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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.

Contents 1 Definition of 'technical diving' 1.1 Depth 1.2 Inability to ascend directly 1.2.1 Decompression stops 1.2.2 Physical ceiling 1.3 Gas mixes 2 Equipment 3 Training 4 See also 5 External links

Several factors lead to a dive being classed as a 'technical dive'.

Technical dives may be defined as being either dives to depths deeper than 130 feet / 40 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 causes a progressively increasing amount of impairment due to nitrogen narcosis that normally becomes serious at depths of 100 feet or greater. Increasing pressure at depth also increases the risk of oxygen toxicity based on the partial pressure of oxygen in the breathing mixture. 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 where the diver cannot safely ascend directly to the surface either due to a mandatory decompression stop or a physical ceiling. This form of diving implies a much larger reliance on redundant equipment and training since the diver must stay underwater until it is safe to ascend or the diver has left the overhead environment.

Long or deep dives may need mandatory decompression stops before the diver can surface safely. The stops may optionally be performed using enriched oxygen breathing gas mixtures such as nitrox or pure oxygen. 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, by doing stops during the ascent, to prevent decompression sickness, also known as the "bends".

These types of overhead diving can prevent the diver surfacing directly:

• 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 dives may also be defined by 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 pressure due to depth also causes nitrogen to become narcotic, resulting in a reduced ability to react or think clearly (see Nitrogen narcosis). By adding helium to the breathing mix, divers can reduce these effects, as helium does not have the same narcotic properties at depth. These gas mixes 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.

Nitrox is another common gas mix, and while it is not used for deep diving, it decreases the build up of nitrogen within the diver's body by increasing the percentage of oxygen. This reduces the nitrogen percentage, and is thus classed as a technical diving mix. Generally, further training and knowledge is required in order to safely use and understand the effects of these gases on the body in a diving situation.

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 specialised equipment and training. Divers interested in technical diving should seek training and dive within their personal limits. There are many technical training organisations: 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.

BSAC training has always had a technical element to its higher qualifications, however it has recently begun to introduce more technical level Skill Development Courses into all its training schemes, by introducing technical awareness into its lowest level qualification of Ocean Diver, for example, nitox will become mandatory. It has also recently introduced trimix qualifications and continues to develop closed circuit training.

• Breathing gas
• Carbon dioxide poisoning
• Diving hazards and precautions
• Oxygen toxicity
• Rebreather
• Solo diving
• Trimix

• Transitioning to technical diving