cave diving equipment

A drysuit is worn for long dives or in cold water. The suit itself is constructed from a laminated waterproof material, with watertight latex seals at the neck and wrists. Pockets on either side carry safety equipment. Undergarments are worn beneath to provide thermal protection. Bodily functions are managed through the use of a catheter condom connected to a “P-valve”, shown just above the diver’s knee.

Cave divers generally prefer compact masks, normally with an opaque skirt to avoid unwanted reflections. Usually at least one diver in each team will carry a spare mask.

Cave divers generally prefer short stiff fins, to provide good control and compactness. The rubber straps on the fins are often replaced with stainless steel springs covered with plastic tubing – these are stronger and reduce the risk of entanglement in the guideline.

Every diver carries at least one depth gauge and timer. These allow the diver to calculate what decompression stops to make when ascending at the end of the dive, using standard decompression tables. Alternatively, all of these functions may be combined in a dive computer which indicates depth, time and the required decompression stops. Most caves in Quintana Roo are so shallow that only a few minutes of decompression are required, provided an appropriate breathing gas is used (see later).

The heart of a cave diver's equipment is the "doubles". These are two tanks held securely together by steel bands, and connected together by a manifold. The manifold has two outlets, each of which can be turned on or off independently in case of problems. The center knob allows the two tanks to be isolated if a problem cannot be solved by turning off one outlet.

Two fully independent air regulator systems are attached to the outlets of the manifold. Each regulator system has a "first stage", which reduces the pressure from approximately 200 atmospheres to about 10 atmospheres, and a "second stage" (the mouthpiece) which supplies air on demand at ambient pressure. A long hose on one regulator allows divers to share air if necessary while swimming in line through narrow caves.

A buoyancy compensation device, or "wing", is attached to the tanks. This is essentially an airtight bag which can be inflated to provide buoyancy. Valves allow air to be injected from the tanks or from the diver's mouth to increase buoyancy, or to be released to reduce buoyancy.

Valves allow air to be injected from the tanks or from the diver's mouth to increase buoyancy, or to be released to reduce buoyancy.

The backplate and harness bolt onto the doubles and holds the wing in position.

The harness is made from nylon webbing threaded through the backplate and holds the equipment firmly in place on the diver.

Each diver carries a powerful primary light. The canister contains a lead-acid "gel cell" of 6.5 AH (shown left), 9AH or 14 AH capacity and is worn on the harness. The light head is a 10W High Intensity Discharge unit and is connected via a wet connector which can be plugged and unplugged under water.

Primary lights fail fairly frequently, perhaps every 50 to 100 dives. Each diver, therefore, also carries two backup lights. These are extremely reliable, and provide sufficient light to exit the cave if all primary lights fail. The backup lights are clipped onto D-rings on the diver's harness.

Also attached to the harness is a short, sharp knife. This allows the diver to cut himself free in the event of entanglement in the guideline or other equipment. It is common for cave divers to carry more than one knife--we normally attach another knife to the handle of the light head.

Cave divers place directional markers (arrows) and non-directional markers (circles) on the guideline to record information. Directional markers point to the nearest exit from the cave, and non-directional markers are used for a number of purposes, including marking the entrance route.

Each diver always carries a small reel or spool of nylon line known as a "safety reel". This is used when conducting a search for a lost guideline or fellow diver, and to repair any breaks in the guideline.

Waterproof notebooks, or "Wet Notes" are used for a number of purposes. One use is for communication under water, and another is to record reference information during the dive, either to help with navigation inside the cave or for later analysis and planning of subsequent dives.

Air was the first gas used for scuba diving. It consists of about 21% oxygen and 79% nitrogen. The high nitrogen component limits the use of air. The reason is that the nitrogen is absorbed by the body tissues while diving, and can cause bubbles to form when the diver surfaces. In addition, the nitrogen acts as a narcotic at depths below about 30 meters, affecting the diver's judgment and performance.

For most of our dives we, therefore, use a gas mixture known as Nitrox 32%. This contains 32% oxygen and only 68% nitrogen. The lower nitrogen content reduces the amount of nitrogen which is absorbed by the body, reducing the risk of bubble formation. The mixture is still narcotic under pressure, and the high oxygen content can be toxic at depth. This limits the safe use of Nitrox 32% to depths of about 30 meters.

To help eliminate any bubbles during ascent, we make a number of decompression stops at different depths during the ascent. For the final stop at six meters, we breathe pure oxygen which rapidly eliminates bubbles. Risks of oxygen toxicity limit the use of pure oxygen to a depth of six meters.

For dives deeper than 30 meters, the narcotic effect of the nitrogen can be avoided by replacing it with another inert gas: helium. A typical mixture for depths up to 60 meters would be "20/50" - this consists of 20% oxygen, 50% helium, and 30% nitrogen. Mixtures of oxygen, helium and nitrogen are called Trimix.

Dives below 60 meters require special considerations. The amount of nitrogen must be reduced to a very low level in order to avoid narcosis. To prevent oxygen toxicity the amount of oxygen must be reduced as well. A typical mixture for dives up to 120 meters would be 10/70, containing 10% oxygen, 70% helium and 20% nitrogen. Breathing such a mixture at shallow depths would result in insufficient oxygen supply for the body and must be avoided.

All tanks are analyzed and labeled before use, to avoid breathing an unsafe mixture at depth.

When the breathing gas requirement exceeds the capacity of the doubles, extra gas can be carried in so-called stage tanks. Stage tanks are fitted with clips to fasten the tank to the diver's harness. Stage tanks can also be left clipped to the guideline - this is common on very long dives, to provide an additional safety margin during the exit.

Stage tanks are also used when different gas mixtures must be carried, most commonly for oxygen. When diving with several gases, it is important that no gas is taken deeper than its maximum safe operating depth.

Each stage tank has a regulator system attached, consisting of one first stage, one second stage, and a pressure gauge to show the tank contents. When not in use, the second stage and hoses are secured neatly in rubber tubes around the tank.

Normal swimming speed for a cave diver is 15-20 meters per minute. We use diver propulsion vehicles (DPVs or "scooters") when large distances must be covered, or when lots of equipment must be carried. These are capable of pulling a fully equipped cave diver with several stage tanks at speeds of 50-60 meters per minute. The small scooters have a range of about three kilometers, and the larger scooters have a range of about six kilometers. The scooters are powered by several large lead-acid get cells housed in the tubes.

The photo to the right shows an exploration diver with a scooter and one stage tank. This equipment configuration is suitable for cave penetrations of up to about two kilometers. For longer penetrations we take two or three stage tanks and tow a second scooter behind us. This allows penetrations of up to about five kilometers. Whenever we use scooters, we allow sufficient reserve breathing gas to swim out from the furthest point if all scooters fail.