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Encyclopedia > Trimix

Trimix is a breathing gas, consisting of oxygen, helium and nitrogen, and is often used in deep commercial diving and during the deep phase of dives carried out using Technical diving techniques. Air is the most common and only natural breathing gas. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Standard atomic weight 4. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... It has been suggested that this article or section be merged with Underwater diving. ... Technical diving is a form of SCUBA diving that exceeds the scope of recreational diving. ...

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 and other physiological effects of the gas at depth. Lowering the oxygen content increases the depth and duration of the dive before which oxygen toxicity becomes a limiting factor. Also, the nitrogen in trimix can prevent High Pressure Nervous Syndrome, a problem when breathing heliox at depths below 130 meters (429 feet). Nitrogen narcosis or inert gas narcosis is a reversible alteration in consciousness producing a state similar to alcohol intoxication in scuba divers at depth. ... Oxygen toxicity or oxygen toxicity syndrome is severe hyperoxia caused by breathing oxygen at elevated partial pressures. ... HPNS, High Pressure Nervous Syndrome or Helium Tremors is a diving disorder caused by using breathing gases that contain helium at depths in excess of 130 metres / 429 feet. ... Heliox is a gas that is composed of a mixture of helium (He) and oxygen (O2). ...

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 and comfortable equivalent air depth for the planned dive. Safe limits for mix of gases in trimix are generally accepted to be a maximum partial pressure of oxygen (ppO2 - see Dalton's law) of 1.0-1.4 bar and maximum equivalent air depth of 30 to 40 meters (100 to 130 feet). At 100 meters (330 feet), "10/70" has a PPO2 of 1.1 bar and an equivalent air depth of 18 meters (60 feet). In technical diving, the maximum operating depth (MOD) of a breathing gas is the depth at which the partial pressure of oxygen (ppO2) of the gas mix exceeds a safe limit. ... In technical diving, the equivalent air depth (EAD) is a way of expressing the narcotic effect of breathing gases such as trimix and heliox. ... 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. ... In chemistry and physics, Daltons law (also called Daltons law of partial pressures) states that the total pressure exerted by a gaseous mixture is equal to the sum of the partial pressures of each individual component in a gas mixture. ...

In open-circuit scuba, two classes of trimix are commonly used: "normoxic" trimix - with a minimum PO2 at the surface of 0.18. A Normoxic mix, such as "19/30", is used in the 30 meters (100 feet) to 60 meters (200 feet) depth range and: "hypoxic" trimix - with a PO2 less than 0.18 at the surface. 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 rebreathers that use trimix diluents, the mix will be "hyperoxic" in shallow water because the rebreather automatically adds oxygen to maintain a specific ppO2. See breathing gas for more information on the composition and choice of gas blends. SCUBA is an acronym for Self-Contained Underwater Breathing Apparatus. ... A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycles exhaled gas. ... Air is the most common and only natural breathing gas. ...

Gas blending of trimix involves 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. A second method called ' continuous blending' is now gaining favour. 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). Air, oxygen and helium gas blending system Gas blending or gas mixing is the filling of diving cylinders with non-air breathing gases. ... 12 litre and 3 litre steel diving cylinders A diving cylinder or SCUBA tank is used to store and transport high pressure breathing gas as a component of an Aqua-Lung. ... Look up air in Wiktionary, the free dictionary. ... A Diving Air Compressor is a gas compressor, which can fill diving cylinders with high pressure air that is pure enough to be used as a breathing gas. ... The use of water pressure - the Captain Cook Memorial Jet in Lake Burley Griffin in Canberra, Australia. ...

  Results from FactBites:
trimiX.net: What Is Trimix (886 words)
Trimix is a combination of oxygen, helium and nitrogen.
Trimix is frequently promoted as the holy grail of scuba diving, so horrifyingly complex that you must take 4-8 levels of training before you can use it.
But it is possible to create a normoxic tank of trimix and treat it similar to air, without multiple mixes, bottles and other complexities, and enjoy the benefits of helium.
trimix-diver (263 words)
The IANTD Trimix Diver programme is designed for those divers who are already involved in deep diving activities.
Trimix affords a safer means for deep water exploration for divers who need to perform with a clear head at depth.
In order to participate on the course students must be Technical or Normoxic Trimix divers and provide proof of at least 200 logged dives of which at least 25 were to depths between 39 and 60 metres.
  More results at FactBites »



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