GB748931A - Improvements in or relating to the production of foam for fire-fighting purposes - Google Patents

Abstract

748,931. Making foam. KERR & CO. (MANCHESTER), Ltd. J. Aug. 8. 1952 [June 21. 1951; May 8, 1952], Nos. 14764/51 and 11610/52. Class 47 An aqueous mechanical foam concentrate for fire-fighting purposes comprises an aqueous solution of a foam-form:ng agent and sufficient electrolyte so as to retain in the form of a suspension an added water-soluble salt of alginic acid in a concentration of from 3 to 16 per cent by weight of the completed concentrate, whereby on dilution of the concentrate to working strength for fire-fighting purposes the alginic acid salt will pass into solution. the foam-forming agent and electrolyte being substances which will not react with a water-soluble salt of alginic acid to form an insoluble alginate. The concentrates yield foams stable in the presence of inflammable water-soluble liquids. It is preferred to use the sodium salt of alginic acid. but the ammonium salt, its mechanical mixture with the sodium salt. and the double sodium-ammonium salt are effective. Sodium or ammonium chloride is the preferred electrolvte. Suitable foam-forming agents include the protein-hydrolysate type which may contain wetting agents, a mixture of glue, wetting agent and sodium or ammonium chloride and a mixture of wetting agent, pectin and sodium chloride. specified wetting agents being "Teepol" and "Perminal" W (both Registered Trade Marks). In use, the foam concentrates are diluted and then aerated to produce the foam. This foam may be rendered gell-like to varying degrees by the action of a calcium salt or other gelling agent. which action may be controlled as regards time by means of retarding agents, e.g., sodium metaphosphate or by selection of calcium salts of appropriate solubilitv. The gelling agent may be added to the diluted concentrate: thus the usual water-stream mav pick up gelling-agent. retarding agent. both contained in powder form in cylinders, and the foam-concentrate prior to the aeration, the pick-up from the two cylinders being adjusted to give the desired degree of gelling and setting time. Alternatively, the foam concentrate is diluted and aerated by a foam-pump or branch-pipe and the foam is contacted with the gelling agent within or outside the apparatus. Specified gelling agents are the chloride, sulphate, phosphate and citrate of calcium. The foam may be used in extinguishing fires or in prevention of fires involving inflammable liquids wherein acetone, for example, may be blanketted by the foam. According to the first Provisional Specification, aqueous foams are stabilized against breakdown by inflammable watersoluble liquids by means of an agent or agents capable of rendering the foam at least temporarily insoluble in the liquid. These agents may be used with mechanical foam compounds and chemical foam mixtures. The agents include substances which are precipitated from aqueous solution by water-soluble solvents, e.g., soluble alginic acid salts and certain alginic acid esters, cellulose esters and ethers, natural gums, polysaccharides and pentosans and pairs of substances which react together to form a precipitate sufficient to render the foambubble walls insoluble, e.g., sodium alginate and calcium chloride, magnesium chloride and sodium carbonate and aluminium sulphate and sodium hydroxide. These may be added to the foam or to the foam compound or water-stream used in making the foam. When using a hydrolyzed protein foaming agent, calcium ions may be added thereto, the resulting calcium proteinate serving as the stabilizer; this reaction may be controlled with sodium hexa-meta phosphate. According to the second Provisional Specification, all the above-mentioned stabilizing agents may be provided in the foam concentrate prior to its dilution and aeration and as further pairs of substances for forming the stabilizing precipitates, sodium carboxymethyl cellulose and ferric, aluminium, copper and lead salts are mentioned.