An Introduction to Technical Diving

The desire for ever-deeper dives and longer periods underwater has led to the development of special gas mixtures. The use of these in technical diving offers an exciting range of new skills and marine environments for qualified technical divers to explore.

Pushing Back Boundaries

Scuba divers are limited, by simple physical laws, to a certain amount of time under water (dependent on the depth of the dive) and an overall maximum depth. Training agencies recommend that recreational divers using compressed air go no deeper than 130 - 165 ft (40-50 m). Beyond this, nitrogen can build up dangerously quickly in the body, greatly increasing the risk of decompression sickness. In addition, the increased levels of nitrogen in the bloodstream below 165 ft (50 m) can lea. i to severe nitrogen narcosis. The oxygen content of air, too, becomes increasingly toxic to the nervous system the deeper you dive.

To extend dive times and allow exploration to greater depths, special mixtures of gas have been developed in which the balance of oxygen and nitrogen has been altered, or that contain new gases to dilute the impact of either oxygen or nitrogen. The use of these mixes is known as technical diving, and involves three types of gas mixes: nitrox, which allows longer dive times, and trimix and heliox, to reach greater depths.

Extending Dive Times

Normal air is composed of around 21 percent oxygen and 79 percent nitrogen. Nitrox is a gas mixture that contains a higher percentage of oxygen and a lower nitrogen content than normal, allowing longer dive times before the diver's body stores up too much nitrogen, and also reducing diver fatigue after the dive. Nitrox can be mixed in various proportions, from 22 to 50 percent oxygen. However, beyond a certain depth the increased oxygen in the nitrox mix becomes toxic and can cause seizures. The more oxygen in the blend, the shallower this will occur, for this reason, diving with nitrox requires special training, although courses are readily available to recreational divers.

Going Deeper

Divers wishing to travel deeper than 165 ft (50 in) use either heliox or trimix, both of which introduce helium into the breathing mixture. Heliox contains only helium and oxygen, whereas trimix is a three-gas combination of helium, oxygen, and (usually) nitrogen. Heliox is used mainly by military and commercial divers, while trimix is more often used by leisure divers. Both succeed in reducing the likelihood of nitrogen narcosis, oxygen toxicity, and DCS. However, since helium conducts heal six times faster than air, these mixes can cause the diver to feel very- cold. Helium is also absorbed rapidly into the body, so lengthy decompression is necessary. Divers wishing to use these gas mixes must undergo appropriate training.

Technical Kit

Diving at extreme depths or in extreme environments, like deep caves, requires special gear. Technical divers meticulously analyze their equipment, and try to eliminate weak points—there is little margin of error during a deep technical dive. To support the extra gas tanks used during technical dives, most divers opt for high-lift "wing"-style buoyancy compensatory. They also choose high-performance regulators that can handle the task of supplying breathing gas at extreme depths. Sophisticated dive computers are used to monitor how technical gas mixes are metabolized during a dive.