Technical diving (sometimes referred to as Tec diving) is a form of scuba diving that exceeds the scope of recreational diving (although the vast majority of technical divers dive for recreation and nothing else). Technical divers require advanced training, extensive experience, specialized equipment and often breathe breathing gases other than air or standard nitrox.
The concept and term, technical diving, are both relatively recent advents, although divers have been engaging in what is now commonly referred to as technical diving for decades. The term technical diving has been credited to Michael Menduno, who was editor of the (now defunct) diving magazine AquaCorps in 1991.
Technical dives may be defined as being dives deeper than about 130 feet (40 m) 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 interiors 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 (30 m) 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.
Inability to ascend directly
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.
A diver at the end of a long or deep dive may need to do decompression stops to avoid decompression sickness, also known as the “bends”. Metabolically inert gases in the diver’s breathing gas, such as nitrogen and helium, are absorbed into body tissues when breathed under high pressure during the deep phase of the dive. These dissolved gases must be released slowly from body tissues by pausing or “doing stops” at various depths during the ascent to the surface. In recent years, most technical divers have greatly increased the depth of the first stops to reduce the risk of bubble formation before the more traditional, long, shallow stops. Most technical divers breathe enriched oxygen breathing gas mixtures such as nitrox during the beginning and ending portion of the dive. To avoid nitrogen narcosis while at maximum depth, it is common to use trimix which adds helium to replace nitrogen in the diver’s breathing mixture. Pure oxygen is then used during shallow decompression stops to reduce the time needed by divers to rid themselves of most of the remaining excess inert gas in their body tissues, reducing the risk of “the bends.” Surface intervals (time spent on the surface between dives) are usually required to prevent the residual nitrogen from building up to dangerous levels on subsequent dives.
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.
Extremely Limited Visibility
Technical dives in waters where the diver’s vision is severely impeded by low-light conditions, caused by silt or depth, require greater knowledge and skill to operate in such an environment, and because vision is often reduced by water currents. The combination of low visibility and swift current make these technical dives extremely risky to all but the most skilled and well-equipped divers.
Technical dives may also be characterised by the use of hypoxic breathing gas mixtures other than air, such as trimix, heliox, and heliair. Breathing normal air (with 21 percent oxygen) at depths greater than 180 feet (55 m) creates a high risk of oxygen toxicity. The first sign of oxygen toxicity is usually a convulsion without warning which usually results in death, as the breathing regulator falls out and the victim drowns. Sometimes the diver may get warning symptoms prior to the convulsion. These can include visual and auditory hallucinations, nausea, twitching (especially in the face and hands), irritability and mood swings, and dizziness. 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 18 percent the mix is known as a hypoxic mix as it does not 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, as well as allowing for a greater number of multiple dives compared to standard air. The depth limit of nitrox is governed by the percentage of oxygen used, as there are multiple oxygen percentages available in nitrox. Further training and knowledge is required in order to use safely and understand the effects of these gases on the body during a dive.
Deep air/extended range diving
One of more divisive subjects in technical diving concerns using compressed air as a breathing gas on dives below 130 feet (40 m).While mainstream training agencies still promote and teach such courses (TDI,IANTD and DSAT/PADI), a minority (NAUI Tec, GUE, UTD) argue that diving deeper on air is unacceptably risky, saying that helium mixes should be used for dives beyond a certain limit (100–130 feet (30–40 m), depending upon agency). Such courses used to be referred to as “deep air” courses, but are now commonly called “extended range” courses.
Deep air proponents base the proper depth limit of air diving upon the risk of oxygen toxicity. Accordingly, they view the limit as being the depth at which partial pressure of oxygen reaches 1.4 ATA, which occurs at about 186 feet (57 m). Helitrox/triox proponents argue that the defining risk should be nitrogen narcosis, and suggest that when the partial pressure of nitrogen reaches approximately 4.0 ATA, which occurs at about 130 feet (40 m), helium is necessary to offset the effects of the narcosis.Both sides of the community tend to present self-supporting data. Divers trained and experienced in deep air diving report less problems with narcosis than those trained and experienced in mixed gas diving trimix/heliox, although scientific evidence does not show that a diver can train to overcome any measure of narcosis at a given depth, or become tolerant of it.
The Divers Alert Network does not formally reject deep air diving per se, but indicates the additional risks involved.
Technical divers may use unusual diving equipment. Typically, technical dives last longer than average recreational scuba dives. Because required decompression stops act as an obstacle preventing a diver in difficulty from surfacing immediately, there is a need for redundant equipment. Technical divers usually carry at least two tanks, each with its own regulator. In the event of a failure, the second tank and regulator act as a back-up system. 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. The stage cylinders are normally carried using an adaptation of a sidemount configuration.
Technical diving requires specialised equipment and training. There are many technical training organisations: see the Technical Diving section in the list of diver training organizations. Technical Diving International (TDI), Global Underwater Explorers (GUE), International Association of Nitrox and Technical Divers (IANTD) and National Association of Underwater Instructors (NAUI) were popular as of 2009. Recent entries into the market include Unified Team Diving (UTD), and Diving Science and Technology (DSAT), the technical arm of Professional Association of Diving Instructors (PADI). The Scuba Schools International (SSI) Technical Diving Program (TechXR – Technical eXtended Range) was launched in 2005.
British Sub-Aqua Club (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, and nitrox will become mandatory. It has also recently introduced trimix qualifications and continues to develop closed circuit training.