First, an admission: I have mixed feelings about writing this. As a cave diver, I understand the desire of cavers and open-water divers to explore the depths of submerged caves, but all too often, gear columns encourage the inexperienced to think that equipment is the key to quantum-leaping their skills. Perhaps nowhere else can this mindset be more dangerous than in cave diving, which demands experience and knowledge as much as equipment if you're to stay in the game for any length of time.
One of the most prolific of all cave explorers, the late, great Sheck Exley, identified five main causes of cave-diving accidents, and these all subsequently had a significant effect on cave diving and its equipment. These are: exceeding the level of one's training; the lack of an underwater guide line; the effects of depth (something that may not always be apparent in an underwater cave); an inadequate supply of air; and insufficient light sources.
So, first and foremost, the most critical thing to lay your hands on is good training. Whatever your background and interest in caves and diving, make sure that you learn properly. Join a caving club, learn about caves, learn to dive and seek proper instruction through organisations such as the UK's Cave Diving Group or the USA's National Association for Cave Diving. When things go wrong underground and underwater, thorough training and a cool head is what will get you home alive, not the latest piece of gear.
MEANS TO AN END
The choices in cave diving equipment were originally driven by the type of cave to be explored, whether they be springs or sumps. Access to spring caves is easily gained from the head-pools of springs, and the original spring divers were mainly open-water divers attracted by the notion of exploration of the caves below. This, along with the fact that spring caves tend to consist of big passageways, meant that open-water diving techniques and equipment could be readily adapted for spring-cave diving. Florida, the Dordogne and Mexico's Yucatan Peninsula are all renowned for their exotic spring diving.
By contrast, sumps are found at the end of terrestrial caves where the roof meets the water level. The original sump divers were cavers who used diving as a way of passing the sump to explore the dry cave systems beyond. So, whereas diving was central in the development of spring exploration, in sumps it was merely a means to an end. Sump diving is best described as caving underwater and usually takes place in much smaller passages where a typical spring-diving equipment rig can't be used. Swildon's Hole and Wookey Hole are two sump caves in Somerset whose history is bound up with that of cave diving.
Whatever type of cave is being explored, the essential tools of the trade are reels, which all divers will use to lay a permanent guide line to the surface. Although cave divers may use different reels with different lengths and types of line depending on the cave, all divers will carry a search reel, which is the main tool a lost diver will use to find the main line in a cave. This is arguably one of the most important drills a cave diver will ever master.
BREATHE EASY
The 'rule of thirds' was developed to provide for enough breathing gas. This allows for a third of your air to be used on the inbound journey, a third for the return, and a third for use in an emergency. In certain circumstances, divers may choose to be even more conservative.
In spring diving, the diver typically carries, their breathing gas in back-mounted twin cylinders linked by manifolded valves. This means that much larger cylinders are used than in open-water diving. Divers may also carry additional 'stage' tanks to allow further penetration into a cave. Whereas a single ten-litre cylinder is a common size in open-water diving, it's not uncommon to see cave divers carrying two back-mounted 20-litre cylinders and several ten-litre stage tanks on some longer dives. Often, just wrangling the tanks into or out of the water is the hardest part of the day.
Two regulators stem from the twinset: one primary regulator with a hose up to seven feet (2.1 metres) long and a back-up secondary regulator. The long hose allows sharing with an out-of-air buddy in a narrow cave passageway, which would be nearly impossible with a conventional open-water octopus rig.
The manifold linking the twinset can be isolated in the event that one valve fails, ensuring that the entire gas supply isn't lost. This, however, requires shoulder flexibility and dexterity wearing gloves, and, sadly, it's all too common these days to see open-water divers using twinsets, but who are unable to perform this manoeuvre satisfactorily.
The long hose is wrapped in a particular fashion around the diver's body to ensure quick deployment in an emergency. Twinsets are mounted to aluminium or stainless steel backplates that use a simple webbing harness.
The low ceilings and small passageways in sumps mean that back-mounted cylinders can rarely be used. Sump diving, therefore, led to the development of specialist techniques such as side-mounting, where cylinders are mounted at the side to allow the diver to pass through narrow openings. This also protects the valves, which lie under the arms and are easily accessible to shut down in the event of failure.
Depending on the length of dive and the access to the sump, cylinder size may vary from three to 20 litres. Although any normal regulator can be used, 'non-sided' regulators such as the Poseidon Cykion have become popular with sump divers since they can be easily used on cylinders mounted on either side of the diver and the regulators can be breathed from in any position. Side-mounting requires special harnesses that allow the cylinders to be fixed at hip height.
Whereas spring divers will often operate in pairs or threes, the restricted nature of sumps means that dives are normally done solo, as partners can present an additional hazard by blocking an exit, reducing visibility by disturbing sediment, or breaking a guide line. Also, sharing gas isn't a real possibility in most sumps. Occasionally, dives may be done as 'team solos', where a group of divers operate together underwater, with each being solely responsible for their own safety.
BUOYANCY CONTROL
Spring divers will tend to use 'wing' style compensators for buoyancy. These are horse-collar or oval bladders that lie between the backplate and the cylinders. They assist the diver in maintaining a stable horizontal position underwater and are far less restrictive than the jacket-style buoyancy compensator (known as a stabilising or 'stab' jacket) often used in open-water recreational diving.
Proper buoyancy control is one of the most important skills in cave diving because it's crucial to avoid disturbing the silted bottom of cave passageways--a few careless fin strokes can reduce visibility to zero in seconds. The shallow depth and small size of sumps may mean that buoyancy isn't an issue, but sometimes wings may be attached to side-mount harnesses for deeper sumps. Some sump divers prefer to wear stab jackets over the top of their side-mount harnesses.
The problems associated with depth are dealt with by wrist-mounted computers or even just a simple depth timer. Used in conjunction with decompression software or tables, these allow for different gas mixes to be incorporated into the dive plan.
To light up the huge passageways in Floridan aquifers, spring divers use handheld high-intensity-discharge or light-emitting-diode (LED) torch systems powered by waist-mounted nickel-metal-hydride battery packs. Capable of outputting 20 watts, these illuminate at a supernova level of brightness.
To avoid snaring the hose in an emergency, helmets are rarely worn in spring diving and all torches are normally handheld to allow better control and to avoid blinding one's buddies. Back-up is usually in the form of two handheld torches carried on the shoulder straps of the backplate harness.
By contrast, the low ceilings in sumps mean that helmets are almost always worn. These not only protect the diver's head but also hold the light sources. Handheld torches are avoided since divers will often need to hold onto the guide line in a zero-visibility situation. Sump divers will often use waterproof caving lamps and back these up with small handheld LED torches, also mounted on the helmet. As the sump diver needs to be totally self-sufficient, it's not uncommon for up to five separate light sources to be carried for adequate redundancy.
Conventional open-water fins and masks are used by all cave divers. Loose straps are usually taped shut with duct tape to prevent cave guide lines becoming trapped underwater. It's crucial to find fins large enough to go over your wellies (see panel). Spare masks will also be carried on longer dives.
Whereas spring divers will carry spare equipment on their waistbelt, side-mounted cylinders can clutter the front and side of the sump diver, so all ancillary equipment tends to be worn on the arms. Computers, compasses, writing slates, cutting tools and safety reels are all arm-mounted. Shears are often preferred to knives as they are less risky to use in low visibility and much more powerful when wire or thick rope is encountered.
At the end of the day, a practical approach is required when diving in sumps, and many divers will use specific rigs for different caves. Sump-diving techniques may also be used in springs or on expeditions as they may be a more applicable and practical technique for the cave in question.
Diving in underwater caves represents one of the last true frontiers of exploration left on Earth. Their surreal beauty is perhaps only matched by their unforgiving nature. Although the equipment enables us to dive below the surface, it's the knowledge to use the gear properly that ensures we return safely.
WETSUIT, DRYSUIT OR WELLIES?
Exposure protection depends on your location: the warm waters of the Yucatan caves mean that thin, five-millimetre wetsuits are the norm in spring diving. Drysuits with suitable under-insulation are preferred on lengthy dives at deeper and chillier depths, even in the bathwater of Florida.
Redundancy is one of cave diving's main bywords, and drysuits also provide redundant buoyancy to the wing. Wetsuits are often preferred by sump divers since they're more flexible, cheap and work even when ripped, which is all too common when crawling underground.
Inexpensive, sturdy rubber Wellington boots are the caver's footwear of choice, so despite the strange look, most sump divers wear these underwater as well.
NICK LEWIS is a qualified diver with the Cave Diving Group. He ranks his greatest cave-diving achievement as producing a cooked breakfast in Wookey Hole's Chamber 24 (which takes four dives to reach) as a support diver during a series of record-breaking dives in 2004
Source Citation
Lewis, Nick. "Dark water: the cave diver's mnemonic--'the good divers always live': training, guide lines, depth, air, lights--highlights the importance of preparation as well as specialist gear for those taking part in what can be an extremely dangerous sport. Nick Lewis describes what's involved." Geographical Sept. 2010: 69+. General OneFile. Web. 10 Dec. 2010.
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