Water Based Fire Protective Composition Applied To Electrical Cable

Abstract

A self-extinguishing fire protective composition and cables coated with such composition are disclosed. The composition includes a water based resinous emulsion, a chlorinated hydrocarbon and inorganic noncombustible fibers.

Description

BACKGROUND OF INVENTION

In electrical utilities and other installations where large numbers of electrical cables are used, there is a constant, very serious danger of fire developing due to the heavy current passing through the cables and the heat which is produced when overloading occurs. Also, such cables frequently are operated under high voltage which can cause arcing among adjacent cables.

Since a typical utility may contain thousands of linear feet of cable, the danger thus created by the fire is enormous. Moreover, the cables are totally destroyed which results in a loss of production and also necessitates a sizable expenditure to replace the cables and other damaged equipment or buildings. In the case of nuclear generating stations, the danger posed by the threat of fire is further and dramatically increased.

When the electrical cables have a coating of polyvinyl chloride, there are additional disruptive results of fires. The high-chlorine content of polyvinyl chloride (which may have a theoretical hydrochloric acid content of about 56 percent by weight) is freed and combines with the humidity of the air or with water which is used for fire extinguishing to form hydrochloric acid which can penetrate concrete foundations and attack the steel reinforcement.

To protect the cables against fire and to minimize the destructive results of fires, a coating of a fire protective material can be applied to the exterior surface. One example of a formulation which has performed well is a chlorinated rubber composition described in U.S. Pat. No. 2,938,937. Such composition, however, is formulated with a volatile organic solvent such as toluene or naphtha. The use of organic solvents, of course, is not desirable since solvent fumes can be hazardous to applicators of the coating. This is especially undesirable when the cables are in underground vaults. Organic solvents have also been found to cause neoprene and butyl rubber insulation on the cables to swell when a thick coating is applied.

It is accordingly highly desirable to have a fire protective composition which does not require the use of an organic solvent and which contains as little chlorine content as possible. To provide such a composition, however, which also is capable of providing satisfactory fire protection when applied to electrical cables, is exceedingly difficult since the composition must protect the cable for several minutes, in some instances as long as 30 minutes, during the fire and prevent propagation of flames beyond the original heat source. The composition must also be capable of providing a coating on the cable which is sufficiently flexible to allow handling of the cables without breaking of the coating and to permit access to and removal of individual cables from a cable tray. The composition should also be capable of protecting electrical cables against the hazards of fire after immersion in water for prolonged periods of time, and should not significantly diminish the current carrying capability of the cables, i.e., the coating will not cause significant heat buildup within the coated cables.

SUMMARY OF INVENTION

The present invention thus provides a fire protective composition which, upon application, forms a self-extinguishing fire barrier and does not significantly retain heat within an electrical cable during normal operation. The composition includes a water based resinous emulsion, a chlorinated hydrocarbon, and inorganic noncombustible fibers.

A principal object of this invention is thus the provision of a fire protective composition which is highly effective in preventing propagation of flames and spreading of a fire when applied to combustible substrates.

Another object of this invention is to provide a fire protective composition which is capable of being formed into a flexible film which permits the cable to be handled easily and which may conveniently be removed from the cable.

A still further object of this invention is to provide a fire protective composition which does not include an organic solvent.

Another object of this invention is to provide a fire protective composition which will not cause swelling of insulation on electrical cables nor affect the electrical or physical properties of the cable insulation in any significant manner.

It is yet a further object of this invention to provide a fire protective composition which contains only a relatively small chlorine content.

Other objects, features, and advantages of this invention will be apparent to those skilled in the art after a reading of the following more detailed description.

DESCRIPTION OF PREFERRED EMBODIMENTS

The water based resinous emulsion is preferably a thermoplastic such as a polyvinyl acetate emulsion, GRS rubber, natural rubber latex, methacrylate and acrylate resins, elastomeric polyurethanes, and copolymers of such materials as vinyl acetate and vinyl chloride. Water emulsified epoxy resins may also be used. The composition must have sufficient emulsion to produce a coherent plastic film or coating when the composition is applied to an electrical cable and also one which adheres well to the surface of the cable insulation but which can be easily removed. Accordingly, at least about 4 weight percent of the emulsion solids will be used, based on the total weight of the composition. In general, the quantity of emulsion solids should not exceed approximately 25 weight percent since a minimum of organic binder, consistent with satisfactory physical properties, is desired to provide a coating which is tough and sufficiently flexible to permit easy handling of the coated cables and which contains as little combustible material as possible. The preferred range of emulsion solids is from about 8 weight percent to about 15 weight percent.

The chlorinated hydrocarbon may be chlorinated paraffin, chlorinated naphthalene, chlorinated terphenyl, mixtures of such materials, etc. From about 1 to about 15 weight percent of the chlorinated hydrocarbon will generally be used, with the preferred range being from about 4 to about 6 weight percent, based on the total weight of the composition.

Preferably, the composition includes a plasticizer to provide flexibility for the coating, although with some emulsions, such as elastomeric polyurethanes and rubbers, it may not be necessary to use a plasticizer. If a plasticizer is used, the selection of a particular plasticizer, of course, depends upon the particular emulsion which is used, with suitable plasticizers being those generally used to plasticize such emulsions. If a polyvinyl acetate emulsion, for example, is used, suitable plasticizers include tris beta chloroethyl phosphate, chlorinated biphenyl, butyl benzyl phthalate, dibutyl phthalate, tricresyl phosphate, triphenyl phosphate, cresyl diphenyl phosphate, tritoyl phosphate or mixtures thereof. Normally, the quantity of plasticizer will be relatively small, within the range of from about 1 to about 5 weight percent based on the total weight of the composition.

The composition also includes inorganic noncombustible fibers such as asbestos or glass. The total quantity of such fibers in the composition is generally within the range of from about 5 to about 50 weight percent. In a preferred form, the composition includes inorganic fibers of different lengths, i.e., short fibers of about one thirty-seconds inch or less in length and relatively longer fibers of up to about one-half inch in length, the shorter fibers generally comprising from about 20 to about 80 weight percent of the total weight of the mixture of fibers, and preferably from about 50 to about 70 weight percent. Particularly good results have been obtained when both the long and short fibers are asbestos as it is believed that the asbestos fines or short fibers together with the long fibers form a tough film, that is a dense interwoven network, which remains about the cable insulation surface after burning. Such structure, in combination with the carbonaceous residue of the decomposed binder, is believed to facilitate removal of heat by radiation and at the same time to limit the access of oxygen to the flammable cable surface.

Preferably, the fire protective composition also includes an antimony containing compound, such as antimony trioxide. Generally, about 0.5 to about 15 weight percent, and preferably from about 2 to about 5 weight percent, of the antimony compound will be used. The antimony oxide is believed to function in combination with the chlorinated hydrocarbon during burning by interfering with the normal combustion process, or to limit burning, possibly by reacting with the chlorinated hydrocarbon to form antimony pentachloride, a heavy gas which forms at the boundary of the burning surface and thus prevents oxygen from getting to such surface.

The fire protective composition may also include various inert inorganic fillers, such as calcium carbonate or silica or other such stable inorganic materials. The quantity of fillers will normally be kept within the range of approximately 5 to about 20 weight percent, based on the total weight of the composition. Similarly, the composition may also include organic or inorganic pigments such as titanium dioxide, ferric oxide, etc., to provide a desired color. The quantity of such pigment will, of course, be relatively small, generally no more than approximately 4 weight percent.

To prepare the composition, polyvinyl acetate or other resinous emulsion containing at least approximately 50 percent solids in water is mixed with the chlorinated hydrocarbon and plasticizer with stirring at room temperature to form a substantially uniform mixture of the ingredients. The calcium carbonate or other inert filler, pigment, and antimony oxide compounds are added and thoroughly mixed therein, after which the asbestos or other inorganic fibers are added with mixing to provide a substantially uniform mixture.

The composition may be applied as a fluid or as a mastic by various methods, including spraying, brushing, trowelling, gunning, etc. Depending upon the form of the composition, the composition will contain the requisite amount of water, slightly greater quantities of water being required if a sprayable composition is to be produced. The composition may also contain minor amounts of various additives to stabilize and protect the emulsion, such as wetting agents, defoaming agents, fungicides, etc. The quantity of such ingredients will usually be within the range of from about 1 to about 5 percent by weight.

It is advisable to clean the surface to which the coating is to be applied if it contains excessive oil or grease contamination. The surface should also be free of excess loose dirt and dust. When the composition is applied to electrical cables, the coating should be approximately one-eighth inch in thickness. To attain such a coating, the initial thickness should be approximately three-sixteenths inch when the wet composition is applied as it will shrink approximately 30 percent in drying. If the fire hazard is minimal, the thickness of the coating may be only approximately one-sixteenth inch, and conversely, if a strong fire hazard exists, the coating may be approximately one-fourth inch thick. Depending upon the thickness applied and the atmospheric conditions, the composition will usually dry to touch between 1 and 2 hours, and after approximately 4 hours, the cable may be handled or removed. Complete drying requires up to approximately 3 days, and consequently, fire testing should not take place until at least 3 days after application since traces of moisture left on the inside of the coating could expand and loosen adhesion.

After drying, the water, of course, will have evaporated and the resulting coating, in one formulation, will comprise the following materials in the indicated approximate percentages:

Resin solids 20.25 wt. % Chlorinated hydrocarbon 7.98 wt. % Plasticizer 3.99 wt. % Inorganic fibers 39.40 wt. % Inorganic fillers 19.06 wt. % Antimony compound 9.31 wt. %

In general, the dried coating will contain, based on the total weight of the coating, from about 6 to about 30 weight percent resin solids from the emulsion, about 1.5 to about 20 weight percent chlorinated hydrocarbon, about 1.5 to about 7.5 weight percent plasticizer, about 7.5 to about 75 weight percent inorganic fibers, about 5 to about 30 weight percent inorganic fillers, pigments, wetting agents, etc., and about 1 to about 20 weight percent of the antimony compound.

Referring to the accompanying drawings:

FIG. 1 is a fragmentary perspective view of an electrical cable having a coating of the composition applied thereto; and

FIG. 2 is a cross section view taken on line 2--2 of FIG. 1.

In the drawing, the numeral 1 denotes generally a piece of electrical cable having a coating 2 of fire protective composition thereabout. In this particular form, the cable core includes a plurality of metal wires 3 having an insulation coating 4 thereon, which may be neoprene rubber, butyl rubber, polyvinyl chloride, cross-linked polyethylene, etc. As shown most clearly in FIG. 2, the coating 2 of fire protective composition surrounds the cable and is adhered to the insulation coating 4.

The invention will be better understood by reference to the following specific but illustrative example.

EXAMPLE

Utilizing the general procedure previously described, approximately 26 percent of a 50 percent solids polyvinyl acetate water emulsion, about 5 percent by weight chlorinated paraffin and about 2.5 weight percent tris beta chloroethyl phosphate plasticizer were mixed in sufficient water to give a final composition containing about 22 weight percent water with stirring at room temperature for approximately 15 minutes to produce a substantially uniform dispersion. Approximately 7 percent by weight of calcium carbonate filler, 3.5 percent titanium dioxide pigment and approximately 6 percent antimony trioxide were then added and mixed thoroughly for approximately 30 minutes. Approximately 27 percent by weight of asbestos fibers, consisting essentially of about 16 percent of asbestos fines having a length of one thirty-seconds inch or less and about 11 percent of asbestos fibers of up to approximately one-half inch in length, were then added to the emulsion and mixed thoroughly for approximately 60 minutes.

After the composition was prepared as above, it was applied by spraying with standard spray coating apparatus to an 8 foot horizontal cable tray containing approximately 20 insulated electrical cables. The coating was applied to one-half of the cable tray, top and bottom, to provide approximately one-eighth inch thickness of coating. The remainder of the cable tray and cables was not coated. The fire protective coating was permitted to dry for 2 days, and the test rig was then positioned in a wind protected area so that wind direction would not influence the results. Burlap bags soaked in transformer oil were then wrapped around the cables and ignited with a propane blow torch. The burning time of the heat source was approximately 6 minutes on the section of the tray which had been coated as described, after which the fire had burned out. On the uncoated cables, the fire did not burn out until the insulation had been totally decomposed and the metal cables charred and badly damaged. In contrast to this, the coated cables, after being permitted to cool, were inspected and found to be substantially unharmed and suitable for further use.

Tests have also been performed on electrical cables coated with the fire protective composition of this invention to determine whether the coating affects the current carrying capability of the cable, as determined by the temperature rise in the cable during operation. It has been found that such coating does not reduce significantly the ampacity, the reduction being generally on the order of only between 2 and about 5 percent, which is not sufficient to derate the cables, the temperature of the insulation on the cables increasing only approximately 2 percent with a one-eighth inch thickness coating of the fire protective composition.

In addition to the previously described qualities, the fire protective composition of this invention is odorless and nontoxic and has a Shore A hardness of up to about 85. An unsupported 1/16-inch thickness film passes a 1.8 inch mandrel bend per ASTM D 1737-62. A 1/16-inch film on aluminum is capable of withstanding an impact of at least 24 inches per pound on a Gardener Impact Tester.

As will be appreciated from the foregoing, the fire protective composition of this invention is very effective in preventing the spreading of fire and thus of protecting electrical cables from the destructive effects of fires. Also, the coating provided by such composition is highly flexible and it does not interfere in any way with the normal use of the cables. Additionally, the composition does not cause a significant temperature rise in the cables during operation and has also been found to be stable as a coating over long periods of time. Although the composition is particularly suitable for use as a coating for electrical cables, it is also quite suitable for use as a fire stop for wall penetrations in which the composition is applied to the cavity between electrical cables and walls or ceilings to seal around the cables and thus prevent the fire from being transmitted to other areas of the plant.

Claims

I claim:

1. An electrical cable comprising a metal core, a layer of insulation surrounding said core, and a self-extinguishing fire protective coating about said layer of insulation, said coating being the dried residue of an aqueous emulsion and comprising from about 6 to about 30 weight percent of water emulsified resin solids, about 1.5 to about 20 weight percent of a chlorinated hydrocarbon, and about 7.5 to about 75 weight percent of inorganic noncombustible fibers.

2. The cable of claim 1 in which said water emulsified resin is polyvinyl acetate.

3. The cable of claim 1 in which said inorganic fibers include, based on the total weight of the fibers, about 20 to about 80 weight percent of relatively short fibers having a maximum length of approximately one thirty-seconds inch with the remainder of said fibers having a maximum length of about one-half inch.

4. The cable of claim 3 in which said relatively short fibers and said longer fibers are asbestos.

5. The cable of claim 1 in which said chlorinated hydrocarbon is selected from the group consisting of chlorinated paraffin, chlorinated napthalene, and chlorinated terphenyl.

6. The cable of claim 1 in which said dried residue includes approximately 1 to about 20 weight percent of an antimony containing compound.

7. The cable of claim 1 wherein said dried residue includes approximately 1.5 to about 7.5 weight percent of a plasticizer for said water emulsified resin.

8. The cable of claim 1 in which said layer of insulation is selected from the group consisting of neoprene rubber, butyl rubber, polyvinyl chloride, and cross-linked polyethylene.

9. The cable of claim 7 in which said dried residue includes about 5 to about 30 weight percent wetting agents and inert materials consisting of inorganic fillers and coloring agents.

10. The cable of claim 6 in which said dried residue includes approximately 1.5 to about 7.5 weight percent of a plasticizer for said water emulsified resin.

11. The cable of claim 1 in which said resin is selected from the group consisting of polyvinyl acetate, GRS rubber, natural rubber latex, methacrylates, acrylates, elastomeric polyurethanes, copolymers of vinyl acetate and vinyl chloride, and epoxy resins.

12. An electrical cable having a self-extinguishing fire protective coating on the exterior surface to protect said cable from the destructive effects of fire and to prevent the propagation of flames, said cable comprising a metal core, a layer of insulation surrounding said core, and said fire protective coating surrounding said layer of insulation, said coating being the dried residue of an aqueous emulsion and comprising from about 6 to about 30 weight percent of water emulsified thermoplastic resin solids, about 1.5 to about 20 weight percent of a chlorinated hydrocarbon, and about 7.5 to about 75 weight percent of inorganic noncombustible fibers.

13. The coated cable of claim 12 in which said dried residue includes approximately 1 to about 20 weight percent of an antimony containing compound and about 1.5 to about 7.5 weight percent of a plasticizer for said water emulsified resin.

14. The coated cable of claim 12 in which said dried residue includes about 5 to about 30 weight percent wetting agents and inert materials consisting of inorganic fillers and coloring agents.

15. The coated cable of claim 12 in which said resin comprises a vinyl acetate polymer.

16. The coated cable of claim 15 in which said dried residue contains approximately 20.25 weight percent of said resin solids, approximately 7.98 weight percent of said chlorinated hydrocarbon, about 3.99 weight percent of said plasticizer, approximately 39.40 weight percent of said inorganic fibers, approximately 19.06 weight percent of said inert materials, and approximately 9.31 weight percent of said antimony compound.