Cave-diving is underwater diving in water-filled caves. It may be done as an extreme sport, a way of exploring flooded caves for scientific investigation, or for the search for and recovery of divers or, as in the 2018 Thai cave rescue, other cave users. 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 specialized configurations with redundancies such as sidemount or backmounted twinset. Recreational 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 planned decompression stops. A distinction is made by recreational diver training agencies between cave-diving and cavern-diving, where cavern diving is deemed to be diving in those parts of a cave where the exit to open water can be seen by natural light. An arbitrary distance limit to the open water surface may also be specified.
In the United Kingdom, cave-diving developed from the locally more common activity of caving. Its origins in the United States are more closely associated to recreational 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 and skill sets required, and in part because of the high potential risks due to the specific environment.
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.
Procedures
Entrance to Peacock Springs Cave System
The procedures of cave-diving have much in common with procedures used for other types of penetration diving. They differ from open-water diving procedures mainly in the emphasis on navigation, gas management, operating in confined spaces, and that the diver is physically constrained from direct ascent to the surface during much of the dive.
As most cave-diving is done in an environment where there is no free surface with breathable air allowing an above-water exit, it is critically important to be able to find the way out before the breathing gas runs out. This is ensured by the use of a continuous guideline between the dive team and a point outside of the flooded part of the cave, and diligent planning and monitoring of gas supplies. Two basic types of guideline are used: permanent lines, and temporary lines. Permanent lines may include a main line starting near the entrance/exit, and side lines or branch lines, and are marked to indicate the direction along the line to the nearest exit. Temporary lines include exploration lines and jump lines.
Decompression procedures may take into account that the cave diver usually follows a very rigidly constrained and precisely defined route, both into and out of the cave, and can reasonably expect to find any equipment such as drop cylinders temporarily stored along the guideline while making the exit. In some cases, changes of depth of the cave along the dive route will constrain decompression depths, and gas mixtures and decompression schedules can be tailored to take this into account.
Skills
A white warning sign with a picture of the Grim Reaper and the headline "Prevent your death. Go no farther" over black text explaining the dangers to divers of proceeding into the cave without proper equipment and certification.
Warning sign near the entrance to a cave
Most open-water diving skills apply to cave-diving, and there are additional skills specific to the environment, and to the chosen equipment configuration.
Good buoyancy control, trim and finning technique help preserve visibility in areas with silt deposits. The ability to reverse kick to back out of restrictions where there is no space to turn around is useful.
Finning skills: Frog kick, which avoids up- and downward directed vortices and are less likely to disturb silt on the bottom or loose material on the ceiling, and modified frog kick, a version which is more suited to narrow spaces; modified flutter kick, a version of flutter kick which minimizes downward directed vortices; back kick, which produces thrust towards the feet, used to move backwards along the long axis of the diver, and helicopter turns, which rotate the diver on the spot around a vertical axis, using lower leg and ankle movements.
The ability to navigate in total darkness using the guideline to find the way out is a safety critical emergency skill. Line management skills required for cave-diving include laying and recovering guide lines using a reel, tie-offs, the use of a jump line to cross gaps or find a lost guide line in silted out conditions, identifying the direction along the guideline leading to the exit, and the skills of dealing with a break in a guideline.
Emergency skills for dealing with gas supply problems are complicated by the possibility of the emergency occurring in a confined space and low visibility or darkness, and at a considerable horizontal distance from a free surface to the atmosphere.
Communicating by touch and light signals.
Providing and receiving emergency breathing gas while swimming through narrow spaces.
Line management
The essential cave-diving procedure is navigation using a guide line. This includes laying and marking line, following line and interpreting line markers, avoiding entanglement, recovering from entanglement, maintaining and repairing line, finding lost line, jumping gaps, and recovering line, any of which may need to be done in zero visibility, total darkness, tight confined spaces or a combination of these conditions.
Laying a cave line: the procedure of running line (unreeling line under light tension as one advances) to avoid snagging on the diver and so that it runs fairly straight between placements, placing the line so it can all be seen and reached, so it can be followed in good or bad visibility, avoiding line traps, and securing the line sufficiently at suitable places to keep it in position.
Making placements - securing the guideline as it is being run and the choice of primary and secondary tie offs.
Temporary line – line that is laid on the way into parts of a cave without permanent line, and recovered to the reel on the way out.
Permanent line – line that is thicker, and therefore easier to see, stronger, and more abrasion resistant, and more securely fastened, intended to be left in place for use by other divers. It may be secured to placements at closer intervals to facilitate finding the other end and reconnection in case of a break. It is not recovered during exit, and will generally be marked.
Marking line: Permanent line is marked to indicate the direction to the nearest exit, and to indicate where dive teams have passed but have not yet returned by looping the line onto a line marker, ensuring that a directional marker points in the correct direction, and that all markers are sufficiently securely attached, while remaining easily removable if temporary.
Directional markers - cave arrows used to indicate the way out along the line.
Personal markers – cookies – temporary markers to indicate that a diver has passed beyond a point but has not returned yet, particularly where the group leaves the permanent line or makes a jump to a secondary permanent (branch) line. A personal directional marker may be attached to a line to indicate that the owner has gone in that direction, which can happen after divers are separated if one, finds the line but not the other divers, and decides to exit independently.
Following a line – the skills of navigating back out of a cave using the line as a guide, particularly in the dark and low visibility.
Finding a lost line: although cave-diving procedures are intended to minimize the risk of losing the guide line, it can happen, and as the chance of finding one's way out without the line are drastically reduced, losing the line is considered a life-threatening situation, and the diver must be competent in the methods for relocating the line in all reasonably foreseeable circumstances, which include a bad silt-out, total darkness, and loss of contact with the other divers in the team. Methods of search should prevent the diver from drifting away from the vicinity of the line, so the start position for the search should be secured by tying off a search line. In principle, if the diver feels their way around the cross section of the cave orthogonal to the line direction until they get back to the starting point, the guideline should be either found directly, or be within the loop of the search line, but even this is not guaranteed to work, as the shape of the cave and limited breathing gas supplies could make this impossible.
Fixing a line break, this requires the ability to tie reliable knots, which may have to be done in bad visibility. It also requires the diver to find the other end of the break. On the way into a cave a line break is an inconvenience, as if the other side cannot be found, the divers can still find their way out. On the way out a line break is a life-threatening emergency until the other end is found, as gas supply is limited and there is no infallible way to find the other end while there is enough gas to complete the exit.
Jumping a gap to a branch line – this involves tying off to the permanent line in a way that is unlikely to come loose, but may be released quickly on the return. Passing a loop on the end of the jump line round the permanent line and over the reel is a standard method. A tag on the end of the loop helps release it quickly. This method cannot be inadvertently released by other divers following the main line.
Recovering temporary line – this is done by the last diver in line on the way out, so the others can follow the line out of the cave, even in reduced visibility, without risking losing the line. They may prepare the line for the reel operator, by releasing tie-offs, which cuts down on delays. In an emergency exit the reel and line may be temporarily abandoned, as it can be retrieved later. The reel operator keeps a light tension on the line and tries to keep it evenly distributed over the width of the reel while winding in. The divers further ahead on the line can feel the presence of others behind them by line tension and small movements of the line as it is reeled in.
Lost line
Losing the guide line in a cave is a potentially life-threatening emergency. While following recommended best practice makes it highly unlikely that a diver will lose the line, it can and does happen, and there are procedures which will usually work to find it again. Any reliable information on where the diver is likely to be relative to the last known position of the line may be critical, and the procedure of choice will depend on what is reliably known. In all situations, the diver will attempt to stabilize the situation and avoid getting further lost, and make a thorough visual check in all directions from where they are at the time, taking into account the possibility of the line being in a line trap. If the diver has not also separated from their buddy, the buddy may know where the line is, and can be asked, and if the diver is separated from their buddy, the buddy may be at the line, and the buddy's light may be visible.
Stabilizing the position is generally done by finding the nearest feasible tie-off point and securely tying off a search line. The direction of the guide line when last seen should be known, and therefore the direction the diver was swimming in before losing the line. If the diver was neutrally buoyant while following the line, the approximate depth can be reconstructed by finding the depth of neutral buoyancy again, without adjusting inflation of BCD or dry suit. Unless the line was lost by the diver not noticing a change of direction, it is likely to be at much the same depth, in much the same direction, and at a similar lateral and vertical distance as when last seen, making it logical to try that direction first. While swimming towards the estimated position of the line and slowly paying out search line, the diver will search visually, and in low visibility or darkness, also by feel, making arm sweeps across the expected direction of the line, while defending the head from impact with the other arm. The distance swum towards the estimated position of the lost line can be measured by the spacing and number of knots paid out on the search line. If the search fails, the diver will return to the tie off and try again in the next best guess for the direction the line may be. The diver may also choose to try a different search method. The best search method for any given situation will depend on the water conditions, the layout of the section of cave, the way the line was laid, the situational knowledge and skills of the diver, and the equipment available – a method that would be ideal for one situation might not work at all for another.
If the line is found, but not the other divers, the diver can tie off their search reel to the guide line as an indicator to other members of the team that they were lost but have found the guide line, and indicate the direction that they intend to proceed along the guideline with a personal directional marker so that others who see it while searching for the lost diver will know whether the diver chose the right direction to exit the cave.
Lost buddy
This is generally the converse situation to the lost guide line, in that the diver loses contact with their buddy or team but remains in contact with the guide line, so is not they lost. Their first priority is to not get lost or disorientated, and in furtherance of this aim would attach a directional line marker to the guide line indicating the direction to the exit before starting a search. The search line can be tied to the directional maker to prevent it from sliding along the line during the search. The direction for the search would depend on the layout of that part of the cave, and where the missing diver should have been in the group. The search party must consider their own safety first, regarding how much gas they can afford to use in a search, which will depend on the stage of the dive when the diver is noticed to be missing. When searching in darkness, the searches should periodically turn off their lights as this will allow them to see the lost diver's light more easily.
Gas planning and management
Gas planning is the aspect of dive planning which deals with the calculation or estimation of the amounts and mixtures of gases to be used for a planned dive profile. It usually assumes that the dive profile, including decompression, is known, but the process may be iterative, involving changes to the dive profile as a consequence of the gas requirement calculation, or changes to the gas mixtures chosen. Use of calculated reserves based on planned dive profile and estimated gas consumption rates rather than an arbitrary pressure based on a fraction of the initial gas supply is sometimes referred to as rock bottom gas management. The purpose of gas planning is to ensure that for all reasonably foreseeable contingencies, the divers of a team have sufficient breathing gas to safely return to a place where more breathing gas is available. In almost all cases this will be the surface.
Gas planning includes the following aspects:
Choice of breathing gases to suit the depth at which they will be used,
Choice of Scuba configuration, to conveniently carry the gas, or store it at stage points along the route
Estimation of gas quantities required for the planned dive, including bottom gas, travel gas, and decompression gases, as appropriate to the profile.
Estimation of gas quantities for reasonably foreseeable contingencies. Under stress it is likely that a diver will increase breathing rate and decrease swimming speed. Both of these lead to a higher gas consumption during an emergency exit or ascent.
Choice of cylinders to carry the required gases. Each cylinder volume and working pressure must be sufficient to contain the required quantity of gas.
Calculation of the pressures for each of the gases in each of the cylinders to provide the required quantities.
Specifying the critical pressures of relevant gas mixtures for appropriate stages (waypoints) of the planned dive profile (gas matching).
The primary breathing apparatus may be open circuit scuba or rebreather, and bailout may also be open circuit or rebreather. Emergency gas may be shared among the team members, or each diver may carry their own, but in all cases each diver must be able to bail out onto a gas supply of their own for long enough to get to the next planned source of emergency gas. If for any reason this situation no longer applies, there is a single point of critical failure, and the risk becomes unacceptable, so the dive should be turned.
Gas management also includes the blending, filling, analyzing, marking, storage, and transportation of gas cylinders for a dive, and the monitoring and switching of breathing gases during a dive, and the provision of emergency gas to another member of the dive team. The primary aim is to ensure that everyone has enough to breathe of a gas suitable for the current depth at all times, and is aware of the gas mixture in use and its effect on decompression obligations and oxygen toxicity risk.
Gas management rules of thumb
The rule of thirds for gas management is a rule of thumb used by divers to plan dives so they have enough breathing gas remaining in their diving cylinder at the end of the dive to be able to complete the dive safely. This rule mostly applies to diving in overhead environments, such as caves and wrecks, where a direct ascent to the surface is impossible and the divers must return the way they came.
For divers following the rule, one third of the gas supply is planned for the outward journey, one third is for the return journey and one third is a safety reserve. However, when diving with a buddy with a higher breathing rate or a different volume of gas, it may be necessary to set one third of the buddy's gas supply as the remaining 'third'. This means that the turn point to exit is earlier, or that the diver with the lower breathing rate carries a larger volume of gas than he alone requires.
A different option for penetration dives is the Half + 15 bar (half + 200 psi) method, in which the contingency gas for the stage is carried in the primary cylinders. Some divers consider this method to be the most conservative when multi-staging. If all goes to plan when using this method, the diver’s surface with stages nearly empty, but with all the contingency gas still in their primary cylinders. With a single stage drop, this means the primary cylinders will still be about half-full.
Training
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.[clarification needed][citation needed] Cave diver training also stresses the importance of risk management and cave conservation ethics.[citation needed] Most training systems offer progressive stages of education and certification.
Cavern training covers the basic skills needed to enter the overhead environment. Training will generally consist of gas planning, propulsion techniques needed to deal with the silty environments in many cases, reel and handling, and communication. Once certified as a cavern diver, a diver may undertake cavern diving with a cavern or cave certified "buddy", as well as continue into cave-diving training.
Introduction into cave training builds on 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 cases. 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 transition from intro to full certification and includes the training needed to penetrate deep into caves working from permanent guide lines as well as limited exposure to side lines that exist in many cases. 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 as the final level of basic training and includes the training needed to penetrate deep into the cave working from both permanent guidelines and 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 certified as competent to do multiple jumps or gaps (a break in the guideline from two sections of mainline or between mainline and sideline) during the dive.
Further training may be available in skills for cave surveying and mapping.
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