Cave Diving: A deep dive on how it works

Introduction

Cave diving in the simplest term 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 lost while diving for one of these reasons. 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 specialised 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.

How cave diving works

Heavy with scuba gear, you make your way deeper and deeper into the coastal waters. For a while, the surface of the water is right above you, and the sun creates shimmering, broken ripples on the ocean ceiling. But soon enough, you catch a glimpse of an opening — the entrance to a cavern. As you swim inside, various plants, unfamiliar fish and interesting rock formations like stalactites and stalagmites color the interior.

But this isn’t your final stop. As you continue further, the surrounding area becomes darker and darker. A narrow, pitch-black hole is in your line of sight, and going into it will be a much more challenging and dangerous experience than what you’ve just been through. Because of the extreme darkness and potentially uncharted areas, you’ll need lights, special equipment and loads of experience for the practice of cave diving.

There are three main classifications of diving: cave diving, open-water diving and cavern diving. Open-water diving is where all divers start gaining experience, and it’s defined as a dive in which linear access to the surface is directly available — in other words, by swimming straight up, a diver should be able to get a head above water, and sunlight is easily visible. In cavern diving, on the other hand, a diver is exploring permanent, naturally occurring caverns and has a ceiling overhead, but an entrance and visible light from the sun are in sight. Both open-water diving and cavern diving are considered recreational activities that require recreational-level certifications and training, and divers usually limit descents to 130 feet.

Cave diving differs from the other two types of diving in that it’s a form of technical diving instead of a recreational one. It requires a much different set of equipment and several years of training and certification, and professionals constantly stress the need for top-notch fitness and gear. But above all, they admire cave diving for its unique challenge and the potential to discover the undiscovered — scientific research gathered from cave dives can lead to the study of rare organisms and even offer cures to diseases like leukemia.

The stress it can cause

As with all types of scuba diving, it is very important to stay calm in potentially stressful situations. This is particularly true as there is usually no chance to bring a panicking diver to the surface immediately.

In order to know instinctively how to react in such situations and to solve any occurring adversity while being in a cave, so-called “drills” are performed. These include scenarios like running out of air, problems with the equipment (e.g. leak), losing a buddy, the line or visibility as well as various combinations of the above.

So for training reasons you might end up having no air with zero visibility, swimming back to the entrance of the cave. While doing that your buddy might even get entangled in a line and you have to free him.

The course includes a lot of swimming “blind” in zero visibility which might be achieved either by covering/turning the mask or switching off all the torches. Like this, the line must be used to find a way out of the cave. Another scenario is losing the line when you cannot see, which makes you lose all sense of orientation. Without seeing a thing you must still locate the line and follow it back to the entrance.

These drills are stressful as well as difficult but it is crucial to stay calm. Before taking the cave course it is important to be at least reasonably confident that you will be able to handle such situations without going into a tailspin panic.

In a real situation, it will most probably take longer to deal with the problems and divers will often become anxious. This makes it even more important to take the training very seriously, practicing until the exercises feel comfortable and the challenges are solved.

Experience & previous Scuba Training

Many cave divers use either double tanks (backmount or sidemount) or rebreathers. If you do not have any previous experience with either of these techniques this should be acquired before even starting with any cave diving. In addition, buoyancy control has to be very good, as do the propulsion techniques (frog kick, flutter kick, back kick and helicopter turn) needed for maneuverability.

This is very important as improper techniques, for example might lead to stirring up silt which causes loss of visibility. You know this from recreational diving when someone in front of you touches the sandy bottom with his/her fins and no one behind can see anything anymore. In open water, this is not such a big deal as the following divers can swim to the side or up where visibility is normal again. In a cave, this might not be possible and due to less water flow the stirred up silt will stay in suspension for much longer.

For an experienced diver, these techniques will most probably be easier to learn than for a newer diver. However, it might be harder to change bad habits, like adapting an inefficient frog kick that has been practiced for several years.

It’s important to also take into account that the handling of the equipment and the techniques have to be understood and trained before any of the cave diving practices can be started.

Cave Diving Equipment

Many cave divers are using backmount although sidemount is getting more and more popular. Both have advantages and disadvantages and so it is more about personal preferences. It is important to decide before starting the course which one you would want to use and feel most comfortable/confident in using.

It is best to have all the necessary equipment before starting in order to get used to your own gear right from the start. If you’re not sure whether you will love cave diving (or diving with two tanks in general) renting is an option to consider before purchase as gear is not cheap.

Safety

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 unique circumstances of each 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.

Some cave divers are taught to remember the five key components with the mnemonic: “The Good Divers Always Live” (training, guide, depth, air, light).

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 use of mixed gases. Such as trimix for bottom gas, and nitrox and oxygen for decompression reduces the margin for error. Accident analysis suggests that breathing the wrong gas for the depth or not analyzing the breathing gas properly has also led to cave diving accidents.

Cave diving requires a variety of specialized procedures, and divers who do not correctly apply these procedures may significantly increase the risk to the members of their team. 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.

Guidelines

Because there is little to no visibility in caves and cave divers must use their own source of light, guidelines must be placed to ensure people can find their way back to a cave’s entrance.

Most caves already have guidelines in place from past explorers — these are called “gold lines” because of their yellowish color. They consist of braided nylon strings and are usually a bit smaller in diameter than regular rope at about an eighth of an inch. These are placed throughout the main tunnels of a cave. Labyrinthine caves also have smaller side tunnels, and these are provided with smaller, white lines. They don’t contact the main line; instead, they usually end within 5 to 10 feet of the main line.

The main line of a cave does not extend to the exit — this prevents open-water divers or untrained or uncertified people from viewing it as an invitation to enter the cave. Therefore, a main guideline typically starts 50 to 100 feet inside a cave.

Still, it’s a cave diver’s responsibility to run a temporary line, or entry line, along a reel from the outside of the cave in order to maintain a continuous guideline from open-water to the main line. This provides direct access to a cave’s exit. To make an entry line, divers make an initial tie-off to something sturdy, like a big rock. A secondary tie-off is also made in case the first one comes loose. The diver must be able to swim along the line with his hand around it, making an “OK” sign, and with his eyes closed make his way out of the cave. The line shouldn’t be run near obstructions in order to avoid snags and keep out of the way of other divers.

Dorf markers, or small, plastic directional arrows, can be tied to lines. These point toward exits, just in case a diver becomes disoriented. Clips, markers that resemble clothespins, are also used at points for notation reasons, including max penetration (the furthest point reached inside the cave) and points of interest for other divers.

The average cave dive will last in excess of one hour, but some can last for as long as 15 hours if the right equipment and gas supply is available. Divers generally use what’s called the “rule of thirds” — when one third of a diver’s air supply is gone, he will stop the dive and begin moving toward the cave’s entrance.

Moving around the cave

Since cave diving is different from other recreational diving activities, many of the techniques people use are also much different. Divers are taught to swim in a prone, or face down, position, with the knees bent and the fins elevated above the plane of the body. This is mainly a precaution against kicking the bottom of a cave and stirring up sediment, but it also offers a good streamline and creates little resistance to the water.

Cave divers move about a cave by using a simple technique called “pull and glide” — using the tips of their fingers, divers look for crevices in rock for a place to hook onto. The rock is usually something hard and porous like limestone, so it should have lots of pockets and places to grab. After grabbing hold, divers pull and release, gliding through the cave with relative ease.

Cave divers learn how to use mostly their feet for directional changes along with short flutter kicks, and, in the case of solid limestone, some can push off a cave ceiling with their feet to propel themselves along.

Divers can also take along battery-powered diver propulsion vehicles (DPVs) to make swimming easier. Although there are many different types, tow-behind DPVs are the most common, which pull divers through caves. DVPs help divers use less oxygen since they’re not exerting themselves as much, and they can significantly increase the length of a dive.

Summary

So if cave diving is something you desire to experience. You first need to become experienced in open water diving. I would recommend having 50, preferably 100 open water dives done before you even consider doing cave diving. Then take a cave diving course. Find a good instructor and go through a rigorous course in cave diving. So, train, train, train, is the best way forward. And always ensure you have the right equipment.

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