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Trimix is a breathing gas
Breathing gas

Air is the most common and only natural breathing gas. Other artificial gases, either pure gases or mixtures of gases, are used in breathing equipment and enclosed habitats such as Scuba set, surface supplied diving equipment, recompression chambers, submarines, space suits, spacecraft and anaesthetic machines....
, consisting of oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
, helium
Helium

Helium is a colorless, odorless, tasteless, non-toxic, inert monatomic chemical element that heads the noble gas group in the periodic table and whose atomic number is 2....
 and nitrogen
Nitrogen

Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674?. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere....
, and is often used in deep commercial diving
Commercial Diving

Professional Diving is a type of diving activities where the divers are paid for their work. There are several branches of professional diving, the most well known of which is probably commercial diving....
 and during the deep phase of dives carried out using technical diving
Technical diving

Technical diving is a form of scuba diving that exceeds the scope of recreational diving . Technical divers require advanced training, extensive experience, specialized equipment and often breathe breathing gases other than air or standard nitrox....
 techniques.

With a mixture of three gases it is possible to create mixes suitable for different depths or purposes by adjusting the proportions of each gas.

Advantages of helium in the mix The main reason for adding helium to the breathing mix is to reduce the proportions of nitrogen and oxygen, below those of air, to allow the gas mix to be breathed safely on deep dives.






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Trimix is a breathing gas
Breathing gas

Air is the most common and only natural breathing gas. Other artificial gases, either pure gases or mixtures of gases, are used in breathing equipment and enclosed habitats such as Scuba set, surface supplied diving equipment, recompression chambers, submarines, space suits, spacecraft and anaesthetic machines....
, consisting of oxygen
Oxygen

Oxygen no O2 produced; 2) O2 produced, but absorbed in oceans & seabed rock; 3) O2 starts to gas out of the oceans, but is absorbed by land surfaces and formation of ozone layer; 4-5) O2 sinks filled and the gas accumulates]]...
, helium
Helium

Helium is a colorless, odorless, tasteless, non-toxic, inert monatomic chemical element that heads the noble gas group in the periodic table and whose atomic number is 2....
 and nitrogen
Nitrogen

Nitrogen is a chemical element that has the symbol N and atomic number 7 and atomic mass 14.00674?. Elemental nitrogen is a colorless, odorless, tasteless and mostly inert diatomic gas at standard conditions, constituting 78% by volume of Earth's atmosphere....
, and is often used in deep commercial diving
Commercial Diving

Professional Diving is a type of diving activities where the divers are paid for their work. There are several branches of professional diving, the most well known of which is probably commercial diving....
 and during the deep phase of dives carried out using technical diving
Technical diving

Technical diving is a form of scuba diving that exceeds the scope of recreational diving . Technical divers require advanced training, extensive experience, specialized equipment and often breathe breathing gases other than air or standard nitrox....
 techniques.

With a mixture of three gases it is possible to create mixes suitable for different depths or purposes by adjusting the proportions of each gas.

Mixes


Advantages of helium in the mix

The main reason for adding helium to the breathing mix is to reduce the proportions of nitrogen and oxygen, below those of air, to allow the gas mix to be breathed safely on deep dives. A lower proportion of nitrogen is required to reduce nitrogen narcosis
Nitrogen narcosis

Narcosis while diving, commonly called nitrogen narcosis, inert gas narcosis or rapture of the deep, is a reversible alteration in consciousness in Scuba diving at depth....
 and other physiological effects of the gas at depth. Helium has very little narcotic effect.

The lower density of helium reduces breathing resistance at depth.

Helium off-gas
Off-Gas

Off-Gas is a hazardous by-product of manufacturing. It is the undissolved ozone air collected from the reaction tanks or de-ozonizing filters that can cover various manufactured parts, such as some computer parts....
ses rapidly and it does not enter slow tissues as readily as nitrogen.

Disadvantages of helium in the mix


Helium conducts heat 5 times faster than air; often helium breathing divers carry separate gas supplies to inflate drysuits.

Some divers suffer from hyperbaric arthralgia
Arthralgia

Arthralgia literally means joint pain; it is a symptom of injury, infection, illnesses or an allergic reaction to medication.According to MeSH, the term "arthralgia" should only be used when the condition is non-inflammatory, and the term "arthritis" should be used when the condition is inflammatory....
 during descent.

Helium on-gasses rapidly and usually requires deeper decompression stops than a similar decompression dive using air.

Advantages of reducing oxygen in the mix

Lowering the oxygen content increases the maximum operating depth
Maximum operating depth

In technical diving, the maximum operating depth of a breathing gas is the depth at which the partial pressure of oxygen of the gas mix exceeds a safe limit....
 and duration of the dive before which 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, hyperoxia, or the Paul Bert effect and Lorrain Smith effect, after the researchers who pioneered its discovery and desc...
 becomes a limiting factor.

Advantages of keeping some nitrogen in the mix

Retaining nitrogen in trimix can contribute to the prevention of High Pressure Nervous Syndrome
High pressure nervous syndrome

High pressure nervous syndrome is a neurological and physiological diving disorders that results when a SCUBA diving spends too much time breathing a high-pressure mixture of helium and oxygen ....
, a problem that can occur when breathing 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 the low density of the gas....
 at depths below 130 meters (429 feet).

Naming

Conventionally, the mix is named by its oxygen percentage, helium percentage and optionally the balance percentage, nitrogen. For example, a mix named "trimix 10/70" consisting of 10% oxygen, 70% helium, 20% nitrogen is suitable for a 100 meters (330 feet) dive.

The ratio of gases in a particular mix is chosen to give a safe maximum operating depth
Maximum operating depth

In technical diving, the maximum operating depth of a breathing gas is the depth at which the partial pressure of oxygen of the gas mix exceeds a safe limit....
 and comfortable equivalent air depth
Equivalent air depth

The equivalent air depth is a way of approximating the Decompression sickness requirements of breathing gas mixtures that contain nitrogen and oxygen in different proportions to those in air, known as nitrox....
 for the planned dive. Safe limits for mix of gases in trimix are generally accepted to be a maximum 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 (ppO2 - see Dalton's law
Dalton's law

In chemistry and physics, Dalton's law states that the total pressure exerted by a gas mixture is equal to the sum of the partial pressures of each individual component in a gas mixture....
) of 1.0-1.6 bar and maximum equivalent air depth of 30 to 50 meters (100 to 165 feet). At 100 meters (330 feet), "12/52" has a PPO2 of 1.3 bar and an equivalent air (narcotic) depth of 43 meters (140 feet).

In open-circuit scuba, two classes of trimix are commonly used: "normoxic" trimix - with a minimum PO2 at the surface of 0.18 and "hypoxic" trimix - with a PO2 less than 0.18 at the surface. A Normoxic mix, such as "19/30", is used in the 30 meters (100 feet) to 60 meters (200 feet) depth range and a hypoxic mix, such as "10/50", is used for deeper diving, as a "bottom" gas only and cannot safely be breathed at shallow depths where the ppO2 is less than 0.18 bar.

In fully closed circuit 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 humans cannot safely breathe from the atmosphere....
s that use trimix diluents, the mix can be "hyperoxic" in shallow water because the rebreather automatically adds oxygen to maintain a specific ppO2.

See breathing gas
Breathing gas

Air is the most common and only natural breathing gas. Other artificial gases, either pure gases or mixtures of gases, are used in breathing equipment and enclosed habitats such as Scuba set, surface supplied diving equipment, recompression chambers, submarines, space suits, spacecraft and anaesthetic machines....
 for more information on the composition and choice of gas blends.

Blending

Gas blending
Gas blending

Gas blending or gas mixing is the filling of diving cylinders with non-air breathing gases such as nitrox, trimix and heliox....
 of trimix involves decanting oxygen and helium into the diving cylinder
Diving cylinder

A diving cylinder, scuba tank or diving tank is used to store and transport high pressure breathing gas as a component of SCUBA . It provides gas to the Scuba diving through the demand valve of a diving regulator....
 and then topping up the mix with air
AIR

Air is the part of Earth's atmosphere that humans breath and as such Air .Air may also refer to:...
 from a diving air compressor
Diving air compressor

A Diving Air Compressor is a gas compressor that can fill diving cylinders with high-pressure air pure enough to be used as a breathing gas....
. To ensure an accurate mix, after each helium and oxygen transfer, the mix is allowed to cool, its pressure is measured and further gas is decanted until the correct pressure
Pressure

Pressure is the force per unit area applied to an object in a direction surface normal to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure....
 is achieved. This process often takes hours and is sometimes spread over days at busy blending stations.

A second method called 'continuous blending' is now gaining favor. Oxygen, helium and air are blended on the intake side of a compressor. The oxygen and helium are fed into the air stream using flow meters, so as to achieve the rough mix. The low pressure air is analyzed for oxygen content and the oxygen (and helium) flows adjusted accordingly. On the high pressure side of the compressor a regulator is used to reduce pressure and the trimix is metered through an analyzer (preferably helium and oxygen) so that the fine adjustment to the intake gas flows can be made.

The benefit of such a system is that the helium delivery tank pressure need not be as high as that used in the partial pressure method of blending and residual gas can be 'topped up' to best mix after the dive.

Drawbacks may be that the increased compressibility of helium results in the compressor over-heating (especially in tropical climates) and that the hot trimix entering the analyzer on the high pressure side can affect the reliability of the analysis. DIY versions of the continuous blend units can be made for as little as $200 (excluding analyzers).

History of trimix as a diving gas


1919: Professor Elihu Thompson speculates that helium could be used instead of nitrogen to dilute the oxygen content of a breathing mix and thus reduce narcosis, but because of high prices of helium at that time, the idea remained strictly hypothetical.

1925: The US Navy begins examining helium's potential usage and by the mid 1920's lab animals were exposed to experimental chamber dives using heliox. Soon, human subjects breathing heliox 20/80 (20% oxygen, 80% helium) had been successfully decompressed from deep dives.

1937: Several test dives are conducted with helium mixtures, including salvage diver's Max "Gene" Nohl's dive to 127 meters.

1939: US Navy used heliox in USS Squalus salvage operation.

1965: First saturation dives using heliox.

1970: Hal Watts performs dual body recovery at Mystery Sinkis (126 m). Cave divers
Cave diving

Cave diving is a type of technical diving in which specialized Scuba set is used to enable the exploration of natural or artificial caves which are at least partially filled with water....
 Sheck Exley
Sheck Exley

Sheck Exley was a cave-diving pioneer....
 and Jochen Hasenmayer use heliox to a depth of 212 meters.

1987: First mass use of trimix and heliox: Wakulla Springs
Wakulla Springs

Wakulla Springs is located 14 miles south of Tallahassee, Florida, Florida and 5 miles east of Crawfordville, Florida in Wakulla County, Florida, Florida at the crossroads of State Road 61 and State Road 267 ....
 Project. Exley teaches non-commercial divers in relation to trimix usage in cave diving.

1991: Tom Mount
Tom Mount

Tom Mount is a pioneering technical diving. In 1991 Tom Mount joined Dick Rutkowski in the new organisation formed by Rutkowski, International Association of Nitrox and Technical Divers, dedicated to teaching Nitrox to recreational diving....
 developes first trimix training standards (IANTD). Use of trimix spreads to North East American wreck diving community.

1994: Combined UK/USA team, including leading wreck divers John Chatterton
John Chatterton

John Chatterton is one of the world?s most accomplished and well known wreck diving. Together with Richie Kohler, he was one of the co-hosts for the History Channel Deep Sea Detectives where they have completed work on 57 episodes of this successful series....
 and Gary Gentile
Gary Gentile

Gary Gentile is an United States author and pioneering technical diving....
, succesfully complete a series of wreck dives
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 Sinking ships for wreck diving sites....
 on the RMS Lusitania
RMS Lusitania

RMS Lusitania was a Lusitania-Class Great Britain luxury ocean liner owned by the Cunard Line and built by John Brown and Company of Clydebank, Scotland, torpedoed by a German U-boat on May 7, 1915....
 expedition to a depth of 100 meters using trimix.

2001: John Bennett (diver)
John Bennett (diver)

John Bennett was a United Kingdom Scuba diving who is best known for setting a world record by becoming the first person to deep diving below a depth of 1,000 feet on self contained breathing apparatus....
 The Guiness Book of records recognises John Bennet as the first scuba diver to dive to 1000ft, using Trimix.

Source:

See also

  • Argox (scuba)
    Argox (scuba)

    Argox is the informal name for a scuba diving breathing gas consisting of argon and oxygen. Since argon is not capitalized, in theory argox should not be capitalized either....
  • Nitrox
  • 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 the low density of the gas....
  • Hydreliox
    Hydreliox

    Hydreliox is an exotic breathing gas mixture of helium, oxygen and a small amount of hydrogen.It is used primarily for research and scientific deep diving, usually below 130 metres ....
  • 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....