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French, R.J., 1959. THE EFFECTS OF AGEING ON CHARGED 2-GALLON FOAM EXTINGUISHERS. Fire Research Notes 384
It is known that in time, changes can take place in the solution used in chemical foam extinguishers, and this may affect their efficiently in extinguishing fires. There may be some conversion of the sodium bicarbonate to sodium carbonate, particularly at high temperatures, with a consequent reduction in the amount of carbon dioxide produced by the reaction of the two solutions. Some of the salts of both solutions may be deposited, particularly under cold storage conditions. Little is known about the effects of ageing upon the stabilisers used. During the development of a standard fire test for this type of extinguisher, it was found that many of the proprietary charges used produced unduly stiff foams and this prevented complete coverage of the fire area. It was shown that a more fluid foam, that would extinguish the test fire, could be produced if the amount of stabiliser was considerably reduced. This fluid foam was produced using either 0.18 fl.oz. (5cc) of a protein foam compound or 0.25 oz. (7 grm.) of ground liquorice root as stabilisers, much smaller amounts than would normally be used. The overall effects of the changes that may take place on storage when using these very small amounts of stabiliser were studied.