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.
How does equipment for cave diving differ from other recreational forms of diving? How do divers move around, despite low visibility and winding caves? To learn about cave diving, read the next page.
Cave Diving Equipment
The best way to tell a cave diver apart from an open-water diver or cavern diver is to look at the equipment in use. In this section we'll look at the different kinds of gear a cave diver brings on a dive.
It's important to remember that cave divers carry redundant equipment -- this means that for every piece of equipment they carry, an extra will come along for the dive. This is to make sure that if something undergoes failure, there's a replacement to take over and allow a safe return to the surface. It could be something seemingly unimportant like an extra mask, or a piece of equipment that ensures a diver's survival, like an oxygen tank.
While open-water divers usually use snorkels because they can easily reach the surface for air, cave divers could never afford to bring one along and have no use for it. Cave divers stay submerged in the water for long periods of time, and therefore bring along oxygen tanks for breathing purposes -- a snorkel would only create excess weight and extra drag.
Cave divers usually keep masks simple, preferring standard masks that are solid black. The reason dark masks are well suited for cave diving is because of the light-absorbing qualities of the color black. Any distracting light that might leak into the mask can be absorbed by the dark material of the mask and prevent a diver from losing sight of entrances or important spots. Cave divers also wear hoods made of nylon to protect their heads from water leaks and damage during dives.
Cave divers typically prefer black rubber fins, and ones that aren't very flexible. Light, stiff fins work best because divers already so carry much mass with them into a cave. Moving through the water, they need to use short, controlled kicks to avoid stirring up any sediment on the floor of a cave.
Cave divers use either dry suits or wet suits for protection. The difference between the two kinds of suits is that dry suits are designed to seal off water from entering and getting a diver's body wet. Made of a synthetic rubber called neoprene, dry suits are the preferred choice for cave divers because they allow much less heat loss. The material is double-layered with a small space in between for insulating air, and divers have the option of wearing extra undergarments. Wet suits will still suffice for shorter dives and warmer waters, however.
Other equipment such as flashlights and small knives to cut away snags come along on a dive. There are also several gadgets that help divers during their ascent and descent. Different gauges give information on air pressure and depth, and they may all be fitted onto one device along with a compass for navigation.
Cave divers, of course, need to bring oxygen tanks, or cylinders, with them while underwater. To learn about breathing in deep, high-pressure water, read the next page.
Breathing in Caves and Decompression
To understand the dangers of diving at high pressures underwater, it's best to look at a soda bottle. When you shake a soda bottle, some bubbles go up to the surface. It doesn't look like much at first, but if you quickly open up the cap, there's a burst of fizzy gas as bubbles continue to climb up toward the surface.
There's a way to keep this from happening and making a mess. If you've dropped a bottle of soda on the ground, you can prevent it from bubbling up and creating too much pressure by opening the cap very slowly. If the gas inside the bottle is gradually let out, a small amount of bubbles will form, and the pressure will be decreased.
Our bodies act very much like a shaken soda bottle when we're under high water pressure. We breathe about 78 percent nitrogen and 21 percent oxygen on land -- our bodies use the oxygen, but nitrogen is either discarded or dissolved into our blood and tissue without any harm. At lower depths, however, increased pressure from all the water on top of us causes nitrogen to form in our blood and tissue. If we go down and come up too fast, nitrogen is released from our bodies too quickly and creates bubbles in our blood, much like opening a bottle of soda too quickly. This causes a condition known as decompression sickness (DCS), or "the bends" -- mild cases can lead to a tingling sensation or joint pain, while more serious ones may cause heart attacks, strokes or ruptured blood vessels.
A diver can avoid getting the "the bends" by adhering to dive tables, which can be used to calculate how much time someone should spend at a certain depth before ascending. If a diver follows the dive tables correctly, nitrogen will slowly be released from the body without causing any damage.
Because of the unique circumstances that entail diving at high pressures, cave divers carry with them tanks filled with a variety of special gas mixtures. Compressed air, a mixture of about 78 percent nitrogen and 22 percent oxygen, is cheap and easily accessible, but not the most popular of choices -- too much nitrogen can lead to nitrogen narcosis, a condition similar to drunkenness or laughing gas that comes on suddenly and can cause divers to lose concentration and drown. Too much nitrogen can also lead to decompression sickness, as described above.
Another, more common mixture, called nitrox, puts more oxygen in a tank, roughly 32 to 36 percent oxygen. This decreases the chances of breathing in too much nitrogen, but too much oxygen at high-pressure depths is also dangerous and lead to oxygen toxicity, which causes sudden fatal seizures and can lead to drowning. Divers can avoid this condition by following very strict dive schedules.
There are also mixed-gas supplies available that offer alternative mixtures to air or nitrox. One of these is heliox, a mixture of 79 percent helium and 21 percent oxygen. Like the others, it has its strengths and weaknesses -- helium doesn't have the intoxicating effect that nitrogen does, but divers breathing heliox lose body heat six times faster than if they were breathing compressed air or nitrox, making them more susceptible to hypothermia.
To learn about some of the techniques cave divers use to move around, read the next page.
Cave Diving Techniques
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.
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 string 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.
To learn more about training and certification for cave divers, read the next page.
Cave Diving Training and Certification
So how does someone become a cave diver? Can anyone do it, or does it require a great deal of training and expertise? Because cave diving is technical in nature, the activity isn't something anyone can jump into and do well or safely.
Darren Tedder, a cave photographer and professional cave diver with over 20 years of experience, explains: "More often than not, you need an established open-water history that you can document. You should have a minimum of 50 open-water dives before you even consider cavern or cave diving. From there, once you start cavern diving, you should have close to a week of actual class time."
During classes, divers learn about equipment they'll use, go over in-depth studies of gas laws and how those gas laws affect a person's body, learn how to navigate through the cave on a guideline and find the line if it gets lost or you take your eye off it and become disoriented. Although it's possible to jump straight from cavern diving into cave diving, Tedder recommends diving as cavern diver for at least two years before heading into more dangerous waters inside a cave.
Although there are several organizations that give classes and train future cave divers, some of the most popular groups that offer cave diving certification and training are the National Speleological Society Cave Diving Section (NSS-CDS), the National Association for Cave Diving (NACD), the International Association of Nitrox and Technical Divers (IANTD) and Global Underwater Explorers (GUE).
Although there aren't any laws that regulate what a person can do on a dive, people are generally taught "to not to disturb the environment any more than you have to and to never, ever remove fossils or artifacts from a cave, unless it's under the direction of a museum or a university or something that's going to preserve what you're doing."
Do you need a special permit or permission to cave dive? Says Tedder: "Once you're a certified cave diver, you pretty much have carte blanche to cave dive. More often than not, the restrictions come from the location. Some of the state parks will require you to show certification -- tell them when you're going to be in the water and back out of the water -- and they'll only allow so many people in or out of the cave in a day. There are a lot of generic, 'let's go cave diving' places that charge an admission fee, and you can go into their area and just dive all you want -- nobody monitors what you're doing. Once you're a certified cave diver, it's up to you at that point to make your own dive plans, make determinations about your decompression schedules and the gas mixtures you'll use, et cetera."
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More Great Links
- Phone interview with Darren Tedder. April 2, 2008.
- "Technical diving." Ocean Explorer. National Oceanic and Atmospheric Administration.http://www.oceanexplorer.noaa.gov/technology/diving/technical/technical.html
- The Cave Diving Website. North Florida Cave and Technical Diving. http://www.cavediving.com/index.htm