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AGA CW Handbook A4_32130-UK
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8 purpose of
shielding
gas. 2.3 ozone
– good and bad ozone is a gas appearing naturally in the atmosphere. most of it is loca- ted in the stratosphere, around 25 kilometres above the surface of the earth. this ozone layer is vital to us, filtering the uv radiation of the sun and thus forming a protective shield for life on earth. the depletion of the ozone layer is considered to be the cause of skin cancer becoming more common, a trend which has been established. ozone nearer to the ground has become familiar in certain regions due to often repeated ozone warnings. in large urban areas, large amounts of ozone are generated due to the combined effect of the hydrocarbon and nitrogen dioxide emissions and sunlight. people exposed to ozone experience general symptoms such as a bur- ning sensation in the throat, dry mucous membranes, cough, headach- es, chest pains and breathing difficulties. these are the same symptoms that are detected during welding. for persons suffering from asthma, high ozone levels may be fatal. there is currently no solid data on the long-term effects of high ozone levels, but there are clear signs indica- ting that ozone may cause chronic bronchitis and pulmonary oedemas. 2.4 the mison
® shielding gas programme in 1976, aga was granted a patent for a method reducing the amount of ozone generated during gas arc welding with the help of shielding gas. a revolutionary new shielding gas was brought into the market – mison ® . it had been detected that a small amount of nitrogen mono- xide (no) reacts easily with ozone, forming oxygen (o 2 ) and nitrogen dioxide (no 2 ). the ozone levels in the combustion gases are reduced, resulting in a better work environment for the welder. mison ® is an entire family of shielding gases, including the right shielding gas for all welding applications. for as long as two decades we have received uniform information from the users of the beneficial effects that mison ® shielding gases have on the work environment, and therefore on productivity and quality.the following chapters include more information on mison ® shielding gases. 2.5 science in the background the research performed on the ozone layer in the 1970s (which led to three researchers being awarded with the nobel prize in chemistry in 1995) was the starting point for the development of the mison ® gases. this research showed that nitrogen monoxide (no) is one of the sub- stances easily reacting with ozone. based on the research, aga’s team of researchers began investigating how this phenomenon could be utilised in shielding gases. as a result, aga’s mison ® shielding gases were invented. aga’s founder, gustaf dalén, has received a nobel prize himself in 1912.
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