Editing Trimix (breathing gas)

{{short description| Breathing gas consisting of oxygen, helium and nitrogen }}
{{about|the oxygen-nitrogen-helium gas mixture|the erectile dysfunction drug|Trimix (drug)}}
[[File:Trimix label.png |thumb|Trimix scuba cylinder label]]
[[File:IMCA Trimix shoulder.svg|thumb|[[International Marine Contractors Association|IMCA]] Trimix cylinder shoulder colour code]]
[[File:IMCA Trimix shoulder quartered.svg|thumb|Alternative IMCA Trimix cylinder shoulder colour code]]

'''Trimix''' is a [[breathing gas]] consisting of [[oxygen]], [[helium]], and [[nitrogen]]. It is used in deep [[commercial diving]], during the deep phase of dives carried out using [[technical diving]] techniques,<ref name="Brubakk" /><ref name="gernhardt" /> and in advanced [[recreational diving]].<ref name="IANTD" /><ref name="SSI" />

The helium is included as a substitute for some of the nitrogen, to reduce the [[Nitrogen narcosis|narcotic effect]] of the breathing gas at depth and to reduce the [[work of breathing]]. 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. Oxygen content can be optimised for the depth to limit the risk of [[Oxygen toxicity|toxicity]], and the inert component balanced between nitrogen (which is cheap but narcotic) and helium (which is not narcotic and reduces work of breathing, but is more expensive and can increase [[Thermal conduction|heat loss]]).<ref name="Anthony and Mitchell 2016" />

The mixture of helium and oxygen with a 0% nitrogen content is generally known as [[heliox]]. This is frequently used as a breathing gas in deep commercial diving operations, where it is often recycled to save the expensive helium component. Analysis of two-component gases is much simpler than three-component gases.

==Applications==
Trimix is used as an ambient pressure breathing gas for underwater diving. It has been used in both scuba and surface-supplied applications, for professional and recreational diving, and for surface oriented and saturation diving. The most common use is in recreational technical diving.<ref name="oceanos" /><ref name="Bond1964" />

In [[open-circuit scuba]], two classes of trimix are commonly used: ''[[wikt:normoxic|normoxic]]'' trimix—with a minimum PO<sub>2</sub> at the surface of 0.18 and ''[[wikt:hypoxic|hypoxic]]'' trimix—with a PO<sub>2</sub> less than 0.18 at the surface.<ref name="exoticgases" /> A normoxic mix such as "19/30" is used in the {{convert|30|to|60|m|ft|-1|abbr=on}} depth range; 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 PO<sub>2</sub> is less than 0.18 bar.

In fully closed-circuit [[Diving rebreather|rebreathers]] that use trimix diluents, the mix in the breathing loop can be ''[[wikt:hyperoxic|hyperoxic]]'' (meaning more oxygen than in air, as in [[enriched air nitrox]]) in shallow water, because the rebreather automatically adds oxygen to maintain a specific partial pressure of oxygen.<ref name="rebreather2.0" /> Hyperoxic trimix is also sometimes used on open circuit scuba, to reduce decompression obligations.<ref name="TDISDI 2002" />

== Function of the helium ==
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.<ref name="Brubakk" /> A lower proportion of nitrogen is required to reduce [[nitrogen narcosis]] and other physiological effects of the gas at depth. Helium has very little narcotic effect.<ref name="palautz97" /> A lower proportion of oxygen reduces the risk of [[oxygen toxicity]] on deep dives.

The lower density of helium reduces [[Work of breathing|breathing resistance]] at depth.<ref name="Brubakk" /><ref name="palautz97" /> Work of breathing can limit the use of breathing gas mixtures in underwater breathing apparatus, as with increasing depth a point may be reached where work of breathing exceeds the available effort from the diver. Beyond this point accumulation of carbon dioxide will eventually result in severe and debilitating [[hypercapnia]], which, if not corrected quickly, will cause the diver to attempt to breathe faster, exacerbating the work of breathing, which will lead to loss of consciousness and a high risk of drowning.<ref name="Mitchell et al 2007" />

Because of its low molecular weight, helium [[Graham's law|enters and leaves tissues by diffusion more rapidly]] than nitrogen as the pressure is increased or reduced (this is called on-gassing and off-gassing). Because of its lower solubility, helium does not load tissues as heavily as nitrogen, but at the same time the tissues can not support as high an amount of helium when super-saturated. In effect, helium is a faster gas to saturate and desaturate, which is a distinct advantage in [[saturation diving]], but less so in bounce diving, where the increased rate of off-gassing is largely counterbalanced by the equivalently increased rate of on-gassing.

Some divers suffer from [[compression arthralgia]] during deep descent, and trimix has been shown to help avoid or delay the symptoms of compression arthralgia.<ref name="VannVorosmarti2002" /><ref name="Bennett1974" />

==Disadvantages of the helium==
Helium conducts heat six times faster than air, so helium-breathing divers often carry a separate supply of a different gas to inflate [[drysuit]]s. This is to avoid the risk of hypothermia caused by using helium as inflator gas. [[Argon]], carried in a small, separate tank connected only to the inflator of the drysuit, is preferred to air, since air conducts heat 50% faster than argon.<ref name="engtbox" /> Dry suits (if used together with a buoyancy compensator) still require a minimum of inflation to avoid "[[suit squeeze]]", i.e. injury to skin caused by pinching by tight dry suit folds.

Helium diffuses into tissues (called [[ingassing]]) more rapidly than nitrogen as the ambient pressure is increased. A consequence of the higher loading in some tissues is that some [[decompression algorithm]]s require deeper [[decompression stops]] than a similar pressure exposure dive using air, and helium is more likely to come out of solution and cause [[decompression sickness]] following a fast ascent.<ref name="Fock 2007" />

In addition to physiological disadvantages, the use of trimix also has economic and logistic disadvantages. The price of helium increased by over 51% between the years 2000 and 2011.<ref name="usgshestats" /> This price increase affects open-circuit divers more than closed-circuit divers due to the larger volume of helium consumed on a typical trimix dive. Additionally, as trimix fills require more expensive helium analysis equipment than air and nitrox fills, there are fewer trimix filling stations. The relative scarcity of trimix filling stations may necessitate going far out of one's way in order to procure the necessary mix for a deep dive that requires the gas.

==Advantages of controlling the oxygen fraction==
Lowering the oxygen content of a breathing gas mixture increases the [[maximum operating depth]] and duration of the dive before which [[oxygen toxicity]] becomes a limiting factor. Most trimix divers limit their working oxygen partial pressure [PO<sub>2</sub>] to 1.4 bar and may reduce the P<sub>O<sub>2</sub></sub> further to 1.3 bar or 1.2 bar depending on the depth, the duration and the kind of breathing system used.<ref name="Brubakk" /><ref name="gernhardt" /><ref name="Acott" /><ref name="Gerth2006" /> A maximum oxygen partial pressure of 1.4 bar for the active sectors of the dive, and 1.6 bar for decompression stops is recommended by several recreational and technical diving certification agencies for open circuit,<ref name="Lang2001" /> and 1.2 bar or 1.3 bar as maximum for the active sectors of a dive on closed-circuit rebreather. Increasing the oxygen fraction in a trimix to be used as a decompression gas can accelerate decompression with a lowered risk of isobaric counter diffusion complications.

==Advantages of keeping some nitrogen in the mix==
Retaining nitrogen in trimix can contribute to the prevention of [[High Pressure Nervous Syndrome]], a problem that can occur when breathing [[heliox]] at depths beyond about {{convert|130|m|ft}}.<ref name="Brubakk" /><ref name="Hunger 1974" /><ref name="Bennett et al 1982" /><ref name="Campbell" /> Nitrogen is also much less expensive than helium.

==Naming conventions==
<!--target for redirect from [[Trimix diving]]-->
The term trimix implies that the gas has three functional components, which are helium, nitrogen and oxygen. Since the nitrogen and all or part of the oxygen is usually provided from air, the other components of ordinary atmospheric air are generally ignored. Conventionally, the composition of a mix is specified by its oxygen percentage, helium percentage and optionally the balance percentage, nitrogen, in that order. For example, a mix named "trimix 10/70" or trimix 10/70/20, consisting of 10% oxygen, 70% helium, 20% nitrogen is suitable for a {{convert|100|m|ft|adj=on}} dive. Hyperoxic trimix is sometimes referred to as Helitrox, TriOx, or HOTx (High Oxygen Trimix) with the "x" in HOTx representing the mixture's fraction of helium as a percentage.<ref name="TDISDI 2002" />

The basic term Trimix is sufficient, modified as appropriate with the terms hypoxic, normoxic and hyperoxic, and the usual forms for indicating constituent gas fraction, to describe any possible ratio of gases, but the [[National Association of Underwater Instructors]] (NAUI) uses the term "helitrox" for hyperoxic 26/17 Trimix, i.e. 26% oxygen, 17% helium, 57% nitrogen. Helitrox requires [[decompression stop]]s similar to Nitrox-I (EAN32) and has a [[maximum operating depth]] of {{convert|44|m|ft}}, where it has an [[equivalent narcotic depth]] of {{convert|35|m|ft}}. This allows diving throughout the usual recreational range, while decreasing decompression obligation and narcotic effects compared to air.<ref name="Helitrox" /> [[Global Underwater Explorers|GUE]] and [[Unified Team Diving|UTD]] also promote hyperoxic trimix for this depth range, but prefer the term "TriOx".

The use of trimix as a breathing gas while diving is called trimix diving, and is a sub-category of [[mixed gas diving]], also sometimes referred to simply as [[gas diving]].

==Blending==
[[File:Gas blending equipment.JPG|thumb|Partial pressure gas blending equipment for scuba diving]]
[[File:Gas blending oxygen and helium analyser.JPG|thumb|Gas blending oxygen and helium analyser]]
[[Gas blending]] of trimix generally involves mixing helium and oxygen with air to the desired proportions and pressure. Two methods are in common use:

Partial pressure blending is done by [[decantation|decanting]] oxygen and helium into the [[diving cylinder]] and then topping up the mix with [[air]] from a [[diving air compressor]]. 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]] is achieved. This process often takes hours and is sometimes spread over days at busy blending stations. Corrections can be made for temperature effect, but this requires accurate monitoring of the temperature of the mixture inside the cylinder, which is generally not available.<ref name="oxyhackers" />

A second method called 'continuous blending' is done by mixing oxygen and helium into the intake air of a compressor.<ref name="oxyhackers" /> The oxygen and helium are fed into mixing tubes in the intake air stream using flow meters or analysis of the oxygen content after oxygen addition and before and after the helium addition, and the oxygen and helium flows adjusted accordingly. On the high pressure side of the compressor a regulator or bleed orifice is used to reduce pressure of a sample flow and the trimix is analyzed (preferably for both 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. This is important mainly because of the high cost of helium. Drawbacks may be that the high heat of compression of helium results in the compressor overheating, especially in hot weather. Temperature of the trimix entering the analyser should be kept constant for best reliability of the analysis, and the analyser should be calibrated at ambient temperature before use.<!-- if the gas is released through a regulator or orifice and analysed at ambient pressure it will not be hot--> The mixing tube is a very simple device, and DIY versions of the continuous blend units can be made for a relatively low cost compared to the cost of analysers and compressor.<ref name="oxyhackers" /><ref name="continuous blending" />

===Choice of mixture composition===
{{see also|breathing gas}}
The ratio of gases in a particular mix is chosen to give a safe [[maximum operating depth]] and comfortable [[equivalent narcotic depth]] for the planned dive. Safe limits for mix of gases in trimix are generally accepted to be a maximum [[partial pressure]] of oxygen (PO<sub>2</sub>—see [[Dalton's law]]) of 1.0 to 1.6 bar and maximum equivalent narcotic depth of {{convert|30|to|50|m|ft|-1|abbr=on}}. At {{convert|100|m|ft|abbr=on}}, "12/52" has a PO<sub>2</sub> of 1.3 bar and an equivalent narcotic depth of {{convert|43|m|ft|abbr=on}}.

Mix composition choice is also affected by limitations on [[breathing gas density]] to prevent excessive [[work of breathing]].<ref name="Mitchell et al 2007" /><ref name="Anthony and Mitchell 2016" />

==="Standard" mixes===
Although theoretically trimix can be blended with almost any combination of helium and oxygen, a number of "standard" mixes have evolved (such as 21/35, 18/45 and 15/55—see [[#Naming conventions|''Naming conventions'']]). Most of these mixes originated from starting by decanting a given pressure of helium into an empty cylinder, and then topping up the mix with 32% nitrox. The "standard" mixes evolved because of three coinciding factors — the desire to keep the [[equivalent narcotic depth]] (END) of the mix at approximately {{convert|34|m|ft}}, the requirement to keep the partial pressure of oxygen at 1.4 ATA or below at the deepest point of the dive, and the fact that many dive shops stored standard 32% nitrox in banks, which simplifies mixing.<ref name="TDISDI manual" /> The use of standard mixes makes it relatively easy to top up diving cylinders after a dive using residual mix — only helium and banked nitrox are needed to top up the residual gas from the last fill. This can be also be applied by using a compressor with a [[Nitrox#production|membrane separation]] system or [[Nitrox#Production|continuous blending]] set for a Nitrox32 output.<ref name="Coenen and Zivkovic 2015" />

The method of mixing a known nitrox mix with helium allows analysis of the fractions of each gas using only an oxygen analyser, since the ratio of the oxygen fraction in the final mix to the oxygen fraction in the initial nitrox gives the fraction of nitrox in the final mix, hence the fractions of the three components are easily calculated. It is demonstrably true that the END of a nitrox-helium mixture at its [[maximum operating depth]] (MOD) is equal to the MOD of the nitrox alone.<ref name="Coenen and Zivkovic 2015" />

====Heliair====
<!--targe of redirect [[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. This term, first used by [[Sheck Exley]],<ref name="bowen" /> is mostly used by [[Technical Diving International]] (TDI).

It is easily [[gas blending|blended]] from helium and [[air]] and so has a fixed 21:79 ratio of oxygen to nitrogen with the balance consisting of a variable amount of helium. It is sometimes referred to as "poor man's trimix",<ref name="bowen" /><ref name="gentile" /> because it is much easier to blend than trimix blends with variable oxygen content, since all that is required is to insert the requisite [[partial pressure]] of helium, and then top up with air from a conventional compressor. The more complicated (and dangerous) step of adding pure oxygen at pressure required to blend trimix is absent when blending heliair.

Heliair blends are similar to the standard Trimix blends made with helium and Nitrox 32, but with a deeper END at MOD.
Heliair will always have less than 21% oxygen, and will be hypoxic (less than 17% oxygen) for mixes with more than 20% helium.

==History as a diving gas==
{{see also|History of underwater diving}}
*1919: Professor [[Elihu Thomson]] speculates that helium could be used instead of nitrogen to reduce the breathing resistance at great depth.<ref name="dive_hx" /> [[Heliox]] was used with air tables resulting in a high incidence of decompression sickness, so the use of helium was discontinued.<ref name="behnke" />
*1924: The [[US Navy]] begins examining helium's potential usage and by the mid-1920s 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.<ref name="Kane1998" />
*1937: Several test dives are conducted with helium mixtures, including salvage diver [[Max Nohl|Max "Gene" Nohl's]] dive to 127 meters.<ref name="Nohl1937" /><ref name="CamporesiDAN" />
*1939: US Navy uses heliox in [[USS Sailfish (SS-192)|USS ''Squalus'']] salvage operation. Heliox usage, coupled with the absence of decrement in co-ordination and cognitive function in the salvage divers, confirms Behnke's theory of nitrogen narcosis.<ref name="dive_hx" />
*1965: Nic Flemming's work to study sand ribbons in the English Channel becomes the first to compare diver performance while breathing air and heliox in the open water.<ref name="Davis1996" />
*1963: First saturation dives using trimix as part of [[George F. Bond#Project Genesis|Project Genesis]].<ref name="Bond1964" />
*1970: [[Hal Watts]] recovers two bodies at Mystery Sink (126 m).<ref name="GilliamMaier1995" />
*1979: A research team headed by [[Peter B. Bennett]] at the Duke University Medical Center Hyperbaric Laboratory begins the "Atlantis Dive Series" which proves the mechanisms behind the use of trimix to prevent High Pressure Nervous Syndrome symptoms.<ref name="CamporesiDAN" />
*1983: [[Cave diving|Cave diver]] [[Jochen Hasenmayer]] uses heliox to a depth of 212 meters. Depth is later repeated by [[Sheck Exley]] in 1987.<ref name="GilliamMaier1995" />
*1987: First mass use of trimix and heliox: [[Wakulla Springs]] Project. Exley teaches non-commercial divers in relation to trimix usage in cave diving.<ref name="InDepth 2022" >{{Cite web |last=InDEPTH |date=26 August 2022 |title=The First Helium-based Mix Dives Conducted by Pre-Tech Explorers (1967-1988) |url=https://indepthmag.com/first-helium-based-mixed-gas-dives/ |access-date=1 June 2024 |website=InDEPTH |language=en-US |archive-date=1 June 2024 |archive-url=https://web.archive.org/web/20240601102413/https://indepthmag.com/first-helium-based-mixed-gas-dives/ |url-status=live }}</ref>
*1991: [[Billy Deans (diver)|Billy Deans]] commences teaching of trimix diving for recreational diving. [[Tom Mount]] develops first trimix training standards ([[IANTD]]). Use of trimix spreads rapidly to North East American wreck diving community.<ref name="Mount 2020" >{{Cite web |last=Mount |first=Tom |date=30 April 2020 |title=The Early Evolution of Technical Diving - Overview |url=https://iantd.com/index.php/en-us/iantd-media/articles/63-the-early-evolution-of-technical-diving-overview |access-date=1 June 2024 |website=IANTD World Headquarters |language=en-us |archive-date=1 June 2024 |archive-url=https://web.archive.org/web/20240601102413/https://iantd.com/index.php/en-us/iantd-media/articles/63-the-early-evolution-of-technical-diving-overview |url-status=live }}</ref>
*1992: The National Oceanographic and Atmospheric Administration (NOAA) develops "Monitor Mix" for dives to the USS ''[[USS Monitor|Monitor]]''. This mix became NOAA Trimix I, with decompression tables designed by [[Robert William Hamilton, Jr.|Bill Hamilton]] published in the NOAA Diving Manual.<ref name="Dinsmore1999" />
*1992: NOAA obtains training from Key West Divers to conduct the first NOAA-sponsored trimix dives on the wreck of the USS ''Monitor'' off Cape Hatteras, NC.<ref name="Dinsmore1999" />
*1994: Combined UK/USA team, including wreck divers [[John Chatterton]] and [[Gary Gentile]], successfully completes a series of [[wreck diving|wreck dives]] on the ''[[RMS Lusitania]]'' expedition to a depth of 100 meters using trimix.<ref name="Warwick2015" />
*1994: [[Sheck Exley]] and [[Jim Bowden (diver)|Jim Bowden]] use "heliair" at [[Zacaton]] in the first attempt to make an open circuit scuba dive to 1000&nbsp;ft. Exley, at the time holding the world record for an 881-foot dive, passes out and dies around 900 feet; Bowden aborts at 925 feet and survives despite several life-threatening obstacles.
*2001: [[John Bennett (diver)|John Bennett]] becomes the first scuba diver to dive to {{convert|300|m|ft|sigfig=1}}, using trimix.<ref name="techdive" >{{Cite web |last=techdive |title=A Journey to 308m the John Bennett Story |url=https://techdive.com.au/aboutus/journey/ |access-date=1 June 2024 |website=Tech Dive Academy |archive-date=1 June 2024 |archive-url=https://web.archive.org/web/20240601102418/https://techdive.com.au/aboutus/journey/ |url-status=dead }}</ref>
*2005: [[David Shaw (diver)|David Shaw]] sets depth record for using a trimix [[Diving rebreather|rebreather]], and dies while repeating the dive to attempt to recover the body of another diver.<ref name="Mitchell et al 2007" /><ref name="Shaw" />
*2015: The [[United States Navy Experimental Diving Unit]] shows that bounce dives using trimix are not more decompression efficient than dives on heliox.<ref name="NEDU2015-4" />

==Training and certification==
[[File:CMAS-ISA Normoxic Trimix diver certification card PC160020.jpg|thumb|CMAS-ISA Normoxic Trimix diver certification card]]
Technical diver training and certification agencies may differentiate between levels of trimix diving qualifications, The usual distinction is between normoxic trimix and hypoxic trimix, sometimes also called full trimix. The basic distinction is that for hypoxic trimix diving the dive cannot be started on the bottom mix, and procedures for use of a ''travel mix'' for the first part of the descent, and gas switching during the descent to avoid oxygen toxicity are added to the required skills. Longer decompression using a larger variety of mixtures may also complicate procedures. In closed circuit rebreather diving, use of a hypoxic diluent prevents the diver from conducting a diluent flush at shallow depths while breathing from the loop, so that it remains possible at the maximum depth of the dive, where it may be more critical.

==See also==
* {{annotated link|Argox}}
* {{annotated link|Heliox}}
* {{annotated link|Hydreliox}}
* {{annotated link|Hydrox (breathing gas)|Hydrox}}
* {{annotated link|Nitrox}}

==References==
{{reflist|1=30em|refs=

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<ref name="Anthony and Mitchell 2016" >{{cite conference |url=https://www.omao.noaa.gov/sites/default/files/documents/Rebreathers%20and%20Scientific%20Diving%20Proceedings%202016.pdf |title=Respiratory Physiology of Rebreather Diving |first1=Gavin |last1=Anthony |first2=Simon J. |last2=Mitchell |editor1-last=Pollock |editor1-first=N.W. |editor2-last=Sellers |editor2-first=S.H. |editor3-last=Godfrey |editor3-first=JM |work=Rebreathers and Scientific Diving. Proceedings of NPS/NOAA/DAN/AAUS June 16–19, 2015 Workshop |location=Wrigley Marine Science Center, Catalina Island, CA |year=2016 |pages=66–79 |access-date=2019-11-21 |archive-date=2023-08-11 |archive-url=https://web.archive.org/web/20230811200013/https://www.omao.noaa.gov/sites/default/files/documents/Rebreathers%20and%20Scientific%20Diving%20Proceedings%202016.pdf |url-status=live }}</ref>

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<ref name="bowen">{{cite journal |author=Bowen, Curt |title=Heliair: Poor man's mix |journal=DeepTech |url=http://www.advanceddivermagazine.com/ezinefreearticles/HeliairPoorMansMix.pdf |access-date=13 January 2010 |year=1997 |archive-date=13 May 2016 |archive-url=https://web.archive.org/web/20160513163900/http://www.advanceddivermagazine.com/ezinefreearticles/HeliairPoorMansMix.pdf |url-status=live }}</ref>

<ref name="Brubakk">{{cite book |title=Bennett and Elliott's physiology and medicine of diving, 5th Rev ed. |last=Brubakk |first=A. O. |author2=T. S. Neuman |year=2003 |publisher=Saunders Ltd. |location=United States |isbn=0-7020-2571-2 |page=800}}</ref>

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<ref name="Coenen and Zivkovic 2015" >{{cite journal|last1=Coenen |first1=Michiel |last2=ivkovic |first2=Jelena |date=2015 |title=Graphical description of trimix diving gases using ternary plots |journal=Underwater Technology |volume=33 |issue=2 |pages=127–131 |doi=10.3723/ut.33.127 |url=https://www.researchgate.net/publication/283845260 }}</ref>

<ref name="continuous blending">{{cite web |url=http://shadowdweller.skynetblogs.be/post/3924720/continuous-trimix-blending-with-2-nitrox-stic |title=Continuous trimix blending with 2 nitrox sticks (English) |publisher=The shadowdweller |year=2006 |access-date=2008-08-28 |archive-date=2008-09-19 |archive-url=https://web.archive.org/web/20080919162121/http://shadowdweller.skynetblogs.be/post/3924720/continuous-trimix-blending-with-2-nitrox-stic |url-status=dead }}</ref>

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<ref name="TDISDI 2002">{{Cite book | title=Extended Range Diving & Trimix | year=2002 | publisher=Technical Diving International |page=65 | quote=In addition, to reduce the on-gassing of the diluents (helium and nitrogen) a similar technique to Nitrox has developed, termed 'hyperoxic trimix or 'high oxygen trimix and abbreviated HOTx in at least one form.}}</ref>

<ref name="TDISDI manual">{{cite book|publisher=Technical Diving International |title=Advanced Gas Blender manual}}</ref>

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<ref name="Warwick2015">{{cite journal |author=Warwick, Sam |title=100 years submerged |journal=DIVER |date=May 2015 |url=http://www.divernet.com/wrecks/p303453-100-years-submerged.html |access-date=2015-12-29 |archive-date=2018-01-30 |archive-url=https://web.archive.org/web/20180130013912/http://www.divernet.com/wrecks/p303453-100-years-submerged.html |url-status=live }}</ref>

}}

{{Underwater diving|divequ}}

{{DEFAULTSORT:Trimix (Breathing Gas)}}
[[Category:Breathing gases]]
[[Category:Helium]]
[[Category:Underwater diving safety equipment]]