US2346627A - Extinguishing light metal fires - Google Patents

Description

rosive vapors.

. ture,

Patented Apr. 11, 1944 Richard I. Thrune, .Midland, Micln,

The DowChemical Company, Midland,

corporation of Michigan Application February '7, 1942, Serial No. 429,959

No Drawing.

7 Claims.

than useless with such fires, since they are reactive chemically with the heated metal and freassignoi' to Mich, a

quently actually accelerate the combustion.

Likewise, many common solid extinguishers are either dangerous to use with any but small metal fires or are relatively ineffective unless applied in enormous quantities. Certain proprietary extinguishers are available, but they are usually quite expensive, and in most cases liberate during use a considerable volume of choking or cor- So far as is known, no fully sat isi'actory extinguisher has heretofore been de veloped. It is, therefore, an object of the present invention to provide a composition and method for extinguishing light metal fires, which is nonhazardous, effective, inexpensive, and easy to ap- This object is attained in the compositions of the invention which consist essentially of granular carbon, e. g., ground graphite, together with from about 0.5 to about 3 per cent by weight thereof of an at least semi-liquid high flash point organic substance unreactive chemically with the burning metal, such as a heavy mineral oil. In extinguishing a light metal fire, the mixture is applied to the burning metal, whereupon the graphite in themixture covers the hot metal so'as to exclude air therefrom and also conducts away the heat so rapidly that the temperature of the metal is soon reduced'to below the ignition temperature. The small proportion of heavy oil or like substance evaporates slowly from the mixfilling the interstices between the graphite particles with rising vapor, and thereby displacing air already present and preventing additional air from reaching the hot metal through the graphite. i

The carbon in the extinguishing mixture may be present as any material which is composed principally of carbon and is substantially free of volatile materials, e. g., coke breeze, charcoal, or amorphous carbon powder. However, graphite, usually as ground graphitized foundry coke, is greatly to be preferred in the composition both because of its much higher ignition temperature and its greater thermal conductivity. The carbon or graphite is ordinarily employed in granular form, and should preferably be sufilciently fine that the final mixture is free-flowing, and yet not so fine that packing or caking occurs. Optimum results are obtained with graded graphite powder which is all finer than 8 mesh (Tyler Standard screen scale), but at least 50 per cent of which is coarser than 200 mesh.

The minor constituent of the new composition may be any organic substance which has a high flash point and high boiling point, is at least semi-liquid at room temperature, and is substantially unreactive chemically with the burning metal to be extinguished. In general, 'oils having a flash point above 300 F. are preferred, especially the heavy hydrocarbon or mineral oils. However, various other high flash point oils including vegetable oils, such as cottonseed oil, synthetic oily substances such as diphenyl oxide, and heavy liquids or semi-solids such as glycerine or low melting point coal-tar pitches, may also be used. ,7

In the composition of the invention, the high flash point organic liquid or semi-liquid should be present in a proportion between about 0.5 and about 3 per cent by. weight of the granular car'- bon. With proportions much below 0.5 per cent, the efiectiveness of the composition isimpaired, whereas at percentages of liquid much above 3 percent the advantages of the invention are not I pile of burning magnesium or magnesium-base alloy turnings or an incendiary bomb, the composition ls merely sprinkled over the fire with a shovel so as to cover it uniformly. The heat of the fire is conducted away rapidly and air is exeluded from the hot mass so that the blaze is quenched in a very short time. 1 The. quantity of the extinguishing composition necessary for any given fire depends, of course, upon the size and shape of the burning material. In general, however, there is required roughtly one-third to an 2 i edual amount of extinguisher by weight relative to the weight of the hot metal. The following example will illustrate the'invention:

Example number of advantages which are not shared by other light metal fire extinguishers. The ingredients are cheap and easily compounded. 'The mixture is light in weight, stable, does not tend to absorb moisture from humid atmospheres, and remains free-flowing even after prolonged storage in open air. It is non-abrasive and nonreactive chemically with hot metal. Unburned portions of the metal are not destroyed or coated with residues which are difficult to remove, but

can be recovered very readily. The extinguisher gives off little if any fumes and no corrosive vapors.

Because of the oil content, the composition is virtually non-dusting, even when sprinkled; yet the oil, being present only on the surface of the graphite particles, does not tend to run out of the composition on standing. When the extinguisher is applied to a metal fire, the heavy oil, as explained, evaporates slowly, the vapors so formed filling the space between graphite particles and excluding air from the fire. However, theseva- DOlS are present in such small amount that, although they are flammable, they do not form a sustained flame over the surface of the extinguisher which has been applied to the metal fire. A few scattered flashes may occur momentarily, but there are no continuous heat-producing flames which must be extinguished. As a result,

the application of the new composition does not give rise to secondary fires which sometimes reignite the light metal while it is stil1 hot and which always require attention in main metal fire.

addition to the Extra point above about 300 F.

This application is a continuation-in-part of prior application Serial No. 364,493, filed Novemher 6, 1940.

What is claimed is: a

1. A composition for extinguishing light metal fires-which consists essentially of an intimate mixture of granular carbon together with from 0.5 to about 3 per cent by weight thereof of an at least semi-liquid high flash point organic substance unreactive chemically with the burning metal.

2. A composition according to claim l wherein the carbon is present in the form of graphite.

3. A composition according to claim 1 wherein the organic substance is an oil having a flash 4. A free-flowing substantially non-dusting composition for extinguishing light metal fires which consists essentially of granular graphite, the particles of which are coated with a mineral oil having a flash point above about 300 F., the oil being present in a proportion from between about 0.5 to about 3 per cent by weight of the graphite.

5. A composition according to claim 4 wherein the granular graphite is present as graded powder in which all the material has substantially a particle size-finer than 8 mesh and at least 50 per cent of such material is coarser than 200 mesh.

6. A method of extinguishinga light metal fire which comprises applying to the burning metal a composition consisting essentially of an intimate mixture of granular carbon together with from about 0.5 to about 3 per cent by weight thereof of an at least semi-liquid high flash point organic substance unreactive chemically with the burning metal.

7. A method of extinguishing magnesium and magnesium alloy fires which comprises applying to the burningmetal in a quantity sufficient to extinguish the fire a composition consisting essentially of granular graphite, the particles of which are coated with a mineral oil having a flash point above about 300 F., the oil being present in a proportion from between about 0.5 to about 3 per cent by weight of the graphite.

' RICHARD L THRUNE.