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Plasma torch cutting steel. View of steel being cut by a plasma torch (upper centre). The path cut by the torch is visible as the track at upper left. Sparks are seen falling from the metal being cut. Plasma torches have a temperature of around 8000 degrees Celsius, which rapidly cuts through steel. They use an electric arc to heat gas in their nozzle, which is then forced out as a stream of hot plasma. Plasma is a high energy state of matter in which a gas' atoms are separated into positive ions and free electrons. (KEYSTONE/SCIENCE PHOTO LIBRARY/KLAUS GULDBRANDSEN)