Exploration, surveys and mapping
A significant aspect of cave diving by competent and enthusiastic cave divers is exploration, survey and mapping. Data collected is often shared and may be stored on databases to help optimize the effectiveness of such surveys, and make the information generally available.
Underwater cave mapping is complicated by both a lack of access to the surface for GPS positions, darkness, with short line-of-sight, and limited visibility, which complicate optical measurement. Altitude/depth is relatively simple as accurate depth measurement is available to divers in the form of decompression computers, which log a depth/time record of reasonable accuracy and are available for instantaneous readout at any point, and depth can be referenced to the altitude at the surface. Vertical dimensions can be directly measured or calculated as differences in depth.
Surface coordinates can be collected via GPS and remote sensing, with varying degrees of precision and accuracy depending on the type of entrance. In some cases the water surface is in view of GPS satellites, in others it is a considerable distance along a complex route from the nearest open air. Three dimensional models of varying accuracy and detail can be created by processing measurements collected by whatever methods were available. These can be used in virtual reality models. The usual methods for survey and mapping of underwater caves are dead reckoning and direct measurements of distance, compass direction and depth, by diving teams of two or three scuba divers, who record azimuth of the cave line, measurements of height, width, depth, and slope at intervals along the line, generally using a permanent guide line as a reference baseline, and take photographic records of features and objects of interest. Data are collected on wet-notes and by digital photography.[13] Hand-held sonar may be used for distance measurement where available. Where the depth or other constraints prevent divers from exploring in person, tethered and untethered remotely operated underwater vehicles (ROUVs) have been used effectively, using sonar technology to scan and map the surroundings, and video to record the appearance.
Features, artifacts, remains, and other objects of interest are recorded in situ as effectively as possible, generally by photography.
Hazards
Cave-diving is one of the most challenging and potentially dangerous kinds of diving 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 a 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 very good to very bad 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 30 metres (100 feet)), and penetration not further than 60 m (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 source of light even if the water is clear. Caves often contain sand, mud, clay, silt, or other sediment that can further reduce underwater visibility in seconds when stirred up. Consequently, visibility is often worse during exit, and divers rely on the guideline for finding the way out.
The water in caves can have strong flow. Most caves flooded to the surface at the cave mouth are 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 without-flowing currents, and other tunnels with in-flowing currents. Inflowing currents can cause serious problems for the diver, as they make the exit more difficult, and the diver is carried to spaces that are unfamiliar and may be dangerous, while outflowing currents generally make the exit quicker and the diver is carried through places they have been before and can be prepared for difficult areas.
Cave-diving has been perceived as one of the more deadly sports in the world. This perception may be exaggerated because the majority of divers who have died in caves have either not undergone specialized training or have had inadequate equipment for the environment. Some cave divers have suggested that cave-diving is statistically much safer than recreational diving due to the much larger barriers imposed by experience, training and equipment cost,[4] but there is no definitive statistical evidence for this claim.
There is no reliable worldwide database listing all cave-diving fatalities. Such fractional statistics as are available, however, suggest that few divers have 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.
Safety
Most cave divers recognize five general rules or contributing factors for safe cave-diving, which were popularized, adapted and became generally accepted from Sheck Exley's 1979 publication Basic Cave Diving: A Blueprint for Survival. In this book, Exley included accounts of actual cave-diving accidents, and followed each one with a breakdown of what factors contributed to the accident. Despite the unique circumstances of each individual accident, Exley found that at least one of a small number of major factors contributed to each one. This technique for breaking down accident reports and finding common causes among them is now called accident analysis, and is taught in introductory cave-diving courses. Exley outlined a number of these resulting cave-diving rules, but today these five are the most recognized:
Training: A safety conscious cave diver does not intentionally exceed the scope of their training. Cave-diving is normally taught in stages, each successive stage focusing on more complex aspects of cave-diving. Each stage of training is intended to be reinforced with actual cave-diving experience to develop competence before starting training at a more complex level. Accident analysis of cave-diving fatalities has shown that academic training without sufficient real world experience is not always enough in the event of an underwater emergency. By systematically building experience the diver can develop the confidence, motor skills and reflexes to remain calm and apply the appropriate procedures in an emergency. An inexperienced diver is more likely to panic than an experienced diver when confronted with a similar situation, all other factors being equal. Experience in dealing successfully with real or simulated problems is of the greatest value, experience of dives where nothing goes wrong reinforces the skills used, but not the skills that were not needed but might be critical in an emergency. When trained to the highest available level, further competence can be developed by practice and gradual extension of range of experience.
Guide line: A continuous guide line is maintained at all times between the leader of a dive team and a fixed point selected outside the cave entrance in open water. Often this line is tied off a second time as a backup directly inside the cavern zone. As the dive leader lays the guideline they take great care to ensure there is appropriate tension on the line, and that it does not go into line traps, tying off the line as necessary to keep it leading through a clear route. Other team members remain between the lead diver and the exit, in easy reach of the line at all times. If a silt out occurs, divers can find the line and follow it back to the cave entrance. Failure to use a continuous guide line to open water is cited as the most frequent cause of fatality among untrained, non-certified divers who venture into caves. Greater care to avoid line traps is required for laying permanent line, and more frequent tie-offs would be expected, as a permanent line is more susceptible to breaking over time.
Depth rules: Gas consumption, nitrogen narcosis and decompression obligation increase with depth, and the effects of nitrogen narcosis may be more critical in a cave due to the high task loading and presence of combinations of hazards. Cave divers are advised not to dive to depths exceeding the planned depth and the applicable range of their equipment and the breathing gases in use, and to keep in mind this effective difference between open water depth and cave depth. Excessive depth is frequently cited as a contributory factor in fatal incidents involving fully trained cave divers.
Breathing gas management: The breathing gas supply must last the diver until out of the overhead environment. There are several strategies for gas management. The most common protocol is the 'rule of thirds,' in which one third of the initial gas supply is used for ingress, one third for egress, and one third to support another team member in the case of an emergency. This is a very simple method, but is not always sufficient. UK practice is to adhere to the rule of thirds, but with an added emphasis on keeping depletion of the separate air systems "balanced", so that the complete loss of any single gas supply will still leave the diver with sufficient gas to return safely. The rule of thirds makes no allowance for increased air consumption that the stress caused by the loss of an air system may induce. Dissimilar tank sizes among the divers are also not allowed for by the rule of thirds, and a sufficient reserve should be calculated for each dive. UK practice is to assume that each diver is completely independent, as in a typical UK sump there is usually nothing that a buddy can do to assist a diver in trouble. Most UK cave divers dive solo. US sump divers follow a similar protocol.[citation needed] The rule of thirds was devised as an approach to diving Florida's caves – they typically have high outflow currents, which help to reduce air consumption when exiting. In a cave system with little or no outflow it is prudent to reserve more air than is provided by the rule of thirds.
Lights: Each cave diver should have at least three independent sources of light. One is considered the primary and is intended for general use during the dive. The others are considered backup lights and may be lower powered as they are not intended for exploration. Each light must have an expected burn time of at least the planned duration of the dive. If any diver loses light function so that they have fewer than three working lights, protocol requires that the dive be aborted for all members of the dive team and that they immediately start the exit.
Most cave-diving fatalities are due to running out of gas before reaching the exit. This is often the direct consequence of getting lost, whether the guide line is found again or not, and whether the visibility deteriorates, lights fail, or someone panics. On rare occasions equipment failure is unrecoverable, or a diver becomes inextricably trapped, seriously injured, incapacitated by using an unsuitable gas for the depth, or swept away by strong flow. Getting lost means separation from the continuous guide line to the exit, and not knowing the direction to the exit.
Some cave divers are taught to remember the five key components with the mnemonic: "The Good Divers Always Live" (training, guide, depth, air, light).
In recent years new contributing factors were considered after reviewing accidents involving solo diving, diving with incapable dive partners, video or photography in caves, complex cave dives and cave-diving in large groups. With the establishment of technical diving, the use of mixed gases—such as trimix for bottom gas, and nitrox and oxygen for decompression—reduces the margin for error. Accident analysis suggests that breathing the wrong gas for the depth or not analyzing the breathing gas properly has also led to cave-diving accidents.
Cave-diving requires a variety of specialized procedures, and divers who do not correctly apply these procedures may significantly increase the risk to the members of their team. The cave-diving community works hard to educate the public on the risks they assume when they enter water-filled caves. Warning signs with the likenesses of the Grim Reaper have been placed just inside the openings of many popular caves in the US and Mexico, and others have been placed in nearby parking lots and local dive shops.
Many cave-diving sites around the world include open-water basins, which are popular open-water diving sites. The management of these sites tries to minimize the risk of untrained divers being tempted to venture inside the cave systems. With the support of the cave-diving community, many of these sites enforce a "no-lights rule" for divers who lack cave training—they may not carry any lights into the water with them. It is easy to venture into an underwater cave with a light and not realize how far away from the entrance (and daylight) one has swum; this rule is based on the theory that, without a light, divers will not venture beyond daylight.
In the early phases of cave-diving the analysis shows that 90% of accidents were not trained cave divers; from the 2000s on the trend has reversed to 80% of accidents involving trained cave divers.[citation needed] Modern cave divers' capability and available technology allows divers to venture well beyond traditional training limits[clarification needed] and into actual exploration. The result is an increase of cave-diving accidents, in 2011 the yearly average of 2.5 fatalities a year tripled.[citation needed] In 2012 fatalities reached the highest annual rate to that date at over 20.
As response to the increase in fatalities during the years 2010 onwards, the International Diving Research and Exploration Organization (IDREO) was created in order to "bring awareness of the current safety situation of Cave Diving" by listing current worldwide accidents by year and promoting a community discussion and analysis of accidents through a "Cave Diver Safety Meeting" held annually.
Equipment
Equipment used by cave divers ranges from fairly standard recreational scuba configurations, to more complex arrangements which allow more freedom of movement in confined spaces, extended range in terms of depth and time, allowing greater distances to be covered in acceptable safety, and equipment which helps with navigation, in what are usually dark, and often silty and convoluted spaces.
Scuba configurations which are more often found in cave-diving than in open water diving include independent or manifolded twin cylinder rigs, side-mount harnesses, sling cylinders, rebreathers and backplate and wing harnesses. Bill Stone designed and used epoxy composite tanks for exploration of the San Agustín and Sistema Huautla caves in Mexico to decrease the weight for dry sections and vertical passages.
Stage cylinders are cylinders which are used to provide gas for a portion of the penetration. They may be deposited on the bottom at the guideline on preparation dives, to be picked up for use during the main dive, or may be carried by the divers and dropped off at the line during the penetration to be retrieved on the way out.
One of the high risk hazards of cave-diving is getting lost in the cave. The use of guide lines is the standard mitigation for this risk. Guide lines may be permanent or laid and recovered during the dive, using cave reels to deploy and recover the line. Permanent branch lines may be laid with a gap between the start of the branch line and the nearest point on the main line. Line used for this purpose is known as cave line. Gap spools with a relatively short line are commonly used to make the jump.
Line arrows are used to point towards the nearest exit, and cookies are used to indicate use of a line by a team of divers.
Silt screws are short lengths of rigid tube (usually plastic) with one sharpened end and a notch or slot at the other end to secure the line, which are pushed into the silt or detritus of the cave floor as a place to tie off a guideline when no suitable natural tie-off points are available.
A simple plastic helmet, such as those used in water sports like whitewater kayaking, is good protection in case of accidental contact with the cave ceiling or stalactites.
Diver propulsion vehicles, or Scooters, are sometimes used to extend the range by reducing the work load on the diver and allowing faster travel in open sections of cave. Reliability of the diver propulsion vehicle is very important, as a failure could compromise the ability of the diver to exit the cave before running out of gas. Where this is a significant risk, divers may tow a spare scooter.
Dive lights are critical safety equipment, as it is dark inside caves. Each diver generally carries a primary light, and at least one backup light. A minimum of three lights is recommended. The primary light should last the planned duration of the dive, as should each of the backup lights.
Cavern diving
Cavern diving is an arbitrarily defined, limited scope activity of diving in the naturally illuminated part of underwater caves, where the risk of getting lost is small, as the exit can be seen, and the equipment needed is reduced due to the limited distance to surface air. It is defined as a recreational diving activity as opposed to a technical diving activity on the grounds of low risk and basic equipment requirements.
History
Jacques-Yves Cousteau, co-inventor of the first commercially successful open circuit scuba equipment, was the world's first open circuit scuba cave diver.[citation needed] However, many cave divers penetrated caves prior to the advent of scuba with surface supplied breathing apparatus through the use of umbilical hoses and compressors. SCUBA diving in all its forms, including cave-diving, has advanced in earnest since Cousteau introduced the Aqua-Lung in 1943.
Two regions have had particular influence on cave-diving techniques and equipment due to their very different cave-diving environments. These are the United Kingdom, and the United States, mainly Florida.
UK history
The Cave Diving Group (CDG) was established informally in the United Kingdom in 1935 to organize training and equipment for the exploration of flooded caves in the Mendip Hills of Somerset. The first dive was made by Jack Sheppard on 4 October 1936, using a home-made drysuit surface fed from a modified bicycle pump, which allowed Sheppard to pass Sump 1 of Swildon's Hole. Swildon's is an upstream feeder to the Wookey Hole resurgence system. The difficulty of access to the sump in Swildon's prompted operations to move to the resurgence, and the larger cave there allowed use of standard diving dress which was secured from the Siebe Gorman Company. In UK cave-diving, the term "Sherpa" was used without irony for the people who carry the diver's gear although this has gone out of fashion; support is now more normally used, and before the development of SCUBA equipment such undertakings could be monumental operations.
Diving in the spacious third chamber of Wookey Hole led to a rapid series of advances, each of which was dignified by being given a successive number, until an air surface was reached at what is now known as "Chamber 9." Some of these dives were broadcast live on BBC radio, which must have been a quite surreal experience for both diver and audience.
The number of sites where standard diving dress could be used is clearly limited and there was little further progress before the outbreak of World War II reduced the caving community considerably. However, the rapid development of underwater warfare through the war made a lot of surplus equipment available. The CDG re-formed in 1946 and progress was rapid. Typical equipment at this time was a frogman rubber diving suit for insulation (water temperature in the UK is typically 4 °C), an oxygen diving cylinder, soda lime absorbent canister and counter-lung comprising a rebreather air system and an "AFLOLAUN", meaning "Apparatus For Laying Out Line And Underwater Navigation." The AFLOLAUN consisted of lights, line-reel, compass, notebook (for the survey), batteries, and more.
Progress was typically by "bottom walking", as this was considered less dangerous than swimming (note the absence of buoyancy controls). The use of oxygen put a depth limit on the dive, which was considerably compensated by the extended dive duration. This was the normal diving equipment and methods until approximately 1960 when new techniques using wetsuits (which provide both insulation and buoyancy), twin open-circuit SCUBA air systems the development of side mounting cylinders, helmet-mounted lights and free-swimming with fins. The increasing capacity and pressure rating of air bottles also extended dive durations.
US history
In the 1970s, cave-diving greatly increased in popularity among divers in the United States. However, there were very few experienced cave divers and almost no formal classes to handle the surge in interest. The result was a large number of divers trying to cave dive without any formal training. This resulted in more than 100 fatalities over the course of the decade. The state of Florida came close to banning SCUBA diving around the cave entrances. The cave-diving organizations responded to the problem by creating training programs and certifying instructors, in addition to other measures to try to prevent these fatalities. This included posting signs, adding no-lights rules, and other enforcements.
In the United States, Sheck Exley was a pioneering cave diver who first explored many underwater cave systems in Florida, and many throughout the US and the world. On 6 February 1974, Exley became the first chairman of the Cave Diving Section of the National Speleological Society.
Since the 1980s, cave-diving education has greatly reduced diver fatalities, and it is now rare for an agency trained diver to perish in an underwater cave. Also in the 1980s, refinements were made to the equipment used for cave-diving, most importantly better lights with smaller batteries. In the 1990s, cave-diving equipment configurations became more standardized, due mostly to the adaptation and popularization of the "Hogarthian Rig", developed by several North Florida cave divers, named in honor of William "Hogarth" Main, which promotes equipment choices that "keep it simple and streamlined".
Today, the cave community is most focused on training, exploration, public awareness, and cave conservation.
Documentary films made by Wesley C. Skiles and Jill Heinerth have contributed to the increasing popularity of cave-diving in the early 21st century.
Australian history
Four divers using scuba dived from the Right Imperial Cave in the Jenolan system in the Blue Mountains to an upstream chamber on 30 October 1954.
Cave-diving regions
Cave-diving venues can be found on all continents except Antarctica, where the average temperature is too low for water to remain liquid in caves.
There are few flooded caves in Africa which are known and accessible. There are several in South Africa, a few in Namibia and Zimbabwe, and some large caves recently discovered in Madagascar.
There are a large number of flooded caves in the limestone regions and other regions of Asia, particularly in the karst regions of China and Southeast Asia. Some are accessible for recreational cave-diving, but most have probably not yet been found or explored.
Australia has many spectacular water filled caves and sinkholes, many of them in the Mount Gambier region of South Australia.
Europe has a large number of flooded caves, particularly in the karst regions.
North America has many cave-diving venues, particularly in Florida, USA, and the Yucatán Peninsula of Mexico.
South America has some cave-diving venues in Brazil.
Terminology
Caves and caverns as geographical entities are defined differently from cave-diving and cavern-diving, so it is possible to be cavern diving in what is technically a cave, and cave-diving in what is technically a cavern.
Cave
A cavity or chamber in the earth with an entrance, some part of which is unreachable by direct natural light, large enough for human entry. There are several classes of cave. Some definitions specify a natural cavity caused by geological processes.
Cavern
A type of cave comprising a system of naturally formed chambers in the earth connected by passages. Some authorities do not distinguish between caves and caverns.
Cave Diving
Diving in a cave, cavern, or mine where the exit to open water with a surface in contact with the atmosphere is not always visible by natural illumination from all points of the dive, or where the direct, accessible route to the free surface in contact with the atmosphere is more than an arbitrarily specified distance, commonly 130 feet (40 m), but also quoted as 60 metres (200 ft) from the diver at any time.
Cavern Diving
Diving in a cave, cavern, or mine where the exit to open water with a surface in contact with the atmosphere is always visible by natural illumination from all points of the dive, or where the direct, accessible route to the free surface in contact with the atmosphere is less than an arbitrarily specified distance, commonly 130 feet (40 m), but also quoted as 60 metres (200 ft), from the diver at any time.
Types of Cave Dive
A cave dive can be categorized by the topology of the route, which can be linear, include a circuit, or be a traverse.
Linear
A dive route in which the divers return by the same route as the one they entered by.
Circuit
A dive route in which the divers return partly or completely by a different route to the one they entered by, using the entrance also as the exit.
Traverse
A dive route in which the divers pass through a cave from one entrance to another exit.
Simple
When used to describe a circuit or traverse, simple implies that the full route can be completed before the divers reach critical pressure (generally two thirds of initial pressure, or a pressure calculated for the dive plan) on the breathing gas supply, so it should be possible to safely turn the dive and return along the original route to the starting point at any time.
Complex
When used to describe a circuit or traverse, complex implies that the full route cannot be completed before the divers reach critical pressure on the breathing gas supply. In this case a setting up dive is done first, and the position reached at turnaround pressure is marked with a cookie and the divers return along the same route (linear path). They then dive the route in the other direction, and if they reach the cookie before reaching critical pressure for the same starting gas supply, they know the remaining gas is sufficient to complete the circuit or traverse if it goes according to plan.
Caves by flow type
These terms describe flooded cave areas with reference to flow direction.
Source
Cave where water flows out of the entrance used for diving. The flow will generally help divers on the way out.
Sink
A cave where water flows into the entrance used for diving, which can hinder divers from getting out.
Sump
A locally low-lying water filled passage of a cave. A cave may have several sumps separated by unflooded or partially flooded areas.
Types of cave by method of formation
Aeolian cave
Cave caused by wind erosion.
Coral cave
Enclosed spaces in coral reefs, created by the growth of stony corals.
Flooded mine
Flooded mines and other underground spaces excavated by people and their machinery, by technical definition are not caves, but the activity of diving in such spaces is considered cave-diving, as the procedures and equipment are the same.
Lava tube
Caves caused by volcanic action, where a lava flow cools and solidifies on the outside, and the fluid interior lava flows out at the lower end when the supply stops. They may be branched, but are usually continuously sloped. Other caves formed through volcanic activity include rifts, lava molds, open vertical conduits, inflationary, and blister caves.
Littoral cave
Sea cave
Cave along the shore of a coastal area. Usually created by wave action, and may be affected by tidal currents and wave surge.
Solution cave
Cave formed by groundwater dissolving the rock over long periods. They are more common in rocks which are more soluble in mildly acidic water, such as limestones and dolomites, and may be common in karst regions.
Talus cave
Cave formed by rock falls.
Types of cave by topology
Simple, linear, unbranched
Simply branched
Network, complex branched, anastomosed.
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