Technical dives typically involve dives beyond the established recreational limits of a maximum depth of 40 meters within the no-decompression limits. Today tech divers have conducted dives beyond 250  meters with runtimes exceeding twelve hours, though the bulk of tech dives are in the depth range of 100 meters or less and a few hours long. Tech dives are almost always conducted in an overhead environment of a cave or shipwreck, or the virtual overhead of a decompression obligation, where divers are not able to safely ascend directly to the surface. 

For that reason, technical or tech divers carry a much larger gas supply, compared to their recreational counterparts, in the form of multiple scuba tanks in either back mount or sidemount configuration along with cylinders of specific gas for decompression. Alternatively, they may dive a rebreather, which also offers an extended range, and carry one or more bailout tanks, in the event of a problem with the unit. 

For dives shallower than 30-40 meters, tech divers typically breathe nitrox, an oxygen/nitrogen blend with an oxygen fraction greater than the 21% found in air. Many tech divers have standardized on nitrox 32, a blend of 32% oxygen and 68% nitrogen. Today, of course, nitrox is nearly ubiquitous among recreational divers as well, as it offers distinct physiological advantages over air. 

For deep dives, beyond 30-50 meters, tech divers breathe mixtures of oxygen, helium and nitrogen called trimix during the working portion of their dive, with an oxygen fraction lower than air, and the addition of helium, an inert gas which is non-narcotic, as a substitute for all or most of the nitrogen, which is increasingly narcotic with depth. They do this to minimize the debilitating effects of nitrogen narcosis, named “rapture of the deep” by Jacques Cousteau,  and to avoid oxygen toxicity, caused by raised levels of oxygen, which can lead to convulsions and unconsciousness. 

In addition to their “bottom gas,” tech divers breath an decompression mix, usually nitrox with a higher oxygen fraction and or pure oxygen, upon ascent following a schedule of specific depths, times and gas switches prescribed by a decompression algorithm in their dive computer or desktop software. Tech divers typically also wear dry suits because of the longer runtimes involved and to provide a redundant source of buoyancy, along with a separate suit inflation bottle with air or argon, as helium rapidly dissipates a diver’s body heat.

Because of the nature of technical dives, which tend to be deeper and longer and involve a decompression obligation, tech diving requires additional training and knowledge compared to recreational diving, along with solid foundational diving skills such as good buoyancy control and trim. The dives themselves require rigorous pre-dive planning, checklists, discipline and good teamwork. The reward for all this extra preparation and work is the opportunity for “tekkies” to experience a realm not previously accessible to humans. And there is every reason to think as our technology and knowledge advance that we will be able to push our underwater envelope even farther.