Scuba diving is heavily dependent on technology to be successful. The use of more advanced equipment and training refers to technical diving. Although a vast majority of people go technical diving for recreation, it is beyond the scope of adventure or recreation sport. It requires advanced training, experience, specialized and expensive equipment, and breathing gases―for example, pure oxygen to prevent decompression sickness inside deep water. Professional Association of Diving Instructors (PADI), the world's largest recreational diving membership and training organization, defines it as, "Diving other than conventional commercial or recreational diving that takes divers beyond recreational diving limits. It is further defined as an activity that includes one or more of the following: diving beyond 40 meters/130 feet, required stage decompression, diving in an overhead environment beyond 130 linear feet from the surface, accelerated stage decompression and/or the use of multiple gas mixtures in a single dive." The term was first coined by Michael Menduno, and he used it in his publications. Since then, it has been used to define advanced divers that carry out profiles considered extreme, by many. It requires a planned decompression stop and use of more than one gas mixture. Some examples are:

• Cave diving
• Deep diving
• Ice diving
• Wreck diving

In all the above-mentioned diving types, one cannot surface directly. Depths Technical dives are defined as the dives deeper than 130 feet (40 meters) or the dives in an overhead environment, where the diver cannot surface directly, and there is no access to natural light. Few examples of such environment are inside a shipwreck, fresh and saltwater caves, etc. Such dives have a planned decompression carried out in a number of stages. The depth factor has been included because, breathing regular air while experiencing pressure causes impairment. The increasing depths also increase the toxicity of oxygen. That is the reason why a mixture of gases is taken instead of one gas. Decompression Stops To avoid decompression sickness, a diver at the end of a deep dive is required to do decompression stops. The gases in the diver's breathing tank are absorbed into body tissues when breathed under high pressure, and need to be released by pausing or taking halts, as pausing reduces the bubble formation within the tissues. Gas Mixes They also require the use of hypoxic breathing gases such as trimix, heliox, and heliair. It is because the normal air mixture of oxygen at deeper lengths increases oxygen toxicity. The first signs of oxygen toxicity is convulsion. It often causes accidents and drowns the diver. It can also include visual and auditory hallucinations, twitching, nausea, mood swings, and dizziness. Addition of helium to the breathing gas reduces these effects, and helium doesn't get toxic at deep lengths. These divers use sophisticated equipment that can sustain high pressures easily without malfunctioning. They also carry two tanks, so that if one fails, the other comes to the rescue. Their training also requires high level of physical strength.