Fire extinguishers – Fluid systems – Gas-pressure discharge
Patent
1996-09-18
1998-09-01
Pike, Andrew C.
Fire extinguishers
Fluid systems
Gas-pressure discharge
169 13, 169 14, 169 15, A62C 3568
Patent
active
057997357
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a fire fighting installation, i.e., system comprising a liquid source, a pump connected to said liquid source and preferably having a high liquid pressure and comparatively small flow, and a gas source connected by way of a line to an outlet line of the pump for mixing gas with outbound extinguishing liquid delivered to spray heads.
Certain kinds of gasoline fires, for example a kerosene fire in an aircraft jet engine undergoing an engine test in a hangar designed for that purpose, are nearly impossible to extinguish even by means of strong mist-like jets of liquid, as suggested for example in international patent application PCT/FI92/00155 which was published as WO 092/20454. Such a jet engine fire will only go out when the entire hangar, which may typically have a volume of about 3000 cc, has been subjected to "total flooding", i.e., is in practice entirely filled with liquid mist having very small particles.
The liquid mist can in principle be produced with apparatus as described in international patent application PCT/FI92/00317which was published as WO 93/10859. In that application, an outgoing ascension tube of a hydraulic accumulator is provided with wall apertures, so that the propellent gas of the accumulator initially drives out liquid only, and after the liquid level has sunk to be even with the uppermost tube wall aperture, mixing of propellent gas into the outbound liquid is gradually started as the liquid level sinks and more tube wall apertures are exposed. In the final stage of emptying the accumulator, it is possible to obtain a liquid mist having sufficiently small droplets for the present purpose, but too large a portion of the liquid contained in the hydraulic accumulator will go waste.
It is an object of the present invention to provide a novel installation enabling effective delivery of liquid with immediate effective mixing of gas into the liquid right from the start. The installation of the invention is primarily characterized in that the gas source is connected to the outlet line of the pump for producing a finely divided liquid mist. The purpose of the gas is to enable fine division of the liquid droplets, which produces a finely divided liquid mist. When the pressure in the line leading to the nozzles is increased, the liquid mist becomes even more finely divided. Preferably, the gas source is arranged to mix gas in the outlet line of the pump with at least substantially the same high pressure as the pump.
The gas source can advantageously be constituted by a plurality of compressed-gas bottles coupled in parallel. The gas may be nitrogen, argon, air, etc. In principle, any suitable gas may be used. The contents of the compressed-gas bottles may be partially in liquid form, depending on the type of gas employed. The charge pressure of the gas bottles, like the operating pressure of the pump, may be approximately 50-200 bar, even though both lower and higher pressures are possible.
A comparatively small pump flow in this context means that the flow is smaller than the flow capacity of the relevant sprinklers or spray heads at maximum operating pressure. The pump flow may be 10-80%, preferably 20-50% of the total flow of extinguishing fluid at maximum operating pressure.
Thus, one can cope with a small pump that is inexpensive and requires little electric power.
In so-called pure oil fires, it is often expedient to mix a foam concentrate with the extinguishing liquid to produce a fire-smothering foam that prevents re-ignition. The hitherto known installations for this purpose have usually been ineffective, as the fire smoke will spoil the foam, that is, prevent the foam concentrate from developing into a foam.
The installation in accordance with the present invention enables effective foam formation on account of the comparatively large amount of pure gas, e.g., nitrogen gas, injected concurrently, which will shield the fire smoke from direct contact with the injected foam concentrate.
In a fire for example on the car deck of a car ferry, also other
REFERENCES:
patent: 4390069 (1983-06-01), Rose, Jr.
patent: 4981178 (1991-01-01), Bundy
patent: 5113945 (1992-05-01), Cable
patent: 5255747 (1993-10-01), Teske et al.
Derwent's abstract, No. 86-330389/50, week 8650, Abstract of SU, 787048 (Fire Fighting Eng C), 15 Dec. 1980.
Derwent's abstract, No. 88-166804/24, week 8824, Abstract of SU, 1353444 (Bogomolov AA) 23 Nov. 1987.
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