Technical diving
Encyclopedia
Technical 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 gas
es other than air or standard nitrox.
The concept and term, technical diving, are both relatively recent advents,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. 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.
(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.As most technical diving training agencies point out, references to "decompression diving" is a misnomer, as all dives involve an element of decompression as the diver off-gases. However, the term decompression diving is often used to describe diving which involves one or more mandatory decompression stops prior to surfacing. 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)
The following table tries to describe the differences between technical and recreational diving.
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 (30.5 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.
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 tissue
s 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.
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 diving, some instructors have crafted their own custom training courses to help others become more comfortable sand 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).
mixtures other than air, such as trimix, heliox
, and heliair
. Breathing normal air (with 21 percent oxygen) at depths greater than 180 feet (54.9 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 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 (56.7 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 (39.6 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 cylinder
s 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.
(TDI), Global Underwater Explorers
(GUE), Profesional Scuba Association International(PSAI), International Association of Nitrox and Technical Divers
(IANTD) and National Association of Underwater Instructors
(NAUI) were popular . 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.
Scuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....
that exceeds the scope of recreational diving
Recreational diving
Recreational diving or sport diving is a type of diving that uses SCUBA equipment for the purpose of leisure and enjoyment. In some diving circles, the term "recreational diving" is used in contradistinction to "technical diving", a more demanding aspect of the sport which requires greater levels...
(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 gas
Breathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
es other than air or standard nitrox.
The concept and term, technical diving, are both relatively recent advents,In his 1989 book, Advanced Wreck Diving, author and leading technical diver, Gary Gentile
Gary Gentile
Gary Gentile is an American author and pioneering technical diver.-Diving:Gary Gentile is a wreck diver. It has been suggested that Gary Gentile may be the most experienced wreck diver in the world...
, 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. 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.
Definition of technical diving
There is some professional disagreement as to what the term should encompass. 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 divingPenetration diving
Penetration diving or no clear surface diving is a type of diving where the scuba diver enters a space from which there is no direct, purely vertical ascent to the safety of breathable air of the atmosphere at the surface...
(as opposed to open-water diving
Open-water diving
Open-water diving has at least two different meanings in scuba diving:* In the later stages of initial diver training, divers progress from diving in swimming pools to "open water", which normally implies the sea or a lake, including quarries....
), 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.As most technical diving training agencies point out, references to "decompression diving" is a misnomer, as all dives involve an element of decompression as the diver off-gases. However, the term decompression diving is often used to describe diving which involves one or more mandatory decompression stops prior to surfacing. 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)
- PADIProfessional Association of Diving InstructorsThe Professional Association of Diving Instructors is the world's largest recreational diving membership and diver training organization founded in 1966 by John Cronin and Ralph Erickson...
, the largest recreational diver training agency in North America, 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."
- NOAANational Oceanic and Atmospheric AdministrationThe National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...
defines technical diving in this way: "Technical diving is a term used to describe 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 tries to describe the differences between technical and recreational diving.
| Activity | Recreational | Technical |
|---|---|---|
| Deep diving Deep diving The meaning of the term deep diving is a form of technical diving. It is defined by the level of the diver's diver training, diving equipment, breathing gas, and surface support:... |
Maximum depth of 40 metres (131.2 ft)Many recreational diving agencies recommend diving no deeper than 30 metres (98.4 ft), and suggest an absolute limit of 40 metres (131.2 ft).http://www.padi.com/english/common/courses/rec/continue/deepdiver.asp | Beyond 40 metres (131.2 ft) |
| Decompression divingThere is a reasonable body of professional opinion that considers decompression diving to be the sole differentiator for "technical" diving.SSI | No decompression | Decompression diving |
| Mixed gas diving Gas blending Gas blending or gas mixing is the filling of diving cylinders with non-air breathing gases such as nitrox, trimix and heliox.Filling cylinders with a mixture of gases has dangers for both the filler and the diver. During filling there is a risk of fire due to use of oxygen and a risk of explosion... |
Air and Nitrox | Trimix, Heliox Heliox Heliox is a breathing gas composed of a mixture of helium and oxygen .Heliox has been used medically since the 1930s, and although the medical community adopted it initially to alleviate symptoms of upper airway obstruction, its range of medical uses has since expanded greatly, mostly because of... , Heliair Heliair Heliair is a breathing gas consisting of mixture of oxygen, nitrogen and helium and is often used during the deep phase of dives carried out using technical diving techniques... and Hydrox Hydrox (breathing gas) Hydrox, a gas mixture of hydrogen and oxygen, is used as a breathing gas in very deep diving. It allows divers to descend several hundred metres.... |
| Gas switching | Single gas used | May switch between gases to accelerate decompression and/or "travel mixes" to permit descent carrying hypoxic Hypoxia (medical) Hypoxia, or hypoxiation, is a pathological condition in which the body as a whole or a region of the body is deprived of adequate oxygen supply. Variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise... gas mixes |
| Wreck diving Wreck diving Wreck diving is a type of recreational diving where shipwrecks are explored. Although most wreck dive sites are at shipwrecks, there is an increasing trend to scuttle retired ships to create artificial reef sites... |
Penetration limited to "light zone" or 30 metres (98.4 ft) depth/penetration | Deeper penetration |
| Cave diving Cave diving Cave diving is a type of technical diving in which specialized equipment is used to enable the exploration of caves which are at least partially filled with water. In the United Kingdom it is an extension of the more common sport of caving, and in the United States an extension of the more common... |
Penetration limited to "light zone" or 30 metres (98.4 ft) depth/penetrationSome certification agencies prefer to the term "cavern diving" to cave penetration within recreational diving limits. | Deeper penetration |
| Ice diving Ice diving Ice diving is a type of penetration diving where the dive takes place under ice. Because diving under ice places the diver in an overhead environment typically with only a single entry/exit point, it is considered an advanced type of diving requiring special training... |
Some agencies regard ice diving as recreational diving;PADI others as technical diving.NAUI | |
| Rebreather Rebreather A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where... s |
Some agencies regard use of semi-closed rebreathers as recreational diving;PADI others as technical diving.NAUI | |
| Solo diving Solo diving Solo diving is the practice of scuba diving alone without a "dive buddy". Solo diving, once discouraged, is now beginning to gain acceptance among experienced divers who have skills in self-sufficiency and redundant backup equipment.... |
Recreational diving requires buddy system | Solo divingSome training agencies regard solo diving within the "recreational" sphere.SDI |
Depth
Technical dives may be defined as being dives deeper than about 130 feet (39.6 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
Nitrogen narcosis
Narcosis while diving , is a reversible alteration in consciousness that occurs while scuba diving at depth. The Greek word ναρκωσις is derived from narke, "temporary decline or loss of senses and movement, numbness", a term used by Homer and Hippocrates...
that normally becomes serious at depths of 100 feet (30.5 m) or greater. Increasing pressure at depth also increases the risk of oxygen toxicity based on the partial pressure
Partial pressure
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
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
Decompression sickness
Decompression sickness describes a condition arising from dissolved gases coming out of solution into bubbles inside the body on depressurization...
, also known as the "bends". Metabolically inert gases in the diver's breathing gas, such as nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
and helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
, 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 tissue
Biological tissue
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
s 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
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
breathing gas
Breathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
mixtures such as nitrox during the beginning and ending portion of the dive. To avoid nitrogen narcosis
Nitrogen narcosis
Narcosis while diving , is a reversible alteration in consciousness that occurs while scuba diving at depth. The Greek word ναρκωσις is derived from narke, "temporary decline or loss of senses and movement, numbness", a term used by Homer and Hippocrates...
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 divingCave divingCave diving is a type of technical diving in which specialized equipment is used to enable the exploration of caves which are at least partially filled with water. In the United Kingdom it is an extension of the more common sport of caving, and in the United States an extension of the more common...
- diving into a cave system. - Deep divingDeep divingThe meaning of the term deep diving is a form of technical diving. It is defined by the level of the diver's diver training, diving equipment, breathing gas, and surface support:...
- diving into greater depths. - Ice divingIce divingIce diving is a type of penetration diving where the dive takes place under ice. Because diving under ice places the diver in an overhead environment typically with only a single entry/exit point, it is considered an advanced type of diving requiring special training...
- diving under ice. - Wreck divingWreck divingWreck diving is a type of recreational diving where shipwrecks are explored. Although most wreck dive sites are at shipwrecks, there is an increasing trend to scuttle retired ships to create artificial reef sites...
- 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 siltSilt out
A silt out is a situation when underwater visibility is rapidly reduced to zero.It often happens from divers' swimfins disturbing silt, particularly in caves or in still fresh water....
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 diving, some instructors have crafted their own custom training courses to help others become more comfortable sand 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 gasBreathing gas
Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
mixtures other than air, such as trimix, heliox
Heliox
Heliox is a breathing gas composed of a mixture of helium and oxygen .Heliox has been used medically since the 1930s, and although the medical community adopted it initially to alleviate symptoms of upper airway obstruction, its range of medical uses has since expanded greatly, mostly because of...
, and heliair
Heliair
Heliair is a breathing gas consisting of mixture of oxygen, nitrogen and helium and is often used during the deep phase of dives carried out using technical diving techniques...
. Breathing normal air (with 21 percent oxygen) at depths greater than 180 feet (54.9 m) creates a high risk of oxygen toxicity
Oxygen toxicity
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen at elevated partial pressures. It is also known as oxygen toxicity syndrome, oxygen intoxication, and oxygen poisoning...
. 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
Nitrogen narcosis
Narcosis while diving , is a reversible alteration in consciousness that occurs while scuba diving at depth. The Greek word ναρκωσις is derived from narke, "temporary decline or loss of senses and movement, numbness", a term used by Homer and Hippocrates...
). 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
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. This reduces the nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
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 (39.6 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 –, 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
Oxygen toxicity
Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen at elevated partial pressures. It is also known as oxygen toxicity syndrome, oxygen intoxication, and oxygen poisoning...
. 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 (56.7 m). Helitrox/triox proponents argue that the defining risk should be nitrogen narcosis
Nitrogen narcosis
Narcosis while diving , is a reversible alteration in consciousness that occurs while scuba diving at depth. The Greek word ναρκωσις is derived from narke, "temporary decline or loss of senses and movement, numbness", a term used by Homer and Hippocrates...
, and suggest that when the partial pressure of nitrogen reaches approximately 4.0 ATA, which occurs at about 130 feet (39.6 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
Divers Alert Network
The Divers Alert Network is a non-profit 501 organization devoted to assisting divers in need. The Research department conducts significant medical research on recreational scuba diving safety...
does not formally reject deep air diving per se, but indicates the additional risks involved.
Equipment
Diving equipment
Diving equipment is equipment used by underwater divers for the purpose of facilitating diving activities. This may be equipment primarily intended for this purpose, or equipment intended for other puprposes which is found to be suitable for diving use....
. 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 cylinder
Diving cylinder
A diving cylinder, scuba tank or diving tank is a gas cylinder used to store and transport high pressure breathing gas as a component of a scuba set. It provides gas to the scuba diver through the demand valve of a diving regulator....
s and/or by using a rebreather
Rebreather
A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where...
. 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
Sidemount
Sidemount is a scuba diving configuration which has tanks mounted alongside the diver, below the shoulders and along the hips, instead of on the back of the diver. It is a popular configuration with advanced cave divers, as smaller sections of cave can be penetrated and tanks can be changed with...
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 training organizations. Technical Diving InternationalTechnical Diving International
Technical Diving International is the largest technical diving certification agency in the world. As one of the first agencies to provide training in mixed gas diving and rebreathers, TDI is seen as an innovator of new diving techniques and programs which previously were not available to the...
(TDI), Global Underwater Explorers
Global Underwater Explorers
Global Underwater Explorers is a scuba diving organization that provides education within recreational, technical and cave diving. It is a not-for-profit, membership organization, based in High Springs, Florida, United States....
(GUE), Profesional Scuba Association International(PSAI), International Association of Nitrox and Technical Divers
International Association of Nitrox and Technical Divers
International Association of Nitrox and Technical Divers is a SCUBA diving organization concerned with certification and training in Enriched Air Nitrox diving, Technical diving and Free diving.- History :...
(IANTD) and National Association of Underwater Instructors
National Association of Underwater Instructors
The National Association of Underwater Instructors is a non-profit 501 association of SCUBA instructors. It was officially CE and ISO certified in May 2007 in all three diver levels and both instructor levels.-History:...
(NAUI) were popular . Recent entries into the market include Unified Team Diving
Unified Team Diving
Unified Team Diving is a SCUBA diving training agency founded in 2008 to incorporate DIR/Hogarthian principles into SCUBA education at all levels.-History:...
(UTD), and Diving Science and Technology
Diving Science and Technology
Diving Science and Technology is a corporate affiliate of the Professional Association of Diving Instructors and the developer of the Recreational Dive Planner. DSAT has held scientific workshops for diver safety and education....
(DSAT), the technical arm of Professional Association of Diving Instructors
Professional Association of Diving Instructors
The Professional Association of Diving Instructors is the world's largest recreational diving membership and diver training organization founded in 1966 by John Cronin and Ralph Erickson...
(PADI). The Scuba Schools International
Scuba Schools International
Scuba Schools International or SSI is an organization that teaches the skills involved in scuba diving and supports Dive Businesses and Dive Resorts.SSI has well over 2,500 authorized dealers and 35 Regional Centers and Area Offices all over the World....
(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.
See also
- Breathing gasBreathing gasBreathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...
- Carbon dioxide poisoning
- Diving hazards and precautionsDiving hazards and precautionsDivers face specific physical and health risks when they go underwater or use high pressure breathing gases. Some of these conditions also affect people who work in raised pressure environments out of water, e.g...
- Oxygen toxicityOxygen toxicityOxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen at elevated partial pressures. It is also known as oxygen toxicity syndrome, oxygen intoxication, and oxygen poisoning...
- RebreatherRebreatherA rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where...
- Solo divingSolo divingSolo diving is the practice of scuba diving alone without a "dive buddy". Solo diving, once discouraged, is now beginning to gain acceptance among experienced divers who have skills in self-sufficiency and redundant backup equipment....
- Trimix
External links
- http://www.TechDivingMag.com
- http://www.TechnicalDiving.com
- Select publications on technical diving and technical diving history hosted by the Rubicon FoundationRubicon FoundationRubicon Foundation, Inc. is a non-profit organization devoted to contributing to the interdependent dynamic between research, exploration, science and education. The foundation, started in 2002, is located in Durham, North Carolina and is primarily supported by donations and grants. Funding has...
- RebreatherPro Jill Heinerth's interactive multimedia technical diving site
- Transitioning to technical diving