A basic tenet of safe cave diving is to have a continuous guideline to the surface. Properly used, the guideline prevents two types of accidents that would prevent one from reaching the exit of the cave–(1) getting lost through a navigational error, and (ii) not being able to see the passage to exit due to a loss of visibility caused by silt, or a (very rare) failure of multiple lights.
Over the years, a robust and relatively uniform system for running guidelines (both temporary and permanent), and a related system for navigation has developed and been incorporated into technical and cave diving. The navigational system allows the branching nature of caves to be negotiated through “T” intersections and “jumps.” A jump is made from two permanent lines that approach each other but aren’t connected until the diver navigates them with a jump line and a directional or non-directional marker to indicate the exit side of the newly-formed intersection.
Guidelines are made from strong, thin nylon line and are secured in the cave using tie-offs and placements around cave formations that keep tension in the line to prevent entanglements and to make following the line with your hands possible.
While mindlessly following a guideline, rather than maintaining situational awareness and a sense of direction is poor practice, the guideline could be used in good visibility to see the path to the exit of the cave, and can also be navigated even in zero visibility and for very long distances by using your hand around the guideline and by feeling for navigational markers at each intersection.
Zero or limited visibility in the cave is a real risk, since the floor of most caves is a vast expanse of silt or clay. Cave divers have extremely good buoyancy control and use refined propulsion techniques to avoid silting the water. But a momentary buoyancy issue or an errant fin kick can happen even in normal cave diving, and when conducting cave exploration, there can be periods of limited or no visibility due to “percolation” raining down from the ceiling of the cave that has never been disturbed before, or by squeezing through a small passage where disrupting the silt is unavoidable.
Cave divers can therefore encounter distances of limited or zero visibility, and are prepared to exit the cave using the “continuous guideline” that is formed by the combination of permanent lines, jumps, the entrance line that may have been run by the dive team if the permanent line doesn’t start in “open water” in the cave entrance. Normally, distances with limited visibility should be short; but water flow or a rare geological event could push the silt towards the exit, turning a localized zero visibility incident into something that spreads to the whole cave.
Sound technique and experience are important. Most cave divers fondly remember their training where a zero visibility exit was simulated with a blindfold–so that the diver used “touch contact” with their buddy through many hundreds of feet of cave and navigated their way to the exit with no vision at all. This exercise is repeated with increasing amounts of equipment and other challenges as training progresses until one is blindfolded, sharing gas, and following a line with their hand while swimming their doubles, two stages, a primary scooter and a tow scooter across a landscape that one can’t see but that becomes quite comfortable as experience progresses. Cave diving is learned over time, and even though training is rigorous, cave divers gradually build up their experience doing real dives over the course of years, and most never reach the point that they are doing exploration-level dives.
With proper technique and care, the guideline and navigational system is a powerful technique to ensure that divers can’t get lost due to a navigation error or due to zero visibility. In addition to this utility, the guideline also forms the basic building block for cave surveys and maps, which we cover here.