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Trimix is a breathing gas mixture of oxygen , nitrogen and helium that is used in technical diving to reach great depths. The addition of helium in the breathing gas, the O 2 and N - 2 - partial pressure adjusted to acceptable levels. The helium itself has practically no interaction with the human body, as it is very inert as a noble gas. The negative effects of oxygen and nitrogen ( nitrogen anesthesia , oxygen poisoning of the CNS ) and the risk of decompression sickness are thereby reduced. Generally, the term is used when the percentage of oxygen is 21% or less. If the oxygen content is> 21%, the mixture is called Triox .

By adding helium, oxygen / nitrogen anesthesia is largely suppressed so that diving depths below the usual recreational diver limit of 40 meters can be reached. Another advantage is the significantly lower density of the gas mixture compared to air. This results in less work of breathing by the regulator and a reduction in the risk of hypercapnia . As a negative side effect, the High Pressure Nervous Syndrome (HPNS) can occur, which is caused by helium at depths of around 130 meters in connection with high rates of descent.

Tests by the magazine diving (November 2009 issue) have shown that when using Trimix, the temperature in the first stage of the regulator can be up to approx. 25 ° C higher than when using compressed air. This could reduce the risk of the pressure reducer and the regulators icing up, which causes a malfunction of the aforementioned parts, often in the form of an uncontrolled escape of breathing gas.

Designation and examples

Trimix mixtures are named after the proportions of oxygen and helium. The name of the mixture is formed as follows: Tx oxygen content / helium content . For example, a mixture with the designation Tx21 / 35 contains 21% O 2 and 35% He. The remainder of 44% is nitrogen.

Common trimix mixtures

depth mixture
0-45 m Tx21 / 35
0-60 m Tx18 / 45
1-75 m Tx15 / 55
6–90 m Tx12 / 65
9-120 m Tx10 / 70

The mixtures listed have in common that the partial pressure of oxygen at the target depth does not exceed 1.3 bar. The equivalent narcotic depth (END) is shallower than 30 m. In the case of mixtures with an oxygen content below 18%, it should be noted that they cannot be breathed on the surface without the risk of hypoxia .

Special cases and alternatives


When one speaks of trimix, one means a free ratio of the proportions of helium, oxygen and nitrogen to one another. A special case is the so-called heliair , in which a proportion of helium is added to the breathing air. The advantage is the significantly simplified and therefore inexpensive production. The disadvantage here is that the partial pressure of oxygen in the finished mixture drops. Thereby it is u. U. can no longer be used for diving from the water surface if the partial pressure of the oxygen P O 2 is below 0.16 bar.

Professional divers and greater depths

Greater diving depths can also be achieved with mixtures such as Hydrox , which consists of hydrogen (lat. Hydrogenium ) and oxygen, as well as Hydreliox - hydrogen, helium and oxygen. With Hydreliox, divers could be exposed to a pressure that corresponded to a diving depth of approx. 700 m. Because of the complex compression and decompression phases, this "dive" lasted more than 40 days.

Individual evidence

  1. ^ WL Hunger Jr, PB Bennett .: The causes, mechanisms and prevention of the high pressure nervous syndrome . In: Undersea Biomed. Res. . 1, No. 1, 1974, ISSN  0093-5387 , pp. 1-28. PMID 4619860 . Retrieved August 28, 2008.
  2. Bennett, PB, Coggin, R.; M. McLeod .: Effect of compression rate on use of trimix to ameliorate HPNS in man to 686 m (2250 ft) . In: Undersea Biomed. Res. . 9, No. 4, 1982, ISSN  0093-5387 , pp. 335-51. PMID 7168098 . Retrieved April 7, 2008.
  3. Campbell, E: High Pressure Nervous Syndrome . Diving Medicine Online. Retrieved August 28, 2008.
  4. Jochen Steinbrenner: The world of trimix - from helium in the body to the oxygen window ( Memento of the original from April 24, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 1.7 MB). cmas .ch. Retrieved September 19, 2013. @1@ 2Template: Webachiv / IABot /
  5. Lafay V, Barthelemy P, Comet B, Frances Y, Jammes Y: ECG changes during the experimental human dive HYDRA 10 (71 atm / 7,200 kPa) . In: Undersea Hyperb Med . 22, No. 1, March 1995, pp. 51-60. PMID 7742710 . Retrieved September 15, 2008.