Prerequisites -, Training &, Equipment
While cavern diving by recreational divers can be performed relatively safely, for full-cave dives far from daylight or the next exit you need a high redundancy in the survival components of your diving quipment as well as special diving skills. These can be acquired in special cave-diving courses. Since cave diving is often subject to approval and involves substantial risks, you should avoid an autodidactic approach. Basically, cave-diving training takes place in three (or sometimes four) stages:
The diver learns to dive in the daylight area of the cave entrance. Depending on the organization, the maximum penetration distance is set at 50-60m with a maximum depth of 18 to 20m. This type of cave diving is popular among normal recreational divers. There are other limiting conditions such as minimum size of the passage, minimum visibility, junctions (prohibition of jumps), minimal gear size and air as the sole gas, pure decompression dives, just to name a few. In terms of equipment redundancy and gas management there are similar rules. Nevertheless, a “normal” recreational diver can, with little adaptation of their open-water equipment and with a relatively short theoretical training, become “fit” in order to undertake safe dives under the supervision and guidance of an experienced cave guide or instructor.
(Basic) Introductory Cave Diver:
Here the daylight area is definitively left behind; you are in the zone of permanent darkness. Decompression dives are not uncommon, as well as those with nitrox (depending on the training organization). The cave zone is further defined (partly dependent on the organization) with respect to a specific minimum visibility, prohibition of diving through restrictions (narrow passages with a specific minimum size), a maximum depth of usually 30m, the (at this stage) absence of using stage bottles, no post-siphon dives and other limitations. Some organizations separate this level into two “sub-levels:” Introduction to cave diving and Cave diver. Depending on the environment where the dive is to take place, there are further requirements related to equipment.
(Full) Cave Diver:
The full-cave zone is the highest and most demanding level of cave diving. This includes everything which is not covered by the previous two (or three) levels, especially: any desired penetration distances, narrow passages, post-siphon dives, depths up to 40m EAD, any desired visibility up to 0m visibility, other gasses than air, use of stage bottles, long-distance dives, decompression dives and narrow passages down to the size of so-called “squeezes.”pment and training, which based on the nature of the dive are much more rigid than for the cavern area. It is definitely a cave area, and is no place for a “normal” recreational diver to be without the right equipment AND the proper training.
Problems and special risks
Pressure compensation: Since natural caves are seldom on one horizontal plane nor linear, there are constantly ascents and descents to be made. Different diving depths, however, mean different pressure conditions (0m = 1 bar , 10m = 2 bar, 20m = 3 bar etc.), which must be compensated for by the diver.
Loss of orientation: The fin kick of the diver can stir up sediment from the floor of the cave (silt out). Bubbles from exhaled air can also dislodge particles from the ceiling of the cave (“percolation”), which then sink to the floor. These suspended sediments can fairly quickly lead to extremely poor visibility. For this reason, the way to the exit is marked by a CONTINUOUS guide line, which has either been previously been installed or has been unwound from a reel or spool and carefully and sensibly mounted by the diver during the exploration of the cave. If the diver loses contact to this guide rope or intentionally leaves it, the danger of becoming confused is very high. In such cases, a fatal outcome for the dive is to be expected.
Breathing gas supply: Cave divers normally dive according to the rule of thirds, which means one third of the gas is used for the trip to the cave (ingress) and one third for the return trip (egress). The last third is a reserve which, in the event of a problem and the ensuing higher gas usage, will ensure a safe return trip. In an emergency, the reserve also needs to be enough to supply the diver’s partner with gas. Breathing gas for the decompression is usually permanently deposited in the mouth of the cave on the main guide rope at the proper depths. In the case of a siphon where it is necessary to surface inside of a cave and decompress there, it will be necessary to transport all the necessary gasses during the entire dive.
The above-mentioned so-called “rule of thirds” can (or must) be changed based on the requirements of the situation or the experience of the diver, in the sense of providing for even better safety. There are other gas management regimens which can be used, such as a rule of fourths or even a rule of sixths. In this sense, the rule of thirds is a minimum rule!
Psychological stability: Fundamentally, divers should take care of problems underwater which occur underwater: as a rule, an emergency ascent to the surface, due to the danger of decompression sickness and pneumothorax, is only a last resort when diving in seas and rivers. For cave divers, the way to the surface is blocked by the roof of the cave anyway. As such, this type of diving requires a high psychological stability and level-headedness; this is extremely important in order to avoid unexpected events which might cause the diver to panic and endanger their life and that of their diving partner (buddy).
Danger of injury: When diving in a cave with protruding rocks, stalactites and other obstructions, there is increased danger of colliding with these obstructions, resulting in external injuries. Abrasions are curtailed by the obligatory wetsuit; the head is protected by a helmet. A helmet can also be used to mount a lamp so that both hands are free to use.
Especially dangerous is the entering of air-filled passages at the end of a siphon. Statistics prove that the most serious accidents are caused by falls in this situation.
Gas pockets: In water-filled caves, one occasionally finds so-called gas-filled pockets. The diver should always resist the temptation to breathe in the gas mixtures in these bubbles, because there is a high probability that it does not contain breathable air with enough oxygen, and it is also likely to contain poisonous gasses.
Current: In general, one should exercise the utmost care when diving in a cave with an in-flowing current (such as a siphon), because the return trip will be entirely against the current, which drastically increases the necessary time, loss of body heat, physical exertion, decompression requirements and gas usage. Therefore it is always recommended to dive against the current (“upstream”) and exit the cave with the current (“downstream”). For a first dive in a cave, one should NEVER dive downstream without the presence of an experienced diver who is familiar with both the area and the situation. If, for whatever reason, a “downstream dive” is undertaken, a much stricter gas management rule is to be followed than the rule of thirds (rule of fifths or of sixths depending on the local conditions)!
The list of problems and special risks includes some clues as to how the equipment for a cave diver differs from that used by a “conventional” recreational diver:
The air supply carried by the diver is larger; it exceeds that of a recreational diver many times over, because due to the safety rule described above, there would otherwise be hardly any time left for exploration (duration of the dive). To ensure a safe return when a diving regulator ceases to work, multiple functioning regulators must be carried.
Especially in caves into which ground water flows, there are comparatively low water temperatures. The wetsuit must be capable of effectively maintaining the warmth of the diver. A drysuit also provides for a redundant buoyancy system.
Due to the absence of daylight, it is necessary to carry artificial light. To prevent being without orientation in complete darkness in the event of lamp failure, it is vital to have multiple redundancy here as well. In the cavern area, a diver is generally required to carry at least one main and one backup lamp. In cave and full-cave areas, each diver is required to carry three or more lamps. Further requirements regarding luminosity and lifetime of the lamp, etc., are dependent on the organization.
Every cave diver is required to carry a so-called “safety-reel” or “safety-spool,” so that in the event of loss of contact with the permanent guide line, it can be relocated. The minimum required length of the safety line is roughly 50m.
In addition, each diver carries a so-called “primary-reel” with approximately 80-100m of line. With it, for the duration of the dive, a temporary connection from an open water surface in the entry area to the beginning of the permanent main guide line (“mainline”) is established.
For temporary connections across artificially open sections of the mainline at junctions (“gaps”, “jumps”), one or usually multiple so-called “jump reels” are carried and used. These normally have 20-30m of line.
The guide line must be marked so that the direction to the exit can be found by the diver at any time. For this purpose, so-called “directional markers” or “line arrows” can be bound to the rope. Especially when the diver has temporarily lost their orientation, it is important that they can determine whether they are moving in the direction of the exit or into the interior of the cave by observing the markers.
For marking presence, so-called “non-directional markers” are used. Since they have the form of a round cookie, they are also nicknamed “cookies.”