Most cave divers recognize five general rules for safe cave diving, which were popularized, adapted and became generally accepted from Sheck Exley`s 1977 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 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 should an emergency occur underwater. Only by slowly building experience can one remain calm enough to recall their training should a situation 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 the number one cause of fatality.
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 too, but with added emphasis that you must keep 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. 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.
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 against them. 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 swam; this rule is based on the theory that, without a light, divers will not venture beyond the point where they can see.