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Gas
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Properties and effects on humans
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CO2
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Carbon dioxide
Colourless, odourless gas. Dangerous because it may displace oxygen in topography depressions, leading to anoxia of people in the viscinity. Carbon dioxide release from a volcanic area has resulted in many deaths. |
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SO2
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Sulphur dioxide
Colourless gas with pungent odour. Concentration of 6-12 ppm causes immediate irritation of nose and throat. People with asthma and other respiritary diseases can be severely affected by sulphur dioxide emissions. |
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H2S
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Hydrogen sulphide
Colourless, flammable gas with pungent smell of rotten eggs. Exposure to 20-150 ppm causes eye irritation. Exposure to 1000-2000 ppm causes coma after a single breath. Hydrogen sulphide has been responsible for at least 10 separate fatal volcanic events in 20th century. |
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H2O
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Water vapour is the main vapour emitted at volcanoes. It produces the characterisitc white plumes seen at active craters and fumaroles. |
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HCl
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Hydrochloric acid
Colourless gas with an irritating, pungent odour. Detectible at 1-5 ppm. The vapour irritates the eyes severely, and may burn the skin. Concentrations of 35 ppm cause throat irritation after a brief exposure. |
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He
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Helium
Helium is a noble gas, which forms from radioactive decay of uranium and thorium in the earth's crust. The 3He/ 4He ratio is a good measure of the degree to which mantle gases contribute to volcanic gas discharges. Helium can be collected as a flank soil emission. Hotspots such as Hawaii have a large 3He/ 4He ratio, and are tap pristine, ungassed parts of the mantle. |
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Rn
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Radon
Radon is a colourless, odourless, radioactive gas formed by radioactive decay of unraium. Chronic exposure has been linked to respiritary disorders. Radon has a half-life of 3.82 days, and can be used to determine faults and fractures on a volcano, when derived from shallow sources. |
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H2SO4
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Sulphuric acid
Sulphuric acid is a colourless, viscous liquid, which reacts vigorously with water. The acid irritates eyes and burns skin. |
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HF
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Hydrofluoric acid
Hydrofluoric acid is a colourless, fuming liquid, with a pungent smell. Irritation of eyes and nose occurs at 5 ppm. Concentrations of 50-250 ppm are dangerous for even a brief exposure. The 1785 eruption of Laki fissure in Iceland released hydrogen fluoride into the environment, destroying pastures, and a famine resulted which killed 10,521 people. |