FIRE PREVENTION SYSTEMS
According to the UNI standards the fire extinguishing system is set of technical elements of the building system with the function of preventing, eliminating, limiting or reporting of the multiplicity of possible types for this system, which can be distinguished in the following fundamental categories: of signaling systems and plants for extinguishing the fire. Fire prevention system may be mandatory by law, in relation to the intended use and the dimensional and functional characteristics of the building. Fire detection is carried out by means of sensors able to signal the presence of smoke or sources of heat, while for shutdown, hydrants, spears, rotating reels and mobile extinguishers are set up and properly distributed.
More rarely, a pressurized hydraulic network can be inserted, automatically operating, controlled by the fire detection system and equipped with diffusion nozzles (sprinkler network); in rooms where the use of liquids, or foams, would be harmful for the equipment present, it is usually necessary to use halon gas automatic shutdown systems; this is what happens for example in data processing centers, filenet archives, inverter room. The fire extinguishing system, in the case of a residential building, is required when the building exceeds 24 meters in height. The plant is schematically constituted by: water supply network in galvanized iron; fire mouths in a containment box with incorporated hydrant and related equipment (flexible fire hoses and water lances);attack groups for the fire brigade vehicles. The water supply network, consisting of a system of pipes generally buried, provides water to each part of the building to be protected by supplying the various fire-fighting utilities (hydrants, water supply systems, foam systems, etc.) .The correct design must guarantee the following characteristics: independence from every other water network; provision of shut-off valves that allow the sectioning of the network during interventions (maintenance modification, expansion) on the network itself; continuous feeding in network pressure obtainable through a raised tank or through pumps with automatic operation; endowment of a water tank of adequate capacity for the size of the network; presence of at least two pumps for water supply driven by motors with different power supply (electric motor, internal combustion engine);
structure of the ring network to allow the hydrants to be fed from several origins and to contain pressure drops.
Project criteria in relation to the class of risk
The intern web of building for the feeding of the hydrants it is subject to compliance with the following main minimum requirements: in each staircase of the building, in correspondence of each floor must be installed a fireproof mouth from UNI45; the fire mouth be derived with a 1 ½ pipe from a pipe of at least 55 cm by 35 cm; each enclosure must contain at least 15 m of house and its lance, its length must however be such as to reach with the lace each point of the flats of the floor; the water supply system must be made of galvai8nzed iron protect against freezing, distinct from and independent of health service; the water supply system must be constantly under pressure; the water supply system must be provided with the connection for connection to fire brigade’s fir engines, to be installed in the entrance hall on the ground floor I a very visible and comfortable position for the connection of the fire truck pipe (each attack it can not serve more than two scales). The minimum water flow must be such as to guarantee a flow rate of at least 120 liters per minute at pressure of 2 atmospheres to the highest fire pit of each ladder. The rooms use for car packing regardless of the number of floors, must be equipped with UNI 45 vents, arranged so that each lance can cover a minimum radius of 5 meters ( if the building does not have a fire extinguishing system, in as it does not exceed 24 m in height, these mouths can be connected to the water network. In the case of industrial buildings warehouses, depots, garages, workshops, as well as cinemas, theaters and other places with high crowding. Automatic shutdown systems are installed ( according to the Italian Concordat Fire Rules and to the request of the local Fire Fighting Command) These can be classified into two main type: automatic rain systems (sprinkles) and fractional water systems ( of which widespread type, apart from some special applications, is deluge type). The sprinkle system is characterize by delivery nozzles (sprinklers) equipped with a fuse set for a limit temperature (about 70°C). The system may be of the wet type, that is, wit addiction pipes containing water constantly kept under pressure or of the dry type, when, in order to avoid frosts, the pipes contain pressure. In the event of a fire, the fuse determines the direct flow of water ( in the case of “wet” plant) or of the water (in the case of a “dry” plant), which is quickly depleted and determines, as a consequence, the escape of water. The deluge system (to protect class of serious risks) consists of a normally empty network with nozzles that are always open. A system equipped with smoke or temperatures sensing sensors controls a motorized valve which, when opened, causes water to escape from the nozzles. A variant of this system includes normally closed nozzles and air in the circuit: the water leaks, even when the valve is open, only occurs at the nozzles, opened by sensitive local smoke or temperature sensors (system used when an accidental flooding could serious damage).
