Fire extinguishers – Processes – Of extinguishing fire
Patent
1996-05-20
1997-11-11
Pike, Andrew C.
Fire extinguishers
Processes
Of extinguishing fire
169 5, 169 16, 169 70, 239488, A62C 3568
Patent
active
056853769
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a method and a system for extinguishing fires in confined spaces, such as engine rooms, of ships, distribution substations, hotel rooms or open oil tanks. The invention relates to a fire extinguishing system comprising general nozzles disposed above and/or on the sides of the space to be protected for bringing about general fire extinguishment in the space, and/or spot nozzles disposed around objects in the space to be protected which are susceptible to fire, such as engines, feed pipe systems for fuel, or open oil tanks, for extinguishing fires in them. The fire extinguishing system thus corresponds to a so-called sprinkler system. The invention also relates to a fog spray nozzle which is suited for use in the fire extinguishing system.
Conventional sprinkler fire extinguishing installations, in which the extinguishing agent consists of water, comprise a water pipe system disposed in the ceiling and possibly on the walls of the room. In case of fire, the nozzles disposed in the pipe system are released and the pressurized water flows in form of sprays from the nozzles into the room. In order to ensure extinguishment of the fire, the amount of water flowing from the nozzles is usually dimensioned to be many times larger than the amount needed. Because of that, the damage caused by water in connection with small fires is often greater than the damage caused by the fire itself. In sprinkler systems large amounts of water are usually sprayed outside the actual seat of fire or the hot flames, wherefore this water does not evaporate. Also plenty of water has to be used for extinguishment of smouldering fires. Extinguishment of fire by water is especially problematic in spaces containing electric equipment.
It has been found that the smaller the drops of the extinguishing water, the greater the heat absorption capacity of the drops, i.e., the better the cooling effect of the water. It is also known that the penetration capacity of small water drops into the burning material, for instance textiles, is better than that of large drops. Therefore fog sprays in which the diameter of the drops is somewhere between 0.1 and 1 mm have been used for extinguishment of fire. The small drops are produced with nozzles by changing the pressure. In high-pressure fog sprays, even smaller drop sizes than the above-mentioned are used.
The drawback of a small drop size is, however, that with a low pressure, i.e., <10 bar, these small fog drops do not easily penetrate into the seat of fire. If a water fog consisting of small drops is directed directly to the seat of fire at low pressure, the flames of the fire and the water vapour which is produced tend to push the fog away from the seat of fire, whereby the cooling and extinguishing effect will be small. A sufficient spray length has, for the above-mentioned reasons, not yet been achieved with a conventional low-pressure fog spray consisting of small drops. Thus, when extinguishing fires with low-pressure fog sprays, much more water and a longer extinguishing time is needed than when a larger drop size is used. Despite the advantages of the small drop size, it has not been possible to utilize this in a desired manner.
Efforts have been made to find a solution to this problem by raising the pressure of the fog spray to a high level, for instance in the method according to International Patent Publication No. WO 92/22353 to a pressure even above 200bar. A fog sprayed at a too high pressure will however pass very rapidly directly through the flames, wherefore its cooling effect will not be fully utilized.
When using high-pressure sprays, the idea is to smother the fire by force by means of a high-pressure water layer. The surplus water evaporates, spreads to the sides and fills the site of fire with steam, which causes trouble for the firemen. An additional drawback when extinguishing fires with high-pressure sprays is that the spray, when directed to an open liquid tank, such as an oil tank, spreads the liqu
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patent: 3934823 (1976-01-01), Reed
patent: 4142682 (1979-03-01), Bowen
patent: 4570860 (1986-02-01), Aprea et al.
Salmi Pekka
Tirronen Hannu
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