Technical diving is a form of SCUBA diving that exceeds the scope of recreational diving. Technical divers require advanced training, extensive experience, and specialized equipment.
Technical dives may be defined as being either dives to depths deeper than 100 feet / 30 meters or dives in an overhead environment with no direct access to the surface or natural light. Such environments may include fresh and saltwater caves and the interior of shipwrecks. In many cases, technical dives also include planned decompression carried out over a number of stages during a controlled ascent to the surface at the end of the dive.
The depth-based definition is derived from the fact that breathing regular air while experiencing pressures greater than those at 100 feet or deeper causes a progressively increasing amount of impairment due to nitrogen narcosis. Increasing pressures at depth also increase the risk of oxygen toxicity in oxygen-rich breathing gasses. For this reason technical diving often includes the use of breathing mixtures other than air.
These factors increase the level of risk and training required for technical diving far beyond that required for recreational diving. This is a fairly conservative definition of technical diving.
Technical dives may alternatively be defined as dives with durations long enough to require mandatory decompression stops, which may optionally be performed using enriched oxygen breathing gas mixtures such as nitrox or pure oxygen. This definition is derived from the fact that metabolically inert gases, such as nitrogen and helium, in the diver's breathing gas are absorbed into body tissues when breathed under high pressure. These dissolved gases must be allowed to release gradually from body tissues to prevent decompression sickness or the bends. This form of diving implies a much larger reliance on redundancy and training since it is no longer physiologically safe to make a direct ascent to the surface in the case of any problems underwater.
Technical dives may also be defined as being to depths requiring the use of breathing gas mixtures other than air such as trimix, heliox, and heliair. This definition is derived from the fact that breathing a mixture with the same oxygen concentration as is found in air (roughly 21%) at depths greater than 180 feet / 55 meters results in a very rapidly increasing risk of severe symptoms of oxygen toxicity. These symptoms can include visual and auditory hallucinations, loss of muscle control, full body seizures, and loss of consciousness. Increasing depth also causes air to become narcotic and results in impairing diver's ability to react or think clearly. By adding helium to the breathing mix divers can reduce the narcosis. They can also lower the level of oxygen in the mix to reduce the danger of oxygen toxicity. Once the oxygen is reduced below 16% the mix is known as a hypoxic mix as it doesn't contain enough oxygen to be used safely at the surface.
Another gas mix is Nitrox which while not being used for deep diving (it is used for decreasing the build up of nitrogen with in the diver's body by increasing the percentage of oxygen and so reducing the nitrogen percentage) is also classed as a technical diving mix. This is due to the fact that further training & knowledge is required in order to safely use and understand its effects on the body in a diving situation.
Ability to ascend
Technical dives often refer to dives with a ceiling prohibiting a direct ascent to the surface: it can either be a mandatory stop (decompression obligation) or a physical ceiling:
* Cave diving - diving into a cave system.
* Deep diving - diving into greater depths.
* Ice diving - diving under ice.
* Wreck diving - diving inside a shipwreck.
Technical divers may also use various forms of less common diving equipment to accomplish their goals. Typically technical dives involve significantly longer durations than average recreational scuba dives. Technical divers therefore increase their supply of available breathing gas by either connecting multiple high capacity diving cylinders and/or by using a rebreather. The technical diver may also carry additional cylinders, known as stage bottles, to ensure adequate breathing gas supply for decompression with a reserve for bail out in case of failure of their primary breathing gas.
Technical diving requires specialized equipment and training. Divers interested in technical diving should seek training and dive within their personal limits. There are many technical training organizations: see the Technical Diving section of List of diver training organizations. TDI, GUE and IANTD seem to be popular at the time of writing. Recent entries into the market include DSAT the technical arm of PADI. Even more recently BSAC has begun to introduce more technical level Skill Development Courses into its training schemes, along with introducing technical awareness into its lower level qualification packages.