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In 1812 the progenitor of today's flood and sprinkler systems was designed and installed by William Congreve at the Theatre Royal in Drury Lane in the United Kingdom. A water supply fed a network of perforated pipes. These systems (which soon spread to textile factories) needed to be activated manually and acted on the entire area to be protected. Even now, today's flood and water spray systems use water in large quantities and, unlike sprinklers, act simultaneously across the entire protected space. Unlike the Congreve system which exploited gravity and perforated pipes, today, thanks to the force of pumps and control of the delivery through appropriate nozzles, these systems can switch off or contain a fire until the arrival of emergency teams, but also prevent it from spreading, cooling the surrounding environment. They are in fact used where the propagation speed of a fire can be high and where highly effective intervention is required from the very first stages. In particular, the cooling action is particularly effective in safeguarding the resistance of the structures, especially if they are metallic (typically they are used to cool tanks which, if overheated can generate the phenomenon of BLEVE - boiling liquid expanding vapour explosion due to softening of the structural components).

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Flood systems: the reference legislation

The reference standard for this type of solution is the US NFPA 15 - standard water spray fixed system and fire protection and the European technical specification TS 14816.

How a flood system works

The operation of a flood system is theoretically very simple; a network of empty pipes feeds multiple open nozzles constructed in such a way as to distribute a rain of water over the entire protected surface. Depending on the nozzles chosen, the water flow can be spread evenly with rain or can be directed (in this case it involves water spray systems) - through appropriate deflectors - with a particular shape and speed to obtain an effective range to strike particular points of the protected area. For the protection of oil storage, nozzles can be used at high speed or with an “emulsifying” effect, in which the size of the drops, their ability to penetrate the flames and the shape of the jet allow the water to strike the oil that is still not burning, creating an oil-water emulsion that removes available fuel from the fire. As is evident also from this example, it is not enough to simply know how to properly manage the hydraulic aspect. Like any fire extinguishing system, an effective design takes into account the performance of the system during the extinguishing phase and for the entire duration of the event; it is in fact a type of system that may have to operate for relatively long periods, during which different flammable materials may be involved and the structural stability conditions can vary dramatically and where the suffocating and cooling capacity of the extinguishing system must be maintained (in this regard, an essential variable is the ability to maintain the extinguishing efficiency, economising the use of extinguishing agents). Being designed to deal with fires of highly flammable materials that are generally stored outdoors, the system must have technical characteristics that are capable of compensating for environmental variables such as wind, diluting and dispersing flammable vapours. The network is fed by a push unit which is activated by a fire detection system (which can be electronic or via a sprinkler system which activates, triggering the flood valves through a hydraulic system).

Flood system: the importance of quality maintenance

As the pipes of a flood system are subject to wetting and periodic drying, they may undergo significant corrosion.

For these types of system, the quality of the materials and of the workmanship as well as the maintenance becomes particularly important.

Water-foam flood systems

A variant of the flood systems includes a device capable of mixing concentrated foam with water to produce foam in the initial phase, to obtain a smothering effect of the flames and then, with water alone, to continue cooling, while the bed of foam that has formed on the ground hinders the spread and resumption of flames.

There are also flood systems that maintain the ability to dispense foam for the entire period of operation of the system. These latter two systems are regulated by the standards NFPA 11 - standard for low expansion foam system and NFPA 16 standard for installation of foam-water sprinkler and foam water spray system - and for foaming liquids the European standards EN 1568

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