Technical diving

Technical divers preparing for a mixed-gas decompression dive in Bohol, Philippines. Note the backplate and wing setup with sidemounted decompression cylinders stage tanks containing EAN50 (left side) and pure oxygen (right side).

Technical diving (sometimes referred to as tec diving) is a form of scuba diving that exceeds the conventional limits – especially depth and bottom time – of recreational diving. Technical diving exposes the diver to significantly higher risks than recreational diving, including paralysis and death, and therefore requires extensive experience, advanced training, and specialized equipment. Technical diving also often involves breathing gases other than air or standard nitrox.

The term technical diving has been credited to Michael Menduno, who was editor of the (now defunct) diving magazine aquaCorps Journal. 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.

Definition

Technical diver during a decompression stop

There is some professional disagreement as to what technical diving encompasses. Until recently, nitrox diving was considered technical, but this is no longer the case. Some say that technical diving is any type of scuba diving that is considered higher risk than conventional recreational diving. However, some advocate that this should include penetration diving (as opposed to open-water diving), whereas others contend that penetrating overhead environments should be regarded as a separate type of diving. Others seek to define technical diving solely by reference to the use of decompression. Certain minority views contend that certain non-specific higher risk factors should cause diving to be classed as technical diving. Even those who agree on the broad definitions of technical diving may disagree on the precise boundaries between technical and recreational diving. One point upon which most scuba professionals generally agree is that any dive on which the parameters preclude the possibility of a safe and direct ascent to the surface should be considered technical diving of some sort, and must require specialized training and associated advanced certification. Such situations would include:

- Decompression diving (where the absorption of nitrogen gas in the diver's body tissues precludes a safe and direct ascent without decompression stops)

- Cave, ice or wreck diving (where penetration inside the target venue (in a cave or wreck, or under sheet ice) precludes a direct ascent, because a horizontal path must first occur back to the point of penetration).

• NAUI defines technical diving as "Any diving beyond the limits of the defined recreational diving limits which is currently set at the following - diving to 40 meters/130 feet, use of nitrox above 36%, multiple mix gas diving, penetration diving past the daylight zone and any form of decompression diving)."

• PADI defines technical diving 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."

• NOAA defines technical diving as "all diving methods that exceed the limits imposed on depth and/or immersion time for recreational scuba diving. Technical diving often involves the use of special gas mixtures (other than compressed air) for breathing. The type of gas mixture used is determined either by the maximum depth planned for the dive, or by the length of time that the diver intends to spend underwater. While the recommended maximum depth for conventional scuba diving is 130 ft, technical divers may work in the range of 170 ft to 350 ft, sometimes even deeper. Technical diving almost always requires one or more mandatory decompression 'stops' upon ascent, during which the diver may change breathing gas mixes at least once." NOAA does not address issues relating to overhead environments in its definition.

The following table gives an overview of the differences between technical and recreational diving:

Technical Diving

Activity	Recreational	Technical
Deep diving	Maximum depth of 40 metres (130 ft)	Beyond 40 metres (130 ft)
Decompression diving	No decompression	Decompression diving
Mixed gas diving	Air and Nitrox	Trimix, Heliox, Heliair and Hydrox
Gas switching	Single gas used	May switch between gases to accelerate decompression and/or "travel mixes" to permit descent carrying hypoxic gas mixes
Wreck diving	Penetration limited to "light zone" or depth/penetration	Deeper penetration
Cave diving	Penetration limited to "light zone" or depth/penetration	Deeper penetration
Ice diving	Some agencies regard ice diving as recreational diving;PADI others as technical diving.NAUI
Rebreathers	Some agencies regard use of semi-closed rebreathers as recreational diving;PADI others as technical diving.NAUI

Depth

Diver returning from a 600ft dive

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.

Decompression stops

Free floating decompression stop

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 inhaled 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.

Physical ceiling

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 and/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 can make these technical dives extremely risky to all but the most skilled and well-equipped divers. Limited visibility diving can cause additional challenges due to the lack of visibility resulting in disorientation, potentially leading to loss of direction, loss of proper buoyancy, etc. Just as lack of visibility requires that aircraft pilots depend on their instruments as they fly through clouds, so must divers in extremely limited visibility situations depend fully on their instruments—including air gauges, compass, depth gauge, bottom timer, dive computer, etc. Although standardized specialty certifications don't exist for extremely limited visibility diving, some instructors have crafted their own custom training courses to help others become more comfortable and more skilled when diving in such conditions. The Professional Association of Dive Instructors (PADI) allows its instructors to submit such specialized courses for approval as "Distinctive Specialties" allowing students to earn these specialty certifications after completing courses that have been reviewed and approved by PADI as Distinctive Specialty courses (when taught by the course author).

Gas mixes

Technical dives may also be characterised by the use of hypoxic breathing gas mixtures, 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 buildup 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 the 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. There is nothing "special" about 130 feet. This limit entered the recreation and technical communities in the USA from the military diving community where it was the depth at which the US Navy recommended shifting from scuba to surface supplied air. The scientific diving community has never incorporated the 130 foot limit into its protocols and has never experienced any accidents or injuries during air dives between 130 feet and the deepest air dives that the scientific diving community permits, 190 feet, where the U.S. Navy Standard Air Tables shifts to the Exceptional Exposure Tables. In Europe some countries set the recreational diving limit at 50 metres (160 ft), and that corresponds with the limit also imposed in some professional fields, such as police divers in the UK. The major French agencies all teach diving on air to 60 metres (200 ft) as part of their standard recreational certifications.

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 fewer 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 endorse or reject deep air diving, but indicates the additional risks involved.

Equipment

Technical diver with decompression gases in side mounted stage cylinders

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 a variation of a sidemount configuration.

Training

Technical diving requires specialised equipment and training. There are many technical training organisations: see the Technical Diving section in the list of diver certification organizations. Technical Diving International (TDI), Global Underwater Explorers (GUE), Professional Scuba Association International (PSAI), 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 training will become mandatory. It has also recently introduced trimix qualifications and continues to develop closed circuit training.

Operations

Relatively complex technical diving operations may be planned and run like an expedition, with surface and in-water support personnel providing direct assistance or on stand-by to assist the expedition divers.

Surface support might include surface stand-by divers, boat crew, porters, emergency medical personnel, gas blenders. In-water support may provide supplementary breathing gas, monitor divers during long decompression stops, and provide communications services between the surface team and the expedition divers. In an emergency, the support team would provide rescue and if necessary search and recovery assistance.

See also

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

External links

• Tech Diving Mag official website
• TechnicalDiving.com
• Select publications on technical diving and technical diving history hosted by the Rubicon Foundation
• RebreatherPro Jill Heinerth's interactive multimedia technical diving website
• Transitioning to technical diving