These enclosed environments are hazardous to open water divers. Cave diving and wreck diving are more complex than they first appear. Completion of the open water scuba training course is inadequate preparation for cave and wreck diving. Planning involves not only the setting of goal-oriented objectives, but the delineation of maximum limits (depths, distances). The main problems are as follows:
- No direct ascent to the surface (i.e. safety).
- Disorientation and entrapment.
- Loss of visibility.
- Enclosed spaces and panic.
The techniques of cave diving are very rigidly delineated. Specialized training includes dive planning, the use of reels and lines and the lost diver protocols. Most people who have difficulties with cave diving have not followed the recommended rules, and unfortunately cave diving problems tend to cause multiple fatalities.
The diver descends, often through a small access, passes down a shaft, goes around a few bends and is faced with multiple passages, in total darkness. Under these conditions, and to make this particular type of diving safe, it is necessary to be accompanied by a diver who has considerable cave experience – in that cave – and whose judgement is trustworthy. It is equally important that the equipment is both suited to cave diving and totally replaceable with spares during the dive. Apart from the obvious environmental difficulties inherent in diving through a labyrinth of passageways, there are added specific problems.
Safety in cave diving is not usually achievable by immediate surfacing. Thus, all necessary equipment must be duplicated for a long return swim, at depth, and possibly while rescuing a disabled companion.
Air pockets found in the top of caves are sometimes non-respirable because of low oxygen and high carbon dioxide levels (especially in limestone caves), so when entering this pocket, breathing should be continued from the scuba equipment. Sometimes the roof of the cave is supported by the water, and when this water is replaced by air from the diver’s tanks, the roof can collapse. The common claim that ‘the diver was so unlucky for the roof to collapse while he was there’ is incorrect. It collapsed because he was there.
The minimum extra safety equipment includes a compass, powerful lights and a safety reel and line. It is a diving axiom that entry into a cave is based on the presumption that the return will have to be carried out in zero visibility.
For visibility, each diver takes at least two lights; however, other factors can interfere with the function of these lights. A great danger is the silt that can be stirred up if the diver swims along the lower part of the cave or in a head-up position (as when negatively buoyant). If there is little natural water movement, clay silts can be very fine and easily stirred up. It is for this reason that fins should be small, and the diver should be neutrally buoyant and should swim more than a metre above the bottom of the cave. Visibility can be totally lost in a few seconds as the silt curtain ascends, and it may remain that way for weeks. Sometimes it is inevitable, as exhaled bubbles dislodge silt from the ceiling. Layering of salt and fresh waters also causes visual distortion and blurring.
The usual equipment includes double tanks manifolded together, making a common air supply, but offering two regulator outlets. With the failure of one regulator, the second one may be used for the air supply – or as an octopus rig. The second regulator must have a long hose, given that often divers cannot swim alongside each other. Because of space limitations, buddy breathing is often impractical under cave conditions. An extra air supply (‘pony’ bottle) is advisable.
For recreational divers to explore caves, the ideal equipment is a reliable compressed air surface supply, with a complete scuba back-up rig.
All the instruments should be standardized; e.g. the watch goes on the left wrist, the depth gauge above it, the compass on the right wrist and the dive computer (this can include a contents gauge, decompression meter, dive profile display, compass) attached to the harness under the left arm. The gauges and decompression must be modified for fresh water and altitude, if these are applicable. The knife is strapped to the inside of the left leg, to prevent entanglement on any safety lines.
The buoyancy compensator is often bound down at the top, to move the buoyancy centre more toward the centre of gravity (cave divers do not need to be vertical with the head out of water). There is no requirement for excess buoyancy because safety in cave diving is not usually equated with a direct ascent; thus, any carbon dioxide cylinders should be removed and replaced with exhausted ones to prevent accidental inflation of vests. A principle of cave diving is that safety lies in retracing the entry path by the use of lines and not by ascent, as in the normal open ocean diving.
Preferably no more than three divers should undertake a single dive, and on completion of the dive each should have a minimum of one third of the initial air supply. If there is water flow within the cave, and the penetration is with the flow, this reserve air supply may not be adequate because the air consumption is greater when returning against the current.
Vertical penetrations need a heavy shot line moored or buoyed at the surface and weighted or fixed at the bottom. The reel is used for horizontal penetrations, not vertical. Otherwise, entanglement is likely with rapid ascents, especially if divers precede the lead diver. Thin, non-floating lines especially cause entanglement if they are allowed to slacken.
Specialized cave diving training is a prerequisite for this diving environment.
Wreck diving has potentially similar problems to some cave and ice diving. In addition, it has the hazards of instability of the structure and the dangers of unexploded ordnance, sharp objects, toxic cargo and fuel. Exhausted gas from scuba may cause air pockets and disrupt the wreck’s stability.
Silt in wrecks is usually heavier than that in still water caves. Thus, the sudden loss of visibility that can occur when silt is stirred up may be less persistent. The diver should ascend as far as is safe and wait until the silt cloud settles down.