What is Cave Diving?

The following information below is an excerpt from an article published at Wikipedia.com. You may read its entirety at this link: http://en.wikipedia.org/wiki/Cave_diving

A MAD Caver coming out of Hinatuan Cave

Cave diving

is a type of technical diving in which specialized equipment is used to enable the exploration of caves which are at least partially filled with water. 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. Caves often have a wide range of unique physical features (such as stalactites, stalagmites and otherspeleothems), and can contain unique fauna (including trogloxenes, troglophiles and troglobites) not found elsewhere.


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 horizontally or diagonally to escape. 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, 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 is perceived as one of the more dangerous sports in the world. This perception is arguable because the vast majorities 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.


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 uniqueness of any 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 safe cave diver never exceeds the boundaries of his/her training. Cave diving is normally taught in segments, each successive segment focusing on more complex aspects of cave diving. Furthermore, each segment of training must be coupled with real world experience before moving to a more advanced level. Accident analysis of recent cave diving fatalities has proven that academic training without sufficient real world experience is not enough in the event of an underwater emergency. Only by slowly building experience can one remain calm enough to recall their training should a problem arise, whereas an inexperienced diver (who may be recently trained) will tend to panic when confronted with a similar situation.

•           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 he takes great care to ensure there is sufficient tension on the line. Should a silt out occur, divers can find the taut line and successfully follow it back to the cave entrance. It is important to note that not using a guide line is the number one cause of fatality among untrained, non-certified divers who venture into caves.

•           Depth rules: Gas consumption and decompression obligation increase with depth, and it is critical that no cave diver exceeds the dive plan or the maximum operating depth (MOD) of the gas mixture used. Also, the effects of nitrogen narcosis are possibly greater in a cave, even for a diver who has the same depth experience in open water. Cave divers are advised not to dive to “excessive depth,” and to keep in mind this effective difference between open water depth and cave depth. It should be noted that among fully trained cave divers, not paying sufficient attention to depth is a major cause of fatalities.

•           Air (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.UK practice is to adhere to the rule of thirds, but with an added emphasis on keeping depletion of your separate air systems “balanced,” so that the loss of a complete air system will still leave you with sufficient air to return safely.

Note that the rule of thirds makes no allowance for the increased air consumption that the loss of an air system will induce. Dissimilar tank sizes among the divers are also not included and the proper amount of air reserve must be calculated for each dive (if tanks are dissimilar).

UK practice is to assume that anyone else diving with you does not exist, as in a typical UK sump there is absolutely nothing that you can do to assist him/her. Most UK cave divers dive solo. US sump divers follow a similar protocol. Note that 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 mandatory to reserve more air than is dictated by the rule of thirds.

•           Lights: All cave divers must have three independent sources of light. One is considered the primary and the other two are considered backup lights. If any one of the three light sources fail for one diver, the dive is called off and ended for all members of the dive team.

These five rules may be remembered with the mnemonic The Good Divers Are Living, the first letter of each word referring to the first letter of the corresponding rule. An alternative mnemonic taught in the United States is Thank Goodness All Divers Live, requiring a rearrangement of the rules.

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 usage of mixed gases—such as trimix for bottom gas, and nitrox and oxygen for decompression—reduces the margin for error. Accident analysis informs us that breathing the wrong gas at the wrong depth and/or not analyzing the breathing gas properly has led to cave diving accidents.

Cave diving requires a wide variety of very specialized techniques. Divers who do not adhere strictly to these techniques, as well as equipment specifications, greatly increase the amount of risk they undertake. 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 others have been placed in nearby parking lots and local dive shops.

Many cave diving sites around the world contain basins, which are also popular open-water diving sites. These sites try 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.


Cave diving training includes equipment selection and configuration, guideline protocols and techniques, gas management protocols, communication techniques, propulsion techniques, emergency management protocols, and psychological education. As cave diver training stresses the importance of safety it does point out cave conservation ethics as well. Most training programs contain various stages of certification and education.

•           Cavern training explains the basic skills needed to enter into the overhead environment. Training will generally consist of gas planning, propulsion techniques needed to deal with the silty environments in many caves, reel and handling, and communication. Once certified as a cavern diver, a diver may undertake cavern diving with a cavern (or greater) certified “buddy,” as well as advance into cave diving training.

•           Introduction into cave training builds off of the techniques learned during cavern training and includes the training needed to penetrate beyond the cavern zone and working with permanent guidelines that exist in many caves. Once intro to cave certified, a diver may penetrate much further into a cave, usually limited by 1/3 of a single cylinder, or in the case of a basic cave certification, 1/6 of double cylinders. An intro cave diver is usually not certified to do complex navigation.

•           Apprentice cave training serves as the building block from intro to full certification and includes the training needed to penetrate deep into caves working from both permanent guide lines as well as limited exposure to side lines that exist in many caves. Training covers complex dive planning and decompression procedures used for longer dives. Once apprentice certified, a diver may penetrate much further into a cave, usually limited by 1/3 of double cylinders. An apprentice diver is also allowed to do a single jump or gap (a break in the guideline from two sections of mainline or between mainline and sideline) during the dive. An apprentice diver typically has one year to finish full cave or must repeat the apprentice stage.

•           Full cave training serves final level of basic training and includes the training needed to penetrate deep into the cave working from both permanent guidelines as well as sidelines and may plan and complete complex dives deep into a system using decompression to stay longer. Once cave certified, a diver may penetrate much further into a cave, usually limited by 1/3 of double cylinders. A cave diver is also allowed to do multiple jumps or gaps (a break in the guideline from two sections of mainline or between mainline and sideline) during the dive.


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