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Chemically Active Fire – Suppressed
A general approach to fire control has been developed involving use of flame inhibitors. Unlike older fire-extinguishing materials such as water and carbon dioxide, these agents operate indirectly: they interfere with those reactions within a flame that lead to sustained release of heat. As a result, temperature falls below ignition temperature. Chemical flame inhibitors offer one of the greatest hopes for better control of fires of all sizes. Chemical extinguishants are of two types: liquid (or liquefied gas) and dry powder. Liquid chemical extinguishants. The most effective liquids are the halogenated hydrocarbons such as chlorobromomethane and bromotrifluoromerthane (better known as Halon 1301) which are colourless, odourles, and electrically nonconductive. Automatic Halon 1301 extinguishing systems are ideally suited to situations in which damage of equipment or furnishing by water or dry chemicals would cause irreparable harm. It is used in automatic fire protection systems by insurance companies, banks, universities, and other organizations to protect equipment, electrical wiring and libraries. Tests with Halon 1301 have been successful in hyperbaric (pressurized) atmospheres as well. The atmospheres in hyperbaric chambers are oxygen-rich. Materials that are fire-resistant in normal air, burn enthusiastically in such oxygen- rich environments, but can be extinguished by Halon 1301 if they can be detected intime. Dry-powder chemical extinguishants. Ammonium dihydrogen phosphate is the most useful of this type and is rated for class А, В and С fires. Other dry-powder inhibitors are salts of alkali metals (which include lithium, sodium, potassium, rubidium and cesium). Dry chemicals can be effective even when they are applied as a fog in water solutions. Water. Water is still the prime suppressant because of its great cooling power, general availability and low cost. However, application in a solid stream is regarded as damaging to the components and contents of structures. Foams. Foams are also widely used. Protein-type, low-expansion foams, particularly useful in quenching burning volatile petroleum products, are used in crash-rescue operations. High -expansion foams are available for fire suppression in enclosed areas. Some foams of this type are generated at a rate of 424,8 m3/min. They contain sufficient air to allow a human to breathe inside of them. Light water. A film-forming solution of a specific fluorocarbon surfactant inwater, known as light water, was developed by the U. S. Navy for use with dry chemicals to fight aircraft crash fires. It may be used either as a liquid or as a low-expansion foam to interfere with the release of flammable vapours from the burning fuel. Light water is also useful in extinguishing petroleum storage tank fires and may find application to urban fires.
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