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Electrical power, instrument and communication cables constructed with combustible coverings can provide a pathway by which fire might spread. Cable fires within a room or compartment can be arrested by the construction of a properly designed “fire break”placed periodically along a cable run; and ca

Electrical power, instrument and communication cables constructed with combustible coverings can provide a pathway by which fire might spread. Cable fires within a room or compartment can be arrested by the construction of a properly designed “fire break”placed periodically along a cable run; and cable fire spread between rooms can be arrested by a properly placed “fire stop”. Cable runs generally include a cable tray or raceway to contain the cables. An effective fire barrier, e.g., “fire break”or “fire stop”may be constructed in such a cable tray or raceway by filling a portion of the tray or raceway with a gypsum composition comprising gypsum plaster, an inert filler mixture of diatomaceous earth and lightweight expanded aggregate, and very small amounts of glycerin, boric acid and a corrosion inhibitor such as a boron nitride, boron nitrile or mixture of such boron compounds. The fire barrier is formed by placing in a portion of the cable tray/raceway an aqueous slurry of the plaster composition as described above, slurried with water in amounts of about 10 pounds of the plaster composition and 14-16 pounds of water to form a “ pseudo-plastic”mass, and filling all of the voids around and beneath cables therein by applying force to the cable tray/raceway, e.g., as by hammering with a rubber mallet.

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A gypsum cement composition adapted for use in electrical cable fire barrier operations having pseudo-plastic flow in aqueous slurry, having a dry density of about 25 to 35 pounds per cubic foot and having a dry compressive strength when set below 300 pounds per square inch, which comprises by weigh

A gypsum cement composition adapted for use in electrical cable fire barrier operations having pseudo-plastic flow in aqueous slurry, having a dry density of about 25 to 35 pounds per cubic foot and having a dry compressive strength when set below 300 pounds per square inch, which comprises by weight: about 30 to approximately 80% calcium sulfate hemihydrate; about 10 to approximately 40% diatomaceous earth aggregate having an apparent bulk density in the range from about 5 to approximately 16 pounds per cubic foot and a water carrying capacity in the range from about 1.5 to approximately 4 times its weight of water; about 10 to approximately 30% of a second aggregate having a dry bulk density in the range from about 5 to approximately 20 pounds per cubic foot, and a water carrying capacity from about 0.7 to approximately 4 times its weight of water; and by weight based on the weight of hemihydrate about 0.05-1.25% glycerine and about 0.05-0.7% boric acid. A settable pseudo-plastic mass comprising an aqueous slurry of the composition of claim 1.