Automatic fire extinguishing systems are created for fire elimination when use of primary means of elimination of source of ignition is not possible or the personnel are present at the room not round the clock. Features of each system depend on type of ognetusheniye, fire danger of controlled object and the equipment used on it.
Water systems
The sprinkler (water) fire extinguishing system is the most widespread today. Its action is based on water supply under pressure from special raspryskivatel – sprinklers which are connected to the autonomous system of supply. At the moment it is the most inexpensive system available both for large commercial buildings, and for small rooms. For the first time it has been used in 1812 in Great Britain and developed by William Kongriv. The device was supplied from the tank which had the volume of 95000 liters. Sprinklers were used for fire extinguishing in textile workshops across all New England. The first systems capable to be started at ignition have appeared only in the 60th years of the 19th century.
The sprinkler system has 6 versions which are chosen depending on room type: damp, dry, zatopitelny, preliminary action, foam and sprinklers of water fog. Damp systems are used most often and are the most reliable because have the simple device and work completely automatically – at emergence of signs of ignition pressure through pipes moves and fire extinguishing begins. Dry sprinklers are established in places where damp cannot be used because of the probability of freezing of water in pipes because of the absent heating – in parking garages or not heated buildings. In such systems the water supply is carried out only after emergence of the centers of ignition.
Other types of water systems are used rather less often. Zatopitelny systems are connected directly to water supply and water in large volumes is pumped through all open sprinklers of large diameter. Of preliminary action are used by Raspryskivateli in places where accidental activation of fire extinguishing is extremely undesirable – in the museums, data centers and other rooms where water can seriously damage the equipment. This type uses recorders of temperature or smoke which have to work before water supply begins. After that the automatic sprinkler is started and the water supply system opens. Foam sprinkler systems together with water give foam concentrate for more effective fire extinguishing. Such method is used in rooms where there are flammable liquids and also in hangars of the airports. The systems of water fog are applied to cooling of the room and reduction of temperature of flame at the fire that slows down spread of fire.
It is worth carrying big costs of water at fire extinguishing to shortcomings of sprinkler system. Moreover, water is capable to cause extensive damage to finishing of the building. Especially it is unjustified at small ignitions.
Powder system
The majority of office and public buildings and also technical and warehouse, are equipped with automatic powder systems. Suppression of ignition happens through giving of the powder structure which is slowing down spread of fire. This method is very effective and is one of the fastest at fire extinguishing. The used powder is non-toxic and consists of the inorganic salts mixed with water-repellent agents. They are most effective at ignitions of liquid or gas substances. In comparison with water fire extinguishing systems, powder will not do harm to the equipment and rooms, will be to make cleaning only enough. It is worth carrying limited period of validity of powder and need of constant service to shortcomings of this method. It is forbidden to use powder suppression on objects where large number of people and in rooms which cannot be left quickly prior to suppression works. Also powder systems are not used along with the systems of removal of smoke and ventilation.
The choice of suitable system is used depending on room type. For example, it is necessary to refuse use of sprinkler methods of fire extinguishing if indoors there is electrotechnical equipment.
Gas system
Mounting of gas-fired plants is made for detection of the centers of ignition and supply of fire extinguishing nonflammable gas. These systems allow to keep the equipment indoors, and consequences of their use are eliminated by means of simple airing. The gas method is suitable for safe fire extinguishing in rooms where it is used the devices working under voltage. The system, as a rule, consists of containers with gas, detectors of fire, sensors of detection of the fire and the spray. Use of gas in elimination of the center of ignition is used for reduction of temperature of flame, oxygen isolation indoors and prevention of increase in the fire area. Refer their danger to shortcomings of similar systems. At suppression in the similar way the risk appears to choke indoors therefore immediate evacuation is necessary. When cleaning object after elimination of ignition the risk of poisoning with evaporations increases. Moreover, gas increases pressure indoors and is capable to cause damage of windows and walls from gypsum cardboard, and therefore it is necessary to take previously additional safety precautions when mounting gas-fired plants.