Heliox

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Heliox is a mixed gas made from helium and oxygen . It is used as breathing gas in technical diving and is used in emergency care and the treatment of respiratory diseases . Heliox was first used in 1939 in rescuing survivors from the crashed submarine USS Squalus from a depth of around 82 meters.

Use in technical diving

composition

For breathing gases with a helium content, technical helium with a purity of 4.6 or 5.0 according to DIN EN ISO 14175 (nominal foreign gas content 10 −4.6 or 10 −5.0 , corresponds to a purity of 99.997% or 99.999%, respectively) should be used for Application of the tolerances permitted by the standard, minimum purity of 99.996% or 99.999%). Helium of higher purity can of course also be used, but is significantly more expensive and is not available to recreational divers at most dive sites. The use of helium offered as an industrial gas in breathing gas is extremely risky in terms of health, since significantly higher proportions of foreign gas can be present here and there is also no specification of the permissible foreign gases.

For diving with different fixed mixing ratios in several bottles, Heliox is often offered in the following typical compositions for the various diving sections (specification of oxygen content, remainder helium):

  • 21% oxygen (first phase descent and decompression stops, maximum diving depth 50 m)
  • 12% oxygen (diving depths from 10 m to 100 m)
  • 8.5% oxygen (diving depths from 20 m to 150 m)

If a suitable mixing device is available, the mixing ratios can also be individually adapted for the different phases of the planned dive. The partial pressure of the oxygen should never fall below 0.18 bar ( risk of suffocation from 0.16 bar) in the corresponding depth ranges , and never exceed 1.4 bar (oxygen poisoning from around 1.6 bar). Since oxygen partial pressures below 1.6 bar can also have a toxic effect after prolonged exposure, an oxygen clock or O 2 clock (also CNS O 2  % ) must be used and observed, which significantly shortens the possible stay at greater depths.

If helium is used as an admixture gas in a rebreather , the breathing gas of the diver is also heliox. Since the mixing ratio is constantly adjusted by a regulator, mostly to a preset partial pressure of the oxygen, one can dive into great depths with a single device without manual adjustments. In addition, the consumption of the relatively expensive technical (pure) helium is many times lower, since the exhaled gas remains in the device's circuit instead of being released into the water.

advantages

  • No deep intoxication with narcotic effects as it does not contain nitrogen .
  • Greater depths - theoretically up to 600 m - possible.

disadvantage

  • Helium causes the High Pressure Nervous Syndrome ( helium tremors )
  • The high thermal conductivity of helium of 0.1513 W / (m · K) leads to the cooling of the lungs. The gas has to be artificially heated.
  • Moderate breathing resistance at great depths due to the high density of the air in the depths. This effect becomes even stronger with every other inert gas
  • High price: Helium 4.6 and Helium 5.0 are available in containers of 50 liters or more for around € 1.20 per liter (200 bar). Recreational divers usually have to pay a multiple of this amount due to additional costs for logistics, storage, filling in diving bottles and possibly mixing on site at the dive sites. Especially when diving with open systems, due to the high consumption and the additional need for mixing devices for filling different bottles for different depths of the dive, the breathing gas makes up by far the largest part of the costs per dive. When used in rebreathers, the cost share is significantly lower due to the far lower consumption and the elimination of the need for mixing devices.
  • Availability: At many dive sites where recreational divers are offered technical diving, only the more common trimix is ​​available in various mixing ratios, or mixing devices for helium are missing. The presence of mixing devices is not necessary for rebreather because the mixing takes place in the diving device.

Alternatives

Trimix can be mentioned as an alternative to Heliox , which contains oxygen and helium in variable amounts of 20-44% nitrogen . Hydrox is an alternative breathing gas mixture, which consists of hydrogen ( Hydrogenium ) and oxygen ( Oxygenium ) and allows depths of up to about 700 m.

Individual evidence

  1. ↑ Diving timetable. (PDF file; 8.18 MB) at divetable.de, p. 93.
  2. ^ Emergency Medicine Journal : Heliox for asthma in the emergency department: a review of the literature
  3. ↑ Ariane Stürmer: Rescue from icy depths. Article in Spiegel Online from May 22, 2009.
  4. ↑ See e.g. B. Product description of Helium 4.6 at Linde
  5. ↑ The oxygen clock describes in a table the relationship between the partial pressure of oxygen, the diving time and the toxicity on the central nervous system .
    see: Hessischer Tauchsportverband (HTSV): Nitrox training ( Memento from January 11, 2012 in the Internet Archive ) - Oxygen clock according to NOAA (PDF)
  6. ^ Text book ANDI TMX Diver
  7. ↑ Webelements.com: Helium .
  8. ↑ Price example helium from the University of Hohenheim price list ( memento of the original from July 14, 2014 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.uni-hohenheim.de
  9. ↑ 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.