill sets required, and in part because of the high potential risks, including decompression sickness and drowning. Despite these risks, water-filled caves attract scuba divers, cavers, and speleologists due to their often unexplored nature, and present divers with a technical diving challenge. Underwater caves have a wide range of physical features, and can contain fauna not found elsewhere. ==Hazards== Cave diving is one of the most challenging and potentially dangerous kinds of diving or caving and presents many hazards. Cave diving is a form of penetration diving, meaning that in an emergency a diver cannot swim vertically to the surface due to the cave's ceilings, and so must swim the entire way back out. The underwater navigation through the cave system may be difficult and exit routes may be at considerable distance, requiring the diver to have sufficient breathing gas to make the journey. The dive may also be deep, resulting in potential deep diving risks. Visibility can vary from nearly unlimited to low, or non-existent, and can go from one extreme to the other in a single dive. While a less-intensive kind of diving called cavern diving does not take divers beyond the reach of natural light (and typically no deeper than 100 ft, and penetration not further than 200 ft), true cave diving can involve penetrations of many thousands of feet, well beyond the reach of sunlight. The level of darkness experienced creates an environment impossible to see in without an artificial form of light. Caves often contain sand, mud, clay, silt, or other sediment that can further reduce underwater visibility in seconds when stirred up. Caves can carry strong water currents. Most caves emerge on the surface as either springs or siphons. Springs have out flowing currents, where water is coming up out of the Earth and flowing out across the land's surface. Siphons have in-flowing currents where, for example, an above-ground river is going underground. Some caves are complex and have some tunnels with out-flowing currents, and other tunnels with in-flowing currents. If currents are not properly managed, they can cause serious problems for the diver. Cave diving has been perceived as one of the more deadly sports in the world. This perception is arguable because the vast majority of divers who have lost their lives in caves have either not undergone specialized training or have had inadequate equipment for the environment.〔 Cave divers have suggested that cave diving is in fact statistically much safer than recreational diving due to the much larger barriers imposed by experience, training, and equipment cost.〔 There is no reliable worldwide database listing all cave diving fatalities. Such fractional statistics as are available, however, suggest that very few divers have ever died while following accepted protocols and while using equipment configurations recognized as acceptable by the cave diving community.〔 In the very rare cases of exceptions to this rule there have typically been unusual circumstances.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「cave diving」の詳細全文を読む スポンサード リンク
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