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A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas, but other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed habitats. Oxygen is the essential component for any breathing gas. Breathing gases for hyperbaric use have been developed to improve on the performance of ordinary air by reducing the risk of decompression sickness, reducing the duration of decompression, reducing nitrogen narcosis or allowing safer deep diving. Description A breathing gas is a mixture of gaseous chemical elements and compounds used for respiration. Air is the most common and only natural breathing gas. Other mixtures of gases, or pure oxygen, are also used in breathing equipment and enclosed habitats such as scuba equipment, surface supplied diving equipment, recompression chambers, high-altitude mountaineering, high-flying aircraft, submarines, space suits, spacecraft, medical life support and first aid equipment, and anaesthetic machines. Contents Oxygen is the essential component for any breathing gas, at a partial pressure of between roughly 0.16 and 1.60 bar at the ambient pressure, occasionally lower for high altitude mountaineering, or higher for hyperbaric oxygen treatment. The oxygen is usually the only metabolically active component unless the gas is an anaesthetic mixture. Some of the oxygen in the breathing gas is consumed by the metabolic processes, and the inert components are unchanged, and serve mainly to dilute the oxygen to an appropriate concentration, and are therefore also known as diluent gases. Most breathing gases therefore are a mixture of oxygen and one or more metabolically inert gases. Breathing gases for hyperbaric use have been developed to improve on the performance of ordinary air by reducing the risk of decompression sickness, reducing the duration of decompression, reducing nitrogen narcosis or allowing safer deep diving. The techniques used to fill diving cylinders with gases other than air are called gas blending. Breathing gases for use at ambient pressures below normal atmospheric pressure are usually pure oxygen or air enriched with oxygen to provide sufficient oxygen to maintain life and consciousness, or to allow higher levels of exertion than would be possible using air. It is common to provide the additional oxygen as a pure gas added to the breathing air at inhalation, or though a life-support system. For diving and other hyperbaric use A safe breathing gas for hyperbaric use has four essential features: It must contain sufficient oxygen to support life, consciousness and work rate of the breather. It must not contain harmful contaminants. Carbon monoxide and carbon dioxide are common poisons which may contaminate breathing gases. There are many other possibilities. It must not become toxic when being breathed at high pressure such as when underwater. Oxygen and nitrogen are examples of gases that become toxic under pressure. It must not be too dense to breathe. Work of breathing increases with density and viscosity. Maximum ventilation drops by about 50% when density is equivalent to air at 30 msw, and carbon dioxide levels rise unacceptably for moderate exercise with a gas density exceeding 6 g/litre. Breathing gas density of 10 g/litre or more may cause runaway hypercapnia even at very low work levels, with potentially fatal effects. These common diving breathing gases are used: Air is a mixture of 21% oxygen, 78% nitrogen, and approximately 1% other trace gases, primarily argon; to simplify calculations this last 1% is usually treated as if it were nitrogen. Being freely available and simple to use, it is the most common diving gas. As its nitrogen component causes nitrogen narcosis, it is considered to have a safe depth limit of about 40 metres (130 feet) for most divers, although the maximum operating depth (MOD) of air taking an allowable oxygen partial pressure of 1,6 bar is 66.2 metres (217 feet). Breathing air is air meeting specified standards for contaminants. Pure oxygen is mainly used to speed the shallow decompression stops at the end of a military, commercial, or technical dive. Risk of acute oxygen toxicity increases rapidly at pressures greater than 6 metres sea water. It was much used in frogmen's rebreathers, and is still used by attack swimmers. Nitrox is a mixture of oxygen and air, and generally refers to mixtures which are more than 21% oxygen. It can be used as a tool to accelerate in-water decompression stops or to decrease the risk of decompression sickness and thus prolong a dive (a common misconception is that the diver can go deeper, this is not true owing to a shallower maximum operating depth than on conventional air). Trimix is a mixture of oxygen, nitrogen and helium and is often used at depth in technical diving and commercial diving instead of air to reduce nitrogen narcosis and to avoid the dangers of oxygen toxicity. Heliox is a mixture of oxygen and helium and is often used in the deep phase of a commercial deep dive to eliminate nitrogen narcosis. Heliox is the standard mixture type for deep offshore saturation diving. Heliair is a form of trimix that is easily blended from helium and air without using pure oxygen. It always has a 21:79 ratio of oxygen to nitrogen; the balance of the mix is helium. Hydreliox is a mixture of oxygen, helium, and hydrogen and is used for dives below 130 metres in commercial diving. Hydrox, a gas mixture of hydrogen and oxygen, is used as a breathing gas in very deep diving. Neox (also called neonox) is a mixture of oxygen and neon sometimes employed in deep commercial diving. It is rarely used due to its cost. Also, DCS symptoms produced by neon ("neox bends") have a poor reputation, being widely reported to be more severe than those produced by an exactly equivalent dive-table and mix with helium. Breathing air Breathing air is atmospheric air with a standard of purity suitable for human breathing in the specified application. For hyperbaric use, the partial pressure of contaminants is increased in proportion to the absolute pressure, and must be limited to a safe composition for the depth or pressure range in which it is to be used. Classification by oxygen fraction Breathing gases for diving are classified by oxygen fraction. The boundaries set by authorities may differ slightly, as the effects vary gradually with concentration and between people, and are not accurately predictable. Normoxic where the oxygen content does not differ greatly from that of air and allows continuous safe use at atmospheric pressure. Hyperoxic, or oxygen enriched where the oxygen content exceeds atmospheric levels, generally to a level where there is some measurable physiological effect over long term use, and sometimes requiring special procedures for handling due to increased fire hazard. The associated risks are oxygen toxicity at depth and fire, parti.... Discover the Ian Peate Muralitharan Nair popular books. Find the top 100 most popular Ian Peate Muralitharan Nair books.