Technical diving
The equipment involves breathing gases other than air or standard nitrox mixtures, and multiple gas sources.
[4] Richard Pyle (1999) defined a technical diver as "anyone who routinely conducts dives with staged stops during an ascent as suggested by a given decompression algorithm".
Consequently, a relatively large number of fatal incidents occurred during the early years, before a reasonably reliable set of operating procedures and standards began to emerge, making the movement somewhat controversial, both within the mainstream diving establishment and between sectors of the technical diving community.
[8] While the motivation to extend the depth and duration range by military and commercial divers was mainly driven by operational needs to get the job done, the motivation to exceed recreational diving depths and endurance ranges was more driven by the urge to explore otherwise inaccessible places, which could not at the time be reached by any other means.
The depth-based definition is based on risk caused by the progressive impairment of mental competence with the increasing partial pressure of respired nitrogen.
Breathing air under pressure causes nitrogen narcosis that usually starts to become a problem at depths of 100 feet (30 m) or greater, but this differs between divers.
These dissolved gases must be released slowly from the body tissues by controlling the ascent rate to restrict the formation and growth of bubbles.
A lifeline fixed to the diver is more reliable as it is not easy to lose, and is often used when diving under ice, where the line is unlikely to snag and the distance is reasonably short, and can be tended by a person at the surface.
[39] Static guidelines are more suitable when a lifeline is likely to snag on the environment or on other divers in the group, and may be left in situ to be used for other dives, or recovered on the way out by winding back onto the reel.
The combination of low visibility and strong current can make dives in these conditions extremely hazardous, particularly in an overhead environment, and greater skill and reliable and familiar equipment are needed to manage this risk.
Training for cave and wreck diving includes techniques for managing extreme low visibility, as finding the way out of an overhead environment before running out of gas is a safety-critical skill.
[30] Because a decompression obligation prevents a diver in difficulty from surfacing immediately, there is a need for redundancy of breathing equipment.
Cylinders may carry a variety of gases depending on when and where they will be used, and as some may not support life if used at the wrong depth, they are marked for positive identification of the contents.
Others, including NAUI Tec, GUE, ISE and UTD consider that diving deeper than 100–130 feet (30–40 m), depending upon agency, on air is unacceptably risky.
The major French agencies all teach diving on air to 60 metres (200 ft) as part of their standard recreational certifications.
[53] The Divers Alert Network does not endorse or reject deep air diving but does note the additional risks involved.
[54] Nitrox is a popular diving gas mix, that reduces the maximum allowable depth as compared to air.
Nitrox also allows greater bottom time and shorter surface intervals by reducing the buildup of nitrogen in the diver's tissues.
[30] Increased pressure due to depth causes nitrogen to become narcotic, resulting in a reduced ability to react or think clearly.
[30] Helitrox/triox proponents argue that the defining risk for air and nitrox diving depth 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) for air, helium is necessary to limit the effects of the narcosis.
These can include visual and auditory hallucinations, nausea, twitching (especially in the face and hands), irritability and mood swings, and dizziness.
This requires planning, situational awareness, and redundancy in critical equipment, and is facilitated by skill and experience in appropriate procedures for managing reasonably foreseeable contingencies.
[56][57] Some rebreather diving safety issues can be addressed by training, others may require a change in technical diver culture.
This redundancy is intended to allow a safe termination of the dive if it occurs underwater, by eliminating a critical failure point.
The techniques and equipment are complex, which increases the risk of errors or omissions - the task loading for a closed circuit rebreather diver during critical phases of a dive is greater than for open circuit scuba equipment, The circumstances of technical diving generally mean that errors or omissions are likely to have more serious consequences than in normal recreational diving, and there is a tendency towards competitiveness and risk-taking among many technical divers which appears to have contributed to some well-publicized accidents.
[30] Some errors and failures that have repeatedly been implicated in technical diving accidents include: Failure to control depth is critical during decompression, where the inability to stay at the correct depth due to excessive buoyancy is associated with a high risk of decompression sickness and a raised risk of barotrauma of ascent.
Drysuit and buoyancy compensator inflation can cause runaway ascent, which can usually be managed if corrected immediately.
All of these failures can be either avoided altogether or the risk minimized by configuration choices, procedural methods, and correct response to the initial problem.
It is less of a problem with surface-supplied diving as the depth that the diver can sink to is limited by the umbilical length, and a sudden or rapid descent can often be quickly stopped by the tender.
[citation needed] Technical diving certification is issued by several recreational diver training agencies, under a variety of names, often with considerable overlap or in some cases split into depth ranges.
