Technical diving

Diver returning from a 600ft dive

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.[1]

The term technical diving has been credited to Michael Menduno, who was editor of the (now defunct) diving magazine aquaCorps Journal.[2] The concept and term, technical diving, are both relatively recent advents,[note 1] although divers have been engaging in what is now commonly referred to as technical diving for decades.

Definition

Technical diver during a decompression stop

Technical diving encompasses multiple forms of diving, that typically share lack of direct access to surface, which may be caused by environmental constraints, like an overhead environment, or physiological, like decompression. In case of emergency, therefore, the diver must be able to troubleshoot and solve the problem underwater. This requires advance planning, experience, situational awareness, and redundant equipment.

There is some professional disagreement as to what exactly technical diving encompasses.[3][4][5] Nitrox diving and rebreather diving were originally considered technical, but this is no longer universally the case as several certification agencies now offer Recreational Nitrox and recreational rebreather training and certification.[6][7][8][9][10][11] 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.[note 2] 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 recreational scuba professionals generally agree is that any dive during which a direct and acceptably safe ascent to the surface is not possible should be considered technical diving of some sort, and requires competence in the appropriate procedures and equipment, and therefore the associated training and certification. Such situations would include decompression diving (where the concentration of inert gas in the diver's body tissues precludes a safe and direct ascent without decompression stops) and cave, ice or wreck diving (where penetration inside a cave or wreck, or under sheet ice - precludes a direct ascent, because an exit from the overhead environment must be made before surfacing is possible).

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

Technical Diving
ActivityRecreationalTechnical
Deep divingMaximum depth of 40 metres (130 ft)[note 3]Beyond 40 metres (130 ft)
Decompression diving[note 4]No decompressionDecompression diving
Mixed gas divingAir and NitroxTrimix, Heliox, Heliair and Hydrox
Gas switchingSingle gas usedMay switch between gases to accelerate decompression and/or "travel mixes" to permit descent carrying hypoxic gas mixes
Wreck divingPenetration limited to "light zone" or 30 metres (100 ft) depth + penetrationDeeper penetration
Cave divingPenetration limited to "light zone" or 30 metres (100 ft) depth + penetration[note 5]Deeper penetration
Ice divingSome agencies regard ice diving as recreational diving;
* PADI[14] 		Others regard it as technical diving.
* NAUI
RebreathersSome agencies regard use of semi-closed rebreathers as recreational diving;
* PADI[14]		 Others as technical diving.
* NAUI

Depth

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.[15] 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:

Extremely limited visibility

Technical dives in waters where the diver's vision is severely impeded by low-visibility conditions, caused by turbidity or silt out and low light conditions due to depth or enclosure, require greater competence. The combination of low visibility and strong current can make dives in these conditions extremely hazardous, and greater skill and reliable and familiar equipment are needed to manage this risk. Limited visibility diving can cause disorientation, potentially leading to loss of sense of direction, loss of effective buoyancy control, etc. Divers in extremely limited visibility situations depend on their instruments such as dive lights, pressure gauges, compass, depth gauge, bottom timer, dive computer, etc, and guidelines for orientation and information. 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.

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.

Equipment configuration

Technical divers preparing for a mixed-gas decompression dive. Note the backplate and wing setup with sidemounted decompression cylinders.

Gas mixes

Technical diving can be done using air as a breathing gas, but other breathing gas mixtures are commonly used to manage specific problems. Some additional knowledge is required to understand the effects of these gases on the body during a dive and additional skills are needed to safely manage their use.

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).[16] Some training agencies still promote and teach courses using air up to depths of 60m. These include TDI,[17] IANTD and DSAT/PADI. Others, including NAUI Tec, GUE, and UTD consider that diving deeper than 100–130 feet (30–40 m), depending upon agency, on air is unacceptably risky. They promote the use of mixtures containing helium to limit the apparent narcotic depth to their agency specified limit should be used for dives beyond a certain limit. Such courses used to be referred to as "deep air" courses, but are now commonly called "extended range" courses. The 130 ft 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 specified a 130 foot limit in 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),[18] 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.[19][20][21]

Deep air proponents base the 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). 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.[22]

The Divers Alert Network does not endorse or reject deep air diving, but indicates the additional risks involved.[23]

Mixtures to reduce decompression time

Nitrox is a popular diving gas mix, and while it is not used for deep diving, it reduces the buildup of nitrogen in the diver's tissues by increasing the percentage of oxygen in the breathing gas as a substitute for part of the nitrogen. The depth limit of a nitrox mixture is governed by the partial pressure of oxygen, which is generally limited to 1.4 to 1.6 bar depending on the activity of the diver and duration of exposure.

Nitrox and pure oxygen are used for accelerated decompression.

Mixtures to reduce nitrogen narcosis

Increased pressure due to depth causes nitrogen to become narcotic, resulting in a reduced ability to react or think clearly. By adding helium to the breathing mix, these effects can be reduced, as helium does not have the same narcotic properties at depth. 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.

Mixtures to reduce oxygen toxicity

Technical dives may also be characterised by the use of hypoxic breathing gas mixtures, including hypoxic trimix, heliox, and heliair. Breathing normal air (with 21 percent oxygen) at depths greater than 180 feet (55 m) creates a high risk of acute oxygen toxicity. The first sign of oxygen toxicity is usually a convulsion without warning which usually results in death when the demand valve mouthpiece 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.

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.

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.

Training

Tech diver 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.[24]

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.

See also

References

  1. ↑ Richardson, Drew (2003). "Taking 'tec' to 'rec': the future of technical diving". South Pacific Underwater Medicine Society Journal 33 (4). Retrieved 2009-08-07.
  2. ↑ Bret Gilliam (1995-01-25). Deep Diving. p. 15. ISBN 978-0-922769-31-5. Retrieved 2009-09-14..
  3. ↑ Gorman, Des F (1992). "High-tech diving". South Pacific Underwater Medicine Society Journal 22 (1).
  4. ↑ Gorman, Des F (1995). "Safe Limits: A International Dive Symposium. Introduction.". South Pacific Underwater Medicine Society Journal 25 (1). Retrieved 2009-08-07.
  5. ↑ Hamilton Jr, RW (1996). "What is technical diving? (letter to editor)". South Pacific Underwater Medicine Society Journal 26 (1). Retrieved 2009-08-07.
  6. ↑ Rossier, Robert N. (January 2000). "Recreational Nitrox Diving". Best Publishing Company; 1 edition. ISBN 978-0941332835. Retrieved 25 April 2016.
  7. ↑ Douglas, Eric (2011). "Nitrox". Alert Diver online - Fall 2011. Divers Alert Network. Retrieved 25 April 2016.
  8. ↑ Staff (2016). "Recreational Diver Level 1 - Nitrox diver". Global Underwater Explorers website. Global Underwater Explorers. Retrieved 25 April 2016.
  9. ↑ Menduno, Michael (2014). "Rise of the Recreational Rebreather". Diver magazine - online. Diver magazine. Retrieved 25 April 2016.
  10. ↑ Staff (2016). "Explorer rebreather". Hollis website. Hollis. Retrieved 25 April 2016.
  11. ↑ Staff (2016). "Rebreather diver". PADI website. PADI. Retrieved 25 April 2016.
  12. ↑ PADI, Enriched Air Diving, page 91. ISBN 978-1-878663-31-3
  13. ↑ "Technical Diving". NOAA. February 24, 2006. Retrieved 2008-09-25.
  14. 1 2 Staff (2016). "Diver-Level Courses". PADI website. PADI. Retrieved 25 April 2016.
  15. ↑ Mitchell, SJ (2007). "Technical Diving.". In: Moon RE, Piantadosi CA, Camporesi EM (eds.). Dr. Peter Bennett Symposium Proceedings. Held May 1, 2004. Durham, N.C.: (Divers Alert Network). Retrieved 2011-01-15.
  16. ↑ "Deep Air IS Stupdity". Archived from the original on August 29, 2009. Retrieved 2009-09-03.
  17. ↑ "TDI - Extended Range Diver". Retrieved 2009-09-03.
  18. ↑ Brittain, Colin (2004). "Diving Air and Deep Diving". Let's Dive: Sub-Aqua Association Club Diver Manual (2nd ed.). Wigan, UK: Dive Print. p. 80. ISBN 0-9532904-3-3. The Association strongly endorses a maximum depth of 50 metres (50 metres (160 ft))
  19. ↑ http://www.ffessm.fr/gestionenligne/manuel/43_Qualification_PE60m.pdf FFESSM: Le plongeur titulaire de la qualification PE60 est capable d’évoluer en exploration dans l’espace 0 - 60 m au sein d’une palanquée prise en charge par un Guide de Palanquée (E4).
  20. ↑ http://www.plongee.fsgt.org/IMG/pdf/Manuel_Moniteur-2.pdf FSGT: Plongeur autonome 60m. Ce module doit permettre de compléter l’expérience d’un plongeur autonome confirmé qui souhaiterait évoluer à l’air et en sécurité dans l’espace sub-lointain (40 à 60m).
  21. ↑ http://www.anmp-plongee.com/texte/cursus_anmp.pdf
  22. ↑ Hamilton, K; Laliberté, MF; Heslegrave, R (1992). "Subjective and behavioral effects associated with repeated exposure to narcosis". Aviation, space, and environmental medicine 63 (10): 865–9. PMID 1417647.
  23. ↑ John Lippmann, DAN. "How deep is too deep?". Retrieved 2009-09-03.
  24. ↑ "SSI TechXR - Technical diving program". Scuba Schools International. Retrieved 2009-06-22.

Footnotes

  1. ↑ In his 1989 book, Advanced Wreck Diving, author and leading technical diver, Gary Gentile, commented that there was no accepted term for divers who dived beyond agency-specified recreational limits for non-professional purposes. Revised editions use the term technical diving, and Gary Gentile published a further book in 1999 entitled The Technical Diving Handbook.
  2. ↑ While most technical diving training agencies point out that decompression diving as a separate form of diving is technically a misnomer, since all dives involve an element of decompression as the diver off-gases, the types of diving included in the category of decompression diving involve one or more mandatory decompression stops prior to surfacing, which can be an important distinction.
  3. ↑ Many recreational diving agencies recommend diving no deeper than 30 metres (100 ft), and suggest an absolute limit of 40 metres (130 ft).
  4. ↑ There is a reasonable body of professional opinion that considers decompression diving to be the sole differentiator for "technical" diving.SSI
  5. ↑ Some certification agencies prefer to the term "cavern diving" to cave penetration within recreational diving limits.

External links

This article is issued from Wikipedia - version of the Tuesday, April 26, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.